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, const TargetLibraryInfo *TLI) {
351 if (isa<Constant>(V))
355 if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) ||
358 if (isAllocationFn(V, TLI))
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 const TargetLibraryInfo *TLI) {
381 // A brief explanation of leak checkers. The goal is to find bugs where
382 // pointers are forgotten, causing an accumulating growth in memory
383 // usage over time. The common strategy for leak checkers is to whitelist the
384 // memory pointed to by globals at exit. This is popular because it also
385 // solves another problem where the main thread of a C++ program may shut down
386 // before other threads that are still expecting to use those globals. To
387 // handle that case, we expect the program may create a singleton and never
390 bool Changed = false;
392 // If Dead[n].first is the only use of a malloc result, we can delete its
393 // chain of computation and the store to the global in Dead[n].second.
394 SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
396 // Constants can't be pointers to dynamically allocated memory.
397 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
400 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
401 Value *V = SI->getValueOperand();
402 if (isa<Constant>(V)) {
404 SI->eraseFromParent();
405 } else if (Instruction *I = dyn_cast<Instruction>(V)) {
407 Dead.push_back(std::make_pair(I, SI));
409 } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
410 if (isa<Constant>(MSI->getValue())) {
412 MSI->eraseFromParent();
413 } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
415 Dead.push_back(std::make_pair(I, MSI));
417 } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
418 GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
419 if (MemSrc && MemSrc->isConstant()) {
421 MTI->eraseFromParent();
422 } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) {
424 Dead.push_back(std::make_pair(I, MTI));
426 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
427 if (CE->use_empty()) {
428 CE->destroyConstant();
431 } else if (Constant *C = dyn_cast<Constant>(U)) {
432 if (SafeToDestroyConstant(C)) {
433 C->destroyConstant();
434 // This could have invalidated UI, start over from scratch.
436 CleanupPointerRootUsers(GV, TLI);
442 for (int i = 0, e = Dead.size(); i != e; ++i) {
443 if (IsSafeComputationToRemove(Dead[i].first, TLI)) {
444 Dead[i].second->eraseFromParent();
445 Instruction *I = Dead[i].first;
447 if (isAllocationFn(I, TLI))
449 Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
452 I->eraseFromParent();
455 I->eraseFromParent();
462 /// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all
463 /// users of the global, cleaning up the obvious ones. This is largely just a
464 /// quick scan over the use list to clean up the easy and obvious cruft. This
465 /// returns true if it made a change.
466 static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
467 TargetData *TD, TargetLibraryInfo *TLI) {
468 bool Changed = false;
469 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) {
472 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
474 // Replace the load with the initializer.
475 LI->replaceAllUsesWith(Init);
476 LI->eraseFromParent();
479 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
480 // Store must be unreachable or storing Init into the global.
481 SI->eraseFromParent();
483 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
484 if (CE->getOpcode() == Instruction::GetElementPtr) {
485 Constant *SubInit = 0;
487 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
488 Changed |= CleanupConstantGlobalUsers(CE, SubInit, TD, TLI);
489 } else if (CE->getOpcode() == Instruction::BitCast &&
490 CE->getType()->isPointerTy()) {
491 // Pointer cast, delete any stores and memsets to the global.
492 Changed |= CleanupConstantGlobalUsers(CE, 0, TD, TLI);
495 if (CE->use_empty()) {
496 CE->destroyConstant();
499 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
500 // Do not transform "gepinst (gep constexpr (GV))" here, because forming
501 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
502 // and will invalidate our notion of what Init is.
503 Constant *SubInit = 0;
504 if (!isa<ConstantExpr>(GEP->getOperand(0))) {
506 dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, TD, TLI));
507 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
508 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
510 // If the initializer is an all-null value and we have an inbounds GEP,
511 // we already know what the result of any load from that GEP is.
512 // TODO: Handle splats.
513 if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
514 SubInit = Constant::getNullValue(GEP->getType()->getElementType());
516 Changed |= CleanupConstantGlobalUsers(GEP, SubInit, TD, TLI);
518 if (GEP->use_empty()) {
519 GEP->eraseFromParent();
522 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
523 if (MI->getRawDest() == V) {
524 MI->eraseFromParent();
528 } else if (Constant *C = dyn_cast<Constant>(U)) {
529 // If we have a chain of dead constantexprs or other things dangling from
530 // us, and if they are all dead, nuke them without remorse.
531 if (SafeToDestroyConstant(C)) {
532 C->destroyConstant();
533 // This could have invalidated UI, start over from scratch.
534 CleanupConstantGlobalUsers(V, Init, TD, TLI);
542 /// isSafeSROAElementUse - Return true if the specified instruction is a safe
543 /// user of a derived expression from a global that we want to SROA.
544 static bool isSafeSROAElementUse(Value *V) {
545 // We might have a dead and dangling constant hanging off of here.
546 if (Constant *C = dyn_cast<Constant>(V))
547 return SafeToDestroyConstant(C);
549 Instruction *I = dyn_cast<Instruction>(V);
550 if (!I) return false;
553 if (isa<LoadInst>(I)) return true;
555 // Stores *to* the pointer are ok.
556 if (StoreInst *SI = dyn_cast<StoreInst>(I))
557 return SI->getOperand(0) != V;
559 // Otherwise, it must be a GEP.
560 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
561 if (GEPI == 0) return false;
563 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
564 !cast<Constant>(GEPI->getOperand(1))->isNullValue())
567 for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end();
569 if (!isSafeSROAElementUse(*I))
575 /// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value.
576 /// Look at it and its uses and decide whether it is safe to SROA this global.
578 static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
579 // The user of the global must be a GEP Inst or a ConstantExpr GEP.
580 if (!isa<GetElementPtrInst>(U) &&
581 (!isa<ConstantExpr>(U) ||
582 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
585 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we
586 // don't like < 3 operand CE's, and we don't like non-constant integer
587 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
589 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
590 !cast<Constant>(U->getOperand(1))->isNullValue() ||
591 !isa<ConstantInt>(U->getOperand(2)))
594 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
595 ++GEPI; // Skip over the pointer index.
597 // If this is a use of an array allocation, do a bit more checking for sanity.
598 if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
599 uint64_t NumElements = AT->getNumElements();
600 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
602 // Check to make sure that index falls within the array. If not,
603 // something funny is going on, so we won't do the optimization.
605 if (Idx->getZExtValue() >= NumElements)
608 // We cannot scalar repl this level of the array unless any array
609 // sub-indices are in-range constants. In particular, consider:
610 // A[0][i]. We cannot know that the user isn't doing invalid things like
611 // allowing i to index an out-of-range subscript that accesses A[1].
613 // Scalar replacing *just* the outer index of the array is probably not
614 // going to be a win anyway, so just give up.
615 for (++GEPI; // Skip array index.
618 uint64_t NumElements;
619 if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
620 NumElements = SubArrayTy->getNumElements();
621 else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
622 NumElements = SubVectorTy->getNumElements();
624 assert((*GEPI)->isStructTy() &&
625 "Indexed GEP type is not array, vector, or struct!");
629 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
630 if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
635 for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I)
636 if (!isSafeSROAElementUse(*I))
641 /// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it
642 /// is safe for us to perform this transformation.
644 static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
645 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
647 if (!IsUserOfGlobalSafeForSRA(*UI, GV))
654 /// SRAGlobal - Perform scalar replacement of aggregates on the specified global
655 /// variable. This opens the door for other optimizations by exposing the
656 /// behavior of the program in a more fine-grained way. We have determined that
657 /// this transformation is safe already. We return the first global variable we
658 /// insert so that the caller can reprocess it.
659 static GlobalVariable *SRAGlobal(GlobalVariable *GV, const TargetData &TD) {
660 // Make sure this global only has simple uses that we can SRA.
661 if (!GlobalUsersSafeToSRA(GV))
664 assert(GV->hasLocalLinkage() && !GV->isConstant());
665 Constant *Init = GV->getInitializer();
666 Type *Ty = Init->getType();
668 std::vector<GlobalVariable*> NewGlobals;
669 Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
671 // Get the alignment of the global, either explicit or target-specific.
672 unsigned StartAlignment = GV->getAlignment();
673 if (StartAlignment == 0)
674 StartAlignment = TD.getABITypeAlignment(GV->getType());
676 if (StructType *STy = dyn_cast<StructType>(Ty)) {
677 NewGlobals.reserve(STy->getNumElements());
678 const StructLayout &Layout = *TD.getStructLayout(STy);
679 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
680 Constant *In = Init->getAggregateElement(i);
681 assert(In && "Couldn't get element of initializer?");
682 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
683 GlobalVariable::InternalLinkage,
684 In, GV->getName()+"."+Twine(i),
685 GV->getThreadLocalMode(),
686 GV->getType()->getAddressSpace());
687 Globals.insert(GV, NGV);
688 NewGlobals.push_back(NGV);
690 // Calculate the known alignment of the field. If the original aggregate
691 // had 256 byte alignment for example, something might depend on that:
692 // propagate info to each field.
693 uint64_t FieldOffset = Layout.getElementOffset(i);
694 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
695 if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i)))
696 NGV->setAlignment(NewAlign);
698 } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
699 unsigned NumElements = 0;
700 if (ArrayType *ATy = dyn_cast<ArrayType>(STy))
701 NumElements = ATy->getNumElements();
703 NumElements = cast<VectorType>(STy)->getNumElements();
705 if (NumElements > 16 && GV->hasNUsesOrMore(16))
706 return 0; // It's not worth it.
707 NewGlobals.reserve(NumElements);
709 uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType());
710 unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType());
711 for (unsigned i = 0, e = NumElements; i != e; ++i) {
712 Constant *In = Init->getAggregateElement(i);
713 assert(In && "Couldn't get element of initializer?");
715 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
716 GlobalVariable::InternalLinkage,
717 In, GV->getName()+"."+Twine(i),
718 GV->getThreadLocalMode(),
719 GV->getType()->getAddressSpace());
720 Globals.insert(GV, NGV);
721 NewGlobals.push_back(NGV);
723 // Calculate the known alignment of the field. If the original aggregate
724 // had 256 byte alignment for example, something might depend on that:
725 // propagate info to each field.
