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(); }
100 /// isLeakCheckerRoot - Is this global variable possibly used by a leak checker
101 /// as a root? If so, we might not really want to eliminate the stores to it.
102 static bool isLeakCheckerRoot(GlobalVariable *GV) {
103 // A global variable is a root if it is a pointer, or could plausibly contain
104 // a pointer. There are two challenges; one is that we could have a struct
105 // the has an inner member which is a pointer. We recurse through the type to
106 // detect these (up to a point). The other is that we may actually be a union
107 // of a pointer and another type, and so our LLVM type is an integer which
108 // gets converted into a pointer, or our type is an [i8 x #] with a pointer
109 // potentially contained here.
111 if (GV->hasPrivateLinkage())
114 SmallVector<Type *, 4> Types;
115 Types.push_back(cast<PointerType>(GV->getType())->getElementType());
119 Type *Ty = Types.pop_back_val();
120 switch (Ty->getTypeID()) {
122 case Type::PointerTyID: return true;
123 case Type::ArrayTyID:
124 case Type::VectorTyID: {
125 SequentialType *STy = cast<SequentialType>(Ty);
126 Types.push_back(STy->getElementType());
129 case Type::StructTyID: {
130 StructType *STy = cast<StructType>(Ty);
131 if (STy->isOpaque()) return true;
132 for (StructType::element_iterator I = STy->element_begin(),
133 E = STy->element_end(); I != E; ++I) {
135 if (isa<PointerType>(InnerTy)) return true;
136 if (isa<CompositeType>(InnerTy))
137 Types.push_back(InnerTy);
142 if (--Limit == 0) return true;
143 } while (!Types.empty());
147 /// Given a value that is stored to a global but never read, determine whether
148 /// it's safe to remove the store and the chain of computation that feeds the
150 static bool IsSafeComputationToRemove(Value *V, const TargetLibraryInfo *TLI) {
152 if (isa<Constant>(V))
156 if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) ||
159 if (isAllocationFn(V, TLI))
162 Instruction *I = cast<Instruction>(V);
163 if (I->mayHaveSideEffects())
165 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
166 if (!GEP->hasAllConstantIndices())
168 } else if (I->getNumOperands() != 1) {
172 V = I->getOperand(0);
176 /// CleanupPointerRootUsers - This GV is a pointer root. Loop over all users
177 /// of the global and clean up any that obviously don't assign the global a
178 /// value that isn't dynamically allocated.
180 static bool CleanupPointerRootUsers(GlobalVariable *GV,
181 const TargetLibraryInfo *TLI) {
182 // A brief explanation of leak checkers. The goal is to find bugs where
183 // pointers are forgotten, causing an accumulating growth in memory
184 // usage over time. The common strategy for leak checkers is to whitelist the
185 // memory pointed to by globals at exit. This is popular because it also
186 // solves another problem where the main thread of a C++ program may shut down
187 // before other threads that are still expecting to use those globals. To
188 // handle that case, we expect the program may create a singleton and never
191 bool Changed = false;
193 // If Dead[n].first is the only use of a malloc result, we can delete its
194 // chain of computation and the store to the global in Dead[n].second.
195 SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
197 // Constants can't be pointers to dynamically allocated memory.
198 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
201 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
202 Value *V = SI->getValueOperand();
203 if (isa<Constant>(V)) {
205 SI->eraseFromParent();
206 } else if (Instruction *I = dyn_cast<Instruction>(V)) {
208 Dead.push_back(std::make_pair(I, SI));
210 } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
211 if (isa<Constant>(MSI->getValue())) {
213 MSI->eraseFromParent();
214 } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
216 Dead.push_back(std::make_pair(I, MSI));
218 } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
219 GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
220 if (MemSrc && MemSrc->isConstant()) {
222 MTI->eraseFromParent();
223 } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) {
225 Dead.push_back(std::make_pair(I, MTI));
227 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
228 if (CE->use_empty()) {
229 CE->destroyConstant();
232 } else if (Constant *C = dyn_cast<Constant>(U)) {
233 if (isSafeToDestroyConstant(C)) {
234 C->destroyConstant();
235 // This could have invalidated UI, start over from scratch.
237 CleanupPointerRootUsers(GV, TLI);
243 for (int i = 0, e = Dead.size(); i != e; ++i) {
244 if (IsSafeComputationToRemove(Dead[i].first, TLI)) {
245 Dead[i].second->eraseFromParent();
246 Instruction *I = Dead[i].first;
248 if (isAllocationFn(I, TLI))
250 Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
253 I->eraseFromParent();
256 I->eraseFromParent();
263 /// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all
264 /// users of the global, cleaning up the obvious ones. This is largely just a
265 /// quick scan over the use list to clean up the easy and obvious cruft. This
266 /// returns true if it made a change.
267 static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
268 DataLayout *TD, TargetLibraryInfo *TLI) {
269 bool Changed = false;
270 SmallVector<User*, 8> WorkList(V->use_begin(), V->use_end());
271 while (!WorkList.empty()) {
272 User *U = WorkList.pop_back_val();
274 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
276 // Replace the load with the initializer.
277 LI->replaceAllUsesWith(Init);
278 LI->eraseFromParent();
281 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
282 // Store must be unreachable or storing Init into the global.
283 SI->eraseFromParent();
285 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
286 if (CE->getOpcode() == Instruction::GetElementPtr) {
287 Constant *SubInit = 0;
289 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
290 Changed |= CleanupConstantGlobalUsers(CE, SubInit, TD, TLI);
291 } else if (CE->getOpcode() == Instruction::BitCast &&
292 CE->getType()->isPointerTy()) {
293 // Pointer cast, delete any stores and memsets to the global.
294 Changed |= CleanupConstantGlobalUsers(CE, 0, TD, TLI);
297 if (CE->use_empty()) {
298 CE->destroyConstant();
301 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
302 // Do not transform "gepinst (gep constexpr (GV))" here, because forming
303 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
304 // and will invalidate our notion of what Init is.
305 Constant *SubInit = 0;
306 if (!isa<ConstantExpr>(GEP->getOperand(0))) {
308 dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, TD, TLI));
309 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
310 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
312 // If the initializer is an all-null value and we have an inbounds GEP,
313 // we already know what the result of any load from that GEP is.
314 // TODO: Handle splats.
315 if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
316 SubInit = Constant::getNullValue(GEP->getType()->getElementType());
318 Changed |= CleanupConstantGlobalUsers(GEP, SubInit, TD, TLI);
320 if (GEP->use_empty()) {
321 GEP->eraseFromParent();
324 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
325 if (MI->getRawDest() == V) {
326 MI->eraseFromParent();
330 } else if (Constant *C = dyn_cast<Constant>(U)) {
331 // If we have a chain of dead constantexprs or other things dangling from
332 // us, and if they are all dead, nuke them without remorse.
333 if (isSafeToDestroyConstant(C)) {
334 C->destroyConstant();
335 CleanupConstantGlobalUsers(V, Init, TD, TLI);
343 /// isSafeSROAElementUse - Return true if the specified instruction is a safe
344 /// user of a derived expression from a global that we want to SROA.
345 static bool isSafeSROAElementUse(Value *V) {
346 // We might have a dead and dangling constant hanging off of here.
347 if (Constant *C = dyn_cast<Constant>(V))
348 return isSafeToDestroyConstant(C);
350 Instruction *I = dyn_cast<Instruction>(V);
351 if (!I) return false;
354 if (isa<LoadInst>(I)) return true;
356 // Stores *to* the pointer are ok.
357 if (StoreInst *SI = dyn_cast<StoreInst>(I))
358 return SI->getOperand(0) != V;
360 // Otherwise, it must be a GEP.
361 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
362 if (GEPI == 0) return false;
364 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
365 !cast<Constant>(GEPI->getOperand(1))->isNullValue())
368 for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end();
370 if (!isSafeSROAElementUse(*I))
376 /// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value.
377 /// Look at it and its uses and decide whether it is safe to SROA this global.
379 static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
380 // The user of the global must be a GEP Inst or a ConstantExpr GEP.
381 if (!isa<GetElementPtrInst>(U) &&
382 (!isa<ConstantExpr>(U) ||
383 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
386 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we
387 // don't like < 3 operand CE's, and we don't like non-constant integer
388 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
390 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
391 !cast<Constant>(U->getOperand(1))->isNullValue() ||
392 !isa<ConstantInt>(U->getOperand(2)))
395 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
396 ++GEPI; // Skip over the pointer index.
398 // If this is a use of an array allocation, do a bit more checking for sanity.
399 if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
400 uint64_t NumElements = AT->getNumElements();
401 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
403 // Check to make sure that index falls within the array. If not,
404 // something funny is going on, so we won't do the optimization.
406 if (Idx->getZExtValue() >= NumElements)
409 // We cannot scalar repl this level of the array unless any array
410 // sub-indices are in-range constants. In particular, consider:
411 // A[0][i]. We cannot know that the user isn't doing invalid things like
412 // allowing i to index an out-of-range subscript that accesses A[1].
414 // Scalar replacing *just* the outer index of the array is probably not
415 // going to be a win anyway, so just give up.
416 for (++GEPI; // Skip array index.
419 uint64_t NumElements;
420 if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
421 NumElements = SubArrayTy->getNumElements();
422 else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
423 NumElements = SubVectorTy->getNumElements();
425 assert((*GEPI)->isStructTy() &&
426 "Indexed GEP type is not array, vector, or struct!");
430 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
431 if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
436 for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I)
437 if (!isSafeSROAElementUse(*I))
442 /// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it
443 /// is safe for us to perform this transformation.
445 static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
446 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
448 if (!IsUserOfGlobalSafeForSRA(*UI, GV))
455 /// SRAGlobal - Perform scalar replacement of aggregates on the specified global
456 /// variable. This opens the door for other optimizations by exposing the
457 /// behavior of the program in a more fine-grained way. We have determined that
458 /// this transformation is safe already. We return the first global variable we
459 /// insert so that the caller can reprocess it.
460 static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &TD) {
461 // Make sure this global only has simple uses that we can SRA.
462 if (!GlobalUsersSafeToSRA(GV))
465 assert(GV->hasLocalLinkage() && !GV->isConstant());
466 Constant *Init = GV->getInitializer();
467 Type *Ty = Init->getType();
469 std::vector<GlobalVariable*> NewGlobals;
470 Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
472 // Get the alignment of the global, either explicit or target-specific.
473 unsigned StartAlignment = GV->getAlignment();
474 if (StartAlignment == 0)
475 StartAlignment = TD.getABITypeAlignment(GV->getType());
477 if (StructType *STy = dyn_cast<StructType>(Ty)) {
478 NewGlobals.reserve(STy->getNumElements());
479 const StructLayout &Layout = *TD.getStructLayout(STy);
480 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
481 Constant *In = Init->getAggregateElement(i);
482 assert(In && "Couldn't get element of initializer?");
483 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
484 GlobalVariable::InternalLinkage,
485 In, GV->getName()+"."+Twine(i),
486 GV->getThreadLocalMode(),
487 GV->getType()->getAddressSpace());
488 Globals.insert(GV, NGV);
489 NewGlobals.push_back(NGV);
491 // Calculate the known alignment of the field. If the original aggregate
492 // had 256 byte alignment for example, something might depend on that:
493 // propagate info to each field.
