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/CallingConv.h"
19 #include "llvm/Constants.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Instructions.h"
22 #include "llvm/IntrinsicInst.h"
23 #include "llvm/Module.h"
24 #include "llvm/Operator.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Analysis/ConstantFolding.h"
27 #include "llvm/Analysis/MemoryBuiltins.h"
28 #include "llvm/Target/TargetData.h"
29 #include "llvm/Target/TargetLibraryInfo.h"
30 #include "llvm/Support/CallSite.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/ErrorHandling.h"
33 #include "llvm/Support/GetElementPtrTypeIterator.h"
34 #include "llvm/Support/MathExtras.h"
35 #include "llvm/Support/raw_ostream.h"
36 #include "llvm/ADT/DenseMap.h"
37 #include "llvm/ADT/SmallPtrSet.h"
38 #include "llvm/ADT/SmallVector.h"
39 #include "llvm/ADT/Statistic.h"
40 #include "llvm/ADT/STLExtras.h"
44 STATISTIC(NumMarked , "Number of globals marked constant");
45 STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr");
46 STATISTIC(NumSRA , "Number of aggregate globals broken into scalars");
47 STATISTIC(NumHeapSRA , "Number of heap objects SRA'd");
48 STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
49 STATISTIC(NumDeleted , "Number of globals deleted");
50 STATISTIC(NumFnDeleted , "Number of functions deleted");
51 STATISTIC(NumGlobUses , "Number of global uses devirtualized");
52 STATISTIC(NumLocalized , "Number of globals localized");
53 STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans");
54 STATISTIC(NumFastCallFns , "Number of functions converted to fastcc");
55 STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");
56 STATISTIC(NumNestRemoved , "Number of nest attributes removed");
57 STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
58 STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
59 STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
63 struct GlobalOpt : public ModulePass {
64 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
65 AU.addRequired<TargetLibraryInfo>();
67 static char ID; // Pass identification, replacement for typeid
68 GlobalOpt() : ModulePass(ID) {
69 initializeGlobalOptPass(*PassRegistry::getPassRegistry());
72 bool runOnModule(Module &M);
75 GlobalVariable *FindGlobalCtors(Module &M);
76 bool OptimizeFunctions(Module &M);
77 bool OptimizeGlobalVars(Module &M);
78 bool OptimizeGlobalAliases(Module &M);
79 bool OptimizeGlobalCtorsList(GlobalVariable *&GCL);
80 bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
81 bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI,
82 const SmallPtrSet<const PHINode*, 16> &PHIUsers,
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(); }
102 /// GlobalStatus - As we analyze each global, keep track of some information
103 /// about it. If we find out that the address of the global is taken, none of
104 /// this info will be accurate.
105 struct GlobalStatus {
106 /// isCompared - True if the global's address is used in a comparison.
109 /// isLoaded - True if the global is ever loaded. If the global isn't ever
110 /// loaded it can be deleted.
113 /// StoredType - Keep track of what stores to the global look like.
116 /// NotStored - There is no store to this global. It can thus be marked
120 /// isInitializerStored - This global is stored to, but the only thing
121 /// stored is the constant it was initialized with. This is only tracked
122 /// for scalar globals.
125 /// isStoredOnce - This global is stored to, but only its initializer and
126 /// one other value is ever stored to it. If this global isStoredOnce, we
127 /// track the value stored to it in StoredOnceValue below. This is only
128 /// tracked for scalar globals.
131 /// isStored - This global is stored to by multiple values or something else
132 /// that we cannot track.
136 /// StoredOnceValue - If only one value (besides the initializer constant) is
137 /// ever stored to this global, keep track of what value it is.
138 Value *StoredOnceValue;
140 /// AccessingFunction/HasMultipleAccessingFunctions - These start out
141 /// null/false. When the first accessing function is noticed, it is recorded.
142 /// When a second different accessing function is noticed,
143 /// HasMultipleAccessingFunctions is set to true.
144 const Function *AccessingFunction;
145 bool HasMultipleAccessingFunctions;
147 /// HasNonInstructionUser - Set to true if this global has a user that is not
148 /// an instruction (e.g. a constant expr or GV initializer).
149 bool HasNonInstructionUser;
151 /// HasPHIUser - Set to true if this global has a user that is a PHI node.
154 /// AtomicOrdering - Set to the strongest atomic ordering requirement.
155 AtomicOrdering Ordering;
157 GlobalStatus() : isCompared(false), isLoaded(false), StoredType(NotStored),
158 StoredOnceValue(0), AccessingFunction(0),
159 HasMultipleAccessingFunctions(false),
160 HasNonInstructionUser(false), HasPHIUser(false),
161 Ordering(NotAtomic) {}
166 /// StrongerOrdering - Return the stronger of the two ordering. If the two
167 /// orderings are acquire and release, then return AcquireRelease.
169 static AtomicOrdering StrongerOrdering(AtomicOrdering X, AtomicOrdering Y) {
170 if (X == Acquire && Y == Release) return AcquireRelease;
171 if (Y == Acquire && X == Release) return AcquireRelease;
172 return (AtomicOrdering)std::max(X, Y);
175 /// SafeToDestroyConstant - It is safe to destroy a constant iff it is only used
176 /// by constants itself. Note that constants cannot be cyclic, so this test is
177 /// pretty easy to implement recursively.
179 static bool SafeToDestroyConstant(const Constant *C) {
180 if (isa<GlobalValue>(C)) return false;
182 for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E;
184 if (const Constant *CU = dyn_cast<Constant>(*UI)) {
185 if (!SafeToDestroyConstant(CU)) return false;
192 /// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
193 /// structure. If the global has its address taken, return true to indicate we
194 /// can't do anything with it.
196 static bool AnalyzeGlobal(const Value *V, GlobalStatus &GS,
197 SmallPtrSet<const PHINode*, 16> &PHIUsers) {
198 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
201 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
202 GS.HasNonInstructionUser = true;
204 // If the result of the constantexpr isn't pointer type, then we won't
205 // know to expect it in various places. Just reject early.
206 if (!isa<PointerType>(CE->getType())) return true;
208 if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
209 } else if (const Instruction *I = dyn_cast<Instruction>(U)) {
210 if (!GS.HasMultipleAccessingFunctions) {
211 const Function *F = I->getParent()->getParent();
212 if (GS.AccessingFunction == 0)
213 GS.AccessingFunction = F;
214 else if (GS.AccessingFunction != F)
215 GS.HasMultipleAccessingFunctions = true;
217 if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
219 // Don't hack on volatile loads.
220 if (LI->isVolatile()) return true;
221 GS.Ordering = StrongerOrdering(GS.Ordering, LI->getOrdering());
222 } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
223 // Don't allow a store OF the address, only stores TO the address.
224 if (SI->getOperand(0) == V) return true;
226 // Don't hack on volatile stores.
227 if (SI->isVolatile()) return true;
228 GS.Ordering = StrongerOrdering(GS.Ordering, SI->getOrdering());
230 // If this is a direct store to the global (i.e., the global is a scalar
231 // value, not an aggregate), keep more specific information about
233 if (GS.StoredType != GlobalStatus::isStored) {
234 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(
235 SI->getOperand(1))) {
236 Value *StoredVal = SI->getOperand(0);
237 if (StoredVal == GV->getInitializer()) {
238 if (GS.StoredType < GlobalStatus::isInitializerStored)
239 GS.StoredType = GlobalStatus::isInitializerStored;
240 } else if (isa<LoadInst>(StoredVal) &&
241 cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
242 if (GS.StoredType < GlobalStatus::isInitializerStored)
243 GS.StoredType = GlobalStatus::isInitializerStored;
244 } else if (GS.StoredType < GlobalStatus::isStoredOnce) {
245 GS.StoredType = GlobalStatus::isStoredOnce;
246 GS.StoredOnceValue = StoredVal;
247 } else if (GS.StoredType == GlobalStatus::isStoredOnce &&
248 GS.StoredOnceValue == StoredVal) {
251 GS.StoredType = GlobalStatus::isStored;
254 GS.StoredType = GlobalStatus::isStored;
257 } else if (isa<BitCastInst>(I)) {
258 if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
259 } else if (isa<GetElementPtrInst>(I)) {
260 if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
261 } else if (isa<SelectInst>(I)) {
262 if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
263 } else if (const PHINode *PN = dyn_cast<PHINode>(I)) {
264 // PHI nodes we can check just like select or GEP instructions, but we
265 // have to be careful about infinite recursion.
266 if (PHIUsers.insert(PN)) // Not already visited.
267 if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
268 GS.HasPHIUser = true;
269 } else if (isa<CmpInst>(I)) {
270 GS.isCompared = true;
271 } else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
272 if (MTI->isVolatile()) return true;
273 if (MTI->getArgOperand(0) == V)
274 GS.StoredType = GlobalStatus::isStored;
275 if (MTI->getArgOperand(1) == V)
277 } else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
278 assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
279 if (MSI->isVolatile()) return true;
280 GS.StoredType = GlobalStatus::isStored;
282 return true; // Any other non-load instruction might take address!
284 } else if (const Constant *C = dyn_cast<Constant>(U)) {
285 GS.HasNonInstructionUser = true;
286 // We might have a dead and dangling constant hanging off of here.
287 if (!SafeToDestroyConstant(C))
290 GS.HasNonInstructionUser = true;
291 // Otherwise must be some other user.
299 /// isLeakCheckerRoot - Is this global variable possibly used by a leak checker
300 /// as a root? If so, we might not really want to eliminate the stores to it.
301 static bool isLeakCheckerRoot(GlobalVariable *GV) {
302 // A global variable is a root if it is a pointer, or could plausibly contain
303 // a pointer. There are two challenges; one is that we could have a struct
304 // the has an inner member which is a pointer. We recurse through the type to
305 // detect these (up to a point). The other is that we may actually be a union
306 // of a pointer and another type, and so our LLVM type is an integer which
307 // gets converted into a pointer, or our type is an [i8 x #] with a pointer
308 // potentially contained here.
310 if (GV->hasPrivateLinkage())
313 SmallVector<Type *, 4> Types;
314 Types.push_back(cast<PointerType>(GV->getType())->getElementType());
318 Type *Ty = Types.pop_back_val();
319 switch (Ty->getTypeID()) {
321 case Type::PointerTyID: return true;
322 case Type::ArrayTyID:
323 case Type::VectorTyID: {
324 SequentialType *STy = cast<SequentialType>(Ty);
325 Types.push_back(STy->getElementType());
328 case Type::StructTyID: {
329 StructType *STy = cast<StructType>(Ty);
330 if (STy->isOpaque()) return true;
331 for (StructType::element_iterator I = STy->element_begin(),
332 E = STy->element_end(); I != E; ++I) {
334 if (isa<PointerType>(InnerTy)) return true;
335 if (isa<CompositeType>(InnerTy))
336 Types.push_back(InnerTy);
341 if (--Limit == 0) return true;
342 } while (!Types.empty());
346 /// Given a value that is stored to a global but never read, determine whether
347 /// it's safe to remove the store and the chain of computation that feeds the
349 static bool IsSafeComputationToRemove(Value *V) {
351 if (isa<Constant>(V))
355 if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) ||
358 if (isAllocationFn(V))
361 Instruction *I = cast<Instruction>(V);
362 if (I->mayHaveSideEffects())
364 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
365 if (!GEP->hasAllConstantIndices())
367 } else if (I->getNumOperands() != 1) {
371 V = I->getOperand(0);
375 /// CleanupPointerRootUsers - This GV is a pointer root. Loop over all users
376 /// of the global and clean up any that obviously don't assign the global a
377 /// value that isn't dynamically allocated.
