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/ADT/Twine.h"
24 #include "llvm/ADT/iterator_range.h"
25 #include "llvm/Analysis/ConstantFolding.h"
26 #include "llvm/Analysis/MemoryBuiltins.h"
27 #include "llvm/Analysis/TargetLibraryInfo.h"
28 #include "llvm/BinaryFormat/Dwarf.h"
29 #include "llvm/IR/Attributes.h"
30 #include "llvm/IR/BasicBlock.h"
31 #include "llvm/IR/CallSite.h"
32 #include "llvm/IR/CallingConv.h"
33 #include "llvm/IR/Constant.h"
34 #include "llvm/IR/Constants.h"
35 #include "llvm/IR/DataLayout.h"
36 #include "llvm/IR/DebugInfoMetadata.h"
37 #include "llvm/IR/DerivedTypes.h"
38 #include "llvm/IR/Dominators.h"
39 #include "llvm/IR/Function.h"
40 #include "llvm/IR/GetElementPtrTypeIterator.h"
41 #include "llvm/IR/GlobalAlias.h"
42 #include "llvm/IR/GlobalValue.h"
43 #include "llvm/IR/GlobalVariable.h"
44 #include "llvm/IR/InstrTypes.h"
45 #include "llvm/IR/Instruction.h"
46 #include "llvm/IR/Instructions.h"
47 #include "llvm/IR/IntrinsicInst.h"
48 #include "llvm/IR/Module.h"
49 #include "llvm/IR/Operator.h"
50 #include "llvm/IR/Type.h"
51 #include "llvm/IR/Use.h"
52 #include "llvm/IR/User.h"
53 #include "llvm/IR/Value.h"
54 #include "llvm/IR/ValueHandle.h"
55 #include "llvm/Pass.h"
56 #include "llvm/Support/AtomicOrdering.h"
57 #include "llvm/Support/Casting.h"
58 #include "llvm/Support/Debug.h"
59 #include "llvm/Support/ErrorHandling.h"
60 #include "llvm/Support/MathExtras.h"
61 #include "llvm/Support/raw_ostream.h"
62 #include "llvm/Transforms/IPO.h"
63 #include "llvm/Transforms/Utils/CtorUtils.h"
64 #include "llvm/Transforms/Utils/Evaluator.h"
65 #include "llvm/Transforms/Utils/GlobalStatus.h"
66 #include "llvm/Transforms/Utils/Local.h"
74 #define DEBUG_TYPE "globalopt"
76 STATISTIC(NumMarked , "Number of globals marked constant");
77 STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr");
78 STATISTIC(NumSRA , "Number of aggregate globals broken into scalars");
79 STATISTIC(NumHeapSRA , "Number of heap objects SRA'd");
80 STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
81 STATISTIC(NumDeleted , "Number of globals deleted");
82 STATISTIC(NumGlobUses , "Number of global uses devirtualized");
83 STATISTIC(NumLocalized , "Number of globals localized");
84 STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans");
85 STATISTIC(NumFastCallFns , "Number of functions converted to fastcc");
86 STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");
87 STATISTIC(NumNestRemoved , "Number of nest attributes removed");
88 STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
89 STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
90 STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
92 /// Is this global variable possibly used by a leak checker as a root? If so,
93 /// we might not really want to eliminate the stores to it.
94 static bool isLeakCheckerRoot(GlobalVariable *GV) {
95 // A global variable is a root if it is a pointer, or could plausibly contain
96 // a pointer. There are two challenges; one is that we could have a struct
97 // the has an inner member which is a pointer. We recurse through the type to
98 // detect these (up to a point). The other is that we may actually be a union
99 // of a pointer and another type, and so our LLVM type is an integer which
100 // gets converted into a pointer, or our type is an [i8 x #] with a pointer
101 // potentially contained here.
103 if (GV->hasPrivateLinkage())
106 SmallVector<Type *, 4> Types;
107 Types.push_back(GV->getValueType());
111 Type *Ty = Types.pop_back_val();
112 switch (Ty->getTypeID()) {
114 case Type::PointerTyID: return true;
115 case Type::ArrayTyID:
116 case Type::VectorTyID: {
117 SequentialType *STy = cast<SequentialType>(Ty);
118 Types.push_back(STy->getElementType());
121 case Type::StructTyID: {
122 StructType *STy = cast<StructType>(Ty);
123 if (STy->isOpaque()) return true;
124 for (StructType::element_iterator I = STy->element_begin(),
125 E = STy->element_end(); I != E; ++I) {
127 if (isa<PointerType>(InnerTy)) return true;
128 if (isa<CompositeType>(InnerTy))
129 Types.push_back(InnerTy);
134 if (--Limit == 0) return true;
135 } while (!Types.empty());
139 /// Given a value that is stored to a global but never read, determine whether
140 /// it's safe to remove the store and the chain of computation that feeds the
142 static bool IsSafeComputationToRemove(Value *V, const TargetLibraryInfo *TLI) {
144 if (isa<Constant>(V))
148 if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) ||
151 if (isAllocationFn(V, TLI))
154 Instruction *I = cast<Instruction>(V);
155 if (I->mayHaveSideEffects())
157 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
158 if (!GEP->hasAllConstantIndices())
160 } else if (I->getNumOperands() != 1) {
164 V = I->getOperand(0);
168 /// This GV is a pointer root. Loop over all users of the global and clean up
169 /// any that obviously don't assign the global a value that isn't dynamically
171 static bool CleanupPointerRootUsers(GlobalVariable *GV,
172 const TargetLibraryInfo *TLI) {
173 // A brief explanation of leak checkers. The goal is to find bugs where
174 // pointers are forgotten, causing an accumulating growth in memory
175 // usage over time. The common strategy for leak checkers is to whitelist the
176 // memory pointed to by globals at exit. This is popular because it also
177 // solves another problem where the main thread of a C++ program may shut down
178 // before other threads that are still expecting to use those globals. To
179 // handle that case, we expect the program may create a singleton and never
182 bool Changed = false;
184 // If Dead[n].first is the only use of a malloc result, we can delete its
185 // chain of computation and the store to the global in Dead[n].second.
186 SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
188 // Constants can't be pointers to dynamically allocated memory.
189 for (Value::user_iterator UI = GV->user_begin(), E = GV->user_end();
192 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
193 Value *V = SI->getValueOperand();
194 if (isa<Constant>(V)) {
196 SI->eraseFromParent();
197 } else if (Instruction *I = dyn_cast<Instruction>(V)) {
199 Dead.push_back(std::make_pair(I, SI));
201 } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
202 if (isa<Constant>(MSI->getValue())) {
204 MSI->eraseFromParent();
205 } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
207 Dead.push_back(std::make_pair(I, MSI));
209 } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
210 GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
211 if (MemSrc && MemSrc->isConstant()) {
213 MTI->eraseFromParent();
214 } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) {
216 Dead.push_back(std::make_pair(I, MTI));
218 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
219 if (CE->use_empty()) {
220 CE->destroyConstant();
223 } else if (Constant *C = dyn_cast<Constant>(U)) {
224 if (isSafeToDestroyConstant(C)) {
225 C->destroyConstant();
226 // This could have invalidated UI, start over from scratch.
228 CleanupPointerRootUsers(GV, TLI);
234 for (int i = 0, e = Dead.size(); i != e; ++i) {
235 if (IsSafeComputationToRemove(Dead[i].first, TLI)) {
236 Dead[i].second->eraseFromParent();
237 Instruction *I = Dead[i].first;
239 if (isAllocationFn(I, TLI))
241 Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
244 I->eraseFromParent();
247 I->eraseFromParent();
254 /// We just marked GV constant. Loop over all users of the global, cleaning up
255 /// the obvious ones. This is largely just a quick scan over the use list to
256 /// clean up the easy and obvious cruft. This returns true if it made a change.
257 static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
258 const DataLayout &DL,
259 TargetLibraryInfo *TLI) {
260 bool Changed = false;
261 // Note that we need to use a weak value handle for the worklist items. When
262 // we delete a constant array, we may also be holding pointer to one of its
263 // elements (or an element of one of its elements if we're dealing with an
264 // array of arrays) in the worklist.
265 SmallVector<WeakTrackingVH, 8> WorkList(V->user_begin(), V->user_end());
266 while (!WorkList.empty()) {
267 Value *UV = WorkList.pop_back_val();
271 User *U = cast<User>(UV);
273 if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
275 // Replace the load with the initializer.
276 LI->replaceAllUsesWith(Init);
277 LI->eraseFromParent();
280 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
281 // Store must be unreachable or storing Init into the global.
282 SI->eraseFromParent();
284 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
285 if (CE->getOpcode() == Instruction::GetElementPtr) {
286 Constant *SubInit = nullptr;
288 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
289 Changed |= CleanupConstantGlobalUsers(CE, SubInit, DL, TLI);
290 } else if ((CE->getOpcode() == Instruction::BitCast &&
291 CE->getType()->isPointerTy()) ||
292 CE->getOpcode() == Instruction::AddrSpaceCast) {
293 // Pointer cast, delete any stores and memsets to the global.
294 Changed |= CleanupConstantGlobalUsers(CE, nullptr, DL, TLI);
297 if (CE->use_empty()) {
298 CE->destroyConstant();
301 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
302 // Do not transform "gepinst (gep constexpr (GV))" here, because forming
303 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
304 // and will invalidate our notion of what Init is.
305 Constant *SubInit = nullptr;
306 if (!isa<ConstantExpr>(GEP->getOperand(0))) {
307 ConstantExpr *CE = dyn_cast_or_null<ConstantExpr>(
308 ConstantFoldInstruction(GEP, DL, TLI));
309 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
310 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
312 // If the initializer is an all-null value and we have an inbounds GEP,
313 // we already know what the result of any load from that GEP is.
314 // TODO: Handle splats.
315 if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
316 SubInit = Constant::getNullValue(GEP->getResultElementType());
318 Changed |= CleanupConstantGlobalUsers(GEP, SubInit, DL, TLI);
320 if (GEP->use_empty()) {
321 GEP->eraseFromParent();
324 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
325 if (MI->getRawDest() == V) {
326 MI->eraseFromParent();
330 } else if (Constant *C = dyn_cast<Constant>(U)) {
331 // If we have a chain of dead constantexprs or other things dangling from
332 // us, and if they are all dead, nuke them without remorse.
333 if (isSafeToDestroyConstant(C)) {
334 C->destroyConstant();
335 CleanupConstantGlobalUsers(V, Init, DL, TLI);
343 /// Return true if the specified instruction is a safe user of a derived
344 /// expression from a global that we want to SROA.
345 static bool isSafeSROAElementUse(Value *V) {
346 // We might have a dead and dangling constant hanging off of here.
347 if (Constant *C = dyn_cast<Constant>(V))
348 return isSafeToDestroyConstant(C);
350 Instruction *I = dyn_cast<Instruction>(V);
351 if (!I) return false;
354 if (isa<LoadInst>(I)) return true;
356 // Stores *to* the pointer are ok.