494 uint64_t FieldOffset = Layout.getElementOffset(i);
495 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
496 if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i)))
497 NGV->setAlignment(NewAlign);
499 } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
500 unsigned NumElements = 0;
501 if (ArrayType *ATy = dyn_cast<ArrayType>(STy))
502 NumElements = ATy->getNumElements();
504 NumElements = cast<VectorType>(STy)->getNumElements();
506 if (NumElements > 16 && GV->hasNUsesOrMore(16))
507 return 0; // It's not worth it.
508 NewGlobals.reserve(NumElements);
510 uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType());
511 unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType());
512 for (unsigned i = 0, e = NumElements; i != e; ++i) {
513 Constant *In = Init->getAggregateElement(i);
514 assert(In && "Couldn't get element of initializer?");
516 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
517 GlobalVariable::InternalLinkage,
518 In, GV->getName()+"."+Twine(i),
519 GV->getThreadLocalMode(),
520 GV->getType()->getAddressSpace());
521 Globals.insert(GV, NGV);
522 NewGlobals.push_back(NGV);
524 // Calculate the known alignment of the field. If the original aggregate
525 // had 256 byte alignment for example, something might depend on that:
526 // propagate info to each field.
527 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
528 if (NewAlign > EltAlign)
529 NGV->setAlignment(NewAlign);
533 if (NewGlobals.empty())
536 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV);
538 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
540 // Loop over all of the uses of the global, replacing the constantexpr geps,
541 // with smaller constantexpr geps or direct references.
542 while (!GV->use_empty()) {
543 User *GEP = GV->use_back();
544 assert(((isa<ConstantExpr>(GEP) &&
545 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
546 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
548 // Ignore the 1th operand, which has to be zero or else the program is quite
549 // broken (undefined). Get the 2nd operand, which is the structure or array
551 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
552 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
554 Value *NewPtr = NewGlobals[Val];
556 // Form a shorter GEP if needed.
557 if (GEP->getNumOperands() > 3) {
558 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
559 SmallVector<Constant*, 8> Idxs;
560 Idxs.push_back(NullInt);
561 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
562 Idxs.push_back(CE->getOperand(i));
563 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs);
565 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
566 SmallVector<Value*, 8> Idxs;
567 Idxs.push_back(NullInt);
568 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
569 Idxs.push_back(GEPI->getOperand(i));
570 NewPtr = GetElementPtrInst::Create(NewPtr, Idxs,
571 GEPI->getName()+"."+Twine(Val),GEPI);
574 GEP->replaceAllUsesWith(NewPtr);
576 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
577 GEPI->eraseFromParent();
579 cast<ConstantExpr>(GEP)->destroyConstant();
582 // Delete the old global, now that it is dead.
586 // Loop over the new globals array deleting any globals that are obviously
587 // dead. This can arise due to scalarization of a structure or an array that
588 // has elements that are dead.
589 unsigned FirstGlobal = 0;
590 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
591 if (NewGlobals[i]->use_empty()) {
592 Globals.erase(NewGlobals[i]);
593 if (FirstGlobal == i) ++FirstGlobal;
596 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0;
599 /// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified
600 /// value will trap if the value is dynamically null. PHIs keeps track of any
601 /// phi nodes we've seen to avoid reprocessing them.
602 static bool AllUsesOfValueWillTrapIfNull(const Value *V,
603 SmallPtrSet<const PHINode*, 8> &PHIs) {
604 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
608 if (isa<LoadInst>(U)) {
610 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
611 if (SI->getOperand(0) == V) {
612 //cerr << "NONTRAPPING USE: " << *U;
613 return false; // Storing the value.
615 } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
616 if (CI->getCalledValue() != V) {
617 //cerr << "NONTRAPPING USE: " << *U;
618 return false; // Not calling the ptr
620 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
621 if (II->getCalledValue() != V) {
622 //cerr << "NONTRAPPING USE: " << *U;
623 return false; // Not calling the ptr
625 } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
626 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
627 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
628 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
629 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
630 // If we've already seen this phi node, ignore it, it has already been
632 if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
634 } else if (isa<ICmpInst>(U) &&
635 isa<ConstantPointerNull>(UI->getOperand(1))) {
636 // Ignore icmp X, null
638 //cerr << "NONTRAPPING USE: " << *U;
645 /// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads
646 /// from GV will trap if the loaded value is null. Note that this also permits
647 /// comparisons of the loaded value against null, as a special case.
648 static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
649 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
653 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
654 SmallPtrSet<const PHINode*, 8> PHIs;
655 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
657 } else if (isa<StoreInst>(U)) {
658 // Ignore stores to the global.
660 // We don't know or understand this user, bail out.
661 //cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
668 static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
669 bool Changed = false;
670 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) {
671 Instruction *I = cast<Instruction>(*UI++);
672 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
673 LI->setOperand(0, NewV);
675 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
676 if (SI->getOperand(1) == V) {
677 SI->setOperand(1, NewV);
680 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
682 if (CS.getCalledValue() == V) {
683 // Calling through the pointer! Turn into a direct call, but be careful
684 // that the pointer is not also being passed as an argument.
685 CS.setCalledFunction(NewV);
687 bool PassedAsArg = false;
688 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
689 if (CS.getArgument(i) == V) {
691 CS.setArgument(i, NewV);
695 // Being passed as an argument also. Be careful to not invalidate UI!
699 } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
700 Changed |= OptimizeAwayTrappingUsesOfValue(CI,
701 ConstantExpr::getCast(CI->getOpcode(),
702 NewV, CI->getType()));
703 if (CI->use_empty()) {
705 CI->eraseFromParent();
707 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
708 // Should handle GEP here.
709 SmallVector<Constant*, 8> Idxs;
710 Idxs.reserve(GEPI->getNumOperands()-1);
711 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
713 if (Constant *C = dyn_cast<Constant>(*i))
717 if (Idxs.size() == GEPI->getNumOperands()-1)
718 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
719 ConstantExpr::getGetElementPtr(NewV, Idxs));
720 if (GEPI->use_empty()) {
722 GEPI->eraseFromParent();
731 /// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null
732 /// value stored into it. If there are uses of the loaded value that would trap
733 /// if the loaded value is dynamically null, then we know that they cannot be
734 /// reachable with a null optimize away the load.
735 static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV,
737 TargetLibraryInfo *TLI) {
738 bool Changed = false;
740 // Keep track of whether we are able to remove all the uses of the global
741 // other than the store that defines it.
742 bool AllNonStoreUsesGone = true;
744 // Replace all uses of loads with uses of uses of the stored value.
745 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){
746 User *GlobalUser = *GUI++;
747 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
748 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
749 // If we were able to delete all uses of the loads
750 if (LI->use_empty()) {
751 LI->eraseFromParent();
754 AllNonStoreUsesGone = false;
756 } else if (isa<StoreInst>(GlobalUser)) {
757 // Ignore the store that stores "LV" to the global.
758 assert(GlobalUser->getOperand(1) == GV &&
759 "Must be storing *to* the global");
761 AllNonStoreUsesGone = false;
763 // If we get here we could have other crazy uses that are transitively
765 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
766 isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) ||
767 isa<BitCastInst>(GlobalUser) ||
768 isa<GetElementPtrInst>(GlobalUser)) &&
769 "Only expect load and stores!");
774 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV);
778 // If we nuked all of the loads, then none of the stores are needed either,
779 // nor is the global.
780 if (AllNonStoreUsesGone) {
781 if (isLeakCheckerRoot(GV)) {
782 Changed |= CleanupPointerRootUsers(GV, TLI);
785 CleanupConstantGlobalUsers(GV, 0, TD, TLI);
787 if (GV->use_empty()) {
788 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
790 GV->eraseFromParent();
797 /// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
798 /// instructions that are foldable.
799 static void ConstantPropUsersOf(Value *V,
800 DataLayout *TD, TargetLibraryInfo *TLI) {
801 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; )
802 if (Instruction *I = dyn_cast<Instruction>(*UI++))
803 if (Constant *NewC = ConstantFoldInstruction(I, TD, TLI)) {
804 I->replaceAllUsesWith(NewC);
806 // Advance UI to the next non-I use to avoid invalidating it!
807 // Instructions could multiply use V.
808 while (UI != E && *UI == I)
810 I->eraseFromParent();
814 /// OptimizeGlobalAddressOfMalloc - This function takes the specified global
815 /// variable, and transforms the program as if it always contained the result of
816 /// the specified malloc. Because it is always the result of the specified
817 /// malloc, there is no reason to actually DO the malloc. Instead, turn the
818 /// malloc into a global, and any loads of GV as uses of the new global.
819 static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
822 ConstantInt *NElements,
824 TargetLibraryInfo *TLI) {
825 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n');
828 if (NElements->getZExtValue() == 1)
829 GlobalType = AllocTy;
831 // If we have an array allocation, the global variable is of an array.
832 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
834 // Create the new global variable. The contents of the malloc'd memory is
835 // undefined, so initialize with an undef value.
836 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(),
838 GlobalValue::InternalLinkage,
839 UndefValue::get(GlobalType),
840 GV->getName()+".body",
842 GV->getThreadLocalMode());
844 // If there are bitcast users of the malloc (which is typical, usually we have
845 // a malloc + bitcast) then replace them with uses of the new global. Update
846 // other users to use the global as well.
847 BitCastInst *TheBC = 0;
848 while (!CI->use_empty()) {
849 Instruction *User = cast<Instruction>(CI->use_back());
850 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
851 if (BCI->getType() == NewGV->getType()) {
852 BCI->replaceAllUsesWith(NewGV);
853 BCI->eraseFromParent();
855 BCI->setOperand(0, NewGV);
859 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
860 User->replaceUsesOfWith(CI, TheBC);
864 Constant *RepValue = NewGV;
865 if (NewGV->getType() != GV->getType()->getElementType())
866 RepValue = ConstantExpr::getBitCast(RepValue,
867 GV->getType()->getElementType());
869 // If there is a comparison against null, we will insert a global bool to
870 // keep track of whether the global was initialized yet or not.
871 GlobalVariable *InitBool =
872 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
873 GlobalValue::InternalLinkage,
874 ConstantInt::getFalse(GV->getContext()),
875 GV->getName()+".init", GV->getThreadLocalMode());
876 bool InitBoolUsed = false;
878 // Loop over all uses of GV, processing them in turn.
879 while (!GV->use_empty()) {
880 if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) {
881 // The global is initialized when the store to it occurs.
882 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
883 SI->getOrdering(), SI->getSynchScope(), SI);
884 SI->eraseFromParent();
888 LoadInst *LI = cast<LoadInst>(GV->use_back());
889 while (!LI->use_empty()) {
890 Use &LoadUse = LI->use_begin().getUse();
891 if (!isa<ICmpInst>(LoadUse.getUser())) {
896 ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser());
897 // Replace the cmp X, 0 with a use of the bool value.
898 // Sink the load to where the compare was, if atomic rules allow us to.
