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 #define DEBUG_TYPE "globalopt"
17 #include "llvm/Transforms/IPO.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/STLExtras.h"
20 #include "llvm/ADT/SmallPtrSet.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/IR/CallingConv.h"
26 #include "llvm/IR/Constants.h"
27 #include "llvm/IR/DataLayout.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/IR/IntrinsicInst.h"
31 #include "llvm/IR/Module.h"
32 #include "llvm/IR/Operator.h"
33 #include "llvm/Pass.h"
34 #include "llvm/Support/CallSite.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/ErrorHandling.h"
37 #include "llvm/Support/GetElementPtrTypeIterator.h"
38 #include "llvm/Support/MathExtras.h"
39 #include "llvm/Support/raw_ostream.h"
40 #include "llvm/Target/TargetLibraryInfo.h"
41 #include "llvm/Transforms/Utils/GlobalStatus.h"
42 #include "llvm/Transforms/Utils/ModuleUtils.h"
46 STATISTIC(NumMarked , "Number of globals marked constant");
47 STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr");
48 STATISTIC(NumSRA , "Number of aggregate globals broken into scalars");
49 STATISTIC(NumHeapSRA , "Number of heap objects SRA'd");
50 STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
51 STATISTIC(NumDeleted , "Number of globals deleted");
52 STATISTIC(NumFnDeleted , "Number of functions deleted");
53 STATISTIC(NumGlobUses , "Number of global uses devirtualized");
54 STATISTIC(NumLocalized , "Number of globals localized");
55 STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans");
56 STATISTIC(NumFastCallFns , "Number of functions converted to fastcc");
57 STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");
58 STATISTIC(NumNestRemoved , "Number of nest attributes removed");
59 STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
60 STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
61 STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
64 struct GlobalOpt : public ModulePass {
65 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
66 AU.addRequired<TargetLibraryInfo>();
68 static char ID; // Pass identification, replacement for typeid
69 GlobalOpt() : ModulePass(ID) {
70 initializeGlobalOptPass(*PassRegistry::getPassRegistry());
73 bool runOnModule(Module &M);
76 GlobalVariable *FindGlobalCtors(Module &M);
77 bool OptimizeFunctions(Module &M);
78 bool OptimizeGlobalVars(Module &M);
79 bool OptimizeGlobalAliases(Module &M);
80 bool OptimizeGlobalCtorsList(GlobalVariable *&GCL);
81 bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
82 bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI,
83 const GlobalStatus &GS);
84 bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn);
87 TargetLibraryInfo *TLI;
91 char GlobalOpt::ID = 0;
92 INITIALIZE_PASS_BEGIN(GlobalOpt, "globalopt",
93 "Global Variable Optimizer", false, false)
94 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
95 INITIALIZE_PASS_END(GlobalOpt, "globalopt",
96 "Global Variable Optimizer", false, false)
98 ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
106 /// isLeakCheckerRoot - Is this global variable possibly used by a leak checker
107 /// as a root? If so, we might not really want to eliminate the stores to it.
108 static bool isLeakCheckerRoot(GlobalVariable *GV) {
109 // A global variable is a root if it is a pointer, or could plausibly contain
110 // a pointer. There are two challenges; one is that we could have a struct
111 // the has an inner member which is a pointer. We recurse through the type to
112 // detect these (up to a point). The other is that we may actually be a union
113 // of a pointer and another type, and so our LLVM type is an integer which
114 // gets converted into a pointer, or our type is an [i8 x #] with a pointer
115 // potentially contained here.
117 if (GV->hasPrivateLinkage())
120 SmallVector<Type *, 4> Types;
121 Types.push_back(cast<PointerType>(GV->getType())->getElementType());
125 Type *Ty = Types.pop_back_val();
126 switch (Ty->getTypeID()) {
128 case Type::PointerTyID: return true;
129 case Type::ArrayTyID:
130 case Type::VectorTyID: {
131 SequentialType *STy = cast<SequentialType>(Ty);
132 Types.push_back(STy->getElementType());
135 case Type::StructTyID: {
136 StructType *STy = cast<StructType>(Ty);
137 if (STy->isOpaque()) return true;
138 for (StructType::element_iterator I = STy->element_begin(),
139 E = STy->element_end(); I != E; ++I) {
141 if (isa<PointerType>(InnerTy)) return true;
142 if (isa<CompositeType>(InnerTy))
143 Types.push_back(InnerTy);
148 if (--Limit == 0) return true;
149 } while (!Types.empty());
153 /// Given a value that is stored to a global but never read, determine whether
154 /// it's safe to remove the store and the chain of computation that feeds the
156 static bool IsSafeComputationToRemove(Value *V, const TargetLibraryInfo *TLI) {
158 if (isa<Constant>(V))
162 if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) ||
165 if (isAllocationFn(V, TLI))
168 Instruction *I = cast<Instruction>(V);
169 if (I->mayHaveSideEffects())
171 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
172 if (!GEP->hasAllConstantIndices())
174 } else if (I->getNumOperands() != 1) {
178 V = I->getOperand(0);
182 /// CleanupPointerRootUsers - This GV is a pointer root. Loop over all users
183 /// of the global and clean up any that obviously don't assign the global a
184 /// value that isn't dynamically allocated.
186 static bool CleanupPointerRootUsers(GlobalVariable *GV,
187 const TargetLibraryInfo *TLI) {
188 // A brief explanation of leak checkers. The goal is to find bugs where
189 // pointers are forgotten, causing an accumulating growth in memory
190 // usage over time. The common strategy for leak checkers is to whitelist the
191 // memory pointed to by globals at exit. This is popular because it also
192 // solves another problem where the main thread of a C++ program may shut down
193 // before other threads that are still expecting to use those globals. To
194 // handle that case, we expect the program may create a singleton and never
197 bool Changed = false;
199 // If Dead[n].first is the only use of a malloc result, we can delete its
200 // chain of computation and the store to the global in Dead[n].second.
201 SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
203 // Constants can't be pointers to dynamically allocated memory.
204 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
207 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
208 Value *V = SI->getValueOperand();
209 if (isa<Constant>(V)) {
211 SI->eraseFromParent();
212 } else if (Instruction *I = dyn_cast<Instruction>(V)) {
214 Dead.push_back(std::make_pair(I, SI));
216 } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
217 if (isa<Constant>(MSI->getValue())) {
219 MSI->eraseFromParent();
220 } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
222 Dead.push_back(std::make_pair(I, MSI));
224 } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
225 GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
226 if (MemSrc && MemSrc->isConstant()) {
228 MTI->eraseFromParent();
229 } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) {
231 Dead.push_back(std::make_pair(I, MTI));
233 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
234 if (CE->use_empty()) {
235 CE->destroyConstant();
238 } else if (Constant *C = dyn_cast<Constant>(U)) {
239 if (isSafeToDestroyConstant(C)) {
240 C->destroyConstant();
241 // This could have invalidated UI, start over from scratch.
243 CleanupPointerRootUsers(GV, TLI);
249 for (int i = 0, e = Dead.size(); i != e; ++i) {
250 if (IsSafeComputationToRemove(Dead[i].first, TLI)) {
251 Dead[i].second->eraseFromParent();
252 Instruction *I = Dead[i].first;
254 if (isAllocationFn(I, TLI))
256 Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
259 I->eraseFromParent();
262 I->eraseFromParent();
269 /// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all
270 /// users of the global, cleaning up the obvious ones. This is largely just a
271 /// quick scan over the use list to clean up the easy and obvious cruft. This
272 /// returns true if it made a change.
273 static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
274 DataLayout *TD, TargetLibraryInfo *TLI) {
275 bool Changed = false;
276 SmallVector<User*, 8> WorkList(V->use_begin(), V->use_end());
277 while (!WorkList.empty()) {
278 User *U = WorkList.pop_back_val();
280 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
282 // Replace the load with the initializer.
283 LI->replaceAllUsesWith(Init);
284 LI->eraseFromParent();
287 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
288 // Store must be unreachable or storing Init into the global.
289 SI->eraseFromParent();
291 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
292 if (CE->getOpcode() == Instruction::GetElementPtr) {
293 Constant *SubInit = 0;
295 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
296 Changed |= CleanupConstantGlobalUsers(CE, SubInit, TD, TLI);
297 } else if (CE->getOpcode() == Instruction::BitCast &&
298 CE->getType()->isPointerTy()) {
299 // Pointer cast, delete any stores and memsets to the global.
300 Changed |= CleanupConstantGlobalUsers(CE, 0, TD, TLI);
303 if (CE->use_empty()) {
304 CE->destroyConstant();
307 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
308 // Do not transform "gepinst (gep constexpr (GV))" here, because forming
309 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
310 // and will invalidate our notion of what Init is.
311 Constant *SubInit = 0;
312 if (!isa<ConstantExpr>(GEP->getOperand(0))) {
314 dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, TD, TLI));
315 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
316 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
318 // If the initializer is an all-null value and we have an inbounds GEP,
319 // we already know what the result of any load from that GEP is.
320 // TODO: Handle splats.
321 if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
322 SubInit = Constant::getNullValue(GEP->getType()->getElementType());
324 Changed |= CleanupConstantGlobalUsers(GEP, SubInit, TD, TLI);
326 if (GEP->use_empty()) {
327 GEP->eraseFromParent();
330 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
331 if (MI->getRawDest() == V) {
332 MI->eraseFromParent();
336 } else if (Constant *C = dyn_cast<Constant>(U)) {
337 // If we have a chain of dead constantexprs or other things dangling from
338 // us, and if they are all dead, nuke them without remorse.
339 if (isSafeToDestroyConstant(C)) {
340 C->destroyConstant();
341 CleanupConstantGlobalUsers(V, Init, TD, TLI);
349 /// isSafeSROAElementUse - Return true if the specified instruction is a safe
350 /// user of a derived expression from a global that we want to SROA.
351 static bool isSafeSROAElementUse(Value *V) {
352 // We might have a dead and dangling constant hanging off of here.
353 if (Constant *C = dyn_cast<Constant>(V))
354 return isSafeToDestroyConstant(C);
356 Instruction *I = dyn_cast<Instruction>(V);
357 if (!I) return false;
360 if (isa<LoadInst>(I)) return true;
362 // Stores *to* the pointer are ok.
363 if (StoreInst *SI = dyn_cast<StoreInst>(I))
364 return SI->getOperand(0) != V;
366 // Otherwise, it must be a GEP.
367 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
368 if (GEPI == 0) return false;
370 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
371 !cast<Constant>(GEPI->getOperand(1))->isNullValue())
374 for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end();
376 if (!isSafeSROAElementUse(*I))
382 /// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value.
383 /// Look at it and its uses and decide whether it is safe to SROA this global.
385 static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
386 // The user of the global must be a GEP Inst or a ConstantExpr GEP.
387 if (!isa<GetElementPtrInst>(U) &&
388 (!isa<ConstantExpr>(U) ||
389 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
392 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we
393 // don't like < 3 operand CE's, and we don't like non-constant integer
394 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
396 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
397 !cast<Constant>(U->getOperand(1))->isNullValue() ||
398 !isa<ConstantInt>(U->getOperand(2)))
401 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
402 ++GEPI; // Skip over the pointer index.
404 // If this is a use of an array allocation, do a bit more checking for sanity.