379 static bool CleanupPointerRootUsers(GlobalVariable *GV) {
380 // A brief explanation of leak checkers. The goal is to find bugs where
381 // pointers are forgotten, causing an accumulating growth in memory
382 // usage over time. The common strategy for leak checkers is to whitelist the
383 // memory pointed to by globals at exit. This is popular because it also
384 // solves another problem where the main thread of a C++ program may shut down
385 // before other threads that are still expecting to use those globals. To
386 // handle that case, we expect the program may create a singleton and never
389 bool Changed = false;
391 // If Dead[n].first is the only use of a malloc result, we can delete its
392 // chain of computation and the store to the global in Dead[n].second.
393 SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
395 // Constants can't be pointers to dynamically allocated memory.
396 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
399 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
400 Value *V = SI->getValueOperand();
401 if (isa<Constant>(V)) {
403 SI->eraseFromParent();
404 } else if (Instruction *I = dyn_cast<Instruction>(V)) {
406 Dead.push_back(std::make_pair(I, SI));
408 } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
409 if (isa<Constant>(MSI->getValue())) {
411 MSI->eraseFromParent();
412 } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
414 Dead.push_back(std::make_pair(I, MSI));
416 } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
417 GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
418 if (MemSrc && MemSrc->isConstant()) {
420 MTI->eraseFromParent();
421 } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) {
423 Dead.push_back(std::make_pair(I, MTI));
425 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
426 if (CE->use_empty()) {
427 CE->destroyConstant();
430 } else if (Constant *C = dyn_cast<Constant>(U)) {
431 if (SafeToDestroyConstant(C)) {
432 C->destroyConstant();
433 // This could have invalidated UI, start over from scratch.
435 CleanupPointerRootUsers(GV);
441 for (int i = 0, e = Dead.size(); i != e; ++i) {
442 if (IsSafeComputationToRemove(Dead[i].first)) {
443 Dead[i].second->eraseFromParent();
444 Instruction *I = Dead[i].first;
446 if (isAllocationFn(I))
448 Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
451 I->eraseFromParent();
454 I->eraseFromParent();
461 /// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all
462 /// users of the global, cleaning up the obvious ones. This is largely just a
463 /// quick scan over the use list to clean up the easy and obvious cruft. This
464 /// returns true if it made a change.
465 static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
466 TargetData *TD, TargetLibraryInfo *TLI) {
467 bool Changed = false;
468 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) {
471 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
473 // Replace the load with the initializer.
474 LI->replaceAllUsesWith(Init);
475 LI->eraseFromParent();
478 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
479 // Store must be unreachable or storing Init into the global.
480 SI->eraseFromParent();
482 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
483 if (CE->getOpcode() == Instruction::GetElementPtr) {
484 Constant *SubInit = 0;
486 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
487 Changed |= CleanupConstantGlobalUsers(CE, SubInit, TD, TLI);
488 } else if (CE->getOpcode() == Instruction::BitCast &&
489 CE->getType()->isPointerTy()) {
490 // Pointer cast, delete any stores and memsets to the global.
491 Changed |= CleanupConstantGlobalUsers(CE, 0, TD, TLI);
494 if (CE->use_empty()) {
495 CE->destroyConstant();
498 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
499 // Do not transform "gepinst (gep constexpr (GV))" here, because forming
500 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
501 // and will invalidate our notion of what Init is.
502 Constant *SubInit = 0;
503 if (!isa<ConstantExpr>(GEP->getOperand(0))) {
505 dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, TD, TLI));
506 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
507 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
509 // If the initializer is an all-null value and we have an inbounds GEP,
510 // we already know what the result of any load from that GEP is.
511 // TODO: Handle splats.
512 if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
513 SubInit = Constant::getNullValue(GEP->getType()->getElementType());
515 Changed |= CleanupConstantGlobalUsers(GEP, SubInit, TD, TLI);
517 if (GEP->use_empty()) {
518 GEP->eraseFromParent();
521 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
522 if (MI->getRawDest() == V) {
523 MI->eraseFromParent();
527 } else if (Constant *C = dyn_cast<Constant>(U)) {
528 // If we have a chain of dead constantexprs or other things dangling from
529 // us, and if they are all dead, nuke them without remorse.
530 if (SafeToDestroyConstant(C)) {
531 C->destroyConstant();
532 // This could have invalidated UI, start over from scratch.
533 CleanupConstantGlobalUsers(V, Init, TD, TLI);
541 /// isSafeSROAElementUse - Return true if the specified instruction is a safe
542 /// user of a derived expression from a global that we want to SROA.
543 static bool isSafeSROAElementUse(Value *V) {
544 // We might have a dead and dangling constant hanging off of here.
545 if (Constant *C = dyn_cast<Constant>(V))
546 return SafeToDestroyConstant(C);
548 Instruction *I = dyn_cast<Instruction>(V);
549 if (!I) return false;
552 if (isa<LoadInst>(I)) return true;
554 // Stores *to* the pointer are ok.
555 if (StoreInst *SI = dyn_cast<StoreInst>(I))
556 return SI->getOperand(0) != V;
558 // Otherwise, it must be a GEP.
559 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
560 if (GEPI == 0) return false;
562 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
563 !cast<Constant>(GEPI->getOperand(1))->isNullValue())
566 for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end();
568 if (!isSafeSROAElementUse(*I))
574 /// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value.
575 /// Look at it and its uses and decide whether it is safe to SROA this global.
577 static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
578 // The user of the global must be a GEP Inst or a ConstantExpr GEP.
579 if (!isa<GetElementPtrInst>(U) &&
580 (!isa<ConstantExpr>(U) ||
581 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
584 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we
585 // don't like < 3 operand CE's, and we don't like non-constant integer
586 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
588 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
589 !cast<Constant>(U->getOperand(1))->isNullValue() ||
590 !isa<ConstantInt>(U->getOperand(2)))
593 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
594 ++GEPI; // Skip over the pointer index.
596 // If this is a use of an array allocation, do a bit more checking for sanity.
597 if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
598 uint64_t NumElements = AT->getNumElements();
599 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
601 // Check to make sure that index falls within the array. If not,
602 // something funny is going on, so we won't do the optimization.
604 if (Idx->getZExtValue() >= NumElements)
607 // We cannot scalar repl this level of the array unless any array
608 // sub-indices are in-range constants. In particular, consider:
609 // A[0][i]. We cannot know that the user isn't doing invalid things like
610 // allowing i to index an out-of-range subscript that accesses A[1].
612 // Scalar replacing *just* the outer index of the array is probably not
613 // going to be a win anyway, so just give up.
614 for (++GEPI; // Skip array index.
617 uint64_t NumElements;
618 if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
619 NumElements = SubArrayTy->getNumElements();
620 else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
621 NumElements = SubVectorTy->getNumElements();
623 assert((*GEPI)->isStructTy() &&
624 "Indexed GEP type is not array, vector, or struct!");
628 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
629 if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
634 for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I)
635 if (!isSafeSROAElementUse(*I))
640 /// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it
641 /// is safe for us to perform this transformation.
643 static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
644 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
646 if (!IsUserOfGlobalSafeForSRA(*UI, GV))
653 /// SRAGlobal - Perform scalar replacement of aggregates on the specified global
654 /// variable. This opens the door for other optimizations by exposing the
655 /// behavior of the program in a more fine-grained way. We have determined that
656 /// this transformation is safe already. We return the first global variable we
657 /// insert so that the caller can reprocess it.
658 static GlobalVariable *SRAGlobal(GlobalVariable *GV, const TargetData &TD) {
659 // Make sure this global only has simple uses that we can SRA.
660 if (!GlobalUsersSafeToSRA(GV))
663 assert(GV->hasLocalLinkage() && !GV->isConstant());
664 Constant *Init = GV->getInitializer();
665 Type *Ty = Init->getType();
667 std::vector<GlobalVariable*> NewGlobals;
668 Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
670 // Get the alignment of the global, either explicit or target-specific.
671 unsigned StartAlignment = GV->getAlignment();
672 if (StartAlignment == 0)
673 StartAlignment = TD.getABITypeAlignment(GV->getType());
675 if (StructType *STy = dyn_cast<StructType>(Ty)) {
676 NewGlobals.reserve(STy->getNumElements());
677 const StructLayout &Layout = *TD.getStructLayout(STy);
678 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
679 Constant *In = Init->getAggregateElement(i);
680 assert(In && "Couldn't get element of initializer?");
681 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
682 GlobalVariable::InternalLinkage,
683 In, GV->getName()+"."+Twine(i),
684 GV->getThreadLocalMode(),
685 GV->getType()->getAddressSpace());
686 Globals.insert(GV, NGV);
687 NewGlobals.push_back(NGV);
689 // Calculate the known alignment of the field. If the original aggregate
690 // had 256 byte alignment for example, something might depend on that:
691 // propagate info to each field.
692 uint64_t FieldOffset = Layout.getElementOffset(i);
693 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
694 if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i)))
695 NGV->setAlignment(NewAlign);
697 } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
698 unsigned NumElements = 0;
699 if (ArrayType *ATy = dyn_cast<ArrayType>(STy))
700 NumElements = ATy->getNumElements();
702 NumElements = cast<VectorType>(STy)->getNumElements();
704 if (NumElements > 16 && GV->hasNUsesOrMore(16))
705 return 0; // It's not worth it.
706 NewGlobals.reserve(NumElements);
708 uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType());
709 unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType());
710 for (unsigned i = 0, e = NumElements; i != e; ++i) {
711 Constant *In = Init->getAggregateElement(i);
712 assert(In && "Couldn't get element of initializer?");
714 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
715 GlobalVariable::InternalLinkage,
716 In, GV->getName()+"."+Twine(i),
717 GV->getThreadLocalMode(),
718 GV->getType()->getAddressSpace());
719 Globals.insert(GV, NGV);
720 NewGlobals.push_back(NGV);
722 // Calculate the known alignment of the field. If the original aggregate
723 // had 256 byte alignment for example, something might depend on that:
724 // propagate info to each field.
725 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
726 if (NewAlign > EltAlign)
727 NGV->setAlignment(NewAlign);
731 if (NewGlobals.empty())
734 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV);
736 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
738 // Loop over all of the uses of the global, replacing the constantexpr geps,
739 // with smaller constantexpr geps or direct references.
740 while (!GV->use_empty()) {
741 User *GEP = GV->use_back();
742 assert(((isa<ConstantExpr>(GEP) &&
743 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
744 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
746 // Ignore the 1th operand, which has to be zero or else the program is quite
747 // broken (undefined). Get the 2nd operand, which is the structure or array
749 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
750 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
752 Value *NewPtr = NewGlobals[Val];
754 // Form a shorter GEP if needed.
755 if (GEP->getNumOperands() > 3) {
756 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
757 SmallVector<Constant*, 8> Idxs;
758 Idxs.push_back(NullInt);
759 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
760 Idxs.push_back(CE->getOperand(i));
761 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs);
763 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
764 SmallVector<Value*, 8> Idxs;
765 Idxs.push_back(NullInt);
766 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
767 Idxs.push_back(GEPI->getOperand(i));
768 NewPtr = GetElementPtrInst::Create(NewPtr, Idxs,
769 GEPI->getName()+"."+Twine(Val),GEPI);
772 GEP->replaceAllUsesWith(NewPtr);
774 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
775 GEPI->eraseFromParent();
777 cast<ConstantExpr>(GEP)->destroyConstant();
780 // Delete the old global, now that it is dead.
