1 //===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass transforms simple global variables that never have their address
11 // taken. If obviously true, it marks read/write globals as constant, deletes
12 // variables only stored to, etc.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Transforms/IPO.h"
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/STLExtras.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/ADT/SmallSet.h"
21 #include "llvm/ADT/SmallVector.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/Analysis/ConstantFolding.h"
24 #include "llvm/Analysis/MemoryBuiltins.h"
25 #include "llvm/Analysis/TargetLibraryInfo.h"
26 #include "llvm/IR/CallSite.h"
27 #include "llvm/IR/CallingConv.h"
28 #include "llvm/IR/Constants.h"
29 #include "llvm/IR/DataLayout.h"
30 #include "llvm/IR/DerivedTypes.h"
31 #include "llvm/IR/Dominators.h"
32 #include "llvm/IR/GetElementPtrTypeIterator.h"
33 #include "llvm/IR/Instructions.h"
34 #include "llvm/IR/IntrinsicInst.h"
35 #include "llvm/IR/Module.h"
36 #include "llvm/IR/Operator.h"
37 #include "llvm/IR/ValueHandle.h"
38 #include "llvm/Pass.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/ErrorHandling.h"
41 #include "llvm/Support/MathExtras.h"
42 #include "llvm/Support/raw_ostream.h"
43 #include "llvm/Transforms/Utils/CtorUtils.h"
44 #include "llvm/Transforms/Utils/GlobalStatus.h"
45 #include "llvm/Transforms/Utils/ModuleUtils.h"
50 #define DEBUG_TYPE "globalopt"
52 STATISTIC(NumMarked , "Number of globals marked constant");
53 STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr");
54 STATISTIC(NumSRA , "Number of aggregate globals broken into scalars");
55 STATISTIC(NumHeapSRA , "Number of heap objects SRA'd");
56 STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
57 STATISTIC(NumDeleted , "Number of globals deleted");
58 STATISTIC(NumFnDeleted , "Number of functions deleted");
59 STATISTIC(NumGlobUses , "Number of global uses devirtualized");
60 STATISTIC(NumLocalized , "Number of globals localized");
61 STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans");
62 STATISTIC(NumFastCallFns , "Number of functions converted to fastcc");
63 STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");
64 STATISTIC(NumNestRemoved , "Number of nest attributes removed");
65 STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
66 STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
67 STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
70 struct GlobalOpt : public ModulePass {
71 void getAnalysisUsage(AnalysisUsage &AU) const override {
72 AU.addRequired<TargetLibraryInfoWrapperPass>();
73 AU.addRequired<DominatorTreeWrapperPass>();
75 static char ID; // Pass identification, replacement for typeid
76 GlobalOpt() : ModulePass(ID) {
77 initializeGlobalOptPass(*PassRegistry::getPassRegistry());
80 bool runOnModule(Module &M) override;
83 bool OptimizeFunctions(Module &M);
84 bool OptimizeGlobalVars(Module &M);
85 bool OptimizeGlobalAliases(Module &M);
86 bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
87 bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI,
88 const GlobalStatus &GS);
89 bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn);
91 bool isPointerValueDeadOnEntryToFunction(const Function *F,
94 TargetLibraryInfo *TLI;
95 SmallSet<const Comdat *, 8> NotDiscardableComdats;
99 char GlobalOpt::ID = 0;
100 INITIALIZE_PASS_BEGIN(GlobalOpt, "globalopt",
101 "Global Variable Optimizer", false, false)
102 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
103 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
104 INITIALIZE_PASS_END(GlobalOpt, "globalopt",
105 "Global Variable Optimizer", false, false)
107 ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
109 /// Is this global variable possibly used by a leak checker as a root? If so,
110 /// we might not really want to eliminate the stores to it.
111 static bool isLeakCheckerRoot(GlobalVariable *GV) {
112 // A global variable is a root if it is a pointer, or could plausibly contain
113 // a pointer. There are two challenges; one is that we could have a struct
114 // the has an inner member which is a pointer. We recurse through the type to
115 // detect these (up to a point). The other is that we may actually be a union
116 // of a pointer and another type, and so our LLVM type is an integer which
117 // gets converted into a pointer, or our type is an [i8 x #] with a pointer
118 // potentially contained here.
120 if (GV->hasPrivateLinkage())
123 SmallVector<Type *, 4> Types;
124 Types.push_back(cast<PointerType>(GV->getType())->getElementType());
128 Type *Ty = Types.pop_back_val();
129 switch (Ty->getTypeID()) {
131 case Type::PointerTyID: return true;
132 case Type::ArrayTyID:
133 case Type::VectorTyID: {
134 SequentialType *STy = cast<SequentialType>(Ty);
135 Types.push_back(STy->getElementType());
138 case Type::StructTyID: {
139 StructType *STy = cast<StructType>(Ty);
140 if (STy->isOpaque()) return true;
141 for (StructType::element_iterator I = STy->element_begin(),
142 E = STy->element_end(); I != E; ++I) {
144 if (isa<PointerType>(InnerTy)) return true;
145 if (isa<CompositeType>(InnerTy))
146 Types.push_back(InnerTy);
151 if (--Limit == 0) return true;
152 } while (!Types.empty());
156 /// Given a value that is stored to a global but never read, determine whether
157 /// it's safe to remove the store and the chain of computation that feeds the
159 static bool IsSafeComputationToRemove(Value *V, const TargetLibraryInfo *TLI) {
161 if (isa<Constant>(V))
165 if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) ||
168 if (isAllocationFn(V, TLI))
171 Instruction *I = cast<Instruction>(V);
172 if (I->mayHaveSideEffects())
174 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
175 if (!GEP->hasAllConstantIndices())
177 } else if (I->getNumOperands() != 1) {
181 V = I->getOperand(0);
185 /// This GV is a pointer root. Loop over all users of the global and clean up
186 /// any that obviously don't assign the global a value that isn't dynamically
188 static bool CleanupPointerRootUsers(GlobalVariable *GV,
189 const TargetLibraryInfo *TLI) {
190 // A brief explanation of leak checkers. The goal is to find bugs where
191 // pointers are forgotten, causing an accumulating growth in memory
192 // usage over time. The common strategy for leak checkers is to whitelist the
193 // memory pointed to by globals at exit. This is popular because it also
194 // solves another problem where the main thread of a C++ program may shut down
195 // before other threads that are still expecting to use those globals. To
196 // handle that case, we expect the program may create a singleton and never
199 bool Changed = false;
201 // If Dead[n].first is the only use of a malloc result, we can delete its
202 // chain of computation and the store to the global in Dead[n].second.
203 SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
205 // Constants can't be pointers to dynamically allocated memory.
206 for (Value::user_iterator UI = GV->user_begin(), E = GV->user_end();
209 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
210 Value *V = SI->getValueOperand();
211 if (isa<Constant>(V)) {
213 SI->eraseFromParent();
214 } else if (Instruction *I = dyn_cast<Instruction>(V)) {
216 Dead.push_back(std::make_pair(I, SI));
218 } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
219 if (isa<Constant>(MSI->getValue())) {
221 MSI->eraseFromParent();
222 } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
224 Dead.push_back(std::make_pair(I, MSI));
226 } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
227 GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
228 if (MemSrc && MemSrc->isConstant()) {
230 MTI->eraseFromParent();
231 } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) {
233 Dead.push_back(std::make_pair(I, MTI));
235 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
236 if (CE->use_empty()) {
237 CE->destroyConstant();
240 } else if (Constant *C = dyn_cast<Constant>(U)) {
241 if (isSafeToDestroyConstant(C)) {
242 C->destroyConstant();
243 // This could have invalidated UI, start over from scratch.
245 CleanupPointerRootUsers(GV, TLI);
251 for (int i = 0, e = Dead.size(); i != e; ++i) {
252 if (IsSafeComputationToRemove(Dead[i].first, TLI)) {
253 Dead[i].second->eraseFromParent();
254 Instruction *I = Dead[i].first;
256 if (isAllocationFn(I, TLI))
258 Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
261 I->eraseFromParent();
264 I->eraseFromParent();
271 /// We just marked GV constant. Loop over all users of the global, cleaning up
272 /// the obvious ones. This is largely just a quick scan over the use list to
273 /// clean up the easy and obvious cruft. This returns true if it made a change.
274 static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
275 const DataLayout &DL,
276 TargetLibraryInfo *TLI) {
277 bool Changed = false;
278 // Note that we need to use a weak value handle for the worklist items. When
279 // we delete a constant array, we may also be holding pointer to one of its
280 // elements (or an element of one of its elements if we're dealing with an
281 // array of arrays) in the worklist.
282 SmallVector<WeakVH, 8> WorkList(V->user_begin(), V->user_end());
283 while (!WorkList.empty()) {
284 Value *UV = WorkList.pop_back_val();
288 User *U = cast<User>(UV);
290 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
292 // Replace the load with the initializer.
293 LI->replaceAllUsesWith(Init);
294 LI->eraseFromParent();
297 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
298 // Store must be unreachable or storing Init into the global.
299 SI->eraseFromParent();
301 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
302 if (CE->getOpcode() == Instruction::GetElementPtr) {
303 Constant *SubInit = nullptr;
305 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
306 Changed |= CleanupConstantGlobalUsers(CE, SubInit, DL, TLI);
307 } else if ((CE->getOpcode() == Instruction::BitCast &&
308 CE->getType()->isPointerTy()) ||
309 CE->getOpcode() == Instruction::AddrSpaceCast) {
310 // Pointer cast, delete any stores and memsets to the global.
311 Changed |= CleanupConstantGlobalUsers(CE, nullptr, DL, TLI);
314 if (CE->use_empty()) {
315 CE->destroyConstant();
318 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
319 // Do not transform "gepinst (gep constexpr (GV))" here, because forming
320 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
321 // and will invalidate our notion of what Init is.
322 Constant *SubInit = nullptr;
323 if (!isa<ConstantExpr>(GEP->getOperand(0))) {
324 ConstantExpr *CE = dyn_cast_or_null<ConstantExpr>(
325 ConstantFoldInstruction(GEP, DL, TLI));
326 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
327 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
329 // If the initializer is an all-null value and we have an inbounds GEP,
330 // we already know what the result of any load from that GEP is.
331 // TODO: Handle splats.
332 if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
333 SubInit = Constant::getNullValue(GEP->getType()->getElementType());
335 Changed |= CleanupConstantGlobalUsers(GEP, SubInit, DL, TLI);
337 if (GEP->use_empty()) {
338 GEP->eraseFromParent();
341 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
342 if (MI->getRawDest() == V) {
343 MI->eraseFromParent();
347 } else if (Constant *C = dyn_cast<Constant>(U)) {
348 // If we have a chain of dead constantexprs or other things dangling from
349 // us, and if they are all dead, nuke them without remorse.
350 if (isSafeToDestroyConstant(C)) {
351 C->destroyConstant();
352 CleanupConstantGlobalUsers(V, Init, DL, TLI);
360 /// Return true if the specified instruction is a safe user of a derived
361 /// expression from a global that we want to SROA.
362 static bool isSafeSROAElementUse(Value *V) {
363 // We might have a dead and dangling constant hanging off of here.
364 if (Constant *C = dyn_cast<Constant>(V))
365 return isSafeToDestroyConstant(C);
367 Instruction *I = dyn_cast<Instruction>(V);
368 if (!I) return false;
371 if (isa<LoadInst>(I)) return true;
373 // Stores *to* the pointer are ok.
374 if (StoreInst *SI = dyn_cast<StoreInst>(I))
375 return SI->getOperand(0) != V;
377 // Otherwise, it must be a GEP.
378 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
379 if (!GEPI) return false;
381 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
382 !cast<Constant>(GEPI->getOperand(1))->isNullValue())
385 for (User *U : GEPI->users())
386 if (!isSafeSROAElementUse(U))
392 /// U is a direct user of the specified global value. Look at it and its uses
393 /// and decide whether it is safe to SROA this global.
394 static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
395 // The user of the global must be a GEP Inst or a ConstantExpr GEP.
396 if (!isa<GetElementPtrInst>(U) &&
397 (!isa<ConstantExpr>(U) ||
398 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
401 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we
402 // don't like < 3 operand CE's, and we don't like non-constant integer
403 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
405 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
406 !cast<Constant>(U->getOperand(1))->isNullValue() ||
407 !isa<ConstantInt>(U->getOperand(2)))
410 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
411 ++GEPI; // Skip over the pointer index.
413 // If this is a use of an array allocation, do a bit more checking for sanity.