899 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
900 LI->getOrdering(), LI->getSynchScope(),
901 LI->isUnordered() ? (Instruction*)ICI : LI);
903 switch (ICI->getPredicate()) {
904 default: llvm_unreachable("Unknown ICmp Predicate!");
905 case ICmpInst::ICMP_ULT:
906 case ICmpInst::ICMP_SLT: // X < null -> always false
907 LV = ConstantInt::getFalse(GV->getContext());
909 case ICmpInst::ICMP_ULE:
910 case ICmpInst::ICMP_SLE:
911 case ICmpInst::ICMP_EQ:
912 LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
914 case ICmpInst::ICMP_NE:
915 case ICmpInst::ICMP_UGE:
916 case ICmpInst::ICMP_SGE:
917 case ICmpInst::ICMP_UGT:
918 case ICmpInst::ICMP_SGT:
921 ICI->replaceAllUsesWith(LV);
922 ICI->eraseFromParent();
924 LI->eraseFromParent();
927 // If the initialization boolean was used, insert it, otherwise delete it.
929 while (!InitBool->use_empty()) // Delete initializations
930 cast<StoreInst>(InitBool->use_back())->eraseFromParent();
933 GV->getParent()->getGlobalList().insert(GV, InitBool);
935 // Now the GV is dead, nuke it and the malloc..
936 GV->eraseFromParent();
937 CI->eraseFromParent();
939 // To further other optimizations, loop over all users of NewGV and try to
940 // constant prop them. This will promote GEP instructions with constant
941 // indices into GEP constant-exprs, which will allow global-opt to hack on it.
942 ConstantPropUsersOf(NewGV, TD, TLI);
943 if (RepValue != NewGV)
944 ConstantPropUsersOf(RepValue, TD, TLI);
949 /// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking
950 /// to make sure that there are no complex uses of V. We permit simple things
951 /// like dereferencing the pointer, but not storing through the address, unless
952 /// it is to the specified global.
953 static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
954 const GlobalVariable *GV,
955 SmallPtrSet<const PHINode*, 8> &PHIs) {
956 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end();
958 const Instruction *Inst = cast<Instruction>(*UI);
960 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
961 continue; // Fine, ignore.
964 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
965 if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
966 return false; // Storing the pointer itself... bad.
967 continue; // Otherwise, storing through it, or storing into GV... fine.
970 // Must index into the array and into the struct.
971 if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
972 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
977 if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
978 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI
981 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
986 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
987 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
997 /// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV
998 /// somewhere. Transform all uses of the allocation into loads from the
999 /// global and uses of the resultant pointer. Further, delete the store into
1000 /// GV. This assumes that these value pass the
1001 /// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
1002 static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc,
1003 GlobalVariable *GV) {
1004 while (!Alloc->use_empty()) {
1005 Instruction *U = cast<Instruction>(*Alloc->use_begin());
1006 Instruction *InsertPt = U;
1007 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
1008 // If this is the store of the allocation into the global, remove it.
1009 if (SI->getOperand(1) == GV) {
1010 SI->eraseFromParent();
1013 } else if (PHINode *PN = dyn_cast<PHINode>(U)) {
1014 // Insert the load in the corresponding predecessor, not right before the
1016 InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator();
1017 } else if (isa<BitCastInst>(U)) {
1018 // Must be bitcast between the malloc and store to initialize the global.
1019 ReplaceUsesOfMallocWithGlobal(U, GV);
1020 U->eraseFromParent();
1022 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
1023 // If this is a "GEP bitcast" and the user is a store to the global, then
1024 // just process it as a bitcast.
1025 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse())
1026 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back()))
1027 if (SI->getOperand(1) == GV) {
1028 // Must be bitcast GEP between the malloc and store to initialize
1030 ReplaceUsesOfMallocWithGlobal(GEPI, GV);
1031 GEPI->eraseFromParent();
1036 // Insert a load from the global, and use it instead of the malloc.
1037 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt);
1038 U->replaceUsesOfWith(Alloc, NL);
1042 /// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi
1043 /// of a load) are simple enough to perform heap SRA on. This permits GEP's
1044 /// that index through the array and struct field, icmps of null, and PHIs.
1045 static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
1046 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs,
1047 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) {
1048 // We permit two users of the load: setcc comparing against the null
1049 // pointer, and a getelementptr of a specific form.
1050 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
1052 const Instruction *User = cast<Instruction>(*UI);
1054 // Comparison against null is ok.
1055 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(User)) {
1056 if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
1061 // getelementptr is also ok, but only a simple form.
1062 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
1063 // Must index into the array and into the struct.
1064 if (GEPI->getNumOperands() < 3)
1067 // Otherwise the GEP is ok.
1071 if (const PHINode *PN = dyn_cast<PHINode>(User)) {
1072 if (!LoadUsingPHIsPerLoad.insert(PN))
1073 // This means some phi nodes are dependent on each other.
1074 // Avoid infinite looping!
1076 if (!LoadUsingPHIs.insert(PN))
1077 // If we have already analyzed this PHI, then it is safe.
1080 // Make sure all uses of the PHI are simple enough to transform.
1081 if (!LoadUsesSimpleEnoughForHeapSRA(PN,
1082 LoadUsingPHIs, LoadUsingPHIsPerLoad))
1088 // Otherwise we don't know what this is, not ok.
1096 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from
1097 /// GV are simple enough to perform HeapSRA, return true.
1098 static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
1099 Instruction *StoredVal) {
1100 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
1101 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
1102 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
1104 if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1105 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
1106 LoadUsingPHIsPerLoad))
1108 LoadUsingPHIsPerLoad.clear();
1111 // If we reach here, we know that all uses of the loads and transitive uses
1112 // (through PHI nodes) are simple enough to transform. However, we don't know
1113 // that all inputs the to the PHI nodes are in the same equivalence sets.
1114 // Check to verify that all operands of the PHIs are either PHIS that can be
1115 // transformed, loads from GV, or MI itself.
1116 for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin()
1117 , E = LoadUsingPHIs.end(); I != E; ++I) {
1118 const PHINode *PN = *I;
1119 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
1120 Value *InVal = PN->getIncomingValue(op);
1122 // PHI of the stored value itself is ok.
1123 if (InVal == StoredVal) continue;
1125 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
1126 // One of the PHIs in our set is (optimistically) ok.
1127 if (LoadUsingPHIs.count(InPN))
1132 // Load from GV is ok.
1133 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
1134 if (LI->getOperand(0) == GV)
1139 // Anything else is rejected.
1147 static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
1148 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1149 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1150 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
1152 if (FieldNo >= FieldVals.size())
1153 FieldVals.resize(FieldNo+1);
1155 // If we already have this value, just reuse the previously scalarized
1157 if (Value *FieldVal = FieldVals[FieldNo])
1160 // Depending on what instruction this is, we have several cases.
1162 if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
1163 // This is a scalarized version of the load from the global. Just create
1164 // a new Load of the scalarized global.
1165 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
1166 InsertedScalarizedValues,
1168 LI->getName()+".f"+Twine(FieldNo), LI);
1169 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
1170 // PN's type is pointer to struct. Make a new PHI of pointer to struct
1172 StructType *ST = cast<StructType>(PN->getType()->getPointerElementType());
1175 PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)),
1176 PN->getNumIncomingValues(),
1177 PN->getName()+".f"+Twine(FieldNo), PN);
1179 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
1181 llvm_unreachable("Unknown usable value");
1184 return FieldVals[FieldNo] = Result;
1187 /// RewriteHeapSROALoadUser - Given a load instruction and a value derived from
1188 /// the load, rewrite the derived value to use the HeapSRoA'd load.
1189 static void RewriteHeapSROALoadUser(Instruction *LoadUser,
1190 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1191 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1192 // If this is a comparison against null, handle it.
1193 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
1194 assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
1195 // If we have a setcc of the loaded pointer, we can use a setcc of any
1197 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
1198 InsertedScalarizedValues, PHIsToRewrite);
1200 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
1201 Constant::getNullValue(NPtr->getType()),
1203 SCI->replaceAllUsesWith(New);
1204 SCI->eraseFromParent();
1208 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
1209 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
1210 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
1211 && "Unexpected GEPI!");
1213 // Load the pointer for this field.
1214 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
1215 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
1216 InsertedScalarizedValues, PHIsToRewrite);
1218 // Create the new GEP idx vector.
1219 SmallVector<Value*, 8> GEPIdx;
1220 GEPIdx.push_back(GEPI->getOperand(1));
1221 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
1223 Value *NGEPI = GetElementPtrInst::Create(NewPtr, GEPIdx,
1224 GEPI->getName(), GEPI);
1225 GEPI->replaceAllUsesWith(NGEPI);
1226 GEPI->eraseFromParent();
1230 // Recursively transform the users of PHI nodes. This will lazily create the
1231 // PHIs that are needed for individual elements. Keep track of what PHIs we
1232 // see in InsertedScalarizedValues so that we don't get infinite loops (very
1233 // antisocial). If the PHI is already in InsertedScalarizedValues, it has
1234 // already been seen first by another load, so its uses have already been
1236 PHINode *PN = cast<PHINode>(LoadUser);
1237 if (!InsertedScalarizedValues.insert(std::make_pair(PN,
1238 std::vector<Value*>())).second)
1241 // If this is the first time we've seen this PHI, recursively process all
1243 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) {
1244 Instruction *User = cast<Instruction>(*UI++);
1245 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1249 /// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr
1250 /// is a value loaded from the global. Eliminate all uses of Ptr, making them
1251 /// use FieldGlobals instead. All uses of loaded values satisfy
1252 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA.
1253 static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
1254 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1255 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1256 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end();
1258 Instruction *User = cast<Instruction>(*UI++);
1259 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1262 if (Load->use_empty()) {
1263 Load->eraseFromParent();
1264 InsertedScalarizedValues.erase(Load);
1268 /// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break
1269 /// it up into multiple allocations of arrays of the fields.
1270 static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
1271 Value *NElems, DataLayout *TD,
1272 const TargetLibraryInfo *TLI) {
1273 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n');
1274 Type *MAT = getMallocAllocatedType(CI, TLI);
1275 StructType *STy = cast<StructType>(MAT);
1277 // There is guaranteed to be at least one use of the malloc (storing
1278 // it into GV). If there are other uses, change them to be uses of
1279 // the global to simplify later code. This also deletes the store
1281 ReplaceUsesOfMallocWithGlobal(CI, GV);
1283 // Okay, at this point, there are no users of the malloc. Insert N
1284 // new mallocs at the same place as CI, and N globals.