784 // Loop over the new globals array deleting any globals that are obviously
785 // dead. This can arise due to scalarization of a structure or an array that
786 // has elements that are dead.
787 unsigned FirstGlobal = 0;
788 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
789 if (NewGlobals[i]->use_empty()) {
790 Globals.erase(NewGlobals[i]);
791 if (FirstGlobal == i) ++FirstGlobal;
794 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0;
797 /// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified
798 /// value will trap if the value is dynamically null. PHIs keeps track of any
799 /// phi nodes we've seen to avoid reprocessing them.
800 static bool AllUsesOfValueWillTrapIfNull(const Value *V,
801 SmallPtrSet<const PHINode*, 8> &PHIs) {
802 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
806 if (isa<LoadInst>(U)) {
808 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
809 if (SI->getOperand(0) == V) {
810 //cerr << "NONTRAPPING USE: " << *U;
811 return false; // Storing the value.
813 } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
814 if (CI->getCalledValue() != V) {
815 //cerr << "NONTRAPPING USE: " << *U;
816 return false; // Not calling the ptr
818 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
819 if (II->getCalledValue() != V) {
820 //cerr << "NONTRAPPING USE: " << *U;
821 return false; // Not calling the ptr
823 } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
824 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
825 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
826 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
827 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
828 // If we've already seen this phi node, ignore it, it has already been
830 if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
832 } else if (isa<ICmpInst>(U) &&
833 isa<ConstantPointerNull>(UI->getOperand(1))) {
834 // Ignore icmp X, null
836 //cerr << "NONTRAPPING USE: " << *U;
843 /// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads
844 /// from GV will trap if the loaded value is null. Note that this also permits
845 /// comparisons of the loaded value against null, as a special case.
846 static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
847 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
851 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
852 SmallPtrSet<const PHINode*, 8> PHIs;
853 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
855 } else if (isa<StoreInst>(U)) {
856 // Ignore stores to the global.
858 // We don't know or understand this user, bail out.
859 //cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
866 static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
867 bool Changed = false;
868 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) {
869 Instruction *I = cast<Instruction>(*UI++);
870 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
871 LI->setOperand(0, NewV);
873 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
874 if (SI->getOperand(1) == V) {
875 SI->setOperand(1, NewV);
878 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
880 if (CS.getCalledValue() == V) {
881 // Calling through the pointer! Turn into a direct call, but be careful
882 // that the pointer is not also being passed as an argument.
883 CS.setCalledFunction(NewV);
885 bool PassedAsArg = false;
886 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
887 if (CS.getArgument(i) == V) {
889 CS.setArgument(i, NewV);
893 // Being passed as an argument also. Be careful to not invalidate UI!
897 } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
898 Changed |= OptimizeAwayTrappingUsesOfValue(CI,
899 ConstantExpr::getCast(CI->getOpcode(),
900 NewV, CI->getType()));
901 if (CI->use_empty()) {
903 CI->eraseFromParent();
905 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
906 // Should handle GEP here.
907 SmallVector<Constant*, 8> Idxs;
908 Idxs.reserve(GEPI->getNumOperands()-1);
909 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
911 if (Constant *C = dyn_cast<Constant>(*i))
915 if (Idxs.size() == GEPI->getNumOperands()-1)
916 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
917 ConstantExpr::getGetElementPtr(NewV, Idxs));
918 if (GEPI->use_empty()) {
920 GEPI->eraseFromParent();
929 /// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null
930 /// value stored into it. If there are uses of the loaded value that would trap
931 /// if the loaded value is dynamically null, then we know that they cannot be
932 /// reachable with a null optimize away the load.
933 static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV,
935 TargetLibraryInfo *TLI) {
936 bool Changed = false;
938 // Keep track of whether we are able to remove all the uses of the global
939 // other than the store that defines it.
940 bool AllNonStoreUsesGone = true;
942 // Replace all uses of loads with uses of uses of the stored value.
943 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){
944 User *GlobalUser = *GUI++;
945 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
946 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
947 // If we were able to delete all uses of the loads
948 if (LI->use_empty()) {
949 LI->eraseFromParent();
952 AllNonStoreUsesGone = false;
954 } else if (isa<StoreInst>(GlobalUser)) {
955 // Ignore the store that stores "LV" to the global.
956 assert(GlobalUser->getOperand(1) == GV &&
957 "Must be storing *to* the global");
959 AllNonStoreUsesGone = false;
961 // If we get here we could have other crazy uses that are transitively
963 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
964 isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser)) &&
965 "Only expect load and stores!");
970 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV);
974 // If we nuked all of the loads, then none of the stores are needed either,
975 // nor is the global.
976 if (AllNonStoreUsesGone) {
977 if (isLeakCheckerRoot(GV)) {
978 Changed |= CleanupPointerRootUsers(GV);
981 CleanupConstantGlobalUsers(GV, 0, TD, TLI);
983 if (GV->use_empty()) {
984 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
986 GV->eraseFromParent();
993 /// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
994 /// instructions that are foldable.
995 static void ConstantPropUsersOf(Value *V,
996 TargetData *TD, TargetLibraryInfo *TLI) {
997 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; )
998 if (Instruction *I = dyn_cast<Instruction>(*UI++))
999 if (Constant *NewC = ConstantFoldInstruction(I, TD, TLI)) {
1000 I->replaceAllUsesWith(NewC);
1002 // Advance UI to the next non-I use to avoid invalidating it!
1003 // Instructions could multiply use V.
1004 while (UI != E && *UI == I)
1006 I->eraseFromParent();
1010 /// OptimizeGlobalAddressOfMalloc - This function takes the specified global
1011 /// variable, and transforms the program as if it always contained the result of
1012 /// the specified malloc. Because it is always the result of the specified
1013 /// malloc, there is no reason to actually DO the malloc. Instead, turn the
1014 /// malloc into a global, and any loads of GV as uses of the new global.
1015 static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
1018 ConstantInt *NElements,
1020 TargetLibraryInfo *TLI) {
1021 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n');
1024 if (NElements->getZExtValue() == 1)
1025 GlobalType = AllocTy;
1027 // If we have an array allocation, the global variable is of an array.
1028 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
1030 // Create the new global variable. The contents of the malloc'd memory is
1031 // undefined, so initialize with an undef value.
1032 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(),
1034 GlobalValue::InternalLinkage,
1035 UndefValue::get(GlobalType),
1036 GV->getName()+".body",
1038 GV->getThreadLocalMode());
1040 // If there are bitcast users of the malloc (which is typical, usually we have
1041 // a malloc + bitcast) then replace them with uses of the new global. Update
1042 // other users to use the global as well.
1043 BitCastInst *TheBC = 0;
1044 while (!CI->use_empty()) {
1045 Instruction *User = cast<Instruction>(CI->use_back());
1046 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
1047 if (BCI->getType() == NewGV->getType()) {
1048 BCI->replaceAllUsesWith(NewGV);
1049 BCI->eraseFromParent();
1051 BCI->setOperand(0, NewGV);
1055 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
1056 User->replaceUsesOfWith(CI, TheBC);
1060 Constant *RepValue = NewGV;
1061 if (NewGV->getType() != GV->getType()->getElementType())
1062 RepValue = ConstantExpr::getBitCast(RepValue,
1063 GV->getType()->getElementType());
1065 // If there is a comparison against null, we will insert a global bool to
1066 // keep track of whether the global was initialized yet or not.
1067 GlobalVariable *InitBool =
1068 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
1069 GlobalValue::InternalLinkage,
1070 ConstantInt::getFalse(GV->getContext()),
1071 GV->getName()+".init", GV->getThreadLocalMode());
1072 bool InitBoolUsed = false;
1074 // Loop over all uses of GV, processing them in turn.
1075 while (!GV->use_empty()) {
1076 if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) {
1077 // The global is initialized when the store to it occurs.
1078 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
1079 SI->getOrdering(), SI->getSynchScope(), SI);
1080 SI->eraseFromParent();
1084 LoadInst *LI = cast<LoadInst>(GV->use_back());
1085 while (!LI->use_empty()) {
1086 Use &LoadUse = LI->use_begin().getUse();
1087 if (!isa<ICmpInst>(LoadUse.getUser())) {
1092 ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser());
1093 // Replace the cmp X, 0 with a use of the bool value.
1094 // Sink the load to where the compare was, if atomic rules allow us to.
1095 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
1096 LI->getOrdering(), LI->getSynchScope(),
1097 LI->isUnordered() ? (Instruction*)ICI : LI);
1098 InitBoolUsed = true;
1099 switch (ICI->getPredicate()) {
1100 default: llvm_unreachable("Unknown ICmp Predicate!");
1101 case ICmpInst::ICMP_ULT:
1102 case ICmpInst::ICMP_SLT: // X < null -> always false
1103 LV = ConstantInt::getFalse(GV->getContext());
1105 case ICmpInst::ICMP_ULE:
1106 case ICmpInst::ICMP_SLE:
1107 case ICmpInst::ICMP_EQ:
1108 LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
1110 case ICmpInst::ICMP_NE:
1111 case ICmpInst::ICMP_UGE:
1112 case ICmpInst::ICMP_SGE:
1113 case ICmpInst::ICMP_UGT:
1114 case ICmpInst::ICMP_SGT:
1115 break; // no change.
1117 ICI->replaceAllUsesWith(LV);
1118 ICI->eraseFromParent();
1120 LI->eraseFromParent();
1123 // If the initialization boolean was used, insert it, otherwise delete it.
1124 if (!InitBoolUsed) {
1125 while (!InitBool->use_empty()) // Delete initializations
1126 cast<StoreInst>(InitBool->use_back())->eraseFromParent();
1129 GV->getParent()->getGlobalList().insert(GV, InitBool);
1131 // Now the GV is dead, nuke it and the malloc..
1132 GV->eraseFromParent();
1133 CI->eraseFromParent();
1135 // To further other optimizations, loop over all users of NewGV and try to
1136 // constant prop them. This will promote GEP instructions with constant
1137 // indices into GEP constant-exprs, which will allow global-opt to hack on it.
1138 ConstantPropUsersOf(NewGV, TD, TLI);
1139 if (RepValue != NewGV)
1140 ConstantPropUsersOf(RepValue, TD, TLI);
1145 /// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking
1146 /// to make sure that there are no complex uses of V. We permit simple things
1147 /// like dereferencing the pointer, but not storing through the address, unless
1148 /// it is to the specified global.
1149 static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
1150 const GlobalVariable *GV,
1151 SmallPtrSet<const PHINode*, 8> &PHIs) {
1152 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end();
1154 const Instruction *Inst = cast<Instruction>(*UI);
1156 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
1157 continue; // Fine, ignore.
1160 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
1161 if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
1162 return false; // Storing the pointer itself... bad.
1163 continue; // Otherwise, storing through it, or storing into GV... fine.
1166 // Must index into the array and into the struct.