357 if (StoreInst *SI = dyn_cast<StoreInst>(I))
358 return SI->getOperand(0) != V;
360 // Otherwise, it must be a GEP.
361 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
362 if (!GEPI) return false;
364 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
365 !cast<Constant>(GEPI->getOperand(1))->isNullValue())
368 for (User *U : GEPI->users())
369 if (!isSafeSROAElementUse(U))
374 /// U is a direct user of the specified global value. Look at it and its uses
375 /// and decide whether it is safe to SROA this global.
376 static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
377 // The user of the global must be a GEP Inst or a ConstantExpr GEP.
378 if (!isa<GetElementPtrInst>(U) &&
379 (!isa<ConstantExpr>(U) ||
380 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
383 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we
384 // don't like < 3 operand CE's, and we don't like non-constant integer
385 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
387 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
388 !cast<Constant>(U->getOperand(1))->isNullValue() ||
389 !isa<ConstantInt>(U->getOperand(2)))
392 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
393 ++GEPI; // Skip over the pointer index.
395 // If this is a use of an array allocation, do a bit more checking for sanity.
396 if (GEPI.isSequential()) {
397 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
399 // Check to make sure that index falls within the array. If not,
400 // something funny is going on, so we won't do the optimization.
402 if (GEPI.isBoundedSequential() &&
403 Idx->getZExtValue() >= GEPI.getSequentialNumElements())
406 // We cannot scalar repl this level of the array unless any array
407 // sub-indices are in-range constants. In particular, consider:
408 // A[0][i]. We cannot know that the user isn't doing invalid things like
409 // allowing i to index an out-of-range subscript that accesses A[1].
411 // Scalar replacing *just* the outer index of the array is probably not
412 // going to be a win anyway, so just give up.
413 for (++GEPI; // Skip array index.
419 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
421 (GEPI.isBoundedSequential() &&
422 IdxVal->getZExtValue() >= GEPI.getSequentialNumElements()))
427 return llvm::all_of(U->users(),
428 [](User *UU) { return isSafeSROAElementUse(UU); });
431 /// Look at all uses of the global and decide whether it is safe for us to
432 /// perform this transformation.
433 static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
434 for (User *U : GV->users())
435 if (!IsUserOfGlobalSafeForSRA(U, GV))
441 /// Copy over the debug info for a variable to its SRA replacements.
442 static void transferSRADebugInfo(GlobalVariable *GV, GlobalVariable *NGV,
443 uint64_t FragmentOffsetInBits,
444 uint64_t FragmentSizeInBits,
445 unsigned NumElements) {
446 SmallVector<DIGlobalVariableExpression *, 1> GVs;
447 GV->getDebugInfo(GVs);
448 for (auto *GVE : GVs) {
449 DIVariable *Var = GVE->getVariable();
450 DIExpression *Expr = GVE->getExpression();
451 if (NumElements > 1) {
452 if (auto E = DIExpression::createFragmentExpression(
453 Expr, FragmentOffsetInBits, FragmentSizeInBits))
458 auto *NGVE = DIGlobalVariableExpression::get(GVE->getContext(), Var, Expr);
459 NGV->addDebugInfo(NGVE);
463 /// Perform scalar replacement of aggregates on the specified global variable.
464 /// This opens the door for other optimizations by exposing the behavior of the
465 /// program in a more fine-grained way. We have determined that this
466 /// transformation is safe already. We return the first global variable we
467 /// insert so that the caller can reprocess it.
468 static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) {
469 // Make sure this global only has simple uses that we can SRA.
470 if (!GlobalUsersSafeToSRA(GV))
473 assert(GV->hasLocalLinkage());
474 Constant *Init = GV->getInitializer();
475 Type *Ty = Init->getType();
477 std::vector<GlobalVariable *> NewGlobals;
478 Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
480 // Get the alignment of the global, either explicit or target-specific.
481 unsigned StartAlignment = GV->getAlignment();
482 if (StartAlignment == 0)
483 StartAlignment = DL.getABITypeAlignment(GV->getType());
485 if (StructType *STy = dyn_cast<StructType>(Ty)) {
486 uint64_t FragmentOffset = 0;
487 unsigned NumElements = STy->getNumElements();
488 NewGlobals.reserve(NumElements);
489 const StructLayout &Layout = *DL.getStructLayout(STy);
490 for (unsigned i = 0, e = NumElements; i != e; ++i) {
491 Constant *In = Init->getAggregateElement(i);
492 assert(In && "Couldn't get element of initializer?");
493 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
494 GlobalVariable::InternalLinkage,
495 In, GV->getName()+"."+Twine(i),
496 GV->getThreadLocalMode(),
497 GV->getType()->getAddressSpace());
498 NGV->setExternallyInitialized(GV->isExternallyInitialized());
499 NGV->copyAttributesFrom(GV);
500 Globals.push_back(NGV);
501 NewGlobals.push_back(NGV);
503 // Calculate the known alignment of the field. If the original aggregate
504 // had 256 byte alignment for example, something might depend on that:
505 // propagate info to each field.
506 uint64_t FieldOffset = Layout.getElementOffset(i);
507 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
508 if (NewAlign > DL.getABITypeAlignment(STy->getElementType(i)))
509 NGV->setAlignment(NewAlign);
511 // Copy over the debug info for the variable.
512 FragmentOffset = alignTo(FragmentOffset, NewAlign);
513 uint64_t Size = DL.getTypeSizeInBits(NGV->getValueType());
514 transferSRADebugInfo(GV, NGV, FragmentOffset, Size, NumElements);
515 FragmentOffset += Size;
517 } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
518 unsigned NumElements = STy->getNumElements();
519 if (NumElements > 16 && GV->hasNUsesOrMore(16))
520 return nullptr; // It's not worth it.
521 NewGlobals.reserve(NumElements);
522 auto ElTy = STy->getElementType();
523 uint64_t EltSize = DL.getTypeAllocSize(ElTy);
524 unsigned EltAlign = DL.getABITypeAlignment(ElTy);
525 uint64_t FragmentSizeInBits = DL.getTypeSizeInBits(ElTy);
526 for (unsigned i = 0, e = NumElements; i != e; ++i) {
527 Constant *In = Init->getAggregateElement(i);
528 assert(In && "Couldn't get element of initializer?");
530 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
531 GlobalVariable::InternalLinkage,
532 In, GV->getName()+"."+Twine(i),
533 GV->getThreadLocalMode(),
534 GV->getType()->getAddressSpace());
535 NGV->setExternallyInitialized(GV->isExternallyInitialized());
536 NGV->copyAttributesFrom(GV);
537 Globals.push_back(NGV);
538 NewGlobals.push_back(NGV);
540 // Calculate the known alignment of the field. If the original aggregate
541 // had 256 byte alignment for example, something might depend on that:
542 // propagate info to each field.
543 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
544 if (NewAlign > EltAlign)
545 NGV->setAlignment(NewAlign);
546 transferSRADebugInfo(GV, NGV, FragmentSizeInBits * i, FragmentSizeInBits,
551 if (NewGlobals.empty())
554 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV << "\n");
556 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
558 // Loop over all of the uses of the global, replacing the constantexpr geps,
559 // with smaller constantexpr geps or direct references.
560 while (!GV->use_empty()) {
561 User *GEP = GV->user_back();
562 assert(((isa<ConstantExpr>(GEP) &&
563 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
564 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
566 // Ignore the 1th operand, which has to be zero or else the program is quite
567 // broken (undefined). Get the 2nd operand, which is the structure or array
569 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
570 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
572 Value *NewPtr = NewGlobals[Val];
573 Type *NewTy = NewGlobals[Val]->getValueType();
575 // Form a shorter GEP if needed.
576 if (GEP->getNumOperands() > 3) {
577 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
578 SmallVector<Constant*, 8> Idxs;
579 Idxs.push_back(NullInt);
580 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
581 Idxs.push_back(CE->getOperand(i));
583 ConstantExpr::getGetElementPtr(NewTy, cast<Constant>(NewPtr), Idxs);
585 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
586 SmallVector<Value*, 8> Idxs;
587 Idxs.push_back(NullInt);
588 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
589 Idxs.push_back(GEPI->getOperand(i));
590 NewPtr = GetElementPtrInst::Create(
591 NewTy, NewPtr, Idxs, GEPI->getName() + "." + Twine(Val), GEPI);
594 GEP->replaceAllUsesWith(NewPtr);
596 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
597 GEPI->eraseFromParent();
599 cast<ConstantExpr>(GEP)->destroyConstant();
602 // Delete the old global, now that it is dead.
606 // Loop over the new globals array deleting any globals that are obviously
607 // dead. This can arise due to scalarization of a structure or an array that
608 // has elements that are dead.
609 unsigned FirstGlobal = 0;
610 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
611 if (NewGlobals[i]->use_empty()) {
612 Globals.erase(NewGlobals[i]);
613 if (FirstGlobal == i) ++FirstGlobal;
616 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : nullptr;
619 /// Return true if all users of the specified value will trap if the value is
620 /// dynamically null. PHIs keeps track of any phi nodes we've seen to avoid
621 /// reprocessing them.
622 static bool AllUsesOfValueWillTrapIfNull(const Value *V,
623 SmallPtrSetImpl<const PHINode*> &PHIs) {
624 for (const User *U : V->users())
625 if (isa<LoadInst>(U)) {
627 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
628 if (SI->getOperand(0) == V) {
629 //cerr << "NONTRAPPING USE: " << *U;
630 return false; // Storing the value.
632 } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
633 if (CI->getCalledValue() != V) {
634 //cerr << "NONTRAPPING USE: " << *U;
635 return false; // Not calling the ptr
637 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
638 if (II->getCalledValue() != V) {
639 //cerr << "NONTRAPPING USE: " << *U;
640 return false; // Not calling the ptr
642 } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
643 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
644 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
645 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
646 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
647 // If we've already seen this phi node, ignore it, it has already been
649 if (PHIs.insert(PN).second && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
651 } else if (isa<ICmpInst>(U) &&
652 isa<ConstantPointerNull>(U->getOperand(1))) {
653 // Ignore icmp X, null
655 //cerr << "NONTRAPPING USE: " << *U;
662 /// Return true if all uses of any loads from GV will trap if the loaded value
663 /// is null. Note that this also permits comparisons of the loaded value
664 /// against null, as a special case.
665 static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
666 for (const User *U : GV->users())
667 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
668 SmallPtrSet<const PHINode*, 8> PHIs;
669 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
671 } else if (isa<StoreInst>(U)) {
672 // Ignore stores to the global.
674 // We don't know or understand this user, bail out.
675 //cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
681 static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
682 bool Changed = false;
683 for (auto UI = V->user_begin(), E = V->user_end(); UI != E; ) {
684 Instruction *I = cast<Instruction>(*UI++);
685 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
686 LI->setOperand(0, NewV);
688 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
689 if (SI->getOperand(1) == V) {
690 SI->setOperand(1, NewV);
693 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
695 if (CS.getCalledValue() == V) {
696 // Calling through the pointer! Turn into a direct call, but be careful
697 // that the pointer is not also being passed as an argument.