405 if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
406 uint64_t NumElements = AT->getNumElements();
407 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
409 // Check to make sure that index falls within the array. If not,
410 // something funny is going on, so we won't do the optimization.
412 if (Idx->getZExtValue() >= NumElements)
415 // We cannot scalar repl this level of the array unless any array
416 // sub-indices are in-range constants. In particular, consider:
417 // A[0][i]. We cannot know that the user isn't doing invalid things like
418 // allowing i to index an out-of-range subscript that accesses A[1].
420 // Scalar replacing *just* the outer index of the array is probably not
421 // going to be a win anyway, so just give up.
422 for (++GEPI; // Skip array index.
425 uint64_t NumElements;
426 if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
427 NumElements = SubArrayTy->getNumElements();
428 else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
429 NumElements = SubVectorTy->getNumElements();
431 assert((*GEPI)->isStructTy() &&
432 "Indexed GEP type is not array, vector, or struct!");
436 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
437 if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
442 for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I)
443 if (!isSafeSROAElementUse(*I))
448 /// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it
449 /// is safe for us to perform this transformation.
451 static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
452 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
454 if (!IsUserOfGlobalSafeForSRA(*UI, GV))
461 /// SRAGlobal - Perform scalar replacement of aggregates on the specified global
462 /// variable. This opens the door for other optimizations by exposing the
463 /// behavior of the program in a more fine-grained way. We have determined that
464 /// this transformation is safe already. We return the first global variable we
465 /// insert so that the caller can reprocess it.
466 static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &TD) {
467 // Make sure this global only has simple uses that we can SRA.
468 if (!GlobalUsersSafeToSRA(GV))
471 assert(GV->hasLocalLinkage() && !GV->isConstant());
472 Constant *Init = GV->getInitializer();
473 Type *Ty = Init->getType();
475 std::vector<GlobalVariable*> NewGlobals;
476 Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
478 // Get the alignment of the global, either explicit or target-specific.
479 unsigned StartAlignment = GV->getAlignment();
480 if (StartAlignment == 0)
481 StartAlignment = TD.getABITypeAlignment(GV->getType());
483 if (StructType *STy = dyn_cast<StructType>(Ty)) {
484 NewGlobals.reserve(STy->getNumElements());
485 const StructLayout &Layout = *TD.getStructLayout(STy);
486 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
487 Constant *In = Init->getAggregateElement(i);
488 assert(In && "Couldn't get element of initializer?");
489 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
490 GlobalVariable::InternalLinkage,
491 In, GV->getName()+"."+Twine(i),
492 GV->getThreadLocalMode(),
493 GV->getType()->getAddressSpace());
494 Globals.insert(GV, NGV);
495 NewGlobals.push_back(NGV);
497 // Calculate the known alignment of the field. If the original aggregate
498 // had 256 byte alignment for example, something might depend on that:
499 // propagate info to each field.
500 uint64_t FieldOffset = Layout.getElementOffset(i);
501 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
502 if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i)))
503 NGV->setAlignment(NewAlign);
505 } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
506 unsigned NumElements = 0;
507 if (ArrayType *ATy = dyn_cast<ArrayType>(STy))
508 NumElements = ATy->getNumElements();
510 NumElements = cast<VectorType>(STy)->getNumElements();
512 if (NumElements > 16 && GV->hasNUsesOrMore(16))
513 return 0; // It's not worth it.
514 NewGlobals.reserve(NumElements);
516 uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType());
517 unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType());
518 for (unsigned i = 0, e = NumElements; i != e; ++i) {
519 Constant *In = Init->getAggregateElement(i);
520 assert(In && "Couldn't get element of initializer?");
522 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
523 GlobalVariable::InternalLinkage,
524 In, GV->getName()+"."+Twine(i),
525 GV->getThreadLocalMode(),
526 GV->getType()->getAddressSpace());
527 Globals.insert(GV, NGV);
528 NewGlobals.push_back(NGV);
530 // Calculate the known alignment of the field. If the original aggregate
531 // had 256 byte alignment for example, something might depend on that:
532 // propagate info to each field.
533 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
534 if (NewAlign > EltAlign)
535 NGV->setAlignment(NewAlign);
539 if (NewGlobals.empty())
542 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV);
544 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
546 // Loop over all of the uses of the global, replacing the constantexpr geps,
547 // with smaller constantexpr geps or direct references.
548 while (!GV->use_empty()) {
549 User *GEP = GV->use_back();
550 assert(((isa<ConstantExpr>(GEP) &&
551 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
552 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
554 // Ignore the 1th operand, which has to be zero or else the program is quite
555 // broken (undefined). Get the 2nd operand, which is the structure or array
557 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
558 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
560 Value *NewPtr = NewGlobals[Val];
562 // Form a shorter GEP if needed.
563 if (GEP->getNumOperands() > 3) {
564 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
565 SmallVector<Constant*, 8> Idxs;
566 Idxs.push_back(NullInt);
567 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
568 Idxs.push_back(CE->getOperand(i));
569 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs);
571 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
572 SmallVector<Value*, 8> Idxs;
573 Idxs.push_back(NullInt);
574 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
575 Idxs.push_back(GEPI->getOperand(i));
576 NewPtr = GetElementPtrInst::Create(NewPtr, Idxs,
577 GEPI->getName()+"."+Twine(Val),GEPI);
580 GEP->replaceAllUsesWith(NewPtr);
582 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
583 GEPI->eraseFromParent();
585 cast<ConstantExpr>(GEP)->destroyConstant();
588 // Delete the old global, now that it is dead.
592 // Loop over the new globals array deleting any globals that are obviously
593 // dead. This can arise due to scalarization of a structure or an array that
594 // has elements that are dead.
595 unsigned FirstGlobal = 0;
596 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
597 if (NewGlobals[i]->use_empty()) {
598 Globals.erase(NewGlobals[i]);
599 if (FirstGlobal == i) ++FirstGlobal;
602 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0;
605 /// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified
606 /// value will trap if the value is dynamically null. PHIs keeps track of any
607 /// phi nodes we've seen to avoid reprocessing them.
608 static bool AllUsesOfValueWillTrapIfNull(const Value *V,
609 SmallPtrSet<const PHINode*, 8> &PHIs) {
610 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
614 if (isa<LoadInst>(U)) {
616 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
617 if (SI->getOperand(0) == V) {
618 //cerr << "NONTRAPPING USE: " << *U;
619 return false; // Storing the value.
621 } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
622 if (CI->getCalledValue() != V) {
623 //cerr << "NONTRAPPING USE: " << *U;
624 return false; // Not calling the ptr
626 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
627 if (II->getCalledValue() != V) {
628 //cerr << "NONTRAPPING USE: " << *U;
629 return false; // Not calling the ptr
631 } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
632 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
633 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
634 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
635 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
636 // If we've already seen this phi node, ignore it, it has already been
638 if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
640 } else if (isa<ICmpInst>(U) &&
641 isa<ConstantPointerNull>(UI->getOperand(1))) {
642 // Ignore icmp X, null
644 //cerr << "NONTRAPPING USE: " << *U;
651 /// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads
652 /// from GV will trap if the loaded value is null. Note that this also permits
653 /// comparisons of the loaded value against null, as a special case.
654 static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
655 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
659 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
660 SmallPtrSet<const PHINode*, 8> PHIs;
661 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
663 } else if (isa<StoreInst>(U)) {
664 // Ignore stores to the global.
666 // We don't know or understand this user, bail out.
667 //cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
674 static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
675 bool Changed = false;
676 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) {
677 Instruction *I = cast<Instruction>(*UI++);
678 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
679 LI->setOperand(0, NewV);
681 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
682 if (SI->getOperand(1) == V) {
683 SI->setOperand(1, NewV);
686 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
688 if (CS.getCalledValue() == V) {
689 // Calling through the pointer! Turn into a direct call, but be careful
690 // that the pointer is not also being passed as an argument.
691 CS.setCalledFunction(NewV);
693 bool PassedAsArg = false;
694 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
695 if (CS.getArgument(i) == V) {
697 CS.setArgument(i, NewV);
701 // Being passed as an argument also. Be careful to not invalidate UI!
705 } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
706 Changed |= OptimizeAwayTrappingUsesOfValue(CI,
707 ConstantExpr::getCast(CI->getOpcode(),
708 NewV, CI->getType()));
709 if (CI->use_empty()) {
711 CI->eraseFromParent();
713 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
714 // Should handle GEP here.
715 SmallVector<Constant*, 8> Idxs;
716 Idxs.reserve(GEPI->getNumOperands()-1);
717 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
719 if (Constant *C = dyn_cast<Constant>(*i))
723 if (Idxs.size() == GEPI->getNumOperands()-1)
724 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
725 ConstantExpr::getGetElementPtr(NewV, Idxs));
726 if (GEPI->use_empty()) {
728 GEPI->eraseFromParent();
737 /// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null
738 /// value stored into it. If there are uses of the loaded value that would trap
739 /// if the loaded value is dynamically null, then we know that they cannot be
740 /// reachable with a null optimize away the load.
741 static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV,
743 TargetLibraryInfo *TLI) {
744 bool Changed = false;
746 // Keep track of whether we are able to remove all the uses of the global
747 // other than the store that defines it.
748 bool AllNonStoreUsesGone = true;
750 // Replace all uses of loads with uses of uses of the stored value.
751 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){
752 User *GlobalUser = *GUI++;
753 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
754 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
755 // If we were able to delete all uses of the loads
756 if (LI->use_empty()) {
757 LI->eraseFromParent();
760 AllNonStoreUsesGone = false;
762 } else if (isa<StoreInst>(GlobalUser)) {
763 // Ignore the store that stores "LV" to the global.
764 assert(GlobalUser->getOperand(1) == GV &&
765 "Must be storing *to* the global");
767 AllNonStoreUsesGone = false;
769 // If we get here we could have other crazy uses that are transitively
771 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
772 isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) ||
773 isa<BitCastInst>(GlobalUser) ||
774 isa<GetElementPtrInst>(GlobalUser)) &&
775 "Only expect load and stores!");
780 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV);
784 // If we nuked all of the loads, then none of the stores are needed either,
785 // nor is the global.
786 if (AllNonStoreUsesGone) {
787 if (isLeakCheckerRoot(GV)) {
788 Changed |= CleanupPointerRootUsers(GV, TLI);
791 CleanupConstantGlobalUsers(GV, 0, TD, TLI);
793 if (GV->use_empty()) {
794 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
796 GV->eraseFromParent();
803 /// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
804 /// instructions that are foldable.
805 static void ConstantPropUsersOf(Value *V,
806 DataLayout *TD, TargetLibraryInfo *TLI) {
807 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; )
808 if (Instruction *I = dyn_cast<Instruction>(*UI++))
809 if (Constant *NewC = ConstantFoldInstruction(I, TD, TLI)) {
810 I->replaceAllUsesWith(NewC);
812 // Advance UI to the next non-I use to avoid invalidating it!
813 // Instructions could multiply use V.
814 while (UI != E && *UI == I)
816 I->eraseFromParent();
820 /// OptimizeGlobalAddressOfMalloc - This function takes the specified global
821 /// variable, and transforms the program as if it always contained the result of
822 /// the specified malloc. Because it is always the result of the specified
823 /// malloc, there is no reason to actually DO the malloc. Instead, turn the
824 /// malloc into a global, and any loads of GV as uses of the new global.