1167 if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
1168 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
1173 if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
1174 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI
1176 if (PHIs.insert(PN))
1177 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
1182 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
1183 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
1193 /// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV
1194 /// somewhere. Transform all uses of the allocation into loads from the
1195 /// global and uses of the resultant pointer. Further, delete the store into
1196 /// GV. This assumes that these value pass the
1197 /// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
1198 static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc,
1199 GlobalVariable *GV) {
1200 while (!Alloc->use_empty()) {
1201 Instruction *U = cast<Instruction>(*Alloc->use_begin());
1202 Instruction *InsertPt = U;
1203 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
1204 // If this is the store of the allocation into the global, remove it.
1205 if (SI->getOperand(1) == GV) {
1206 SI->eraseFromParent();
1209 } else if (PHINode *PN = dyn_cast<PHINode>(U)) {
1210 // Insert the load in the corresponding predecessor, not right before the
1212 InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator();
1213 } else if (isa<BitCastInst>(U)) {
1214 // Must be bitcast between the malloc and store to initialize the global.
1215 ReplaceUsesOfMallocWithGlobal(U, GV);
1216 U->eraseFromParent();
1218 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
1219 // If this is a "GEP bitcast" and the user is a store to the global, then
1220 // just process it as a bitcast.
1221 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse())
1222 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back()))
1223 if (SI->getOperand(1) == GV) {
1224 // Must be bitcast GEP between the malloc and store to initialize
1226 ReplaceUsesOfMallocWithGlobal(GEPI, GV);
1227 GEPI->eraseFromParent();
1232 // Insert a load from the global, and use it instead of the malloc.
1233 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt);
1234 U->replaceUsesOfWith(Alloc, NL);
1238 /// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi
1239 /// of a load) are simple enough to perform heap SRA on. This permits GEP's
1240 /// that index through the array and struct field, icmps of null, and PHIs.
1241 static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
1242 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs,
1243 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) {
1244 // We permit two users of the load: setcc comparing against the null
1245 // pointer, and a getelementptr of a specific form.
1246 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
1248 const Instruction *User = cast<Instruction>(*UI);
1250 // Comparison against null is ok.
1251 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(User)) {
1252 if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
1257 // getelementptr is also ok, but only a simple form.
1258 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
1259 // Must index into the array and into the struct.
1260 if (GEPI->getNumOperands() < 3)
1263 // Otherwise the GEP is ok.
1267 if (const PHINode *PN = dyn_cast<PHINode>(User)) {
1268 if (!LoadUsingPHIsPerLoad.insert(PN))
1269 // This means some phi nodes are dependent on each other.
1270 // Avoid infinite looping!
1272 if (!LoadUsingPHIs.insert(PN))
1273 // If we have already analyzed this PHI, then it is safe.
1276 // Make sure all uses of the PHI are simple enough to transform.
1277 if (!LoadUsesSimpleEnoughForHeapSRA(PN,
1278 LoadUsingPHIs, LoadUsingPHIsPerLoad))
1284 // Otherwise we don't know what this is, not ok.
1292 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from
1293 /// GV are simple enough to perform HeapSRA, return true.
1294 static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
1295 Instruction *StoredVal) {
1296 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
1297 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
1298 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
1300 if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1301 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
1302 LoadUsingPHIsPerLoad))
1304 LoadUsingPHIsPerLoad.clear();
1307 // If we reach here, we know that all uses of the loads and transitive uses
1308 // (through PHI nodes) are simple enough to transform. However, we don't know
1309 // that all inputs the to the PHI nodes are in the same equivalence sets.
1310 // Check to verify that all operands of the PHIs are either PHIS that can be
1311 // transformed, loads from GV, or MI itself.
1312 for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin()
1313 , E = LoadUsingPHIs.end(); I != E; ++I) {
1314 const PHINode *PN = *I;
1315 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
1316 Value *InVal = PN->getIncomingValue(op);
1318 // PHI of the stored value itself is ok.
1319 if (InVal == StoredVal) continue;
1321 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
1322 // One of the PHIs in our set is (optimistically) ok.
1323 if (LoadUsingPHIs.count(InPN))
1328 // Load from GV is ok.
1329 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
1330 if (LI->getOperand(0) == GV)
1335 // Anything else is rejected.
1343 static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
1344 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1345 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1346 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
1348 if (FieldNo >= FieldVals.size())
1349 FieldVals.resize(FieldNo+1);
1351 // If we already have this value, just reuse the previously scalarized
1353 if (Value *FieldVal = FieldVals[FieldNo])
1356 // Depending on what instruction this is, we have several cases.
1358 if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
1359 // This is a scalarized version of the load from the global. Just create
1360 // a new Load of the scalarized global.
1361 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
1362 InsertedScalarizedValues,
1364 LI->getName()+".f"+Twine(FieldNo), LI);
1365 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
1366 // PN's type is pointer to struct. Make a new PHI of pointer to struct
1369 cast<StructType>(cast<PointerType>(PN->getType())->getElementType());
1372 PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)),
1373 PN->getNumIncomingValues(),
1374 PN->getName()+".f"+Twine(FieldNo), PN);
1376 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
1378 llvm_unreachable("Unknown usable value");
1381 return FieldVals[FieldNo] = Result;
1384 /// RewriteHeapSROALoadUser - Given a load instruction and a value derived from
1385 /// the load, rewrite the derived value to use the HeapSRoA'd load.
1386 static void RewriteHeapSROALoadUser(Instruction *LoadUser,
1387 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1388 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1389 // If this is a comparison against null, handle it.
1390 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
1391 assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
1392 // If we have a setcc of the loaded pointer, we can use a setcc of any
1394 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
1395 InsertedScalarizedValues, PHIsToRewrite);
1397 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
1398 Constant::getNullValue(NPtr->getType()),
1400 SCI->replaceAllUsesWith(New);
1401 SCI->eraseFromParent();
1405 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
1406 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
1407 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
1408 && "Unexpected GEPI!");
1410 // Load the pointer for this field.
1411 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
1412 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
1413 InsertedScalarizedValues, PHIsToRewrite);
1415 // Create the new GEP idx vector.
1416 SmallVector<Value*, 8> GEPIdx;
1417 GEPIdx.push_back(GEPI->getOperand(1));
1418 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
1420 Value *NGEPI = GetElementPtrInst::Create(NewPtr, GEPIdx,
1421 GEPI->getName(), GEPI);
1422 GEPI->replaceAllUsesWith(NGEPI);
1423 GEPI->eraseFromParent();
1427 // Recursively transform the users of PHI nodes. This will lazily create the
1428 // PHIs that are needed for individual elements. Keep track of what PHIs we
1429 // see in InsertedScalarizedValues so that we don't get infinite loops (very
1430 // antisocial). If the PHI is already in InsertedScalarizedValues, it has
1431 // already been seen first by another load, so its uses have already been
1433 PHINode *PN = cast<PHINode>(LoadUser);
1434 if (!InsertedScalarizedValues.insert(std::make_pair(PN,
1435 std::vector<Value*>())).second)
1438 // If this is the first time we've seen this PHI, recursively process all
1440 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) {
1441 Instruction *User = cast<Instruction>(*UI++);
1442 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1446 /// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr
1447 /// is a value loaded from the global. Eliminate all uses of Ptr, making them
1448 /// use FieldGlobals instead. All uses of loaded values satisfy
1449 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA.
1450 static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
1451 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1452 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1453 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end();
1455 Instruction *User = cast<Instruction>(*UI++);
1456 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1459 if (Load->use_empty()) {
1460 Load->eraseFromParent();
1461 InsertedScalarizedValues.erase(Load);
1465 /// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break
1466 /// it up into multiple allocations of arrays of the fields.
1467 static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
1468 Value *NElems, TargetData *TD) {
1469 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n');
1470 Type *MAT = getMallocAllocatedType(CI);
1471 StructType *STy = cast<StructType>(MAT);
1473 // There is guaranteed to be at least one use of the malloc (storing
1474 // it into GV). If there are other uses, change them to be uses of
1475 // the global to simplify later code. This also deletes the store
1477 ReplaceUsesOfMallocWithGlobal(CI, GV);
1479 // Okay, at this point, there are no users of the malloc. Insert N
1480 // new mallocs at the same place as CI, and N globals.
1481 std::vector<Value*> FieldGlobals;
1482 std::vector<Value*> FieldMallocs;
1484 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
1485 Type *FieldTy = STy->getElementType(FieldNo);
1486 PointerType *PFieldTy = PointerType::getUnqual(FieldTy);
1488 GlobalVariable *NGV =
1489 new GlobalVariable(*GV->getParent(),
1490 PFieldTy, false, GlobalValue::InternalLinkage,
1491 Constant::getNullValue(PFieldTy),
1492 GV->getName() + ".f" + Twine(FieldNo), GV,
1493 GV->getThreadLocalMode());
1494 FieldGlobals.push_back(NGV);
1496 unsigned TypeSize = TD->getTypeAllocSize(FieldTy);
1497 if (StructType *ST = dyn_cast<StructType>(FieldTy))
1498 TypeSize = TD->getStructLayout(ST)->getSizeInBytes();
1499 Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
1500 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
1501 ConstantInt::get(IntPtrTy, TypeSize),
1503 CI->getName() + ".f" + Twine(FieldNo));
1504 FieldMallocs.push_back(NMI);
1505 new StoreInst(NMI, NGV, CI);
1508 // The tricky aspect of this transformation is handling the case when malloc
1509 // fails. In the original code, malloc failing would set the result pointer
1510 // of malloc to null. In this case, some mallocs could succeed and others
1511 // could fail. As such, we emit code that looks like this:
1512 // F0 = malloc(field0)
1513 // F1 = malloc(field1)
1514 // F2 = malloc(field2)
1515 // if (F0 == 0 || F1 == 0 || F2 == 0) {
1516 // if (F0) { free(F0); F0 = 0; }
1517 // if (F1) { free(F1); F1 = 0; }
1518 // if (F2) { free(F2); F2 = 0; }
1520 // The malloc can also fail if its argument is too large.
1521 Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
1522 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
1523 ConstantZero, "isneg");
1524 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
1525 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
1526 Constant::getNullValue(FieldMallocs[i]->getType()),
1528 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
1531 // Split the basic block at the old malloc.
1532 BasicBlock *OrigBB = CI->getParent();
1533 BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont");
1535 // Create the block to check the first condition. Put all these blocks at the
1536 // end of the function as they are unlikely to be executed.
1537 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
1539 OrigBB->getParent());
1541 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
1542 // branch on RunningOr.
1543 OrigBB->getTerminator()->eraseFromParent();
1544 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
1546 // Within the NullPtrBlock, we need to emit a comparison and branch for each
1547 // pointer, because some may be null while others are not.
1548 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1549 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
1550 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
1551 Constant::getNullValue(GVVal->getType()));
1552 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
1553 OrigBB->getParent());
1554 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
1555 OrigBB->getParent());
1556 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
1559 // Fill in FreeBlock.
1560 CallInst::CreateFree(GVVal, BI);
1561 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
1563 BranchInst::Create(NextBlock, FreeBlock);
1565 NullPtrBlock = NextBlock;
1568 BranchInst::Create(ContBB, NullPtrBlock);
1570 // CI is no longer needed, remove it.
1571 CI->eraseFromParent();
1573 /// InsertedScalarizedLoads - As we process loads, if we can't immediately
1574 /// update all uses of the load, keep track of what scalarized loads are
1575 /// inserted for a given load.