698 CS.setCalledFunction(NewV);
700 bool PassedAsArg = false;
701 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
702 if (CS.getArgument(i) == V) {
704 CS.setArgument(i, NewV);
708 // Being passed as an argument also. Be careful to not invalidate UI!
709 UI = V->user_begin();
712 } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
713 Changed |= OptimizeAwayTrappingUsesOfValue(CI,
714 ConstantExpr::getCast(CI->getOpcode(),
715 NewV, CI->getType()));
716 if (CI->use_empty()) {
718 CI->eraseFromParent();
720 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
721 // Should handle GEP here.
722 SmallVector<Constant*, 8> Idxs;
723 Idxs.reserve(GEPI->getNumOperands()-1);
724 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
726 if (Constant *C = dyn_cast<Constant>(*i))
730 if (Idxs.size() == GEPI->getNumOperands()-1)
731 Changed |= OptimizeAwayTrappingUsesOfValue(
732 GEPI, ConstantExpr::getGetElementPtr(nullptr, NewV, Idxs));
733 if (GEPI->use_empty()) {
735 GEPI->eraseFromParent();
743 /// The specified global has only one non-null value stored into it. If there
744 /// are uses of the loaded value that would trap if the loaded value is
745 /// dynamically null, then we know that they cannot be reachable with a null
746 /// optimize away the load.
747 static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV,
748 const DataLayout &DL,
749 TargetLibraryInfo *TLI) {
750 bool Changed = false;
752 // Keep track of whether we are able to remove all the uses of the global
753 // other than the store that defines it.
754 bool AllNonStoreUsesGone = true;
756 // Replace all uses of loads with uses of uses of the stored value.
757 for (Value::user_iterator GUI = GV->user_begin(), E = GV->user_end(); GUI != E;){
758 User *GlobalUser = *GUI++;
759 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
760 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
761 // If we were able to delete all uses of the loads
762 if (LI->use_empty()) {
763 LI->eraseFromParent();
766 AllNonStoreUsesGone = false;
768 } else if (isa<StoreInst>(GlobalUser)) {
769 // Ignore the store that stores "LV" to the global.
770 assert(GlobalUser->getOperand(1) == GV &&
771 "Must be storing *to* the global");
773 AllNonStoreUsesGone = false;
775 // If we get here we could have other crazy uses that are transitively
777 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
778 isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) ||
779 isa<BitCastInst>(GlobalUser) ||
780 isa<GetElementPtrInst>(GlobalUser)) &&
781 "Only expect load and stores!");
786 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV << "\n");
790 // If we nuked all of the loads, then none of the stores are needed either,
791 // nor is the global.
792 if (AllNonStoreUsesGone) {
793 if (isLeakCheckerRoot(GV)) {
794 Changed |= CleanupPointerRootUsers(GV, TLI);
797 CleanupConstantGlobalUsers(GV, nullptr, DL, TLI);
799 if (GV->use_empty()) {
800 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
802 GV->eraseFromParent();
809 /// Walk the use list of V, constant folding all of the instructions that are
811 static void ConstantPropUsersOf(Value *V, const DataLayout &DL,
812 TargetLibraryInfo *TLI) {
813 for (Value::user_iterator UI = V->user_begin(), E = V->user_end(); UI != E; )
814 if (Instruction *I = dyn_cast<Instruction>(*UI++))
815 if (Constant *NewC = ConstantFoldInstruction(I, DL, TLI)) {
816 I->replaceAllUsesWith(NewC);
818 // Advance UI to the next non-I use to avoid invalidating it!
819 // Instructions could multiply use V.
820 while (UI != E && *UI == I)
822 if (isInstructionTriviallyDead(I, TLI))
823 I->eraseFromParent();
827 /// This function takes the specified global variable, and transforms the
828 /// program as if it always contained the result of the specified malloc.
829 /// Because it is always the result of the specified malloc, there is no reason
830 /// to actually DO the malloc. Instead, turn the malloc into a global, and any
831 /// loads of GV as uses of the new global.
832 static GlobalVariable *
833 OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, CallInst *CI, Type *AllocTy,
834 ConstantInt *NElements, const DataLayout &DL,
835 TargetLibraryInfo *TLI) {
836 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n');
839 if (NElements->getZExtValue() == 1)
840 GlobalType = AllocTy;
842 // If we have an array allocation, the global variable is of an array.
843 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
845 // Create the new global variable. The contents of the malloc'd memory is
846 // undefined, so initialize with an undef value.
847 GlobalVariable *NewGV = new GlobalVariable(
848 *GV->getParent(), GlobalType, false, GlobalValue::InternalLinkage,
849 UndefValue::get(GlobalType), GV->getName() + ".body", nullptr,
850 GV->getThreadLocalMode());
852 // If there are bitcast users of the malloc (which is typical, usually we have
853 // a malloc + bitcast) then replace them with uses of the new global. Update
854 // other users to use the global as well.
855 BitCastInst *TheBC = nullptr;
856 while (!CI->use_empty()) {
857 Instruction *User = cast<Instruction>(CI->user_back());
858 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
859 if (BCI->getType() == NewGV->getType()) {
860 BCI->replaceAllUsesWith(NewGV);
861 BCI->eraseFromParent();
863 BCI->setOperand(0, NewGV);
867 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
868 User->replaceUsesOfWith(CI, TheBC);
872 Constant *RepValue = NewGV;
873 if (NewGV->getType() != GV->getValueType())
874 RepValue = ConstantExpr::getBitCast(RepValue, GV->getValueType());
876 // If there is a comparison against null, we will insert a global bool to
877 // keep track of whether the global was initialized yet or not.
878 GlobalVariable *InitBool =
879 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
880 GlobalValue::InternalLinkage,
881 ConstantInt::getFalse(GV->getContext()),
882 GV->getName()+".init", GV->getThreadLocalMode());
883 bool InitBoolUsed = false;
885 // Loop over all uses of GV, processing them in turn.
886 while (!GV->use_empty()) {
887 if (StoreInst *SI = dyn_cast<StoreInst>(GV->user_back())) {
888 // The global is initialized when the store to it occurs.
889 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
890 SI->getOrdering(), SI->getSyncScopeID(), SI);
891 SI->eraseFromParent();
895 LoadInst *LI = cast<LoadInst>(GV->user_back());
896 while (!LI->use_empty()) {
897 Use &LoadUse = *LI->use_begin();
898 ICmpInst *ICI = dyn_cast<ICmpInst>(LoadUse.getUser());
904 // Replace the cmp X, 0 with a use of the bool value.
905 // Sink the load to where the compare was, if atomic rules allow us to.
906 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
907 LI->getOrdering(), LI->getSyncScopeID(),
908 LI->isUnordered() ? (Instruction*)ICI : LI);
910 switch (ICI->getPredicate()) {
911 default: llvm_unreachable("Unknown ICmp Predicate!");
912 case ICmpInst::ICMP_ULT:
913 case ICmpInst::ICMP_SLT: // X < null -> always false
914 LV = ConstantInt::getFalse(GV->getContext());
916 case ICmpInst::ICMP_ULE:
917 case ICmpInst::ICMP_SLE:
918 case ICmpInst::ICMP_EQ:
919 LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
921 case ICmpInst::ICMP_NE:
922 case ICmpInst::ICMP_UGE:
923 case ICmpInst::ICMP_SGE:
924 case ICmpInst::ICMP_UGT:
925 case ICmpInst::ICMP_SGT:
928 ICI->replaceAllUsesWith(LV);
929 ICI->eraseFromParent();
931 LI->eraseFromParent();
934 // If the initialization boolean was used, insert it, otherwise delete it.
936 while (!InitBool->use_empty()) // Delete initializations
937 cast<StoreInst>(InitBool->user_back())->eraseFromParent();
940 GV->getParent()->getGlobalList().insert(GV->getIterator(), InitBool);
942 // Now the GV is dead, nuke it and the malloc..
943 GV->eraseFromParent();
944 CI->eraseFromParent();
946 // To further other optimizations, loop over all users of NewGV and try to
947 // constant prop them. This will promote GEP instructions with constant
948 // indices into GEP constant-exprs, which will allow global-opt to hack on it.
949 ConstantPropUsersOf(NewGV, DL, TLI);
950 if (RepValue != NewGV)
951 ConstantPropUsersOf(RepValue, DL, TLI);
956 /// Scan the use-list of V checking to make sure that there are no complex uses
957 /// of V. We permit simple things like dereferencing the pointer, but not
958 /// storing through the address, unless it is to the specified global.
959 static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
960 const GlobalVariable *GV,
961 SmallPtrSetImpl<const PHINode*> &PHIs) {
962 for (const User *U : V->users()) {
963 const Instruction *Inst = cast<Instruction>(U);
965 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
966 continue; // Fine, ignore.
969 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
970 if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
971 return false; // Storing the pointer itself... bad.
972 continue; // Otherwise, storing through it, or storing into GV... fine.
975 // Must index into the array and into the struct.
976 if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
977 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
982 if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
983 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI
985 if (PHIs.insert(PN).second)
986 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
991 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
992 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
1002 /// The Alloc pointer is stored into GV somewhere. Transform all uses of the
1003 /// allocation into loads from the global and uses of the resultant pointer.
1004 /// Further, delete the store into GV. This assumes that these value pass the
1005 /// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
1006 static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc,
1007 GlobalVariable *GV) {
1008 while (!Alloc->use_empty()) {
1009 Instruction *U = cast<Instruction>(*Alloc->user_begin());
1010 Instruction *InsertPt = U;
1011 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
1012 // If this is the store of the allocation into the global, remove it.
1013 if (SI->getOperand(1) == GV) {
1014 SI->eraseFromParent();
1017 } else if (PHINode *PN = dyn_cast<PHINode>(U)) {
1018 // Insert the load in the corresponding predecessor, not right before the
1020 InsertPt = PN->getIncomingBlock(*Alloc->use_begin())->getTerminator();
1021 } else if (isa<BitCastInst>(U)) {
1022 // Must be bitcast between the malloc and store to initialize the global.
1023 ReplaceUsesOfMallocWithGlobal(U, GV);
1024 U->eraseFromParent();
1026 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
1027 // If this is a "GEP bitcast" and the user is a store to the global, then
1028 // just process it as a bitcast.
1029 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse())
1030 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->user_back()))
1031 if (SI->getOperand(1) == GV) {
1032 // Must be bitcast GEP between the malloc and store to initialize
1034 ReplaceUsesOfMallocWithGlobal(GEPI, GV);
1035 GEPI->eraseFromParent();
1040 // Insert a load from the global, and use it instead of the malloc.
1041 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt);
1042 U->replaceUsesOfWith(Alloc, NL);
1046 /// Verify that all uses of V (a load, or a phi of a load) are simple enough to
1047 /// perform heap SRA on. This permits GEP's that index through the array and
1048 /// struct field, icmps of null, and PHIs.