825 static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
828 ConstantInt *NElements,
830 TargetLibraryInfo *TLI) {
831 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n');
834 if (NElements->getZExtValue() == 1)
835 GlobalType = AllocTy;
837 // If we have an array allocation, the global variable is of an array.
838 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
840 // Create the new global variable. The contents of the malloc'd memory is
841 // undefined, so initialize with an undef value.
842 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(),
844 GlobalValue::InternalLinkage,
845 UndefValue::get(GlobalType),
846 GV->getName()+".body",
848 GV->getThreadLocalMode());
850 // If there are bitcast users of the malloc (which is typical, usually we have
851 // a malloc + bitcast) then replace them with uses of the new global. Update
852 // other users to use the global as well.
853 BitCastInst *TheBC = 0;
854 while (!CI->use_empty()) {
855 Instruction *User = cast<Instruction>(CI->use_back());
856 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
857 if (BCI->getType() == NewGV->getType()) {
858 BCI->replaceAllUsesWith(NewGV);
859 BCI->eraseFromParent();
861 BCI->setOperand(0, NewGV);
865 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
866 User->replaceUsesOfWith(CI, TheBC);
870 Constant *RepValue = NewGV;
871 if (NewGV->getType() != GV->getType()->getElementType())
872 RepValue = ConstantExpr::getBitCast(RepValue,
873 GV->getType()->getElementType());
875 // If there is a comparison against null, we will insert a global bool to
876 // keep track of whether the global was initialized yet or not.
877 GlobalVariable *InitBool =
878 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
879 GlobalValue::InternalLinkage,
880 ConstantInt::getFalse(GV->getContext()),
881 GV->getName()+".init", GV->getThreadLocalMode());
882 bool InitBoolUsed = false;
884 // Loop over all uses of GV, processing them in turn.
885 while (!GV->use_empty()) {
886 if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) {
887 // The global is initialized when the store to it occurs.
888 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
889 SI->getOrdering(), SI->getSynchScope(), SI);
890 SI->eraseFromParent();
894 LoadInst *LI = cast<LoadInst>(GV->use_back());
895 while (!LI->use_empty()) {
896 Use &LoadUse = LI->use_begin().getUse();
897 if (!isa<ICmpInst>(LoadUse.getUser())) {
902 ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser());
903 // Replace the cmp X, 0 with a use of the bool value.
904 // Sink the load to where the compare was, if atomic rules allow us to.
905 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
906 LI->getOrdering(), LI->getSynchScope(),
907 LI->isUnordered() ? (Instruction*)ICI : LI);
909 switch (ICI->getPredicate()) {
910 default: llvm_unreachable("Unknown ICmp Predicate!");
911 case ICmpInst::ICMP_ULT:
912 case ICmpInst::ICMP_SLT: // X < null -> always false
913 LV = ConstantInt::getFalse(GV->getContext());
915 case ICmpInst::ICMP_ULE:
916 case ICmpInst::ICMP_SLE:
917 case ICmpInst::ICMP_EQ:
918 LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
920 case ICmpInst::ICMP_NE:
921 case ICmpInst::ICMP_UGE:
922 case ICmpInst::ICMP_SGE:
923 case ICmpInst::ICMP_UGT:
924 case ICmpInst::ICMP_SGT:
927 ICI->replaceAllUsesWith(LV);
928 ICI->eraseFromParent();
930 LI->eraseFromParent();
933 // If the initialization boolean was used, insert it, otherwise delete it.
935 while (!InitBool->use_empty()) // Delete initializations
936 cast<StoreInst>(InitBool->use_back())->eraseFromParent();
939 GV->getParent()->getGlobalList().insert(GV, InitBool);
941 // Now the GV is dead, nuke it and the malloc..
942 GV->eraseFromParent();
943 CI->eraseFromParent();
945 // To further other optimizations, loop over all users of NewGV and try to
946 // constant prop them. This will promote GEP instructions with constant
947 // indices into GEP constant-exprs, which will allow global-opt to hack on it.
948 ConstantPropUsersOf(NewGV, TD, TLI);
949 if (RepValue != NewGV)
950 ConstantPropUsersOf(RepValue, TD, TLI);
955 /// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking
956 /// to make sure that there are no complex uses of V. We permit simple things
957 /// like dereferencing the pointer, but not storing through the address, unless
958 /// it is to the specified global.
959 static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
960 const GlobalVariable *GV,
961 SmallPtrSet<const PHINode*, 8> &PHIs) {
962 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end();
964 const Instruction *Inst = cast<Instruction>(*UI);
966 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
967 continue; // Fine, ignore.
970 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
971 if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
972 return false; // Storing the pointer itself... bad.
973 continue; // Otherwise, storing through it, or storing into GV... fine.
976 // Must index into the array and into the struct.
977 if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
978 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
983 if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
984 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI
987 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
992 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
993 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
1003 /// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV
1004 /// somewhere. Transform all uses of the allocation into loads from the
1005 /// global and uses of the resultant pointer. Further, delete the store into
1006 /// 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->use_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->use_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 /// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi
1049 /// of a load) are simple enough to perform heap SRA on. This permits GEP's
1050 /// that index through the array and struct field, icmps of null, and PHIs.
1051 static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
1052 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs,
1053 SmallPtrSet<const PHINode*, 32> &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 (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
1058 const Instruction *User = cast<Instruction>(*UI);
1060 // Comparison against null is ok.
1061 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(User)) {
1062 if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
1067 // getelementptr is also ok, but only a simple form.
1068 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
1069 // Must index into the array and into the struct.
1070 if (GEPI->getNumOperands() < 3)
1073 // Otherwise the GEP is ok.
1077 if (const PHINode *PN = dyn_cast<PHINode>(User)) {
1078 if (!LoadUsingPHIsPerLoad.insert(PN))
1079 // This means some phi nodes are dependent on each other.
1080 // Avoid infinite looping!
1082 if (!LoadUsingPHIs.insert(PN))
1083 // If we have already analyzed this PHI, then it is safe.
1086 // Make sure all uses of the PHI are simple enough to transform.
1087 if (!LoadUsesSimpleEnoughForHeapSRA(PN,
1088 LoadUsingPHIs, LoadUsingPHIsPerLoad))
1094 // Otherwise we don't know what this is, not ok.
1102 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from
1103 /// GV are simple enough to perform HeapSRA, return true.
1104 static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
1105 Instruction *StoredVal) {
1106 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
1107 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
1108 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
1110 if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1111 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
1112 LoadUsingPHIsPerLoad))
1114 LoadUsingPHIsPerLoad.clear();
1117 // If we reach here, we know that all uses of the loads and transitive uses
1118 // (through PHI nodes) are simple enough to transform. However, we don't know
1119 // that all inputs the to the PHI nodes are in the same equivalence sets.
1120 // Check to verify that all operands of the PHIs are either PHIS that can be
1121 // transformed, loads from GV, or MI itself.
1122 for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin()
1123 , E = LoadUsingPHIs.end(); I != E; ++I) {
1124 const PHINode *PN = *I;
1125 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
1126 Value *InVal = PN->getIncomingValue(op);
1128 // PHI of the stored value itself is ok.
1129 if (InVal == StoredVal) continue;
1131 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
1132 // One of the PHIs in our set is (optimistically) ok.
1133 if (LoadUsingPHIs.count(InPN))
1138 // Load from GV is ok.
1139 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
1140 if (LI->getOperand(0) == GV)
1145 // Anything else is rejected.
1153 static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
1154 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1155 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1156 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
1158 if (FieldNo >= FieldVals.size())
1159 FieldVals.resize(FieldNo+1);
1161 // If we already have this value, just reuse the previously scalarized
1163 if (Value *FieldVal = FieldVals[FieldNo])
1166 // Depending on what instruction this is, we have several cases.
1168 if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
1169 // This is a scalarized version of the load from the global. Just create
1170 // a new Load of the scalarized global.
1171 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
1172 InsertedScalarizedValues,
1174 LI->getName()+".f"+Twine(FieldNo), LI);
1175 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
1176 // PN's type is pointer to struct. Make a new PHI of pointer to struct
1178 StructType *ST = cast<StructType>(PN->getType()->getPointerElementType());
1181 PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)),
1182 PN->getNumIncomingValues(),
1183 PN->getName()+".f"+Twine(FieldNo), PN);
1185 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
1187 llvm_unreachable("Unknown usable value");
1190 return FieldVals[FieldNo] = Result;
1193 /// RewriteHeapSROALoadUser - Given a load instruction and a value derived from
1194 /// the load, rewrite the derived value to use the HeapSRoA'd load.
1195 static void RewriteHeapSROALoadUser(Instruction *LoadUser,
1196 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1197 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1198 // If this is a comparison against null, handle it.
1199 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
1200 assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
1201 // If we have a setcc of the loaded pointer, we can use a setcc of any
1203 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
1204 InsertedScalarizedValues, PHIsToRewrite);
1206 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
1207 Constant::getNullValue(NPtr->getType()),
1209 SCI->replaceAllUsesWith(New);
1210 SCI->eraseFromParent();
1214 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
1215 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
1216 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
1217 && "Unexpected GEPI!");
1219 // Load the pointer for this field.
1220 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
1221 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
1222 InsertedScalarizedValues, PHIsToRewrite);
1224 // Create the new GEP idx vector.
1225 SmallVector<Value*, 8> GEPIdx;
1226 GEPIdx.push_back(GEPI->getOperand(1));
1227 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
1229 Value *NGEPI = GetElementPtrInst::Create(NewPtr, GEPIdx,
1230 GEPI->getName(), GEPI);
1231 GEPI->replaceAllUsesWith(NGEPI);
1232 GEPI->eraseFromParent();
1236 // Recursively transform the users of PHI nodes. This will lazily create the
1237 // PHIs that are needed for individual elements. Keep track of what PHIs we
1238 // see in InsertedScalarizedValues so that we don't get infinite loops (very
1239 // antisocial). If the PHI is already in InsertedScalarizedValues, it has
1240 // already been seen first by another load, so its uses have already been
1242 PHINode *PN = cast<PHINode>(LoadUser);
1243 if (!InsertedScalarizedValues.insert(std::make_pair(PN,
1244 std::vector<Value*>())).second)
1247 // If this is the first time we've seen this PHI, recursively process all
1249 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) {
1250 Instruction *User = cast<Instruction>(*UI++);
1251 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1255 /// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr
1256 /// is a value loaded from the global. Eliminate all uses of Ptr, making them
1257 /// use FieldGlobals instead. All uses of loaded values satisfy
1258 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA.
1259 static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
1260 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1261 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1262 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end();
1264 Instruction *User = cast<Instruction>(*UI++);
1265 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1268 if (Load->use_empty()) {
1269 Load->eraseFromParent();
1270 InsertedScalarizedValues.erase(Load);
1274 /// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break
1275 /// it up into multiple allocations of arrays of the fields.
1276 static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
1277 Value *NElems, DataLayout *TD,
1278 const TargetLibraryInfo *TLI) {
1279 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n');
1280 Type *MAT = getMallocAllocatedType(CI, TLI);
1281 StructType *STy = cast<StructType>(MAT);
1283 // There is guaranteed to be at least one use of the malloc (storing
1284 // it into GV). If there are other uses, change them to be uses of
1285 // the global to simplify later code. This also deletes the store
1287 ReplaceUsesOfMallocWithGlobal(CI, GV);
1289 // Okay, at this point, there are no users of the malloc. Insert N
1290 // new mallocs at the same place as CI, and N globals.