726 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
727 if (NewAlign > EltAlign)
728 NGV->setAlignment(NewAlign);
732 if (NewGlobals.empty())
735 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV);
737 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
739 // Loop over all of the uses of the global, replacing the constantexpr geps,
740 // with smaller constantexpr geps or direct references.
741 while (!GV->use_empty()) {
742 User *GEP = GV->use_back();
743 assert(((isa<ConstantExpr>(GEP) &&
744 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
745 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
747 // Ignore the 1th operand, which has to be zero or else the program is quite
748 // broken (undefined). Get the 2nd operand, which is the structure or array
750 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
751 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
753 Value *NewPtr = NewGlobals[Val];
755 // Form a shorter GEP if needed.
756 if (GEP->getNumOperands() > 3) {
757 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
758 SmallVector<Constant*, 8> Idxs;
759 Idxs.push_back(NullInt);
760 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
761 Idxs.push_back(CE->getOperand(i));
762 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs);
764 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
765 SmallVector<Value*, 8> Idxs;
766 Idxs.push_back(NullInt);
767 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
768 Idxs.push_back(GEPI->getOperand(i));
769 NewPtr = GetElementPtrInst::Create(NewPtr, Idxs,
770 GEPI->getName()+"."+Twine(Val),GEPI);
773 GEP->replaceAllUsesWith(NewPtr);
775 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
776 GEPI->eraseFromParent();
778 cast<ConstantExpr>(GEP)->destroyConstant();
781 // Delete the old global, now that it is dead.
785 // Loop over the new globals array deleting any globals that are obviously
786 // dead. This can arise due to scalarization of a structure or an array that
787 // has elements that are dead.
788 unsigned FirstGlobal = 0;
789 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
790 if (NewGlobals[i]->use_empty()) {
791 Globals.erase(NewGlobals[i]);
792 if (FirstGlobal == i) ++FirstGlobal;
795 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0;
798 /// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified
799 /// value will trap if the value is dynamically null. PHIs keeps track of any
800 /// phi nodes we've seen to avoid reprocessing them.
801 static bool AllUsesOfValueWillTrapIfNull(const Value *V,
802 SmallPtrSet<const PHINode*, 8> &PHIs) {
803 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
807 if (isa<LoadInst>(U)) {
809 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
810 if (SI->getOperand(0) == V) {
811 //cerr << "NONTRAPPING USE: " << *U;
812 return false; // Storing the value.
814 } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
815 if (CI->getCalledValue() != V) {
816 //cerr << "NONTRAPPING USE: " << *U;
817 return false; // Not calling the ptr
819 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
820 if (II->getCalledValue() != V) {
821 //cerr << "NONTRAPPING USE: " << *U;
822 return false; // Not calling the ptr
824 } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
825 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
826 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
827 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
828 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
829 // If we've already seen this phi node, ignore it, it has already been
831 if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
833 } else if (isa<ICmpInst>(U) &&
834 isa<ConstantPointerNull>(UI->getOperand(1))) {
835 // Ignore icmp X, null
837 //cerr << "NONTRAPPING USE: " << *U;
844 /// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads
845 /// from GV will trap if the loaded value is null. Note that this also permits
846 /// comparisons of the loaded value against null, as a special case.
847 static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
848 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
852 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
853 SmallPtrSet<const PHINode*, 8> PHIs;
854 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
856 } else if (isa<StoreInst>(U)) {
857 // Ignore stores to the global.
859 // We don't know or understand this user, bail out.
860 //cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
867 static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
868 bool Changed = false;
869 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) {
870 Instruction *I = cast<Instruction>(*UI++);
871 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
872 LI->setOperand(0, NewV);
874 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
875 if (SI->getOperand(1) == V) {
876 SI->setOperand(1, NewV);
879 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
881 if (CS.getCalledValue() == V) {
882 // Calling through the pointer! Turn into a direct call, but be careful
883 // that the pointer is not also being passed as an argument.
884 CS.setCalledFunction(NewV);
886 bool PassedAsArg = false;
887 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
888 if (CS.getArgument(i) == V) {
890 CS.setArgument(i, NewV);
894 // Being passed as an argument also. Be careful to not invalidate UI!
898 } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
899 Changed |= OptimizeAwayTrappingUsesOfValue(CI,
900 ConstantExpr::getCast(CI->getOpcode(),
901 NewV, CI->getType()));
902 if (CI->use_empty()) {
904 CI->eraseFromParent();
906 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
907 // Should handle GEP here.
908 SmallVector<Constant*, 8> Idxs;
909 Idxs.reserve(GEPI->getNumOperands()-1);
910 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
912 if (Constant *C = dyn_cast<Constant>(*i))
916 if (Idxs.size() == GEPI->getNumOperands()-1)
917 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
918 ConstantExpr::getGetElementPtr(NewV, Idxs));
919 if (GEPI->use_empty()) {
921 GEPI->eraseFromParent();
930 /// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null
931 /// value stored into it. If there are uses of the loaded value that would trap
932 /// if the loaded value is dynamically null, then we know that they cannot be
933 /// reachable with a null optimize away the load.
934 static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV,
936 TargetLibraryInfo *TLI) {
937 bool Changed = false;
939 // Keep track of whether we are able to remove all the uses of the global
940 // other than the store that defines it.
941 bool AllNonStoreUsesGone = true;
943 // Replace all uses of loads with uses of uses of the stored value.
944 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){
945 User *GlobalUser = *GUI++;
946 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
947 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
948 // If we were able to delete all uses of the loads
949 if (LI->use_empty()) {
950 LI->eraseFromParent();
953 AllNonStoreUsesGone = false;
955 } else if (isa<StoreInst>(GlobalUser)) {
956 // Ignore the store that stores "LV" to the global.
957 assert(GlobalUser->getOperand(1) == GV &&
958 "Must be storing *to* the global");
960 AllNonStoreUsesGone = false;
962 // If we get here we could have other crazy uses that are transitively
964 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
965 isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser)) &&
966 "Only expect load and stores!");
971 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV);
975 // If we nuked all of the loads, then none of the stores are needed either,
976 // nor is the global.
977 if (AllNonStoreUsesGone) {
978 if (isLeakCheckerRoot(GV)) {
979 Changed |= CleanupPointerRootUsers(GV, TLI);
982 CleanupConstantGlobalUsers(GV, 0, TD, TLI);
984 if (GV->use_empty()) {
985 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
987 GV->eraseFromParent();
994 /// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
995 /// instructions that are foldable.
996 static void ConstantPropUsersOf(Value *V,
997 TargetData *TD, TargetLibraryInfo *TLI) {
998 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; )
999 if (Instruction *I = dyn_cast<Instruction>(*UI++))
1000 if (Constant *NewC = ConstantFoldInstruction(I, TD, TLI)) {
1001 I->replaceAllUsesWith(NewC);
1003 // Advance UI to the next non-I use to avoid invalidating it!
1004 // Instructions could multiply use V.
1005 while (UI != E && *UI == I)
1007 I->eraseFromParent();
1011 /// OptimizeGlobalAddressOfMalloc - This function takes the specified global
1012 /// variable, and transforms the program as if it always contained the result of
1013 /// the specified malloc. Because it is always the result of the specified
1014 /// malloc, there is no reason to actually DO the malloc. Instead, turn the
1015 /// malloc into a global, and any loads of GV as uses of the new global.
1016 static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
1019 ConstantInt *NElements,
1021 TargetLibraryInfo *TLI) {
1022 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n');
1025 if (NElements->getZExtValue() == 1)
1026 GlobalType = AllocTy;
1028 // If we have an array allocation, the global variable is of an array.
1029 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
1031 // Create the new global variable. The contents of the malloc'd memory is
1032 // undefined, so initialize with an undef value.
1033 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(),
1035 GlobalValue::InternalLinkage,
1036 UndefValue::get(GlobalType),
1037 GV->getName()+".body",
1039 GV->getThreadLocalMode());
1041 // If there are bitcast users of the malloc (which is typical, usually we have
1042 // a malloc + bitcast) then replace them with uses of the new global. Update
1043 // other users to use the global as well.
1044 BitCastInst *TheBC = 0;
1045 while (!CI->use_empty()) {
1046 Instruction *User = cast<Instruction>(CI->use_back());
1047 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
1048 if (BCI->getType() == NewGV->getType()) {
1049 BCI->replaceAllUsesWith(NewGV);
1050 BCI->eraseFromParent();
1052 BCI->setOperand(0, NewGV);
1056 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
1057 User->replaceUsesOfWith(CI, TheBC);
1061 Constant *RepValue = NewGV;
1062 if (NewGV->getType() != GV->getType()->getElementType())
1063 RepValue = ConstantExpr::getBitCast(RepValue,
1064 GV->getType()->getElementType());
1066 // If there is a comparison against null, we will insert a global bool to
1067 // keep track of whether the global was initialized yet or not.
1068 GlobalVariable *InitBool =
1069 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
1070 GlobalValue::InternalLinkage,
1071 ConstantInt::getFalse(GV->getContext()),
1072 GV->getName()+".init", GV->getThreadLocalMode());
1073 bool InitBoolUsed = false;
1075 // Loop over all uses of GV, processing them in turn.
1076 while (!GV->use_empty()) {
1077 if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) {
1078 // The global is initialized when the store to it occurs.
1079 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
1080 SI->getOrdering(), SI->getSynchScope(), SI);
1081 SI->eraseFromParent();
1085 LoadInst *LI = cast<LoadInst>(GV->use_back());
1086 while (!LI->use_empty()) {
1087 Use &LoadUse = LI->use_begin().getUse();
1088 if (!isa<ICmpInst>(LoadUse.getUser())) {
1093 ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser());
1094 // Replace the cmp X, 0 with a use of the bool value.
1095 // Sink the load to where the compare was, if atomic rules allow us to.
