1 //===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass transforms simple global variables that never have their address
11 // taken. If obviously true, it marks read/write globals as constant, deletes
12 // variables only stored to, etc.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Transforms/IPO/GlobalOpt.h"
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/STLExtras.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/ADT/SmallSet.h"
21 #include "llvm/ADT/SmallVector.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/Analysis/ConstantFolding.h"
24 #include "llvm/Analysis/MemoryBuiltins.h"
25 #include "llvm/Analysis/TargetLibraryInfo.h"
26 #include "llvm/IR/CallSite.h"
27 #include "llvm/IR/CallingConv.h"
28 #include "llvm/IR/Constants.h"
29 #include "llvm/IR/DataLayout.h"
30 #include "llvm/IR/DerivedTypes.h"
31 #include "llvm/IR/Dominators.h"
32 #include "llvm/IR/GetElementPtrTypeIterator.h"
33 #include "llvm/IR/Instructions.h"
34 #include "llvm/IR/IntrinsicInst.h"
35 #include "llvm/IR/Module.h"
36 #include "llvm/IR/Operator.h"
37 #include "llvm/IR/ValueHandle.h"
38 #include "llvm/Pass.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/ErrorHandling.h"
41 #include "llvm/Support/MathExtras.h"
42 #include "llvm/Support/raw_ostream.h"
43 #include "llvm/Transforms/IPO.h"
44 #include "llvm/Transforms/Utils/CtorUtils.h"
45 #include "llvm/Transforms/Utils/Evaluator.h"
46 #include "llvm/Transforms/Utils/GlobalStatus.h"
47 #include "llvm/Transforms/Utils/Local.h"
51 #define DEBUG_TYPE "globalopt"
53 STATISTIC(NumMarked , "Number of globals marked constant");
54 STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr");
55 STATISTIC(NumSRA , "Number of aggregate globals broken into scalars");
56 STATISTIC(NumHeapSRA , "Number of heap objects SRA'd");
57 STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
58 STATISTIC(NumDeleted , "Number of globals deleted");
59 STATISTIC(NumGlobUses , "Number of global uses devirtualized");
60 STATISTIC(NumLocalized , "Number of globals localized");
61 STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans");
62 STATISTIC(NumFastCallFns , "Number of functions converted to fastcc");
63 STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");
64 STATISTIC(NumNestRemoved , "Number of nest attributes removed");
65 STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
66 STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
67 STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
69 /// Is this global variable possibly used by a leak checker as a root? If so,
70 /// we might not really want to eliminate the stores to it.
71 static bool isLeakCheckerRoot(GlobalVariable *GV) {
72 // A global variable is a root if it is a pointer, or could plausibly contain
73 // a pointer. There are two challenges; one is that we could have a struct
74 // the has an inner member which is a pointer. We recurse through the type to
75 // detect these (up to a point). The other is that we may actually be a union
76 // of a pointer and another type, and so our LLVM type is an integer which
77 // gets converted into a pointer, or our type is an [i8 x #] with a pointer
78 // potentially contained here.
80 if (GV->hasPrivateLinkage())
83 SmallVector<Type *, 4> Types;
84 Types.push_back(GV->getValueType());
88 Type *Ty = Types.pop_back_val();
89 switch (Ty->getTypeID()) {
91 case Type::PointerTyID: return true;
93 case Type::VectorTyID: {
94 SequentialType *STy = cast<SequentialType>(Ty);
95 Types.push_back(STy->getElementType());
98 case Type::StructTyID: {
99 StructType *STy = cast<StructType>(Ty);
100 if (STy->isOpaque()) return true;
101 for (StructType::element_iterator I = STy->element_begin(),
102 E = STy->element_end(); I != E; ++I) {
104 if (isa<PointerType>(InnerTy)) return true;
105 if (isa<CompositeType>(InnerTy))
106 Types.push_back(InnerTy);
111 if (--Limit == 0) return true;
112 } while (!Types.empty());
116 /// Given a value that is stored to a global but never read, determine whether
117 /// it's safe to remove the store and the chain of computation that feeds the
119 static bool IsSafeComputationToRemove(Value *V, const TargetLibraryInfo *TLI) {
121 if (isa<Constant>(V))
125 if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) ||
128 if (isAllocationFn(V, TLI))
131 Instruction *I = cast<Instruction>(V);
132 if (I->mayHaveSideEffects())
134 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
135 if (!GEP->hasAllConstantIndices())
137 } else if (I->getNumOperands() != 1) {
141 V = I->getOperand(0);
145 /// This GV is a pointer root. Loop over all users of the global and clean up
146 /// any that obviously don't assign the global a value that isn't dynamically
148 static bool CleanupPointerRootUsers(GlobalVariable *GV,
149 const TargetLibraryInfo *TLI) {
150 // A brief explanation of leak checkers. The goal is to find bugs where
151 // pointers are forgotten, causing an accumulating growth in memory
152 // usage over time. The common strategy for leak checkers is to whitelist the
153 // memory pointed to by globals at exit. This is popular because it also
154 // solves another problem where the main thread of a C++ program may shut down
155 // before other threads that are still expecting to use those globals. To
156 // handle that case, we expect the program may create a singleton and never
159 bool Changed = false;
161 // If Dead[n].first is the only use of a malloc result, we can delete its
162 // chain of computation and the store to the global in Dead[n].second.
163 SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
165 // Constants can't be pointers to dynamically allocated memory.
166 for (Value::user_iterator UI = GV->user_begin(), E = GV->user_end();
169 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
170 Value *V = SI->getValueOperand();
171 if (isa<Constant>(V)) {
173 SI->eraseFromParent();
174 } else if (Instruction *I = dyn_cast<Instruction>(V)) {
176 Dead.push_back(std::make_pair(I, SI));
178 } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
179 if (isa<Constant>(MSI->getValue())) {
181 MSI->eraseFromParent();
182 } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
184 Dead.push_back(std::make_pair(I, MSI));
186 } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
187 GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
188 if (MemSrc && MemSrc->isConstant()) {
190 MTI->eraseFromParent();
191 } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) {
193 Dead.push_back(std::make_pair(I, MTI));
195 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
196 if (CE->use_empty()) {
197 CE->destroyConstant();
200 } else if (Constant *C = dyn_cast<Constant>(U)) {
201 if (isSafeToDestroyConstant(C)) {
202 C->destroyConstant();
203 // This could have invalidated UI, start over from scratch.
205 CleanupPointerRootUsers(GV, TLI);
211 for (int i = 0, e = Dead.size(); i != e; ++i) {
212 if (IsSafeComputationToRemove(Dead[i].first, TLI)) {
213 Dead[i].second->eraseFromParent();
214 Instruction *I = Dead[i].first;
216 if (isAllocationFn(I, TLI))
218 Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
221 I->eraseFromParent();
224 I->eraseFromParent();
231 /// We just marked GV constant. Loop over all users of the global, cleaning up
232 /// the obvious ones. This is largely just a quick scan over the use list to
233 /// clean up the easy and obvious cruft. This returns true if it made a change.
234 static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
235 const DataLayout &DL,
236 TargetLibraryInfo *TLI) {
237 bool Changed = false;
238 // Note that we need to use a weak value handle for the worklist items. When
239 // we delete a constant array, we may also be holding pointer to one of its
240 // elements (or an element of one of its elements if we're dealing with an
241 // array of arrays) in the worklist.
242 SmallVector<WeakVH, 8> WorkList(V->user_begin(), V->user_end());
243 while (!WorkList.empty()) {
244 Value *UV = WorkList.pop_back_val();
248 User *U = cast<User>(UV);
250 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
252 // Replace the load with the initializer.
253 LI->replaceAllUsesWith(Init);
254 LI->eraseFromParent();
257 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
258 // Store must be unreachable or storing Init into the global.
259 SI->eraseFromParent();
261 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
262 if (CE->getOpcode() == Instruction::GetElementPtr) {
263 Constant *SubInit = nullptr;
265 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
266 Changed |= CleanupConstantGlobalUsers(CE, SubInit, DL, TLI);
267 } else if ((CE->getOpcode() == Instruction::BitCast &&
268 CE->getType()->isPointerTy()) ||
269 CE->getOpcode() == Instruction::AddrSpaceCast) {
270 // Pointer cast, delete any stores and memsets to the global.
271 Changed |= CleanupConstantGlobalUsers(CE, nullptr, DL, TLI);
274 if (CE->use_empty()) {
275 CE->destroyConstant();
278 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
279 // Do not transform "gepinst (gep constexpr (GV))" here, because forming
280 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
281 // and will invalidate our notion of what Init is.
282 Constant *SubInit = nullptr;
283 if (!isa<ConstantExpr>(GEP->getOperand(0))) {
284 ConstantExpr *CE = dyn_cast_or_null<ConstantExpr>(
285 ConstantFoldInstruction(GEP, DL, TLI));
286 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
287 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
289 // If the initializer is an all-null value and we have an inbounds GEP,
290 // we already know what the result of any load from that GEP is.
291 // TODO: Handle splats.
292 if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
293 SubInit = Constant::getNullValue(GEP->getResultElementType());
295 Changed |= CleanupConstantGlobalUsers(GEP, SubInit, DL, TLI);
297 if (GEP->use_empty()) {
298 GEP->eraseFromParent();
301 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
302 if (MI->getRawDest() == V) {
303 MI->eraseFromParent();
307 } else if (Constant *C = dyn_cast<Constant>(U)) {
308 // If we have a chain of dead constantexprs or other things dangling from
309 // us, and if they are all dead, nuke them without remorse.
310 if (isSafeToDestroyConstant(C)) {
311 C->destroyConstant();
312 CleanupConstantGlobalUsers(V, Init, DL, TLI);
320 /// Return true if the specified instruction is a safe user of a derived
321 /// expression from a global that we want to SROA.
322 static bool isSafeSROAElementUse(Value *V) {
323 // We might have a dead and dangling constant hanging off of here.
324 if (Constant *C = dyn_cast<Constant>(V))
325 return isSafeToDestroyConstant(C);
327 Instruction *I = dyn_cast<Instruction>(V);
328 if (!I) return false;
331 if (isa<LoadInst>(I)) return true;
333 // Stores *to* the pointer are ok.