1049 static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
1050 SmallPtrSetImpl<const PHINode*> &LoadUsingPHIs,
1051 SmallPtrSetImpl<const PHINode*> &LoadUsingPHIsPerLoad) {
1052 // We permit two users of the load: setcc comparing against the null
1053 // pointer, and a getelementptr of a specific form.
1054 for (const User *U : V->users()) {
1055 const Instruction *UI = cast<Instruction>(U);
1057 // Comparison against null is ok.
1058 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UI)) {
1059 if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
1064 // getelementptr is also ok, but only a simple form.
1065 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(UI)) {
1066 // Must index into the array and into the struct.
1067 if (GEPI->getNumOperands() < 3)
1070 // Otherwise the GEP is ok.
1074 if (const PHINode *PN = dyn_cast<PHINode>(UI)) {
1075 if (!LoadUsingPHIsPerLoad.insert(PN).second)
1076 // This means some phi nodes are dependent on each other.
1077 // Avoid infinite looping!
1079 if (!LoadUsingPHIs.insert(PN).second)
1080 // If we have already analyzed this PHI, then it is safe.
1083 // Make sure all uses of the PHI are simple enough to transform.
1084 if (!LoadUsesSimpleEnoughForHeapSRA(PN,
1085 LoadUsingPHIs, LoadUsingPHIsPerLoad))
1091 // Otherwise we don't know what this is, not ok.
1098 /// If all users of values loaded from GV are simple enough to perform HeapSRA,
1100 static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
1101 Instruction *StoredVal) {
1102 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
1103 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
1104 for (const User *U : GV->users())
1105 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
1106 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
1107 LoadUsingPHIsPerLoad))
1109 LoadUsingPHIsPerLoad.clear();
1112 // If we reach here, we know that all uses of the loads and transitive uses
1113 // (through PHI nodes) are simple enough to transform. However, we don't know
1114 // that all inputs the to the PHI nodes are in the same equivalence sets.
1115 // Check to verify that all operands of the PHIs are either PHIS that can be
1116 // transformed, loads from GV, or MI itself.
1117 for (const PHINode *PN : LoadUsingPHIs) {
1118 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
1119 Value *InVal = PN->getIncomingValue(op);
1121 // PHI of the stored value itself is ok.
1122 if (InVal == StoredVal) continue;
1124 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
1125 // One of the PHIs in our set is (optimistically) ok.
1126 if (LoadUsingPHIs.count(InPN))
1131 // Load from GV is ok.
1132 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
1133 if (LI->getOperand(0) == GV)
1138 // Anything else is rejected.
1146 static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
1147 DenseMap<Value *, std::vector<Value *>> &InsertedScalarizedValues,
1148 std::vector<std::pair<PHINode *, unsigned>> &PHIsToRewrite) {
1149 std::vector<Value *> &FieldVals = InsertedScalarizedValues[V];
1151 if (FieldNo >= FieldVals.size())
1152 FieldVals.resize(FieldNo+1);
1154 // If we already have this value, just reuse the previously scalarized
1156 if (Value *FieldVal = FieldVals[FieldNo])
1159 // Depending on what instruction this is, we have several cases.
1161 if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
1162 // This is a scalarized version of the load from the global. Just create
1163 // a new Load of the scalarized global.
1164 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
1165 InsertedScalarizedValues,
1167 LI->getName()+".f"+Twine(FieldNo), LI);
1169 PHINode *PN = cast<PHINode>(V);
1170 // PN's type is pointer to struct. Make a new PHI of pointer to struct
1173 PointerType *PTy = cast<PointerType>(PN->getType());
1174 StructType *ST = cast<StructType>(PTy->getElementType());
1176 unsigned AS = PTy->getAddressSpace();
1178 PHINode::Create(PointerType::get(ST->getElementType(FieldNo), AS),
1179 PN->getNumIncomingValues(),
1180 PN->getName()+".f"+Twine(FieldNo), PN);
1182 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
1185 return FieldVals[FieldNo] = Result;
1188 /// Given a load instruction and a value derived from the load, rewrite the
1189 /// derived value to use the HeapSRoA'd load.
1190 static void RewriteHeapSROALoadUser(Instruction *LoadUser,
1191 DenseMap<Value *, std::vector<Value *>> &InsertedScalarizedValues,
1192 std::vector<std::pair<PHINode *, unsigned>> &PHIsToRewrite) {
1193 // If this is a comparison against null, handle it.
1194 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
1195 assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
1196 // If we have a setcc of the loaded pointer, we can use a setcc of any
1198 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
1199 InsertedScalarizedValues, PHIsToRewrite);
1201 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
1202 Constant::getNullValue(NPtr->getType()),
1204 SCI->replaceAllUsesWith(New);
1205 SCI->eraseFromParent();
1209 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
1210 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
1211 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
1212 && "Unexpected GEPI!");
1214 // Load the pointer for this field.
1215 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
1216 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
1217 InsertedScalarizedValues, PHIsToRewrite);
1219 // Create the new GEP idx vector.
1220 SmallVector<Value*, 8> GEPIdx;
1221 GEPIdx.push_back(GEPI->getOperand(1));
1222 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
1224 Value *NGEPI = GetElementPtrInst::Create(GEPI->getResultElementType(), NewPtr, GEPIdx,
1225 GEPI->getName(), GEPI);
1226 GEPI->replaceAllUsesWith(NGEPI);
1227 GEPI->eraseFromParent();
1231 // Recursively transform the users of PHI nodes. This will lazily create the
1232 // PHIs that are needed for individual elements. Keep track of what PHIs we
1233 // see in InsertedScalarizedValues so that we don't get infinite loops (very
1234 // antisocial). If the PHI is already in InsertedScalarizedValues, it has
1235 // already been seen first by another load, so its uses have already been
1237 PHINode *PN = cast<PHINode>(LoadUser);
1238 if (!InsertedScalarizedValues.insert(std::make_pair(PN,
1239 std::vector<Value *>())).second)
1242 // If this is the first time we've seen this PHI, recursively process all
1244 for (auto UI = PN->user_begin(), E = PN->user_end(); UI != E;) {
1245 Instruction *User = cast<Instruction>(*UI++);
1246 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1250 /// We are performing Heap SRoA on a global. Ptr is a value loaded from the
1251 /// global. Eliminate all uses of Ptr, making them use FieldGlobals instead.
1252 /// All uses of loaded values satisfy AllGlobalLoadUsesSimpleEnoughForHeapSRA.
1253 static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
1254 DenseMap<Value *, std::vector<Value *>> &InsertedScalarizedValues,
1255 std::vector<std::pair<PHINode *, unsigned> > &PHIsToRewrite) {
1256 for (auto UI = Load->user_begin(), E = Load->user_end(); UI != E;) {
1257 Instruction *User = cast<Instruction>(*UI++);
1258 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
1261 if (Load->use_empty()) {
1262 Load->eraseFromParent();
1263 InsertedScalarizedValues.erase(Load);
1267 /// CI is an allocation of an array of structures. Break it up into multiple
1268 /// allocations of arrays of the fields.
1269 static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
1270 Value *NElems, const DataLayout &DL,
1271 const TargetLibraryInfo *TLI) {
1272 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n');
1273 Type *MAT = getMallocAllocatedType(CI, TLI);
1274 StructType *STy = cast<StructType>(MAT);
1276 // There is guaranteed to be at least one use of the malloc (storing
1277 // it into GV). If there are other uses, change them to be uses of
1278 // the global to simplify later code. This also deletes the store
1280 ReplaceUsesOfMallocWithGlobal(CI, GV);
1282 // Okay, at this point, there are no users of the malloc. Insert N
1283 // new mallocs at the same place as CI, and N globals.
1284 std::vector<Value *> FieldGlobals;
1285 std::vector<Value *> FieldMallocs;
1287 SmallVector<OperandBundleDef, 1> OpBundles;
1288 CI->getOperandBundlesAsDefs(OpBundles);
1290 unsigned AS = GV->getType()->getPointerAddressSpace();
1291 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
1292 Type *FieldTy = STy->getElementType(FieldNo);
1293 PointerType *PFieldTy = PointerType::get(FieldTy, AS);
1295 GlobalVariable *NGV = new GlobalVariable(
1296 *GV->getParent(), PFieldTy, false, GlobalValue::InternalLinkage,
1297 Constant::getNullValue(PFieldTy), GV->getName() + ".f" + Twine(FieldNo),
1298 nullptr, GV->getThreadLocalMode());
1299 NGV->copyAttributesFrom(GV);
1300 FieldGlobals.push_back(NGV);
1302 unsigned TypeSize = DL.getTypeAllocSize(FieldTy);
1303 if (StructType *ST = dyn_cast<StructType>(FieldTy))
1304 TypeSize = DL.getStructLayout(ST)->getSizeInBytes();
1305 Type *IntPtrTy = DL.getIntPtrType(CI->getType());
1306 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
1307 ConstantInt::get(IntPtrTy, TypeSize),
1308 NElems, OpBundles, nullptr,
1309 CI->getName() + ".f" + Twine(FieldNo));
1310 FieldMallocs.push_back(NMI);
1311 new StoreInst(NMI, NGV, CI);
1314 // The tricky aspect of this transformation is handling the case when malloc
1315 // fails. In the original code, malloc failing would set the result pointer
1316 // of malloc to null. In this case, some mallocs could succeed and others
1317 // could fail. As such, we emit code that looks like this:
1318 // F0 = malloc(field0)
1319 // F1 = malloc(field1)
1320 // F2 = malloc(field2)
1321 // if (F0 == 0 || F1 == 0 || F2 == 0) {
1322 // if (F0) { free(F0); F0 = 0; }
1323 // if (F1) { free(F1); F1 = 0; }
1324 // if (F2) { free(F2); F2 = 0; }
1326 // The malloc can also fail if its argument is too large.
1327 Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
1328 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
1329 ConstantZero, "isneg");
1330 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
1331 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
1332 Constant::getNullValue(FieldMallocs[i]->getType()),
1334 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
1337 // Split the basic block at the old malloc.
1338 BasicBlock *OrigBB = CI->getParent();
1339 BasicBlock *ContBB =
1340 OrigBB->splitBasicBlock(CI->getIterator(), "malloc_cont");
1342 // Create the block to check the first condition. Put all these blocks at the
1343 // end of the function as they are unlikely to be executed.
1344 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
1346 OrigBB->getParent());
1348 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
1349 // branch on RunningOr.
1350 OrigBB->getTerminator()->eraseFromParent();
1351 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
1353 // Within the NullPtrBlock, we need to emit a comparison and branch for each
1354 // pointer, because some may be null while others are not.
1355 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1356 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
1357 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
1358 Constant::getNullValue(GVVal->getType()));
1359 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
1360 OrigBB->getParent());
1361 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
1362 OrigBB->getParent());
1363 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
1366 // Fill in FreeBlock.
1367 CallInst::CreateFree(GVVal, OpBundles, BI);
1368 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
1370 BranchInst::Create(NextBlock, FreeBlock);
1372 NullPtrBlock = NextBlock;
1375 BranchInst::Create(ContBB, NullPtrBlock);
1377 // CI is no longer needed, remove it.