414 if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
415 uint64_t NumElements = AT->getNumElements();
416 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
418 // Check to make sure that index falls within the array. If not,
419 // something funny is going on, so we won't do the optimization.
421 if (Idx->getZExtValue() >= NumElements)
424 // We cannot scalar repl this level of the array unless any array
425 // sub-indices are in-range constants. In particular, consider:
426 // A[0][i]. We cannot know that the user isn't doing invalid things like
427 // allowing i to index an out-of-range subscript that accesses A[1].
429 // Scalar replacing *just* the outer index of the array is probably not
430 // going to be a win anyway, so just give up.
431 for (++GEPI; // Skip array index.
434 uint64_t NumElements;
435 if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
436 NumElements = SubArrayTy->getNumElements();
437 else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
438 NumElements = SubVectorTy->getNumElements();
440 assert((*GEPI)->isStructTy() &&
441 "Indexed GEP type is not array, vector, or struct!");
445 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
446 if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
451 for (User *UU : U->users())
452 if (!isSafeSROAElementUse(UU))
458 /// Look at all uses of the global and decide whether it is safe for us to
459 /// perform this transformation.
460 static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
461 for (User *U : GV->users())
462 if (!IsUserOfGlobalSafeForSRA(U, GV))
469 /// Perform scalar replacement of aggregates on the specified global variable.
470 /// This opens the door for other optimizations by exposing the behavior of the
471 /// program in a more fine-grained way. We have determined that this
472 /// transformation is safe already. We return the first global variable we
473 /// insert so that the caller can reprocess it.
474 static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) {
475 // Make sure this global only has simple uses that we can SRA.
476 if (!GlobalUsersSafeToSRA(GV))
479 assert(GV->hasLocalLinkage() && !GV->isConstant());
480 Constant *Init = GV->getInitializer();
481 Type *Ty = Init->getType();
483 std::vector<GlobalVariable*> NewGlobals;
484 Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
486 // Get the alignment of the global, either explicit or target-specific.
487 unsigned StartAlignment = GV->getAlignment();
488 if (StartAlignment == 0)
489 StartAlignment = DL.getABITypeAlignment(GV->getType());
491 if (StructType *STy = dyn_cast<StructType>(Ty)) {
492 NewGlobals.reserve(STy->getNumElements());
493 const StructLayout &Layout = *DL.getStructLayout(STy);
494 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
495 Constant *In = Init->getAggregateElement(i);
496 assert(In && "Couldn't get element of initializer?");
497 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
498 GlobalVariable::InternalLinkage,
499 In, GV->getName()+"."+Twine(i),
500 GV->getThreadLocalMode(),
501 GV->getType()->getAddressSpace());
502 NGV->setExternallyInitialized(GV->isExternallyInitialized());
503 Globals.insert(GV->getIterator(), NGV);
504 NewGlobals.push_back(NGV);
506 // Calculate the known alignment of the field. If the original aggregate
507 // had 256 byte alignment for example, something might depend on that:
508 // propagate info to each field.
509 uint64_t FieldOffset = Layout.getElementOffset(i);
510 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
511 if (NewAlign > DL.getABITypeAlignment(STy->getElementType(i)))
512 NGV->setAlignment(NewAlign);
514 } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
515 unsigned NumElements = 0;
516 if (ArrayType *ATy = dyn_cast<ArrayType>(STy))
517 NumElements = ATy->getNumElements();
519 NumElements = cast<VectorType>(STy)->getNumElements();
521 if (NumElements > 16 && GV->hasNUsesOrMore(16))
522 return nullptr; // It's not worth it.
523 NewGlobals.reserve(NumElements);
525 uint64_t EltSize = DL.getTypeAllocSize(STy->getElementType());
526 unsigned EltAlign = DL.getABITypeAlignment(STy->getElementType());
527 for (unsigned i = 0, e = NumElements; i != e; ++i) {
528 Constant *In = Init->getAggregateElement(i);
529 assert(In && "Couldn't get element of initializer?");
531 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
532 GlobalVariable::InternalLinkage,
533 In, GV->getName()+"."+Twine(i),
534 GV->getThreadLocalMode(),
535 GV->getType()->getAddressSpace());
536 NGV->setExternallyInitialized(GV->isExternallyInitialized());
537 Globals.insert(GV->getIterator(), NGV);
538 NewGlobals.push_back(NGV);
540 // Calculate the known alignment of the field. If the original aggregate
541 // had 256 byte alignment for example, something might depend on that:
542 // propagate info to each field.
543 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
544 if (NewAlign > EltAlign)
545 NGV->setAlignment(NewAlign);
549 if (NewGlobals.empty())
552 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV << "\n");
554 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
556 // Loop over all of the uses of the global, replacing the constantexpr geps,
557 // with smaller constantexpr geps or direct references.
558 while (!GV->use_empty()) {
559 User *GEP = GV->user_back();
560 assert(((isa<ConstantExpr>(GEP) &&
561 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
562 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
564 // Ignore the 1th operand, which has to be zero or else the program is quite
565 // broken (undefined). Get the 2nd operand, which is the structure or array
567 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
568 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
570 Value *NewPtr = NewGlobals[Val];
571 Type *NewTy = NewGlobals[Val]->getValueType();
573 // Form a shorter GEP if needed.
574 if (GEP->getNumOperands() > 3) {
575 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
576 SmallVector<Constant*, 8> Idxs;
577 Idxs.push_back(NullInt);
578 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
579 Idxs.push_back(CE->getOperand(i));
581 ConstantExpr::getGetElementPtr(NewTy, cast<Constant>(NewPtr), Idxs);
583 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
584 SmallVector<Value*, 8> Idxs;
585 Idxs.push_back(NullInt);
586 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
587 Idxs.push_back(GEPI->getOperand(i));
588 NewPtr = GetElementPtrInst::Create(
589 NewTy, NewPtr, Idxs, GEPI->getName() + "." + Twine(Val), GEPI);
592 GEP->replaceAllUsesWith(NewPtr);
594 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
595 GEPI->eraseFromParent();
597 cast<ConstantExpr>(GEP)->destroyConstant();
600 // Delete the old global, now that it is dead.
604 // Loop over the new globals array deleting any globals that are obviously
605 // dead. This can arise due to scalarization of a structure or an array that
606 // has elements that are dead.
607 unsigned FirstGlobal = 0;
608 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
609 if (NewGlobals[i]->use_empty()) {
610 Globals.erase(NewGlobals[i]);
611 if (FirstGlobal == i) ++FirstGlobal;
614 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : nullptr;
617 /// Return true if all users of the specified value will trap if the value is
618 /// dynamically null. PHIs keeps track of any phi nodes we've seen to avoid
619 /// reprocessing them.
620 static bool AllUsesOfValueWillTrapIfNull(const Value *V,
621 SmallPtrSetImpl<const PHINode*> &PHIs) {
622 for (const User *U : V->users())
623 if (isa<LoadInst>(U)) {
625 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
626 if (SI->getOperand(0) == V) {
627 //cerr << "NONTRAPPING USE: " << *U;
628 return false; // Storing the value.
630 } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
631 if (CI->getCalledValue() != V) {
632 //cerr << "NONTRAPPING USE: " << *U;
633 return false; // Not calling the ptr
635 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
636 if (II->getCalledValue() != V) {
637 //cerr << "NONTRAPPING USE: " << *U;
638 return false; // Not calling the ptr
640 } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
641 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
642 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
643 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
644 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
645 // If we've already seen this phi node, ignore it, it has already been
647 if (PHIs.insert(PN).second && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
649 } else if (isa<ICmpInst>(U) &&
650 isa<ConstantPointerNull>(U->getOperand(1))) {
651 // Ignore icmp X, null
653 //cerr << "NONTRAPPING USE: " << *U;
660 /// Return true if all uses of any loads from GV will trap if the loaded value
661 /// is null. Note that this also permits comparisons of the loaded value
662 /// against null, as a special case.
663 static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
664 for (const User *U : GV->users())
665 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
666 SmallPtrSet<const PHINode*, 8> PHIs;
667 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
669 } else if (isa<StoreInst>(U)) {
670 // Ignore stores to the global.
672 // We don't know or understand this user, bail out.
673 //cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
679 static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
680 bool Changed = false;
681 for (auto UI = V->user_begin(), E = V->user_end(); UI != E; ) {
682 Instruction *I = cast<Instruction>(*UI++);
683 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
684 LI->setOperand(0, NewV);
686 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
687 if (SI->getOperand(1) == V) {
688 SI->setOperand(1, NewV);
691 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
693 if (CS.getCalledValue() == V) {
694 // Calling through the pointer! Turn into a direct call, but be careful
695 // that the pointer is not also being passed as an argument.
696 CS.setCalledFunction(NewV);
698 bool PassedAsArg = false;
699 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
700 if (CS.getArgument(i) == V) {
702 CS.setArgument(i, NewV);
706 // Being passed as an argument also. Be careful to not invalidate UI!
707 UI = V->user_begin();
710 } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
711 Changed |= OptimizeAwayTrappingUsesOfValue(CI,
712 ConstantExpr::getCast(CI->getOpcode(),
713 NewV, CI->getType()));
714 if (CI->use_empty()) {
716 CI->eraseFromParent();
718 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
719 // Should handle GEP here.
720 SmallVector<Constant*, 8> Idxs;
721 Idxs.reserve(GEPI->getNumOperands()-1);
722 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
724 if (Constant *C = dyn_cast<Constant>(*i))
728 if (Idxs.size() == GEPI->getNumOperands()-1)
729 Changed |= OptimizeAwayTrappingUsesOfValue(
730 GEPI, ConstantExpr::getGetElementPtr(nullptr, NewV, Idxs));
731 if (GEPI->use_empty()) {
733 GEPI->eraseFromParent();
742 /// The specified global has only one non-null value stored into it. If there
743 /// are uses of the loaded value that would trap if the loaded value is
744 /// dynamically null, then we know that they cannot be reachable with a null
745 /// optimize away the load.
746 static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV,
747 const DataLayout &DL,
748 TargetLibraryInfo *TLI) {
749 bool Changed = false;
751 // Keep track of whether we are able to remove all the uses of the global
752 // other than the store that defines it.
753 bool AllNonStoreUsesGone = true;
755 // Replace all uses of loads with uses of uses of the stored value.
756 for (Value::user_iterator GUI = GV->user_begin(), E = GV->user_end(); GUI != E;){
757 User *GlobalUser = *GUI++;
758 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
759 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
760 // If we were able to delete all uses of the loads
761 if (LI->use_empty()) {
762 LI->eraseFromParent();
765 AllNonStoreUsesGone = false;
767 } else if (isa<StoreInst>(GlobalUser)) {
768 // Ignore the store that stores "LV" to the global.
769 assert(GlobalUser->getOperand(1) == GV &&
770 "Must be storing *to* the global");
772 AllNonStoreUsesGone = false;
774 // If we get here we could have other crazy uses that are transitively
776 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
777 isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) ||
778 isa<BitCastInst>(GlobalUser) ||
779 isa<GetElementPtrInst>(GlobalUser)) &&
780 "Only expect load and stores!");
785 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV << "\n");
789 // If we nuked all of the loads, then none of the stores are needed either,
790 // nor is the global.
791 if (AllNonStoreUsesGone) {
792 if (isLeakCheckerRoot(GV)) {
793 Changed |= CleanupPointerRootUsers(GV, TLI);
796 CleanupConstantGlobalUsers(GV, nullptr, DL, TLI);
798 if (GV->use_empty()) {
799 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
801 GV->eraseFromParent();
808 /// Walk the use list of V, constant folding all of the instructions that are
810 static void ConstantPropUsersOf(Value *V, const DataLayout &DL,
811 TargetLibraryInfo *TLI) {
812 for (Value::user_iterator UI = V->user_begin(), E = V->user_end(); UI != E; )
813 if (Instruction *I = dyn_cast<Instruction>(*UI++))
814 if (Constant *NewC = ConstantFoldInstruction(I, DL, TLI)) {
815 I->replaceAllUsesWith(NewC);
817 // Advance UI to the next non-I use to avoid invalidating it!
818 // Instructions could multiply use V.
819 while (UI != E && *UI == I)
821 I->eraseFromParent();
825 /// This function takes the specified global variable, and transforms the
826 /// program as if it always contained the result of the specified malloc.
827 /// Because it is always the result of the specified malloc, there is no reason
828 /// to actually DO the malloc. Instead, turn the malloc into a global, and any
829 /// loads of GV as uses of the new global.