334 if (StoreInst *SI = dyn_cast<StoreInst>(I))
335 return SI->getOperand(0) != V;
337 // Otherwise, it must be a GEP.
338 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
339 if (!GEPI) return false;
341 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
342 !cast<Constant>(GEPI->getOperand(1))->isNullValue())
345 for (User *U : GEPI->users())
346 if (!isSafeSROAElementUse(U))
352 /// U is a direct user of the specified global value. Look at it and its uses
353 /// and decide whether it is safe to SROA this global.
354 static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
355 // The user of the global must be a GEP Inst or a ConstantExpr GEP.
356 if (!isa<GetElementPtrInst>(U) &&
357 (!isa<ConstantExpr>(U) ||
358 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
361 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we
362 // don't like < 3 operand CE's, and we don't like non-constant integer
363 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
365 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
366 !cast<Constant>(U->getOperand(1))->isNullValue() ||
367 !isa<ConstantInt>(U->getOperand(2)))
370 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
371 ++GEPI; // Skip over the pointer index.
373 // If this is a use of an array allocation, do a bit more checking for sanity.
374 if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
375 uint64_t NumElements = AT->getNumElements();
376 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
378 // Check to make sure that index falls within the array. If not,
379 // something funny is going on, so we won't do the optimization.
381 if (Idx->getZExtValue() >= NumElements)
384 // We cannot scalar repl this level of the array unless any array
385 // sub-indices are in-range constants. In particular, consider:
386 // A[0][i]. We cannot know that the user isn't doing invalid things like
387 // allowing i to index an out-of-range subscript that accesses A[1].
389 // Scalar replacing *just* the outer index of the array is probably not
390 // going to be a win anyway, so just give up.
391 for (++GEPI; // Skip array index.
394 uint64_t NumElements;
395 if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
396 NumElements = SubArrayTy->getNumElements();
397 else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
398 NumElements = SubVectorTy->getNumElements();
400 assert((*GEPI)->isStructTy() &&
401 "Indexed GEP type is not array, vector, or struct!");
405 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
406 if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
411 for (User *UU : U->users())
412 if (!isSafeSROAElementUse(UU))
418 /// Look at all uses of the global and decide whether it is safe for us to
419 /// perform this transformation.
420 static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
421 for (User *U : GV->users())
422 if (!IsUserOfGlobalSafeForSRA(U, GV))
429 /// Perform scalar replacement of aggregates on the specified global variable.
430 /// This opens the door for other optimizations by exposing the behavior of the
431 /// program in a more fine-grained way. We have determined that this
432 /// transformation is safe already. We return the first global variable we
433 /// insert so that the caller can reprocess it.
434 static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) {
435 // Make sure this global only has simple uses that we can SRA.
436 if (!GlobalUsersSafeToSRA(GV))
439 assert(GV->hasLocalLinkage());
440 Constant *Init = GV->getInitializer();
441 Type *Ty = Init->getType();
443 std::vector<GlobalVariable*> NewGlobals;
444 Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
446 // Get the alignment of the global, either explicit or target-specific.
447 unsigned StartAlignment = GV->getAlignment();
448 if (StartAlignment == 0)
449 StartAlignment = DL.getABITypeAlignment(GV->getType());
451 if (StructType *STy = dyn_cast<StructType>(Ty)) {
452 NewGlobals.reserve(STy->getNumElements());
453 const StructLayout &Layout = *DL.getStructLayout(STy);
454 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
455 Constant *In = Init->getAggregateElement(i);
456 assert(In && "Couldn't get element of initializer?");
457 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
458 GlobalVariable::InternalLinkage,
459 In, GV->getName()+"."+Twine(i),
460 GV->getThreadLocalMode(),
461 GV->getType()->getAddressSpace());
462 NGV->setExternallyInitialized(GV->isExternallyInitialized());
463 NGV->copyAttributesFrom(GV);
464 Globals.push_back(NGV);
465 NewGlobals.push_back(NGV);
467 // Calculate the known alignment of the field. If the original aggregate
468 // had 256 byte alignment for example, something might depend on that:
469 // propagate info to each field.
470 uint64_t FieldOffset = Layout.getElementOffset(i);
471 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
472 if (NewAlign > DL.getABITypeAlignment(STy->getElementType(i)))
473 NGV->setAlignment(NewAlign);
475 } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
476 unsigned NumElements = 0;
477 if (ArrayType *ATy = dyn_cast<ArrayType>(STy))
478 NumElements = ATy->getNumElements();
480 NumElements = cast<VectorType>(STy)->getNumElements();
482 if (NumElements > 16 && GV->hasNUsesOrMore(16))
483 return nullptr; // It's not worth it.
484 NewGlobals.reserve(NumElements);
486 uint64_t EltSize = DL.getTypeAllocSize(STy->getElementType());
487 unsigned EltAlign = DL.getABITypeAlignment(STy->getElementType());
488 for (unsigned i = 0, e = NumElements; i != e; ++i) {
489 Constant *In = Init->getAggregateElement(i);
490 assert(In && "Couldn't get element of initializer?");
492 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
493 GlobalVariable::InternalLinkage,
494 In, GV->getName()+"."+Twine(i),
495 GV->getThreadLocalMode(),
496 GV->getType()->getAddressSpace());
497 NGV->setExternallyInitialized(GV->isExternallyInitialized());
498 NGV->copyAttributesFrom(GV);
499 Globals.push_back(NGV);
500 NewGlobals.push_back(NGV);
502 // Calculate the known alignment of the field. If the original aggregate
503 // had 256 byte alignment for example, something might depend on that:
504 // propagate info to each field.
505 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
506 if (NewAlign > EltAlign)
507 NGV->setAlignment(NewAlign);
511 if (NewGlobals.empty())
514 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV << "\n");
516 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
518 // Loop over all of the uses of the global, replacing the constantexpr geps,
519 // with smaller constantexpr geps or direct references.
520 while (!GV->use_empty()) {
521 User *GEP = GV->user_back();
522 assert(((isa<ConstantExpr>(GEP) &&
523 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
524 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
526 // Ignore the 1th operand, which has to be zero or else the program is quite
527 // broken (undefined). Get the 2nd operand, which is the structure or array
529 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
530 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
532 Value *NewPtr = NewGlobals[Val];
533 Type *NewTy = NewGlobals[Val]->getValueType();
535 // Form a shorter GEP if needed.
536 if (GEP->getNumOperands() > 3) {
537 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
538 SmallVector<Constant*, 8> Idxs;
539 Idxs.push_back(NullInt);
540 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
541 Idxs.push_back(CE->getOperand(i));
543 ConstantExpr::getGetElementPtr(NewTy, cast<Constant>(NewPtr), Idxs);
545 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
546 SmallVector<Value*, 8> Idxs;
547 Idxs.push_back(NullInt);
548 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
549 Idxs.push_back(GEPI->getOperand(i));
550 NewPtr = GetElementPtrInst::Create(
551 NewTy, NewPtr, Idxs, GEPI->getName() + "." + Twine(Val), GEPI);
554 GEP->replaceAllUsesWith(NewPtr);
556 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
557 GEPI->eraseFromParent();
559 cast<ConstantExpr>(GEP)->destroyConstant();
562 // Delete the old global, now that it is dead.
566 // Loop over the new globals array deleting any globals that are obviously
567 // dead. This can arise due to scalarization of a structure or an array that
568 // has elements that are dead.
569 unsigned FirstGlobal = 0;
570 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
571 if (NewGlobals[i]->use_empty()) {
572 Globals.erase(NewGlobals[i]);
573 if (FirstGlobal == i) ++FirstGlobal;
576 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : nullptr;
579 /// Return true if all users of the specified value will trap if the value is
580 /// dynamically null. PHIs keeps track of any phi nodes we've seen to avoid
581 /// reprocessing them.
582 static bool AllUsesOfValueWillTrapIfNull(const Value *V,
583 SmallPtrSetImpl<const PHINode*> &PHIs) {
584 for (const User *U : V->users())
585 if (isa<LoadInst>(U)) {
587 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
588 if (SI->getOperand(0) == V) {
589 //cerr << "NONTRAPPING USE: " << *U;
590 return false; // Storing the value.
592 } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
593 if (CI->getCalledValue() != V) {
594 //cerr << "NONTRAPPING USE: " << *U;
595 return false; // Not calling the ptr
597 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
598 if (II->getCalledValue() != V) {
599 //cerr << "NONTRAPPING USE: " << *U;
600 return false; // Not calling the ptr
602 } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
603 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
604 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
605 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
606 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
607 // If we've already seen this phi node, ignore it, it has already been
609 if (PHIs.insert(PN).second && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
611 } else if (isa<ICmpInst>(U) &&
612 isa<ConstantPointerNull>(U->getOperand(1))) {
613 // Ignore icmp X, null
615 //cerr << "NONTRAPPING USE: " << *U;
622 /// Return true if all uses of any loads from GV will trap if the loaded value
623 /// is null. Note that this also permits comparisons of the loaded value
624 /// against null, as a special case.
625 static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
626 for (const User *U : GV->users())
627 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
628 SmallPtrSet<const PHINode*, 8> PHIs;
629 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
631 } else if (isa<StoreInst>(U)) {
632 // Ignore stores to the global.
634 // We don't know or understand this user, bail out.
635 //cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
641 static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
642 bool Changed = false;
643 for (auto UI = V->user_begin(), E = V->user_end(); UI != E; ) {
644 Instruction *I = cast<Instruction>(*UI++);
645 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
646 LI->setOperand(0, NewV);
648 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
649 if (SI->getOperand(1) == V) {
650 SI->setOperand(1, NewV);
653 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
655 if (CS.getCalledValue() == V) {
656 // Calling through the pointer! Turn into a direct call, but be careful
657 // that the pointer is not also being passed as an argument.
658 CS.setCalledFunction(NewV);
660 bool PassedAsArg = false;
661 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
662 if (CS.getArgument(i) == V) {
664 CS.setArgument(i, NewV);
668 // Being passed as an argument also. Be careful to not invalidate UI!
669 UI = V->user_begin();
672 } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
673 Changed |= OptimizeAwayTrappingUsesOfValue(CI,
674 ConstantExpr::getCast(CI->getOpcode(),
675 NewV, CI->getType()));
676 if (CI->use_empty()) {
678 CI->eraseFromParent();
680 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
681 // Should handle GEP here.