1291 std::vector<Value*> FieldGlobals;
1292 std::vector<Value*> FieldMallocs;
1294 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
1295 Type *FieldTy = STy->getElementType(FieldNo);
1296 PointerType *PFieldTy = PointerType::getUnqual(FieldTy);
1298 GlobalVariable *NGV =
1299 new GlobalVariable(*GV->getParent(),
1300 PFieldTy, false, GlobalValue::InternalLinkage,
1301 Constant::getNullValue(PFieldTy),
1302 GV->getName() + ".f" + Twine(FieldNo), GV,
1303 GV->getThreadLocalMode());
1304 FieldGlobals.push_back(NGV);
1306 unsigned TypeSize = TD->getTypeAllocSize(FieldTy);
1307 if (StructType *ST = dyn_cast<StructType>(FieldTy))
1308 TypeSize = TD->getStructLayout(ST)->getSizeInBytes();
1309 Type *IntPtrTy = TD->getIntPtrType(CI->getType());
1310 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
1311 ConstantInt::get(IntPtrTy, TypeSize),
1313 CI->getName() + ".f" + Twine(FieldNo));
1314 FieldMallocs.push_back(NMI);
1315 new StoreInst(NMI, NGV, CI);
1318 // The tricky aspect of this transformation is handling the case when malloc
1319 // fails. In the original code, malloc failing would set the result pointer
1320 // of malloc to null. In this case, some mallocs could succeed and others
1321 // could fail. As such, we emit code that looks like this:
1322 // F0 = malloc(field0)
1323 // F1 = malloc(field1)
1324 // F2 = malloc(field2)
1325 // if (F0 == 0 || F1 == 0 || F2 == 0) {
1326 // if (F0) { free(F0); F0 = 0; }
1327 // if (F1) { free(F1); F1 = 0; }
1328 // if (F2) { free(F2); F2 = 0; }
1330 // The malloc can also fail if its argument is too large.
1331 Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
1332 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
1333 ConstantZero, "isneg");
1334 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
1335 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
1336 Constant::getNullValue(FieldMallocs[i]->getType()),
1338 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
1341 // Split the basic block at the old malloc.
1342 BasicBlock *OrigBB = CI->getParent();
1343 BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont");
1345 // Create the block to check the first condition. Put all these blocks at the
1346 // end of the function as they are unlikely to be executed.
1347 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
1349 OrigBB->getParent());
1351 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
1352 // branch on RunningOr.
1353 OrigBB->getTerminator()->eraseFromParent();
1354 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
1356 // Within the NullPtrBlock, we need to emit a comparison and branch for each
1357 // pointer, because some may be null while others are not.
1358 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1359 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
1360 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
1361 Constant::getNullValue(GVVal->getType()));
1362 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
1363 OrigBB->getParent());
1364 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
1365 OrigBB->getParent());
1366 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
1369 // Fill in FreeBlock.
1370 CallInst::CreateFree(GVVal, BI);
1371 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
1373 BranchInst::Create(NextBlock, FreeBlock);
1375 NullPtrBlock = NextBlock;
1378 BranchInst::Create(ContBB, NullPtrBlock);
1380 // CI is no longer needed, remove it.
1381 CI->eraseFromParent();
1383 /// InsertedScalarizedLoads - As we process loads, if we can't immediately
1384 /// update all uses of the load, keep track of what scalarized loads are
1385 /// inserted for a given load.
1386 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues;
1387 InsertedScalarizedValues[GV] = FieldGlobals;
1389 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite;
1391 // Okay, the malloc site is completely handled. All of the uses of GV are now
1392 // loads, and all uses of those loads are simple. Rewrite them to use loads
1393 // of the per-field globals instead.
1394 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) {
1395 Instruction *User = cast<Instruction>(*UI++);
1397 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1398 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
1402 // Must be a store of null.
1403 StoreInst *SI = cast<StoreInst>(User);
1404 assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
1405 "Unexpected heap-sra user!");
1407 // Insert a store of null into each global.
1408 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1409 PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType());
1410 Constant *Null = Constant::getNullValue(PT->getElementType());
1411 new StoreInst(Null, FieldGlobals[i], SI);
1413 // Erase the original store.
1414 SI->eraseFromParent();
1417 // While we have PHIs that are interesting to rewrite, do it.
1418 while (!PHIsToRewrite.empty()) {
1419 PHINode *PN = PHIsToRewrite.back().first;
1420 unsigned FieldNo = PHIsToRewrite.back().second;
1421 PHIsToRewrite.pop_back();
1422 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
1423 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
1425 // Add all the incoming values. This can materialize more phis.
1426 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1427 Value *InVal = PN->getIncomingValue(i);
1428 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
1430 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
1434 // Drop all inter-phi links and any loads that made it this far.
1435 for (DenseMap<Value*, std::vector<Value*> >::iterator
1436 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1438 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1439 PN->dropAllReferences();
1440 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1441 LI->dropAllReferences();
1444 // Delete all the phis and loads now that inter-references are dead.
1445 for (DenseMap<Value*, std::vector<Value*> >::iterator
1446 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1448 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1449 PN->eraseFromParent();
1450 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1451 LI->eraseFromParent();
1454 // The old global is now dead, remove it.
1455 GV->eraseFromParent();
1458 return cast<GlobalVariable>(FieldGlobals[0]);
1461 /// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a
1462 /// pointer global variable with a single value stored it that is a malloc or
1464 static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
1467 AtomicOrdering Ordering,
1468 Module::global_iterator &GVI,
1470 TargetLibraryInfo *TLI) {
1474 // If this is a malloc of an abstract type, don't touch it.
1475 if (!AllocTy->isSized())
1478 // We can't optimize this global unless all uses of it are *known* to be
1479 // of the malloc value, not of the null initializer value (consider a use
1480 // that compares the global's value against zero to see if the malloc has
1481 // been reached). To do this, we check to see if all uses of the global
1482 // would trap if the global were null: this proves that they must all
1483 // happen after the malloc.
1484 if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
1487 // We can't optimize this if the malloc itself is used in a complex way,
1488 // for example, being stored into multiple globals. This allows the
1489 // malloc to be stored into the specified global, loaded icmp'd, and
1490 // GEP'd. These are all things we could transform to using the global
1492 SmallPtrSet<const PHINode*, 8> PHIs;
1493 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
1496 // If we have a global that is only initialized with a fixed size malloc,
1497 // transform the program to use global memory instead of malloc'd memory.
1498 // This eliminates dynamic allocation, avoids an indirection accessing the
1499 // data, and exposes the resultant global to further GlobalOpt.
1500 // We cannot optimize the malloc if we cannot determine malloc array size.
1501 Value *NElems = getMallocArraySize(CI, TD, TLI, true);
1505 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
1506 // Restrict this transformation to only working on small allocations
1507 // (2048 bytes currently), as we don't want to introduce a 16M global or
1509 if (NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) {
1510 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD, TLI);
1514 // If the allocation is an array of structures, consider transforming this
1515 // into multiple malloc'd arrays, one for each field. This is basically
1516 // SRoA for malloc'd memory.
1518 if (Ordering != NotAtomic)
1521 // If this is an allocation of a fixed size array of structs, analyze as a
1522 // variable size array. malloc [100 x struct],1 -> malloc struct, 100
1523 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
1524 if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
1525 AllocTy = AT->getElementType();
1527 StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
1531 // This the structure has an unreasonable number of fields, leave it
1533 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
1534 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
1536 // If this is a fixed size array, transform the Malloc to be an alloc of
1537 // structs. malloc [100 x struct],1 -> malloc struct, 100
1538 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) {
1539 Type *IntPtrTy = TD->getIntPtrType(CI->getType());
1540 unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes();
1541 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
1542 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
1543 Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy,
1544 AllocSize, NumElements,
1546 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
1547 CI->replaceAllUsesWith(Cast);
1548 CI->eraseFromParent();
1549 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc))
1550 CI = cast<CallInst>(BCI->getOperand(0));
1552 CI = cast<CallInst>(Malloc);
1555 GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, TLI, true),
1563 // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
1564 // that only one value (besides its initializer) is ever stored to the global.
1565 static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
1566 AtomicOrdering Ordering,
1567 Module::global_iterator &GVI,
1568 DataLayout *TD, TargetLibraryInfo *TLI) {
1569 // Ignore no-op GEPs and bitcasts.
1570 StoredOnceVal = StoredOnceVal->stripPointerCasts();
1572 // If we are dealing with a pointer global that is initialized to null and
1573 // only has one (non-null) value stored into it, then we can optimize any
1574 // users of the loaded value (often calls and loads) that would trap if the
1576 if (GV->getInitializer()->getType()->isPointerTy() &&
1577 GV->getInitializer()->isNullValue()) {
1578 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
1579 if (GV->getInitializer()->getType() != SOVC->getType())
1580 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
1582 // Optimize away any trapping uses of the loaded value.
1583 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, TD, TLI))
1585 } else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) {
1586 Type *MallocType = getMallocAllocatedType(CI, TLI);
1588 TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, Ordering, GVI,
1597 /// TryToShrinkGlobalToBoolean - At this point, we have learned that the only
1598 /// two values ever stored into GV are its initializer and OtherVal. See if we
1599 /// can shrink the global into a boolean and select between the two values
1600 /// whenever it is used. This exposes the values to other scalar optimizations.
1601 static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
1602 Type *GVElType = GV->getType()->getElementType();
1604 // If GVElType is already i1, it is already shrunk. If the type of the GV is
1605 // an FP value, pointer or vector, don't do this optimization because a select
1606 // between them is very expensive and unlikely to lead to later
1607 // simplification. In these cases, we typically end up with "cond ? v1 : v2"
1608 // where v1 and v2 both require constant pool loads, a big loss.
1609 if (GVElType == Type::getInt1Ty(GV->getContext()) ||
1610 GVElType->isFloatingPointTy() ||
1611 GVElType->isPointerTy() || GVElType->isVectorTy())
1614 // Walk the use list of the global seeing if all the uses are load or store.
1615 // If there is anything else, bail out.
1616 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){
1618 if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
1622 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV);
1624 // Create the new global, initializing it to false.
1625 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
1627 GlobalValue::InternalLinkage,
1628 ConstantInt::getFalse(GV->getContext()),
1630 GV->getThreadLocalMode(),
1631 GV->getType()->getAddressSpace());
1632 GV->getParent()->getGlobalList().insert(GV, NewGV);
1634 Constant *InitVal = GV->getInitializer();
1635 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
1636 "No reason to shrink to bool!");
1638 // If initialized to zero and storing one into the global, we can use a cast
1639 // instead of a select to synthesize the desired value.
1640 bool IsOneZero = false;
1641 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
1642 IsOneZero = InitVal->isNullValue() && CI->isOne();
1644 while (!GV->use_empty()) {
1645 Instruction *UI = cast<Instruction>(GV->use_back());
1646 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
1647 // Change the store into a boolean store.
1648 bool StoringOther = SI->getOperand(0) == OtherVal;
1649 // Only do this if we weren't storing a loaded value.
1651 if (StoringOther || SI->getOperand(0) == InitVal) {
1652 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
1655 // Otherwise, we are storing a previously loaded copy. To do this,
1656 // change the copy from copying the original value to just copying the
1658 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
1660 // If we've already replaced the input, StoredVal will be a cast or
1661 // select instruction. If not, it will be a load of the original
1663 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
1664 assert(LI->getOperand(0) == GV && "Not a copy!");
1665 // Insert a new load, to preserve the saved value.