830 static GlobalVariable *
831 OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, CallInst *CI, Type *AllocTy,
832 ConstantInt *NElements, const DataLayout &DL,
833 TargetLibraryInfo *TLI) {
834 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n');
837 if (NElements->getZExtValue() == 1)
838 GlobalType = AllocTy;
840 // If we have an array allocation, the global variable is of an array.
841 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
843 // Create the new global variable. The contents of the malloc'd memory is
844 // undefined, so initialize with an undef value.
845 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(),
847 GlobalValue::InternalLinkage,
848 UndefValue::get(GlobalType),
849 GV->getName()+".body",
851 GV->getThreadLocalMode());
853 // If there are bitcast users of the malloc (which is typical, usually we have
854 // a malloc + bitcast) then replace them with uses of the new global. Update
855 // other users to use the global as well.
856 BitCastInst *TheBC = nullptr;
857 while (!CI->use_empty()) {
858 Instruction *User = cast<Instruction>(CI->user_back());
859 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
860 if (BCI->getType() == NewGV->getType()) {
861 BCI->replaceAllUsesWith(NewGV);
862 BCI->eraseFromParent();
864 BCI->setOperand(0, NewGV);
868 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
869 User->replaceUsesOfWith(CI, TheBC);
873 Constant *RepValue = NewGV;
874 if (NewGV->getType() != GV->getType()->getElementType())
875 RepValue = ConstantExpr::getBitCast(RepValue,
876 GV->getType()->getElementType());
878 // If there is a comparison against null, we will insert a global bool to
879 // keep track of whether the global was initialized yet or not.
880 GlobalVariable *InitBool =
881 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
882 GlobalValue::InternalLinkage,
883 ConstantInt::getFalse(GV->getContext()),
884 GV->getName()+".init", GV->getThreadLocalMode());
885 bool InitBoolUsed = false;
887 // Loop over all uses of GV, processing them in turn.
888 while (!GV->use_empty()) {
889 if (StoreInst *SI = dyn_cast<StoreInst>(GV->user_back())) {
890 // The global is initialized when the store to it occurs.
891 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
892 SI->getOrdering(), SI->getSynchScope(), SI);
893 SI->eraseFromParent();
897 LoadInst *LI = cast<LoadInst>(GV->user_back());
898 while (!LI->use_empty()) {
899 Use &LoadUse = *LI->use_begin();
900 ICmpInst *ICI = dyn_cast<ICmpInst>(LoadUse.getUser());
906 // Replace the cmp X, 0 with a use of the bool value.
907 // Sink the load to where the compare was, if atomic rules allow us to.
908 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
909 LI->getOrdering(), LI->getSynchScope(),
910 LI->isUnordered() ? (Instruction*)ICI : LI);
912 switch (ICI->getPredicate()) {
913 default: llvm_unreachable("Unknown ICmp Predicate!");
914 case ICmpInst::ICMP_ULT:
915 case ICmpInst::ICMP_SLT: // X < null -> always false
916 LV = ConstantInt::getFalse(GV->getContext());
918 case ICmpInst::ICMP_ULE:
919 case ICmpInst::ICMP_SLE:
920 case ICmpInst::ICMP_EQ:
921 LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
923 case ICmpInst::ICMP_NE:
924 case ICmpInst::ICMP_UGE:
925 case ICmpInst::ICMP_SGE:
926 case ICmpInst::ICMP_UGT:
927 case ICmpInst::ICMP_SGT:
930 ICI->replaceAllUsesWith(LV);
931 ICI->eraseFromParent();
933 LI->eraseFromParent();
936 // If the initialization boolean was used, insert it, otherwise delete it.
938 while (!InitBool->use_empty()) // Delete initializations
939 cast<StoreInst>(InitBool->user_back())->eraseFromParent();
942 GV->getParent()->getGlobalList().insert(GV->getIterator(), InitBool);
944 // Now the GV is dead, nuke it and the malloc..
945 GV->eraseFromParent();
946 CI->eraseFromParent();
948 // To further other optimizations, loop over all users of NewGV and try to
949 // constant prop them. This will promote GEP instructions with constant
950 // indices into GEP constant-exprs, which will allow global-opt to hack on it.
951 ConstantPropUsersOf(NewGV, DL, TLI);
952 if (RepValue != NewGV)
953 ConstantPropUsersOf(RepValue, DL, TLI);
958 /// Scan the use-list of V checking to make sure that there are no complex uses
959 /// of V. We permit simple things like dereferencing the pointer, but not
960 /// storing through the address, unless it is to the specified global.
961 static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
962 const GlobalVariable *GV,
963 SmallPtrSetImpl<const PHINode*> &PHIs) {
964 for (const User *U : V->users()) {
965 const Instruction *Inst = cast<Instruction>(U);
967 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
968 continue; // Fine, ignore.
971 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
972 if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
973 return false; // Storing the pointer itself... bad.
974 continue; // Otherwise, storing through it, or storing into GV... fine.
977 // Must index into the array and into the struct.
978 if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
979 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
984 if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
985 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI
987 if (PHIs.insert(PN).second)
988 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
993 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
994 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
1004 /// The Alloc pointer is stored into GV somewhere. Transform all uses of the
1005 /// allocation into loads from the global and uses of the resultant pointer.
1006 /// Further, delete the store into GV. This assumes that these value pass the
1007 /// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
1008 static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc,
1009 GlobalVariable *GV) {
1010 while (!Alloc->use_empty()) {
1011 Instruction *U = cast<Instruction>(*Alloc->user_begin());
1012 Instruction *InsertPt = U;
1013 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
1014 // If this is the store of the allocation into the global, remove it.
1015 if (SI->getOperand(1) == GV) {
1016 SI->eraseFromParent();
1019 } else if (PHINode *PN = dyn_cast<PHINode>(U)) {
1020 // Insert the load in the corresponding predecessor, not right before the
1022 InsertPt = PN->getIncomingBlock(*Alloc->use_begin())->getTerminator();
1023 } else if (isa<BitCastInst>(U)) {
1024 // Must be bitcast between the malloc and store to initialize the global.
1025 ReplaceUsesOfMallocWithGlobal(U, GV);
1026 U->eraseFromParent();
1028 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
1029 // If this is a "GEP bitcast" and the user is a store to the global, then
1030 // just process it as a bitcast.
1031 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse())
1032 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->user_back()))
1033 if (SI->getOperand(1) == GV) {
1034 // Must be bitcast GEP between the malloc and store to initialize
1036 ReplaceUsesOfMallocWithGlobal(GEPI, GV);
1037 GEPI->eraseFromParent();
1042 // Insert a load from the global, and use it instead of the malloc.
1043 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt);
1044 U->replaceUsesOfWith(Alloc, NL);
1048 /// Verify that all uses of V (a load, or a phi of a load) are simple enough to
1049 /// perform heap SRA on. This permits GEP's that index through the array and
1050 /// struct field, icmps of null, and PHIs.
1051 static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
1052 SmallPtrSetImpl<const PHINode*> &LoadUsingPHIs,
1053 SmallPtrSetImpl<const PHINode*> &LoadUsingPHIsPerLoad) {
1054 // We permit two users of the load: setcc comparing against the null
1055 // pointer, and a getelementptr of a specific form.
1056 for (const User *U : V->users()) {
1057 const Instruction *UI = cast<Instruction>(U);
1059 // Comparison against null is ok.
1060 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UI)) {
1061 if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
1066 // getelementptr is also ok, but only a simple form.
1067 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(UI)) {
1068 // Must index into the array and into the struct.
1069 if (GEPI->getNumOperands() < 3)
1072 // Otherwise the GEP is ok.
1076 if (const PHINode *PN = dyn_cast<PHINode>(UI)) {
1077 if (!LoadUsingPHIsPerLoad.insert(PN).second)
1078 // This means some phi nodes are dependent on each other.
1079 // Avoid infinite looping!
1081 if (!LoadUsingPHIs.insert(PN).second)
1082 // If we have already analyzed this PHI, then it is safe.
1085 // Make sure all uses of the PHI are simple enough to transform.
1086 if (!LoadUsesSimpleEnoughForHeapSRA(PN,
1087 LoadUsingPHIs, LoadUsingPHIsPerLoad))
1093 // Otherwise we don't know what this is, not ok.
1101 /// If all users of values loaded from GV are simple enough to perform HeapSRA,
1103 static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
1104 Instruction *StoredVal) {
1105 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
1106 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
1107 for (const User *U : GV->users())
1108 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
1109 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
1110 LoadUsingPHIsPerLoad))
1112 LoadUsingPHIsPerLoad.clear();
1115 // If we reach here, we know that all uses of the loads and transitive uses
1116 // (through PHI nodes) are simple enough to transform. However, we don't know
1117 // that all inputs the to the PHI nodes are in the same equivalence sets.
1118 // Check to verify that all operands of the PHIs are either PHIS that can be
1119 // transformed, loads from GV, or MI itself.
1120 for (const PHINode *PN : LoadUsingPHIs) {
1121 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
1122 Value *InVal = PN->getIncomingValue(op);
1124 // PHI of the stored value itself is ok.
1125 if (InVal == StoredVal) continue;
1127 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
1128 // One of the PHIs in our set is (optimistically) ok.
1129 if (LoadUsingPHIs.count(InPN))
1134 // Load from GV is ok.
1135 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
1136 if (LI->getOperand(0) == GV)
1141 // Anything else is rejected.
1149 static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
1150 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1151 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1152 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
1154 if (FieldNo >= FieldVals.size())
1155 FieldVals.resize(FieldNo+1);
1157 // If we already have this value, just reuse the previously scalarized
1159 if (Value *FieldVal = FieldVals[FieldNo])
1162 // Depending on what instruction this is, we have several cases.
1164 if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
1165 // This is a scalarized version of the load from the global. Just create
1166 // a new Load of the scalarized global.
1167 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
1168 InsertedScalarizedValues,
1170 LI->getName()+".f"+Twine(FieldNo), LI);
1172 PHINode *PN = cast<PHINode>(V);
1173 // PN's type is pointer to struct. Make a new PHI of pointer to struct
1176 PointerType *PTy = cast<PointerType>(PN->getType());
1177 StructType *ST = cast<StructType>(PTy->getElementType());
1179 unsigned AS = PTy->getAddressSpace();
1181 PHINode::Create(PointerType::get(ST->getElementType(FieldNo), AS),
1182 PN->getNumIncomingValues(),
1183 PN->getName()+".f"+Twine(FieldNo), PN);
1185 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
1188 return FieldVals[FieldNo] = Result;
1191 /// Given a load instruction and a value derived from the load, rewrite the
1192 /// derived value to use the HeapSRoA'd load.
1193 static void RewriteHeapSROALoadUser(Instruction *LoadUser,
1194 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1195 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1196 // If this is a comparison against null, handle it.
1197 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
1198 assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
1199 // If we have a setcc of the loaded pointer, we can use a setcc of any
1201 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
1202 InsertedScalarizedValues, PHIsToRewrite);
1204 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
1205 Constant::getNullValue(NPtr->getType()),
1207 SCI->replaceAllUsesWith(New);
1208 SCI->eraseFromParent();
1212 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
1213 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
1214 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
1215 && "Unexpected GEPI!");
1217 // Load the pointer for this field.
1218 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
1219 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
1220 InsertedScalarizedValues, PHIsToRewrite);
1222 // Create the new GEP idx vector.
1223 SmallVector<Value*, 8> GEPIdx;
1224 GEPIdx.push_back(GEPI->getOperand(1));
1225 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
1227 Value *NGEPI = GetElementPtrInst::Create(GEPI->getResultElementType(), NewPtr, GEPIdx,
1228 GEPI->getName(), GEPI);
1229 GEPI->replaceAllUsesWith(NGEPI);
1230 GEPI->eraseFromParent();
1234 // Recursively transform the users of PHI nodes. This will lazily create the
1235 // PHIs that are needed for individual elements. Keep track of what PHIs we
1236 // see in InsertedScalarizedValues so that we don't get infinite loops (very
1237 // antisocial). If the PHI is already in InsertedScalarizedValues, it has
1238 // already been seen first by another load, so its uses have already been
1240 PHINode *PN = cast<PHINode>(LoadUser);
1241 if (!InsertedScalarizedValues.insert(std::make_pair(PN,
1242 std::vector<Value*>())).second)
1245 // If this is the first time we've seen this PHI, recursively process all
1247 for (auto UI = PN->user_begin(), E = PN->user_end(); UI != E;) {
1248 Instruction *User = cast<Instruction>(*UI++);
1249 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1253 /// We are performing Heap SRoA on a global. Ptr is a value loaded from the
1254 /// global. Eliminate all uses of Ptr, making them use FieldGlobals instead.
