1 //===- MergeFunctions.cpp - Merge identical functions ---------------------===//
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 looks for equivalent functions that are mergable and folds them.
12 // A hash is computed from the function, based on its type and number of
15 // Once all hashes are computed, we perform an expensive equality comparison
16 // on each function pair. This takes n^2/2 comparisons per bucket, so it's
17 // important that the hash function be high quality. The equality comparison
18 // iterates through each instruction in each basic block.
20 // When a match is found the functions are folded. If both functions are
21 // overridable, we move the functionality into a new internal function and
22 // leave two overridable thunks to it.
24 //===----------------------------------------------------------------------===//
28 // * virtual functions.
30 // Many functions have their address taken by the virtual function table for
31 // the object they belong to. However, as long as it's only used for a lookup
32 // and call, this is irrelevant, and we'd like to fold such functions.
34 // * switch from n^2 pair-wise comparisons to an n-way comparison for each
37 // * be smarter about bitcasts.
39 // In order to fold functions, we will sometimes add either bitcast instructions
40 // or bitcast constant expressions. Unfortunately, this can confound further
41 // analysis since the two functions differ where one has a bitcast and the
42 // other doesn't. We should learn to look through bitcasts.
44 //===----------------------------------------------------------------------===//
46 #define DEBUG_TYPE "mergefunc"
47 #include "llvm/Transforms/IPO.h"
48 #include "llvm/ADT/DenseSet.h"
49 #include "llvm/ADT/FoldingSet.h"
50 #include "llvm/ADT/STLExtras.h"
51 #include "llvm/ADT/SmallSet.h"
52 #include "llvm/ADT/Statistic.h"
53 #include "llvm/IR/Constants.h"
54 #include "llvm/IR/DataLayout.h"
55 #include "llvm/IR/IRBuilder.h"
56 #include "llvm/IR/InlineAsm.h"
57 #include "llvm/IR/Instructions.h"
58 #include "llvm/IR/LLVMContext.h"
59 #include "llvm/IR/Module.h"
60 #include "llvm/IR/Operator.h"
61 #include "llvm/Pass.h"
62 #include "llvm/Support/CallSite.h"
63 #include "llvm/Support/Debug.h"
64 #include "llvm/Support/ErrorHandling.h"
65 #include "llvm/Support/ValueHandle.h"
66 #include "llvm/Support/raw_ostream.h"
70 STATISTIC(NumFunctionsMerged, "Number of functions merged");
71 STATISTIC(NumThunksWritten, "Number of thunks generated");
72 STATISTIC(NumAliasesWritten, "Number of aliases generated");
73 STATISTIC(NumDoubleWeak, "Number of new functions created");
75 /// Returns the type id for a type to be hashed. We turn pointer types into
76 /// integers here because the actual compare logic below considers pointers and
77 /// integers of the same size as equal.
78 static Type::TypeID getTypeIDForHash(Type *Ty) {
79 if (Ty->isPointerTy())
80 return Type::IntegerTyID;
81 return Ty->getTypeID();
84 /// Creates a hash-code for the function which is the same for any two
85 /// functions that will compare equal, without looking at the instructions
86 /// inside the function.
87 static unsigned profileFunction(const Function *F) {
88 FunctionType *FTy = F->getFunctionType();
91 ID.AddInteger(F->size());
92 ID.AddInteger(F->getCallingConv());
93 ID.AddBoolean(F->hasGC());
94 ID.AddBoolean(FTy->isVarArg());
95 ID.AddInteger(getTypeIDForHash(FTy->getReturnType()));
96 for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
97 ID.AddInteger(getTypeIDForHash(FTy->getParamType(i)));
98 return ID.ComputeHash();
103 /// ComparableFunction - A struct that pairs together functions with a
104 /// DataLayout so that we can keep them together as elements in the DenseSet.