1666 StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1667 LI->getOrdering(), LI->getSynchScope(), LI);
1669 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
1670 "This is not a form that we understand!");
1671 StoreVal = StoredVal->getOperand(0);
1672 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
1675 new StoreInst(StoreVal, NewGV, false, 0,
1676 SI->getOrdering(), SI->getSynchScope(), SI);
1678 // Change the load into a load of bool then a select.
1679 LoadInst *LI = cast<LoadInst>(UI);
1680 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1681 LI->getOrdering(), LI->getSynchScope(), LI);
1684 NSI = new ZExtInst(NLI, LI->getType(), "", LI);
1686 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
1688 LI->replaceAllUsesWith(NSI);
1690 UI->eraseFromParent();
1693 // Retain the name of the old global variable. People who are debugging their
1694 // programs may expect these variables to be named the same.
1695 NewGV->takeName(GV);
1696 GV->eraseFromParent();
1701 /// ProcessGlobal - Analyze the specified global variable and optimize it if
1702 /// possible. If we make a change, return true.
1703 bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
1704 Module::global_iterator &GVI) {
1705 if (!GV->isDiscardableIfUnused())
1708 // Do more involved optimizations if the global is internal.
1709 GV->removeDeadConstantUsers();
1711 if (GV->use_empty()) {
1712 DEBUG(dbgs() << "GLOBAL DEAD: " << *GV);
1713 GV->eraseFromParent();
1718 if (!GV->hasLocalLinkage())
1723 if (GlobalStatus::analyzeGlobal(GV, GS))
1726 GV->setAddressMaybeTaken(false);
1727 if (!GS.IsCompared && !GV->hasUnnamedAddr()) {
1728 GV->setUnnamedAddr(true);
1732 if (GV->isConstant() || !GV->hasInitializer())
1735 return ProcessInternalGlobal(GV, GVI, GS);
1738 /// ProcessInternalGlobal - Analyze the specified global variable and optimize
1739 /// it if possible. If we make a change, return true.
1740 bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
1741 Module::global_iterator &GVI,
1742 const GlobalStatus &GS) {
1743 // If this is a first class global and has only one accessing function
1744 // and this function is main (which we know is not recursive), we replace
1745 // the global with a local alloca in this function.
1747 // NOTE: It doesn't make sense to promote non single-value types since we
1748 // are just replacing static memory to stack memory.
1750 // If the global is in different address space, don't bring it to stack.
1751 if (!GS.HasMultipleAccessingFunctions &&
1752 GS.AccessingFunction && !GS.HasNonInstructionUser &&
1753 GV->getType()->getElementType()->isSingleValueType() &&
1754 GS.AccessingFunction->getName() == "main" &&
1755 GS.AccessingFunction->hasExternalLinkage() &&
1756 GV->getType()->getAddressSpace() == 0) {
1757 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV);
1758 Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction
1759 ->getEntryBlock().begin());
1760 Type *ElemTy = GV->getType()->getElementType();
1761 // FIXME: Pass Global's alignment when globals have alignment
1762 AllocaInst *Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI);
1763 if (!isa<UndefValue>(GV->getInitializer()))
1764 new StoreInst(GV->getInitializer(), Alloca, &FirstI);
1766 GV->replaceAllUsesWith(Alloca);
1767 GV->eraseFromParent();
1772 // If the global is never loaded (but may be stored to), it is dead.
1775 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV);
1778 if (isLeakCheckerRoot(GV)) {
1779 // Delete any constant stores to the global.
1780 Changed = CleanupPointerRootUsers(GV, TLI);
1782 // Delete any stores we can find to the global. We may not be able to
1783 // make it completely dead though.
1784 Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1787 // If the global is dead now, delete it.
1788 if (GV->use_empty()) {
1789 GV->eraseFromParent();
1795 } else if (GS.StoredType <= GlobalStatus::InitializerStored) {
1796 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n");
1797 GV->setConstant(true);
1799 // Clean up any obviously simplifiable users now.
1800 CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1802 // If the global is dead now, just nuke it.
1803 if (GV->use_empty()) {
1804 DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
1805 << "all users and delete global!\n");
1806 GV->eraseFromParent();
1812 } else if (!GV->getInitializer()->getType()->isSingleValueType()) {
1813 if (DataLayout *TD = getAnalysisIfAvailable<DataLayout>())
1814 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) {
1815 GVI = FirstNewGV; // Don't skip the newly produced globals!
1818 } else if (GS.StoredType == GlobalStatus::StoredOnce) {
1819 // If the initial value for the global was an undef value, and if only
1820 // one other value was stored into it, we can just change the
1821 // initializer to be the stored value, then delete all stores to the
1822 // global. This allows us to mark it constant.
1823 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
1824 if (isa<UndefValue>(GV->getInitializer())) {
1825 // Change the initial value here.
1826 GV->setInitializer(SOVConstant);
1828 // Clean up any obviously simplifiable users now.
1829 CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1831 if (GV->use_empty()) {
1832 DEBUG(dbgs() << " *** Substituting initializer allowed us to "
1833 << "simplify all users and delete global!\n");
1834 GV->eraseFromParent();
1843 // Try to optimize globals based on the knowledge that only one value
1844 // (besides its initializer) is ever stored to the global.
1845 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, GVI,
1849 // Otherwise, if the global was not a boolean, we can shrink it to be a
1851 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) {
1852 if (GS.Ordering == NotAtomic) {
1853 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
1864 /// ChangeCalleesToFastCall - Walk all of the direct calls of the specified
1865 /// function, changing them to FastCC.
1866 static void ChangeCalleesToFastCall(Function *F) {
1867 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
1868 if (isa<BlockAddress>(*UI))
1870 CallSite User(cast<Instruction>(*UI));
1871 User.setCallingConv(CallingConv::Fast);
1875 static AttributeSet StripNest(LLVMContext &C, const AttributeSet &Attrs) {
1876 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
1877 unsigned Index = Attrs.getSlotIndex(i);
1878 if (!Attrs.getSlotAttributes(i).hasAttribute(Index, Attribute::Nest))
1881 // There can be only one.
1882 return Attrs.removeAttribute(C, Index, Attribute::Nest);
1888 static void RemoveNestAttribute(Function *F) {
1889 F->setAttributes(StripNest(F->getContext(), F->getAttributes()));
1890 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
1891 if (isa<BlockAddress>(*UI))
1893 CallSite User(cast<Instruction>(*UI));
1894 User.setAttributes(StripNest(F->getContext(), User.getAttributes()));
1898 bool GlobalOpt::OptimizeFunctions(Module &M) {
1899 bool Changed = false;
1900 // Optimize functions.
1901 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
1903 // Functions without names cannot be referenced outside this module.
1904 if (!F->hasName() && !F->isDeclaration())
1905 F->setLinkage(GlobalValue::InternalLinkage);
1906 F->removeDeadConstantUsers();
1907 if (F->isDefTriviallyDead()) {
1908 F->eraseFromParent();
1911 } else if (F->hasLocalLinkage()) {
1912 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() &&
1913 !F->hasAddressTaken()) {
1914 // If this function has C calling conventions, is not a varargs
1915 // function, and is only called directly, promote it to use the Fast
1916 // calling convention.
1917 F->setCallingConv(CallingConv::Fast);
1918 ChangeCalleesToFastCall(F);
1923 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
1924 !F->hasAddressTaken()) {
1925 // The function is not used by a trampoline intrinsic, so it is safe
1926 // to remove the 'nest' attribute.
1927 RemoveNestAttribute(F);
1936 bool GlobalOpt::OptimizeGlobalVars(Module &M) {
1937 bool Changed = false;
1938 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
1940 GlobalVariable *GV = GVI++;
1941 // Global variables without names cannot be referenced outside this module.
1942 if (!GV->hasName() && !GV->isDeclaration())
1943 GV->setLinkage(GlobalValue::InternalLinkage);
1944 // Simplify the initializer.
1945 if (GV->hasInitializer())
1946 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
1947 Constant *New = ConstantFoldConstantExpression(CE, TD, TLI);
1948 if (New && New != CE)
1949 GV->setInitializer(New);
1952 Changed |= ProcessGlobal(GV, GVI);
1957 /// FindGlobalCtors - Find the llvm.global_ctors list, verifying that all
1958 /// initializers have an init priority of 65535.
1959 GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) {
1960 GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
1961 if (GV == 0) return 0;
1963 // Verify that the initializer is simple enough for us to handle. We are
1964 // only allowed to optimize the initializer if it is unique.
1965 if (!GV->hasUniqueInitializer()) return 0;
1967 if (isa<ConstantAggregateZero>(GV->getInitializer()))
1969 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
1971 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
1972 if (isa<ConstantAggregateZero>(*i))
1974 ConstantStruct *CS = cast<ConstantStruct>(*i);
1975 if (isa<ConstantPointerNull>(CS->getOperand(1)))
1978 // Must have a function or null ptr.
1979 if (!isa<Function>(CS->getOperand(1)))
1982 // Init priority must be standard.
1983 ConstantInt *CI = cast<ConstantInt>(CS->getOperand(0));
1984 if (CI->getZExtValue() != 65535)
1991 /// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand,
1992 /// return a list of the functions and null terminator as a vector.
1993 static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) {
1994 if (GV->getInitializer()->isNullValue())
1995 return std::vector<Function*>();
1996 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
1997 std::vector<Function*> Result;
1998 Result.reserve(CA->getNumOperands());
1999 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
2000 ConstantStruct *CS = cast<ConstantStruct>(*i);
2001 Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
2006 /// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the
2007 /// specified array, returning the new global to use.
2008 static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL,
2009 const std::vector<Function*> &Ctors) {
2010 // If we made a change, reassemble the initializer list.
2011 Constant *CSVals[2];
2012 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 65535);
2015 StructType *StructTy =
2016 cast<StructType>(GCL->getType()->getElementType()->getArrayElementType());
2018 // Create the new init list.
2019 std::vector<Constant*> CAList;
2020 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) {
2022 CSVals[1] = Ctors[i];
2024 Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()),
2026 PointerType *PFTy = PointerType::getUnqual(FTy);
2027 CSVals[1] = Constant::getNullValue(PFTy);
2028 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()),
2031 CAList.push_back(ConstantStruct::get(StructTy, CSVals));
2034 // Create the array initializer.
2035 Constant *CA = ConstantArray::get(ArrayType::get(StructTy,
2036 CAList.size()), CAList);
2038 // If we didn't change the number of elements, don't create a new GV.
2039 if (CA->getType() == GCL->getInitializer()->getType()) {
2040 GCL->setInitializer(CA);
2044 // Create the new global and insert it next to the existing list.
2045 GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(),
2046 GCL->getLinkage(), CA, "",
2047 GCL->getThreadLocalMode());
2048 GCL->getParent()->getGlobalList().insert(GCL, NGV);
2051 // Nuke the old list, replacing any uses with the new one.