1255 /// All uses of loaded values satisfy AllGlobalLoadUsesSimpleEnoughForHeapSRA.
1256 static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
1257 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1258 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1259 for (auto UI = Load->user_begin(), E = Load->user_end(); UI != E;) {
1260 Instruction *User = cast<Instruction>(*UI++);
1261 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1264 if (Load->use_empty()) {
1265 Load->eraseFromParent();
1266 InsertedScalarizedValues.erase(Load);
1270 /// CI is an allocation of an array of structures. Break it up into multiple
1271 /// allocations of arrays of the fields.
1272 static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
1273 Value *NElems, const DataLayout &DL,
1274 const TargetLibraryInfo *TLI) {
1275 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n');
1276 Type *MAT = getMallocAllocatedType(CI, TLI);
1277 StructType *STy = cast<StructType>(MAT);
1279 // There is guaranteed to be at least one use of the malloc (storing
1280 // it into GV). If there are other uses, change them to be uses of
1281 // the global to simplify later code. This also deletes the store
1283 ReplaceUsesOfMallocWithGlobal(CI, GV);
1285 // Okay, at this point, there are no users of the malloc. Insert N
1286 // new mallocs at the same place as CI, and N globals.
1287 std::vector<Value*> FieldGlobals;
1288 std::vector<Value*> FieldMallocs;
1290 unsigned AS = GV->getType()->getPointerAddressSpace();
1291 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
1292 Type *FieldTy = STy->getElementType(FieldNo);
1293 PointerType *PFieldTy = PointerType::get(FieldTy, AS);
1295 GlobalVariable *NGV =
1296 new GlobalVariable(*GV->getParent(),
1297 PFieldTy, false, GlobalValue::InternalLinkage,
1298 Constant::getNullValue(PFieldTy),
1299 GV->getName() + ".f" + Twine(FieldNo), GV,
1300 GV->getThreadLocalMode());
1301 FieldGlobals.push_back(NGV);
1303 unsigned TypeSize = DL.getTypeAllocSize(FieldTy);
1304 if (StructType *ST = dyn_cast<StructType>(FieldTy))
1305 TypeSize = DL.getStructLayout(ST)->getSizeInBytes();
1306 Type *IntPtrTy = DL.getIntPtrType(CI->getType());
1307 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
1308 ConstantInt::get(IntPtrTy, TypeSize),
1310 CI->getName() + ".f" + Twine(FieldNo));
1311 FieldMallocs.push_back(NMI);
1312 new StoreInst(NMI, NGV, CI);
1315 // The tricky aspect of this transformation is handling the case when malloc
1316 // fails. In the original code, malloc failing would set the result pointer
1317 // of malloc to null. In this case, some mallocs could succeed and others
1318 // could fail. As such, we emit code that looks like this:
1319 // F0 = malloc(field0)
1320 // F1 = malloc(field1)
1321 // F2 = malloc(field2)
1322 // if (F0 == 0 || F1 == 0 || F2 == 0) {
1323 // if (F0) { free(F0); F0 = 0; }
1324 // if (F1) { free(F1); F1 = 0; }
1325 // if (F2) { free(F2); F2 = 0; }
1327 // The malloc can also fail if its argument is too large.
1328 Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
1329 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
1330 ConstantZero, "isneg");
1331 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
1332 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
1333 Constant::getNullValue(FieldMallocs[i]->getType()),
1335 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
1338 // Split the basic block at the old malloc.
1339 BasicBlock *OrigBB = CI->getParent();
1340 BasicBlock *ContBB =
1341 OrigBB->splitBasicBlock(CI->getIterator(), "malloc_cont");
1343 // Create the block to check the first condition. Put all these blocks at the
1344 // end of the function as they are unlikely to be executed.
1345 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
1347 OrigBB->getParent());
1349 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
1350 // branch on RunningOr.
1351 OrigBB->getTerminator()->eraseFromParent();
1352 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
1354 // Within the NullPtrBlock, we need to emit a comparison and branch for each
1355 // pointer, because some may be null while others are not.
1356 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1357 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
1358 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
1359 Constant::getNullValue(GVVal->getType()));
1360 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
1361 OrigBB->getParent());
1362 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
1363 OrigBB->getParent());
1364 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
1367 // Fill in FreeBlock.
1368 CallInst::CreateFree(GVVal, BI);
1369 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
1371 BranchInst::Create(NextBlock, FreeBlock);
1373 NullPtrBlock = NextBlock;
1376 BranchInst::Create(ContBB, NullPtrBlock);
1378 // CI is no longer needed, remove it.
1379 CI->eraseFromParent();
1381 /// As we process loads, if we can't immediately update all uses of the load,
1382 /// keep track of what scalarized loads are inserted for a given load.
1383 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues;
1384 InsertedScalarizedValues[GV] = FieldGlobals;
1386 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite;
1388 // Okay, the malloc site is completely handled. All of the uses of GV are now
1389 // loads, and all uses of those loads are simple. Rewrite them to use loads
1390 // of the per-field globals instead.
1391 for (auto UI = GV->user_begin(), E = GV->user_end(); UI != E;) {
1392 Instruction *User = cast<Instruction>(*UI++);
1394 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1395 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
1399 // Must be a store of null.
1400 StoreInst *SI = cast<StoreInst>(User);
1401 assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
1402 "Unexpected heap-sra user!");
1404 // Insert a store of null into each global.
1405 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1406 PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType());
1407 Constant *Null = Constant::getNullValue(PT->getElementType());
1408 new StoreInst(Null, FieldGlobals[i], SI);
1410 // Erase the original store.
1411 SI->eraseFromParent();
1414 // While we have PHIs that are interesting to rewrite, do it.
1415 while (!PHIsToRewrite.empty()) {
1416 PHINode *PN = PHIsToRewrite.back().first;
1417 unsigned FieldNo = PHIsToRewrite.back().second;
1418 PHIsToRewrite.pop_back();
1419 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
1420 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
1422 // Add all the incoming values. This can materialize more phis.
1423 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1424 Value *InVal = PN->getIncomingValue(i);
1425 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
1427 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
1431 // Drop all inter-phi links and any loads that made it this far.
1432 for (DenseMap<Value*, std::vector<Value*> >::iterator
1433 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1435 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1436 PN->dropAllReferences();
1437 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1438 LI->dropAllReferences();
1441 // Delete all the phis and loads now that inter-references are dead.
1442 for (DenseMap<Value*, std::vector<Value*> >::iterator
1443 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1445 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1446 PN->eraseFromParent();
1447 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1448 LI->eraseFromParent();
1451 // The old global is now dead, remove it.
1452 GV->eraseFromParent();
1455 return cast<GlobalVariable>(FieldGlobals[0]);
1458 /// This function is called when we see a pointer global variable with a single
1459 /// value stored it that is a malloc or cast of malloc.
1460 static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, CallInst *CI,
1462 AtomicOrdering Ordering,
1463 Module::global_iterator &GVI,
1464 const DataLayout &DL,
1465 TargetLibraryInfo *TLI) {
1466 // If this is a malloc of an abstract type, don't touch it.
1467 if (!AllocTy->isSized())
1470 // We can't optimize this global unless all uses of it are *known* to be
1471 // of the malloc value, not of the null initializer value (consider a use
1472 // that compares the global's value against zero to see if the malloc has
1473 // been reached). To do this, we check to see if all uses of the global
1474 // would trap if the global were null: this proves that they must all
1475 // happen after the malloc.
1476 if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
1479 // We can't optimize this if the malloc itself is used in a complex way,
1480 // for example, being stored into multiple globals. This allows the
1481 // malloc to be stored into the specified global, loaded icmp'd, and
1482 // GEP'd. These are all things we could transform to using the global
1484 SmallPtrSet<const PHINode*, 8> PHIs;
1485 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
1488 // If we have a global that is only initialized with a fixed size malloc,
1489 // transform the program to use global memory instead of malloc'd memory.
1490 // This eliminates dynamic allocation, avoids an indirection accessing the
1491 // data, and exposes the resultant global to further GlobalOpt.
1492 // We cannot optimize the malloc if we cannot determine malloc array size.
1493 Value *NElems = getMallocArraySize(CI, DL, TLI, true);
1497 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
1498 // Restrict this transformation to only working on small allocations
1499 // (2048 bytes currently), as we don't want to introduce a 16M global or
1501 if (NElements->getZExtValue() * DL.getTypeAllocSize(AllocTy) < 2048) {
1502 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, DL, TLI)
1507 // If the allocation is an array of structures, consider transforming this
1508 // into multiple malloc'd arrays, one for each field. This is basically
1509 // SRoA for malloc'd memory.
1511 if (Ordering != NotAtomic)
1514 // If this is an allocation of a fixed size array of structs, analyze as a
1515 // variable size array. malloc [100 x struct],1 -> malloc struct, 100
1516 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
1517 if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
1518 AllocTy = AT->getElementType();
1520 StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
1524 // This the structure has an unreasonable number of fields, leave it
1526 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
1527 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
1529 // If this is a fixed size array, transform the Malloc to be an alloc of
1530 // structs. malloc [100 x struct],1 -> malloc struct, 100
1531 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) {
1532 Type *IntPtrTy = DL.getIntPtrType(CI->getType());
1533 unsigned TypeSize = DL.getStructLayout(AllocSTy)->getSizeInBytes();
1534 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
1535 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
1536 Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy,
1537 AllocSize, NumElements,
1538 nullptr, CI->getName());
1539 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
1540 CI->replaceAllUsesWith(Cast);
1541 CI->eraseFromParent();
1542 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc))
1543 CI = cast<CallInst>(BCI->getOperand(0));
1545 CI = cast<CallInst>(Malloc);
1548 GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, DL, TLI, true),
1557 // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
1558 // that only one value (besides its initializer) is ever stored to the global.
1559 static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
1560 AtomicOrdering Ordering,
1561 Module::global_iterator &GVI,
1562 const DataLayout &DL,
1563 TargetLibraryInfo *TLI) {
1564 // Ignore no-op GEPs and bitcasts.
1565 StoredOnceVal = StoredOnceVal->stripPointerCasts();
1567 // If we are dealing with a pointer global that is initialized to null and
1568 // only has one (non-null) value stored into it, then we can optimize any
1569 // users of the loaded value (often calls and loads) that would trap if the
1571 if (GV->getInitializer()->getType()->isPointerTy() &&
1572 GV->getInitializer()->isNullValue()) {
1573 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
1574 if (GV->getInitializer()->getType() != SOVC->getType())
1575 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
1577 // Optimize away any trapping uses of the loaded value.
1578 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, DL, TLI))
1580 } else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) {
1581 Type *MallocType = getMallocAllocatedType(CI, TLI);
1583 TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, Ordering, GVI,
1592 /// At this point, we have learned that the only two values ever stored into GV
1593 /// are its initializer and OtherVal. See if we can shrink the global into a
1594 /// boolean and select between the two values whenever it is used. This exposes
1595 /// the values to other scalar optimizations.
1596 static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
1597 Type *GVElType = GV->getType()->getElementType();
1599 // If GVElType is already i1, it is already shrunk. If the type of the GV is
1600 // an FP value, pointer or vector, don't do this optimization because a select
1601 // between them is very expensive and unlikely to lead to later
1602 // simplification. In these cases, we typically end up with "cond ? v1 : v2"
1603 // where v1 and v2 both require constant pool loads, a big loss.
1604 if (GVElType == Type::getInt1Ty(GV->getContext()) ||
1605 GVElType->isFloatingPointTy() ||
1606 GVElType->isPointerTy() || GVElType->isVectorTy())
1609 // Walk the use list of the global seeing if all the uses are load or store.
1610 // If there is anything else, bail out.
1611 for (User *U : GV->users())
1612 if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
1615 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV << "\n");
1617 // Create the new global, initializing it to false.
1618 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
1620 GlobalValue::InternalLinkage,
1621 ConstantInt::getFalse(GV->getContext()),
1623 GV->getThreadLocalMode(),
1624 GV->getType()->getAddressSpace());
1625 GV->getParent()->getGlobalList().insert(GV->getIterator(), NewGV);
1627 Constant *InitVal = GV->getInitializer();
1628 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
1629 "No reason to shrink to bool!");
1631 // If initialized to zero and storing one into the global, we can use a cast
1632 // instead of a select to synthesize the desired value.