1378 CI->eraseFromParent();
1380 /// As we process loads, if we can't immediately update all uses of the load,
1381 /// keep track of what scalarized loads are inserted for a given load.
1382 DenseMap<Value *, std::vector<Value *>> InsertedScalarizedValues;
1383 InsertedScalarizedValues[GV] = FieldGlobals;
1385 std::vector<std::pair<PHINode *, unsigned>> PHIsToRewrite;
1387 // Okay, the malloc site is completely handled. All of the uses of GV are now
1388 // loads, and all uses of those loads are simple. Rewrite them to use loads
1389 // of the per-field globals instead.
1390 for (auto UI = GV->user_begin(), E = GV->user_end(); UI != E;) {
1391 Instruction *User = cast<Instruction>(*UI++);
1393 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1394 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
1398 // Must be a store of null.
1399 StoreInst *SI = cast<StoreInst>(User);
1400 assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
1401 "Unexpected heap-sra user!");
1403 // Insert a store of null into each global.
1404 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
1405 Type *ValTy = cast<GlobalValue>(FieldGlobals[i])->getValueType();
1406 Constant *Null = Constant::getNullValue(ValTy);
1407 new StoreInst(Null, FieldGlobals[i], SI);
1409 // Erase the original store.
1410 SI->eraseFromParent();
1413 // While we have PHIs that are interesting to rewrite, do it.
1414 while (!PHIsToRewrite.empty()) {
1415 PHINode *PN = PHIsToRewrite.back().first;
1416 unsigned FieldNo = PHIsToRewrite.back().second;
1417 PHIsToRewrite.pop_back();
1418 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
1419 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
1421 // Add all the incoming values. This can materialize more phis.
1422 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1423 Value *InVal = PN->getIncomingValue(i);
1424 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
1426 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
1430 // Drop all inter-phi links and any loads that made it this far.
1431 for (DenseMap<Value *, std::vector<Value *>>::iterator
1432 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1434 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1435 PN->dropAllReferences();
1436 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1437 LI->dropAllReferences();
1440 // Delete all the phis and loads now that inter-references are dead.
1441 for (DenseMap<Value *, std::vector<Value *>>::iterator
1442 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
1444 if (PHINode *PN = dyn_cast<PHINode>(I->first))
1445 PN->eraseFromParent();
1446 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
1447 LI->eraseFromParent();
1450 // The old global is now dead, remove it.
1451 GV->eraseFromParent();
1454 return cast<GlobalVariable>(FieldGlobals[0]);
1457 /// This function is called when we see a pointer global variable with a single
1458 /// value stored it that is a malloc or cast of malloc.
1459 static bool tryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, CallInst *CI,
1461 AtomicOrdering Ordering,
1462 const DataLayout &DL,
1463 TargetLibraryInfo *TLI) {
1464 // If this is a malloc of an abstract type, don't touch it.
1465 if (!AllocTy->isSized())
1468 // We can't optimize this global unless all uses of it are *known* to be
1469 // of the malloc value, not of the null initializer value (consider a use
1470 // that compares the global's value against zero to see if the malloc has
1471 // been reached). To do this, we check to see if all uses of the global
1472 // would trap if the global were null: this proves that they must all
1473 // happen after the malloc.
1474 if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
1477 // We can't optimize this if the malloc itself is used in a complex way,
1478 // for example, being stored into multiple globals. This allows the
1479 // malloc to be stored into the specified global, loaded icmp'd, and
1480 // GEP'd. These are all things we could transform to using the global
1482 SmallPtrSet<const PHINode*, 8> PHIs;
1483 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
1486 // If we have a global that is only initialized with a fixed size malloc,
1487 // transform the program to use global memory instead of malloc'd memory.
1488 // This eliminates dynamic allocation, avoids an indirection accessing the
1489 // data, and exposes the resultant global to further GlobalOpt.
1490 // We cannot optimize the malloc if we cannot determine malloc array size.
1491 Value *NElems = getMallocArraySize(CI, DL, TLI, true);
1495 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
1496 // Restrict this transformation to only working on small allocations
1497 // (2048 bytes currently), as we don't want to introduce a 16M global or
1499 if (NElements->getZExtValue() * DL.getTypeAllocSize(AllocTy) < 2048) {
1500 OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, DL, TLI);
1504 // If the allocation is an array of structures, consider transforming this
1505 // into multiple malloc'd arrays, one for each field. This is basically
1506 // SRoA for malloc'd memory.
1508 if (Ordering != AtomicOrdering::NotAtomic)
1511 // If this is an allocation of a fixed size array of structs, analyze as a
1512 // variable size array. malloc [100 x struct],1 -> malloc struct, 100
1513 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
1514 if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
1515 AllocTy = AT->getElementType();
1517 StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
1521 // This the structure has an unreasonable number of fields, leave it
1523 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
1524 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
1526 // If this is a fixed size array, transform the Malloc to be an alloc of
1527 // structs. malloc [100 x struct],1 -> malloc struct, 100
1528 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) {
1529 Type *IntPtrTy = DL.getIntPtrType(CI->getType());
1530 unsigned TypeSize = DL.getStructLayout(AllocSTy)->getSizeInBytes();
1531 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
1532 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
1533 SmallVector<OperandBundleDef, 1> OpBundles;
1534 CI->getOperandBundlesAsDefs(OpBundles);
1535 Instruction *Malloc =
1536 CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy, AllocSize, NumElements,
1537 OpBundles, nullptr, CI->getName());
1538 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
1539 CI->replaceAllUsesWith(Cast);
1540 CI->eraseFromParent();
1541 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc))
1542 CI = cast<CallInst>(BCI->getOperand(0));
1544 CI = cast<CallInst>(Malloc);
1547 PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, DL, TLI, true), DL,
1555 // Try to optimize globals based on the knowledge that only one value (besides
1556 // its initializer) is ever stored to the global.
1557 static bool optimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
1558 AtomicOrdering Ordering,
1559 const DataLayout &DL,
1560 TargetLibraryInfo *TLI) {
1561 // Ignore no-op GEPs and bitcasts.
1562 StoredOnceVal = StoredOnceVal->stripPointerCasts();
1564 // If we are dealing with a pointer global that is initialized to null and
1565 // only has one (non-null) value stored into it, then we can optimize any
1566 // users of the loaded value (often calls and loads) that would trap if the
1568 if (GV->getInitializer()->getType()->isPointerTy() &&
1569 GV->getInitializer()->isNullValue()) {
1570 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
1571 if (GV->getInitializer()->getType() != SOVC->getType())
1572 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
1574 // Optimize away any trapping uses of the loaded value.
1575 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, DL, TLI))
1577 } else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) {
1578 Type *MallocType = getMallocAllocatedType(CI, TLI);
1579 if (MallocType && tryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType,
1588 /// At this point, we have learned that the only two values ever stored into GV
1589 /// are its initializer and OtherVal. See if we can shrink the global into a
1590 /// boolean and select between the two values whenever it is used. This exposes
1591 /// the values to other scalar optimizations.
1592 static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
1593 Type *GVElType = GV->getValueType();
1595 // If GVElType is already i1, it is already shrunk. If the type of the GV is
1596 // an FP value, pointer or vector, don't do this optimization because a select
1597 // between them is very expensive and unlikely to lead to later
1598 // simplification. In these cases, we typically end up with "cond ? v1 : v2"
1599 // where v1 and v2 both require constant pool loads, a big loss.
1600 if (GVElType == Type::getInt1Ty(GV->getContext()) ||
1601 GVElType->isFloatingPointTy() ||
1602 GVElType->isPointerTy() || GVElType->isVectorTy())
1605 // Walk the use list of the global seeing if all the uses are load or store.
1606 // If there is anything else, bail out.
1607 for (User *U : GV->users())
1608 if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
1611 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV << "\n");
1613 // Create the new global, initializing it to false.
1614 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
1616 GlobalValue::InternalLinkage,
1617 ConstantInt::getFalse(GV->getContext()),
1619 GV->getThreadLocalMode(),
1620 GV->getType()->getAddressSpace());
1621 NewGV->copyAttributesFrom(GV);
1622 GV->getParent()->getGlobalList().insert(GV->getIterator(), NewGV);
1624 Constant *InitVal = GV->getInitializer();
1625 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
1626 "No reason to shrink to bool!");
1628 SmallVector<DIGlobalVariableExpression *, 1> GVs;
1629 GV->getDebugInfo(GVs);
1631 // If initialized to zero and storing one into the global, we can use a cast
1632 // instead of a select to synthesize the desired value.
1633 bool IsOneZero = false;
1634 bool EmitOneOrZero = true;
1635 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)){
1636 IsOneZero = InitVal->isNullValue() && CI->isOne();
1638 if (ConstantInt *CIInit = dyn_cast<ConstantInt>(GV->getInitializer())){
1639 uint64_t ValInit = CIInit->getZExtValue();
1640 uint64_t ValOther = CI->getZExtValue();
1641 uint64_t ValMinus = ValOther - ValInit;
1643 for(auto *GVe : GVs){
1644 DIGlobalVariable *DGV = GVe->getVariable();
1645 DIExpression *E = GVe->getExpression();
1647 // It is expected that the address of global optimized variable is on
1648 // top of the stack. After optimization, value of that variable will
1649 // be ether 0 for initial value or 1 for other value. The following
1650 // expression should return constant integer value depending on the
1651 // value at global object address:
1652 // val * (ValOther - ValInit) + ValInit:
1653 // DW_OP_deref DW_OP_constu <ValMinus>
1654 // DW_OP_mul DW_OP_constu <ValInit> DW_OP_plus DW_OP_stack_value
1655 E = DIExpression::get(NewGV->getContext(),
1656 {dwarf::DW_OP_deref,
1657 dwarf::DW_OP_constu,
1660 dwarf::DW_OP_constu,
1663 dwarf::DW_OP_stack_value});
1664 DIGlobalVariableExpression *DGVE =
1665 DIGlobalVariableExpression::get(NewGV->getContext(), DGV, E);
1666 NewGV->addDebugInfo(DGVE);
1668 EmitOneOrZero = false;
1672 if (EmitOneOrZero) {
1673 // FIXME: This will only emit address for debugger on which will
1674 // be written only 0 or 1.
1676 NewGV->addDebugInfo(GV);
1679 while (!GV->use_empty()) {
1680 Instruction *UI = cast<Instruction>(GV->user_back());
1681 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
1682 // Change the store into a boolean store.
1683 bool StoringOther = SI->getOperand(0) == OtherVal;
1684 // Only do this if we weren't storing a loaded value.
1686 if (StoringOther || SI->getOperand(0) == InitVal) {
1687 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
1690 // Otherwise, we are storing a previously loaded copy. To do this,
1691 // change the copy from copying the original value to just copying the
1693 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
1695 // If we've already replaced the input, StoredVal will be a cast or
1696 // select instruction. If not, it will be a load of the original
1698 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
1699 assert(LI->getOperand(0) == GV && "Not a copy!");
1700 // Insert a new load, to preserve the saved value.