2052 if (!GCL->use_empty()) {
2054 if (V->getType() != GCL->getType())
2055 V = ConstantExpr::getBitCast(V, GCL->getType());
2056 GCL->replaceAllUsesWith(V);
2058 GCL->eraseFromParent();
2068 isSimpleEnoughValueToCommit(Constant *C,
2069 SmallPtrSet<Constant*, 8> &SimpleConstants,
2070 const DataLayout *TD);
2073 /// isSimpleEnoughValueToCommit - Return true if the specified constant can be
2074 /// handled by the code generator. We don't want to generate something like:
2075 /// void *X = &X/42;
2076 /// because the code generator doesn't have a relocation that can handle that.
2078 /// This function should be called if C was not found (but just got inserted)
2079 /// in SimpleConstants to avoid having to rescan the same constants all the
2081 static bool isSimpleEnoughValueToCommitHelper(Constant *C,
2082 SmallPtrSet<Constant*, 8> &SimpleConstants,
2083 const DataLayout *TD) {
2084 // Simple integer, undef, constant aggregate zero, global addresses, etc are
2086 if (C->getNumOperands() == 0 || isa<BlockAddress>(C) ||
2087 isa<GlobalValue>(C))
2090 // Aggregate values are safe if all their elements are.
2091 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) ||
2092 isa<ConstantVector>(C)) {
2093 for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
2094 Constant *Op = cast<Constant>(C->getOperand(i));
2095 if (!isSimpleEnoughValueToCommit(Op, SimpleConstants, TD))
2101 // We don't know exactly what relocations are allowed in constant expressions,
2102 // so we allow &global+constantoffset, which is safe and uniformly supported
2104 ConstantExpr *CE = cast<ConstantExpr>(C);
2105 switch (CE->getOpcode()) {
2106 case Instruction::BitCast:
2107 // Bitcast is fine if the casted value is fine.
2108 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2110 case Instruction::IntToPtr:
2111 case Instruction::PtrToInt:
2112 // int <=> ptr is fine if the int type is the same size as the
2114 if (!TD || TD->getTypeSizeInBits(CE->getType()) !=
2115 TD->getTypeSizeInBits(CE->getOperand(0)->getType()))
2117 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2119 // GEP is fine if it is simple + constant offset.
2120 case Instruction::GetElementPtr:
2121 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
2122 if (!isa<ConstantInt>(CE->getOperand(i)))
2124 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2126 case Instruction::Add:
2127 // We allow simple+cst.
2128 if (!isa<ConstantInt>(CE->getOperand(1)))
2130 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2136 isSimpleEnoughValueToCommit(Constant *C,
2137 SmallPtrSet<Constant*, 8> &SimpleConstants,
2138 const DataLayout *TD) {
2139 // If we already checked this constant, we win.
2140 if (!SimpleConstants.insert(C)) return true;
2141 // Check the constant.
2142 return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, TD);
2146 /// isSimpleEnoughPointerToCommit - Return true if this constant is simple
2147 /// enough for us to understand. In particular, if it is a cast to anything
2148 /// other than from one pointer type to another pointer type, we punt.
2149 /// We basically just support direct accesses to globals and GEP's of
2150 /// globals. This should be kept up to date with CommitValueTo.
2151 static bool isSimpleEnoughPointerToCommit(Constant *C) {
2152 // Conservatively, avoid aggregate types. This is because we don't
2153 // want to worry about them partially overlapping other stores.
2154 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
2157 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
2158 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2159 // external globals.
2160 return GV->hasUniqueInitializer();
2162 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
2163 // Handle a constantexpr gep.
2164 if (CE->getOpcode() == Instruction::GetElementPtr &&
2165 isa<GlobalVariable>(CE->getOperand(0)) &&
2166 cast<GEPOperator>(CE)->isInBounds()) {
2167 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2168 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2169 // external globals.
2170 if (!GV->hasUniqueInitializer())
2173 // The first index must be zero.
2174 ConstantInt *CI = dyn_cast<ConstantInt>(*llvm::next(CE->op_begin()));
2175 if (!CI || !CI->isZero()) return false;
2177 // The remaining indices must be compile-time known integers within the
2178 // notional bounds of the corresponding static array types.
2179 if (!CE->isGEPWithNoNotionalOverIndexing())
2182 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2184 // A constantexpr bitcast from a pointer to another pointer is a no-op,
2185 // and we know how to evaluate it by moving the bitcast from the pointer
2186 // operand to the value operand.
2187 } else if (CE->getOpcode() == Instruction::BitCast &&
2188 isa<GlobalVariable>(CE->getOperand(0))) {
2189 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2190 // external globals.
2191 return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
2198 /// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global
2199 /// initializer. This returns 'Init' modified to reflect 'Val' stored into it.
2200 /// At this point, the GEP operands of Addr [0, OpNo) have been stepped into.
2201 static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
2202 ConstantExpr *Addr, unsigned OpNo) {
2203 // Base case of the recursion.
2204 if (OpNo == Addr->getNumOperands()) {
2205 assert(Val->getType() == Init->getType() && "Type mismatch!");
2209 SmallVector<Constant*, 32> Elts;
2210 if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
2211 // Break up the constant into its elements.
2212 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
2213 Elts.push_back(Init->getAggregateElement(i));
2215 // Replace the element that we are supposed to.
2216 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
2217 unsigned Idx = CU->getZExtValue();
2218 assert(Idx < STy->getNumElements() && "Struct index out of range!");
2219 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
2221 // Return the modified struct.
2222 return ConstantStruct::get(STy, Elts);
2225 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
2226 SequentialType *InitTy = cast<SequentialType>(Init->getType());
2229 if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
2230 NumElts = ATy->getNumElements();
2232 NumElts = InitTy->getVectorNumElements();
2234 // Break up the array into elements.
2235 for (uint64_t i = 0, e = NumElts; i != e; ++i)
2236 Elts.push_back(Init->getAggregateElement(i));
2238 assert(CI->getZExtValue() < NumElts);
2239 Elts[CI->getZExtValue()] =
2240 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
2242 if (Init->getType()->isArrayTy())
2243 return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
2244 return ConstantVector::get(Elts);
2247 /// CommitValueTo - We have decided that Addr (which satisfies the predicate
2248 /// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen.
2249 static void CommitValueTo(Constant *Val, Constant *Addr) {
2250 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
2251 assert(GV->hasInitializer());
2252 GV->setInitializer(Val);
2256 ConstantExpr *CE = cast<ConstantExpr>(Addr);
2257 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2258 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
2263 /// Evaluator - This class evaluates LLVM IR, producing the Constant
2264 /// representing each SSA instruction. Changes to global variables are stored
2265 /// in a mapping that can be iterated over after the evaluation is complete.
2266 /// Once an evaluation call fails, the evaluation object should not be reused.
2269 Evaluator(const DataLayout *TD, const TargetLibraryInfo *TLI)
2270 : TD(TD), TLI(TLI) {
2271 ValueStack.push_back(new DenseMap<Value*, Constant*>);
2275 DeleteContainerPointers(ValueStack);
2276 while (!AllocaTmps.empty()) {
2277 GlobalVariable *Tmp = AllocaTmps.back();
2278 AllocaTmps.pop_back();
2280 // If there are still users of the alloca, the program is doing something
2281 // silly, e.g. storing the address of the alloca somewhere and using it
2282 // later. Since this is undefined, we'll just make it be null.
2283 if (!Tmp->use_empty())
2284 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
2289 /// EvaluateFunction - Evaluate a call to function F, returning true if
2290 /// successful, false if we can't evaluate it. ActualArgs contains the formal
2291 /// arguments for the function.
2292 bool EvaluateFunction(Function *F, Constant *&RetVal,
2293 const SmallVectorImpl<Constant*> &ActualArgs);
2295 /// EvaluateBlock - Evaluate all instructions in block BB, returning true if
2296 /// successful, false if we can't evaluate it. NewBB returns the next BB that
2297 /// control flows into, or null upon return.
2298 bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB);
2300 Constant *getVal(Value *V) {
2301 if (Constant *CV = dyn_cast<Constant>(V)) return CV;
2302 Constant *R = ValueStack.back()->lookup(V);
2303 assert(R && "Reference to an uncomputed value!");
2307 void setVal(Value *V, Constant *C) {
2308 ValueStack.back()->operator[](V) = C;
2311 const DenseMap<Constant*, Constant*> &getMutatedMemory() const {
2312 return MutatedMemory;
2315 const SmallPtrSet<GlobalVariable*, 8> &getInvariants() const {
2320 Constant *ComputeLoadResult(Constant *P);
2322 /// ValueStack - As we compute SSA register values, we store their contents
2323 /// here. The back of the vector contains the current function and the stack
2324 /// contains the values in the calling frames.
2325 SmallVector<DenseMap<Value*, Constant*>*, 4> ValueStack;
2327 /// CallStack - This is used to detect recursion. In pathological situations
2328 /// we could hit exponential behavior, but at least there is nothing
2330 SmallVector<Function*, 4> CallStack;
2332 /// MutatedMemory - For each store we execute, we update this map. Loads
2333 /// check this to get the most up-to-date value. If evaluation is successful,
2334 /// this state is committed to the process.
2335 DenseMap<Constant*, Constant*> MutatedMemory;
2337 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable
2338 /// to represent its body. This vector is needed so we can delete the
2339 /// temporary globals when we are done.
2340 SmallVector<GlobalVariable*, 32> AllocaTmps;
2342 /// Invariants - These global variables have been marked invariant by the
2343 /// static constructor.
2344 SmallPtrSet<GlobalVariable*, 8> Invariants;
2346 /// SimpleConstants - These are constants we have checked and know to be
2347 /// simple enough to live in a static initializer of a global.
2348 SmallPtrSet<Constant*, 8> SimpleConstants;
2350 const DataLayout *TD;
2351 const TargetLibraryInfo *TLI;
2354 } // anonymous namespace
2356 /// ComputeLoadResult - Return the value that would be computed by a load from
2357 /// P after the stores reflected by 'memory' have been performed. If we can't
2358 /// decide, return null.
2359 Constant *Evaluator::ComputeLoadResult(Constant *P) {
2360 // If this memory location has been recently stored, use the stored value: it
2361 // is the most up-to-date.
2362 DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P);
2363 if (I != MutatedMemory.end()) return I->second;
2366 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
2367 if (GV->hasDefinitiveInitializer())
2368 return GV->getInitializer();
2372 // Handle a constantexpr getelementptr.
2373 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
2374 if (CE->getOpcode() == Instruction::GetElementPtr &&
2375 isa<GlobalVariable>(CE->getOperand(0))) {
2376 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2377 if (GV->hasDefinitiveInitializer())
2378 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2381 return 0; // don't know how to evaluate.
2384 /// EvaluateBlock - Evaluate all instructions in block BB, returning true if
2385 /// successful, false if we can't evaluate it. NewBB returns the next BB that
2386 /// control flows into, or null upon return.
2387 bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst,
2388 BasicBlock *&NextBB) {
2389 // This is the main evaluation loop.
2391 Constant *InstResult = 0;
2393 DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
2395 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
2396 if (!SI->isSimple()) {
2397 DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
2398 return false; // no volatile/atomic accesses.
2400 Constant *Ptr = getVal(SI->getOperand(1));
2401 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
2402 DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
2403 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2404 DEBUG(dbgs() << "; To: " << *Ptr << "\n");
2406 if (!isSimpleEnoughPointerToCommit(Ptr)) {
2407 // If this is too complex for us to commit, reject it.
2408 DEBUG(dbgs() << "Pointer is too complex for us to evaluate store.");
2412 Constant *Val = getVal(SI->getOperand(0));
2414 // If this might be too difficult for the backend to handle (e.g. the addr
2415 // of one global variable divided by another) then we can't commit it.