1285 std::vector<Value*> FieldGlobals;
1286 std::vector<Value*> FieldMallocs;
1288 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
1289 Type *FieldTy = STy->getElementType(FieldNo);
1290 PointerType *PFieldTy = PointerType::getUnqual(FieldTy);
1292 GlobalVariable *NGV =
1293 new GlobalVariable(*GV->getParent(),
1294 PFieldTy, false, GlobalValue::InternalLinkage,
1295 Constant::getNullValue(PFieldTy),
1296 GV->getName() + ".f" + Twine(FieldNo), GV,
1297 GV->getThreadLocalMode());
1298 FieldGlobals.push_back(NGV);
1300 unsigned TypeSize = TD->getTypeAllocSize(FieldTy);
1301 if (StructType *ST = dyn_cast<StructType>(FieldTy))
1302 TypeSize = TD->getStructLayout(ST)->getSizeInBytes();
1303 Type *IntPtrTy = TD->getIntPtrType(CI->getType());
1304 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
1305 ConstantInt::get(IntPtrTy, TypeSize),
1307 CI->getName() + ".f" + Twine(FieldNo));
1308 FieldMallocs.push_back(NMI);
1309 new StoreInst(NMI, NGV, CI);
1312 // The tricky aspect of this transformation is handling the case when malloc
1313 // fails. In the original code, malloc failing would set the result pointer
1314 // of malloc to null. In this case, some mallocs could succeed and others
1315 // could fail. As such, we emit code that looks like this:
1316 // F0 = malloc(field0)
1317 // F1 = malloc(field1)
1318 // F2 = malloc(field2)
1319 // if (F0 == 0 || F1 == 0 || F2 == 0) {
1320 // if (F0) { free(F0); F0 = 0; }
1321 // if (F1) { free(F1); F1 = 0; }
1322 // if (F2) { free(F2); F2 = 0; }
1324 // The malloc can also fail if its argument is too large.
1325 Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
1326 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
1327 ConstantZero, "isneg");
1328 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
1329 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
1330 Constant::getNullValue(FieldMallocs[i]->getType()),
1332 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
1335 // Split the basic block at the old malloc.
1336 BasicBlock *OrigBB = CI->getParent();
1337 BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont");
1339 // Create the block to check the first condition. Put all these blocks at the
1340 // end of the function as they are unlikely to be executed.
1341 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
1343 OrigBB->getParent());
1345 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
1346 // branch on RunningOr.
1347 OrigBB->getTerminator()->eraseFromParent();
1348 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
1350 // Within the NullPtrBlock, we need to emit a comparison and branch for each
1351 // pointer, because some may be null while others are not.
1352 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1353 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
1354 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
1355 Constant::getNullValue(GVVal->getType()));
1356 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
1357 OrigBB->getParent());
1358 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
1359 OrigBB->getParent());
1360 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
1363 // Fill in FreeBlock.
1364 CallInst::CreateFree(GVVal, BI);
1365 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
1367 BranchInst::Create(NextBlock, FreeBlock);
1369 NullPtrBlock = NextBlock;
1372 BranchInst::Create(ContBB, NullPtrBlock);
1374 // CI is no longer needed, remove it.
1375 CI->eraseFromParent();
1377 /// InsertedScalarizedLoads - As we process loads, if we can't immediately
1378 /// update all uses of the load, keep track of what scalarized loads are
1379 /// inserted for a given load.
1380 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues;
1381 InsertedScalarizedValues[GV] = FieldGlobals;
1383 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite;
1385 // Okay, the malloc site is completely handled. All of the uses of GV are now
1386 // loads, and all uses of those loads are simple. Rewrite them to use loads
1387 // of the per-field globals instead.
1388 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) {
1389 Instruction *User = cast<Instruction>(*UI++);
1391 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1392 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
1396 // Must be a store of null.
1397 StoreInst *SI = cast<StoreInst>(User);
1398 assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
1399 "Unexpected heap-sra user!");
1401 // Insert a store of null into each global.
1402 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1403 PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType());
1404 Constant *Null = Constant::getNullValue(PT->getElementType());
1405 new StoreInst(Null, FieldGlobals[i], SI);
1407 // Erase the original store.
1408 SI->eraseFromParent();
1411 // While we have PHIs that are interesting to rewrite, do it.
1412 while (!PHIsToRewrite.empty()) {
1413 PHINode *PN = PHIsToRewrite.back().first;
1414 unsigned FieldNo = PHIsToRewrite.back().second;
1415 PHIsToRewrite.pop_back();
1416 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
1417 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
1419 // Add all the incoming values. This can materialize more phis.
1420 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1421 Value *InVal = PN->getIncomingValue(i);
1422 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
1424 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
1428 // Drop all inter-phi links and any loads that made it this far.
1429 for (DenseMap<Value*, std::vector<Value*> >::iterator
1430 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1432 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1433 PN->dropAllReferences();
1434 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1435 LI->dropAllReferences();
1438 // Delete all the phis and loads now that inter-references are dead.
1439 for (DenseMap<Value*, std::vector<Value*> >::iterator
1440 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1442 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1443 PN->eraseFromParent();
1444 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1445 LI->eraseFromParent();
1448 // The old global is now dead, remove it.
1449 GV->eraseFromParent();
1452 return cast<GlobalVariable>(FieldGlobals[0]);
1455 /// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a
1456 /// pointer global variable with a single value stored it that is a malloc or
1458 static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
1461 AtomicOrdering Ordering,
1462 Module::global_iterator &GVI,
1464 TargetLibraryInfo *TLI) {
1468 // If this is a malloc of an abstract type, don't touch it.
1469 if (!AllocTy->isSized())
1472 // We can't optimize this global unless all uses of it are *known* to be
1473 // of the malloc value, not of the null initializer value (consider a use
1474 // that compares the global's value against zero to see if the malloc has
1475 // been reached). To do this, we check to see if all uses of the global
1476 // would trap if the global were null: this proves that they must all
1477 // happen after the malloc.
1478 if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
1481 // We can't optimize this if the malloc itself is used in a complex way,
1482 // for example, being stored into multiple globals. This allows the
1483 // malloc to be stored into the specified global, loaded icmp'd, and
1484 // GEP'd. These are all things we could transform to using the global
1486 SmallPtrSet<const PHINode*, 8> PHIs;
1487 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
1490 // If we have a global that is only initialized with a fixed size malloc,
1491 // transform the program to use global memory instead of malloc'd memory.
1492 // This eliminates dynamic allocation, avoids an indirection accessing the
1493 // data, and exposes the resultant global to further GlobalOpt.
1494 // We cannot optimize the malloc if we cannot determine malloc array size.
1495 Value *NElems = getMallocArraySize(CI, TD, TLI, true);
1499 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
1500 // Restrict this transformation to only working on small allocations
1501 // (2048 bytes currently), as we don't want to introduce a 16M global or
1503 if (NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) {
1504 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD, TLI);
1508 // If the allocation is an array of structures, consider transforming this
1509 // into multiple malloc'd arrays, one for each field. This is basically
1510 // SRoA for malloc'd memory.
1512 if (Ordering != NotAtomic)
1515 // If this is an allocation of a fixed size array of structs, analyze as a
1516 // variable size array. malloc [100 x struct],1 -> malloc struct, 100
1517 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
1518 if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
1519 AllocTy = AT->getElementType();
1521 StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
1525 // This the structure has an unreasonable number of fields, leave it
1527 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
1528 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
1530 // If this is a fixed size array, transform the Malloc to be an alloc of
1531 // structs. malloc [100 x struct],1 -> malloc struct, 100
1532 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) {
1533 Type *IntPtrTy = TD->getIntPtrType(CI->getType());
1534 unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes();
1535 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
1536 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
1537 Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy,
1538 AllocSize, NumElements,
1540 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
1541 CI->replaceAllUsesWith(Cast);
1542 CI->eraseFromParent();
1543 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc))
1544 CI = cast<CallInst>(BCI->getOperand(0));
1546 CI = cast<CallInst>(Malloc);
1549 GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, TLI, true),
1557 // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
1558 // that only one value (besides its initializer) is ever stored to the global.
1559 static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
1560 AtomicOrdering Ordering,
1561 Module::global_iterator &GVI,
1562 DataLayout *TD, TargetLibraryInfo *TLI) {
1563 // Ignore no-op GEPs and bitcasts.
1564 StoredOnceVal = StoredOnceVal->stripPointerCasts();
1566 // If we are dealing with a pointer global that is initialized to null and
1567 // only has one (non-null) value stored into it, then we can optimize any
1568 // users of the loaded value (often calls and loads) that would trap if the
1570 if (GV->getInitializer()->getType()->isPointerTy() &&
1571 GV->getInitializer()->isNullValue()) {
1572 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
1573 if (GV->getInitializer()->getType() != SOVC->getType())
1574 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
1576 // Optimize away any trapping uses of the loaded value.
1577 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, TD, TLI))
1579 } else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) {
1580 Type *MallocType = getMallocAllocatedType(CI, TLI);
1582 TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, Ordering, GVI,
1591 /// TryToShrinkGlobalToBoolean - At this point, we have learned that the only
1592 /// two values ever stored into GV are its initializer and OtherVal. See if we
1593 /// can shrink the global into a boolean and select between the two values
1594 /// whenever it is used. This exposes the values to other scalar optimizations.
1595 static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
1596 Type *GVElType = GV->getType()->getElementType();
1598 // If GVElType is already i1, it is already shrunk. If the type of the GV is
1599 // an FP value, pointer or vector, don't do this optimization because a select
1600 // between them is very expensive and unlikely to lead to later
1601 // simplification. In these cases, we typically end up with "cond ? v1 : v2"
1602 // where v1 and v2 both require constant pool loads, a big loss.
1603 if (GVElType == Type::getInt1Ty(GV->getContext()) ||
1604 GVElType->isFloatingPointTy() ||
1605 GVElType->isPointerTy() || GVElType->isVectorTy())
1608 // Walk the use list of the global seeing if all the uses are load or store.
1609 // If there is anything else, bail out.
1610 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){
1612 if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
1616 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV);
1618 // Create the new global, initializing it to false.
1619 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
1621 GlobalValue::InternalLinkage,
1622 ConstantInt::getFalse(GV->getContext()),
1624 GV->getThreadLocalMode(),
1625 GV->getType()->getAddressSpace());
1626 GV->getParent()->getGlobalList().insert(GV, NewGV);
1628 Constant *InitVal = GV->getInitializer();
1629 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
1630 "No reason to shrink to bool!");
1632 // If initialized to zero and storing one into the global, we can use a cast
1633 // instead of a select to synthesize the desired value.
1634 bool IsOneZero = false;
1635 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
1636 IsOneZero = InitVal->isNullValue() && CI->isOne();
1638 while (!GV->use_empty()) {
1639 Instruction *UI = cast<Instruction>(GV->use_back());
1640 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
1641 // Change the store into a boolean store.
1642 bool StoringOther = SI->getOperand(0) == OtherVal;
1643 // Only do this if we weren't storing a loaded value.
1645 if (StoringOther || SI->getOperand(0) == InitVal) {
1646 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
1649 // Otherwise, we are storing a previously loaded copy. To do this,
1650 // change the copy from copying the original value to just copying the
1652 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
1654 // If we've already replaced the input, StoredVal will be a cast or
1655 // select instruction. If not, it will be a load of the original
1657 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
1658 assert(LI->getOperand(0) == GV && "Not a copy!");
1659 // Insert a new load, to preserve the saved value.
1660 StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1661 LI->getOrdering(), LI->getSynchScope(), LI);
1663 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
1664 "This is not a form that we understand!");
1665 StoreVal = StoredVal->getOperand(0);
1666 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
1669 new StoreInst(StoreVal, NewGV, false, 0,
1670 SI->getOrdering(), SI->getSynchScope(), SI);
1672 // Change the load into a load of bool then a select.