1701 StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1702 LI->getOrdering(), LI->getSyncScopeID(), LI);
1704 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
1705 "This is not a form that we understand!");
1706 StoreVal = StoredVal->getOperand(0);
1707 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
1710 new StoreInst(StoreVal, NewGV, false, 0,
1711 SI->getOrdering(), SI->getSyncScopeID(), SI);
1713 // Change the load into a load of bool then a select.
1714 LoadInst *LI = cast<LoadInst>(UI);
1715 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
1716 LI->getOrdering(), LI->getSyncScopeID(), LI);
1719 NSI = new ZExtInst(NLI, LI->getType(), "", LI);
1721 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
1723 LI->replaceAllUsesWith(NSI);
1725 UI->eraseFromParent();
1728 // Retain the name of the old global variable. People who are debugging their
1729 // programs may expect these variables to be named the same.
1730 NewGV->takeName(GV);
1731 GV->eraseFromParent();
1735 static bool deleteIfDead(GlobalValue &GV,
1736 SmallSet<const Comdat *, 8> &NotDiscardableComdats) {
1737 GV.removeDeadConstantUsers();
1739 if (!GV.isDiscardableIfUnused() && !GV.isDeclaration())
1742 if (const Comdat *C = GV.getComdat())
1743 if (!GV.hasLocalLinkage() && NotDiscardableComdats.count(C))
1747 if (auto *F = dyn_cast<Function>(&GV))
1748 Dead = (F->isDeclaration() && F->use_empty()) || F->isDefTriviallyDead();
1750 Dead = GV.use_empty();
1754 DEBUG(dbgs() << "GLOBAL DEAD: " << GV << "\n");
1755 GV.eraseFromParent();
1760 static bool isPointerValueDeadOnEntryToFunction(
1761 const Function *F, GlobalValue *GV,
1762 function_ref<DominatorTree &(Function &)> LookupDomTree) {
1763 // Find all uses of GV. We expect them all to be in F, and if we can't
1764 // identify any of the uses we bail out.
1766 // On each of these uses, identify if the memory that GV points to is
1767 // used/required/live at the start of the function. If it is not, for example
1768 // if the first thing the function does is store to the GV, the GV can
1769 // possibly be demoted.
1771 // We don't do an exhaustive search for memory operations - simply look
1772 // through bitcasts as they're quite common and benign.
1773 const DataLayout &DL = GV->getParent()->getDataLayout();
1774 SmallVector<LoadInst *, 4> Loads;
1775 SmallVector<StoreInst *, 4> Stores;
1776 for (auto *U : GV->users()) {
1777 if (Operator::getOpcode(U) == Instruction::BitCast) {
1778 for (auto *UU : U->users()) {
1779 if (auto *LI = dyn_cast<LoadInst>(UU))
1780 Loads.push_back(LI);
1781 else if (auto *SI = dyn_cast<StoreInst>(UU))
1782 Stores.push_back(SI);
1789 Instruction *I = dyn_cast<Instruction>(U);
1792 assert(I->getParent()->getParent() == F);
1794 if (auto *LI = dyn_cast<LoadInst>(I))
1795 Loads.push_back(LI);
1796 else if (auto *SI = dyn_cast<StoreInst>(I))
1797 Stores.push_back(SI);
1802 // We have identified all uses of GV into loads and stores. Now check if all
1803 // of them are known not to depend on the value of the global at the function
1804 // entry point. We do this by ensuring that every load is dominated by at
1806 auto &DT = LookupDomTree(*const_cast<Function *>(F));
1808 // The below check is quadratic. Check we're not going to do too many tests.
1809 // FIXME: Even though this will always have worst-case quadratic time, we
1810 // could put effort into minimizing the average time by putting stores that
1811 // have been shown to dominate at least one load at the beginning of the
1812 // Stores array, making subsequent dominance checks more likely to succeed
1815 // The threshold here is fairly large because global->local demotion is a
1816 // very powerful optimization should it fire.
1817 const unsigned Threshold = 100;
1818 if (Loads.size() * Stores.size() > Threshold)
1821 for (auto *L : Loads) {
1822 auto *LTy = L->getType();
1823 if (none_of(Stores, [&](const StoreInst *S) {
1824 auto *STy = S->getValueOperand()->getType();
1825 // The load is only dominated by the store if DomTree says so
1826 // and the number of bits loaded in L is less than or equal to
1827 // the number of bits stored in S.
1828 return DT.dominates(S, L) &&
1829 DL.getTypeStoreSize(LTy) <= DL.getTypeStoreSize(STy);
1833 // All loads have known dependences inside F, so the global can be localized.
1837 /// C may have non-instruction users. Can all of those users be turned into
1839 static bool allNonInstructionUsersCanBeMadeInstructions(Constant *C) {
1840 // We don't do this exhaustively. The most common pattern that we really need
1841 // to care about is a constant GEP or constant bitcast - so just looking
1842 // through one single ConstantExpr.
1844 // The set of constants that this function returns true for must be able to be
1845 // handled by makeAllConstantUsesInstructions.
1846 for (auto *U : C->users()) {
1847 if (isa<Instruction>(U))
1849 if (!isa<ConstantExpr>(U))
1850 // Non instruction, non-constantexpr user; cannot convert this.
1852 for (auto *UU : U->users())
1853 if (!isa<Instruction>(UU))
1854 // A constantexpr used by another constant. We don't try and recurse any
1855 // further but just bail out at this point.
1862 /// C may have non-instruction users, and
1863 /// allNonInstructionUsersCanBeMadeInstructions has returned true. Convert the
1864 /// non-instruction users to instructions.
1865 static void makeAllConstantUsesInstructions(Constant *C) {
1866 SmallVector<ConstantExpr*,4> Users;
1867 for (auto *U : C->users()) {
1868 if (isa<ConstantExpr>(U))
1869 Users.push_back(cast<ConstantExpr>(U));
1871 // We should never get here; allNonInstructionUsersCanBeMadeInstructions
1872 // should not have returned true for C.
1874 isa<Instruction>(U) &&
1875 "Can't transform non-constantexpr non-instruction to instruction!");
1878 SmallVector<Value*,4> UUsers;
1879 for (auto *U : Users) {
1881 for (auto *UU : U->users())
1882 UUsers.push_back(UU);
1883 for (auto *UU : UUsers) {
1884 Instruction *UI = cast<Instruction>(UU);
1885 Instruction *NewU = U->getAsInstruction();
1886 NewU->insertBefore(UI);
1887 UI->replaceUsesOfWith(U, NewU);
1889 // We've replaced all the uses, so destroy the constant. (destroyConstant
1890 // will update value handles and metadata.)
1891 U->destroyConstant();
1895 /// Analyze the specified global variable and optimize
1896 /// it if possible. If we make a change, return true.
1897 static bool processInternalGlobal(
1898 GlobalVariable *GV, const GlobalStatus &GS, TargetLibraryInfo *TLI,
1899 function_ref<DominatorTree &(Function &)> LookupDomTree) {
1900 auto &DL = GV->getParent()->getDataLayout();
1901 // If this is a first class global and has only one accessing function and
1902 // this function is non-recursive, we replace the global with a local alloca
1903 // in this function.
1905 // NOTE: It doesn't make sense to promote non-single-value types since we
1906 // are just replacing static memory to stack memory.
1908 // If the global is in different address space, don't bring it to stack.
1909 if (!GS.HasMultipleAccessingFunctions &&
1910 GS.AccessingFunction &&
1911 GV->getValueType()->isSingleValueType() &&
1912 GV->getType()->getAddressSpace() == 0 &&
1913 !GV->isExternallyInitialized() &&
1914 allNonInstructionUsersCanBeMadeInstructions(GV) &&
1915 GS.AccessingFunction->doesNotRecurse() &&
1916 isPointerValueDeadOnEntryToFunction(GS.AccessingFunction, GV,
1918 const DataLayout &DL = GV->getParent()->getDataLayout();
1920 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV << "\n");
1921 Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction
1922 ->getEntryBlock().begin());
1923 Type *ElemTy = GV->getValueType();
1924 // FIXME: Pass Global's alignment when globals have alignment
1925 AllocaInst *Alloca = new AllocaInst(ElemTy, DL.getAllocaAddrSpace(), nullptr,
1926 GV->getName(), &FirstI);
1927 if (!isa<UndefValue>(GV->getInitializer()))
1928 new StoreInst(GV->getInitializer(), Alloca, &FirstI);
1930 makeAllConstantUsesInstructions(GV);
1932 GV->replaceAllUsesWith(Alloca);
1933 GV->eraseFromParent();
1938 // If the global is never loaded (but may be stored to), it is dead.
1941 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV << "\n");
1944 if (isLeakCheckerRoot(GV)) {
1945 // Delete any constant stores to the global.
1946 Changed = CleanupPointerRootUsers(GV, TLI);
1948 // Delete any stores we can find to the global. We may not be able to
1949 // make it completely dead though.
1950 Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
1953 // If the global is dead now, delete it.
1954 if (GV->use_empty()) {
1955 GV->eraseFromParent();
1962 if (GS.StoredType <= GlobalStatus::InitializerStored) {
1963 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n");
1964 GV->setConstant(true);
1966 // Clean up any obviously simplifiable users now.
1967 CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
1969 // If the global is dead now, just nuke it.
1970 if (GV->use_empty()) {
1971 DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
1972 << "all users and delete global!\n");
1973 GV->eraseFromParent();
1978 // Fall through to the next check; see if we can optimize further.
1981 if (!GV->getInitializer()->getType()->isSingleValueType()) {
1982 const DataLayout &DL = GV->getParent()->getDataLayout();
1983 if (SRAGlobal(GV, DL))
1986 if (GS.StoredType == GlobalStatus::StoredOnce && GS.StoredOnceValue) {
1987 // If the initial value for the global was an undef value, and if only
1988 // one other value was stored into it, we can just change the
1989 // initializer to be the stored value, then delete all stores to the
1990 // global. This allows us to mark it constant.
1991 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
1992 if (isa<UndefValue>(GV->getInitializer())) {
1993 // Change the initial value here.
1994 GV->setInitializer(SOVConstant);
1996 // Clean up any obviously simplifiable users now.
1997 CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
1999 if (GV->use_empty()) {
2000 DEBUG(dbgs() << " *** Substituting initializer allowed us to "
2001 << "simplify all users and delete global!\n");
2002 GV->eraseFromParent();
2009 // Try to optimize globals based on the knowledge that only one value
2010 // (besides its initializer) is ever stored to the global.
2011 if (optimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, DL, TLI))
2014 // Otherwise, if the global was not a boolean, we can shrink it to be a
2016 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) {
2017 if (GS.Ordering == AtomicOrdering::NotAtomic) {
2018 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
2029 /// Analyze the specified global variable and optimize it if possible. If we
2030 /// make a change, return true.
2032 processGlobal(GlobalValue &GV, TargetLibraryInfo *TLI,
2033 function_ref<DominatorTree &(Function &)> LookupDomTree) {
2034 if (GV.getName().startswith("llvm."))