682 SmallVector<Constant*, 8> Idxs;
683 Idxs.reserve(GEPI->getNumOperands()-1);
684 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
686 if (Constant *C = dyn_cast<Constant>(*i))
690 if (Idxs.size() == GEPI->getNumOperands()-1)
691 Changed |= OptimizeAwayTrappingUsesOfValue(
692 GEPI, ConstantExpr::getGetElementPtr(nullptr, NewV, Idxs));
693 if (GEPI->use_empty()) {
695 GEPI->eraseFromParent();
704 /// The specified global has only one non-null value stored into it. If there
705 /// are uses of the loaded value that would trap if the loaded value is
706 /// dynamically null, then we know that they cannot be reachable with a null
707 /// optimize away the load.
708 static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV,
709 const DataLayout &DL,
710 TargetLibraryInfo *TLI) {
711 bool Changed = false;
713 // Keep track of whether we are able to remove all the uses of the global
714 // other than the store that defines it.
715 bool AllNonStoreUsesGone = true;
717 // Replace all uses of loads with uses of uses of the stored value.
718 for (Value::user_iterator GUI = GV->user_begin(), E = GV->user_end(); GUI != E;){
719 User *GlobalUser = *GUI++;
720 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
721 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
722 // If we were able to delete all uses of the loads
723 if (LI->use_empty()) {
724 LI->eraseFromParent();
727 AllNonStoreUsesGone = false;
729 } else if (isa<StoreInst>(GlobalUser)) {
730 // Ignore the store that stores "LV" to the global.
731 assert(GlobalUser->getOperand(1) == GV &&
732 "Must be storing *to* the global");
734 AllNonStoreUsesGone = false;
736 // If we get here we could have other crazy uses that are transitively
738 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
739 isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) ||
740 isa<BitCastInst>(GlobalUser) ||
741 isa<GetElementPtrInst>(GlobalUser)) &&
742 "Only expect load and stores!");
747 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV << "\n");
751 // If we nuked all of the loads, then none of the stores are needed either,
752 // nor is the global.
753 if (AllNonStoreUsesGone) {
754 if (isLeakCheckerRoot(GV)) {
755 Changed |= CleanupPointerRootUsers(GV, TLI);
758 CleanupConstantGlobalUsers(GV, nullptr, DL, TLI);
760 if (GV->use_empty()) {
761 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
763 GV->eraseFromParent();
770 /// Walk the use list of V, constant folding all of the instructions that are
772 static void ConstantPropUsersOf(Value *V, const DataLayout &DL,
773 TargetLibraryInfo *TLI) {
774 for (Value::user_iterator UI = V->user_begin(), E = V->user_end(); UI != E; )
775 if (Instruction *I = dyn_cast<Instruction>(*UI++))
776 if (Constant *NewC = ConstantFoldInstruction(I, DL, TLI)) {
777 I->replaceAllUsesWith(NewC);
779 // Advance UI to the next non-I use to avoid invalidating it!
780 // Instructions could multiply use V.
781 while (UI != E && *UI == I)
783 if (isInstructionTriviallyDead(I, TLI))
784 I->eraseFromParent();
788 /// This function takes the specified global variable, and transforms the
789 /// program as if it always contained the result of the specified malloc.
790 /// Because it is always the result of the specified malloc, there is no reason
791 /// to actually DO the malloc. Instead, turn the malloc into a global, and any
792 /// loads of GV as uses of the new global.
793 static GlobalVariable *
794 OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, CallInst *CI, Type *AllocTy,
795 ConstantInt *NElements, const DataLayout &DL,
796 TargetLibraryInfo *TLI) {
797 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n');
800 if (NElements->getZExtValue() == 1)
801 GlobalType = AllocTy;
803 // If we have an array allocation, the global variable is of an array.
804 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
806 // Create the new global variable. The contents of the malloc'd memory is
807 // undefined, so initialize with an undef value.
808 GlobalVariable *NewGV = new GlobalVariable(
809 *GV->getParent(), GlobalType, false, GlobalValue::InternalLinkage,
810 UndefValue::get(GlobalType), GV->getName() + ".body", nullptr,
811 GV->getThreadLocalMode());
813 // If there are bitcast users of the malloc (which is typical, usually we have
814 // a malloc + bitcast) then replace them with uses of the new global. Update
815 // other users to use the global as well.
816 BitCastInst *TheBC = nullptr;
817 while (!CI->use_empty()) {
818 Instruction *User = cast<Instruction>(CI->user_back());
819 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
820 if (BCI->getType() == NewGV->getType()) {
821 BCI->replaceAllUsesWith(NewGV);
822 BCI->eraseFromParent();
824 BCI->setOperand(0, NewGV);
828 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
829 User->replaceUsesOfWith(CI, TheBC);
833 Constant *RepValue = NewGV;
834 if (NewGV->getType() != GV->getValueType())
835 RepValue = ConstantExpr::getBitCast(RepValue, GV->getValueType());
837 // If there is a comparison against null, we will insert a global bool to
838 // keep track of whether the global was initialized yet or not.
839 GlobalVariable *InitBool =
840 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
841 GlobalValue::InternalLinkage,
842 ConstantInt::getFalse(GV->getContext()),
843 GV->getName()+".init", GV->getThreadLocalMode());
844 bool InitBoolUsed = false;
846 // Loop over all uses of GV, processing them in turn.
847 while (!GV->use_empty()) {
848 if (StoreInst *SI = dyn_cast<StoreInst>(GV->user_back())) {
849 // The global is initialized when the store to it occurs.
850 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
851 SI->getOrdering(), SI->getSynchScope(), SI);
852 SI->eraseFromParent();
856 LoadInst *LI = cast<LoadInst>(GV->user_back());
857 while (!LI->use_empty()) {
858 Use &LoadUse = *LI->use_begin();
859 ICmpInst *ICI = dyn_cast<ICmpInst>(LoadUse.getUser());
865 // Replace the cmp X, 0 with a use of the bool value.
866 // Sink the load to where the compare was, if atomic rules allow us to.
867 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
868 LI->getOrdering(), LI->getSynchScope(),
869 LI->isUnordered() ? (Instruction*)ICI : LI);
871 switch (ICI->getPredicate()) {
872 default: llvm_unreachable("Unknown ICmp Predicate!");
873 case ICmpInst::ICMP_ULT:
874 case ICmpInst::ICMP_SLT: // X < null -> always false
875 LV = ConstantInt::getFalse(GV->getContext());
877 case ICmpInst::ICMP_ULE:
878 case ICmpInst::ICMP_SLE:
879 case ICmpInst::ICMP_EQ:
880 LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
882 case ICmpInst::ICMP_NE:
883 case ICmpInst::ICMP_UGE:
884 case ICmpInst::ICMP_SGE:
885 case ICmpInst::ICMP_UGT:
886 case ICmpInst::ICMP_SGT:
889 ICI->replaceAllUsesWith(LV);
890 ICI->eraseFromParent();
892 LI->eraseFromParent();
895 // If the initialization boolean was used, insert it, otherwise delete it.
897 while (!InitBool->use_empty()) // Delete initializations
898 cast<StoreInst>(InitBool->user_back())->eraseFromParent();
901 GV->getParent()->getGlobalList().insert(GV->getIterator(), InitBool);
903 // Now the GV is dead, nuke it and the malloc..
904 GV->eraseFromParent();
905 CI->eraseFromParent();
907 // To further other optimizations, loop over all users of NewGV and try to
908 // constant prop them. This will promote GEP instructions with constant
909 // indices into GEP constant-exprs, which will allow global-opt to hack on it.
910 ConstantPropUsersOf(NewGV, DL, TLI);
911 if (RepValue != NewGV)
912 ConstantPropUsersOf(RepValue, DL, TLI);
917 /// Scan the use-list of V checking to make sure that there are no complex uses
918 /// of V. We permit simple things like dereferencing the pointer, but not
919 /// storing through the address, unless it is to the specified global.
920 static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
921 const GlobalVariable *GV,
922 SmallPtrSetImpl<const PHINode*> &PHIs) {
923 for (const User *U : V->users()) {
924 const Instruction *Inst = cast<Instruction>(U);
926 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
927 continue; // Fine, ignore.
930 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
931 if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
932 return false; // Storing the pointer itself... bad.
933 continue; // Otherwise, storing through it, or storing into GV... fine.
936 // Must index into the array and into the struct.
937 if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
938 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
943 if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
944 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI
946 if (PHIs.insert(PN).second)
947 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
952 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
953 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
963 /// The Alloc pointer is stored into GV somewhere. Transform all uses of the
964 /// allocation into loads from the global and uses of the resultant pointer.
965 /// Further, delete the store into GV. This assumes that these value pass the
966 /// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
967 static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc,
968 GlobalVariable *GV) {
969 while (!Alloc->use_empty()) {
970 Instruction *U = cast<Instruction>(*Alloc->user_begin());
971 Instruction *InsertPt = U;
972 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
973 // If this is the store of the allocation into the global, remove it.
974 if (SI->getOperand(1) == GV) {
975 SI->eraseFromParent();
978 } else if (PHINode *PN = dyn_cast<PHINode>(U)) {
979 // Insert the load in the corresponding predecessor, not right before the
981 InsertPt = PN->getIncomingBlock(*Alloc->use_begin())->getTerminator();
982 } else if (isa<BitCastInst>(U)) {
983 // Must be bitcast between the malloc and store to initialize the global.
984 ReplaceUsesOfMallocWithGlobal(U, GV);
985 U->eraseFromParent();
987 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
988 // If this is a "GEP bitcast" and the user is a store to the global, then
989 // just process it as a bitcast.
990 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse())
991 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->user_back()))
992 if (SI->getOperand(1) == GV) {
993 // Must be bitcast GEP between the malloc and store to initialize
995 ReplaceUsesOfMallocWithGlobal(GEPI, GV);
996 GEPI->eraseFromParent();
1001 // Insert a load from the global, and use it instead of the malloc.
1002 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt);
1003 U->replaceUsesOfWith(Alloc, NL);
1007 /// Verify that all uses of V (a load, or a phi of a load) are simple enough to
1008 /// perform heap SRA on. This permits GEP's that index through the array and
1009 /// struct field, icmps of null, and PHIs.