1096 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
1097 LI->getOrdering(), LI->getSynchScope(),
1098 LI->isUnordered() ? (Instruction*)ICI : LI);
1099 InitBoolUsed = true;
1100 switch (ICI->getPredicate()) {
1101 default: llvm_unreachable("Unknown ICmp Predicate!");
1102 case ICmpInst::ICMP_ULT:
1103 case ICmpInst::ICMP_SLT: // X < null -> always false
1104 LV = ConstantInt::getFalse(GV->getContext());
1106 case ICmpInst::ICMP_ULE:
1107 case ICmpInst::ICMP_SLE:
1108 case ICmpInst::ICMP_EQ:
1109 LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
1111 case ICmpInst::ICMP_NE:
1112 case ICmpInst::ICMP_UGE:
1113 case ICmpInst::ICMP_SGE:
1114 case ICmpInst::ICMP_UGT:
1115 case ICmpInst::ICMP_SGT:
1116 break; // no change.
1118 ICI->replaceAllUsesWith(LV);
1119 ICI->eraseFromParent();
1121 LI->eraseFromParent();
1124 // If the initialization boolean was used, insert it, otherwise delete it.
1125 if (!InitBoolUsed) {
1126 while (!InitBool->use_empty()) // Delete initializations
1127 cast<StoreInst>(InitBool->use_back())->eraseFromParent();
1130 GV->getParent()->getGlobalList().insert(GV, InitBool);
1132 // Now the GV is dead, nuke it and the malloc..
1133 GV->eraseFromParent();
1134 CI->eraseFromParent();
1136 // To further other optimizations, loop over all users of NewGV and try to
1137 // constant prop them. This will promote GEP instructions with constant
1138 // indices into GEP constant-exprs, which will allow global-opt to hack on it.
1139 ConstantPropUsersOf(NewGV, TD, TLI);
1140 if (RepValue != NewGV)
1141 ConstantPropUsersOf(RepValue, TD, TLI);
1146 /// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking
1147 /// to make sure that there are no complex uses of V. We permit simple things
1148 /// like dereferencing the pointer, but not storing through the address, unless
1149 /// it is to the specified global.
1150 static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
1151 const GlobalVariable *GV,
1152 SmallPtrSet<const PHINode*, 8> &PHIs) {
1153 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end();
1155 const Instruction *Inst = cast<Instruction>(*UI);
1157 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
1158 continue; // Fine, ignore.
1161 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
1162 if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
1163 return false; // Storing the pointer itself... bad.
1164 continue; // Otherwise, storing through it, or storing into GV... fine.
1167 // Must index into the array and into the struct.
1168 if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
1169 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
1174 if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
1175 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI
1177 if (PHIs.insert(PN))
1178 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
1183 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
1184 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
1194 /// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV
1195 /// somewhere. Transform all uses of the allocation into loads from the
1196 /// global and uses of the resultant pointer. Further, delete the store into
1197 /// GV. This assumes that these value pass the
1198 /// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
1199 static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc,
1200 GlobalVariable *GV) {
1201 while (!Alloc->use_empty()) {
1202 Instruction *U = cast<Instruction>(*Alloc->use_begin());
1203 Instruction *InsertPt = U;
1204 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
1205 // If this is the store of the allocation into the global, remove it.
1206 if (SI->getOperand(1) == GV) {
1207 SI->eraseFromParent();
1210 } else if (PHINode *PN = dyn_cast<PHINode>(U)) {
1211 // Insert the load in the corresponding predecessor, not right before the
1213 InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator();
1214 } else if (isa<BitCastInst>(U)) {
1215 // Must be bitcast between the malloc and store to initialize the global.
1216 ReplaceUsesOfMallocWithGlobal(U, GV);
1217 U->eraseFromParent();
1219 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
1220 // If this is a "GEP bitcast" and the user is a store to the global, then
1221 // just process it as a bitcast.
1222 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse())
1223 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back()))
1224 if (SI->getOperand(1) == GV) {
1225 // Must be bitcast GEP between the malloc and store to initialize
1227 ReplaceUsesOfMallocWithGlobal(GEPI, GV);
1228 GEPI->eraseFromParent();
1233 // Insert a load from the global, and use it instead of the malloc.
1234 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt);
1235 U->replaceUsesOfWith(Alloc, NL);
1239 /// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi
1240 /// of a load) are simple enough to perform heap SRA on. This permits GEP's
1241 /// that index through the array and struct field, icmps of null, and PHIs.
1242 static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
1243 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs,
1244 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) {
1245 // We permit two users of the load: setcc comparing against the null
1246 // pointer, and a getelementptr of a specific form.
1247 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
1249 const Instruction *User = cast<Instruction>(*UI);
1251 // Comparison against null is ok.
1252 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(User)) {
1253 if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
1258 // getelementptr is also ok, but only a simple form.
1259 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
1260 // Must index into the array and into the struct.
1261 if (GEPI->getNumOperands() < 3)
1264 // Otherwise the GEP is ok.
1268 if (const PHINode *PN = dyn_cast<PHINode>(User)) {
1269 if (!LoadUsingPHIsPerLoad.insert(PN))
1270 // This means some phi nodes are dependent on each other.
1271 // Avoid infinite looping!
1273 if (!LoadUsingPHIs.insert(PN))
1274 // If we have already analyzed this PHI, then it is safe.
1277 // Make sure all uses of the PHI are simple enough to transform.
1278 if (!LoadUsesSimpleEnoughForHeapSRA(PN,
1279 LoadUsingPHIs, LoadUsingPHIsPerLoad))
1285 // Otherwise we don't know what this is, not ok.
1293 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from
1294 /// GV are simple enough to perform HeapSRA, return true.
1295 static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
1296 Instruction *StoredVal) {
1297 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
1298 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
1299 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
1301 if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
1302 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
1303 LoadUsingPHIsPerLoad))
1305 LoadUsingPHIsPerLoad.clear();
1308 // If we reach here, we know that all uses of the loads and transitive uses
1309 // (through PHI nodes) are simple enough to transform. However, we don't know
1310 // that all inputs the to the PHI nodes are in the same equivalence sets.
1311 // Check to verify that all operands of the PHIs are either PHIS that can be
1312 // transformed, loads from GV, or MI itself.
1313 for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin()
1314 , E = LoadUsingPHIs.end(); I != E; ++I) {
1315 const PHINode *PN = *I;
1316 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
1317 Value *InVal = PN->getIncomingValue(op);
1319 // PHI of the stored value itself is ok.
1320 if (InVal == StoredVal) continue;
1322 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
1323 // One of the PHIs in our set is (optimistically) ok.
1324 if (LoadUsingPHIs.count(InPN))
1329 // Load from GV is ok.
1330 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
1331 if (LI->getOperand(0) == GV)
1336 // Anything else is rejected.
1344 static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
1345 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1346 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1347 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
1349 if (FieldNo >= FieldVals.size())
1350 FieldVals.resize(FieldNo+1);
1352 // If we already have this value, just reuse the previously scalarized
1354 if (Value *FieldVal = FieldVals[FieldNo])
1357 // Depending on what instruction this is, we have several cases.
1359 if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
1360 // This is a scalarized version of the load from the global. Just create
1361 // a new Load of the scalarized global.
1362 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
1363 InsertedScalarizedValues,
1365 LI->getName()+".f"+Twine(FieldNo), LI);
1366 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
1367 // PN's type is pointer to struct. Make a new PHI of pointer to struct
1370 cast<StructType>(cast<PointerType>(PN->getType())->getElementType());
1373 PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)),
1374 PN->getNumIncomingValues(),
1375 PN->getName()+".f"+Twine(FieldNo), PN);
1377 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
1379 llvm_unreachable("Unknown usable value");
1382 return FieldVals[FieldNo] = Result;
1385 /// RewriteHeapSROALoadUser - Given a load instruction and a value derived from
1386 /// the load, rewrite the derived value to use the HeapSRoA'd load.
1387 static void RewriteHeapSROALoadUser(Instruction *LoadUser,
1388 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1389 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1390 // If this is a comparison against null, handle it.
1391 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
1392 assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
1393 // If we have a setcc of the loaded pointer, we can use a setcc of any
1395 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
1396 InsertedScalarizedValues, PHIsToRewrite);
1398 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
1399 Constant::getNullValue(NPtr->getType()),
1401 SCI->replaceAllUsesWith(New);
1402 SCI->eraseFromParent();
1406 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
1407 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
1408 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
1409 && "Unexpected GEPI!");
1411 // Load the pointer for this field.
1412 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
1413 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
1414 InsertedScalarizedValues, PHIsToRewrite);
1416 // Create the new GEP idx vector.
1417 SmallVector<Value*, 8> GEPIdx;
1418 GEPIdx.push_back(GEPI->getOperand(1));
1419 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
1421 Value *NGEPI = GetElementPtrInst::Create(NewPtr, GEPIdx,
1422 GEPI->getName(), GEPI);
1423 GEPI->replaceAllUsesWith(NGEPI);
1424 GEPI->eraseFromParent();
1428 // Recursively transform the users of PHI nodes. This will lazily create the
1429 // PHIs that are needed for individual elements. Keep track of what PHIs we
1430 // see in InsertedScalarizedValues so that we don't get infinite loops (very
1431 // antisocial). If the PHI is already in InsertedScalarizedValues, it has
1432 // already been seen first by another load, so its uses have already been
1434 PHINode *PN = cast<PHINode>(LoadUser);
1435 if (!InsertedScalarizedValues.insert(std::make_pair(PN,
1436 std::vector<Value*>())).second)
1439 // If this is the first time we've seen this PHI, recursively process all
1441 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) {
1442 Instruction *User = cast<Instruction>(*UI++);
1443 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1447 /// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr
1448 /// is a value loaded from the global. Eliminate all uses of Ptr, making them
1449 /// use FieldGlobals instead. All uses of loaded values satisfy
1450 /// AllGlobalLoadUsesSimpleEnoughForHeapSRA.