1673 LoadInst *LI = cast<LoadInst>(UI);
1674 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1675 LI->getOrdering(), LI->getSynchScope(), LI);
1678 NSI = new ZExtInst(NLI, LI->getType(), "", LI);
1680 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
1682 LI->replaceAllUsesWith(NSI);
1684 UI->eraseFromParent();
1687 // Retain the name of the old global variable. People who are debugging their
1688 // programs may expect these variables to be named the same.
1689 NewGV->takeName(GV);
1690 GV->eraseFromParent();
1695 /// ProcessGlobal - Analyze the specified global variable and optimize it if
1696 /// possible. If we make a change, return true.
1697 bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
1698 Module::global_iterator &GVI) {
1699 if (!GV->isDiscardableIfUnused())
1702 // Do more involved optimizations if the global is internal.
1703 GV->removeDeadConstantUsers();
1705 if (GV->use_empty()) {
1706 DEBUG(dbgs() << "GLOBAL DEAD: " << *GV);
1707 GV->eraseFromParent();
1712 if (!GV->hasLocalLinkage())
1717 if (GlobalStatus::analyzeGlobal(GV, GS))
1720 if (!GS.IsCompared && !GV->hasUnnamedAddr()) {
1721 GV->setUnnamedAddr(true);
1725 if (GV->isConstant() || !GV->hasInitializer())
1728 return ProcessInternalGlobal(GV, GVI, GS);
1731 /// ProcessInternalGlobal - Analyze the specified global variable and optimize
1732 /// it if possible. If we make a change, return true.
1733 bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
1734 Module::global_iterator &GVI,
1735 const GlobalStatus &GS) {
1736 // If this is a first class global and has only one accessing function
1737 // and this function is main (which we know is not recursive), we replace
1738 // the global with a local alloca in this function.
1740 // NOTE: It doesn't make sense to promote non-single-value types since we
1741 // are just replacing static memory to stack memory.
1743 // If the global is in different address space, don't bring it to stack.
1744 if (!GS.HasMultipleAccessingFunctions &&
1745 GS.AccessingFunction && !GS.HasNonInstructionUser &&
1746 GV->getType()->getElementType()->isSingleValueType() &&
1747 GS.AccessingFunction->getName() == "main" &&
1748 GS.AccessingFunction->hasExternalLinkage() &&
1749 GV->getType()->getAddressSpace() == 0) {
1750 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV);
1751 Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction
1752 ->getEntryBlock().begin());
1753 Type *ElemTy = GV->getType()->getElementType();
1754 // FIXME: Pass Global's alignment when globals have alignment
1755 AllocaInst *Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI);
1756 if (!isa<UndefValue>(GV->getInitializer()))
1757 new StoreInst(GV->getInitializer(), Alloca, &FirstI);
1759 GV->replaceAllUsesWith(Alloca);
1760 GV->eraseFromParent();
1765 // If the global is never loaded (but may be stored to), it is dead.
1768 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV);
1771 if (isLeakCheckerRoot(GV)) {
1772 // Delete any constant stores to the global.
1773 Changed = CleanupPointerRootUsers(GV, TLI);
1775 // Delete any stores we can find to the global. We may not be able to
1776 // make it completely dead though.
1777 Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1780 // If the global is dead now, delete it.
1781 if (GV->use_empty()) {
1782 GV->eraseFromParent();
1788 } else if (GS.StoredType <= GlobalStatus::InitializerStored) {
1789 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n");
1790 GV->setConstant(true);
1792 // Clean up any obviously simplifiable users now.
1793 CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1795 // If the global is dead now, just nuke it.
1796 if (GV->use_empty()) {
1797 DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
1798 << "all users and delete global!\n");
1799 GV->eraseFromParent();
1805 } else if (!GV->getInitializer()->getType()->isSingleValueType()) {
1806 if (DataLayout *TD = getAnalysisIfAvailable<DataLayout>())
1807 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) {
1808 GVI = FirstNewGV; // Don't skip the newly produced globals!
1811 } else if (GS.StoredType == GlobalStatus::StoredOnce) {
1812 // If the initial value for the global was an undef value, and if only
1813 // one other value was stored into it, we can just change the
1814 // initializer to be the stored value, then delete all stores to the
1815 // global. This allows us to mark it constant.
1816 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
1817 if (isa<UndefValue>(GV->getInitializer())) {
1818 // Change the initial value here.
1819 GV->setInitializer(SOVConstant);
1821 // Clean up any obviously simplifiable users now.
1822 CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1824 if (GV->use_empty()) {
1825 DEBUG(dbgs() << " *** Substituting initializer allowed us to "
1826 << "simplify all users and delete global!\n");
1827 GV->eraseFromParent();
1836 // Try to optimize globals based on the knowledge that only one value
1837 // (besides its initializer) is ever stored to the global.
1838 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, GVI,
1842 // Otherwise, if the global was not a boolean, we can shrink it to be a
1844 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) {
1845 if (GS.Ordering == NotAtomic) {
1846 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
1857 /// ChangeCalleesToFastCall - Walk all of the direct calls of the specified
1858 /// function, changing them to FastCC.
1859 static void ChangeCalleesToFastCall(Function *F) {
1860 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
1861 if (isa<BlockAddress>(*UI))
1863 CallSite User(cast<Instruction>(*UI));
1864 User.setCallingConv(CallingConv::Fast);
1868 static AttributeSet StripNest(LLVMContext &C, const AttributeSet &Attrs) {
1869 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
1870 unsigned Index = Attrs.getSlotIndex(i);
1871 if (!Attrs.getSlotAttributes(i).hasAttribute(Index, Attribute::Nest))
1874 // There can be only one.
1875 return Attrs.removeAttribute(C, Index, Attribute::Nest);
1881 static void RemoveNestAttribute(Function *F) {
1882 F->setAttributes(StripNest(F->getContext(), F->getAttributes()));
1883 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
1884 if (isa<BlockAddress>(*UI))
1886 CallSite User(cast<Instruction>(*UI));
1887 User.setAttributes(StripNest(F->getContext(), User.getAttributes()));
1891 bool GlobalOpt::OptimizeFunctions(Module &M) {
1892 bool Changed = false;
1893 // Optimize functions.
1894 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
1896 // Functions without names cannot be referenced outside this module.
1897 if (!F->hasName() && !F->isDeclaration())
1898 F->setLinkage(GlobalValue::InternalLinkage);
1899 F->removeDeadConstantUsers();
1900 if (F->isDefTriviallyDead()) {
1901 F->eraseFromParent();
1904 } else if (F->hasLocalLinkage()) {
1905 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() &&
1906 !F->hasAddressTaken()) {
1907 // If this function has C calling conventions, is not a varargs
1908 // function, and is only called directly, promote it to use the Fast
1909 // calling convention.
1910 F->setCallingConv(CallingConv::Fast);
1911 ChangeCalleesToFastCall(F);
1916 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
1917 !F->hasAddressTaken()) {
1918 // The function is not used by a trampoline intrinsic, so it is safe
1919 // to remove the 'nest' attribute.
1920 RemoveNestAttribute(F);
1929 bool GlobalOpt::OptimizeGlobalVars(Module &M) {
1930 bool Changed = false;
1931 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
1933 GlobalVariable *GV = GVI++;
1934 // Global variables without names cannot be referenced outside this module.
1935 if (!GV->hasName() && !GV->isDeclaration())
1936 GV->setLinkage(GlobalValue::InternalLinkage);
1937 // Simplify the initializer.
1938 if (GV->hasInitializer())
1939 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
1940 Constant *New = ConstantFoldConstantExpression(CE, TD, TLI);
1941 if (New && New != CE)
1942 GV->setInitializer(New);
1945 Changed |= ProcessGlobal(GV, GVI);
1950 /// FindGlobalCtors - Find the llvm.global_ctors list, verifying that all
1951 /// initializers have an init priority of 65535.
1952 GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) {
1953 GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
1954 if (GV == 0) return 0;
1956 // Verify that the initializer is simple enough for us to handle. We are
1957 // only allowed to optimize the initializer if it is unique.
1958 if (!GV->hasUniqueInitializer()) return 0;
1960 if (isa<ConstantAggregateZero>(GV->getInitializer()))
1962 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
1964 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
1965 if (isa<ConstantAggregateZero>(*i))
1967 ConstantStruct *CS = cast<ConstantStruct>(*i);
1968 if (isa<ConstantPointerNull>(CS->getOperand(1)))
1971 // Must have a function or null ptr.
1972 if (!isa<Function>(CS->getOperand(1)))
1975 // Init priority must be standard.
1976 ConstantInt *CI = cast<ConstantInt>(CS->getOperand(0));
1977 if (CI->getZExtValue() != 65535)
1984 /// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand,
1985 /// return a list of the functions and null terminator as a vector.
1986 static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) {
1987 if (GV->getInitializer()->isNullValue())
1988 return std::vector<Function*>();
1989 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
1990 std::vector<Function*> Result;
1991 Result.reserve(CA->getNumOperands());
1992 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
1993 ConstantStruct *CS = cast<ConstantStruct>(*i);
1994 Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
1999 /// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the
2000 /// specified array, returning the new global to use.
2001 static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL,
2002 const std::vector<Function*> &Ctors) {
2003 // If we made a change, reassemble the initializer list.
2004 Constant *CSVals[2];
2005 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 65535);
2008 StructType *StructTy =
2009 cast<StructType>(GCL->getType()->getElementType()->getArrayElementType());
2011 // Create the new init list.
2012 std::vector<Constant*> CAList;
2013 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) {
2015 CSVals[1] = Ctors[i];
2017 Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()),
2019 PointerType *PFTy = PointerType::getUnqual(FTy);
2020 CSVals[1] = Constant::getNullValue(PFTy);
2021 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()),
2024 CAList.push_back(ConstantStruct::get(StructTy, CSVals));
2027 // Create the array initializer.
2028 Constant *CA = ConstantArray::get(ArrayType::get(StructTy,
2029 CAList.size()), CAList);
2031 // If we didn't change the number of elements, don't create a new GV.
2032 if (CA->getType() == GCL->getInitializer()->getType()) {
2033 GCL->setInitializer(CA);
2037 // Create the new global and insert it next to the existing list.
2038 GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(),
2039 GCL->getLinkage(), CA, "",
2040 GCL->getThreadLocalMode());
2041 GCL->getParent()->getGlobalList().insert(GCL, NGV);
2044 // Nuke the old list, replacing any uses with the new one.
2045 if (!GCL->use_empty()) {
2047 if (V->getType() != GCL->getType())
2048 V = ConstantExpr::getBitCast(V, GCL->getType());
2049 GCL->replaceAllUsesWith(V);
2051 GCL->eraseFromParent();
2061 isSimpleEnoughValueToCommit(Constant *C,
2062 SmallPtrSet<Constant*, 8> &SimpleConstants,
2063 const DataLayout *TD);
2066 /// isSimpleEnoughValueToCommit - Return true if the specified constant can be
2067 /// handled by the code generator. We don't want to generate something like:
2068 /// void *X = &X/42;
2069 /// because the code generator doesn't have a relocation that can handle that.