1010 static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
1011 SmallPtrSetImpl<const PHINode*> &LoadUsingPHIs,
1012 SmallPtrSetImpl<const PHINode*> &LoadUsingPHIsPerLoad) {
1013 // We permit two users of the load: setcc comparing against the null
1014 // pointer, and a getelementptr of a specific form.
1015 for (const User *U : V->users()) {
1016 const Instruction *UI = cast<Instruction>(U);
1018 // Comparison against null is ok.
1019 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UI)) {
1020 if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
1025 // getelementptr is also ok, but only a simple form.
1026 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(UI)) {
1027 // Must index into the array and into the struct.
1028 if (GEPI->getNumOperands() < 3)
1031 // Otherwise the GEP is ok.
1035 if (const PHINode *PN = dyn_cast<PHINode>(UI)) {
1036 if (!LoadUsingPHIsPerLoad.insert(PN).second)
1037 // This means some phi nodes are dependent on each other.
1038 // Avoid infinite looping!
1040 if (!LoadUsingPHIs.insert(PN).second)
1041 // If we have already analyzed this PHI, then it is safe.
1044 // Make sure all uses of the PHI are simple enough to transform.
1045 if (!LoadUsesSimpleEnoughForHeapSRA(PN,
1046 LoadUsingPHIs, LoadUsingPHIsPerLoad))
1052 // Otherwise we don't know what this is, not ok.
1060 /// If all users of values loaded from GV are simple enough to perform HeapSRA,
1062 static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
1063 Instruction *StoredVal) {
1064 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
1065 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
1066 for (const User *U : GV->users())
1067 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
1068 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
1069 LoadUsingPHIsPerLoad))
1071 LoadUsingPHIsPerLoad.clear();
1074 // If we reach here, we know that all uses of the loads and transitive uses
1075 // (through PHI nodes) are simple enough to transform. However, we don't know
1076 // that all inputs the to the PHI nodes are in the same equivalence sets.
1077 // Check to verify that all operands of the PHIs are either PHIS that can be
1078 // transformed, loads from GV, or MI itself.
1079 for (const PHINode *PN : LoadUsingPHIs) {
1080 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
1081 Value *InVal = PN->getIncomingValue(op);
1083 // PHI of the stored value itself is ok.
1084 if (InVal == StoredVal) continue;
1086 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
1087 // One of the PHIs in our set is (optimistically) ok.
1088 if (LoadUsingPHIs.count(InPN))
1093 // Load from GV is ok.
1094 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
1095 if (LI->getOperand(0) == GV)
1100 // Anything else is rejected.
1108 static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
1109 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1110 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1111 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
1113 if (FieldNo >= FieldVals.size())
1114 FieldVals.resize(FieldNo+1);
1116 // If we already have this value, just reuse the previously scalarized
1118 if (Value *FieldVal = FieldVals[FieldNo])
1121 // Depending on what instruction this is, we have several cases.
1123 if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
1124 // This is a scalarized version of the load from the global. Just create
1125 // a new Load of the scalarized global.
1126 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
1127 InsertedScalarizedValues,
1129 LI->getName()+".f"+Twine(FieldNo), LI);
1131 PHINode *PN = cast<PHINode>(V);
1132 // PN's type is pointer to struct. Make a new PHI of pointer to struct
1135 PointerType *PTy = cast<PointerType>(PN->getType());
1136 StructType *ST = cast<StructType>(PTy->getElementType());
1138 unsigned AS = PTy->getAddressSpace();
1140 PHINode::Create(PointerType::get(ST->getElementType(FieldNo), AS),
1141 PN->getNumIncomingValues(),
1142 PN->getName()+".f"+Twine(FieldNo), PN);
1144 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
1147 return FieldVals[FieldNo] = Result;
1150 /// Given a load instruction and a value derived from the load, rewrite the
1151 /// derived value to use the HeapSRoA'd load.
1152 static void RewriteHeapSROALoadUser(Instruction *LoadUser,
1153 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1154 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1155 // If this is a comparison against null, handle it.
1156 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
1157 assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
1158 // If we have a setcc of the loaded pointer, we can use a setcc of any
1160 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
1161 InsertedScalarizedValues, PHIsToRewrite);
1163 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
1164 Constant::getNullValue(NPtr->getType()),
1166 SCI->replaceAllUsesWith(New);
1167 SCI->eraseFromParent();
1171 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
1172 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
1173 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
1174 && "Unexpected GEPI!");
1176 // Load the pointer for this field.
1177 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
1178 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
1179 InsertedScalarizedValues, PHIsToRewrite);
1181 // Create the new GEP idx vector.
1182 SmallVector<Value*, 8> GEPIdx;
1183 GEPIdx.push_back(GEPI->getOperand(1));
1184 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
1186 Value *NGEPI = GetElementPtrInst::Create(GEPI->getResultElementType(), NewPtr, GEPIdx,
1187 GEPI->getName(), GEPI);
1188 GEPI->replaceAllUsesWith(NGEPI);
1189 GEPI->eraseFromParent();
1193 // Recursively transform the users of PHI nodes. This will lazily create the
1194 // PHIs that are needed for individual elements. Keep track of what PHIs we
1195 // see in InsertedScalarizedValues so that we don't get infinite loops (very
1196 // antisocial). If the PHI is already in InsertedScalarizedValues, it has
1197 // already been seen first by another load, so its uses have already been
1199 PHINode *PN = cast<PHINode>(LoadUser);
1200 if (!InsertedScalarizedValues.insert(std::make_pair(PN,
1201 std::vector<Value*>())).second)
1204 // If this is the first time we've seen this PHI, recursively process all
1206 for (auto UI = PN->user_begin(), E = PN->user_end(); UI != E;) {
1207 Instruction *User = cast<Instruction>(*UI++);
1208 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1212 /// We are performing Heap SRoA on a global. Ptr is a value loaded from the
1213 /// global. Eliminate all uses of Ptr, making them use FieldGlobals instead.
1214 /// All uses of loaded values satisfy AllGlobalLoadUsesSimpleEnoughForHeapSRA.
1215 static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
1216 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
1217 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
1218 for (auto UI = Load->user_begin(), E = Load->user_end(); UI != E;) {
1219 Instruction *User = cast<Instruction>(*UI++);
1220 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1223 if (Load->use_empty()) {
1224 Load->eraseFromParent();
1225 InsertedScalarizedValues.erase(Load);
1229 /// CI is an allocation of an array of structures. Break it up into multiple
1230 /// allocations of arrays of the fields.
1231 static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
1232 Value *NElems, const DataLayout &DL,
1233 const TargetLibraryInfo *TLI) {
1234 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n');
1235 Type *MAT = getMallocAllocatedType(CI, TLI);
1236 StructType *STy = cast<StructType>(MAT);
1238 // There is guaranteed to be at least one use of the malloc (storing
1239 // it into GV). If there are other uses, change them to be uses of
1240 // the global to simplify later code. This also deletes the store
1242 ReplaceUsesOfMallocWithGlobal(CI, GV);
1244 // Okay, at this point, there are no users of the malloc. Insert N
1245 // new mallocs at the same place as CI, and N globals.
1246 std::vector<Value*> FieldGlobals;
1247 std::vector<Value*> FieldMallocs;
1249 SmallVector<OperandBundleDef, 1> OpBundles;
1250 CI->getOperandBundlesAsDefs(OpBundles);
1252 unsigned AS = GV->getType()->getPointerAddressSpace();
1253 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
1254 Type *FieldTy = STy->getElementType(FieldNo);
1255 PointerType *PFieldTy = PointerType::get(FieldTy, AS);
1257 GlobalVariable *NGV = new GlobalVariable(
1258 *GV->getParent(), PFieldTy, false, GlobalValue::InternalLinkage,
1259 Constant::getNullValue(PFieldTy), GV->getName() + ".f" + Twine(FieldNo),
1260 nullptr, GV->getThreadLocalMode());
1261 NGV->copyAttributesFrom(GV);
1262 FieldGlobals.push_back(NGV);
1264 unsigned TypeSize = DL.getTypeAllocSize(FieldTy);
1265 if (StructType *ST = dyn_cast<StructType>(FieldTy))
1266 TypeSize = DL.getStructLayout(ST)->getSizeInBytes();
1267 Type *IntPtrTy = DL.getIntPtrType(CI->getType());
1268 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
1269 ConstantInt::get(IntPtrTy, TypeSize),
1270 NElems, OpBundles, nullptr,
1271 CI->getName() + ".f" + Twine(FieldNo));
1272 FieldMallocs.push_back(NMI);
1273 new StoreInst(NMI, NGV, CI);
1276 // The tricky aspect of this transformation is handling the case when malloc
1277 // fails. In the original code, malloc failing would set the result pointer
1278 // of malloc to null. In this case, some mallocs could succeed and others
1279 // could fail. As such, we emit code that looks like this:
1280 // F0 = malloc(field0)
1281 // F1 = malloc(field1)
1282 // F2 = malloc(field2)
1283 // if (F0 == 0 || F1 == 0 || F2 == 0) {
1284 // if (F0) { free(F0); F0 = 0; }
1285 // if (F1) { free(F1); F1 = 0; }
1286 // if (F2) { free(F2); F2 = 0; }
1288 // The malloc can also fail if its argument is too large.
1289 Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
1290 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
1291 ConstantZero, "isneg");
1292 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
1293 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
1294 Constant::getNullValue(FieldMallocs[i]->getType()),
1296 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
1299 // Split the basic block at the old malloc.
1300 BasicBlock *OrigBB = CI->getParent();
1301 BasicBlock *ContBB =
1302 OrigBB->splitBasicBlock(CI->getIterator(), "malloc_cont");
1304 // Create the block to check the first condition. Put all these blocks at the
1305 // end of the function as they are unlikely to be executed.
1306 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
1308 OrigBB->getParent());
1310 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
1311 // branch on RunningOr.
1312 OrigBB->getTerminator()->eraseFromParent();
1313 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
1315 // Within the NullPtrBlock, we need to emit a comparison and branch for each
1316 // pointer, because some may be null while others are not.
1317 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1318 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
1319 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
1320 Constant::getNullValue(GVVal->getType()));
1321 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
1322 OrigBB->getParent());
1323 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
1324 OrigBB->getParent());
1325 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
1328 // Fill in FreeBlock.