2416 if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, TD)) {
2417 DEBUG(dbgs() << "Store value is too complex to evaluate store. " << *Val
2422 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
2423 if (CE->getOpcode() == Instruction::BitCast) {
2424 DEBUG(dbgs() << "Attempting to resolve bitcast on constant ptr.\n");
2425 // If we're evaluating a store through a bitcast, then we need
2426 // to pull the bitcast off the pointer type and push it onto the
2428 Ptr = CE->getOperand(0);
2430 Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
2432 // In order to push the bitcast onto the stored value, a bitcast
2433 // from NewTy to Val's type must be legal. If it's not, we can try
2434 // introspecting NewTy to find a legal conversion.
2435 while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
2436 // If NewTy is a struct, we can convert the pointer to the struct
2437 // into a pointer to its first member.
2438 // FIXME: This could be extended to support arrays as well.
2439 if (StructType *STy = dyn_cast<StructType>(NewTy)) {
2440 NewTy = STy->getTypeAtIndex(0U);
2442 IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
2443 Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
2444 Constant * const IdxList[] = {IdxZero, IdxZero};
2446 Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList);
2447 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2448 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2450 // If we can't improve the situation by introspecting NewTy,
2451 // we have to give up.
2453 DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
2459 // If we found compatible types, go ahead and push the bitcast
2460 // onto the stored value.
2461 Val = ConstantExpr::getBitCast(Val, NewTy);
2463 DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
2467 MutatedMemory[Ptr] = Val;
2468 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
2469 InstResult = ConstantExpr::get(BO->getOpcode(),
2470 getVal(BO->getOperand(0)),
2471 getVal(BO->getOperand(1)));
2472 DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: " << *InstResult
2474 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
2475 InstResult = ConstantExpr::getCompare(CI->getPredicate(),
2476 getVal(CI->getOperand(0)),
2477 getVal(CI->getOperand(1)));
2478 DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult
2480 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
2481 InstResult = ConstantExpr::getCast(CI->getOpcode(),
2482 getVal(CI->getOperand(0)),
2484 DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult
2486 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
2487 InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
2488 getVal(SI->getOperand(1)),
2489 getVal(SI->getOperand(2)));
2490 DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
2492 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
2493 Constant *P = getVal(GEP->getOperand(0));
2494 SmallVector<Constant*, 8> GEPOps;
2495 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
2497 GEPOps.push_back(getVal(*i));
2499 ConstantExpr::getGetElementPtr(P, GEPOps,
2500 cast<GEPOperator>(GEP)->isInBounds());
2501 DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult
2503 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
2505 if (!LI->isSimple()) {
2506 DEBUG(dbgs() << "Found a Load! Not a simple load, can not evaluate.\n");
2507 return false; // no volatile/atomic accesses.
2510 Constant *Ptr = getVal(LI->getOperand(0));
2511 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
2512 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2513 DEBUG(dbgs() << "Found a constant pointer expression, constant "
2514 "folding: " << *Ptr << "\n");
2516 InstResult = ComputeLoadResult(Ptr);
2517 if (InstResult == 0) {
2518 DEBUG(dbgs() << "Failed to compute load result. Can not evaluate load."
2520 return false; // Could not evaluate load.
2523 DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
2524 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
2525 if (AI->isArrayAllocation()) {
2526 DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
2527 return false; // Cannot handle array allocs.
2529 Type *Ty = AI->getType()->getElementType();
2530 AllocaTmps.push_back(new GlobalVariable(Ty, false,
2531 GlobalValue::InternalLinkage,
2532 UndefValue::get(Ty),
2534 InstResult = AllocaTmps.back();
2535 DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n");
2536 } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
2537 CallSite CS(CurInst);
2539 // Debug info can safely be ignored here.
2540 if (isa<DbgInfoIntrinsic>(CS.getInstruction())) {
2541 DEBUG(dbgs() << "Ignoring debug info.\n");
2546 // Cannot handle inline asm.
2547 if (isa<InlineAsm>(CS.getCalledValue())) {
2548 DEBUG(dbgs() << "Found inline asm, can not evaluate.\n");
2552 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
2553 if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
2554 if (MSI->isVolatile()) {
2555 DEBUG(dbgs() << "Can not optimize a volatile memset " <<
2559 Constant *Ptr = getVal(MSI->getDest());
2560 Constant *Val = getVal(MSI->getValue());
2561 Constant *DestVal = ComputeLoadResult(getVal(Ptr));
2562 if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
2563 // This memset is a no-op.
2564 DEBUG(dbgs() << "Ignoring no-op memset.\n");
2570 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
2571 II->getIntrinsicID() == Intrinsic::lifetime_end) {
2572 DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n");
2577 if (II->getIntrinsicID() == Intrinsic::invariant_start) {
2578 // We don't insert an entry into Values, as it doesn't have a
2579 // meaningful return value.
2580 if (!II->use_empty()) {
2581 DEBUG(dbgs() << "Found unused invariant_start. Cant evaluate.\n");
2584 ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
2585 Value *PtrArg = getVal(II->getArgOperand(1));
2586 Value *Ptr = PtrArg->stripPointerCasts();
2587 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
2588 Type *ElemTy = cast<PointerType>(GV->getType())->getElementType();
2589 if (TD && !Size->isAllOnesValue() &&
2590 Size->getValue().getLimitedValue() >=
2591 TD->getTypeStoreSize(ElemTy)) {
2592 Invariants.insert(GV);
2593 DEBUG(dbgs() << "Found a global var that is an invariant: " << *GV
2596 DEBUG(dbgs() << "Found a global var, but can not treat it as an "
2600 // Continue even if we do nothing.
2605 DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
2609 // Resolve function pointers.
2610 Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue()));
2611 if (!Callee || Callee->mayBeOverridden()) {
2612 DEBUG(dbgs() << "Can not resolve function pointer.\n");
2613 return false; // Cannot resolve.
2616 SmallVector<Constant*, 8> Formals;
2617 for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
2618 Formals.push_back(getVal(*i));
2620 if (Callee->isDeclaration()) {
2621 // If this is a function we can constant fold, do it.
2622 if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) {
2624 DEBUG(dbgs() << "Constant folded function call. Result: " <<
2625 *InstResult << "\n");
2627 DEBUG(dbgs() << "Can not constant fold function call.\n");
2631 if (Callee->getFunctionType()->isVarArg()) {
2632 DEBUG(dbgs() << "Can not constant fold vararg function call.\n");
2636 Constant *RetVal = 0;
2637 // Execute the call, if successful, use the return value.
2638 ValueStack.push_back(new DenseMap<Value*, Constant*>);
2639 if (!EvaluateFunction(Callee, RetVal, Formals)) {
2640 DEBUG(dbgs() << "Failed to evaluate function.\n");
2643 delete ValueStack.pop_back_val();
2644 InstResult = RetVal;
2646 if (InstResult != NULL) {
2647 DEBUG(dbgs() << "Successfully evaluated function. Result: " <<
2648 InstResult << "\n\n");
2650 DEBUG(dbgs() << "Successfully evaluated function. Result: 0\n\n");
2653 } else if (isa<TerminatorInst>(CurInst)) {
2654 DEBUG(dbgs() << "Found a terminator instruction.\n");
2656 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
2657 if (BI->isUnconditional()) {
2658 NextBB = BI->getSuccessor(0);
2661 dyn_cast<ConstantInt>(getVal(BI->getCondition()));
2662 if (!Cond) return false; // Cannot determine.
2664 NextBB = BI->getSuccessor(!Cond->getZExtValue());
2666 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
2668 dyn_cast<ConstantInt>(getVal(SI->getCondition()));
2669 if (!Val) return false; // Cannot determine.
2670 NextBB = SI->findCaseValue(Val).getCaseSuccessor();
2671 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
2672 Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
2673 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
2674 NextBB = BA->getBasicBlock();
2676 return false; // Cannot determine.
2677 } else if (isa<ReturnInst>(CurInst)) {
2680 // invoke, unwind, resume, unreachable.
2681 DEBUG(dbgs() << "Can not handle terminator.");
2682 return false; // Cannot handle this terminator.
2685 // We succeeded at evaluating this block!
2686 DEBUG(dbgs() << "Successfully evaluated block.\n");
2689 // Did not know how to evaluate this!
2690 DEBUG(dbgs() << "Failed to evaluate block due to unhandled instruction."
2695 if (!CurInst->use_empty()) {
2696 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
2697 InstResult = ConstantFoldConstantExpression(CE, TD, TLI);
2699 setVal(CurInst, InstResult);
2702 // If we just processed an invoke, we finished evaluating the block.
2703 if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
2704 NextBB = II->getNormalDest();
2705 DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n");
2709 // Advance program counter.
2714 /// EvaluateFunction - Evaluate a call to function F, returning true if
2715 /// successful, false if we can't evaluate it. ActualArgs contains the formal
2716 /// arguments for the function.
2717 bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal,
2718 const SmallVectorImpl<Constant*> &ActualArgs) {
2719 // Check to see if this function is already executing (recursion). If so,
2720 // bail out. TODO: we might want to accept limited recursion.
2721 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
2724 CallStack.push_back(F);
2726 // Initialize arguments to the incoming values specified.
2728 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
2730 setVal(AI, ActualArgs[ArgNo]);
2732 // ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
2733 // we can only evaluate any one basic block at most once. This set keeps
2734 // track of what we have executed so we can detect recursive cases etc.
2735 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
2737 // CurBB - The current basic block we're evaluating.
2738 BasicBlock *CurBB = F->begin();
2740 BasicBlock::iterator CurInst = CurBB->begin();
2743 BasicBlock *NextBB = 0; // Initialized to avoid compiler warnings.
2744 DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n");
2746 if (!EvaluateBlock(CurInst, NextBB))
2750 // Successfully running until there's no next block means that we found
2751 // the return. Fill it the return value and pop the call stack.
2752 ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
2753 if (RI->getNumOperands())
2754 RetVal = getVal(RI->getOperand(0));
2755 CallStack.pop_back();
2759 // Okay, we succeeded in evaluating this control flow. See if we have
2760 // executed the new block before. If so, we have a looping function,
2761 // which we cannot evaluate in reasonable time.
2762 if (!ExecutedBlocks.insert(NextBB))
2763 return false; // looped!
2765 // Okay, we have never been in this block before. Check to see if there
2766 // are any PHI nodes. If so, evaluate them with information about where
2769 for (CurInst = NextBB->begin();
2770 (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
2771 setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
2773 // Advance to the next block.
2778 /// EvaluateStaticConstructor - Evaluate static constructors in the function, if
2779 /// we can. Return true if we can, false otherwise.
2780 static bool EvaluateStaticConstructor(Function *F, const DataLayout *TD,
2781 const TargetLibraryInfo *TLI) {
2782 // Call the function.
2783 Evaluator Eval(TD, TLI);
2784 Constant *RetValDummy;
2785 bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy,
2786 SmallVector<Constant*, 0>());
2789 // We succeeded at evaluation: commit the result.
2790 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
2791 << F->getName() << "' to " << Eval.getMutatedMemory().size()
2793 for (DenseMap<Constant*, Constant*>::const_iterator I =
2794 Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end();
2796 CommitValueTo(I->second, I->first);
2797 for (SmallPtrSet<GlobalVariable*, 8>::const_iterator I =
2798 Eval.getInvariants().begin(), E = Eval.getInvariants().end();
2800 (*I)->setConstant(true);
2806 /// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible.