1633 bool IsOneZero = false;
1634 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
1635 IsOneZero = InitVal->isNullValue() && CI->isOne();
1637 while (!GV->use_empty()) {
1638 Instruction *UI = cast<Instruction>(GV->user_back());
1639 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
1640 // Change the store into a boolean store.
1641 bool StoringOther = SI->getOperand(0) == OtherVal;
1642 // Only do this if we weren't storing a loaded value.
1644 if (StoringOther || SI->getOperand(0) == InitVal) {
1645 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
1648 // Otherwise, we are storing a previously loaded copy. To do this,
1649 // change the copy from copying the original value to just copying the
1651 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
1653 // If we've already replaced the input, StoredVal will be a cast or
1654 // select instruction. If not, it will be a load of the original
1656 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
1657 assert(LI->getOperand(0) == GV && "Not a copy!");
1658 // Insert a new load, to preserve the saved value.
1659 StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1660 LI->getOrdering(), LI->getSynchScope(), LI);
1662 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
1663 "This is not a form that we understand!");
1664 StoreVal = StoredVal->getOperand(0);
1665 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
1668 new StoreInst(StoreVal, NewGV, false, 0,
1669 SI->getOrdering(), SI->getSynchScope(), SI);
1671 // Change the load into a load of bool then a select.
1672 LoadInst *LI = cast<LoadInst>(UI);
1673 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1674 LI->getOrdering(), LI->getSynchScope(), LI);
1677 NSI = new ZExtInst(NLI, LI->getType(), "", LI);
1679 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
1681 LI->replaceAllUsesWith(NSI);
1683 UI->eraseFromParent();
1686 // Retain the name of the old global variable. People who are debugging their
1687 // programs may expect these variables to be named the same.
1688 NewGV->takeName(GV);
1689 GV->eraseFromParent();
1694 /// Analyze the specified global variable and optimize it if possible. If we
1695 /// make a change, return true.
1696 bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
1697 Module::global_iterator &GVI) {
1698 // Do more involved optimizations if the global is internal.
1699 GV->removeDeadConstantUsers();
1701 if (GV->use_empty()) {
1702 DEBUG(dbgs() << "GLOBAL DEAD: " << *GV << "\n");
1703 GV->eraseFromParent();
1708 if (!GV->hasLocalLinkage())
1713 if (GlobalStatus::analyzeGlobal(GV, GS))
1716 if (!GS.IsCompared && !GV->hasUnnamedAddr()) {
1717 GV->setUnnamedAddr(true);
1721 if (GV->isConstant() || !GV->hasInitializer())
1724 return ProcessInternalGlobal(GV, GVI, GS);
1727 bool GlobalOpt::isPointerValueDeadOnEntryToFunction(const Function *F, GlobalValue *GV) {
1728 // Find all uses of GV. We expect them all to be in F, and if we can't
1729 // identify any of the uses we bail out.
1731 // On each of these uses, identify if the memory that GV points to is
1732 // used/required/live at the start of the function. If it is not, for example
1733 // if the first thing the function does is store to the GV, the GV can
1734 // possibly be demoted.
1736 // We don't do an exhaustive search for memory operations - simply look
1737 // through bitcasts as they're quite common and benign.
1738 const DataLayout &DL = GV->getParent()->getDataLayout();
1739 SmallVector<LoadInst *, 4> Loads;
1740 SmallVector<StoreInst *, 4> Stores;
1741 for (auto *U : GV->users()) {
1742 if (Operator::getOpcode(U) == Instruction::BitCast) {
1743 for (auto *UU : U->users()) {
1744 if (auto *LI = dyn_cast<LoadInst>(UU))
1745 Loads.push_back(LI);
1746 else if (auto *SI = dyn_cast<StoreInst>(UU))
1747 Stores.push_back(SI);
1754 Instruction *I = dyn_cast<Instruction>(U);
1757 assert(I->getParent()->getParent() == F);
1759 if (auto *LI = dyn_cast<LoadInst>(I))
1760 Loads.push_back(LI);
1761 else if (auto *SI = dyn_cast<StoreInst>(I))
1762 Stores.push_back(SI);
1767 // We have identified all uses of GV into loads and stores. Now check if all
1768 // of them are known not to depend on the value of the global at the function
1769 // entry point. We do this by ensuring that every load is dominated by at
1771 auto &DT = getAnalysis<DominatorTreeWrapperPass>(*const_cast<Function *>(F))
1774 // The below check is quadratic. Check we're not going to do too many tests.
1775 // FIXME: Even though this will always have worst-case quadratic time, we
1776 // could put effort into minimizing the average time by putting stores that
1777 // have been shown to dominate at least one load at the beginning of the
1778 // Stores array, making subsequent dominance checks more likely to succeed
1781 // The threshold here is fairly large because global->local demotion is a
1782 // very powerful optimization should it fire.
1783 const unsigned Threshold = 100;
1784 if (Loads.size() * Stores.size() > Threshold)
1787 for (auto *L : Loads) {
1788 auto *LTy = L->getType();
1789 if (!std::any_of(Stores.begin(), Stores.end(), [&](StoreInst *S) {
1790 auto *STy = S->getValueOperand()->getType();
1791 // The load is only dominated by the store if DomTree says so
1792 // and the number of bits loaded in L is less than or equal to
1793 // the number of bits stored in S.
1794 return DT.dominates(S, L) &&
1795 DL.getTypeStoreSize(LTy) <= DL.getTypeStoreSize(STy);
1799 // All loads have known dependences inside F, so the global can be localized.
1803 /// C may have non-instruction users. Can all of those users be turned into
1805 static bool allNonInstructionUsersCanBeMadeInstructions(Constant *C) {
1806 // We don't do this exhaustively. The most common pattern that we really need
1807 // to care about is a constant GEP or constant bitcast - so just looking
1808 // through one single ConstantExpr.
1810 // The set of constants that this function returns true for must be able to be
1811 // handled by makeAllConstantUsesInstructions.
1812 for (auto *U : C->users()) {
1813 if (isa<Instruction>(U))
1815 if (!isa<ConstantExpr>(U))
1816 // Non instruction, non-constantexpr user; cannot convert this.
1818 for (auto *UU : U->users())
1819 if (!isa<Instruction>(UU))
1820 // A constantexpr used by another constant. We don't try and recurse any
1821 // further but just bail out at this point.
1828 /// C may have non-instruction users, and
1829 /// allNonInstructionUsersCanBeMadeInstructions has returned true. Convert the
1830 /// non-instruction users to instructions.
1831 static void makeAllConstantUsesInstructions(Constant *C) {
1832 SmallVector<ConstantExpr*,4> Users;
1833 for (auto *U : C->users()) {
1834 if (isa<ConstantExpr>(U))
1835 Users.push_back(cast<ConstantExpr>(U));
1837 // We should never get here; allNonInstructionUsersCanBeMadeInstructions
1838 // should not have returned true for C.
1840 isa<Instruction>(U) &&
1841 "Can't transform non-constantexpr non-instruction to instruction!");
1844 SmallVector<Value*,4> UUsers;
1845 for (auto *U : Users) {
1847 for (auto *UU : U->users())
1848 UUsers.push_back(UU);
1849 for (auto *UU : UUsers) {
1850 Instruction *UI = cast<Instruction>(UU);
1851 Instruction *NewU = U->getAsInstruction();
1852 NewU->insertBefore(UI);
1853 UI->replaceUsesOfWith(U, NewU);
1855 U->dropAllReferences();
1859 /// Analyze the specified global variable and optimize
1860 /// it if possible. If we make a change, return true.
1861 bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
1862 Module::global_iterator &GVI,
1863 const GlobalStatus &GS) {
1864 auto &DL = GV->getParent()->getDataLayout();
1865 // If this is a first class global and has only one accessing function and
1866 // this function is non-recursive, we replace the global with a local alloca
1867 // in this function.
1869 // NOTE: It doesn't make sense to promote non-single-value types since we
1870 // are just replacing static memory to stack memory.
1872 // If the global is in different address space, don't bring it to stack.
1873 if (!GS.HasMultipleAccessingFunctions &&
1874 GS.AccessingFunction &&
1875 GV->getType()->getElementType()->isSingleValueType() &&
1876 GV->getType()->getAddressSpace() == 0 &&
1877 !GV->isExternallyInitialized() &&
1878 allNonInstructionUsersCanBeMadeInstructions(GV) &&
1879 GS.AccessingFunction->doesNotRecurse() &&
1880 isPointerValueDeadOnEntryToFunction(GS.AccessingFunction, GV) ) {
1881 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV << "\n");
1882 Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction
1883 ->getEntryBlock().begin());
1884 Type *ElemTy = GV->getType()->getElementType();
1885 // FIXME: Pass Global's alignment when globals have alignment
1886 AllocaInst *Alloca = new AllocaInst(ElemTy, nullptr,
1887 GV->getName(), &FirstI);
1888 if (!isa<UndefValue>(GV->getInitializer()))
1889 new StoreInst(GV->getInitializer(), Alloca, &FirstI);
1891 makeAllConstantUsesInstructions(GV);
1893 GV->replaceAllUsesWith(Alloca);
1894 GV->eraseFromParent();
1899 // If the global is never loaded (but may be stored to), it is dead.
1902 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV << "\n");
1905 if (isLeakCheckerRoot(GV)) {
1906 // Delete any constant stores to the global.
1907 Changed = CleanupPointerRootUsers(GV, TLI);
1909 // Delete any stores we can find to the global. We may not be able to
1910 // make it completely dead though.
1911 Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
1914 // If the global is dead now, delete it.
1915 if (GV->use_empty()) {
1916 GV->eraseFromParent();
1922 } else if (GS.StoredType <= GlobalStatus::InitializerStored) {
1923 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n");
1924 GV->setConstant(true);
1926 // Clean up any obviously simplifiable users now.
1927 CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
1929 // If the global is dead now, just nuke it.
1930 if (GV->use_empty()) {
1931 DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
1932 << "all users and delete global!\n");
1933 GV->eraseFromParent();
1939 } else if (!GV->getInitializer()->getType()->isSingleValueType()) {
1940 const DataLayout &DL = GV->getParent()->getDataLayout();
1941 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, DL)) {
1942 GVI = FirstNewGV->getIterator(); // Don't skip the newly produced globals!
1945 } else if (GS.StoredType == GlobalStatus::StoredOnce && GS.StoredOnceValue) {
1946 // If the initial value for the global was an undef value, and if only
1947 // one other value was stored into it, we can just change the
1948 // initializer to be the stored value, then delete all stores to the
1949 // global. This allows us to mark it constant.
1950 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
1951 if (isa<UndefValue>(GV->getInitializer())) {
1952 // Change the initial value here.
1953 GV->setInitializer(SOVConstant);
1955 // Clean up any obviously simplifiable users now.
1956 CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
1958 if (GV->use_empty()) {
1959 DEBUG(dbgs() << " *** Substituting initializer allowed us to "
1960 << "simplify all users and delete global!\n");
1961 GV->eraseFromParent();
1964 GVI = GV->getIterator();
1970 // Try to optimize globals based on the knowledge that only one value
1971 // (besides its initializer) is ever stored to the global.
1972 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, GVI,
1976 // Otherwise, if the global was not a boolean, we can shrink it to be a
1978 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) {
1979 if (GS.Ordering == NotAtomic) {
1980 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
1991 /// Walk all of the direct calls of the specified function, changing them to
1993 static void ChangeCalleesToFastCall(Function *F) {
1994 for (User *U : F->users()) {
1995 if (isa<BlockAddress>(U))
1997 CallSite CS(cast<Instruction>(U));
1998 CS.setCallingConv(CallingConv::Fast);
2002 static AttributeSet StripNest(LLVMContext &C, const AttributeSet &Attrs) {
2003 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
2004 unsigned Index = Attrs.getSlotIndex(i);
2005 if (!Attrs.getSlotAttributes(i).hasAttribute(Index, Attribute::Nest))
2008 // There can be only one.
2009 return Attrs.removeAttribute(C, Index, Attribute::Nest);
2015 static void RemoveNestAttribute(Function *F) {
2016 F->setAttributes(StripNest(F->getContext(), F->getAttributes()));
2017 for (User *U : F->users()) {
2018 if (isa<BlockAddress>(U))
2020 CallSite CS(cast<Instruction>(U));
2021 CS.setAttributes(StripNest(F->getContext(), CS.getAttributes()));
2025 /// Return true if this is a calling convention that we'd like to change. The
2026 /// idea here is that we don't want to mess with the convention if the user
2027 /// explicitly requested something with performance implications like coldcc,
2028 /// GHC, or anyregcc.