105 class ComparableFunction {
107 static const ComparableFunction EmptyKey;
108 static const ComparableFunction TombstoneKey;
109 static DataLayout * const LookupOnly;
111 ComparableFunction(Function *Func, DataLayout *TD)
112 : Func(Func), Hash(profileFunction(Func)), TD(TD) {}
114 Function *getFunc() const { return Func; }
115 unsigned getHash() const { return Hash; }
116 DataLayout *getTD() const { return TD; }
118 // Drops AssertingVH reference to the function. Outside of debug mode, this
122 "Attempted to release function twice, or release empty/tombstone!");
127 explicit ComparableFunction(unsigned Hash)
128 : Func(NULL), Hash(Hash), TD(NULL) {}
130 AssertingVH<Function> Func;
135 const ComparableFunction ComparableFunction::EmptyKey = ComparableFunction(0);
136 const ComparableFunction ComparableFunction::TombstoneKey =
137 ComparableFunction(1);
138 DataLayout *const ComparableFunction::LookupOnly = (DataLayout*)(-1);
144 struct DenseMapInfo<ComparableFunction> {
145 static ComparableFunction getEmptyKey() {
146 return ComparableFunction::EmptyKey;
148 static ComparableFunction getTombstoneKey() {
149 return ComparableFunction::TombstoneKey;
151 static unsigned getHashValue(const ComparableFunction &CF) {
154 static bool isEqual(const ComparableFunction &LHS,
155 const ComparableFunction &RHS);
161 /// FunctionComparator - Compares two functions to determine whether or not
162 /// they will generate machine code with the same behaviour. DataLayout is
163 /// used if available. The comparator always fails conservatively (erring on the
164 /// side of claiming that two functions are different).
165 class FunctionComparator {
167 FunctionComparator(const DataLayout *TD, const Function *F1,
169 : F1(F1), F2(F2), TD(TD) {}
171 /// Test whether the two functions have equivalent behaviour.
175 /// Test whether two basic blocks have equivalent behaviour.
176 bool compare(const BasicBlock *BB1, const BasicBlock *BB2);
178 /// Assign or look up previously assigned numbers for the two values, and
179 /// return whether the numbers are equal. Numbers are assigned in the order
181 bool enumerate(const Value *V1, const Value *V2);
183 /// Compare two Instructions for equivalence, similar to
184 /// Instruction::isSameOperationAs but with modifications to the type
186 bool isEquivalentOperation(const Instruction *I1,
187 const Instruction *I2) const;
189 /// Compare two GEPs for equivalent pointer arithmetic.
190 bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2);
191 bool isEquivalentGEP(const GetElementPtrInst *GEP1,
192 const GetElementPtrInst *GEP2) {
193 return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2));
196 /// Compare two Types, treating all pointer types as equal.
197 bool isEquivalentType(Type *Ty1, Type *Ty2) const;
199 // The two functions undergoing comparison.
200 const Function *F1, *F2;
202 const DataLayout *TD;
204 DenseMap<const Value *, const Value *> id_map;
205 DenseSet<const Value *> seen_values;
210 // Any two pointers in the same address space are equivalent, intptr_t and
211 // pointers are equivalent. Otherwise, standard type equivalence rules apply.
212 bool FunctionComparator::isEquivalentType(Type *Ty1, Type *Ty2) const {
215 if (Ty1->getTypeID() != Ty2->getTypeID()) {
217 LLVMContext &Ctx = Ty1->getContext();
218 if (isa<PointerType>(Ty1) && Ty2 == TD->getIntPtrType(Ctx)) return true;
219 if (isa<PointerType>(Ty2) && Ty1 == TD->getIntPtrType(Ctx)) return true;
224 switch (Ty1->getTypeID()) {
226 llvm_unreachable("Unknown type!");
227 // Fall through in Release mode.
228 case Type::IntegerTyID:
229 case Type::VectorTyID:
230 // Ty1 == Ty2 would have returned true earlier.