1329 CallInst::CreateFree(GVVal, OpBundles, BI);
1330 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
1332 BranchInst::Create(NextBlock, FreeBlock);
1334 NullPtrBlock = NextBlock;
1337 BranchInst::Create(ContBB, NullPtrBlock);
1339 // CI is no longer needed, remove it.
1340 CI->eraseFromParent();
1342 /// As we process loads, if we can't immediately update all uses of the load,
1343 /// keep track of what scalarized loads are inserted for a given load.
1344 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues;
1345 InsertedScalarizedValues[GV] = FieldGlobals;
1347 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite;
1349 // Okay, the malloc site is completely handled. All of the uses of GV are now
1350 // loads, and all uses of those loads are simple. Rewrite them to use loads
1351 // of the per-field globals instead.
1352 for (auto UI = GV->user_begin(), E = GV->user_end(); UI != E;) {
1353 Instruction *User = cast<Instruction>(*UI++);
1355 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1356 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
1360 // Must be a store of null.
1361 StoreInst *SI = cast<StoreInst>(User);
1362 assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
1363 "Unexpected heap-sra user!");
1365 // Insert a store of null into each global.
1366 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1367 Type *ValTy = cast<GlobalValue>(FieldGlobals[i])->getValueType();
1368 Constant *Null = Constant::getNullValue(ValTy);
1369 new StoreInst(Null, FieldGlobals[i], SI);
1371 // Erase the original store.
1372 SI->eraseFromParent();
1375 // While we have PHIs that are interesting to rewrite, do it.
1376 while (!PHIsToRewrite.empty()) {
1377 PHINode *PN = PHIsToRewrite.back().first;
1378 unsigned FieldNo = PHIsToRewrite.back().second;
1379 PHIsToRewrite.pop_back();
1380 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
1381 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
1383 // Add all the incoming values. This can materialize more phis.
1384 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1385 Value *InVal = PN->getIncomingValue(i);
1386 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
1388 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
1392 // Drop all inter-phi links and any loads that made it this far.
1393 for (DenseMap<Value*, std::vector<Value*> >::iterator
1394 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1396 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1397 PN->dropAllReferences();
1398 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1399 LI->dropAllReferences();
1402 // Delete all the phis and loads now that inter-references are dead.
1403 for (DenseMap<Value*, std::vector<Value*> >::iterator
1404 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1406 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1407 PN->eraseFromParent();
1408 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1409 LI->eraseFromParent();
1412 // The old global is now dead, remove it.
1413 GV->eraseFromParent();
1416 return cast<GlobalVariable>(FieldGlobals[0]);
1419 /// This function is called when we see a pointer global variable with a single
1420 /// value stored it that is a malloc or cast of malloc.
1421 static bool tryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, CallInst *CI,
1423 AtomicOrdering Ordering,
1424 const DataLayout &DL,
1425 TargetLibraryInfo *TLI) {
1426 // If this is a malloc of an abstract type, don't touch it.
1427 if (!AllocTy->isSized())
1430 // We can't optimize this global unless all uses of it are *known* to be
1431 // of the malloc value, not of the null initializer value (consider a use
1432 // that compares the global's value against zero to see if the malloc has
1433 // been reached). To do this, we check to see if all uses of the global
1434 // would trap if the global were null: this proves that they must all
1435 // happen after the malloc.
1436 if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
1439 // We can't optimize this if the malloc itself is used in a complex way,
1440 // for example, being stored into multiple globals. This allows the
1441 // malloc to be stored into the specified global, loaded icmp'd, and
1442 // GEP'd. These are all things we could transform to using the global
1444 SmallPtrSet<const PHINode*, 8> PHIs;
1445 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
1448 // If we have a global that is only initialized with a fixed size malloc,
1449 // transform the program to use global memory instead of malloc'd memory.
1450 // This eliminates dynamic allocation, avoids an indirection accessing the
1451 // data, and exposes the resultant global to further GlobalOpt.
1452 // We cannot optimize the malloc if we cannot determine malloc array size.
1453 Value *NElems = getMallocArraySize(CI, DL, TLI, true);
1457 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
1458 // Restrict this transformation to only working on small allocations
1459 // (2048 bytes currently), as we don't want to introduce a 16M global or
1461 if (NElements->getZExtValue() * DL.getTypeAllocSize(AllocTy) < 2048) {
1462 OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, DL, TLI);
1466 // If the allocation is an array of structures, consider transforming this
1467 // into multiple malloc'd arrays, one for each field. This is basically
1468 // SRoA for malloc'd memory.
1470 if (Ordering != AtomicOrdering::NotAtomic)
1473 // If this is an allocation of a fixed size array of structs, analyze as a
1474 // variable size array. malloc [100 x struct],1 -> malloc struct, 100
1475 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
1476 if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
1477 AllocTy = AT->getElementType();
1479 StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
1483 // This the structure has an unreasonable number of fields, leave it
1485 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
1486 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
1488 // If this is a fixed size array, transform the Malloc to be an alloc of
1489 // structs. malloc [100 x struct],1 -> malloc struct, 100
1490 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) {
1491 Type *IntPtrTy = DL.getIntPtrType(CI->getType());
1492 unsigned TypeSize = DL.getStructLayout(AllocSTy)->getSizeInBytes();
1493 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
1494 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
1495 SmallVector<OperandBundleDef, 1> OpBundles;
1496 CI->getOperandBundlesAsDefs(OpBundles);
1497 Instruction *Malloc =
1498 CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy, AllocSize, NumElements,
1499 OpBundles, nullptr, CI->getName());
1500 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
1501 CI->replaceAllUsesWith(Cast);
1502 CI->eraseFromParent();
1503 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc))
1504 CI = cast<CallInst>(BCI->getOperand(0));
1506 CI = cast<CallInst>(Malloc);
1509 PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, DL, TLI, true), DL,
1517 // Try to optimize globals based on the knowledge that only one value (besides
1518 // its initializer) is ever stored to the global.
1519 static bool optimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
1520 AtomicOrdering Ordering,
1521 const DataLayout &DL,
1522 TargetLibraryInfo *TLI) {
1523 // Ignore no-op GEPs and bitcasts.
1524 StoredOnceVal = StoredOnceVal->stripPointerCasts();
1526 // If we are dealing with a pointer global that is initialized to null and
1527 // only has one (non-null) value stored into it, then we can optimize any
1528 // users of the loaded value (often calls and loads) that would trap if the
1530 if (GV->getInitializer()->getType()->isPointerTy() &&
1531 GV->getInitializer()->isNullValue()) {
1532 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
1533 if (GV->getInitializer()->getType() != SOVC->getType())
1534 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
1536 // Optimize away any trapping uses of the loaded value.
1537 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, DL, TLI))
1539 } else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) {
1540 Type *MallocType = getMallocAllocatedType(CI, TLI);
1541 if (MallocType && tryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType,
1550 /// At this point, we have learned that the only two values ever stored into GV
1551 /// are its initializer and OtherVal. See if we can shrink the global into a
1552 /// boolean and select between the two values whenever it is used. This exposes
1553 /// the values to other scalar optimizations.
1554 static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
1555 Type *GVElType = GV->getValueType();
1557 // If GVElType is already i1, it is already shrunk. If the type of the GV is
1558 // an FP value, pointer or vector, don't do this optimization because a select
1559 // between them is very expensive and unlikely to lead to later
1560 // simplification. In these cases, we typically end up with "cond ? v1 : v2"
1561 // where v1 and v2 both require constant pool loads, a big loss.
1562 if (GVElType == Type::getInt1Ty(GV->getContext()) ||
1563 GVElType->isFloatingPointTy() ||
1564 GVElType->isPointerTy() || GVElType->isVectorTy())
1567 // Walk the use list of the global seeing if all the uses are load or store.
1568 // If there is anything else, bail out.
1569 for (User *U : GV->users())
1570 if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
1573 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV << "\n");
1575 // Create the new global, initializing it to false.
1576 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
1578 GlobalValue::InternalLinkage,
1579 ConstantInt::getFalse(GV->getContext()),
1581 GV->getThreadLocalMode(),
1582 GV->getType()->getAddressSpace());
1583 NewGV->copyAttributesFrom(GV);
1584 GV->getParent()->getGlobalList().insert(GV->getIterator(), NewGV);
1586 Constant *InitVal = GV->getInitializer();
1587 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
1588 "No reason to shrink to bool!");
1590 // If initialized to zero and storing one into the global, we can use a cast
1591 // instead of a select to synthesize the desired value.
1592 bool IsOneZero = false;
1593 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
1594 IsOneZero = InitVal->isNullValue() && CI->isOne();
1596 while (!GV->use_empty()) {
1597 Instruction *UI = cast<Instruction>(GV->user_back());
1598 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
1599 // Change the store into a boolean store.
1600 bool StoringOther = SI->getOperand(0) == OtherVal;
1601 // Only do this if we weren't storing a loaded value.
1603 if (StoringOther || SI->getOperand(0) == InitVal) {
1604 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
1607 // Otherwise, we are storing a previously loaded copy. To do this,
1608 // change the copy from copying the original value to just copying the
1610 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
1612 // If we've already replaced the input, StoredVal will be a cast or
1613 // select instruction. If not, it will be a load of the original
1615 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
1616 assert(LI->getOperand(0) == GV && "Not a copy!");
1617 // Insert a new load, to preserve the saved value.
1618 StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1619 LI->getOrdering(), LI->getSynchScope(), LI);
1621 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
1622 "This is not a form that we understand!");
1623 StoreVal = StoredVal->getOperand(0);
1624 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
1627 new StoreInst(StoreVal, NewGV, false, 0,
1628 SI->getOrdering(), SI->getSynchScope(), SI);
1630 // Change the load into a load of bool then a select.
1631 LoadInst *LI = cast<LoadInst>(UI);
1632 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1633 LI->getOrdering(), LI->getSynchScope(), LI);
1636 NSI = new ZExtInst(NLI, LI->getType(), "", LI);
1638 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
1640 LI->replaceAllUsesWith(NSI);
1642 UI->eraseFromParent();
1645 // Retain the name of the old global variable. People who are debugging their
1646 // programs may expect these variables to be named the same.