2039 if (GlobalStatus::analyzeGlobal(&GV, GS))
2042 bool Changed = false;
2043 if (!GS.IsCompared && !GV.hasGlobalUnnamedAddr()) {
2044 auto NewUnnamedAddr = GV.hasLocalLinkage() ? GlobalValue::UnnamedAddr::Global
2045 : GlobalValue::UnnamedAddr::Local;
2046 if (NewUnnamedAddr != GV.getUnnamedAddr()) {
2047 GV.setUnnamedAddr(NewUnnamedAddr);
2053 // Do more involved optimizations if the global is internal.
2054 if (!GV.hasLocalLinkage())
2057 auto *GVar = dyn_cast<GlobalVariable>(&GV);
2061 if (GVar->isConstant() || !GVar->hasInitializer())
2064 return processInternalGlobal(GVar, GS, TLI, LookupDomTree) || Changed;
2067 /// Walk all of the direct calls of the specified function, changing them to
2069 static void ChangeCalleesToFastCall(Function *F) {
2070 for (User *U : F->users()) {
2071 if (isa<BlockAddress>(U))
2073 CallSite CS(cast<Instruction>(U));
2074 CS.setCallingConv(CallingConv::Fast);
2078 static AttributeList StripNest(LLVMContext &C, AttributeList Attrs) {
2079 // There can be at most one attribute set with a nest attribute.
2081 if (Attrs.hasAttrSomewhere(Attribute::Nest, &NestIndex))
2082 return Attrs.removeAttribute(C, NestIndex, Attribute::Nest);
2086 static void RemoveNestAttribute(Function *F) {
2087 F->setAttributes(StripNest(F->getContext(), F->getAttributes()));
2088 for (User *U : F->users()) {
2089 if (isa<BlockAddress>(U))
2091 CallSite CS(cast<Instruction>(U));
2092 CS.setAttributes(StripNest(F->getContext(), CS.getAttributes()));
2096 /// Return true if this is a calling convention that we'd like to change. The
2097 /// idea here is that we don't want to mess with the convention if the user
2098 /// explicitly requested something with performance implications like coldcc,
2099 /// GHC, or anyregcc.
2100 static bool isProfitableToMakeFastCC(Function *F) {
2101 CallingConv::ID CC = F->getCallingConv();
2103 // FIXME: Is it worth transforming x86_stdcallcc and x86_fastcallcc?
2104 if (CC != CallingConv::C && CC != CallingConv::X86_ThisCall)
2107 // FIXME: Change CC for the whole chain of musttail calls when possible.
2109 // Can't change CC of the function that either has musttail calls, or is a
2110 // musttail callee itself
2111 for (User *U : F->users()) {
2112 if (isa<BlockAddress>(U))
2114 CallInst* CI = dyn_cast<CallInst>(U);
2118 if (CI->isMustTailCall())
2122 for (BasicBlock &BB : *F)
2123 if (BB.getTerminatingMustTailCall())
2130 OptimizeFunctions(Module &M, TargetLibraryInfo *TLI,
2131 function_ref<DominatorTree &(Function &)> LookupDomTree,
2132 SmallSet<const Comdat *, 8> &NotDiscardableComdats) {
2133 bool Changed = false;
2134 // Optimize functions.
2135 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
2136 Function *F = &*FI++;
2137 // Functions without names cannot be referenced outside this module.
2138 if (!F->hasName() && !F->isDeclaration() && !F->hasLocalLinkage())
2139 F->setLinkage(GlobalValue::InternalLinkage);
2141 if (deleteIfDead(*F, NotDiscardableComdats)) {
2146 // LLVM's definition of dominance allows instructions that are cyclic
2147 // in unreachable blocks, e.g.:
2148 // %pat = select i1 %condition, @global, i16* %pat
2149 // because any instruction dominates an instruction in a block that's
2150 // not reachable from entry.
2151 // So, remove unreachable blocks from the function, because a) there's
2152 // no point in analyzing them and b) GlobalOpt should otherwise grow
2153 // some more complicated logic to break these cycles.
2154 // Removing unreachable blocks might invalidate the dominator so we
2156 if (!F->isDeclaration()) {
2157 if (removeUnreachableBlocks(*F)) {
2158 auto &DT = LookupDomTree(*F);
2164 Changed |= processGlobal(*F, TLI, LookupDomTree);
2166 if (!F->hasLocalLinkage())
2168 if (isProfitableToMakeFastCC(F) && !F->isVarArg() &&
2169 !F->hasAddressTaken()) {
2170 // If this function has a calling convention worth changing, is not a
2171 // varargs function, and is only called directly, promote it to use the
2172 // Fast calling convention.
2173 F->setCallingConv(CallingConv::Fast);
2174 ChangeCalleesToFastCall(F);
2179 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
2180 !F->hasAddressTaken()) {
2181 // The function is not used by a trampoline intrinsic, so it is safe
2182 // to remove the 'nest' attribute.
2183 RemoveNestAttribute(F);
2192 OptimizeGlobalVars(Module &M, TargetLibraryInfo *TLI,
2193 function_ref<DominatorTree &(Function &)> LookupDomTree,
2194 SmallSet<const Comdat *, 8> &NotDiscardableComdats) {
2195 bool Changed = false;
2197 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
2199 GlobalVariable *GV = &*GVI++;
2200 // Global variables without names cannot be referenced outside this module.
2201 if (!GV->hasName() && !GV->isDeclaration() && !GV->hasLocalLinkage())
2202 GV->setLinkage(GlobalValue::InternalLinkage);
2203 // Simplify the initializer.
2204 if (GV->hasInitializer())
2205 if (auto *C = dyn_cast<Constant>(GV->getInitializer())) {
2206 auto &DL = M.getDataLayout();
2207 Constant *New = ConstantFoldConstant(C, DL, TLI);
2208 if (New && New != C)
2209 GV->setInitializer(New);
2212 if (deleteIfDead(*GV, NotDiscardableComdats)) {
2217 Changed |= processGlobal(*GV, TLI, LookupDomTree);
2222 /// Evaluate a piece of a constantexpr store into a global initializer. This
2223 /// returns 'Init' modified to reflect 'Val' stored into it. At this point, the
2224 /// GEP operands of Addr [0, OpNo) have been stepped into.
2225 static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
2226 ConstantExpr *Addr, unsigned OpNo) {
2227 // Base case of the recursion.
2228 if (OpNo == Addr->getNumOperands()) {
2229 assert(Val->getType() == Init->getType() && "Type mismatch!");
2233 SmallVector<Constant*, 32> Elts;
2234 if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
2235 // Break up the constant into its elements.
2236 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
2237 Elts.push_back(Init->getAggregateElement(i));
2239 // Replace the element that we are supposed to.
2240 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
2241 unsigned Idx = CU->getZExtValue();
2242 assert(Idx < STy->getNumElements() && "Struct index out of range!");
2243 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
2245 // Return the modified struct.
2246 return ConstantStruct::get(STy, Elts);
2249 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
2250 SequentialType *InitTy = cast<SequentialType>(Init->getType());
2251 uint64_t NumElts = InitTy->getNumElements();
2253 // Break up the array into elements.
2254 for (uint64_t i = 0, e = NumElts; i != e; ++i)
2255 Elts.push_back(Init->getAggregateElement(i));
2257 assert(CI->getZExtValue() < NumElts);
2258 Elts[CI->getZExtValue()] =
2259 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
2261 if (Init->getType()->isArrayTy())
2262 return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
2263 return ConstantVector::get(Elts);
2266 /// We have decided that Addr (which satisfies the predicate
2267 /// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen.
2268 static void CommitValueTo(Constant *Val, Constant *Addr) {
2269 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
2270 assert(GV->hasInitializer());
2271 GV->setInitializer(Val);
2275 ConstantExpr *CE = cast<ConstantExpr>(Addr);
2276 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
2277 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
2280 /// Evaluate static constructors in the function, if we can. Return true if we
2281 /// can, false otherwise.
2282 static bool EvaluateStaticConstructor(Function *F, const DataLayout &DL,
2283 TargetLibraryInfo *TLI) {
2284 // Call the function.
2285 Evaluator Eval(DL, TLI);
2286 Constant *RetValDummy;
2287 bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy,
2288 SmallVector<Constant*, 0>());
2291 ++NumCtorsEvaluated;
2293 // We succeeded at evaluation: commit the result.
2294 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
2295 << F->getName() << "' to " << Eval.getMutatedMemory().size()
2297 for (const auto &I : Eval.getMutatedMemory())
2298 CommitValueTo(I.second, I.first);
2299 for (GlobalVariable *GV : Eval.getInvariants())
2300 GV->setConstant(true);
2306 static int compareNames(Constant *const *A, Constant *const *B) {
2307 Value *AStripped = (*A)->stripPointerCastsNoFollowAliases();
2308 Value *BStripped = (*B)->stripPointerCastsNoFollowAliases();
2309 return AStripped->getName().compare(BStripped->getName());
2312 static void setUsedInitializer(GlobalVariable &V,
2313 const SmallPtrSet<GlobalValue *, 8> &Init) {
2315 V.eraseFromParent();
2319 // Type of pointer to the array of pointers.
2320 PointerType *Int8PtrTy = Type::getInt8PtrTy(V.getContext(), 0);
2322 SmallVector<Constant *, 8> UsedArray;
2323 for (GlobalValue *GV : Init) {
2325 = ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, Int8PtrTy);
2326 UsedArray.push_back(Cast);
2328 // Sort to get deterministic order.
2329 array_pod_sort(UsedArray.begin(), UsedArray.end(), compareNames);
2330 ArrayType *ATy = ArrayType::get(Int8PtrTy, UsedArray.size());
2332 Module *M = V.getParent();
2333 V.removeFromParent();
2334 GlobalVariable *NV =
2335 new GlobalVariable(*M, ATy, false, GlobalValue::AppendingLinkage,
2336 ConstantArray::get(ATy, UsedArray), "");
2338 NV->setSection("llvm.metadata");
2344 /// An easy to access representation of llvm.used and llvm.compiler.used.
2346 SmallPtrSet<GlobalValue *, 8> Used;
2347 SmallPtrSet<GlobalValue *, 8> CompilerUsed;
2348 GlobalVariable *UsedV;
2349 GlobalVariable *CompilerUsedV;
2352 LLVMUsed(Module &M) {
2353 UsedV = collectUsedGlobalVariables(M, Used, false);
2354 CompilerUsedV = collectUsedGlobalVariables(M, CompilerUsed, true);
2357 using iterator = SmallPtrSet<GlobalValue *, 8>::iterator;
2358 using used_iterator_range = iterator_range<iterator>;
2360 iterator usedBegin() { return Used.begin(); }
2361 iterator usedEnd() { return Used.end(); }
2363 used_iterator_range used() {
2364 return used_iterator_range(usedBegin(), usedEnd());
2367 iterator compilerUsedBegin() { return CompilerUsed.begin(); }
2368 iterator compilerUsedEnd() { return CompilerUsed.end(); }
2370 used_iterator_range compilerUsed() {
2371 return used_iterator_range(compilerUsedBegin(), compilerUsedEnd());
2374 bool usedCount(GlobalValue *GV) const { return Used.count(GV); }
2376 bool compilerUsedCount(GlobalValue *GV) const {
2377 return CompilerUsed.count(GV);
2380 bool usedErase(GlobalValue *GV) { return Used.erase(GV); }
2381 bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(GV); }
2382 bool usedInsert(GlobalValue *GV) { return Used.insert(GV).second; }
2384 bool compilerUsedInsert(GlobalValue *GV) {
2385 return CompilerUsed.insert(GV).second;
2388 void syncVariablesAndSets() {
2390 setUsedInitializer(*UsedV, Used);
2392 setUsedInitializer(*CompilerUsedV, CompilerUsed);
2396 } // end anonymous namespace
2398 static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) {
2399 if (GA.use_empty()) // No use at all.