1576 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues;
1577 InsertedScalarizedValues[GV] = FieldGlobals;
1579 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite;
1581 // Okay, the malloc site is completely handled. All of the uses of GV are now
1582 // loads, and all uses of those loads are simple. Rewrite them to use loads
1583 // of the per-field globals instead.
1584 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) {
1585 Instruction *User = cast<Instruction>(*UI++);
1587 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1588 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
1592 // Must be a store of null.
1593 StoreInst *SI = cast<StoreInst>(User);
1594 assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
1595 "Unexpected heap-sra user!");
1597 // Insert a store of null into each global.
1598 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1599 PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType());
1600 Constant *Null = Constant::getNullValue(PT->getElementType());
1601 new StoreInst(Null, FieldGlobals[i], SI);
1603 // Erase the original store.
1604 SI->eraseFromParent();
1607 // While we have PHIs that are interesting to rewrite, do it.
1608 while (!PHIsToRewrite.empty()) {
1609 PHINode *PN = PHIsToRewrite.back().first;
1610 unsigned FieldNo = PHIsToRewrite.back().second;
1611 PHIsToRewrite.pop_back();
1612 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
1613 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
1615 // Add all the incoming values. This can materialize more phis.
1616 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1617 Value *InVal = PN->getIncomingValue(i);
1618 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
1620 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
1624 // Drop all inter-phi links and any loads that made it this far.
1625 for (DenseMap<Value*, std::vector<Value*> >::iterator
1626 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1628 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1629 PN->dropAllReferences();
1630 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1631 LI->dropAllReferences();
1634 // Delete all the phis and loads now that inter-references are dead.
1635 for (DenseMap<Value*, std::vector<Value*> >::iterator
1636 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1638 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1639 PN->eraseFromParent();
1640 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1641 LI->eraseFromParent();
1644 // The old global is now dead, remove it.
1645 GV->eraseFromParent();
1648 return cast<GlobalVariable>(FieldGlobals[0]);
1651 /// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a
1652 /// pointer global variable with a single value stored it that is a malloc or
1654 static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
1657 AtomicOrdering Ordering,
1658 Module::global_iterator &GVI,
1660 TargetLibraryInfo *TLI) {
1664 // If this is a malloc of an abstract type, don't touch it.
1665 if (!AllocTy->isSized())
1668 // We can't optimize this global unless all uses of it are *known* to be
1669 // of the malloc value, not of the null initializer value (consider a use
1670 // that compares the global's value against zero to see if the malloc has
1671 // been reached). To do this, we check to see if all uses of the global
1672 // would trap if the global were null: this proves that they must all
1673 // happen after the malloc.
1674 if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
1677 // We can't optimize this if the malloc itself is used in a complex way,
1678 // for example, being stored into multiple globals. This allows the
1679 // malloc to be stored into the specified global, loaded icmp'd, and
1680 // GEP'd. These are all things we could transform to using the global
1682 SmallPtrSet<const PHINode*, 8> PHIs;
1683 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
1686 // If we have a global that is only initialized with a fixed size malloc,
1687 // transform the program to use global memory instead of malloc'd memory.
1688 // This eliminates dynamic allocation, avoids an indirection accessing the
1689 // data, and exposes the resultant global to further GlobalOpt.
1690 // We cannot optimize the malloc if we cannot determine malloc array size.
1691 Value *NElems = getMallocArraySize(CI, TD, true);
1695 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
1696 // Restrict this transformation to only working on small allocations
1697 // (2048 bytes currently), as we don't want to introduce a 16M global or
1699 if (NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) {
1700 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD, TLI);
1704 // If the allocation is an array of structures, consider transforming this
1705 // into multiple malloc'd arrays, one for each field. This is basically
1706 // SRoA for malloc'd memory.
1708 if (Ordering != NotAtomic)
1711 // If this is an allocation of a fixed size array of structs, analyze as a
1712 // variable size array. malloc [100 x struct],1 -> malloc struct, 100
1713 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
1714 if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
1715 AllocTy = AT->getElementType();
1717 StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
1721 // This the structure has an unreasonable number of fields, leave it
1723 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
1724 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
1726 // If this is a fixed size array, transform the Malloc to be an alloc of
1727 // structs. malloc [100 x struct],1 -> malloc struct, 100
1728 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI))) {
1729 Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
1730 unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes();
1731 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
1732 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
1733 Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy,
1734 AllocSize, NumElements,
1736 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
1737 CI->replaceAllUsesWith(Cast);
1738 CI->eraseFromParent();
1739 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc))
1740 CI = cast<CallInst>(BCI->getOperand(0));
1742 CI = cast<CallInst>(Malloc);
1745 GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, true), TD);
1752 // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
1753 // that only one value (besides its initializer) is ever stored to the global.
1754 static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
1755 AtomicOrdering Ordering,
1756 Module::global_iterator &GVI,
1757 TargetData *TD, TargetLibraryInfo *TLI) {
1758 // Ignore no-op GEPs and bitcasts.
1759 StoredOnceVal = StoredOnceVal->stripPointerCasts();
1761 // If we are dealing with a pointer global that is initialized to null and
1762 // only has one (non-null) value stored into it, then we can optimize any
1763 // users of the loaded value (often calls and loads) that would trap if the
1765 if (GV->getInitializer()->getType()->isPointerTy() &&
1766 GV->getInitializer()->isNullValue()) {
1767 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
1768 if (GV->getInitializer()->getType() != SOVC->getType())
1769 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
1771 // Optimize away any trapping uses of the loaded value.
1772 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, TD, TLI))
1774 } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) {
1775 Type *MallocType = getMallocAllocatedType(CI);
1777 TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, Ordering, GVI,
1786 /// TryToShrinkGlobalToBoolean - At this point, we have learned that the only
1787 /// two values ever stored into GV are its initializer and OtherVal. See if we
1788 /// can shrink the global into a boolean and select between the two values
1789 /// whenever it is used. This exposes the values to other scalar optimizations.
1790 static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
1791 Type *GVElType = GV->getType()->getElementType();
1793 // If GVElType is already i1, it is already shrunk. If the type of the GV is
1794 // an FP value, pointer or vector, don't do this optimization because a select
1795 // between them is very expensive and unlikely to lead to later
1796 // simplification. In these cases, we typically end up with "cond ? v1 : v2"
1797 // where v1 and v2 both require constant pool loads, a big loss.
1798 if (GVElType == Type::getInt1Ty(GV->getContext()) ||
1799 GVElType->isFloatingPointTy() ||
1800 GVElType->isPointerTy() || GVElType->isVectorTy())
1803 // Walk the use list of the global seeing if all the uses are load or store.
1804 // If there is anything else, bail out.
1805 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){
1807 if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
1811 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV);
1813 // Create the new global, initializing it to false.
1814 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
1816 GlobalValue::InternalLinkage,
1817 ConstantInt::getFalse(GV->getContext()),
1819 GV->getThreadLocalMode());
1820 GV->getParent()->getGlobalList().insert(GV, NewGV);
1822 Constant *InitVal = GV->getInitializer();
1823 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
1824 "No reason to shrink to bool!");
1826 // If initialized to zero and storing one into the global, we can use a cast
1827 // instead of a select to synthesize the desired value.
1828 bool IsOneZero = false;
1829 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
1830 IsOneZero = InitVal->isNullValue() && CI->isOne();
1832 while (!GV->use_empty()) {
1833 Instruction *UI = cast<Instruction>(GV->use_back());
1834 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
1835 // Change the store into a boolean store.
1836 bool StoringOther = SI->getOperand(0) == OtherVal;
1837 // Only do this if we weren't storing a loaded value.
1839 if (StoringOther || SI->getOperand(0) == InitVal)
1840 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
1843 // Otherwise, we are storing a previously loaded copy. To do this,
1844 // change the copy from copying the original value to just copying the
1846 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
1848 // If we've already replaced the input, StoredVal will be a cast or
1849 // select instruction. If not, it will be a load of the original
1851 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
1852 assert(LI->getOperand(0) == GV && "Not a copy!");
1853 // Insert a new load, to preserve the saved value.
1854 StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1855 LI->getOrdering(), LI->getSynchScope(), LI);
1857 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
1858 "This is not a form that we understand!");
1859 StoreVal = StoredVal->getOperand(0);
1860 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
1863 new StoreInst(StoreVal, NewGV, false, 0,
1864 SI->getOrdering(), SI->getSynchScope(), SI);
1866 // Change the load into a load of bool then a select.
1867 LoadInst *LI = cast<LoadInst>(UI);
1868 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1869 LI->getOrdering(), LI->getSynchScope(), LI);
1872 NSI = new ZExtInst(NLI, LI->getType(), "", LI);
1874 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
1876 LI->replaceAllUsesWith(NSI);
1878 UI->eraseFromParent();
1881 GV->eraseFromParent();
1886 /// ProcessGlobal - Analyze the specified global variable and optimize it if
1887 /// possible. If we make a change, return true.
1888 bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
1889 Module::global_iterator &GVI) {
1890 if (!GV->isDiscardableIfUnused())
1893 // Do more involved optimizations if the global is internal.
1894 GV->removeDeadConstantUsers();
1896 if (GV->use_empty()) {
1897 DEBUG(dbgs() << "GLOBAL DEAD: " << *GV);
1898 GV->eraseFromParent();
1903 if (!GV->hasLocalLinkage())
1906 SmallPtrSet<const PHINode*, 16> PHIUsers;
1909 if (AnalyzeGlobal(GV, GS, PHIUsers))
1912 if (!GS.isCompared && !GV->hasUnnamedAddr()) {
1913 GV->setUnnamedAddr(true);
1917 if (GV->isConstant() || !GV->hasInitializer())
1920 return ProcessInternalGlobal(GV, GVI, PHIUsers, GS);
1923 /// ProcessInternalGlobal - Analyze the specified global variable and optimize
1924 /// it if possible. If we make a change, return true.
1925 bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
1926 Module::global_iterator &GVI,
1927 const SmallPtrSet<const PHINode*, 16> &PHIUsers,
1928 const GlobalStatus &GS) {
1929 // If this is a first class global and has only one accessing function
1930 // and this function is main (which we know is not recursive we can make
1931 // this global a local variable) we replace the global with a local alloca
1932 // in this function.
1934 // NOTE: It doesn't make sense to promote non single-value types since we
1935 // are just replacing static memory to stack memory.
1937 // If the global is in different address space, don't bring it to stack.
1938 if (!GS.HasMultipleAccessingFunctions &&
1939 GS.AccessingFunction && !GS.HasNonInstructionUser &&
1940 GV->getType()->getElementType()->isSingleValueType() &&
1941 GS.AccessingFunction->getName() == "main" &&
1942 GS.AccessingFunction->hasExternalLinkage() &&
1943 GV->getType()->getAddressSpace() == 0) {
1944 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV);
1945 Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction
1946 ->getEntryBlock().begin());
1947 Type *ElemTy = GV->getType()->getElementType();
1948 // FIXME: Pass Global's alignment when globals have alignment
1949 AllocaInst *Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI);
1950 if (!isa<UndefValue>(GV->getInitializer()))
1951 new StoreInst(GV->getInitializer(), Alloca, &FirstI);
1953 GV->replaceAllUsesWith(Alloca);
1954 GV->eraseFromParent();
1959 // If the global is never loaded (but may be stored to), it is dead.
1962 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV);
1965 if (isLeakCheckerRoot(GV)) {
1966 // Delete any constant stores to the global.