2071 /// This function should be called if C was not found (but just got inserted)
2072 /// in SimpleConstants to avoid having to rescan the same constants all the
2074 static bool isSimpleEnoughValueToCommitHelper(Constant *C,
2075 SmallPtrSet<Constant*, 8> &SimpleConstants,
2076 const DataLayout *TD) {
2077 // Simple integer, undef, constant aggregate zero, global addresses, etc are
2079 if (C->getNumOperands() == 0 || isa<BlockAddress>(C) ||
2080 isa<GlobalValue>(C))
2083 // Aggregate values are safe if all their elements are.
2084 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) ||
2085 isa<ConstantVector>(C)) {
2086 for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
2087 Constant *Op = cast<Constant>(C->getOperand(i));
2088 if (!isSimpleEnoughValueToCommit(Op, SimpleConstants, TD))
2094 // We don't know exactly what relocations are allowed in constant expressions,
2095 // so we allow &global+constantoffset, which is safe and uniformly supported
2097 ConstantExpr *CE = cast<ConstantExpr>(C);
2098 switch (CE->getOpcode()) {
2099 case Instruction::BitCast:
2100 // Bitcast is fine if the casted value is fine.
2101 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2103 case Instruction::IntToPtr:
2104 case Instruction::PtrToInt:
2105 // int <=> ptr is fine if the int type is the same size as the
2107 if (!TD || TD->getTypeSizeInBits(CE->getType()) !=
2108 TD->getTypeSizeInBits(CE->getOperand(0)->getType()))
2110 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2112 // GEP is fine if it is simple + constant offset.
2113 case Instruction::GetElementPtr:
2114 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
2115 if (!isa<ConstantInt>(CE->getOperand(i)))
2117 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2119 case Instruction::Add:
2120 // We allow simple+cst.
2121 if (!isa<ConstantInt>(CE->getOperand(1)))
2123 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2129 isSimpleEnoughValueToCommit(Constant *C,
2130 SmallPtrSet<Constant*, 8> &SimpleConstants,
2131 const DataLayout *TD) {
2132 // If we already checked this constant, we win.
2133 if (!SimpleConstants.insert(C)) return true;
2134 // Check the constant.
2135 return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, TD);
2139 /// isSimpleEnoughPointerToCommit - Return true if this constant is simple
2140 /// enough for us to understand. In particular, if it is a cast to anything
2141 /// other than from one pointer type to another pointer type, we punt.
2142 /// We basically just support direct accesses to globals and GEP's of
2143 /// globals. This should be kept up to date with CommitValueTo.
2144 static bool isSimpleEnoughPointerToCommit(Constant *C) {
2145 // Conservatively, avoid aggregate types. This is because we don't
2146 // want to worry about them partially overlapping other stores.
2147 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
2150 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
2151 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2152 // external globals.
2153 return GV->hasUniqueInitializer();
2155 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
2156 // Handle a constantexpr gep.
2157 if (CE->getOpcode() == Instruction::GetElementPtr &&
2158 isa<GlobalVariable>(CE->getOperand(0)) &&
2159 cast<GEPOperator>(CE)->isInBounds()) {
2160 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2161 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2162 // external globals.
2163 if (!GV->hasUniqueInitializer())
2166 // The first index must be zero.
2167 ConstantInt *CI = dyn_cast<ConstantInt>(*llvm::next(CE->op_begin()));
2168 if (!CI || !CI->isZero()) return false;
2170 // The remaining indices must be compile-time known integers within the
2171 // notional bounds of the corresponding static array types.
2172 if (!CE->isGEPWithNoNotionalOverIndexing())
2175 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2177 // A constantexpr bitcast from a pointer to another pointer is a no-op,
2178 // and we know how to evaluate it by moving the bitcast from the pointer
2179 // operand to the value operand.
2180 } else if (CE->getOpcode() == Instruction::BitCast &&
2181 isa<GlobalVariable>(CE->getOperand(0))) {
2182 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2183 // external globals.
2184 return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
2191 /// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global
2192 /// initializer. This returns 'Init' modified to reflect 'Val' stored into it.
2193 /// At this point, the GEP operands of Addr [0, OpNo) have been stepped into.
2194 static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
2195 ConstantExpr *Addr, unsigned OpNo) {
2196 // Base case of the recursion.
2197 if (OpNo == Addr->getNumOperands()) {
2198 assert(Val->getType() == Init->getType() && "Type mismatch!");
2202 SmallVector<Constant*, 32> Elts;
2203 if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
2204 // Break up the constant into its elements.
2205 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
2206 Elts.push_back(Init->getAggregateElement(i));
2208 // Replace the element that we are supposed to.
2209 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
2210 unsigned Idx = CU->getZExtValue();
2211 assert(Idx < STy->getNumElements() && "Struct index out of range!");
2212 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
2214 // Return the modified struct.
2215 return ConstantStruct::get(STy, Elts);
2218 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
2219 SequentialType *InitTy = cast<SequentialType>(Init->getType());
2222 if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
2223 NumElts = ATy->getNumElements();
2225 NumElts = InitTy->getVectorNumElements();
2227 // Break up the array into elements.
2228 for (uint64_t i = 0, e = NumElts; i != e; ++i)
2229 Elts.push_back(Init->getAggregateElement(i));
2231 assert(CI->getZExtValue() < NumElts);
2232 Elts[CI->getZExtValue()] =
2233 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
2235 if (Init->getType()->isArrayTy())
2236 return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
2237 return ConstantVector::get(Elts);
2240 /// CommitValueTo - We have decided that Addr (which satisfies the predicate
2241 /// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen.
2242 static void CommitValueTo(Constant *Val, Constant *Addr) {
2243 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
2244 assert(GV->hasInitializer());
2245 GV->setInitializer(Val);
2249 ConstantExpr *CE = cast<ConstantExpr>(Addr);
2250 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2251 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
2256 /// Evaluator - This class evaluates LLVM IR, producing the Constant
2257 /// representing each SSA instruction. Changes to global variables are stored
2258 /// in a mapping that can be iterated over after the evaluation is complete.
2259 /// Once an evaluation call fails, the evaluation object should not be reused.
2262 Evaluator(const DataLayout *TD, const TargetLibraryInfo *TLI)
2263 : TD(TD), TLI(TLI) {
2264 ValueStack.push_back(new DenseMap<Value*, Constant*>);
2268 DeleteContainerPointers(ValueStack);
2269 while (!AllocaTmps.empty()) {
2270 GlobalVariable *Tmp = AllocaTmps.back();
2271 AllocaTmps.pop_back();
2273 // If there are still users of the alloca, the program is doing something
2274 // silly, e.g. storing the address of the alloca somewhere and using it
2275 // later. Since this is undefined, we'll just make it be null.
2276 if (!Tmp->use_empty())
2277 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
2282 /// EvaluateFunction - Evaluate a call to function F, returning true if
2283 /// successful, false if we can't evaluate it. ActualArgs contains the formal
2284 /// arguments for the function.
2285 bool EvaluateFunction(Function *F, Constant *&RetVal,
2286 const SmallVectorImpl<Constant*> &ActualArgs);
2288 /// EvaluateBlock - Evaluate all instructions in block BB, returning true if
2289 /// successful, false if we can't evaluate it. NewBB returns the next BB that
2290 /// control flows into, or null upon return.
2291 bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB);
2293 Constant *getVal(Value *V) {
2294 if (Constant *CV = dyn_cast<Constant>(V)) return CV;
2295 Constant *R = ValueStack.back()->lookup(V);
2296 assert(R && "Reference to an uncomputed value!");
2300 void setVal(Value *V, Constant *C) {
2301 ValueStack.back()->operator[](V) = C;
2304 const DenseMap<Constant*, Constant*> &getMutatedMemory() const {
2305 return MutatedMemory;
2308 const SmallPtrSet<GlobalVariable*, 8> &getInvariants() const {
2313 Constant *ComputeLoadResult(Constant *P);
2315 /// ValueStack - As we compute SSA register values, we store their contents
2316 /// here. The back of the vector contains the current function and the stack
2317 /// contains the values in the calling frames.
2318 SmallVector<DenseMap<Value*, Constant*>*, 4> ValueStack;
2320 /// CallStack - This is used to detect recursion. In pathological situations
2321 /// we could hit exponential behavior, but at least there is nothing
2323 SmallVector<Function*, 4> CallStack;
2325 /// MutatedMemory - For each store we execute, we update this map. Loads
2326 /// check this to get the most up-to-date value. If evaluation is successful,
2327 /// this state is committed to the process.
2328 DenseMap<Constant*, Constant*> MutatedMemory;
2330 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable
2331 /// to represent its body. This vector is needed so we can delete the
2332 /// temporary globals when we are done.
2333 SmallVector<GlobalVariable*, 32> AllocaTmps;
2335 /// Invariants - These global variables have been marked invariant by the
2336 /// static constructor.
2337 SmallPtrSet<GlobalVariable*, 8> Invariants;
2339 /// SimpleConstants - These are constants we have checked and know to be
2340 /// simple enough to live in a static initializer of a global.
2341 SmallPtrSet<Constant*, 8> SimpleConstants;
2343 const DataLayout *TD;
2344 const TargetLibraryInfo *TLI;
2347 } // anonymous namespace
2349 /// ComputeLoadResult - Return the value that would be computed by a load from
2350 /// P after the stores reflected by 'memory' have been performed. If we can't
2351 /// decide, return null.
2352 Constant *Evaluator::ComputeLoadResult(Constant *P) {
2353 // If this memory location has been recently stored, use the stored value: it
2354 // is the most up-to-date.
2355 DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P);
2356 if (I != MutatedMemory.end()) return I->second;
2359 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
2360 if (GV->hasDefinitiveInitializer())
2361 return GV->getInitializer();
2365 // Handle a constantexpr getelementptr.
2366 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
2367 if (CE->getOpcode() == Instruction::GetElementPtr &&
2368 isa<GlobalVariable>(CE->getOperand(0))) {
2369 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2370 if (GV->hasDefinitiveInitializer())
2371 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2374 return 0; // don't know how to evaluate.
2377 /// EvaluateBlock - Evaluate all instructions in block BB, returning true if
2378 /// successful, false if we can't evaluate it. NewBB returns the next BB that
2379 /// control flows into, or null upon return.
2380 bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst,
2381 BasicBlock *&NextBB) {
2382 // This is the main evaluation loop.
2384 Constant *InstResult = 0;
2386 DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
2388 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
2389 if (!SI->isSimple()) {
2390 DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
2391 return false; // no volatile/atomic accesses.
2393 Constant *Ptr = getVal(SI->getOperand(1));
2394 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
2395 DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
2396 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2397 DEBUG(dbgs() << "; To: " << *Ptr << "\n");
2399 if (!isSimpleEnoughPointerToCommit(Ptr)) {
2400 // If this is too complex for us to commit, reject it.
2401 DEBUG(dbgs() << "Pointer is too complex for us to evaluate store.");
2405 Constant *Val = getVal(SI->getOperand(0));
2407 // If this might be too difficult for the backend to handle (e.g. the addr
2408 // of one global variable divided by another) then we can't commit it.