1647 NewGV->takeName(GV);
1648 GV->eraseFromParent();
1652 static bool deleteIfDead(GlobalValue &GV,
1653 SmallSet<const Comdat *, 8> &NotDiscardableComdats) {
1654 GV.removeDeadConstantUsers();
1656 if (!GV.isDiscardableIfUnused())
1659 if (const Comdat *C = GV.getComdat())
1660 if (!GV.hasLocalLinkage() && NotDiscardableComdats.count(C))
1664 if (auto *F = dyn_cast<Function>(&GV))
1665 Dead = F->isDefTriviallyDead();
1667 Dead = GV.use_empty();
1671 DEBUG(dbgs() << "GLOBAL DEAD: " << GV << "\n");
1672 GV.eraseFromParent();
1677 static bool isPointerValueDeadOnEntryToFunction(
1678 const Function *F, GlobalValue *GV,
1679 function_ref<DominatorTree &(Function &)> LookupDomTree) {
1680 // Find all uses of GV. We expect them all to be in F, and if we can't
1681 // identify any of the uses we bail out.
1683 // On each of these uses, identify if the memory that GV points to is
1684 // used/required/live at the start of the function. If it is not, for example
1685 // if the first thing the function does is store to the GV, the GV can
1686 // possibly be demoted.
1688 // We don't do an exhaustive search for memory operations - simply look
1689 // through bitcasts as they're quite common and benign.
1690 const DataLayout &DL = GV->getParent()->getDataLayout();
1691 SmallVector<LoadInst *, 4> Loads;
1692 SmallVector<StoreInst *, 4> Stores;
1693 for (auto *U : GV->users()) {
1694 if (Operator::getOpcode(U) == Instruction::BitCast) {
1695 for (auto *UU : U->users()) {
1696 if (auto *LI = dyn_cast<LoadInst>(UU))
1697 Loads.push_back(LI);
1698 else if (auto *SI = dyn_cast<StoreInst>(UU))
1699 Stores.push_back(SI);
1706 Instruction *I = dyn_cast<Instruction>(U);
1709 assert(I->getParent()->getParent() == F);
1711 if (auto *LI = dyn_cast<LoadInst>(I))
1712 Loads.push_back(LI);
1713 else if (auto *SI = dyn_cast<StoreInst>(I))
1714 Stores.push_back(SI);
1719 // We have identified all uses of GV into loads and stores. Now check if all
1720 // of them are known not to depend on the value of the global at the function
1721 // entry point. We do this by ensuring that every load is dominated by at
1723 auto &DT = LookupDomTree(*const_cast<Function *>(F));
1725 // The below check is quadratic. Check we're not going to do too many tests.
1726 // FIXME: Even though this will always have worst-case quadratic time, we
1727 // could put effort into minimizing the average time by putting stores that
1728 // have been shown to dominate at least one load at the beginning of the
1729 // Stores array, making subsequent dominance checks more likely to succeed
1732 // The threshold here is fairly large because global->local demotion is a
1733 // very powerful optimization should it fire.
1734 const unsigned Threshold = 100;
1735 if (Loads.size() * Stores.size() > Threshold)
1738 for (auto *L : Loads) {
1739 auto *LTy = L->getType();
1740 if (!std::any_of(Stores.begin(), Stores.end(), [&](StoreInst *S) {
1741 auto *STy = S->getValueOperand()->getType();
1742 // The load is only dominated by the store if DomTree says so
1743 // and the number of bits loaded in L is less than or equal to
1744 // the number of bits stored in S.
1745 return DT.dominates(S, L) &&
1746 DL.getTypeStoreSize(LTy) <= DL.getTypeStoreSize(STy);
1750 // All loads have known dependences inside F, so the global can be localized.
1754 /// C may have non-instruction users. Can all of those users be turned into
1756 static bool allNonInstructionUsersCanBeMadeInstructions(Constant *C) {
1757 // We don't do this exhaustively. The most common pattern that we really need
1758 // to care about is a constant GEP or constant bitcast - so just looking
1759 // through one single ConstantExpr.
1761 // The set of constants that this function returns true for must be able to be
1762 // handled by makeAllConstantUsesInstructions.
1763 for (auto *U : C->users()) {
1764 if (isa<Instruction>(U))
1766 if (!isa<ConstantExpr>(U))
1767 // Non instruction, non-constantexpr user; cannot convert this.
1769 for (auto *UU : U->users())
1770 if (!isa<Instruction>(UU))
1771 // A constantexpr used by another constant. We don't try and recurse any
1772 // further but just bail out at this point.
1779 /// C may have non-instruction users, and
1780 /// allNonInstructionUsersCanBeMadeInstructions has returned true. Convert the
1781 /// non-instruction users to instructions.
1782 static void makeAllConstantUsesInstructions(Constant *C) {
1783 SmallVector<ConstantExpr*,4> Users;
1784 for (auto *U : C->users()) {
1785 if (isa<ConstantExpr>(U))
1786 Users.push_back(cast<ConstantExpr>(U));
1788 // We should never get here; allNonInstructionUsersCanBeMadeInstructions
1789 // should not have returned true for C.
1791 isa<Instruction>(U) &&
1792 "Can't transform non-constantexpr non-instruction to instruction!");
1795 SmallVector<Value*,4> UUsers;
1796 for (auto *U : Users) {
1798 for (auto *UU : U->users())
1799 UUsers.push_back(UU);
1800 for (auto *UU : UUsers) {
1801 Instruction *UI = cast<Instruction>(UU);
1802 Instruction *NewU = U->getAsInstruction();
1803 NewU->insertBefore(UI);
1804 UI->replaceUsesOfWith(U, NewU);
1806 U->dropAllReferences();
1810 /// Analyze the specified global variable and optimize
1811 /// it if possible. If we make a change, return true.
1812 static bool processInternalGlobal(
1813 GlobalVariable *GV, const GlobalStatus &GS, TargetLibraryInfo *TLI,
1814 function_ref<DominatorTree &(Function &)> LookupDomTree) {
1815 auto &DL = GV->getParent()->getDataLayout();
1816 // If this is a first class global and has only one accessing function and
1817 // this function is non-recursive, we replace the global with a local alloca
1818 // in this function.
1820 // NOTE: It doesn't make sense to promote non-single-value types since we
1821 // are just replacing static memory to stack memory.
1823 // If the global is in different address space, don't bring it to stack.
1824 if (!GS.HasMultipleAccessingFunctions &&
1825 GS.AccessingFunction &&
1826 GV->getValueType()->isSingleValueType() &&
1827 GV->getType()->getAddressSpace() == 0 &&
1828 !GV->isExternallyInitialized() &&
1829 allNonInstructionUsersCanBeMadeInstructions(GV) &&
1830 GS.AccessingFunction->doesNotRecurse() &&
1831 isPointerValueDeadOnEntryToFunction(GS.AccessingFunction, GV,
1833 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV << "\n");
1834 Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction
1835 ->getEntryBlock().begin());
1836 Type *ElemTy = GV->getValueType();
1837 // FIXME: Pass Global's alignment when globals have alignment
1838 AllocaInst *Alloca = new AllocaInst(ElemTy, nullptr,
1839 GV->getName(), &FirstI);
1840 if (!isa<UndefValue>(GV->getInitializer()))
1841 new StoreInst(GV->getInitializer(), Alloca, &FirstI);
1843 makeAllConstantUsesInstructions(GV);
1845 GV->replaceAllUsesWith(Alloca);
1846 GV->eraseFromParent();
1851 // If the global is never loaded (but may be stored to), it is dead.
1854 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV << "\n");
1857 if (isLeakCheckerRoot(GV)) {
1858 // Delete any constant stores to the global.
1859 Changed = CleanupPointerRootUsers(GV, TLI);
1861 // Delete any stores we can find to the global. We may not be able to
1862 // make it completely dead though.
1863 Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
1866 // If the global is dead now, delete it.
1867 if (GV->use_empty()) {
1868 GV->eraseFromParent();
1875 if (GS.StoredType <= GlobalStatus::InitializerStored) {
1876 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n");
1877 GV->setConstant(true);
1879 // Clean up any obviously simplifiable users now.
1880 CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
1882 // If the global is dead now, just nuke it.
1883 if (GV->use_empty()) {
1884 DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
1885 << "all users and delete global!\n");
1886 GV->eraseFromParent();
1891 // Fall through to the next check; see if we can optimize further.
1894 if (!GV->getInitializer()->getType()->isSingleValueType()) {
1895 const DataLayout &DL = GV->getParent()->getDataLayout();
1896 if (SRAGlobal(GV, DL))
1899 if (GS.StoredType == GlobalStatus::StoredOnce && GS.StoredOnceValue) {
1900 // If the initial value for the global was an undef value, and if only
1901 // one other value was stored into it, we can just change the
1902 // initializer to be the stored value, then delete all stores to the
1903 // global. This allows us to mark it constant.
1904 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
1905 if (isa<UndefValue>(GV->getInitializer())) {
1906 // Change the initial value here.
1907 GV->setInitializer(SOVConstant);
1909 // Clean up any obviously simplifiable users now.
1910 CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
1912 if (GV->use_empty()) {
1913 DEBUG(dbgs() << " *** Substituting initializer allowed us to "
1914 << "simplify all users and delete global!\n");
1915 GV->eraseFromParent();
1922 // Try to optimize globals based on the knowledge that only one value
1923 // (besides its initializer) is ever stored to the global.
1924 if (optimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, DL, TLI))
1927 // Otherwise, if the global was not a boolean, we can shrink it to be a
1929 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) {
1930 if (GS.Ordering == AtomicOrdering::NotAtomic) {
1931 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
1942 /// Analyze the specified global variable and optimize it if possible. If we
1943 /// make a change, return true.
1945 processGlobal(GlobalValue &GV, TargetLibraryInfo *TLI,
1946 function_ref<DominatorTree &(Function &)> LookupDomTree) {
1947 if (GV.getName().startswith("llvm."))
1952 if (GlobalStatus::analyzeGlobal(&GV, GS))
1955 bool Changed = false;
1956 if (!GS.IsCompared && !GV.hasGlobalUnnamedAddr()) {
1957 auto NewUnnamedAddr = GV.hasLocalLinkage() ? GlobalValue::UnnamedAddr::Global
1958 : GlobalValue::UnnamedAddr::Local;
1959 if (NewUnnamedAddr != GV.getUnnamedAddr()) {
1960 GV.setUnnamedAddr(NewUnnamedAddr);
1966 // Do more involved optimizations if the global is internal.