1967 Changed = CleanupPointerRootUsers(GV);
1969 // Delete any stores we can find to the global. We may not be able to
1970 // make it completely dead though.
1971 Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1974 // If the global is dead now, delete it.
1975 if (GV->use_empty()) {
1976 GV->eraseFromParent();
1982 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
1983 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV);
1984 GV->setConstant(true);
1986 // Clean up any obviously simplifiable users now.
1987 CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1989 // If the global is dead now, just nuke it.
1990 if (GV->use_empty()) {
1991 DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
1992 << "all users and delete global!\n");
1993 GV->eraseFromParent();
1999 } else if (!GV->getInitializer()->getType()->isSingleValueType()) {
2000 if (TargetData *TD = getAnalysisIfAvailable<TargetData>())
2001 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) {
2002 GVI = FirstNewGV; // Don't skip the newly produced globals!
2005 } else if (GS.StoredType == GlobalStatus::isStoredOnce) {
2006 // If the initial value for the global was an undef value, and if only
2007 // one other value was stored into it, we can just change the
2008 // initializer to be the stored value, then delete all stores to the
2009 // global. This allows us to mark it constant.
2010 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
2011 if (isa<UndefValue>(GV->getInitializer())) {
2012 // Change the initial value here.
2013 GV->setInitializer(SOVConstant);
2015 // Clean up any obviously simplifiable users now.
2016 CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
2018 if (GV->use_empty()) {
2019 DEBUG(dbgs() << " *** Substituting initializer allowed us to "
2020 << "simplify all users and delete global!\n");
2021 GV->eraseFromParent();
2030 // Try to optimize globals based on the knowledge that only one value
2031 // (besides its initializer) is ever stored to the global.
2032 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, GVI,
2036 // Otherwise, if the global was not a boolean, we can shrink it to be a
2038 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
2039 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
2048 /// ChangeCalleesToFastCall - Walk all of the direct calls of the specified
2049 /// function, changing them to FastCC.
2050 static void ChangeCalleesToFastCall(Function *F) {
2051 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
2052 if (isa<BlockAddress>(*UI))
2054 CallSite User(cast<Instruction>(*UI));
2055 User.setCallingConv(CallingConv::Fast);
2059 static AttrListPtr StripNest(const AttrListPtr &Attrs) {
2060 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
2061 if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0)
2064 // There can be only one.
2065 return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest);
2071 static void RemoveNestAttribute(Function *F) {
2072 F->setAttributes(StripNest(F->getAttributes()));
2073 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
2074 if (isa<BlockAddress>(*UI))
2076 CallSite User(cast<Instruction>(*UI));
2077 User.setAttributes(StripNest(User.getAttributes()));
2081 bool GlobalOpt::OptimizeFunctions(Module &M) {
2082 bool Changed = false;
2083 // Optimize functions.
2084 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
2086 // Functions without names cannot be referenced outside this module.
2087 if (!F->hasName() && !F->isDeclaration())
2088 F->setLinkage(GlobalValue::InternalLinkage);
2089 F->removeDeadConstantUsers();
2090 if (F->isDefTriviallyDead()) {
2091 F->eraseFromParent();
2094 } else if (F->hasLocalLinkage()) {
2095 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() &&
2096 !F->hasAddressTaken()) {
2097 // If this function has C calling conventions, is not a varargs
2098 // function, and is only called directly, promote it to use the Fast
2099 // calling convention.
2100 F->setCallingConv(CallingConv::Fast);
2101 ChangeCalleesToFastCall(F);
2106 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
2107 !F->hasAddressTaken()) {
2108 // The function is not used by a trampoline intrinsic, so it is safe
2109 // to remove the 'nest' attribute.
2110 RemoveNestAttribute(F);
2119 bool GlobalOpt::OptimizeGlobalVars(Module &M) {
2120 bool Changed = false;
2121 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
2123 GlobalVariable *GV = GVI++;
2124 // Global variables without names cannot be referenced outside this module.
2125 if (!GV->hasName() && !GV->isDeclaration())
2126 GV->setLinkage(GlobalValue::InternalLinkage);
2127 // Simplify the initializer.
2128 if (GV->hasInitializer())
2129 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
2130 Constant *New = ConstantFoldConstantExpression(CE, TD, TLI);
2131 if (New && New != CE)
2132 GV->setInitializer(New);
2135 Changed |= ProcessGlobal(GV, GVI);
2140 /// FindGlobalCtors - Find the llvm.global_ctors list, verifying that all
2141 /// initializers have an init priority of 65535.
2142 GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) {
2143 GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
2144 if (GV == 0) return 0;
2146 // Verify that the initializer is simple enough for us to handle. We are
2147 // only allowed to optimize the initializer if it is unique.
2148 if (!GV->hasUniqueInitializer()) return 0;
2150 if (isa<ConstantAggregateZero>(GV->getInitializer()))
2152 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
2154 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
2155 if (isa<ConstantAggregateZero>(*i))
2157 ConstantStruct *CS = cast<ConstantStruct>(*i);
2158 if (isa<ConstantPointerNull>(CS->getOperand(1)))
2161 // Must have a function or null ptr.
2162 if (!isa<Function>(CS->getOperand(1)))
2165 // Init priority must be standard.
2166 ConstantInt *CI = cast<ConstantInt>(CS->getOperand(0));
2167 if (CI->getZExtValue() != 65535)
2174 /// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand,
2175 /// return a list of the functions and null terminator as a vector.
2176 static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) {
2177 if (GV->getInitializer()->isNullValue())
2178 return std::vector<Function*>();
2179 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
2180 std::vector<Function*> Result;
2181 Result.reserve(CA->getNumOperands());
2182 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
2183 ConstantStruct *CS = cast<ConstantStruct>(*i);
2184 Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
2189 /// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the
2190 /// specified array, returning the new global to use.
2191 static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL,
2192 const std::vector<Function*> &Ctors) {
2193 // If we made a change, reassemble the initializer list.
2194 Constant *CSVals[2];
2195 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 65535);
2198 StructType *StructTy =
2200 cast<ArrayType>(GCL->getType()->getElementType())->getElementType());
2202 // Create the new init list.
2203 std::vector<Constant*> CAList;
2204 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) {
2206 CSVals[1] = Ctors[i];
2208 Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()),
2210 PointerType *PFTy = PointerType::getUnqual(FTy);
2211 CSVals[1] = Constant::getNullValue(PFTy);
2212 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()),
2215 CAList.push_back(ConstantStruct::get(StructTy, CSVals));
2218 // Create the array initializer.
2219 Constant *CA = ConstantArray::get(ArrayType::get(StructTy,
2220 CAList.size()), CAList);
2222 // If we didn't change the number of elements, don't create a new GV.
2223 if (CA->getType() == GCL->getInitializer()->getType()) {
2224 GCL->setInitializer(CA);
2228 // Create the new global and insert it next to the existing list.
2229 GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(),
2230 GCL->getLinkage(), CA, "",
2231 GCL->getThreadLocalMode());
2232 GCL->getParent()->getGlobalList().insert(GCL, NGV);
2235 // Nuke the old list, replacing any uses with the new one.
2236 if (!GCL->use_empty()) {
2238 if (V->getType() != GCL->getType())
2239 V = ConstantExpr::getBitCast(V, GCL->getType());
2240 GCL->replaceAllUsesWith(V);
2242 GCL->eraseFromParent();
2252 isSimpleEnoughValueToCommit(Constant *C,
2253 SmallPtrSet<Constant*, 8> &SimpleConstants,
2254 const TargetData *TD);
2257 /// isSimpleEnoughValueToCommit - Return true if the specified constant can be
2258 /// handled by the code generator. We don't want to generate something like:
2259 /// void *X = &X/42;
2260 /// because the code generator doesn't have a relocation that can handle that.
2262 /// This function should be called if C was not found (but just got inserted)
2263 /// in SimpleConstants to avoid having to rescan the same constants all the
2265 static bool isSimpleEnoughValueToCommitHelper(Constant *C,
2266 SmallPtrSet<Constant*, 8> &SimpleConstants,
2267 const TargetData *TD) {
2268 // Simple integer, undef, constant aggregate zero, global addresses, etc are
2270 if (C->getNumOperands() == 0 || isa<BlockAddress>(C) ||
2271 isa<GlobalValue>(C))
2274 // Aggregate values are safe if all their elements are.
2275 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) ||
2276 isa<ConstantVector>(C)) {
2277 for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
2278 Constant *Op = cast<Constant>(C->getOperand(i));
2279 if (!isSimpleEnoughValueToCommit(Op, SimpleConstants, TD))
2285 // We don't know exactly what relocations are allowed in constant expressions,
2286 // so we allow &global+constantoffset, which is safe and uniformly supported
2288 ConstantExpr *CE = cast<ConstantExpr>(C);
2289 switch (CE->getOpcode()) {
2290 case Instruction::BitCast:
2291 // Bitcast is fine if the casted value is fine.
2292 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2294 case Instruction::IntToPtr:
2295 case Instruction::PtrToInt:
2296 // int <=> ptr is fine if the int type is the same size as the
2298 if (!TD || TD->getTypeSizeInBits(CE->getType()) !=
2299 TD->getTypeSizeInBits(CE->getOperand(0)->getType()))
2301 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2303 // GEP is fine if it is simple + constant offset.
2304 case Instruction::GetElementPtr:
2305 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
2306 if (!isa<ConstantInt>(CE->getOperand(i)))
2308 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2310 case Instruction::Add:
2311 // We allow simple+cst.
2312 if (!isa<ConstantInt>(CE->getOperand(1)))
2314 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2320 isSimpleEnoughValueToCommit(Constant *C,
2321 SmallPtrSet<Constant*, 8> &SimpleConstants,
2322 const TargetData *TD) {
2323 // If we already checked this constant, we win.
2324 if (!SimpleConstants.insert(C)) return true;
2325 // Check the constant.
2326 return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, TD);
2330 /// isSimpleEnoughPointerToCommit - Return true if this constant is simple
2331 /// enough for us to understand. In particular, if it is a cast to anything
2332 /// other than from one pointer type to another pointer type, we punt.
2333 /// We basically just support direct accesses to globals and GEP's of
2334 /// globals. This should be kept up to date with CommitValueTo.
2335 static bool isSimpleEnoughPointerToCommit(Constant *C) {
2336 // Conservatively, avoid aggregate types. This is because we don't
2337 // want to worry about them partially overlapping other stores.
2338 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
2341 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
2342 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2343 // external globals.
2344 return GV->hasUniqueInitializer();
2346 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
2347 // Handle a constantexpr gep.
2348 if (CE->getOpcode() == Instruction::GetElementPtr &&
2349 isa<GlobalVariable>(CE->getOperand(0)) &&
2350 cast<GEPOperator>(CE)->isInBounds()) {
2351 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2352 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2353 // external globals.
2354 if (!GV->hasUniqueInitializer())
2357 // The first index must be zero.
2358 ConstantInt *CI = dyn_cast<ConstantInt>(*llvm::next(CE->op_begin()));
2359 if (!CI || !CI->isZero()) return false;
2361 // The remaining indices must be compile-time known integers within the
2362 // notional bounds of the corresponding static array types.
2363 if (!CE->isGEPWithNoNotionalOverIndexing())
2366 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2368 // A constantexpr bitcast from a pointer to another pointer is a no-op,
2369 // and we know how to evaluate it by moving the bitcast from the pointer
2370 // operand to the value operand.