1451 static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
1452 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1453 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1454 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end();
1456 Instruction *User = cast<Instruction>(*UI++);
1457 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1460 if (Load->use_empty()) {
1461 Load->eraseFromParent();
1462 InsertedScalarizedValues.erase(Load);
1466 /// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break
1467 /// it up into multiple allocations of arrays of the fields.
1468 static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
1469 Value *NElems, TargetData *TD,
1470 const TargetLibraryInfo *TLI) {
1471 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n');
1472 Type *MAT = getMallocAllocatedType(CI, TLI);
1473 StructType *STy = cast<StructType>(MAT);
1475 // There is guaranteed to be at least one use of the malloc (storing
1476 // it into GV). If there are other uses, change them to be uses of
1477 // the global to simplify later code. This also deletes the store
1479 ReplaceUsesOfMallocWithGlobal(CI, GV);
1481 // Okay, at this point, there are no users of the malloc. Insert N
1482 // new mallocs at the same place as CI, and N globals.
1483 std::vector<Value*> FieldGlobals;
1484 std::vector<Value*> FieldMallocs;
1486 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
1487 Type *FieldTy = STy->getElementType(FieldNo);
1488 PointerType *PFieldTy = PointerType::getUnqual(FieldTy);
1490 GlobalVariable *NGV =
1491 new GlobalVariable(*GV->getParent(),
1492 PFieldTy, false, GlobalValue::InternalLinkage,
1493 Constant::getNullValue(PFieldTy),
1494 GV->getName() + ".f" + Twine(FieldNo), GV,
1495 GV->getThreadLocalMode());
1496 FieldGlobals.push_back(NGV);
1498 unsigned TypeSize = TD->getTypeAllocSize(FieldTy);
1499 if (StructType *ST = dyn_cast<StructType>(FieldTy))
1500 TypeSize = TD->getStructLayout(ST)->getSizeInBytes();
1501 Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
1502 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
1503 ConstantInt::get(IntPtrTy, TypeSize),
1505 CI->getName() + ".f" + Twine(FieldNo));
1506 FieldMallocs.push_back(NMI);
1507 new StoreInst(NMI, NGV, CI);
1510 // The tricky aspect of this transformation is handling the case when malloc
1511 // fails. In the original code, malloc failing would set the result pointer
1512 // of malloc to null. In this case, some mallocs could succeed and others
1513 // could fail. As such, we emit code that looks like this:
1514 // F0 = malloc(field0)
1515 // F1 = malloc(field1)
1516 // F2 = malloc(field2)
1517 // if (F0 == 0 || F1 == 0 || F2 == 0) {
1518 // if (F0) { free(F0); F0 = 0; }
1519 // if (F1) { free(F1); F1 = 0; }
1520 // if (F2) { free(F2); F2 = 0; }
1522 // The malloc can also fail if its argument is too large.
1523 Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
1524 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
1525 ConstantZero, "isneg");
1526 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
1527 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
1528 Constant::getNullValue(FieldMallocs[i]->getType()),
1530 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
1533 // Split the basic block at the old malloc.
1534 BasicBlock *OrigBB = CI->getParent();
1535 BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont");
1537 // Create the block to check the first condition. Put all these blocks at the
1538 // end of the function as they are unlikely to be executed.
1539 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
1541 OrigBB->getParent());
1543 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
1544 // branch on RunningOr.
1545 OrigBB->getTerminator()->eraseFromParent();
1546 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
1548 // Within the NullPtrBlock, we need to emit a comparison and branch for each
1549 // pointer, because some may be null while others are not.
1550 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1551 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
1552 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
1553 Constant::getNullValue(GVVal->getType()));
1554 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
1555 OrigBB->getParent());
1556 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
1557 OrigBB->getParent());
1558 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
1561 // Fill in FreeBlock.
1562 CallInst::CreateFree(GVVal, BI);
1563 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
1565 BranchInst::Create(NextBlock, FreeBlock);
1567 NullPtrBlock = NextBlock;
1570 BranchInst::Create(ContBB, NullPtrBlock);
1572 // CI is no longer needed, remove it.
1573 CI->eraseFromParent();
1575 /// InsertedScalarizedLoads - As we process loads, if we can't immediately
1576 /// update all uses of the load, keep track of what scalarized loads are
1577 /// inserted for a given load.
1578 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues;
1579 InsertedScalarizedValues[GV] = FieldGlobals;
1581 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite;
1583 // Okay, the malloc site is completely handled. All of the uses of GV are now
1584 // loads, and all uses of those loads are simple. Rewrite them to use loads
1585 // of the per-field globals instead.
1586 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) {
1587 Instruction *User = cast<Instruction>(*UI++);
1589 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1590 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
1594 // Must be a store of null.
1595 StoreInst *SI = cast<StoreInst>(User);
1596 assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
1597 "Unexpected heap-sra user!");
1599 // Insert a store of null into each global.
1600 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1601 PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType());
1602 Constant *Null = Constant::getNullValue(PT->getElementType());
1603 new StoreInst(Null, FieldGlobals[i], SI);
1605 // Erase the original store.
1606 SI->eraseFromParent();
1609 // While we have PHIs that are interesting to rewrite, do it.
1610 while (!PHIsToRewrite.empty()) {
1611 PHINode *PN = PHIsToRewrite.back().first;
1612 unsigned FieldNo = PHIsToRewrite.back().second;
1613 PHIsToRewrite.pop_back();
1614 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
1615 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
1617 // Add all the incoming values. This can materialize more phis.
1618 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1619 Value *InVal = PN->getIncomingValue(i);
1620 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
1622 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
1626 // Drop all inter-phi links and any loads that made it this far.
1627 for (DenseMap<Value*, std::vector<Value*> >::iterator
1628 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1630 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1631 PN->dropAllReferences();
1632 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1633 LI->dropAllReferences();
1636 // Delete all the phis and loads now that inter-references are dead.
1637 for (DenseMap<Value*, std::vector<Value*> >::iterator
1638 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1640 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1641 PN->eraseFromParent();
1642 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1643 LI->eraseFromParent();
1646 // The old global is now dead, remove it.
1647 GV->eraseFromParent();
1650 return cast<GlobalVariable>(FieldGlobals[0]);
1653 /// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a
1654 /// pointer global variable with a single value stored it that is a malloc or
1656 static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
1659 AtomicOrdering Ordering,
1660 Module::global_iterator &GVI,
1662 TargetLibraryInfo *TLI) {
1666 // If this is a malloc of an abstract type, don't touch it.
1667 if (!AllocTy->isSized())
1670 // We can't optimize this global unless all uses of it are *known* to be
1671 // of the malloc value, not of the null initializer value (consider a use
1672 // that compares the global's value against zero to see if the malloc has
1673 // been reached). To do this, we check to see if all uses of the global
1674 // would trap if the global were null: this proves that they must all
1675 // happen after the malloc.
1676 if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
1679 // We can't optimize this if the malloc itself is used in a complex way,
1680 // for example, being stored into multiple globals. This allows the
1681 // malloc to be stored into the specified global, loaded icmp'd, and
1682 // GEP'd. These are all things we could transform to using the global
1684 SmallPtrSet<const PHINode*, 8> PHIs;
1685 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
1688 // If we have a global that is only initialized with a fixed size malloc,
1689 // transform the program to use global memory instead of malloc'd memory.
1690 // This eliminates dynamic allocation, avoids an indirection accessing the
1691 // data, and exposes the resultant global to further GlobalOpt.
1692 // We cannot optimize the malloc if we cannot determine malloc array size.
1693 Value *NElems = getMallocArraySize(CI, TD, TLI, true);
1697 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
1698 // Restrict this transformation to only working on small allocations
1699 // (2048 bytes currently), as we don't want to introduce a 16M global or
1701 if (NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) {
1702 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD, TLI);
1706 // If the allocation is an array of structures, consider transforming this
1707 // into multiple malloc'd arrays, one for each field. This is basically
1708 // SRoA for malloc'd memory.
1710 if (Ordering != NotAtomic)
1713 // If this is an allocation of a fixed size array of structs, analyze as a
1714 // variable size array. malloc [100 x struct],1 -> malloc struct, 100
1715 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
1716 if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
1717 AllocTy = AT->getElementType();
1719 StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
1723 // This the structure has an unreasonable number of fields, leave it
1725 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
1726 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
1728 // If this is a fixed size array, transform the Malloc to be an alloc of
1729 // structs. malloc [100 x struct],1 -> malloc struct, 100
1730 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) {
1731 Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
1732 unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes();
1733 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
1734 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
1735 Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy,
1736 AllocSize, NumElements,
1738 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
1739 CI->replaceAllUsesWith(Cast);
1740 CI->eraseFromParent();
1741 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc))
1742 CI = cast<CallInst>(BCI->getOperand(0));
1744 CI = cast<CallInst>(Malloc);
1747 GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, TLI, true),
1755 // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
1756 // that only one value (besides its initializer) is ever stored to the global.
1757 static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
1758 AtomicOrdering Ordering,
1759 Module::global_iterator &GVI,
1760 TargetData *TD, TargetLibraryInfo *TLI) {
1761 // Ignore no-op GEPs and bitcasts.
1762 StoredOnceVal = StoredOnceVal->stripPointerCasts();
1764 // If we are dealing with a pointer global that is initialized to null and
1765 // only has one (non-null) value stored into it, then we can optimize any
1766 // users of the loaded value (often calls and loads) that would trap if the
1768 if (GV->getInitializer()->getType()->isPointerTy() &&
1769 GV->getInitializer()->isNullValue()) {
1770 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
1771 if (GV->getInitializer()->getType() != SOVC->getType())
1772 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
1774 // Optimize away any trapping uses of the loaded value.
1775 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, TD, TLI))
1777 } else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) {
1778 Type *MallocType = getMallocAllocatedType(CI, TLI);
1780 TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, Ordering, GVI,
1789 /// TryToShrinkGlobalToBoolean - At this point, we have learned that the only
1790 /// two values ever stored into GV are its initializer and OtherVal. See if we
1791 /// can shrink the global into a boolean and select between the two values
1792 /// whenever it is used. This exposes the values to other scalar optimizations.