1967 if (!GV.hasLocalLinkage())
1970 auto *GVar = dyn_cast<GlobalVariable>(&GV);
1974 if (GVar->isConstant() || !GVar->hasInitializer())
1977 return processInternalGlobal(GVar, GS, TLI, LookupDomTree) || Changed;
1980 /// Walk all of the direct calls of the specified function, changing them to
1982 static void ChangeCalleesToFastCall(Function *F) {
1983 for (User *U : F->users()) {
1984 if (isa<BlockAddress>(U))
1986 CallSite CS(cast<Instruction>(U));
1987 CS.setCallingConv(CallingConv::Fast);
1991 static AttributeSet StripNest(LLVMContext &C, const AttributeSet &Attrs) {
1992 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
1993 unsigned Index = Attrs.getSlotIndex(i);
1994 if (!Attrs.getSlotAttributes(i).hasAttribute(Index, Attribute::Nest))
1997 // There can be only one.
1998 return Attrs.removeAttribute(C, Index, Attribute::Nest);
2004 static void RemoveNestAttribute(Function *F) {
2005 F->setAttributes(StripNest(F->getContext(), F->getAttributes()));
2006 for (User *U : F->users()) {
2007 if (isa<BlockAddress>(U))
2009 CallSite CS(cast<Instruction>(U));
2010 CS.setAttributes(StripNest(F->getContext(), CS.getAttributes()));
2014 /// Return true if this is a calling convention that we'd like to change. The
2015 /// idea here is that we don't want to mess with the convention if the user
2016 /// explicitly requested something with performance implications like coldcc,
2017 /// GHC, or anyregcc.
2018 static bool isProfitableToMakeFastCC(Function *F) {
2019 CallingConv::ID CC = F->getCallingConv();
2020 // FIXME: Is it worth transforming x86_stdcallcc and x86_fastcallcc?
2021 return CC == CallingConv::C || CC == CallingConv::X86_ThisCall;
2025 OptimizeFunctions(Module &M, TargetLibraryInfo *TLI,
2026 function_ref<DominatorTree &(Function &)> LookupDomTree,
2027 SmallSet<const Comdat *, 8> &NotDiscardableComdats) {
2028 bool Changed = false;
2029 // Optimize functions.
2030 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
2031 Function *F = &*FI++;
2032 // Functions without names cannot be referenced outside this module.
2033 if (!F->hasName() && !F->isDeclaration() && !F->hasLocalLinkage())
2034 F->setLinkage(GlobalValue::InternalLinkage);
2036 if (deleteIfDead(*F, NotDiscardableComdats)) {
2041 Changed |= processGlobal(*F, TLI, LookupDomTree);
2043 if (!F->hasLocalLinkage())
2045 if (isProfitableToMakeFastCC(F) && !F->isVarArg() &&
2046 !F->hasAddressTaken()) {
2047 // If this function has a calling convention worth changing, is not a
2048 // varargs function, and is only called directly, promote it to use the
2049 // Fast calling convention.
2050 F->setCallingConv(CallingConv::Fast);
2051 ChangeCalleesToFastCall(F);
2056 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
2057 !F->hasAddressTaken()) {
2058 // The function is not used by a trampoline intrinsic, so it is safe
2059 // to remove the 'nest' attribute.
2060 RemoveNestAttribute(F);
2069 OptimizeGlobalVars(Module &M, TargetLibraryInfo *TLI,
2070 function_ref<DominatorTree &(Function &)> LookupDomTree,
2071 SmallSet<const Comdat *, 8> &NotDiscardableComdats) {
2072 bool Changed = false;
2074 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
2076 GlobalVariable *GV = &*GVI++;
2077 // Global variables without names cannot be referenced outside this module.
2078 if (!GV->hasName() && !GV->isDeclaration() && !GV->hasLocalLinkage())
2079 GV->setLinkage(GlobalValue::InternalLinkage);
2080 // Simplify the initializer.
2081 if (GV->hasInitializer())
2082 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
2083 auto &DL = M.getDataLayout();
2084 Constant *New = ConstantFoldConstantExpression(CE, DL, TLI);
2085 if (New && New != CE)
2086 GV->setInitializer(New);
2089 if (deleteIfDead(*GV, NotDiscardableComdats)) {
2094 Changed |= processGlobal(*GV, TLI, LookupDomTree);
2099 /// Evaluate a piece of a constantexpr store into a global initializer. This
2100 /// returns 'Init' modified to reflect 'Val' stored into it. At this point, the
2101 /// GEP operands of Addr [0, OpNo) have been stepped into.
2102 static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
2103 ConstantExpr *Addr, unsigned OpNo) {
2104 // Base case of the recursion.
2105 if (OpNo == Addr->getNumOperands()) {
2106 assert(Val->getType() == Init->getType() && "Type mismatch!");
2110 SmallVector<Constant*, 32> Elts;
2111 if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
2112 // Break up the constant into its elements.
2113 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
2114 Elts.push_back(Init->getAggregateElement(i));
2116 // Replace the element that we are supposed to.
2117 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
2118 unsigned Idx = CU->getZExtValue();
2119 assert(Idx < STy->getNumElements() && "Struct index out of range!");
2120 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
2122 // Return the modified struct.
2123 return ConstantStruct::get(STy, Elts);
2126 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
2127 SequentialType *InitTy = cast<SequentialType>(Init->getType());
2130 if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
2131 NumElts = ATy->getNumElements();
2133 NumElts = InitTy->getVectorNumElements();
2135 // Break up the array into elements.
2136 for (uint64_t i = 0, e = NumElts; i != e; ++i)
2137 Elts.push_back(Init->getAggregateElement(i));
2139 assert(CI->getZExtValue() < NumElts);
2140 Elts[CI->getZExtValue()] =
2141 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
2143 if (Init->getType()->isArrayTy())
2144 return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
2145 return ConstantVector::get(Elts);
2148 /// We have decided that Addr (which satisfies the predicate
2149 /// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen.
2150 static void CommitValueTo(Constant *Val, Constant *Addr) {
2151 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
2152 assert(GV->hasInitializer());
2153 GV->setInitializer(Val);
2157 ConstantExpr *CE = cast<ConstantExpr>(Addr);
2158 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2159 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
2162 /// Evaluate static constructors in the function, if we can. Return true if we
2163 /// can, false otherwise.
2164 static bool EvaluateStaticConstructor(Function *F, const DataLayout &DL,
2165 TargetLibraryInfo *TLI) {
2166 // Call the function.
2167 Evaluator Eval(DL, TLI);
2168 Constant *RetValDummy;
2169 bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy,
2170 SmallVector<Constant*, 0>());
2173 ++NumCtorsEvaluated;
2175 // We succeeded at evaluation: commit the result.
2176 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
2177 << F->getName() << "' to " << Eval.getMutatedMemory().size()
2179 for (const auto &I : Eval.getMutatedMemory())
2180 CommitValueTo(I.second, I.first);
2181 for (GlobalVariable *GV : Eval.getInvariants())
2182 GV->setConstant(true);
2188 static int compareNames(Constant *const *A, Constant *const *B) {
2189 Value *AStripped = (*A)->stripPointerCastsNoFollowAliases();
2190 Value *BStripped = (*B)->stripPointerCastsNoFollowAliases();
2191 return AStripped->getName().compare(BStripped->getName());
2194 static void setUsedInitializer(GlobalVariable &V,
2195 const SmallPtrSet<GlobalValue *, 8> &Init) {
2197 V.eraseFromParent();
2201 // Type of pointer to the array of pointers.
2202 PointerType *Int8PtrTy = Type::getInt8PtrTy(V.getContext(), 0);
2204 SmallVector<llvm::Constant *, 8> UsedArray;
2205 for (GlobalValue *GV : Init) {
2207 = ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, Int8PtrTy);
2208 UsedArray.push_back(Cast);
2210 // Sort to get deterministic order.
2211 array_pod_sort(UsedArray.begin(), UsedArray.end(), compareNames);
2212 ArrayType *ATy = ArrayType::get(Int8PtrTy, UsedArray.size());
2214 Module *M = V.getParent();
2215 V.removeFromParent();
2216 GlobalVariable *NV =
2217 new GlobalVariable(*M, ATy, false, llvm::GlobalValue::AppendingLinkage,
2218 llvm::ConstantArray::get(ATy, UsedArray), "");
2220 NV->setSection("llvm.metadata");
2225 /// An easy to access representation of llvm.used and llvm.compiler.used.
2227 SmallPtrSet<GlobalValue *, 8> Used;
2228 SmallPtrSet<GlobalValue *, 8> CompilerUsed;
2229 GlobalVariable *UsedV;
2230 GlobalVariable *CompilerUsedV;
2233 LLVMUsed(Module &M) {
2234 UsedV = collectUsedGlobalVariables(M, Used, false);
2235 CompilerUsedV = collectUsedGlobalVariables(M, CompilerUsed, true);
2237 typedef SmallPtrSet<GlobalValue *, 8>::iterator iterator;
2238 typedef iterator_range<iterator> used_iterator_range;
2239 iterator usedBegin() { return Used.begin(); }
2240 iterator usedEnd() { return Used.end(); }
2241 used_iterator_range used() {
2242 return used_iterator_range(usedBegin(), usedEnd());
2244 iterator compilerUsedBegin() { return CompilerUsed.begin(); }
2245 iterator compilerUsedEnd() { return CompilerUsed.end(); }
2246 used_iterator_range compilerUsed() {
2247 return used_iterator_range(compilerUsedBegin(), compilerUsedEnd());
2249 bool usedCount(GlobalValue *GV) const { return Used.count(GV); }
2250 bool compilerUsedCount(GlobalValue *GV) const {
2251 return CompilerUsed.count(GV);
2253 bool usedErase(GlobalValue *GV) { return Used.erase(GV); }
2254 bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(GV); }
2255 bool usedInsert(GlobalValue *GV) { return Used.insert(GV).second; }
2256 bool compilerUsedInsert(GlobalValue *GV) {
2257 return CompilerUsed.insert(GV).second;
2260 void syncVariablesAndSets() {
2262 setUsedInitializer(*UsedV, Used);
2264 setUsedInitializer(*CompilerUsedV, CompilerUsed);
2269 static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) {
2270 if (GA.use_empty()) // No use at all.