2371 } else if (CE->getOpcode() == Instruction::BitCast &&
2372 isa<GlobalVariable>(CE->getOperand(0))) {
2373 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2374 // external globals.
2375 return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
2382 /// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global
2383 /// initializer. This returns 'Init' modified to reflect 'Val' stored into it.
2384 /// At this point, the GEP operands of Addr [0, OpNo) have been stepped into.
2385 static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
2386 ConstantExpr *Addr, unsigned OpNo) {
2387 // Base case of the recursion.
2388 if (OpNo == Addr->getNumOperands()) {
2389 assert(Val->getType() == Init->getType() && "Type mismatch!");
2393 SmallVector<Constant*, 32> Elts;
2394 if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
2395 // Break up the constant into its elements.
2396 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
2397 Elts.push_back(Init->getAggregateElement(i));
2399 // Replace the element that we are supposed to.
2400 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
2401 unsigned Idx = CU->getZExtValue();
2402 assert(Idx < STy->getNumElements() && "Struct index out of range!");
2403 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
2405 // Return the modified struct.
2406 return ConstantStruct::get(STy, Elts);
2409 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
2410 SequentialType *InitTy = cast<SequentialType>(Init->getType());
2413 if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
2414 NumElts = ATy->getNumElements();
2416 NumElts = InitTy->getVectorNumElements();
2418 // Break up the array into elements.
2419 for (uint64_t i = 0, e = NumElts; i != e; ++i)
2420 Elts.push_back(Init->getAggregateElement(i));
2422 assert(CI->getZExtValue() < NumElts);
2423 Elts[CI->getZExtValue()] =
2424 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
2426 if (Init->getType()->isArrayTy())
2427 return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
2428 return ConstantVector::get(Elts);
2431 /// CommitValueTo - We have decided that Addr (which satisfies the predicate
2432 /// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen.
2433 static void CommitValueTo(Constant *Val, Constant *Addr) {
2434 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
2435 assert(GV->hasInitializer());
2436 GV->setInitializer(Val);
2440 ConstantExpr *CE = cast<ConstantExpr>(Addr);
2441 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2442 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
2447 /// Evaluator - This class evaluates LLVM IR, producing the Constant
2448 /// representing each SSA instruction. Changes to global variables are stored
2449 /// in a mapping that can be iterated over after the evaluation is complete.
2450 /// Once an evaluation call fails, the evaluation object should not be reused.
2453 Evaluator(const TargetData *TD, const TargetLibraryInfo *TLI)
2454 : TD(TD), TLI(TLI) {
2455 ValueStack.push_back(new DenseMap<Value*, Constant*>);
2459 DeleteContainerPointers(ValueStack);
2460 while (!AllocaTmps.empty()) {
2461 GlobalVariable *Tmp = AllocaTmps.back();
2462 AllocaTmps.pop_back();
2464 // If there are still users of the alloca, the program is doing something
2465 // silly, e.g. storing the address of the alloca somewhere and using it
2466 // later. Since this is undefined, we'll just make it be null.
2467 if (!Tmp->use_empty())
2468 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
2473 /// EvaluateFunction - Evaluate a call to function F, returning true if
2474 /// successful, false if we can't evaluate it. ActualArgs contains the formal
2475 /// arguments for the function.
2476 bool EvaluateFunction(Function *F, Constant *&RetVal,
2477 const SmallVectorImpl<Constant*> &ActualArgs);
2479 /// EvaluateBlock - Evaluate all instructions in block BB, returning true if
2480 /// successful, false if we can't evaluate it. NewBB returns the next BB that
2481 /// control flows into, or null upon return.
2482 bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB);
2484 Constant *getVal(Value *V) {
2485 if (Constant *CV = dyn_cast<Constant>(V)) return CV;
2486 Constant *R = ValueStack.back()->lookup(V);
2487 assert(R && "Reference to an uncomputed value!");
2491 void setVal(Value *V, Constant *C) {
2492 ValueStack.back()->operator[](V) = C;
2495 const DenseMap<Constant*, Constant*> &getMutatedMemory() const {
2496 return MutatedMemory;
2499 const SmallPtrSet<GlobalVariable*, 8> &getInvariants() const {
2504 Constant *ComputeLoadResult(Constant *P);
2506 /// ValueStack - As we compute SSA register values, we store their contents
2507 /// here. The back of the vector contains the current function and the stack
2508 /// contains the values in the calling frames.
2509 SmallVector<DenseMap<Value*, Constant*>*, 4> ValueStack;
2511 /// CallStack - This is used to detect recursion. In pathological situations
2512 /// we could hit exponential behavior, but at least there is nothing
2514 SmallVector<Function*, 4> CallStack;
2516 /// MutatedMemory - For each store we execute, we update this map. Loads
2517 /// check this to get the most up-to-date value. If evaluation is successful,
2518 /// this state is committed to the process.
2519 DenseMap<Constant*, Constant*> MutatedMemory;
2521 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable
2522 /// to represent its body. This vector is needed so we can delete the
2523 /// temporary globals when we are done.
2524 SmallVector<GlobalVariable*, 32> AllocaTmps;
2526 /// Invariants - These global variables have been marked invariant by the
2527 /// static constructor.
2528 SmallPtrSet<GlobalVariable*, 8> Invariants;
2530 /// SimpleConstants - These are constants we have checked and know to be
2531 /// simple enough to live in a static initializer of a global.
2532 SmallPtrSet<Constant*, 8> SimpleConstants;
2534 const TargetData *TD;
2535 const TargetLibraryInfo *TLI;
2538 } // anonymous namespace
2540 /// ComputeLoadResult - Return the value that would be computed by a load from
2541 /// P after the stores reflected by 'memory' have been performed. If we can't
2542 /// decide, return null.
2543 Constant *Evaluator::ComputeLoadResult(Constant *P) {
2544 // If this memory location has been recently stored, use the stored value: it
2545 // is the most up-to-date.
2546 DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P);
2547 if (I != MutatedMemory.end()) return I->second;
2550 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
2551 if (GV->hasDefinitiveInitializer())
2552 return GV->getInitializer();
2556 // Handle a constantexpr getelementptr.
2557 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
2558 if (CE->getOpcode() == Instruction::GetElementPtr &&
2559 isa<GlobalVariable>(CE->getOperand(0))) {
2560 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2561 if (GV->hasDefinitiveInitializer())
2562 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2565 return 0; // don't know how to evaluate.
2568 /// EvaluateBlock - Evaluate all instructions in block BB, returning true if
2569 /// successful, false if we can't evaluate it. NewBB returns the next BB that
2570 /// control flows into, or null upon return.
2571 bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst,
2572 BasicBlock *&NextBB) {
2573 // This is the main evaluation loop.
2575 Constant *InstResult = 0;
2577 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
2578 if (!SI->isSimple()) return false; // no volatile/atomic accesses.
2579 Constant *Ptr = getVal(SI->getOperand(1));
2580 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2581 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2582 if (!isSimpleEnoughPointerToCommit(Ptr))
2583 // If this is too complex for us to commit, reject it.
2586 Constant *Val = getVal(SI->getOperand(0));
2588 // If this might be too difficult for the backend to handle (e.g. the addr
2589 // of one global variable divided by another) then we can't commit it.
2590 if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, TD))
2593 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2594 if (CE->getOpcode() == Instruction::BitCast) {
2595 // If we're evaluating a store through a bitcast, then we need
2596 // to pull the bitcast off the pointer type and push it onto the
2598 Ptr = CE->getOperand(0);
2600 Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
2602 // In order to push the bitcast onto the stored value, a bitcast
2603 // from NewTy to Val's type must be legal. If it's not, we can try
2604 // introspecting NewTy to find a legal conversion.
2605 while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
2606 // If NewTy is a struct, we can convert the pointer to the struct
2607 // into a pointer to its first member.
2608 // FIXME: This could be extended to support arrays as well.
2609 if (StructType *STy = dyn_cast<StructType>(NewTy)) {
2610 NewTy = STy->getTypeAtIndex(0U);
2612 IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
2613 Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
2614 Constant * const IdxList[] = {IdxZero, IdxZero};
2616 Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList);
2617 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2618 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2620 // If we can't improve the situation by introspecting NewTy,
2621 // we have to give up.
2627 // If we found compatible types, go ahead and push the bitcast
2628 // onto the stored value.
2629 Val = ConstantExpr::getBitCast(Val, NewTy);
2632 MutatedMemory[Ptr] = Val;
2633 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
2634 InstResult = ConstantExpr::get(BO->getOpcode(),
2635 getVal(BO->getOperand(0)),
2636 getVal(BO->getOperand(1)));
2637 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
2638 InstResult = ConstantExpr::getCompare(CI->getPredicate(),
2639 getVal(CI->getOperand(0)),
2640 getVal(CI->getOperand(1)));
2641 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
2642 InstResult = ConstantExpr::getCast(CI->getOpcode(),
2643 getVal(CI->getOperand(0)),
2645 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
2646 InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
2647 getVal(SI->getOperand(1)),
2648 getVal(SI->getOperand(2)));
2649 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
2650 Constant *P = getVal(GEP->getOperand(0));
2651 SmallVector<Constant*, 8> GEPOps;
2652 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
2654 GEPOps.push_back(getVal(*i));
2656 ConstantExpr::getGetElementPtr(P, GEPOps,
2657 cast<GEPOperator>(GEP)->isInBounds());
2658 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
2659 if (!LI->isSimple()) return false; // no volatile/atomic accesses.
2660 Constant *Ptr = getVal(LI->getOperand(0));
2661 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2662 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2663 InstResult = ComputeLoadResult(Ptr);
2664 if (InstResult == 0) return false; // Could not evaluate load.
2665 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
2666 if (AI->isArrayAllocation()) return false; // Cannot handle array allocs.
2667 Type *Ty = AI->getType()->getElementType();
2668 AllocaTmps.push_back(new GlobalVariable(Ty, false,
2669 GlobalValue::InternalLinkage,
2670 UndefValue::get(Ty),
2672 InstResult = AllocaTmps.back();
2673 } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
2674 CallSite CS(CurInst);
2676 // Debug info can safely be ignored here.
2677 if (isa<DbgInfoIntrinsic>(CS.getInstruction())) {
2682 // Cannot handle inline asm.
2683 if (isa<InlineAsm>(CS.getCalledValue())) return false;
2685 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
2686 if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
2687 if (MSI->isVolatile()) return false;
2688 Constant *Ptr = getVal(MSI->getDest());
2689 Constant *Val = getVal(MSI->getValue());
2690 Constant *DestVal = ComputeLoadResult(getVal(Ptr));
2691 if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
2692 // This memset is a no-op.
2698 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
2699 II->getIntrinsicID() == Intrinsic::lifetime_end) {
2704 if (II->getIntrinsicID() == Intrinsic::invariant_start) {
2705 // We don't insert an entry into Values, as it doesn't have a
2706 // meaningful return value.
2707 if (!II->use_empty())
2709 ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
2710 Value *PtrArg = getVal(II->getArgOperand(1));
2711 Value *Ptr = PtrArg->stripPointerCasts();
2712 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
2713 Type *ElemTy = cast<PointerType>(GV->getType())->getElementType();
2714 if (!Size->isAllOnesValue() &&
2715 Size->getValue().getLimitedValue() >=
2716 TD->getTypeStoreSize(ElemTy))
2717 Invariants.insert(GV);
2719 // Continue even if we do nothing.