234 case Type::FloatTyID:
235 case Type::DoubleTyID:
236 case Type::X86_FP80TyID:
237 case Type::FP128TyID:
238 case Type::PPC_FP128TyID:
239 case Type::LabelTyID:
240 case Type::MetadataTyID:
243 case Type::PointerTyID: {
244 PointerType *PTy1 = cast<PointerType>(Ty1);
245 PointerType *PTy2 = cast<PointerType>(Ty2);
246 return PTy1->getAddressSpace() == PTy2->getAddressSpace();
249 case Type::StructTyID: {
250 StructType *STy1 = cast<StructType>(Ty1);
251 StructType *STy2 = cast<StructType>(Ty2);
252 if (STy1->getNumElements() != STy2->getNumElements())
255 if (STy1->isPacked() != STy2->isPacked())
258 for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) {
259 if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i)))
265 case Type::FunctionTyID: {
266 FunctionType *FTy1 = cast<FunctionType>(Ty1);
267 FunctionType *FTy2 = cast<FunctionType>(Ty2);
268 if (FTy1->getNumParams() != FTy2->getNumParams() ||
269 FTy1->isVarArg() != FTy2->isVarArg())
272 if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType()))
275 for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) {
276 if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i)))
282 case Type::ArrayTyID: {
283 ArrayType *ATy1 = cast<ArrayType>(Ty1);
284 ArrayType *ATy2 = cast<ArrayType>(Ty2);
285 return ATy1->getNumElements() == ATy2->getNumElements() &&
286 isEquivalentType(ATy1->getElementType(), ATy2->getElementType());
291 // Determine whether the two operations are the same except that pointer-to-A
292 // and pointer-to-B are equivalent. This should be kept in sync with
293 // Instruction::isSameOperationAs.
294 bool FunctionComparator::isEquivalentOperation(const Instruction *I1,
295 const Instruction *I2) const {
296 // Differences from Instruction::isSameOperationAs:
297 // * replace type comparison with calls to isEquivalentType.
298 // * we test for I->hasSameSubclassOptionalData (nuw/nsw/tail) at the top
299 // * because of the above, we don't test for the tail bit on calls later on
300 if (I1->getOpcode() != I2->getOpcode() ||
301 I1->getNumOperands() != I2->getNumOperands() ||
302 !isEquivalentType(I1->getType(), I2->getType()) ||
303 !I1->hasSameSubclassOptionalData(I2))
306 // We have two instructions of identical opcode and #operands. Check to see
307 // if all operands are the same type
308 for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i)
309 if (!isEquivalentType(I1->getOperand(i)->getType(),
310 I2->getOperand(i)->getType()))
313 // Check special state that is a part of some instructions.
314 if (const LoadInst *LI = dyn_cast<LoadInst>(I1))
315 return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() &&
316 LI->getAlignment() == cast<LoadInst>(I2)->getAlignment() &&
317 LI->getOrdering() == cast<LoadInst>(I2)->getOrdering() &&
318 LI->getSynchScope() == cast<LoadInst>(I2)->getSynchScope();
319 if (const StoreInst *SI = dyn_cast<StoreInst>(I1))
320 return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() &&
321 SI->getAlignment() == cast<StoreInst>(I2)->getAlignment() &&
322 SI->getOrdering() == cast<StoreInst>(I2)->getOrdering() &&
323 SI->getSynchScope() == cast<StoreInst>(I2)->getSynchScope();
324 if (const CmpInst *CI = dyn_cast<CmpInst>(I1))
325 return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate();
326 if (const CallInst *CI = dyn_cast<CallInst>(I1))
327 return CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() &&
328 CI->getAttributes() == cast<CallInst>(I2)->getAttributes();
329 if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1))
330 return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() &&
331 CI->getAttributes() == cast<InvokeInst>(I2)->getAttributes();
332 if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1))
333 return IVI->getIndices() == cast<InsertValueInst>(I2)->getIndices();
334 if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1))
335 return EVI->getIndices() == cast<ExtractValueInst>(I2)->getIndices();
336 if (const FenceInst *FI = dyn_cast<FenceInst>(I1))
337 return FI->getOrdering() == cast<FenceInst>(I2)->getOrdering() &&
338 FI->getSynchScope() == cast<FenceInst>(I2)->getSynchScope();
339 if (const AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(I1))
340 return CXI->isVolatile() == cast<AtomicCmpXchgInst>(I2)->isVolatile() &&
341 CXI->getOrdering() == cast<AtomicCmpXchgInst>(I2)->getOrdering() &&
342 CXI->getSynchScope() == cast<AtomicCmpXchgInst>(I2)->getSynchScope();
343 if (const AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(I1))
344 return RMWI->getOperation() == cast<AtomicRMWInst>(I2)->getOperation() &&
345 RMWI->isVolatile() == cast<AtomicRMWInst>(I2)->isVolatile() &&
346 RMWI->getOrdering() == cast<AtomicRMWInst>(I2)->getOrdering() &&
347 RMWI->getSynchScope() == cast<AtomicRMWInst>(I2)->getSynchScope();
352 // Determine whether two GEP operations perform the same underlying arithmetic.