2029 static bool isProfitableToMakeFastCC(Function *F) {
2030 CallingConv::ID CC = F->getCallingConv();
2031 // FIXME: Is it worth transforming x86_stdcallcc and x86_fastcallcc?
2032 return CC == CallingConv::C || CC == CallingConv::X86_ThisCall;
2035 bool GlobalOpt::OptimizeFunctions(Module &M) {
2036 bool Changed = false;
2037 // Optimize functions.
2038 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
2039 Function *F = &*FI++;
2040 // Functions without names cannot be referenced outside this module.
2041 if (!F->hasName() && !F->isDeclaration() && !F->hasLocalLinkage())
2042 F->setLinkage(GlobalValue::InternalLinkage);
2044 const Comdat *C = F->getComdat();
2045 bool inComdat = C && NotDiscardableComdats.count(C);
2046 F->removeDeadConstantUsers();
2047 if ((!inComdat || F->hasLocalLinkage()) && F->isDefTriviallyDead()) {
2048 F->eraseFromParent();
2051 } else if (F->hasLocalLinkage()) {
2052 if (isProfitableToMakeFastCC(F) && !F->isVarArg() &&
2053 !F->hasAddressTaken()) {
2054 // If this function has a calling convention worth changing, is not a
2055 // varargs function, and is only called directly, promote it to use the
2056 // Fast calling convention.
2057 F->setCallingConv(CallingConv::Fast);
2058 ChangeCalleesToFastCall(F);
2063 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
2064 !F->hasAddressTaken()) {
2065 // The function is not used by a trampoline intrinsic, so it is safe
2066 // to remove the 'nest' attribute.
2067 RemoveNestAttribute(F);
2076 bool GlobalOpt::OptimizeGlobalVars(Module &M) {
2077 bool Changed = false;
2079 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
2081 GlobalVariable *GV = &*GVI++;
2082 // Global variables without names cannot be referenced outside this module.
2083 if (!GV->hasName() && !GV->isDeclaration() && !GV->hasLocalLinkage())
2084 GV->setLinkage(GlobalValue::InternalLinkage);
2085 // Simplify the initializer.
2086 if (GV->hasInitializer())
2087 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
2088 auto &DL = M.getDataLayout();
2089 Constant *New = ConstantFoldConstantExpression(CE, DL, TLI);
2090 if (New && New != CE)
2091 GV->setInitializer(New);
2094 if (GV->isDiscardableIfUnused()) {
2095 if (const Comdat *C = GV->getComdat())
2096 if (NotDiscardableComdats.count(C) && !GV->hasLocalLinkage())
2098 Changed |= ProcessGlobal(GV, GVI);
2105 isSimpleEnoughValueToCommit(Constant *C,
2106 SmallPtrSetImpl<Constant *> &SimpleConstants,
2107 const DataLayout &DL);
2109 /// Return true if the specified constant can be handled by the code generator.
2110 /// We don't want to generate something like:
2111 /// void *X = &X/42;
2112 /// because the code generator doesn't have a relocation that can handle that.
2114 /// This function should be called if C was not found (but just got inserted)
2115 /// in SimpleConstants to avoid having to rescan the same constants all the
2118 isSimpleEnoughValueToCommitHelper(Constant *C,
2119 SmallPtrSetImpl<Constant *> &SimpleConstants,
2120 const DataLayout &DL) {
2121 // Simple global addresses are supported, do not allow dllimport or
2122 // thread-local globals.
2123 if (auto *GV = dyn_cast<GlobalValue>(C))
2124 return !GV->hasDLLImportStorageClass() && !GV->isThreadLocal();
2126 // Simple integer, undef, constant aggregate zero, etc are all supported.
2127 if (C->getNumOperands() == 0 || isa<BlockAddress>(C))
2130 // Aggregate values are safe if all their elements are.
2131 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) ||
2132 isa<ConstantVector>(C)) {
2133 for (Value *Op : C->operands())
2134 if (!isSimpleEnoughValueToCommit(cast<Constant>(Op), SimpleConstants, DL))
2139 // We don't know exactly what relocations are allowed in constant expressions,
2140 // so we allow &global+constantoffset, which is safe and uniformly supported
2142 ConstantExpr *CE = cast<ConstantExpr>(C);
2143 switch (CE->getOpcode()) {
2144 case Instruction::BitCast:
2145 // Bitcast is fine if the casted value is fine.
2146 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
2148 case Instruction::IntToPtr:
2149 case Instruction::PtrToInt:
2150 // int <=> ptr is fine if the int type is the same size as the
2152 if (DL.getTypeSizeInBits(CE->getType()) !=
2153 DL.getTypeSizeInBits(CE->getOperand(0)->getType()))
2155 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
2157 // GEP is fine if it is simple + constant offset.
2158 case Instruction::GetElementPtr:
2159 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
2160 if (!isa<ConstantInt>(CE->getOperand(i)))
2162 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
2164 case Instruction::Add:
2165 // We allow simple+cst.
2166 if (!isa<ConstantInt>(CE->getOperand(1)))
2168 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL);
2174 isSimpleEnoughValueToCommit(Constant *C,
2175 SmallPtrSetImpl<Constant *> &SimpleConstants,
2176 const DataLayout &DL) {
2177 // If we already checked this constant, we win.
2178 if (!SimpleConstants.insert(C).second)
2180 // Check the constant.
2181 return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, DL);
2185 /// Return true if this constant is simple enough for us to understand. In
2186 /// particular, if it is a cast to anything other than from one pointer type to
2187 /// another pointer type, we punt. We basically just support direct accesses to
2188 /// globals and GEP's of globals. This should be kept up to date with
2190 static bool isSimpleEnoughPointerToCommit(Constant *C) {
2191 // Conservatively, avoid aggregate types. This is because we don't
2192 // want to worry about them partially overlapping other stores.
2193 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
2196 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
2197 // Do not allow weak/*_odr/linkonce linkage or external globals.
2198 return GV->hasUniqueInitializer();
2200 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
2201 // Handle a constantexpr gep.
2202 if (CE->getOpcode() == Instruction::GetElementPtr &&
2203 isa<GlobalVariable>(CE->getOperand(0)) &&
2204 cast<GEPOperator>(CE)->isInBounds()) {
2205 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2206 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2207 // external globals.
2208 if (!GV->hasUniqueInitializer())
2211 // The first index must be zero.
2212 ConstantInt *CI = dyn_cast<ConstantInt>(*std::next(CE->op_begin()));
2213 if (!CI || !CI->isZero()) return false;
2215 // The remaining indices must be compile-time known integers within the
2216 // notional bounds of the corresponding static array types.
2217 if (!CE->isGEPWithNoNotionalOverIndexing())
2220 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2222 // A constantexpr bitcast from a pointer to another pointer is a no-op,
2223 // and we know how to evaluate it by moving the bitcast from the pointer
2224 // operand to the value operand.
2225 } else if (CE->getOpcode() == Instruction::BitCast &&
2226 isa<GlobalVariable>(CE->getOperand(0))) {
2227 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2228 // external globals.
2229 return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
2236 /// Evaluate a piece of a constantexpr store into a global initializer. This
2237 /// returns 'Init' modified to reflect 'Val' stored into it. At this point, the
2238 /// GEP operands of Addr [0, OpNo) have been stepped into.
2239 static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
2240 ConstantExpr *Addr, unsigned OpNo) {
2241 // Base case of the recursion.
2242 if (OpNo == Addr->getNumOperands()) {
2243 assert(Val->getType() == Init->getType() && "Type mismatch!");
2247 SmallVector<Constant*, 32> Elts;
2248 if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
2249 // Break up the constant into its elements.
2250 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
2251 Elts.push_back(Init->getAggregateElement(i));
2253 // Replace the element that we are supposed to.
2254 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
2255 unsigned Idx = CU->getZExtValue();
2256 assert(Idx < STy->getNumElements() && "Struct index out of range!");
2257 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
2259 // Return the modified struct.
2260 return ConstantStruct::get(STy, Elts);
2263 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
2264 SequentialType *InitTy = cast<SequentialType>(Init->getType());
2267 if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
2268 NumElts = ATy->getNumElements();
2270 NumElts = InitTy->getVectorNumElements();
2272 // Break up the array into elements.
2273 for (uint64_t i = 0, e = NumElts; i != e; ++i)
2274 Elts.push_back(Init->getAggregateElement(i));
2276 assert(CI->getZExtValue() < NumElts);
2277 Elts[CI->getZExtValue()] =
2278 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
2280 if (Init->getType()->isArrayTy())
2281 return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
2282 return ConstantVector::get(Elts);
2285 /// We have decided that Addr (which satisfies the predicate
2286 /// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen.
2287 static void CommitValueTo(Constant *Val, Constant *Addr) {
2288 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
2289 assert(GV->hasInitializer());
2290 GV->setInitializer(Val);
2294 ConstantExpr *CE = cast<ConstantExpr>(Addr);
2295 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2296 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
2301 /// This class evaluates LLVM IR, producing the Constant representing each SSA
2302 /// instruction. Changes to global variables are stored in a mapping that can
2303 /// be iterated over after the evaluation is complete. Once an evaluation call
2304 /// fails, the evaluation object should not be reused.
2307 Evaluator(const DataLayout &DL, const TargetLibraryInfo *TLI)
2308 : DL(DL), TLI(TLI) {
2309 ValueStack.emplace_back();
2313 for (auto &Tmp : AllocaTmps)
2314 // If there are still users of the alloca, the program is doing something
2315 // silly, e.g. storing the address of the alloca somewhere and using it
2316 // later. Since this is undefined, we'll just make it be null.
2317 if (!Tmp->use_empty())
2318 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
2321 /// Evaluate a call to function F, returning true if successful, false if we
2322 /// can't evaluate it. ActualArgs contains the formal arguments for the
2324 bool EvaluateFunction(Function *F, Constant *&RetVal,
2325 const SmallVectorImpl<Constant*> &ActualArgs);
2327 /// Evaluate all instructions in block BB, returning true if successful, false
2328 /// if we can't evaluate it. NewBB returns the next BB that control flows
2329 /// into, or null upon return.
2330 bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB);
2332 Constant *getVal(Value *V) {
2333 if (Constant *CV = dyn_cast<Constant>(V)) return CV;
2334 Constant *R = ValueStack.back().lookup(V);
2335 assert(R && "Reference to an uncomputed value!");
2339 void setVal(Value *V, Constant *C) {
2340 ValueStack.back()[V] = C;
2343 const DenseMap<Constant*, Constant*> &getMutatedMemory() const {
2344 return MutatedMemory;
2347 const SmallPtrSetImpl<GlobalVariable*> &getInvariants() const {
2352 Constant *ComputeLoadResult(Constant *P);
2354 /// As we compute SSA register values, we store their contents here. The back
2355 /// of the deque contains the current function and the stack contains the
2356 /// values in the calling frames.
2357 std::deque<DenseMap<Value*, Constant*>> ValueStack;
2359 /// This is used to detect recursion. In pathological situations we could hit
2360 /// exponential behavior, but at least there is nothing unbounded.
2361 SmallVector<Function*, 4> CallStack;
2363 /// For each store we execute, we update this map. Loads check this to get
2364 /// the most up-to-date value. If evaluation is successful, this state is
2365 /// committed to the process.
2366 DenseMap<Constant*, Constant*> MutatedMemory;
2368 /// To 'execute' an alloca, we create a temporary global variable to represent
2369 /// its body. This vector is needed so we can delete the temporary globals
2370 /// when we are done.
2371 SmallVector<std::unique_ptr<GlobalVariable>, 32> AllocaTmps;
2373 /// These global variables have been marked invariant by the static
2375 SmallPtrSet<GlobalVariable*, 8> Invariants;
2377 /// These are constants we have checked and know to be simple enough to live
2378 /// in a static initializer of a global.
2379 SmallPtrSet<Constant*, 8> SimpleConstants;
2381 const DataLayout &DL;
2382 const TargetLibraryInfo *TLI;
2385 } // anonymous namespace
2387 /// Return the value that would be computed by a load from P after the stores
2388 /// reflected by 'memory' have been performed. If we can't decide, return null.
2389 Constant *Evaluator::ComputeLoadResult(Constant *P) {
2390 // If this memory location has been recently stored, use the stored value: it
2391 // is the most up-to-date.
2392 DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P);
2393 if (I != MutatedMemory.end()) return I->second;
2396 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
2397 if (GV->hasDefinitiveInitializer())
2398 return GV->getInitializer();
2402 // Handle a constantexpr getelementptr.