2402 assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) &&
2403 "We should have removed the duplicated "
2404 "element from llvm.compiler.used");
2405 if (!GA.hasOneUse())
2406 // Strictly more than one use. So at least one is not in llvm.used and
2407 // llvm.compiler.used.
2410 // Exactly one use. Check if it is in llvm.used or llvm.compiler.used.
2411 return !U.usedCount(&GA) && !U.compilerUsedCount(&GA);
2414 static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V,
2415 const LLVMUsed &U) {
2417 assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) &&
2418 "We should have removed the duplicated "
2419 "element from llvm.compiler.used");
2420 if (U.usedCount(&V) || U.compilerUsedCount(&V))
2422 return V.hasNUsesOrMore(N);
2425 static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) {
2426 if (!GA.hasLocalLinkage())
2429 return U.usedCount(&GA) || U.compilerUsedCount(&GA);
2432 static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
2433 bool &RenameTarget) {
2434 RenameTarget = false;
2436 if (hasUseOtherThanLLVMUsed(GA, U))
2439 // If the alias is externally visible, we may still be able to simplify it.
2440 if (!mayHaveOtherReferences(GA, U))
2443 // If the aliasee has internal linkage, give it the name and linkage
2444 // of the alias, and delete the alias. This turns:
2445 // define internal ... @f(...)
2446 // @a = alias ... @f
2448 // define ... @a(...)
2449 Constant *Aliasee = GA.getAliasee();
2450 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
2451 if (!Target->hasLocalLinkage())
2454 // Do not perform the transform if multiple aliases potentially target the
2455 // aliasee. This check also ensures that it is safe to replace the section
2456 // and other attributes of the aliasee with those of the alias.
2457 if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U))
2460 RenameTarget = true;
2465 OptimizeGlobalAliases(Module &M,
2466 SmallSet<const Comdat *, 8> &NotDiscardableComdats) {
2467 bool Changed = false;
2470 for (GlobalValue *GV : Used.used())
2471 Used.compilerUsedErase(GV);
2473 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
2475 GlobalAlias *J = &*I++;
2477 // Aliases without names cannot be referenced outside this module.
2478 if (!J->hasName() && !J->isDeclaration() && !J->hasLocalLinkage())
2479 J->setLinkage(GlobalValue::InternalLinkage);
2481 if (deleteIfDead(*J, NotDiscardableComdats)) {
2486 // If the aliasee may change at link time, nothing can be done - bail out.
2487 if (J->isInterposable())
2490 Constant *Aliasee = J->getAliasee();
2491 GlobalValue *Target = dyn_cast<GlobalValue>(Aliasee->stripPointerCasts());
2492 // We can't trivially replace the alias with the aliasee if the aliasee is
2493 // non-trivial in some way.
2494 // TODO: Try to handle non-zero GEPs of local aliasees.
2497 Target->removeDeadConstantUsers();
2499 // Make all users of the alias use the aliasee instead.
2501 if (!hasUsesToReplace(*J, Used, RenameTarget))
2504 J->replaceAllUsesWith(ConstantExpr::getBitCast(Aliasee, J->getType()));
2505 ++NumAliasesResolved;
2509 // Give the aliasee the name, linkage and other attributes of the alias.
2510 Target->takeName(&*J);
2511 Target->setLinkage(J->getLinkage());
2512 Target->setVisibility(J->getVisibility());
2513 Target->setDLLStorageClass(J->getDLLStorageClass());
2515 if (Used.usedErase(&*J))
2516 Used.usedInsert(Target);
2518 if (Used.compilerUsedErase(&*J))
2519 Used.compilerUsedInsert(Target);
2520 } else if (mayHaveOtherReferences(*J, Used))
2523 // Delete the alias.
2524 M.getAliasList().erase(J);
2525 ++NumAliasesRemoved;
2529 Used.syncVariablesAndSets();
2534 static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) {
2535 LibFunc F = LibFunc_cxa_atexit;
2539 Function *Fn = M.getFunction(TLI->getName(F));
2543 // Make sure that the function has the correct prototype.
2544 if (!TLI->getLibFunc(*Fn, F) || F != LibFunc_cxa_atexit)
2550 /// Returns whether the given function is an empty C++ destructor and can
2551 /// therefore be eliminated.
2552 /// Note that we assume that other optimization passes have already simplified
2553 /// the code so we only look for a function with a single basic block, where
2554 /// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and
2555 /// other side-effect free instructions.
2556 static bool cxxDtorIsEmpty(const Function &Fn,
2557 SmallPtrSet<const Function *, 8> &CalledFunctions) {
2558 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
2559 // nounwind, but that doesn't seem worth doing.
2560 if (Fn.isDeclaration())
2563 if (++Fn.begin() != Fn.end())
2566 const BasicBlock &EntryBlock = Fn.getEntryBlock();
2567 for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
2569 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
2570 // Ignore debug intrinsics.
2571 if (isa<DbgInfoIntrinsic>(CI))
2574 const Function *CalledFn = CI->getCalledFunction();
2579 SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
2581 // Don't treat recursive functions as empty.
2582 if (!NewCalledFunctions.insert(CalledFn).second)
2585 if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
2587 } else if (isa<ReturnInst>(*I))
2588 return true; // We're done.
2589 else if (I->mayHaveSideEffects())
2590 return false; // Destructor with side effects, bail.
2596 static bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
2597 /// Itanium C++ ABI p3.3.5:
2599 /// After constructing a global (or local static) object, that will require
2600 /// destruction on exit, a termination function is registered as follows:
2602 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
2604 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
2605 /// call f(p) when DSO d is unloaded, before all such termination calls
2606 /// registered before this one. It returns zero if registration is
2607 /// successful, nonzero on failure.
2609 // This pass will look for calls to __cxa_atexit where the function is trivial
2611 bool Changed = false;
2613 for (auto I = CXAAtExitFn->user_begin(), E = CXAAtExitFn->user_end();
2615 // We're only interested in calls. Theoretically, we could handle invoke
2616 // instructions as well, but neither llvm-gcc nor clang generate invokes
2618 CallInst *CI = dyn_cast<CallInst>(*I++);
2623 dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
2627 SmallPtrSet<const Function *, 8> CalledFunctions;
2628 if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
2631 // Just remove the call.
2632 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
2633 CI->eraseFromParent();
2635 ++NumCXXDtorsRemoved;
2643 static bool optimizeGlobalsInModule(
2644 Module &M, const DataLayout &DL, TargetLibraryInfo *TLI,
2645 function_ref<DominatorTree &(Function &)> LookupDomTree) {
2646 SmallSet<const Comdat *, 8> NotDiscardableComdats;
2647 bool Changed = false;
2648 bool LocalChange = true;
2649 while (LocalChange) {
2650 LocalChange = false;
2652 NotDiscardableComdats.clear();
2653 for (const GlobalVariable &GV : M.globals())
2654 if (const Comdat *C = GV.getComdat())
2655 if (!GV.isDiscardableIfUnused() || !GV.use_empty())
2656 NotDiscardableComdats.insert(C);
2657 for (Function &F : M)
2658 if (const Comdat *C = F.getComdat())
2659 if (!F.isDefTriviallyDead())
2660 NotDiscardableComdats.insert(C);
2661 for (GlobalAlias &GA : M.aliases())
2662 if (const Comdat *C = GA.getComdat())
2663 if (!GA.isDiscardableIfUnused() || !GA.use_empty())
2664 NotDiscardableComdats.insert(C);
2666 // Delete functions that are trivially dead, ccc -> fastcc
2668 OptimizeFunctions(M, TLI, LookupDomTree, NotDiscardableComdats);
2670 // Optimize global_ctors list.
2671 LocalChange |= optimizeGlobalCtorsList(M, [&](Function *F) {
2672 return EvaluateStaticConstructor(F, DL, TLI);
2675 // Optimize non-address-taken globals.
2676 LocalChange |= OptimizeGlobalVars(M, TLI, LookupDomTree,
2677 NotDiscardableComdats);
2679 // Resolve aliases, when possible.
2680 LocalChange |= OptimizeGlobalAliases(M, NotDiscardableComdats);
2682 // Try to remove trivial global destructors if they are not removed
2684 Function *CXAAtExitFn = FindCXAAtExit(M, TLI);
2686 LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
2688 Changed |= LocalChange;
2691 // TODO: Move all global ctors functions to the end of the module for code
2697 PreservedAnalyses GlobalOptPass::run(Module &M, ModuleAnalysisManager &AM) {
2698 auto &DL = M.getDataLayout();
2699 auto &TLI = AM.getResult<TargetLibraryAnalysis>(M);
2701 AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
2702 auto LookupDomTree = [&FAM](Function &F) -> DominatorTree &{
2703 return FAM.getResult<DominatorTreeAnalysis>(F);
2705 if (!optimizeGlobalsInModule(M, DL, &TLI, LookupDomTree))
2706 return PreservedAnalyses::all();
2707 return PreservedAnalyses::none();
2712 struct GlobalOptLegacyPass : public ModulePass {
2713 static char ID; // Pass identification, replacement for typeid
2715 GlobalOptLegacyPass() : ModulePass(ID) {
2716 initializeGlobalOptLegacyPassPass(*PassRegistry::getPassRegistry());
2719 bool runOnModule(Module &M) override {
2723 auto &DL = M.getDataLayout();
2724 auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
2725 auto LookupDomTree = [this](Function &F) -> DominatorTree & {
2726 return this->getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
2728 return optimizeGlobalsInModule(M, DL, TLI, LookupDomTree);
2731 void getAnalysisUsage(AnalysisUsage &AU) const override {
2732 AU.addRequired<TargetLibraryInfoWrapperPass>();
2733 AU.addRequired<DominatorTreeWrapperPass>();
2737 } // end anonymous namespace
2739 char GlobalOptLegacyPass::ID = 0;
2741 INITIALIZE_PASS_BEGIN(GlobalOptLegacyPass, "globalopt",
2742 "Global Variable Optimizer", false, false)
2743 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
2744 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
2745 INITIALIZE_PASS_END(GlobalOptLegacyPass, "globalopt",
2746 "Global Variable Optimizer", false, false)
2748 ModulePass *llvm::createGlobalOptimizerPass() {
2749 return new GlobalOptLegacyPass();