353 bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1,
354 const GEPOperator *GEP2) {
355 // When we have target data, we can reduce the GEP down to the value in bytes
356 // added to the address.
357 unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 1;
358 APInt Offset1(BitWidth, 0), Offset2(BitWidth, 0);
360 GEP1->accumulateConstantOffset(*TD, Offset1) &&
361 GEP2->accumulateConstantOffset(*TD, Offset2)) {
362 return Offset1 == Offset2;
365 if (GEP1->getPointerOperand()->getType() !=
366 GEP2->getPointerOperand()->getType())
369 if (GEP1->getNumOperands() != GEP2->getNumOperands())
372 for (unsigned i = 0, e = GEP1->getNumOperands(); i != e; ++i) {
373 if (!enumerate(GEP1->getOperand(i), GEP2->getOperand(i)))
380 // Compare two values used by the two functions under pair-wise comparison. If
381 // this is the first time the values are seen, they're added to the mapping so
382 // that we will detect mismatches on next use.
383 bool FunctionComparator::enumerate(const Value *V1, const Value *V2) {
384 // Check for function @f1 referring to itself and function @f2 referring to
385 // itself, or referring to each other, or both referring to either of them.
386 // They're all equivalent if the two functions are otherwise equivalent.
387 if (V1 == F1 && V2 == F2)
389 if (V1 == F2 && V2 == F1)
392 if (const Constant *C1 = dyn_cast<Constant>(V1)) {
393 if (V1 == V2) return true;
394 const Constant *C2 = dyn_cast<Constant>(V2);
395 if (!C2) return false;
396 // TODO: constant expressions with GEP or references to F1 or F2.
397 if (C1->isNullValue() && C2->isNullValue() &&
398 isEquivalentType(C1->getType(), C2->getType()))
400 // Try bitcasting C2 to C1's type. If the bitcast is legal and returns C1
401 // then they must have equal bit patterns.
402 return C1->getType()->canLosslesslyBitCastTo(C2->getType()) &&
403 C1 == ConstantExpr::getBitCast(const_cast<Constant*>(C2), C1->getType());
406 if (isa<InlineAsm>(V1) || isa<InlineAsm>(V2))
409 // Check that V1 maps to V2. If we find a value that V1 maps to then we simply
410 // check whether it's equal to V2. When there is no mapping then we need to
411 // ensure that V2 isn't already equivalent to something else. For this
412 // purpose, we track the V2 values in a set.
414 const Value *&map_elem = id_map[V1];
416 return map_elem == V2;
417 if (!seen_values.insert(V2).second)
423 // Test whether two basic blocks have equivalent behaviour.
424 bool FunctionComparator::compare(const BasicBlock *BB1, const BasicBlock *BB2) {
425 BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end();
426 BasicBlock::const_iterator F2I = BB2->begin(), F2E = BB2->end();
429 if (!enumerate(F1I, F2I))
432 if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(F1I)) {
433 const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(F2I);
437 if (!enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand()))
440 if (!isEquivalentGEP(GEP1, GEP2))
443 if (!isEquivalentOperation(F1I, F2I))
446 assert(F1I->getNumOperands() == F2I->getNumOperands());
447 for (unsigned i = 0, e = F1I->getNumOperands(); i != e; ++i) {
448 Value *OpF1 = F1I->getOperand(i);
449 Value *OpF2 = F2I->getOperand(i);
451 if (!enumerate(OpF1, OpF2))
454 if (OpF1->getValueID() != OpF2->getValueID() ||
455 !isEquivalentType(OpF1->getType(), OpF2->getType()))
461 } while (F1I != F1E && F2I != F2E);
463 return F1I == F1E && F2I == F2E;
466 // Test whether the two functions have equivalent behaviour.