2403 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
2404 if (CE->getOpcode() == Instruction::GetElementPtr &&
2405 isa<GlobalVariable>(CE->getOperand(0))) {
2406 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2407 if (GV->hasDefinitiveInitializer())
2408 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2411 return nullptr; // don't know how to evaluate.
2414 /// Evaluate all instructions in block BB, returning true if successful, false
2415 /// if we can't evaluate it. NewBB returns the next BB that control flows into,
2416 /// or null upon return.
2417 bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst,
2418 BasicBlock *&NextBB) {
2419 // This is the main evaluation loop.
2421 Constant *InstResult = nullptr;
2423 DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
2425 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
2426 if (!SI->isSimple()) {
2427 DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
2428 return false; // no volatile/atomic accesses.
2430 Constant *Ptr = getVal(SI->getOperand(1));
2431 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
2432 DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
2433 Ptr = ConstantFoldConstantExpression(CE, DL, TLI);
2434 DEBUG(dbgs() << "; To: " << *Ptr << "\n");
2436 if (!isSimpleEnoughPointerToCommit(Ptr)) {
2437 // If this is too complex for us to commit, reject it.
2438 DEBUG(dbgs() << "Pointer is too complex for us to evaluate store.");
2442 Constant *Val = getVal(SI->getOperand(0));
2444 // If this might be too difficult for the backend to handle (e.g. the addr
2445 // of one global variable divided by another) then we can't commit it.
2446 if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, DL)) {
2447 DEBUG(dbgs() << "Store value is too complex to evaluate store. " << *Val
2452 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
2453 if (CE->getOpcode() == Instruction::BitCast) {
2454 DEBUG(dbgs() << "Attempting to resolve bitcast on constant ptr.\n");
2455 // If we're evaluating a store through a bitcast, then we need
2456 // to pull the bitcast off the pointer type and push it onto the
2458 Ptr = CE->getOperand(0);
2460 Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
2462 // In order to push the bitcast onto the stored value, a bitcast
2463 // from NewTy to Val's type must be legal. If it's not, we can try
2464 // introspecting NewTy to find a legal conversion.
2465 while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
2466 // If NewTy is a struct, we can convert the pointer to the struct
2467 // into a pointer to its first member.
2468 // FIXME: This could be extended to support arrays as well.
2469 if (StructType *STy = dyn_cast<StructType>(NewTy)) {
2470 NewTy = STy->getTypeAtIndex(0U);
2472 IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
2473 Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
2474 Constant * const IdxList[] = {IdxZero, IdxZero};
2476 Ptr = ConstantExpr::getGetElementPtr(nullptr, Ptr, IdxList);
2477 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2478 Ptr = ConstantFoldConstantExpression(CE, DL, TLI);
2480 // If we can't improve the situation by introspecting NewTy,
2481 // we have to give up.
2483 DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
2489 // If we found compatible types, go ahead and push the bitcast
2490 // onto the stored value.
2491 Val = ConstantExpr::getBitCast(Val, NewTy);
2493 DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
2497 MutatedMemory[Ptr] = Val;
2498 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
2499 InstResult = ConstantExpr::get(BO->getOpcode(),
2500 getVal(BO->getOperand(0)),
2501 getVal(BO->getOperand(1)));
2502 DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: " << *InstResult
2504 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
2505 InstResult = ConstantExpr::getCompare(CI->getPredicate(),
2506 getVal(CI->getOperand(0)),
2507 getVal(CI->getOperand(1)));
2508 DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult
2510 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
2511 InstResult = ConstantExpr::getCast(CI->getOpcode(),
2512 getVal(CI->getOperand(0)),
2514 DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult
2516 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
2517 InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
2518 getVal(SI->getOperand(1)),
2519 getVal(SI->getOperand(2)));
2520 DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
2522 } else if (auto *EVI = dyn_cast<ExtractValueInst>(CurInst)) {
2523 InstResult = ConstantExpr::getExtractValue(
2524 getVal(EVI->getAggregateOperand()), EVI->getIndices());
2525 DEBUG(dbgs() << "Found an ExtractValueInst! Simplifying: " << *InstResult
2527 } else if (auto *IVI = dyn_cast<InsertValueInst>(CurInst)) {
2528 InstResult = ConstantExpr::getInsertValue(
2529 getVal(IVI->getAggregateOperand()),
2530 getVal(IVI->getInsertedValueOperand()), IVI->getIndices());
2531 DEBUG(dbgs() << "Found an InsertValueInst! Simplifying: " << *InstResult
2533 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
2534 Constant *P = getVal(GEP->getOperand(0));
2535 SmallVector<Constant*, 8> GEPOps;
2536 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
2538 GEPOps.push_back(getVal(*i));
2540 ConstantExpr::getGetElementPtr(GEP->getSourceElementType(), P, GEPOps,
2541 cast<GEPOperator>(GEP)->isInBounds());
2542 DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult
2544 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
2546 if (!LI->isSimple()) {
2547 DEBUG(dbgs() << "Found a Load! Not a simple load, can not evaluate.\n");
2548 return false; // no volatile/atomic accesses.
2551 Constant *Ptr = getVal(LI->getOperand(0));
2552 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
2553 Ptr = ConstantFoldConstantExpression(CE, DL, TLI);
2554 DEBUG(dbgs() << "Found a constant pointer expression, constant "
2555 "folding: " << *Ptr << "\n");
2557 InstResult = ComputeLoadResult(Ptr);
2559 DEBUG(dbgs() << "Failed to compute load result. Can not evaluate load."
2561 return false; // Could not evaluate load.
2564 DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
2565 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
2566 if (AI->isArrayAllocation()) {
2567 DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
2568 return false; // Cannot handle array allocs.
2570 Type *Ty = AI->getType()->getElementType();
2571 AllocaTmps.push_back(
2572 make_unique<GlobalVariable>(Ty, false, GlobalValue::InternalLinkage,
2573 UndefValue::get(Ty), AI->getName()));
2574 InstResult = AllocaTmps.back().get();
2575 DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n");
2576 } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
2577 CallSite CS(&*CurInst);
2579 // Debug info can safely be ignored here.
2580 if (isa<DbgInfoIntrinsic>(CS.getInstruction())) {
2581 DEBUG(dbgs() << "Ignoring debug info.\n");
2586 // Cannot handle inline asm.
2587 if (isa<InlineAsm>(CS.getCalledValue())) {
2588 DEBUG(dbgs() << "Found inline asm, can not evaluate.\n");
2592 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
2593 if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
2594 if (MSI->isVolatile()) {
2595 DEBUG(dbgs() << "Can not optimize a volatile memset " <<
2599 Constant *Ptr = getVal(MSI->getDest());
2600 Constant *Val = getVal(MSI->getValue());
2601 Constant *DestVal = ComputeLoadResult(getVal(Ptr));
2602 if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
2603 // This memset is a no-op.
2604 DEBUG(dbgs() << "Ignoring no-op memset.\n");
2610 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
2611 II->getIntrinsicID() == Intrinsic::lifetime_end) {
2612 DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n");
2617 if (II->getIntrinsicID() == Intrinsic::invariant_start) {
2618 // We don't insert an entry into Values, as it doesn't have a
2619 // meaningful return value.
2620 if (!II->use_empty()) {
2621 DEBUG(dbgs() << "Found unused invariant_start. Can't evaluate.\n");
2624 ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
2625 Value *PtrArg = getVal(II->getArgOperand(1));
2626 Value *Ptr = PtrArg->stripPointerCasts();
2627 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
2628 Type *ElemTy = cast<PointerType>(GV->getType())->getElementType();
2629 if (!Size->isAllOnesValue() &&
2630 Size->getValue().getLimitedValue() >=
2631 DL.getTypeStoreSize(ElemTy)) {
2632 Invariants.insert(GV);
2633 DEBUG(dbgs() << "Found a global var that is an invariant: " << *GV
2636 DEBUG(dbgs() << "Found a global var, but can not treat it as an "
2640 // Continue even if we do nothing.
2643 } else if (II->getIntrinsicID() == Intrinsic::assume) {
2644 DEBUG(dbgs() << "Skipping assume intrinsic.\n");
2649 DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
2653 // Resolve function pointers.
2654 Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue()));
2655 if (!Callee || Callee->mayBeOverridden()) {
2656 DEBUG(dbgs() << "Can not resolve function pointer.\n");
2657 return false; // Cannot resolve.
2660 SmallVector<Constant*, 8> Formals;
2661 for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
2662 Formals.push_back(getVal(*i));
2664 if (Callee->isDeclaration()) {
2665 // If this is a function we can constant fold, do it.
2666 if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) {
2668 DEBUG(dbgs() << "Constant folded function call. Result: " <<
2669 *InstResult << "\n");
2671 DEBUG(dbgs() << "Can not constant fold function call.\n");
2675 if (Callee->getFunctionType()->isVarArg()) {
2676 DEBUG(dbgs() << "Can not constant fold vararg function call.\n");
2680 Constant *RetVal = nullptr;
2681 // Execute the call, if successful, use the return value.
2682 ValueStack.emplace_back();
2683 if (!EvaluateFunction(Callee, RetVal, Formals)) {
2684 DEBUG(dbgs() << "Failed to evaluate function.\n");
2687 ValueStack.pop_back();
2688 InstResult = RetVal;
2691 DEBUG(dbgs() << "Successfully evaluated function. Result: " <<
2692 InstResult << "\n\n");
2694 DEBUG(dbgs() << "Successfully evaluated function. Result: 0\n\n");
2697 } else if (isa<TerminatorInst>(CurInst)) {
2698 DEBUG(dbgs() << "Found a terminator instruction.\n");
2700 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
2701 if (BI->isUnconditional()) {
2702 NextBB = BI->getSuccessor(0);
2705 dyn_cast<ConstantInt>(getVal(BI->getCondition()));
2706 if (!Cond) return false; // Cannot determine.
2708 NextBB = BI->getSuccessor(!Cond->getZExtValue());
2710 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
2712 dyn_cast<ConstantInt>(getVal(SI->getCondition()));
2713 if (!Val) return false; // Cannot determine.
2714 NextBB = SI->findCaseValue(Val).getCaseSuccessor();
2715 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
2716 Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
2717 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
2718 NextBB = BA->getBasicBlock();
2720 return false; // Cannot determine.
2721 } else if (isa<ReturnInst>(CurInst)) {
2724 // invoke, unwind, resume, unreachable.
2725 DEBUG(dbgs() << "Can not handle terminator.");
2726 return false; // Cannot handle this terminator.
2729 // We succeeded at evaluating this block!
2730 DEBUG(dbgs() << "Successfully evaluated block.\n");
2733 // Did not know how to evaluate this!
2734 DEBUG(dbgs() << "Failed to evaluate block due to unhandled instruction."
2739 if (!CurInst->use_empty()) {
2740 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
2741 InstResult = ConstantFoldConstantExpression(CE, DL, TLI);
2743 setVal(&*CurInst, InstResult);
2746 // If we just processed an invoke, we finished evaluating the block.
2747 if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
2748 NextBB = II->getNormalDest();
2749 DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n");
2753 // Advance program counter.
2758 /// Evaluate a call to function F, returning true if successful, false if we
2759 /// can't evaluate it. ActualArgs contains the formal arguments for the
2761 bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal,
2762 const SmallVectorImpl<Constant*> &ActualArgs) {
2763 // Check to see if this function is already executing (recursion). If so,
2764 // bail out. TODO: we might want to accept limited recursion.
2765 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
2768 CallStack.push_back(F);
2770 // Initialize arguments to the incoming values specified.
2772 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
2774 setVal(&*AI, ActualArgs[ArgNo]);
2776 // ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
2777 // we can only evaluate any one basic block at most once. This set keeps
2778 // track of what we have executed so we can detect recursive cases etc.
2779 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
2781 // CurBB - The current basic block we're evaluating.
2782 BasicBlock *CurBB = &F->front();
2784 BasicBlock::iterator CurInst = CurBB->begin();
2787 BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings.
2788 DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n");
2790 if (!EvaluateBlock(CurInst, NextBB))
2794 // Successfully running until there's no next block means that we found
2795 // the return. Fill it the return value and pop the call stack.
2796 ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
2797 if (RI->getNumOperands())
2798 RetVal = getVal(RI->getOperand(0));
2799 CallStack.pop_back();
2803 // Okay, we succeeded in evaluating this control flow. See if we have
2804 // executed the new block before. If so, we have a looping function,
2805 // which we cannot evaluate in reasonable time.