2273 assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) &&
2274 "We should have removed the duplicated "
2275 "element from llvm.compiler.used");
2276 if (!GA.hasOneUse())
2277 // Strictly more than one use. So at least one is not in llvm.used and
2278 // llvm.compiler.used.
2281 // Exactly one use. Check if it is in llvm.used or llvm.compiler.used.
2282 return !U.usedCount(&GA) && !U.compilerUsedCount(&GA);
2285 static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V,
2286 const LLVMUsed &U) {
2288 assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) &&
2289 "We should have removed the duplicated "
2290 "element from llvm.compiler.used");
2291 if (U.usedCount(&V) || U.compilerUsedCount(&V))
2293 return V.hasNUsesOrMore(N);
2296 static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) {
2297 if (!GA.hasLocalLinkage())
2300 return U.usedCount(&GA) || U.compilerUsedCount(&GA);
2303 static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
2304 bool &RenameTarget) {
2305 RenameTarget = false;
2307 if (hasUseOtherThanLLVMUsed(GA, U))
2310 // If the alias is externally visible, we may still be able to simplify it.
2311 if (!mayHaveOtherReferences(GA, U))
2314 // If the aliasee has internal linkage, give it the name and linkage
2315 // of the alias, and delete the alias. This turns:
2316 // define internal ... @f(...)
2317 // @a = alias ... @f
2319 // define ... @a(...)
2320 Constant *Aliasee = GA.getAliasee();
2321 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
2322 if (!Target->hasLocalLinkage())
2325 // Do not perform the transform if multiple aliases potentially target the
2326 // aliasee. This check also ensures that it is safe to replace the section
2327 // and other attributes of the aliasee with those of the alias.
2328 if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U))
2331 RenameTarget = true;
2336 OptimizeGlobalAliases(Module &M,
2337 SmallSet<const Comdat *, 8> &NotDiscardableComdats) {
2338 bool Changed = false;
2341 for (GlobalValue *GV : Used.used())
2342 Used.compilerUsedErase(GV);
2344 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
2346 GlobalAlias *J = &*I++;
2348 // Aliases without names cannot be referenced outside this module.
2349 if (!J->hasName() && !J->isDeclaration() && !J->hasLocalLinkage())
2350 J->setLinkage(GlobalValue::InternalLinkage);
2352 if (deleteIfDead(*J, NotDiscardableComdats)) {
2357 // If the aliasee may change at link time, nothing can be done - bail out.
2358 if (J->isInterposable())
2361 Constant *Aliasee = J->getAliasee();
2362 GlobalValue *Target = dyn_cast<GlobalValue>(Aliasee->stripPointerCasts());
2363 // We can't trivially replace the alias with the aliasee if the aliasee is
2364 // non-trivial in some way.
2365 // TODO: Try to handle non-zero GEPs of local aliasees.
2368 Target->removeDeadConstantUsers();
2370 // Make all users of the alias use the aliasee instead.
2372 if (!hasUsesToReplace(*J, Used, RenameTarget))
2375 J->replaceAllUsesWith(ConstantExpr::getBitCast(Aliasee, J->getType()));
2376 ++NumAliasesResolved;
2380 // Give the aliasee the name, linkage and other attributes of the alias.
2381 Target->takeName(&*J);
2382 Target->setLinkage(J->getLinkage());
2383 Target->setVisibility(J->getVisibility());
2384 Target->setDLLStorageClass(J->getDLLStorageClass());
2386 if (Used.usedErase(&*J))
2387 Used.usedInsert(Target);
2389 if (Used.compilerUsedErase(&*J))
2390 Used.compilerUsedInsert(Target);
2391 } else if (mayHaveOtherReferences(*J, Used))
2394 // Delete the alias.
2395 M.getAliasList().erase(J);
2396 ++NumAliasesRemoved;
2400 Used.syncVariablesAndSets();
2405 static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) {
2406 LibFunc::Func F = LibFunc::cxa_atexit;
2410 Function *Fn = M.getFunction(TLI->getName(F));
2414 // Make sure that the function has the correct prototype.
2415 if (!TLI->getLibFunc(*Fn, F) || F != LibFunc::cxa_atexit)
2421 /// Returns whether the given function is an empty C++ destructor and can
2422 /// therefore be eliminated.
2423 /// Note that we assume that other optimization passes have already simplified
2424 /// the code so we only look for a function with a single basic block, where
2425 /// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and
2426 /// other side-effect free instructions.
2427 static bool cxxDtorIsEmpty(const Function &Fn,
2428 SmallPtrSet<const Function *, 8> &CalledFunctions) {
2429 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
2430 // nounwind, but that doesn't seem worth doing.
2431 if (Fn.isDeclaration())
2434 if (++Fn.begin() != Fn.end())
2437 const BasicBlock &EntryBlock = Fn.getEntryBlock();
2438 for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
2440 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
2441 // Ignore debug intrinsics.
2442 if (isa<DbgInfoIntrinsic>(CI))
2445 const Function *CalledFn = CI->getCalledFunction();
2450 SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
2452 // Don't treat recursive functions as empty.
2453 if (!NewCalledFunctions.insert(CalledFn).second)
2456 if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
2458 } else if (isa<ReturnInst>(*I))
2459 return true; // We're done.
2460 else if (I->mayHaveSideEffects())
2461 return false; // Destructor with side effects, bail.
2467 static bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
2468 /// Itanium C++ ABI p3.3.5:
2470 /// After constructing a global (or local static) object, that will require
2471 /// destruction on exit, a termination function is registered as follows:
2473 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
2475 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
2476 /// call f(p) when DSO d is unloaded, before all such termination calls
2477 /// registered before this one. It returns zero if registration is
2478 /// successful, nonzero on failure.
2480 // This pass will look for calls to __cxa_atexit where the function is trivial
2482 bool Changed = false;
2484 for (auto I = CXAAtExitFn->user_begin(), E = CXAAtExitFn->user_end();
2486 // We're only interested in calls. Theoretically, we could handle invoke
2487 // instructions as well, but neither llvm-gcc nor clang generate invokes
2489 CallInst *CI = dyn_cast<CallInst>(*I++);
2494 dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
2498 SmallPtrSet<const Function *, 8> CalledFunctions;
2499 if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
2502 // Just remove the call.
2503 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
2504 CI->eraseFromParent();
2506 ++NumCXXDtorsRemoved;
2514 static bool optimizeGlobalsInModule(
2515 Module &M, const DataLayout &DL, TargetLibraryInfo *TLI,
2516 function_ref<DominatorTree &(Function &)> LookupDomTree) {
2517 SmallSet<const Comdat *, 8> NotDiscardableComdats;
2518 bool Changed = false;
2519 bool LocalChange = true;
2520 while (LocalChange) {
2521 LocalChange = false;
2523 NotDiscardableComdats.clear();
2524 for (const GlobalVariable &GV : M.globals())
2525 if (const Comdat *C = GV.getComdat())
2526 if (!GV.isDiscardableIfUnused() || !GV.use_empty())
2527 NotDiscardableComdats.insert(C);
2528 for (Function &F : M)
2529 if (const Comdat *C = F.getComdat())
2530 if (!F.isDefTriviallyDead())
2531 NotDiscardableComdats.insert(C);
2532 for (GlobalAlias &GA : M.aliases())
2533 if (const Comdat *C = GA.getComdat())
2534 if (!GA.isDiscardableIfUnused() || !GA.use_empty())
2535 NotDiscardableComdats.insert(C);
2537 // Delete functions that are trivially dead, ccc -> fastcc
2539 OptimizeFunctions(M, TLI, LookupDomTree, NotDiscardableComdats);
2541 // Optimize global_ctors list.
2542 LocalChange |= optimizeGlobalCtorsList(M, [&](Function *F) {
2543 return EvaluateStaticConstructor(F, DL, TLI);
2546 // Optimize non-address-taken globals.
2547 LocalChange |= OptimizeGlobalVars(M, TLI, LookupDomTree,
2548 NotDiscardableComdats);
2550 // Resolve aliases, when possible.
2551 LocalChange |= OptimizeGlobalAliases(M, NotDiscardableComdats);
2553 // Try to remove trivial global destructors if they are not removed
2555 Function *CXAAtExitFn = FindCXAAtExit(M, TLI);
2557 LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
2559 Changed |= LocalChange;
2562 // TODO: Move all global ctors functions to the end of the module for code
2568 PreservedAnalyses GlobalOptPass::run(Module &M, AnalysisManager<Module> &AM) {
2569 auto &DL = M.getDataLayout();
2570 auto &TLI = AM.getResult<TargetLibraryAnalysis>(M);
2572 AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
2573 auto LookupDomTree = [&FAM](Function &F) -> DominatorTree &{
2574 return FAM.getResult<DominatorTreeAnalysis>(F);
2576 if (!optimizeGlobalsInModule(M, DL, &TLI, LookupDomTree))
2577 return PreservedAnalyses::all();
2578 return PreservedAnalyses::none();
2582 struct GlobalOptLegacyPass : public ModulePass {
2583 static char ID; // Pass identification, replacement for typeid
2584 GlobalOptLegacyPass() : ModulePass(ID) {
2585 initializeGlobalOptLegacyPassPass(*PassRegistry::getPassRegistry());
2588 bool runOnModule(Module &M) override {
2592 auto &DL = M.getDataLayout();
2593 auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
2594 auto LookupDomTree = [this](Function &F) -> DominatorTree & {
2595 return this->getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
2597 return optimizeGlobalsInModule(M, DL, TLI, LookupDomTree);
2600 void getAnalysisUsage(AnalysisUsage &AU) const override {
2601 AU.addRequired<TargetLibraryInfoWrapperPass>();
2602 AU.addRequired<DominatorTreeWrapperPass>();
2607 char GlobalOptLegacyPass::ID = 0;
2608 INITIALIZE_PASS_BEGIN(GlobalOptLegacyPass, "globalopt",
2609 "Global Variable Optimizer", false, false)
2610 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
2611 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
2612 INITIALIZE_PASS_END(GlobalOptLegacyPass, "globalopt",
2613 "Global Variable Optimizer", false, false)
2615 ModulePass *llvm::createGlobalOptimizerPass() {
2616 return new GlobalOptLegacyPass();