2409 if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, TD)) {
2410 DEBUG(dbgs() << "Store value is too complex to evaluate store. " << *Val
2415 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
2416 if (CE->getOpcode() == Instruction::BitCast) {
2417 DEBUG(dbgs() << "Attempting to resolve bitcast on constant ptr.\n");
2418 // If we're evaluating a store through a bitcast, then we need
2419 // to pull the bitcast off the pointer type and push it onto the
2421 Ptr = CE->getOperand(0);
2423 Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
2425 // In order to push the bitcast onto the stored value, a bitcast
2426 // from NewTy to Val's type must be legal. If it's not, we can try
2427 // introspecting NewTy to find a legal conversion.
2428 while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
2429 // If NewTy is a struct, we can convert the pointer to the struct
2430 // into a pointer to its first member.
2431 // FIXME: This could be extended to support arrays as well.
2432 if (StructType *STy = dyn_cast<StructType>(NewTy)) {
2433 NewTy = STy->getTypeAtIndex(0U);
2435 IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
2436 Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
2437 Constant * const IdxList[] = {IdxZero, IdxZero};
2439 Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList);
2440 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2441 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2443 // If we can't improve the situation by introspecting NewTy,
2444 // we have to give up.
2446 DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
2452 // If we found compatible types, go ahead and push the bitcast
2453 // onto the stored value.
2454 Val = ConstantExpr::getBitCast(Val, NewTy);
2456 DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
2460 MutatedMemory[Ptr] = Val;
2461 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
2462 InstResult = ConstantExpr::get(BO->getOpcode(),
2463 getVal(BO->getOperand(0)),
2464 getVal(BO->getOperand(1)));
2465 DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: " << *InstResult
2467 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
2468 InstResult = ConstantExpr::getCompare(CI->getPredicate(),
2469 getVal(CI->getOperand(0)),
2470 getVal(CI->getOperand(1)));
2471 DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult
2473 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
2474 InstResult = ConstantExpr::getCast(CI->getOpcode(),
2475 getVal(CI->getOperand(0)),
2477 DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult
2479 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
2480 InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
2481 getVal(SI->getOperand(1)),
2482 getVal(SI->getOperand(2)));
2483 DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
2485 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
2486 Constant *P = getVal(GEP->getOperand(0));
2487 SmallVector<Constant*, 8> GEPOps;
2488 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
2490 GEPOps.push_back(getVal(*i));
2492 ConstantExpr::getGetElementPtr(P, GEPOps,
2493 cast<GEPOperator>(GEP)->isInBounds());
2494 DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult
2496 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
2498 if (!LI->isSimple()) {
2499 DEBUG(dbgs() << "Found a Load! Not a simple load, can not evaluate.\n");
2500 return false; // no volatile/atomic accesses.
2503 Constant *Ptr = getVal(LI->getOperand(0));
2504 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
2505 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2506 DEBUG(dbgs() << "Found a constant pointer expression, constant "
2507 "folding: " << *Ptr << "\n");
2509 InstResult = ComputeLoadResult(Ptr);
2510 if (InstResult == 0) {
2511 DEBUG(dbgs() << "Failed to compute load result. Can not evaluate load."
2513 return false; // Could not evaluate load.
2516 DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
2517 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
2518 if (AI->isArrayAllocation()) {
2519 DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
2520 return false; // Cannot handle array allocs.
2522 Type *Ty = AI->getType()->getElementType();
2523 AllocaTmps.push_back(new GlobalVariable(Ty, false,
2524 GlobalValue::InternalLinkage,
2525 UndefValue::get(Ty),
2527 InstResult = AllocaTmps.back();
2528 DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n");
2529 } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
2530 CallSite CS(CurInst);
2532 // Debug info can safely be ignored here.
2533 if (isa<DbgInfoIntrinsic>(CS.getInstruction())) {
2534 DEBUG(dbgs() << "Ignoring debug info.\n");
2539 // Cannot handle inline asm.
2540 if (isa<InlineAsm>(CS.getCalledValue())) {
2541 DEBUG(dbgs() << "Found inline asm, can not evaluate.\n");
2545 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
2546 if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
2547 if (MSI->isVolatile()) {
2548 DEBUG(dbgs() << "Can not optimize a volatile memset " <<
2552 Constant *Ptr = getVal(MSI->getDest());
2553 Constant *Val = getVal(MSI->getValue());
2554 Constant *DestVal = ComputeLoadResult(getVal(Ptr));
2555 if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
2556 // This memset is a no-op.
2557 DEBUG(dbgs() << "Ignoring no-op memset.\n");
2563 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
2564 II->getIntrinsicID() == Intrinsic::lifetime_end) {
2565 DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n");
2570 if (II->getIntrinsicID() == Intrinsic::invariant_start) {
2571 // We don't insert an entry into Values, as it doesn't have a
2572 // meaningful return value.
2573 if (!II->use_empty()) {
2574 DEBUG(dbgs() << "Found unused invariant_start. Can't evaluate.\n");
2577 ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
2578 Value *PtrArg = getVal(II->getArgOperand(1));
2579 Value *Ptr = PtrArg->stripPointerCasts();
2580 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
2581 Type *ElemTy = cast<PointerType>(GV->getType())->getElementType();
2582 if (TD && !Size->isAllOnesValue() &&
2583 Size->getValue().getLimitedValue() >=
2584 TD->getTypeStoreSize(ElemTy)) {
2585 Invariants.insert(GV);
2586 DEBUG(dbgs() << "Found a global var that is an invariant: " << *GV
2589 DEBUG(dbgs() << "Found a global var, but can not treat it as an "
2593 // Continue even if we do nothing.
2598 DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
2602 // Resolve function pointers.
2603 Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue()));
2604 if (!Callee || Callee->mayBeOverridden()) {
2605 DEBUG(dbgs() << "Can not resolve function pointer.\n");
2606 return false; // Cannot resolve.
2609 SmallVector<Constant*, 8> Formals;
2610 for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
2611 Formals.push_back(getVal(*i));
2613 if (Callee->isDeclaration()) {
2614 // If this is a function we can constant fold, do it.
2615 if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) {
2617 DEBUG(dbgs() << "Constant folded function call. Result: " <<
2618 *InstResult << "\n");
2620 DEBUG(dbgs() << "Can not constant fold function call.\n");
2624 if (Callee->getFunctionType()->isVarArg()) {
2625 DEBUG(dbgs() << "Can not constant fold vararg function call.\n");
2629 Constant *RetVal = 0;
2630 // Execute the call, if successful, use the return value.
2631 ValueStack.push_back(new DenseMap<Value*, Constant*>);
2632 if (!EvaluateFunction(Callee, RetVal, Formals)) {
2633 DEBUG(dbgs() << "Failed to evaluate function.\n");
2636 delete ValueStack.pop_back_val();
2637 InstResult = RetVal;
2639 if (InstResult != NULL) {
2640 DEBUG(dbgs() << "Successfully evaluated function. Result: " <<
2641 InstResult << "\n\n");
2643 DEBUG(dbgs() << "Successfully evaluated function. Result: 0\n\n");
2646 } else if (isa<TerminatorInst>(CurInst)) {
2647 DEBUG(dbgs() << "Found a terminator instruction.\n");
2649 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
2650 if (BI->isUnconditional()) {
2651 NextBB = BI->getSuccessor(0);
2654 dyn_cast<ConstantInt>(getVal(BI->getCondition()));
2655 if (!Cond) return false; // Cannot determine.
2657 NextBB = BI->getSuccessor(!Cond->getZExtValue());
2659 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
2661 dyn_cast<ConstantInt>(getVal(SI->getCondition()));
2662 if (!Val) return false; // Cannot determine.
2663 NextBB = SI->findCaseValue(Val).getCaseSuccessor();
2664 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
2665 Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
2666 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
2667 NextBB = BA->getBasicBlock();
2669 return false; // Cannot determine.
2670 } else if (isa<ReturnInst>(CurInst)) {
2673 // invoke, unwind, resume, unreachable.
2674 DEBUG(dbgs() << "Can not handle terminator.");
2675 return false; // Cannot handle this terminator.
2678 // We succeeded at evaluating this block!
2679 DEBUG(dbgs() << "Successfully evaluated block.\n");
2682 // Did not know how to evaluate this!
2683 DEBUG(dbgs() << "Failed to evaluate block due to unhandled instruction."
2688 if (!CurInst->use_empty()) {
2689 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
2690 InstResult = ConstantFoldConstantExpression(CE, TD, TLI);
2692 setVal(CurInst, InstResult);
2695 // If we just processed an invoke, we finished evaluating the block.
2696 if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
2697 NextBB = II->getNormalDest();
2698 DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n");
2702 // Advance program counter.
2707 /// EvaluateFunction - Evaluate a call to function F, returning true if
2708 /// successful, false if we can't evaluate it. ActualArgs contains the formal
2709 /// arguments for the function.
2710 bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal,
2711 const SmallVectorImpl<Constant*> &ActualArgs) {
2712 // Check to see if this function is already executing (recursion). If so,
2713 // bail out. TODO: we might want to accept limited recursion.
2714 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
2717 CallStack.push_back(F);
2719 // Initialize arguments to the incoming values specified.
2721 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
2723 setVal(AI, ActualArgs[ArgNo]);
2725 // ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
2726 // we can only evaluate any one basic block at most once. This set keeps
2727 // track of what we have executed so we can detect recursive cases etc.
2728 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
2730 // CurBB - The current basic block we're evaluating.
2731 BasicBlock *CurBB = F->begin();
2733 BasicBlock::iterator CurInst = CurBB->begin();
2736 BasicBlock *NextBB = 0; // Initialized to avoid compiler warnings.
2737 DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n");
2739 if (!EvaluateBlock(CurInst, NextBB))
2743 // Successfully running until there's no next block means that we found
2744 // the return. Fill it the return value and pop the call stack.
2745 ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
2746 if (RI->getNumOperands())
2747 RetVal = getVal(RI->getOperand(0));
2748 CallStack.pop_back();
2752 // Okay, we succeeded in evaluating this control flow. See if we have
2753 // executed the new block before. If so, we have a looping function,
2754 // which we cannot evaluate in reasonable time.
2755 if (!ExecutedBlocks.insert(NextBB))
2756 return false; // looped!
2758 // Okay, we have never been in this block before. Check to see if there
2759 // are any PHI nodes. If so, evaluate them with information about where
2762 for (CurInst = NextBB->begin();
2763 (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
2764 setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
2766 // Advance to the next block.
2771 /// EvaluateStaticConstructor - Evaluate static constructors in the function, if
2772 /// we can. Return true if we can, false otherwise.
2773 static bool EvaluateStaticConstructor(Function *F, const DataLayout *TD,
2774 const TargetLibraryInfo *TLI) {
2775 // Call the function.
2776 Evaluator Eval(TD, TLI);
2777 Constant *RetValDummy;
2778 bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy,
2779 SmallVector<Constant*, 0>());
2782 // We succeeded at evaluation: commit the result.
2783 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
2784 << F->getName() << "' to " << Eval.getMutatedMemory().size()
2786 for (DenseMap<Constant*, Constant*>::const_iterator I =
2787 Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end();
2789 CommitValueTo(I->second, I->first);
2790 for (SmallPtrSet<GlobalVariable*, 8>::const_iterator I =
2791 Eval.getInvariants().begin(), E = Eval.getInvariants().end();
2793 (*I)->setConstant(true);
2799 /// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible.