2726 // Resolve function pointers.
2727 Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue()));
2728 if (!Callee || Callee->mayBeOverridden())
2729 return false; // Cannot resolve.
2731 SmallVector<Constant*, 8> Formals;
2732 for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
2733 Formals.push_back(getVal(*i));
2735 if (Callee->isDeclaration()) {
2736 // If this is a function we can constant fold, do it.
2737 if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) {
2743 if (Callee->getFunctionType()->isVarArg())
2747 // Execute the call, if successful, use the return value.
2748 ValueStack.push_back(new DenseMap<Value*, Constant*>);
2749 if (!EvaluateFunction(Callee, RetVal, Formals))
2751 delete ValueStack.pop_back_val();
2752 InstResult = RetVal;
2754 } else if (isa<TerminatorInst>(CurInst)) {
2755 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
2756 if (BI->isUnconditional()) {
2757 NextBB = BI->getSuccessor(0);
2760 dyn_cast<ConstantInt>(getVal(BI->getCondition()));
2761 if (!Cond) return false; // Cannot determine.
2763 NextBB = BI->getSuccessor(!Cond->getZExtValue());
2765 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
2767 dyn_cast<ConstantInt>(getVal(SI->getCondition()));
2768 if (!Val) return false; // Cannot determine.
2769 NextBB = SI->findCaseValue(Val).getCaseSuccessor();
2770 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
2771 Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
2772 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
2773 NextBB = BA->getBasicBlock();
2775 return false; // Cannot determine.
2776 } else if (isa<ReturnInst>(CurInst)) {
2779 // invoke, unwind, resume, unreachable.
2780 return false; // Cannot handle this terminator.
2783 // We succeeded at evaluating this block!
2786 // Did not know how to evaluate this!
2790 if (!CurInst->use_empty()) {
2791 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
2792 InstResult = ConstantFoldConstantExpression(CE, TD, TLI);
2794 setVal(CurInst, InstResult);
2797 // If we just processed an invoke, we finished evaluating the block.
2798 if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
2799 NextBB = II->getNormalDest();
2803 // Advance program counter.
2808 /// EvaluateFunction - Evaluate a call to function F, returning true if
2809 /// successful, false if we can't evaluate it. ActualArgs contains the formal
2810 /// arguments for the function.
2811 bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal,
2812 const SmallVectorImpl<Constant*> &ActualArgs) {
2813 // Check to see if this function is already executing (recursion). If so,
2814 // bail out. TODO: we might want to accept limited recursion.
2815 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
2818 CallStack.push_back(F);
2820 // Initialize arguments to the incoming values specified.
2822 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
2824 setVal(AI, ActualArgs[ArgNo]);
2826 // ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
2827 // we can only evaluate any one basic block at most once. This set keeps
2828 // track of what we have executed so we can detect recursive cases etc.
2829 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
2831 // CurBB - The current basic block we're evaluating.
2832 BasicBlock *CurBB = F->begin();
2834 BasicBlock::iterator CurInst = CurBB->begin();
2837 BasicBlock *NextBB = 0; // Initialized to avoid compiler warnings.
2838 if (!EvaluateBlock(CurInst, NextBB))
2842 // Successfully running until there's no next block means that we found
2843 // the return. Fill it the return value and pop the call stack.
2844 ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
2845 if (RI->getNumOperands())
2846 RetVal = getVal(RI->getOperand(0));
2847 CallStack.pop_back();
2851 // Okay, we succeeded in evaluating this control flow. See if we have
2852 // executed the new block before. If so, we have a looping function,
2853 // which we cannot evaluate in reasonable time.
2854 if (!ExecutedBlocks.insert(NextBB))
2855 return false; // looped!
2857 // Okay, we have never been in this block before. Check to see if there
2858 // are any PHI nodes. If so, evaluate them with information about where
2861 for (CurInst = NextBB->begin();
2862 (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
2863 setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
2865 // Advance to the next block.
2870 /// EvaluateStaticConstructor - Evaluate static constructors in the function, if
2871 /// we can. Return true if we can, false otherwise.
2872 static bool EvaluateStaticConstructor(Function *F, const TargetData *TD,
2873 const TargetLibraryInfo *TLI) {
2874 // Call the function.
2875 Evaluator Eval(TD, TLI);
2876 Constant *RetValDummy;
2877 bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy,
2878 SmallVector<Constant*, 0>());
2881 // We succeeded at evaluation: commit the result.
2882 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
2883 << F->getName() << "' to " << Eval.getMutatedMemory().size()
2885 for (DenseMap<Constant*, Constant*>::const_iterator I =
2886 Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end();
2888 CommitValueTo(I->second, I->first);
2889 for (SmallPtrSet<GlobalVariable*, 8>::const_iterator I =
2890 Eval.getInvariants().begin(), E = Eval.getInvariants().end();
2892 (*I)->setConstant(true);
2898 /// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible.
2899 /// Return true if anything changed.
2900 bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) {
2901 std::vector<Function*> Ctors = ParseGlobalCtors(GCL);
2902 bool MadeChange = false;
2903 if (Ctors.empty()) return false;
2905 // Loop over global ctors, optimizing them when we can.
2906 for (unsigned i = 0; i != Ctors.size(); ++i) {
2907 Function *F = Ctors[i];
2908 // Found a null terminator in the middle of the list, prune off the rest of
2911 if (i != Ctors.size()-1) {
2918 // We cannot simplify external ctor functions.
2919 if (F->empty()) continue;
2921 // If we can evaluate the ctor at compile time, do.
2922 if (EvaluateStaticConstructor(F, TD, TLI)) {
2923 Ctors.erase(Ctors.begin()+i);
2926 ++NumCtorsEvaluated;
2931 if (!MadeChange) return false;
2933 GCL = InstallGlobalCtors(GCL, Ctors);
2937 bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
2938 bool Changed = false;
2940 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
2942 Module::alias_iterator J = I++;
2943 // Aliases without names cannot be referenced outside this module.
2944 if (!J->hasName() && !J->isDeclaration())
2945 J->setLinkage(GlobalValue::InternalLinkage);
2946 // If the aliasee may change at link time, nothing can be done - bail out.
2947 if (J->mayBeOverridden())
2950 Constant *Aliasee = J->getAliasee();
2951 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
2952 Target->removeDeadConstantUsers();
2953 bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse();
2955 // Make all users of the alias use the aliasee instead.
2956 if (!J->use_empty()) {
2957 J->replaceAllUsesWith(Aliasee);
2958 ++NumAliasesResolved;
2962 // If the alias is externally visible, we may still be able to simplify it.
2963 if (!J->hasLocalLinkage()) {
2964 // If the aliasee has internal linkage, give it the name and linkage
2965 // of the alias, and delete the alias. This turns:
2966 // define internal ... @f(...)
2967 // @a = alias ... @f
2969 // define ... @a(...)
2970 if (!Target->hasLocalLinkage())
2973 // Do not perform the transform if multiple aliases potentially target the
2974 // aliasee. This check also ensures that it is safe to replace the section
2975 // and other attributes of the aliasee with those of the alias.
2979 // Give the aliasee the name, linkage and other attributes of the alias.
2980 Target->takeName(J);
2981 Target->setLinkage(J->getLinkage());
2982 Target->GlobalValue::copyAttributesFrom(J);
2985 // Delete the alias.
2986 M.getAliasList().erase(J);
2987 ++NumAliasesRemoved;
2994 static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) {
2995 if (!TLI->has(LibFunc::cxa_atexit))
2998 Function *Fn = M.getFunction(TLI->getName(LibFunc::cxa_atexit));
3003 FunctionType *FTy = Fn->getFunctionType();
3005 // Checking that the function has the right return type, the right number of
3006 // parameters and that they all have pointer types should be enough.
3007 if (!FTy->getReturnType()->isIntegerTy() ||
3008 FTy->getNumParams() != 3 ||
3009 !FTy->getParamType(0)->isPointerTy() ||
3010 !FTy->getParamType(1)->isPointerTy() ||
3011 !FTy->getParamType(2)->isPointerTy())
3017 /// cxxDtorIsEmpty - Returns whether the given function is an empty C++
3018 /// destructor and can therefore be eliminated.
3019 /// Note that we assume that other optimization passes have already simplified
3020 /// the code so we only look for a function with a single basic block, where
3021 /// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and
3022 /// other side-effect free instructions.
3023 static bool cxxDtorIsEmpty(const Function &Fn,
3024 SmallPtrSet<const Function *, 8> &CalledFunctions) {
3025 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
3026 // nounwind, but that doesn't seem worth doing.
3027 if (Fn.isDeclaration())
3030 if (++Fn.begin() != Fn.end())
3033 const BasicBlock &EntryBlock = Fn.getEntryBlock();
3034 for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
3036 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
3037 // Ignore debug intrinsics.
3038 if (isa<DbgInfoIntrinsic>(CI))
3041 const Function *CalledFn = CI->getCalledFunction();
3046 SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
3048 // Don't treat recursive functions as empty.
3049 if (!NewCalledFunctions.insert(CalledFn))
3052 if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
3054 } else if (isa<ReturnInst>(*I))
3055 return true; // We're done.
3056 else if (I->mayHaveSideEffects())
3057 return false; // Destructor with side effects, bail.
3063 bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
3064 /// Itanium C++ ABI p3.3.5:
3066 /// After constructing a global (or local static) object, that will require
3067 /// destruction on exit, a termination function is registered as follows:
3069 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
3071 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
3072 /// call f(p) when DSO d is unloaded, before all such termination calls
3073 /// registered before this one. It returns zero if registration is
3074 /// successful, nonzero on failure.
3076 // This pass will look for calls to __cxa_atexit where the function is trivial
3078 bool Changed = false;
3080 for (Function::use_iterator I = CXAAtExitFn->use_begin(),
3081 E = CXAAtExitFn->use_end(); I != E;) {
3082 // We're only interested in calls. Theoretically, we could handle invoke
3083 // instructions as well, but neither llvm-gcc nor clang generate invokes
3085 CallInst *CI = dyn_cast<CallInst>(*I++);
3090 dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
3094 SmallPtrSet<const Function *, 8> CalledFunctions;
3095 if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
3098 // Just remove the call.
3099 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
3100 CI->eraseFromParent();
3102 ++NumCXXDtorsRemoved;
3110 bool GlobalOpt::runOnModule(Module &M) {
3111 bool Changed = false;
3113 TD = getAnalysisIfAvailable<TargetData>();
3114 TLI = &getAnalysis<TargetLibraryInfo>();
3116 // Try to find the llvm.globalctors list.
3117 GlobalVariable *GlobalCtors = FindGlobalCtors(M);
3119 Function *CXAAtExitFn = FindCXAAtExit(M, TLI);
3121 bool LocalChange = true;
3122 while (LocalChange) {
3123 LocalChange = false;
3125 // Delete functions that are trivially dead, ccc -> fastcc
3126 LocalChange |= OptimizeFunctions(M);
3128 // Optimize global_ctors list.
3130 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors);
3132 // Optimize non-address-taken globals.
3133 LocalChange |= OptimizeGlobalVars(M);
3135 // Resolve aliases, when possible.
3136 LocalChange |= OptimizeGlobalAliases(M);
3138 // Try to remove trivial global destructors.
3140 LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
3142 Changed |= LocalChange;
3145 // TODO: Move all global ctors functions to the end of the module for code