1793 static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
1794 Type *GVElType = GV->getType()->getElementType();
1796 // If GVElType is already i1, it is already shrunk. If the type of the GV is
1797 // an FP value, pointer or vector, don't do this optimization because a select
1798 // between them is very expensive and unlikely to lead to later
1799 // simplification. In these cases, we typically end up with "cond ? v1 : v2"
1800 // where v1 and v2 both require constant pool loads, a big loss.
1801 if (GVElType == Type::getInt1Ty(GV->getContext()) ||
1802 GVElType->isFloatingPointTy() ||
1803 GVElType->isPointerTy() || GVElType->isVectorTy())
1806 // Walk the use list of the global seeing if all the uses are load or store.
1807 // If there is anything else, bail out.
1808 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){
1810 if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
1814 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV);
1816 // Create the new global, initializing it to false.
1817 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
1819 GlobalValue::InternalLinkage,
1820 ConstantInt::getFalse(GV->getContext()),
1822 GV->getThreadLocalMode());
1823 GV->getParent()->getGlobalList().insert(GV, NewGV);
1825 Constant *InitVal = GV->getInitializer();
1826 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
1827 "No reason to shrink to bool!");
1829 // If initialized to zero and storing one into the global, we can use a cast
1830 // instead of a select to synthesize the desired value.
1831 bool IsOneZero = false;
1832 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
1833 IsOneZero = InitVal->isNullValue() && CI->isOne();
1835 while (!GV->use_empty()) {
1836 Instruction *UI = cast<Instruction>(GV->use_back());
1837 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
1838 // Change the store into a boolean store.
1839 bool StoringOther = SI->getOperand(0) == OtherVal;
1840 // Only do this if we weren't storing a loaded value.
1842 if (StoringOther || SI->getOperand(0) == InitVal)
1843 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
1846 // Otherwise, we are storing a previously loaded copy. To do this,
1847 // change the copy from copying the original value to just copying the
1849 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
1851 // If we've already replaced the input, StoredVal will be a cast or
1852 // select instruction. If not, it will be a load of the original
1854 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
1855 assert(LI->getOperand(0) == GV && "Not a copy!");
1856 // Insert a new load, to preserve the saved value.
1857 StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1858 LI->getOrdering(), LI->getSynchScope(), LI);
1860 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
1861 "This is not a form that we understand!");
1862 StoreVal = StoredVal->getOperand(0);
1863 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
1866 new StoreInst(StoreVal, NewGV, false, 0,
1867 SI->getOrdering(), SI->getSynchScope(), SI);
1869 // Change the load into a load of bool then a select.
1870 LoadInst *LI = cast<LoadInst>(UI);
1871 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1872 LI->getOrdering(), LI->getSynchScope(), LI);
1875 NSI = new ZExtInst(NLI, LI->getType(), "", LI);
1877 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
1879 LI->replaceAllUsesWith(NSI);
1881 UI->eraseFromParent();
1884 GV->eraseFromParent();
1889 /// ProcessGlobal - Analyze the specified global variable and optimize it if
1890 /// possible. If we make a change, return true.
1891 bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
1892 Module::global_iterator &GVI) {
1893 if (!GV->isDiscardableIfUnused())
1896 // Do more involved optimizations if the global is internal.
1897 GV->removeDeadConstantUsers();
1899 if (GV->use_empty()) {
1900 DEBUG(dbgs() << "GLOBAL DEAD: " << *GV);
1901 GV->eraseFromParent();
1906 if (!GV->hasLocalLinkage())
1909 SmallPtrSet<const PHINode*, 16> PHIUsers;
1912 if (AnalyzeGlobal(GV, GS, PHIUsers))
1915 if (!GS.isCompared && !GV->hasUnnamedAddr()) {
1916 GV->setUnnamedAddr(true);
1920 if (GV->isConstant() || !GV->hasInitializer())
1923 return ProcessInternalGlobal(GV, GVI, PHIUsers, GS);
1926 /// ProcessInternalGlobal - Analyze the specified global variable and optimize
1927 /// it if possible. If we make a change, return true.
1928 bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
1929 Module::global_iterator &GVI,
1930 const SmallPtrSet<const PHINode*, 16> &PHIUsers,
1931 const GlobalStatus &GS) {
1932 // If this is a first class global and has only one accessing function
1933 // and this function is main (which we know is not recursive we can make
1934 // this global a local variable) we replace the global with a local alloca
1935 // in this function.
1937 // NOTE: It doesn't make sense to promote non single-value types since we
1938 // are just replacing static memory to stack memory.
1940 // If the global is in different address space, don't bring it to stack.
1941 if (!GS.HasMultipleAccessingFunctions &&
1942 GS.AccessingFunction && !GS.HasNonInstructionUser &&
1943 GV->getType()->getElementType()->isSingleValueType() &&
1944 GS.AccessingFunction->getName() == "main" &&
1945 GS.AccessingFunction->hasExternalLinkage() &&
1946 GV->getType()->getAddressSpace() == 0) {
1947 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV);
1948 Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction
1949 ->getEntryBlock().begin());
1950 Type *ElemTy = GV->getType()->getElementType();
1951 // FIXME: Pass Global's alignment when globals have alignment
1952 AllocaInst *Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI);
1953 if (!isa<UndefValue>(GV->getInitializer()))
1954 new StoreInst(GV->getInitializer(), Alloca, &FirstI);
1956 GV->replaceAllUsesWith(Alloca);
1957 GV->eraseFromParent();
1962 // If the global is never loaded (but may be stored to), it is dead.
1965 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV);
1968 if (isLeakCheckerRoot(GV)) {
1969 // Delete any constant stores to the global.
1970 Changed = CleanupPointerRootUsers(GV, TLI);
1972 // Delete any stores we can find to the global. We may not be able to
1973 // make it completely dead though.
1974 Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1977 // If the global is dead now, delete it.
1978 if (GV->use_empty()) {
1979 GV->eraseFromParent();
1985 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
1986 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV);
1987 GV->setConstant(true);
1989 // Clean up any obviously simplifiable users now.
1990 CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
1992 // If the global is dead now, just nuke it.
1993 if (GV->use_empty()) {
1994 DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
1995 << "all users and delete global!\n");
1996 GV->eraseFromParent();
2002 } else if (!GV->getInitializer()->getType()->isSingleValueType()) {
2003 if (TargetData *TD = getAnalysisIfAvailable<TargetData>())
2004 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) {
2005 GVI = FirstNewGV; // Don't skip the newly produced globals!
2008 } else if (GS.StoredType == GlobalStatus::isStoredOnce) {
2009 // If the initial value for the global was an undef value, and if only
2010 // one other value was stored into it, we can just change the
2011 // initializer to be the stored value, then delete all stores to the
2012 // global. This allows us to mark it constant.
2013 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
2014 if (isa<UndefValue>(GV->getInitializer())) {
2015 // Change the initial value here.
2016 GV->setInitializer(SOVConstant);
2018 // Clean up any obviously simplifiable users now.
2019 CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
2021 if (GV->use_empty()) {
2022 DEBUG(dbgs() << " *** Substituting initializer allowed us to "
2023 << "simplify all users and delete global!\n");
2024 GV->eraseFromParent();
2033 // Try to optimize globals based on the knowledge that only one value
2034 // (besides its initializer) is ever stored to the global.
2035 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, GVI,
2039 // Otherwise, if the global was not a boolean, we can shrink it to be a
2041 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
2042 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
2051 /// ChangeCalleesToFastCall - Walk all of the direct calls of the specified
2052 /// function, changing them to FastCC.
2053 static void ChangeCalleesToFastCall(Function *F) {
2054 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
2055 if (isa<BlockAddress>(*UI))
2057 CallSite User(cast<Instruction>(*UI));
2058 User.setCallingConv(CallingConv::Fast);
2062 static AttrListPtr StripNest(const AttrListPtr &Attrs) {
2063 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
2064 if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0)
2067 // There can be only one.
2068 return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest);
2074 static void RemoveNestAttribute(Function *F) {
2075 F->setAttributes(StripNest(F->getAttributes()));
2076 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
2077 if (isa<BlockAddress>(*UI))
2079 CallSite User(cast<Instruction>(*UI));
2080 User.setAttributes(StripNest(User.getAttributes()));
2084 bool GlobalOpt::OptimizeFunctions(Module &M) {
2085 bool Changed = false;
2086 // Optimize functions.
2087 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
2089 // Functions without names cannot be referenced outside this module.
2090 if (!F->hasName() && !F->isDeclaration())
2091 F->setLinkage(GlobalValue::InternalLinkage);
2092 F->removeDeadConstantUsers();
2093 if (F->isDefTriviallyDead()) {
2094 F->eraseFromParent();
2097 } else if (F->hasLocalLinkage()) {
2098 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() &&
2099 !F->hasAddressTaken()) {
2100 // If this function has C calling conventions, is not a varargs
2101 // function, and is only called directly, promote it to use the Fast
2102 // calling convention.
2103 F->setCallingConv(CallingConv::Fast);
2104 ChangeCalleesToFastCall(F);
2109 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
2110 !F->hasAddressTaken()) {
2111 // The function is not used by a trampoline intrinsic, so it is safe
2112 // to remove the 'nest' attribute.
2113 RemoveNestAttribute(F);
2122 bool GlobalOpt::OptimizeGlobalVars(Module &M) {
2123 bool Changed = false;
2124 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
2126 GlobalVariable *GV = GVI++;
2127 // Global variables without names cannot be referenced outside this module.
2128 if (!GV->hasName() && !GV->isDeclaration())
2129 GV->setLinkage(GlobalValue::InternalLinkage);
2130 // Simplify the initializer.
2131 if (GV->hasInitializer())
2132 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
2133 Constant *New = ConstantFoldConstantExpression(CE, TD, TLI);
2134 if (New && New != CE)
2135 GV->setInitializer(New);
2138 Changed |= ProcessGlobal(GV, GVI);
2143 /// FindGlobalCtors - Find the llvm.global_ctors list, verifying that all
2144 /// initializers have an init priority of 65535.