2800 /// Return true if anything changed.
2801 bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) {
2802 std::vector<Function*> Ctors = ParseGlobalCtors(GCL);
2803 bool MadeChange = false;
2804 if (Ctors.empty()) return false;
2806 // Loop over global ctors, optimizing them when we can.
2807 for (unsigned i = 0; i != Ctors.size(); ++i) {
2808 Function *F = Ctors[i];
2809 // Found a null terminator in the middle of the list, prune off the rest of
2812 if (i != Ctors.size()-1) {
2818 DEBUG(dbgs() << "Optimizing Global Constructor: " << *F << "\n");
2820 // We cannot simplify external ctor functions.
2821 if (F->empty()) continue;
2823 // If we can evaluate the ctor at compile time, do.
2824 if (EvaluateStaticConstructor(F, TD, TLI)) {
2825 Ctors.erase(Ctors.begin()+i);
2828 ++NumCtorsEvaluated;
2833 if (!MadeChange) return false;
2835 GCL = InstallGlobalCtors(GCL, Ctors);
2839 static int compareNames(Constant *const *A, Constant *const *B) {
2840 return (*A)->getName().compare((*B)->getName());
2843 static void setUsedInitializer(GlobalVariable &V,
2844 SmallPtrSet<GlobalValue *, 8> Init) {
2846 V.eraseFromParent();
2850 SmallVector<llvm::Constant *, 8> UsedArray;
2851 PointerType *Int8PtrTy = Type::getInt8PtrTy(V.getContext());
2853 for (SmallPtrSet<GlobalValue *, 8>::iterator I = Init.begin(), E = Init.end();
2855 Constant *Cast = llvm::ConstantExpr::getBitCast(*I, Int8PtrTy);
2856 UsedArray.push_back(Cast);
2858 // Sort to get deterministic order.
2859 array_pod_sort(UsedArray.begin(), UsedArray.end(), compareNames);
2860 ArrayType *ATy = ArrayType::get(Int8PtrTy, UsedArray.size());
2862 Module *M = V.getParent();
2863 V.removeFromParent();
2864 GlobalVariable *NV =
2865 new GlobalVariable(*M, ATy, false, llvm::GlobalValue::AppendingLinkage,
2866 llvm::ConstantArray::get(ATy, UsedArray), "");
2868 NV->setSection("llvm.metadata");
2873 /// \brief An easy to access representation of llvm.used and llvm.compiler.used.
2875 SmallPtrSet<GlobalValue *, 8> Used;
2876 SmallPtrSet<GlobalValue *, 8> CompilerUsed;
2877 GlobalVariable *UsedV;
2878 GlobalVariable *CompilerUsedV;
2881 LLVMUsed(Module &M) {
2882 UsedV = collectUsedGlobalVariables(M, Used, false);
2883 CompilerUsedV = collectUsedGlobalVariables(M, CompilerUsed, true);
2885 typedef SmallPtrSet<GlobalValue *, 8>::iterator iterator;
2886 iterator usedBegin() { return Used.begin(); }
2887 iterator usedEnd() { return Used.end(); }
2888 iterator compilerUsedBegin() { return CompilerUsed.begin(); }
2889 iterator compilerUsedEnd() { return CompilerUsed.end(); }
2890 bool usedCount(GlobalValue *GV) const { return Used.count(GV); }
2891 bool compilerUsedCount(GlobalValue *GV) const {
2892 return CompilerUsed.count(GV);
2894 bool usedErase(GlobalValue *GV) { return Used.erase(GV); }
2895 bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(GV); }
2896 bool usedInsert(GlobalValue *GV) { return Used.insert(GV); }
2897 bool compilerUsedInsert(GlobalValue *GV) { return CompilerUsed.insert(GV); }
2899 void syncVariablesAndSets() {
2901 setUsedInitializer(*UsedV, Used);
2903 setUsedInitializer(*CompilerUsedV, CompilerUsed);
2908 static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) {
2909 if (GA.use_empty()) // No use at all.
2912 assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) &&
2913 "We should have removed the duplicated "
2914 "element from llvm.compiler.used");
2915 if (!GA.hasOneUse())
2916 // Strictly more than one use. So at least one is not in llvm.used and
2917 // llvm.compiler.used.
2920 // Exactly one use. Check if it is in llvm.used or llvm.compiler.used.
2921 return !U.usedCount(&GA) && !U.compilerUsedCount(&GA);
2924 static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V,
2925 const LLVMUsed &U) {
2927 assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) &&
2928 "We should have removed the duplicated "
2929 "element from llvm.compiler.used");
2930 if (U.usedCount(&V) || U.compilerUsedCount(&V))
2932 return V.hasNUsesOrMore(N);
2935 static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) {
2936 if (!GA.hasLocalLinkage())
2939 return U.usedCount(&GA) || U.compilerUsedCount(&GA);
2942 static bool hasUsesToReplace(GlobalAlias &GA, LLVMUsed &U, bool &RenameTarget) {
2943 RenameTarget = false;
2945 if (hasUseOtherThanLLVMUsed(GA, U))
2948 // If the alias is externally visible, we may still be able to simplify it.
2949 if (!mayHaveOtherReferences(GA, U))
2952 // If the aliasee has internal linkage, give it the name and linkage
2953 // of the alias, and delete the alias. This turns:
2954 // define internal ... @f(...)
2955 // @a = alias ... @f
2957 // define ... @a(...)
2958 Constant *Aliasee = GA.getAliasee();
2959 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
2960 if (!Target->hasLocalLinkage())
2963 // Do not perform the transform if multiple aliases potentially target the
2964 // aliasee. This check also ensures that it is safe to replace the section
2965 // and other attributes of the aliasee with those of the alias.
2966 if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U))
2969 RenameTarget = true;
2973 bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
2974 bool Changed = false;
2977 for (SmallPtrSet<GlobalValue *, 8>::iterator I = Used.usedBegin(),
2980 Used.compilerUsedErase(*I);
2982 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
2984 Module::alias_iterator J = I++;
2985 // Aliases without names cannot be referenced outside this module.
2986 if (!J->hasName() && !J->isDeclaration())
2987 J->setLinkage(GlobalValue::InternalLinkage);
2988 // If the aliasee may change at link time, nothing can be done - bail out.
2989 if (J->mayBeOverridden())
2992 Constant *Aliasee = J->getAliasee();
2993 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
2994 Target->removeDeadConstantUsers();
2996 // Make all users of the alias use the aliasee instead.
2998 if (!hasUsesToReplace(*J, Used, RenameTarget))
3001 J->replaceAllUsesWith(Aliasee);
3002 ++NumAliasesResolved;
3006 // Give the aliasee the name, linkage and other attributes of the alias.
3007 Target->takeName(J);
3008 Target->setLinkage(J->getLinkage());
3009 Target->GlobalValue::copyAttributesFrom(J);
3011 if (Used.usedErase(J))
3012 Used.usedInsert(Target);
3014 if (Used.compilerUsedErase(J))
3015 Used.compilerUsedInsert(Target);
3016 } else if (mayHaveOtherReferences(*J, Used))
3019 // Delete the alias.
3020 M.getAliasList().erase(J);
3021 ++NumAliasesRemoved;
3025 Used.syncVariablesAndSets();
3030 static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) {
3031 if (!TLI->has(LibFunc::cxa_atexit))
3034 Function *Fn = M.getFunction(TLI->getName(LibFunc::cxa_atexit));
3039 FunctionType *FTy = Fn->getFunctionType();
3041 // Checking that the function has the right return type, the right number of
3042 // parameters and that they all have pointer types should be enough.
3043 if (!FTy->getReturnType()->isIntegerTy() ||
3044 FTy->getNumParams() != 3 ||
3045 !FTy->getParamType(0)->isPointerTy() ||
3046 !FTy->getParamType(1)->isPointerTy() ||
3047 !FTy->getParamType(2)->isPointerTy())
3053 /// cxxDtorIsEmpty - Returns whether the given function is an empty C++
3054 /// destructor and can therefore be eliminated.
3055 /// Note that we assume that other optimization passes have already simplified
3056 /// the code so we only look for a function with a single basic block, where
3057 /// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and
3058 /// other side-effect free instructions.
3059 static bool cxxDtorIsEmpty(const Function &Fn,
3060 SmallPtrSet<const Function *, 8> &CalledFunctions) {
3061 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
3062 // nounwind, but that doesn't seem worth doing.
3063 if (Fn.isDeclaration())
3066 if (++Fn.begin() != Fn.end())
3069 const BasicBlock &EntryBlock = Fn.getEntryBlock();
3070 for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
3072 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
3073 // Ignore debug intrinsics.
3074 if (isa<DbgInfoIntrinsic>(CI))
3077 const Function *CalledFn = CI->getCalledFunction();
3082 SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
3084 // Don't treat recursive functions as empty.
3085 if (!NewCalledFunctions.insert(CalledFn))
3088 if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
3090 } else if (isa<ReturnInst>(*I))
3091 return true; // We're done.
3092 else if (I->mayHaveSideEffects())
3093 return false; // Destructor with side effects, bail.
3099 bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
3100 /// Itanium C++ ABI p3.3.5:
3102 /// After constructing a global (or local static) object, that will require
3103 /// destruction on exit, a termination function is registered as follows:
3105 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
3107 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
3108 /// call f(p) when DSO d is unloaded, before all such termination calls
3109 /// registered before this one. It returns zero if registration is
3110 /// successful, nonzero on failure.
3112 // This pass will look for calls to __cxa_atexit where the function is trivial
3114 bool Changed = false;
3116 for (Function::use_iterator I = CXAAtExitFn->use_begin(),
3117 E = CXAAtExitFn->use_end(); I != E;) {
3118 // We're only interested in calls. Theoretically, we could handle invoke
3119 // instructions as well, but neither llvm-gcc nor clang generate invokes
3121 CallInst *CI = dyn_cast<CallInst>(*I++);
3126 dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
3130 SmallPtrSet<const Function *, 8> CalledFunctions;
3131 if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
3134 // Just remove the call.
3135 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
3136 CI->eraseFromParent();
3138 ++NumCXXDtorsRemoved;
3146 bool GlobalOpt::runOnModule(Module &M) {
3147 bool Changed = false;
3149 TD = getAnalysisIfAvailable<DataLayout>();
3150 TLI = &getAnalysis<TargetLibraryInfo>();
3152 // Try to find the llvm.globalctors list.
3153 GlobalVariable *GlobalCtors = FindGlobalCtors(M);
3155 bool LocalChange = true;
3156 while (LocalChange) {
3157 LocalChange = false;
3159 // Delete functions that are trivially dead, ccc -> fastcc
3160 LocalChange |= OptimizeFunctions(M);
3162 // Optimize global_ctors list.
3164 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors);
3166 // Optimize non-address-taken globals.
3167 LocalChange |= OptimizeGlobalVars(M);
3169 // Resolve aliases, when possible.
3170 LocalChange |= OptimizeGlobalAliases(M);
3172 // Try to remove trivial global destructors if they are not removed
3174 Function *CXAAtExitFn = FindCXAAtExit(M, TLI);
3176 LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
3178 Changed |= LocalChange;
3181 // TODO: Move all global ctors functions to the end of the module for code