467 bool FunctionComparator::compare() {
468 // We need to recheck everything, but check the things that weren't included
469 // in the hash first.
471 if (F1->getAttributes() != F2->getAttributes())
474 if (F1->hasGC() != F2->hasGC())
477 if (F1->hasGC() && F1->getGC() != F2->getGC())
480 if (F1->hasSection() != F2->hasSection())
483 if (F1->hasSection() && F1->getSection() != F2->getSection())
486 if (F1->isVarArg() != F2->isVarArg())
489 // TODO: if it's internal and only used in direct calls, we could handle this
491 if (F1->getCallingConv() != F2->getCallingConv())
494 if (!isEquivalentType(F1->getFunctionType(), F2->getFunctionType()))
497 assert(F1->arg_size() == F2->arg_size() &&
498 "Identically typed functions have different numbers of args!");
500 // Visit the arguments so that they get enumerated in the order they're
502 for (Function::const_arg_iterator f1i = F1->arg_begin(),
503 f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) {
504 if (!enumerate(f1i, f2i))
505 llvm_unreachable("Arguments repeat!");
508 // We do a CFG-ordered walk since the actual ordering of the blocks in the
509 // linked list is immaterial. Our walk starts at the entry block for both
510 // functions, then takes each block from each terminator in order. As an
511 // artifact, this also means that unreachable blocks are ignored.
512 SmallVector<const BasicBlock *, 8> F1BBs, F2BBs;
513 SmallSet<const BasicBlock *, 128> VisitedBBs; // in terms of F1.
515 F1BBs.push_back(&F1->getEntryBlock());
516 F2BBs.push_back(&F2->getEntryBlock());
518 VisitedBBs.insert(F1BBs[0]);
519 while (!F1BBs.empty()) {
520 const BasicBlock *F1BB = F1BBs.pop_back_val();
521 const BasicBlock *F2BB = F2BBs.pop_back_val();
523 if (!enumerate(F1BB, F2BB) || !compare(F1BB, F2BB))
526 const TerminatorInst *F1TI = F1BB->getTerminator();
527 const TerminatorInst *F2TI = F2BB->getTerminator();
529 assert(F1TI->getNumSuccessors() == F2TI->getNumSuccessors());
530 for (unsigned i = 0, e = F1TI->getNumSuccessors(); i != e; ++i) {
531 if (!VisitedBBs.insert(F1TI->getSuccessor(i)))
534 F1BBs.push_back(F1TI->getSuccessor(i));
535 F2BBs.push_back(F2TI->getSuccessor(i));
543 /// MergeFunctions finds functions which will generate identical machine code,
544 /// by considering all pointer types to be equivalent. Once identified,
545 /// MergeFunctions will fold them by replacing a call to one to a call to a
546 /// bitcast of the other.
548 class MergeFunctions : public ModulePass {
552 : ModulePass(ID), HasGlobalAliases(false) {
553 initializeMergeFunctionsPass(*PassRegistry::getPassRegistry());
556 bool runOnModule(Module &M);
559 typedef DenseSet<ComparableFunction> FnSetType;
561 /// A work queue of functions that may have been modified and should be
563 std::vector<WeakVH> Deferred;
565 /// Insert a ComparableFunction into the FnSet, or merge it away if it's
566 /// equal to one that's already present.
567 bool insert(ComparableFunction &NewF);
569 /// Remove a Function from the FnSet and queue it up for a second sweep of
571 void remove(Function *F);
573 /// Find the functions that use this Value and remove them from FnSet and
574 /// queue the functions.