2145 GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) {
2146 GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
2147 if (GV == 0) return 0;
2149 // Verify that the initializer is simple enough for us to handle. We are
2150 // only allowed to optimize the initializer if it is unique.
2151 if (!GV->hasUniqueInitializer()) return 0;
2153 if (isa<ConstantAggregateZero>(GV->getInitializer()))
2155 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
2157 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
2158 if (isa<ConstantAggregateZero>(*i))
2160 ConstantStruct *CS = cast<ConstantStruct>(*i);
2161 if (isa<ConstantPointerNull>(CS->getOperand(1)))
2164 // Must have a function or null ptr.
2165 if (!isa<Function>(CS->getOperand(1)))
2168 // Init priority must be standard.
2169 ConstantInt *CI = cast<ConstantInt>(CS->getOperand(0));
2170 if (CI->getZExtValue() != 65535)
2177 /// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand,
2178 /// return a list of the functions and null terminator as a vector.
2179 static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) {
2180 if (GV->getInitializer()->isNullValue())
2181 return std::vector<Function*>();
2182 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
2183 std::vector<Function*> Result;
2184 Result.reserve(CA->getNumOperands());
2185 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
2186 ConstantStruct *CS = cast<ConstantStruct>(*i);
2187 Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
2192 /// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the
2193 /// specified array, returning the new global to use.
2194 static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL,
2195 const std::vector<Function*> &Ctors) {
2196 // If we made a change, reassemble the initializer list.
2197 Constant *CSVals[2];
2198 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 65535);
2201 StructType *StructTy =
2203 cast<ArrayType>(GCL->getType()->getElementType())->getElementType());
2205 // Create the new init list.
2206 std::vector<Constant*> CAList;
2207 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) {
2209 CSVals[1] = Ctors[i];
2211 Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()),
2213 PointerType *PFTy = PointerType::getUnqual(FTy);
2214 CSVals[1] = Constant::getNullValue(PFTy);
2215 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()),
2218 CAList.push_back(ConstantStruct::get(StructTy, CSVals));
2221 // Create the array initializer.
2222 Constant *CA = ConstantArray::get(ArrayType::get(StructTy,
2223 CAList.size()), CAList);
2225 // If we didn't change the number of elements, don't create a new GV.
2226 if (CA->getType() == GCL->getInitializer()->getType()) {
2227 GCL->setInitializer(CA);
2231 // Create the new global and insert it next to the existing list.
2232 GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(),
2233 GCL->getLinkage(), CA, "",
2234 GCL->getThreadLocalMode());
2235 GCL->getParent()->getGlobalList().insert(GCL, NGV);
2238 // Nuke the old list, replacing any uses with the new one.
2239 if (!GCL->use_empty()) {
2241 if (V->getType() != GCL->getType())
2242 V = ConstantExpr::getBitCast(V, GCL->getType());
2243 GCL->replaceAllUsesWith(V);
2245 GCL->eraseFromParent();
2255 isSimpleEnoughValueToCommit(Constant *C,
2256 SmallPtrSet<Constant*, 8> &SimpleConstants,
2257 const TargetData *TD);
2260 /// isSimpleEnoughValueToCommit - Return true if the specified constant can be
2261 /// handled by the code generator. We don't want to generate something like:
2262 /// void *X = &X/42;
2263 /// because the code generator doesn't have a relocation that can handle that.
2265 /// This function should be called if C was not found (but just got inserted)
2266 /// in SimpleConstants to avoid having to rescan the same constants all the
2268 static bool isSimpleEnoughValueToCommitHelper(Constant *C,
2269 SmallPtrSet<Constant*, 8> &SimpleConstants,
2270 const TargetData *TD) {
2271 // Simple integer, undef, constant aggregate zero, global addresses, etc are
2273 if (C->getNumOperands() == 0 || isa<BlockAddress>(C) ||
2274 isa<GlobalValue>(C))
2277 // Aggregate values are safe if all their elements are.
2278 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) ||
2279 isa<ConstantVector>(C)) {
2280 for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
2281 Constant *Op = cast<Constant>(C->getOperand(i));
2282 if (!isSimpleEnoughValueToCommit(Op, SimpleConstants, TD))
2288 // We don't know exactly what relocations are allowed in constant expressions,
2289 // so we allow &global+constantoffset, which is safe and uniformly supported
2291 ConstantExpr *CE = cast<ConstantExpr>(C);
2292 switch (CE->getOpcode()) {
2293 case Instruction::BitCast:
2294 // Bitcast is fine if the casted value is fine.
2295 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2297 case Instruction::IntToPtr:
2298 case Instruction::PtrToInt:
2299 // int <=> ptr is fine if the int type is the same size as the
2301 if (!TD || TD->getTypeSizeInBits(CE->getType()) !=
2302 TD->getTypeSizeInBits(CE->getOperand(0)->getType()))
2304 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2306 // GEP is fine if it is simple + constant offset.
2307 case Instruction::GetElementPtr:
2308 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
2309 if (!isa<ConstantInt>(CE->getOperand(i)))
2311 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2313 case Instruction::Add:
2314 // We allow simple+cst.
2315 if (!isa<ConstantInt>(CE->getOperand(1)))
2317 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
2323 isSimpleEnoughValueToCommit(Constant *C,
2324 SmallPtrSet<Constant*, 8> &SimpleConstants,
2325 const TargetData *TD) {
2326 // If we already checked this constant, we win.
2327 if (!SimpleConstants.insert(C)) return true;
2328 // Check the constant.
2329 return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, TD);
2333 /// isSimpleEnoughPointerToCommit - Return true if this constant is simple
2334 /// enough for us to understand. In particular, if it is a cast to anything
2335 /// other than from one pointer type to another pointer type, we punt.
2336 /// We basically just support direct accesses to globals and GEP's of
2337 /// globals. This should be kept up to date with CommitValueTo.
2338 static bool isSimpleEnoughPointerToCommit(Constant *C) {
2339 // Conservatively, avoid aggregate types. This is because we don't
2340 // want to worry about them partially overlapping other stores.
2341 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
2344 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
2345 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2346 // external globals.
2347 return GV->hasUniqueInitializer();
2349 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
2350 // Handle a constantexpr gep.
2351 if (CE->getOpcode() == Instruction::GetElementPtr &&
2352 isa<GlobalVariable>(CE->getOperand(0)) &&
2353 cast<GEPOperator>(CE)->isInBounds()) {
2354 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2355 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2356 // external globals.
2357 if (!GV->hasUniqueInitializer())
2360 // The first index must be zero.
2361 ConstantInt *CI = dyn_cast<ConstantInt>(*llvm::next(CE->op_begin()));
2362 if (!CI || !CI->isZero()) return false;
2364 // The remaining indices must be compile-time known integers within the
2365 // notional bounds of the corresponding static array types.
2366 if (!CE->isGEPWithNoNotionalOverIndexing())
2369 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2371 // A constantexpr bitcast from a pointer to another pointer is a no-op,
2372 // and we know how to evaluate it by moving the bitcast from the pointer
2373 // operand to the value operand.
2374 } else if (CE->getOpcode() == Instruction::BitCast &&
2375 isa<GlobalVariable>(CE->getOperand(0))) {
2376 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
2377 // external globals.
2378 return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
2385 /// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global
2386 /// initializer. This returns 'Init' modified to reflect 'Val' stored into it.
2387 /// At this point, the GEP operands of Addr [0, OpNo) have been stepped into.
2388 static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
2389 ConstantExpr *Addr, unsigned OpNo) {
2390 // Base case of the recursion.
2391 if (OpNo == Addr->getNumOperands()) {
2392 assert(Val->getType() == Init->getType() && "Type mismatch!");
2396 SmallVector<Constant*, 32> Elts;
2397 if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
2398 // Break up the constant into its elements.
2399 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
2400 Elts.push_back(Init->getAggregateElement(i));
2402 // Replace the element that we are supposed to.
2403 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
2404 unsigned Idx = CU->getZExtValue();
2405 assert(Idx < STy->getNumElements() && "Struct index out of range!");
2406 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
2408 // Return the modified struct.
2409 return ConstantStruct::get(STy, Elts);
2412 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
2413 SequentialType *InitTy = cast<SequentialType>(Init->getType());
2416 if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
2417 NumElts = ATy->getNumElements();
2419 NumElts = InitTy->getVectorNumElements();
2421 // Break up the array into elements.
2422 for (uint64_t i = 0, e = NumElts; i != e; ++i)
2423 Elts.push_back(Init->getAggregateElement(i));
2425 assert(CI->getZExtValue() < NumElts);
2426 Elts[CI->getZExtValue()] =
2427 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
2429 if (Init->getType()->isArrayTy())
2430 return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
2431 return ConstantVector::get(Elts);
2434 /// CommitValueTo - We have decided that Addr (which satisfies the predicate
2435 /// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen.
2436 static void CommitValueTo(Constant *Val, Constant *Addr) {
2437 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
2438 assert(GV->hasInitializer());
2439 GV->setInitializer(Val);
2443 ConstantExpr *CE = cast<ConstantExpr>(Addr);
2444 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2445 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
2450 /// Evaluator - This class evaluates LLVM IR, producing the Constant
2451 /// representing each SSA instruction. Changes to global variables are stored
2452 /// in a mapping that can be iterated over after the evaluation is complete.
2453 /// Once an evaluation call fails, the evaluation object should not be reused.
2456 Evaluator(const TargetData *TD, const TargetLibraryInfo *TLI)
2457 : TD(TD), TLI(TLI) {
2458 ValueStack.push_back(new DenseMap<Value*, Constant*>);
2462 DeleteContainerPointers(ValueStack);
2463 while (!AllocaTmps.empty()) {
2464 GlobalVariable *Tmp = AllocaTmps.back();
2465 AllocaTmps.pop_back();
2467 // If there are still users of the alloca, the program is doing something
2468 // silly, e.g. storing the address of the alloca somewhere and using it
2469 // later. Since this is undefined, we'll just make it be null.