2807 /// Return true if anything changed.
2808 bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) {
2809 std::vector<Function*> Ctors = ParseGlobalCtors(GCL);
2810 bool MadeChange = false;
2811 if (Ctors.empty()) return false;
2813 // Loop over global ctors, optimizing them when we can.
2814 for (unsigned i = 0; i != Ctors.size(); ++i) {
2815 Function *F = Ctors[i];
2816 // Found a null terminator in the middle of the list, prune off the rest of
2819 if (i != Ctors.size()-1) {
2825 DEBUG(dbgs() << "Optimizing Global Constructor: " << *F << "\n");
2827 // We cannot simplify external ctor functions.
2828 if (F->empty()) continue;
2830 // If we can evaluate the ctor at compile time, do.
2831 if (EvaluateStaticConstructor(F, TD, TLI)) {
2832 Ctors.erase(Ctors.begin()+i);
2835 ++NumCtorsEvaluated;
2840 if (!MadeChange) return false;
2842 GCL = InstallGlobalCtors(GCL, Ctors);
2846 static int compareNames(Constant *const *A, Constant *const *B) {
2847 return (*A)->getName().compare((*B)->getName());
2850 static void setUsedInitializer(GlobalVariable &V,
2851 SmallPtrSet<GlobalValue *, 8> Init) {
2853 V.eraseFromParent();
2857 SmallVector<llvm::Constant *, 8> UsedArray;
2858 PointerType *Int8PtrTy = Type::getInt8PtrTy(V.getContext());
2860 for (SmallPtrSet<GlobalValue *, 8>::iterator I = Init.begin(), E = Init.end();
2862 Constant *Cast = llvm::ConstantExpr::getBitCast(*I, Int8PtrTy);
2863 UsedArray.push_back(Cast);
2865 // Sort to get deterministic order.
2866 array_pod_sort(UsedArray.begin(), UsedArray.end(), compareNames);
2867 ArrayType *ATy = ArrayType::get(Int8PtrTy, UsedArray.size());
2869 Module *M = V.getParent();
2870 V.removeFromParent();
2871 GlobalVariable *NV =
2872 new GlobalVariable(*M, ATy, false, llvm::GlobalValue::AppendingLinkage,
2873 llvm::ConstantArray::get(ATy, UsedArray), "");
2875 NV->setSection("llvm.metadata");
2880 /// \brief An easy to access representation of llvm.used and llvm.compiler.used.
2882 SmallPtrSet<GlobalValue *, 8> Used;
2883 SmallPtrSet<GlobalValue *, 8> CompilerUsed;
2884 GlobalVariable *UsedV;
2885 GlobalVariable *CompilerUsedV;
2888 LLVMUsed(Module &M) {
2889 UsedV = collectUsedGlobalVariables(M, Used, false);
2890 CompilerUsedV = collectUsedGlobalVariables(M, CompilerUsed, true);
2892 typedef SmallPtrSet<GlobalValue *, 8>::iterator iterator;
2893 iterator usedBegin() { return Used.begin(); }
2894 iterator usedEnd() { return Used.end(); }
2895 iterator compilerUsedBegin() { return CompilerUsed.begin(); }
2896 iterator compilerUsedEnd() { return CompilerUsed.end(); }
2897 bool usedCount(GlobalValue *GV) const { return Used.count(GV); }
2898 bool compilerUsedCount(GlobalValue *GV) const {
2899 return CompilerUsed.count(GV);
2901 bool usedErase(GlobalValue *GV) { return Used.erase(GV); }
2902 bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(GV); }
2903 bool usedInsert(GlobalValue *GV) { return Used.insert(GV); }
2904 bool compilerUsedInsert(GlobalValue *GV) { return CompilerUsed.insert(GV); }
2906 void syncVariablesAndSets() {
2908 setUsedInitializer(*UsedV, Used);
2910 setUsedInitializer(*CompilerUsedV, CompilerUsed);
2915 static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) {
2916 if (GA.use_empty()) // No use at all.
2919 assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) &&
2920 "We should have removed the duplicated "
2921 "element from llvm.compiler.used");
2922 if (!GA.hasOneUse())
2923 // Strictly more than one use. So at least one is not in llvm.used and
2924 // llvm.compiler.used.
2927 // Exactly one use. Check if it is in llvm.used or llvm.compiler.used.
2928 return !U.usedCount(&GA) && !U.compilerUsedCount(&GA);
2931 static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V,
2932 const LLVMUsed &U) {
2934 assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) &&
2935 "We should have removed the duplicated "
2936 "element from llvm.compiler.used");
2937 if (U.usedCount(&V) || U.compilerUsedCount(&V))
2939 return V.hasNUsesOrMore(N);
2942 static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) {
2943 if (!GA.hasLocalLinkage())
2946 return U.usedCount(&GA) || U.compilerUsedCount(&GA);
2949 static bool hasUsesToReplace(GlobalAlias &GA, LLVMUsed &U, bool &RenameTarget) {
2950 RenameTarget = false;
2952 if (hasUseOtherThanLLVMUsed(GA, U))
2955 // If the alias is externally visible, we may still be able to simplify it.
2956 if (!mayHaveOtherReferences(GA, U))
2959 // If the aliasee has internal linkage, give it the name and linkage
2960 // of the alias, and delete the alias. This turns:
2961 // define internal ... @f(...)
2962 // @a = alias ... @f
2964 // define ... @a(...)
2965 Constant *Aliasee = GA.getAliasee();
2966 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
2967 if (!Target->hasLocalLinkage())
2970 // Do not perform the transform if multiple aliases potentially target the
2971 // aliasee. This check also ensures that it is safe to replace the section
2972 // and other attributes of the aliasee with those of the alias.
2973 if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U))
2976 RenameTarget = true;
2980 bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
2981 bool Changed = false;
2984 for (SmallPtrSet<GlobalValue *, 8>::iterator I = Used.usedBegin(),
2987 Used.compilerUsedErase(*I);
2989 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
2991 Module::alias_iterator J = I++;
2992 // Aliases without names cannot be referenced outside this module.
2993 if (!J->hasName() && !J->isDeclaration())
2994 J->setLinkage(GlobalValue::InternalLinkage);
2995 // If the aliasee may change at link time, nothing can be done - bail out.
2996 if (J->mayBeOverridden())
2999 Constant *Aliasee = J->getAliasee();
3000 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
3001 Target->removeDeadConstantUsers();
3003 // Make all users of the alias use the aliasee instead.
3005 if (!hasUsesToReplace(*J, Used, RenameTarget))
3008 J->replaceAllUsesWith(Aliasee);
3009 ++NumAliasesResolved;
3013 // Give the aliasee the name, linkage and other attributes of the alias.
3014 Target->takeName(J);
3015 Target->setLinkage(J->getLinkage());
3016 Target->GlobalValue::copyAttributesFrom(J);
3018 if (Used.usedErase(J))
3019 Used.usedInsert(Target);
3021 if (Used.compilerUsedErase(J))
3022 Used.compilerUsedInsert(Target);
3023 } else if (mayHaveOtherReferences(*J, Used))
3026 // Delete the alias.
3027 M.getAliasList().erase(J);
3028 ++NumAliasesRemoved;
3032 Used.syncVariablesAndSets();
3037 static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) {
3038 if (!TLI->has(LibFunc::cxa_atexit))
3041 Function *Fn = M.getFunction(TLI->getName(LibFunc::cxa_atexit));
3046 FunctionType *FTy = Fn->getFunctionType();
3048 // Checking that the function has the right return type, the right number of
3049 // parameters and that they all have pointer types should be enough.
3050 if (!FTy->getReturnType()->isIntegerTy() ||
3051 FTy->getNumParams() != 3 ||
3052 !FTy->getParamType(0)->isPointerTy() ||
3053 !FTy->getParamType(1)->isPointerTy() ||
3054 !FTy->getParamType(2)->isPointerTy())
3060 /// cxxDtorIsEmpty - Returns whether the given function is an empty C++
3061 /// destructor and can therefore be eliminated.
3062 /// Note that we assume that other optimization passes have already simplified
3063 /// the code so we only look for a function with a single basic block, where
3064 /// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and
3065 /// other side-effect free instructions.
3066 static bool cxxDtorIsEmpty(const Function &Fn,
3067 SmallPtrSet<const Function *, 8> &CalledFunctions) {
3068 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
3069 // nounwind, but that doesn't seem worth doing.
3070 if (Fn.isDeclaration())
3073 if (++Fn.begin() != Fn.end())
3076 const BasicBlock &EntryBlock = Fn.getEntryBlock();
3077 for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
3079 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
3080 // Ignore debug intrinsics.
3081 if (isa<DbgInfoIntrinsic>(CI))
3084 const Function *CalledFn = CI->getCalledFunction();
3089 SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
3091 // Don't treat recursive functions as empty.
3092 if (!NewCalledFunctions.insert(CalledFn))
3095 if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
3097 } else if (isa<ReturnInst>(*I))
3098 return true; // We're done.
3099 else if (I->mayHaveSideEffects())
3100 return false; // Destructor with side effects, bail.
3106 bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
3107 /// Itanium C++ ABI p3.3.5:
3109 /// After constructing a global (or local static) object, that will require
3110 /// destruction on exit, a termination function is registered as follows:
3112 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
3114 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
3115 /// call f(p) when DSO d is unloaded, before all such termination calls
3116 /// registered before this one. It returns zero if registration is
3117 /// successful, nonzero on failure.
3119 // This pass will look for calls to __cxa_atexit where the function is trivial
3121 bool Changed = false;
3123 for (Function::use_iterator I = CXAAtExitFn->use_begin(),
3124 E = CXAAtExitFn->use_end(); I != E;) {
3125 // We're only interested in calls. Theoretically, we could handle invoke
3126 // instructions as well, but neither llvm-gcc nor clang generate invokes
3128 CallInst *CI = dyn_cast<CallInst>(*I++);
3133 dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
3137 SmallPtrSet<const Function *, 8> CalledFunctions;
3138 if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
3141 // Just remove the call.
3142 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
3143 CI->eraseFromParent();
3145 ++NumCXXDtorsRemoved;
3153 bool GlobalOpt::runOnModule(Module &M) {
3154 bool Changed = false;
3156 TD = getAnalysisIfAvailable<DataLayout>();
3157 TLI = &getAnalysis<TargetLibraryInfo>();
3159 // Try to find the llvm.globalctors list.
3160 GlobalVariable *GlobalCtors = FindGlobalCtors(M);
3162 bool LocalChange = true;
3163 while (LocalChange) {
3164 LocalChange = false;
3166 // Delete functions that are trivially dead, ccc -> fastcc
3167 LocalChange |= OptimizeFunctions(M);
3169 // Optimize global_ctors list.
3171 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors);
3173 // Optimize non-address-taken globals.
3174 LocalChange |= OptimizeGlobalVars(M);
3176 // Resolve aliases, when possible.
3177 LocalChange |= OptimizeGlobalAliases(M);
3179 // Try to remove trivial global destructors if they are not removed
3181 Function *CXAAtExitFn = FindCXAAtExit(M, TLI);
3183 LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
3185 Changed |= LocalChange;
3188 // TODO: Move all global ctors functions to the end of the module for code