575 void removeUsers(Value *V);
577 /// Replace all direct calls of Old with calls of New. Will bitcast New if
578 /// necessary to make types match.
579 void replaceDirectCallers(Function *Old, Function *New);
581 /// Merge two equivalent functions. Upon completion, G may be deleted, or may
582 /// be converted into a thunk. In either case, it should never be visited
584 void mergeTwoFunctions(Function *F, Function *G);
586 /// Replace G with a thunk or an alias to F. Deletes G.
587 void writeThunkOrAlias(Function *F, Function *G);
589 /// Replace G with a simple tail call to bitcast(F). Also replace direct uses
590 /// of G with bitcast(F). Deletes G.
591 void writeThunk(Function *F, Function *G);
593 /// Replace G with an alias to F. Deletes G.
594 void writeAlias(Function *F, Function *G);
596 /// The set of all distinct functions. Use the insert() and remove() methods
600 /// DataLayout for more accurate GEP comparisons. May be NULL.
603 /// Whether or not the target supports global aliases.
604 bool HasGlobalAliases;
607 } // end anonymous namespace
609 char MergeFunctions::ID = 0;
610 INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false)
612 ModulePass *llvm::createMergeFunctionsPass() {
613 return new MergeFunctions();
616 bool MergeFunctions::runOnModule(Module &M) {
617 bool Changed = false;
618 TD = getAnalysisIfAvailable<DataLayout>();
620 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
621 if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage())
622 Deferred.push_back(WeakVH(I));
624 FnSet.resize(Deferred.size());
627 std::vector<WeakVH> Worklist;
628 Deferred.swap(Worklist);
630 DEBUG(dbgs() << "size of module: " << M.size() << '\n');
631 DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n');
633 // Insert only strong functions and merge them. Strong function merging
634 // always deletes one of them.
635 for (std::vector<WeakVH>::iterator I = Worklist.begin(),
636 E = Worklist.end(); I != E; ++I) {
638 Function *F = cast<Function>(*I);
639 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
640 !F->mayBeOverridden()) {
641 ComparableFunction CF = ComparableFunction(F, TD);
642 Changed |= insert(CF);
646 // Insert only weak functions and merge them. By doing these second we
647 // create thunks to the strong function when possible. When two weak
648 // functions are identical, we create a new strong function with two weak
649 // weak thunks to it which are identical but not mergable.
650 for (std::vector<WeakVH>::iterator I = Worklist.begin(),
651 E = Worklist.end(); I != E; ++I) {
653 Function *F = cast<Function>(*I);
654 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
655 F->mayBeOverridden()) {
656 ComparableFunction CF = ComparableFunction(F, TD);
657 Changed |= insert(CF);
660 DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n');
661 } while (!Deferred.empty());
668 bool DenseMapInfo<ComparableFunction>::isEqual(const ComparableFunction &LHS,
669 const ComparableFunction &RHS) {
670 if (LHS.getFunc() == RHS.getFunc() &&
671 LHS.getHash() == RHS.getHash())
673 if (!LHS.getFunc() || !RHS.getFunc())
676 // One of these is a special "underlying pointer comparison only" object.
677 if (LHS.getTD() == ComparableFunction::LookupOnly ||
678 RHS.getTD() == ComparableFunction::LookupOnly)
681 assert(LHS.getTD() == RHS.getTD() &&
682 "Comparing functions for different targets");
684 return FunctionComparator(LHS.getTD(), LHS.getFunc(),
685 RHS.getFunc()).compare();
688 // Replace direct callers of Old with New.
689 void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) {
690 Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType());
691 for (Value::use_iterator UI = Old->use_begin(), UE = Old->use_end();
693 Value::use_iterator TheIter = UI;
695 CallSite CS(*TheIter);
696 if (CS && CS.isCallee(TheIter)) {
697 remove(CS.getInstruction()->getParent()->getParent());
698 TheIter.getUse().set(BitcastNew);
703 // Replace G with an alias to F if possible, or else a thunk to F. Deletes G.