2470 if (!Tmp->use_empty())
2471 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
2476 /// EvaluateFunction - Evaluate a call to function F, returning true if
2477 /// successful, false if we can't evaluate it. ActualArgs contains the formal
2478 /// arguments for the function.
2479 bool EvaluateFunction(Function *F, Constant *&RetVal,
2480 const SmallVectorImpl<Constant*> &ActualArgs);
2482 /// EvaluateBlock - Evaluate all instructions in block BB, returning true if
2483 /// successful, false if we can't evaluate it. NewBB returns the next BB that
2484 /// control flows into, or null upon return.
2485 bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB);
2487 Constant *getVal(Value *V) {
2488 if (Constant *CV = dyn_cast<Constant>(V)) return CV;
2489 Constant *R = ValueStack.back()->lookup(V);
2490 assert(R && "Reference to an uncomputed value!");
2494 void setVal(Value *V, Constant *C) {
2495 ValueStack.back()->operator[](V) = C;
2498 const DenseMap<Constant*, Constant*> &getMutatedMemory() const {
2499 return MutatedMemory;
2502 const SmallPtrSet<GlobalVariable*, 8> &getInvariants() const {
2507 Constant *ComputeLoadResult(Constant *P);
2509 /// ValueStack - As we compute SSA register values, we store their contents
2510 /// here. The back of the vector contains the current function and the stack
2511 /// contains the values in the calling frames.
2512 SmallVector<DenseMap<Value*, Constant*>*, 4> ValueStack;
2514 /// CallStack - This is used to detect recursion. In pathological situations
2515 /// we could hit exponential behavior, but at least there is nothing
2517 SmallVector<Function*, 4> CallStack;
2519 /// MutatedMemory - For each store we execute, we update this map. Loads
2520 /// check this to get the most up-to-date value. If evaluation is successful,
2521 /// this state is committed to the process.
2522 DenseMap<Constant*, Constant*> MutatedMemory;
2524 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable
2525 /// to represent its body. This vector is needed so we can delete the
2526 /// temporary globals when we are done.
2527 SmallVector<GlobalVariable*, 32> AllocaTmps;
2529 /// Invariants - These global variables have been marked invariant by the
2530 /// static constructor.
2531 SmallPtrSet<GlobalVariable*, 8> Invariants;
2533 /// SimpleConstants - These are constants we have checked and know to be
2534 /// simple enough to live in a static initializer of a global.
2535 SmallPtrSet<Constant*, 8> SimpleConstants;
2537 const TargetData *TD;
2538 const TargetLibraryInfo *TLI;
2541 } // anonymous namespace
2543 /// ComputeLoadResult - Return the value that would be computed by a load from
2544 /// P after the stores reflected by 'memory' have been performed. If we can't
2545 /// decide, return null.
2546 Constant *Evaluator::ComputeLoadResult(Constant *P) {
2547 // If this memory location has been recently stored, use the stored value: it
2548 // is the most up-to-date.
2549 DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P);
2550 if (I != MutatedMemory.end()) return I->second;
2553 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
2554 if (GV->hasDefinitiveInitializer())
2555 return GV->getInitializer();
2559 // Handle a constantexpr getelementptr.
2560 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
2561 if (CE->getOpcode() == Instruction::GetElementPtr &&
2562 isa<GlobalVariable>(CE->getOperand(0))) {
2563 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2564 if (GV->hasDefinitiveInitializer())
2565 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
2568 return 0; // don't know how to evaluate.
2571 /// EvaluateBlock - Evaluate all instructions in block BB, returning true if
2572 /// successful, false if we can't evaluate it. NewBB returns the next BB that
2573 /// control flows into, or null upon return.
2574 bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst,
2575 BasicBlock *&NextBB) {
2576 // This is the main evaluation loop.
2578 Constant *InstResult = 0;
2580 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
2581 if (!SI->isSimple()) return false; // no volatile/atomic accesses.
2582 Constant *Ptr = getVal(SI->getOperand(1));
2583 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2584 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2585 if (!isSimpleEnoughPointerToCommit(Ptr))
2586 // If this is too complex for us to commit, reject it.
2589 Constant *Val = getVal(SI->getOperand(0));
2591 // If this might be too difficult for the backend to handle (e.g. the addr
2592 // of one global variable divided by another) then we can't commit it.
2593 if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, TD))
2596 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2597 if (CE->getOpcode() == Instruction::BitCast) {
2598 // If we're evaluating a store through a bitcast, then we need
2599 // to pull the bitcast off the pointer type and push it onto the
2601 Ptr = CE->getOperand(0);
2603 Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
2605 // In order to push the bitcast onto the stored value, a bitcast
2606 // from NewTy to Val's type must be legal. If it's not, we can try
2607 // introspecting NewTy to find a legal conversion.
2608 while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
2609 // If NewTy is a struct, we can convert the pointer to the struct
2610 // into a pointer to its first member.
2611 // FIXME: This could be extended to support arrays as well.
2612 if (StructType *STy = dyn_cast<StructType>(NewTy)) {
2613 NewTy = STy->getTypeAtIndex(0U);
2615 IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
2616 Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
2617 Constant * const IdxList[] = {IdxZero, IdxZero};
2619 Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList);
2620 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2621 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2623 // If we can't improve the situation by introspecting NewTy,
2624 // we have to give up.
2630 // If we found compatible types, go ahead and push the bitcast
2631 // onto the stored value.
2632 Val = ConstantExpr::getBitCast(Val, NewTy);
2635 MutatedMemory[Ptr] = Val;
2636 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
2637 InstResult = ConstantExpr::get(BO->getOpcode(),
2638 getVal(BO->getOperand(0)),
2639 getVal(BO->getOperand(1)));
2640 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
2641 InstResult = ConstantExpr::getCompare(CI->getPredicate(),
2642 getVal(CI->getOperand(0)),
2643 getVal(CI->getOperand(1)));
2644 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
2645 InstResult = ConstantExpr::getCast(CI->getOpcode(),
2646 getVal(CI->getOperand(0)),
2648 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
2649 InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
2650 getVal(SI->getOperand(1)),
2651 getVal(SI->getOperand(2)));
2652 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
2653 Constant *P = getVal(GEP->getOperand(0));
2654 SmallVector<Constant*, 8> GEPOps;
2655 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
2657 GEPOps.push_back(getVal(*i));
2659 ConstantExpr::getGetElementPtr(P, GEPOps,
2660 cast<GEPOperator>(GEP)->isInBounds());
2661 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
2662 if (!LI->isSimple()) return false; // no volatile/atomic accesses.
2663 Constant *Ptr = getVal(LI->getOperand(0));
2664 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
2665 Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
2666 InstResult = ComputeLoadResult(Ptr);
2667 if (InstResult == 0) return false; // Could not evaluate load.
2668 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
2669 if (AI->isArrayAllocation()) return false; // Cannot handle array allocs.
2670 Type *Ty = AI->getType()->getElementType();
2671 AllocaTmps.push_back(new GlobalVariable(Ty, false,
2672 GlobalValue::InternalLinkage,
2673 UndefValue::get(Ty),
2675 InstResult = AllocaTmps.back();
2676 } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
2677 CallSite CS(CurInst);
2679 // Debug info can safely be ignored here.
2680 if (isa<DbgInfoIntrinsic>(CS.getInstruction())) {
2685 // Cannot handle inline asm.
2686 if (isa<InlineAsm>(CS.getCalledValue())) return false;
2688 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
2689 if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
2690 if (MSI->isVolatile()) return false;
2691 Constant *Ptr = getVal(MSI->getDest());
2692 Constant *Val = getVal(MSI->getValue());
2693 Constant *DestVal = ComputeLoadResult(getVal(Ptr));
2694 if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
2695 // This memset is a no-op.
2701 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
2702 II->getIntrinsicID() == Intrinsic::lifetime_end) {
2707 if (II->getIntrinsicID() == Intrinsic::invariant_start) {
2708 // We don't insert an entry into Values, as it doesn't have a
2709 // meaningful return value.
2710 if (!II->use_empty())
2712 ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
2713 Value *PtrArg = getVal(II->getArgOperand(1));
2714 Value *Ptr = PtrArg->stripPointerCasts();
2715 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
2716 Type *ElemTy = cast<PointerType>(GV->getType())->getElementType();
2717 if (!Size->isAllOnesValue() &&
2718 Size->getValue().getLimitedValue() >=
2719 TD->getTypeStoreSize(ElemTy))
2720 Invariants.insert(GV);
2722 // Continue even if we do nothing.
2729 // Resolve function pointers.
2730 Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue()));
2731 if (!Callee || Callee->mayBeOverridden())
2732 return false; // Cannot resolve.
2734 SmallVector<Constant*, 8> Formals;
2735 for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
2736 Formals.push_back(getVal(*i));
2738 if (Callee->isDeclaration()) {
2739 // If this is a function we can constant fold, do it.
2740 if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) {
2746 if (Callee->getFunctionType()->isVarArg())
2750 // Execute the call, if successful, use the return value.
2751 ValueStack.push_back(new DenseMap<Value*, Constant*>);
2752 if (!EvaluateFunction(Callee, RetVal, Formals))
2754 delete ValueStack.pop_back_val();
2755 InstResult = RetVal;
2757 } else if (isa<TerminatorInst>(CurInst)) {
2758 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
2759 if (BI->isUnconditional()) {
2760 NextBB = BI->getSuccessor(0);
2763 dyn_cast<ConstantInt>(getVal(BI->getCondition()));
2764 if (!Cond) return false; // Cannot determine.
2766 NextBB = BI->getSuccessor(!Cond->getZExtValue());
2768 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
2770 dyn_cast<ConstantInt>(getVal(SI->getCondition()));
2771 if (!Val) return false; // Cannot determine.
2772 NextBB = SI->findCaseValue(Val).getCaseSuccessor();
2773 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
2774 Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
2775 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
2776 NextBB = BA->getBasicBlock();
2778 return false; // Cannot determine.