2806 if (!ExecutedBlocks.insert(NextBB).second)
2807 return false; // looped!
2809 // Okay, we have never been in this block before. Check to see if there
2810 // are any PHI nodes. If so, evaluate them with information about where
2812 PHINode *PN = nullptr;
2813 for (CurInst = NextBB->begin();
2814 (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
2815 setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
2817 // Advance to the next block.
2822 /// Evaluate static constructors in the function, if we can. Return true if we
2823 /// can, false otherwise.
2824 static bool EvaluateStaticConstructor(Function *F, const DataLayout &DL,
2825 const TargetLibraryInfo *TLI) {
2826 // Call the function.
2827 Evaluator Eval(DL, TLI);
2828 Constant *RetValDummy;
2829 bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy,
2830 SmallVector<Constant*, 0>());
2833 ++NumCtorsEvaluated;
2835 // We succeeded at evaluation: commit the result.
2836 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
2837 << F->getName() << "' to " << Eval.getMutatedMemory().size()
2839 for (DenseMap<Constant*, Constant*>::const_iterator I =
2840 Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end();
2842 CommitValueTo(I->second, I->first);
2843 for (GlobalVariable *GV : Eval.getInvariants())
2844 GV->setConstant(true);
2850 static int compareNames(Constant *const *A, Constant *const *B) {
2851 return (*A)->stripPointerCasts()->getName().compare(
2852 (*B)->stripPointerCasts()->getName());
2855 static void setUsedInitializer(GlobalVariable &V,
2856 const SmallPtrSet<GlobalValue *, 8> &Init) {
2858 V.eraseFromParent();
2862 // Type of pointer to the array of pointers.
2863 PointerType *Int8PtrTy = Type::getInt8PtrTy(V.getContext(), 0);
2865 SmallVector<llvm::Constant *, 8> UsedArray;
2866 for (GlobalValue *GV : Init) {
2868 = ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, Int8PtrTy);
2869 UsedArray.push_back(Cast);
2871 // Sort to get deterministic order.
2872 array_pod_sort(UsedArray.begin(), UsedArray.end(), compareNames);
2873 ArrayType *ATy = ArrayType::get(Int8PtrTy, UsedArray.size());
2875 Module *M = V.getParent();
2876 V.removeFromParent();
2877 GlobalVariable *NV =
2878 new GlobalVariable(*M, ATy, false, llvm::GlobalValue::AppendingLinkage,
2879 llvm::ConstantArray::get(ATy, UsedArray), "");
2881 NV->setSection("llvm.metadata");
2886 /// An easy to access representation of llvm.used and llvm.compiler.used.
2888 SmallPtrSet<GlobalValue *, 8> Used;
2889 SmallPtrSet<GlobalValue *, 8> CompilerUsed;
2890 GlobalVariable *UsedV;
2891 GlobalVariable *CompilerUsedV;
2894 LLVMUsed(Module &M) {
2895 UsedV = collectUsedGlobalVariables(M, Used, false);
2896 CompilerUsedV = collectUsedGlobalVariables(M, CompilerUsed, true);
2898 typedef SmallPtrSet<GlobalValue *, 8>::iterator iterator;
2899 typedef iterator_range<iterator> used_iterator_range;
2900 iterator usedBegin() { return Used.begin(); }
2901 iterator usedEnd() { return Used.end(); }
2902 used_iterator_range used() {
2903 return used_iterator_range(usedBegin(), usedEnd());
2905 iterator compilerUsedBegin() { return CompilerUsed.begin(); }
2906 iterator compilerUsedEnd() { return CompilerUsed.end(); }
2907 used_iterator_range compilerUsed() {
2908 return used_iterator_range(compilerUsedBegin(), compilerUsedEnd());
2910 bool usedCount(GlobalValue *GV) const { return Used.count(GV); }
2911 bool compilerUsedCount(GlobalValue *GV) const {
2912 return CompilerUsed.count(GV);
2914 bool usedErase(GlobalValue *GV) { return Used.erase(GV); }
2915 bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(GV); }
2916 bool usedInsert(GlobalValue *GV) { return Used.insert(GV).second; }
2917 bool compilerUsedInsert(GlobalValue *GV) {
2918 return CompilerUsed.insert(GV).second;
2921 void syncVariablesAndSets() {
2923 setUsedInitializer(*UsedV, Used);
2925 setUsedInitializer(*CompilerUsedV, CompilerUsed);
2930 static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) {
2931 if (GA.use_empty()) // No use at all.
2934 assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) &&
2935 "We should have removed the duplicated "
2936 "element from llvm.compiler.used");
2937 if (!GA.hasOneUse())
2938 // Strictly more than one use. So at least one is not in llvm.used and
2939 // llvm.compiler.used.
2942 // Exactly one use. Check if it is in llvm.used or llvm.compiler.used.
2943 return !U.usedCount(&GA) && !U.compilerUsedCount(&GA);
2946 static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V,
2947 const LLVMUsed &U) {
2949 assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) &&
2950 "We should have removed the duplicated "
2951 "element from llvm.compiler.used");
2952 if (U.usedCount(&V) || U.compilerUsedCount(&V))
2954 return V.hasNUsesOrMore(N);
2957 static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) {
2958 if (!GA.hasLocalLinkage())
2961 return U.usedCount(&GA) || U.compilerUsedCount(&GA);
2964 static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
2965 bool &RenameTarget) {
2966 RenameTarget = false;
2968 if (hasUseOtherThanLLVMUsed(GA, U))
2971 // If the alias is externally visible, we may still be able to simplify it.
2972 if (!mayHaveOtherReferences(GA, U))
2975 // If the aliasee has internal linkage, give it the name and linkage
2976 // of the alias, and delete the alias. This turns:
2977 // define internal ... @f(...)
2978 // @a = alias ... @f
2980 // define ... @a(...)
2981 Constant *Aliasee = GA.getAliasee();
2982 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
2983 if (!Target->hasLocalLinkage())
2986 // Do not perform the transform if multiple aliases potentially target the
2987 // aliasee. This check also ensures that it is safe to replace the section
2988 // and other attributes of the aliasee with those of the alias.
2989 if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U))
2992 RenameTarget = true;
2996 bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
2997 bool Changed = false;
3000 for (GlobalValue *GV : Used.used())
3001 Used.compilerUsedErase(GV);
3003 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
3005 Module::alias_iterator J = I++;
3006 // Aliases without names cannot be referenced outside this module.
3007 if (!J->hasName() && !J->isDeclaration() && !J->hasLocalLinkage())
3008 J->setLinkage(GlobalValue::InternalLinkage);
3009 // If the aliasee may change at link time, nothing can be done - bail out.
3010 if (J->mayBeOverridden())
3013 Constant *Aliasee = J->getAliasee();
3014 GlobalValue *Target = dyn_cast<GlobalValue>(Aliasee->stripPointerCasts());
3015 // We can't trivially replace the alias with the aliasee if the aliasee is
3016 // non-trivial in some way.
3017 // TODO: Try to handle non-zero GEPs of local aliasees.
3020 Target->removeDeadConstantUsers();
3022 // Make all users of the alias use the aliasee instead.
3024 if (!hasUsesToReplace(*J, Used, RenameTarget))
3027 J->replaceAllUsesWith(ConstantExpr::getBitCast(Aliasee, J->getType()));
3028 ++NumAliasesResolved;
3032 // Give the aliasee the name, linkage and other attributes of the alias.
3033 Target->takeName(&*J);
3034 Target->setLinkage(J->getLinkage());
3035 Target->setVisibility(J->getVisibility());
3036 Target->setDLLStorageClass(J->getDLLStorageClass());
3038 if (Used.usedErase(&*J))
3039 Used.usedInsert(Target);
3041 if (Used.compilerUsedErase(&*J))
3042 Used.compilerUsedInsert(Target);
3043 } else if (mayHaveOtherReferences(*J, Used))
3046 // Delete the alias.
3047 M.getAliasList().erase(J);
3048 ++NumAliasesRemoved;
3052 Used.syncVariablesAndSets();
3057 static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) {
3058 if (!TLI->has(LibFunc::cxa_atexit))
3061 Function *Fn = M.getFunction(TLI->getName(LibFunc::cxa_atexit));
3066 FunctionType *FTy = Fn->getFunctionType();
3068 // Checking that the function has the right return type, the right number of
3069 // parameters and that they all have pointer types should be enough.
3070 if (!FTy->getReturnType()->isIntegerTy() ||
3071 FTy->getNumParams() != 3 ||
3072 !FTy->getParamType(0)->isPointerTy() ||
3073 !FTy->getParamType(1)->isPointerTy() ||
3074 !FTy->getParamType(2)->isPointerTy())
3080 /// Returns whether the given function is an empty C++ destructor and can
3081 /// therefore be eliminated.
3082 /// Note that we assume that other optimization passes have already simplified
3083 /// the code so we only look for a function with a single basic block, where
3084 /// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and
3085 /// other side-effect free instructions.
3086 static bool cxxDtorIsEmpty(const Function &Fn,
3087 SmallPtrSet<const Function *, 8> &CalledFunctions) {
3088 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
3089 // nounwind, but that doesn't seem worth doing.
3090 if (Fn.isDeclaration())
3093 if (++Fn.begin() != Fn.end())
3096 const BasicBlock &EntryBlock = Fn.getEntryBlock();
3097 for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
3099 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
3100 // Ignore debug intrinsics.
3101 if (isa<DbgInfoIntrinsic>(CI))
3104 const Function *CalledFn = CI->getCalledFunction();
3109 SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
3111 // Don't treat recursive functions as empty.
3112 if (!NewCalledFunctions.insert(CalledFn).second)
3115 if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
3117 } else if (isa<ReturnInst>(*I))
3118 return true; // We're done.
3119 else if (I->mayHaveSideEffects())
3120 return false; // Destructor with side effects, bail.
3126 bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
3127 /// Itanium C++ ABI p3.3.5:
3129 /// After constructing a global (or local static) object, that will require
3130 /// destruction on exit, a termination function is registered as follows:
3132 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
3134 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
3135 /// call f(p) when DSO d is unloaded, before all such termination calls
3136 /// registered before this one. It returns zero if registration is
3137 /// successful, nonzero on failure.
3139 // This pass will look for calls to __cxa_atexit where the function is trivial
3141 bool Changed = false;
3143 for (auto I = CXAAtExitFn->user_begin(), E = CXAAtExitFn->user_end();
3145 // We're only interested in calls. Theoretically, we could handle invoke
3146 // instructions as well, but neither llvm-gcc nor clang generate invokes
3148 CallInst *CI = dyn_cast<CallInst>(*I++);
3153 dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
3157 SmallPtrSet<const Function *, 8> CalledFunctions;
3158 if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
3161 // Just remove the call.
3162 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
3163 CI->eraseFromParent();
3165 ++NumCXXDtorsRemoved;
3173 bool GlobalOpt::runOnModule(Module &M) {
3174 bool Changed = false;
3176 auto &DL = M.getDataLayout();
3177 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
3179 bool LocalChange = true;
3180 while (LocalChange) {
3181 LocalChange = false;
3183 NotDiscardableComdats.clear();
3184 for (const GlobalVariable &GV : M.globals())
3185 if (const Comdat *C = GV.getComdat())
3186 if (!GV.isDiscardableIfUnused() || !GV.use_empty())
3187 NotDiscardableComdats.insert(C);
3188 for (Function &F : M)
3189 if (const Comdat *C = F.getComdat())
3190 if (!F.isDefTriviallyDead())
3191 NotDiscardableComdats.insert(C);
3192 for (GlobalAlias &GA : M.aliases())
3193 if (const Comdat *C = GA.getComdat())
3194 if (!GA.isDiscardableIfUnused() || !GA.use_empty())
3195 NotDiscardableComdats.insert(C);
3197 // Delete functions that are trivially dead, ccc -> fastcc
3198 LocalChange |= OptimizeFunctions(M);
3200 // Optimize global_ctors list.
3201 LocalChange |= optimizeGlobalCtorsList(M, [&](Function *F) {
3202 return EvaluateStaticConstructor(F, DL, TLI);
3205 // Optimize non-address-taken globals.
3206 LocalChange |= OptimizeGlobalVars(M);
3208 // Resolve aliases, when possible.
3209 LocalChange |= OptimizeGlobalAliases(M);
3211 // Try to remove trivial global destructors if they are not removed
3213 Function *CXAAtExitFn = FindCXAAtExit(M, TLI);
3215 LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
3217 Changed |= LocalChange;
3220 // TODO: Move all global ctors functions to the end of the module for code