2779 } else if (isa<ReturnInst>(CurInst)) {
2782 // invoke, unwind, resume, unreachable.
2783 return false; // Cannot handle this terminator.
2786 // We succeeded at evaluating this block!
2789 // Did not know how to evaluate this!
2793 if (!CurInst->use_empty()) {
2794 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
2795 InstResult = ConstantFoldConstantExpression(CE, TD, TLI);
2797 setVal(CurInst, InstResult);
2800 // If we just processed an invoke, we finished evaluating the block.
2801 if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
2802 NextBB = II->getNormalDest();
2806 // Advance program counter.
2811 /// EvaluateFunction - Evaluate a call to function F, returning true if
2812 /// successful, false if we can't evaluate it. ActualArgs contains the formal
2813 /// arguments for the function.
2814 bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal,
2815 const SmallVectorImpl<Constant*> &ActualArgs) {
2816 // Check to see if this function is already executing (recursion). If so,
2817 // bail out. TODO: we might want to accept limited recursion.
2818 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
2821 CallStack.push_back(F);
2823 // Initialize arguments to the incoming values specified.
2825 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
2827 setVal(AI, ActualArgs[ArgNo]);
2829 // ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
2830 // we can only evaluate any one basic block at most once. This set keeps
2831 // track of what we have executed so we can detect recursive cases etc.
2832 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
2834 // CurBB - The current basic block we're evaluating.
2835 BasicBlock *CurBB = F->begin();
2837 BasicBlock::iterator CurInst = CurBB->begin();
2840 BasicBlock *NextBB = 0; // Initialized to avoid compiler warnings.
2841 if (!EvaluateBlock(CurInst, NextBB))
2845 // Successfully running until there's no next block means that we found
2846 // the return. Fill it the return value and pop the call stack.
2847 ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
2848 if (RI->getNumOperands())
2849 RetVal = getVal(RI->getOperand(0));
2850 CallStack.pop_back();
2854 // Okay, we succeeded in evaluating this control flow. See if we have
2855 // executed the new block before. If so, we have a looping function,
2856 // which we cannot evaluate in reasonable time.
2857 if (!ExecutedBlocks.insert(NextBB))
2858 return false; // looped!
2860 // Okay, we have never been in this block before. Check to see if there
2861 // are any PHI nodes. If so, evaluate them with information about where
2864 for (CurInst = NextBB->begin();
2865 (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
2866 setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
2868 // Advance to the next block.
2873 /// EvaluateStaticConstructor - Evaluate static constructors in the function, if
2874 /// we can. Return true if we can, false otherwise.
2875 static bool EvaluateStaticConstructor(Function *F, const TargetData *TD,
2876 const TargetLibraryInfo *TLI) {
2877 // Call the function.
2878 Evaluator Eval(TD, TLI);
2879 Constant *RetValDummy;
2880 bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy,
2881 SmallVector<Constant*, 0>());
2884 // We succeeded at evaluation: commit the result.
2885 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
2886 << F->getName() << "' to " << Eval.getMutatedMemory().size()
2888 for (DenseMap<Constant*, Constant*>::const_iterator I =
2889 Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end();
2891 CommitValueTo(I->second, I->first);
2892 for (SmallPtrSet<GlobalVariable*, 8>::const_iterator I =
2893 Eval.getInvariants().begin(), E = Eval.getInvariants().end();
2895 (*I)->setConstant(true);
2901 /// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible.
2902 /// Return true if anything changed.
2903 bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) {
2904 std::vector<Function*> Ctors = ParseGlobalCtors(GCL);
2905 bool MadeChange = false;
2906 if (Ctors.empty()) return false;
2908 // Loop over global ctors, optimizing them when we can.
2909 for (unsigned i = 0; i != Ctors.size(); ++i) {
2910 Function *F = Ctors[i];
2911 // Found a null terminator in the middle of the list, prune off the rest of
2914 if (i != Ctors.size()-1) {
2921 // We cannot simplify external ctor functions.
2922 if (F->empty()) continue;
2924 // If we can evaluate the ctor at compile time, do.
2925 if (EvaluateStaticConstructor(F, TD, TLI)) {
2926 Ctors.erase(Ctors.begin()+i);
2929 ++NumCtorsEvaluated;
2934 if (!MadeChange) return false;
2936 GCL = InstallGlobalCtors(GCL, Ctors);
2940 bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
2941 bool Changed = false;
2943 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
2945 Module::alias_iterator J = I++;
2946 // Aliases without names cannot be referenced outside this module.
2947 if (!J->hasName() && !J->isDeclaration())
2948 J->setLinkage(GlobalValue::InternalLinkage);
2949 // If the aliasee may change at link time, nothing can be done - bail out.
2950 if (J->mayBeOverridden())
2953 Constant *Aliasee = J->getAliasee();
2954 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
2955 Target->removeDeadConstantUsers();
2956 bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse();
2958 // Make all users of the alias use the aliasee instead.
2959 if (!J->use_empty()) {
2960 J->replaceAllUsesWith(Aliasee);
2961 ++NumAliasesResolved;
2965 // If the alias is externally visible, we may still be able to simplify it.
2966 if (!J->hasLocalLinkage()) {
2967 // If the aliasee has internal linkage, give it the name and linkage
2968 // of the alias, and delete the alias. This turns:
2969 // define internal ... @f(...)
2970 // @a = alias ... @f
2972 // define ... @a(...)
2973 if (!Target->hasLocalLinkage())
2976 // Do not perform the transform if multiple aliases potentially target the
2977 // aliasee. This check also ensures that it is safe to replace the section
2978 // and other attributes of the aliasee with those of the alias.
2982 // Give the aliasee the name, linkage and other attributes of the alias.
2983 Target->takeName(J);
2984 Target->setLinkage(J->getLinkage());
2985 Target->GlobalValue::copyAttributesFrom(J);
2988 // Delete the alias.
2989 M.getAliasList().erase(J);
2990 ++NumAliasesRemoved;
2997 static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) {
2998 if (!TLI->has(LibFunc::cxa_atexit))
3001 Function *Fn = M.getFunction(TLI->getName(LibFunc::cxa_atexit));
3006 FunctionType *FTy = Fn->getFunctionType();
3008 // Checking that the function has the right return type, the right number of
3009 // parameters and that they all have pointer types should be enough.
3010 if (!FTy->getReturnType()->isIntegerTy() ||
3011 FTy->getNumParams() != 3 ||
3012 !FTy->getParamType(0)->isPointerTy() ||
3013 !FTy->getParamType(1)->isPointerTy() ||
3014 !FTy->getParamType(2)->isPointerTy())
3020 /// cxxDtorIsEmpty - Returns whether the given function is an empty C++
3021 /// destructor and can therefore be eliminated.
3022 /// Note that we assume that other optimization passes have already simplified
3023 /// the code so we only look for a function with a single basic block, where
3024 /// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and
3025 /// other side-effect free instructions.
3026 static bool cxxDtorIsEmpty(const Function &Fn,
3027 SmallPtrSet<const Function *, 8> &CalledFunctions) {
3028 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
3029 // nounwind, but that doesn't seem worth doing.
3030 if (Fn.isDeclaration())
3033 if (++Fn.begin() != Fn.end())
3036 const BasicBlock &EntryBlock = Fn.getEntryBlock();
3037 for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
3039 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
3040 // Ignore debug intrinsics.
3041 if (isa<DbgInfoIntrinsic>(CI))
3044 const Function *CalledFn = CI->getCalledFunction();
3049 SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
3051 // Don't treat recursive functions as empty.
3052 if (!NewCalledFunctions.insert(CalledFn))
3055 if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
3057 } else if (isa<ReturnInst>(*I))
3058 return true; // We're done.
3059 else if (I->mayHaveSideEffects())
3060 return false; // Destructor with side effects, bail.
3066 bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
3067 /// Itanium C++ ABI p3.3.5:
3069 /// After constructing a global (or local static) object, that will require
3070 /// destruction on exit, a termination function is registered as follows:
3072 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
3074 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
3075 /// call f(p) when DSO d is unloaded, before all such termination calls
3076 /// registered before this one. It returns zero if registration is
3077 /// successful, nonzero on failure.
3079 // This pass will look for calls to __cxa_atexit where the function is trivial
3081 bool Changed = false;
3083 for (Function::use_iterator I = CXAAtExitFn->use_begin(),
3084 E = CXAAtExitFn->use_end(); I != E;) {
3085 // We're only interested in calls. Theoretically, we could handle invoke
3086 // instructions as well, but neither llvm-gcc nor clang generate invokes
3088 CallInst *CI = dyn_cast<CallInst>(*I++);
3093 dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
3097 SmallPtrSet<const Function *, 8> CalledFunctions;
3098 if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
3101 // Just remove the call.
3102 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
3103 CI->eraseFromParent();
3105 ++NumCXXDtorsRemoved;
3113 bool GlobalOpt::runOnModule(Module &M) {
3114 bool Changed = false;
3116 TD = getAnalysisIfAvailable<TargetData>();
3117 TLI = &getAnalysis<TargetLibraryInfo>();
3119 // Try to find the llvm.globalctors list.
3120 GlobalVariable *GlobalCtors = FindGlobalCtors(M);
3122 Function *CXAAtExitFn = FindCXAAtExit(M, TLI);
3124 bool LocalChange = true;
3125 while (LocalChange) {
3126 LocalChange = false;
3128 // Delete functions that are trivially dead, ccc -> fastcc
3129 LocalChange |= OptimizeFunctions(M);
3131 // Optimize global_ctors list.
3133 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors);
3135 // Optimize non-address-taken globals.
3136 LocalChange |= OptimizeGlobalVars(M);
3138 // Resolve aliases, when possible.
3139 LocalChange |= OptimizeGlobalAliases(M);
3141 // Try to remove trivial global destructors.
3143 LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
3145 Changed |= LocalChange;
3148 // TODO: Move all global ctors functions to the end of the module for code