704 void MergeFunctions::writeThunkOrAlias(Function *F, Function *G) {
705 if (HasGlobalAliases && G->hasUnnamedAddr()) {
706 if (G->hasExternalLinkage() || G->hasLocalLinkage() ||
707 G->hasWeakLinkage()) {
716 // Replace G with a simple tail call to bitcast(F). Also replace direct uses
717 // of G with bitcast(F). Deletes G.
718 void MergeFunctions::writeThunk(Function *F, Function *G) {
719 if (!G->mayBeOverridden()) {
720 // Redirect direct callers of G to F.
721 replaceDirectCallers(G, F);
724 // If G was internal then we may have replaced all uses of G with F. If so,
725 // stop here and delete G. There's no need for a thunk.
726 if (G->hasLocalLinkage() && G->use_empty()) {
727 G->eraseFromParent();
731 Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
733 BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG);
734 IRBuilder<false> Builder(BB);
736 SmallVector<Value *, 16> Args;
738 FunctionType *FFTy = F->getFunctionType();
739 for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end();
741 Args.push_back(Builder.CreateBitCast(AI, FFTy->getParamType(i)));
745 CallInst *CI = Builder.CreateCall(F, Args);
747 CI->setCallingConv(F->getCallingConv());
748 if (NewG->getReturnType()->isVoidTy()) {
749 Builder.CreateRetVoid();
751 Type *RetTy = NewG->getReturnType();
752 if (CI->getType()->isIntegerTy() && RetTy->isPointerTy())
753 Builder.CreateRet(Builder.CreateIntToPtr(CI, RetTy));
754 else if (CI->getType()->isPointerTy() && RetTy->isIntegerTy())
755 Builder.CreateRet(Builder.CreatePtrToInt(CI, RetTy));
757 Builder.CreateRet(Builder.CreateBitCast(CI, RetTy));
760 NewG->copyAttributesFrom(G);
763 G->replaceAllUsesWith(NewG);
764 G->eraseFromParent();
766 DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n');
770 // Replace G with an alias to F and delete G.
771 void MergeFunctions::writeAlias(Function *F, Function *G) {
772 Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
773 GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "",
774 BitcastF, G->getParent());
775 F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
777 GA->setVisibility(G->getVisibility());
779 G->replaceAllUsesWith(GA);
780 G->eraseFromParent();
782 DEBUG(dbgs() << "writeAlias: " << GA->getName() << '\n');
786 // Merge two equivalent functions. Upon completion, Function G is deleted.
787 void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
788 if (F->mayBeOverridden()) {
789 assert(G->mayBeOverridden());
791 if (HasGlobalAliases) {
792 // Make them both thunks to the same internal function.
793 Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
795 H->copyAttributesFrom(F);
798 F->replaceAllUsesWith(H);
800 unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
805 F->setAlignment(MaxAlignment);
806 F->setLinkage(GlobalValue::PrivateLinkage);
808 // We can't merge them. Instead, pick one and update all direct callers
809 // to call it and hope that we improve the instruction cache hit rate.
810 replaceDirectCallers(G, F);
815 writeThunkOrAlias(F, G);
818 ++NumFunctionsMerged;
821 // Insert a ComparableFunction into the FnSet, or merge it away if equal to one
822 // that was already inserted.
823 bool MergeFunctions::insert(ComparableFunction &NewF) {
824 std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF);
826 DEBUG(dbgs() << "Inserting as unique: " << NewF.getFunc()->getName() << '\n');
830 const ComparableFunction &OldF = *Result.first;
832 // Never thunk a strong function to a weak function.
833 assert(!OldF.getFunc()->mayBeOverridden() ||
834 NewF.getFunc()->mayBeOverridden());
836 DEBUG(dbgs() << " " << OldF.getFunc()->getName() << " == "
837 << NewF.getFunc()->getName() << '\n');
839 Function *DeleteF = NewF.getFunc();
841 mergeTwoFunctions(OldF.getFunc(), DeleteF);
845 // Remove a function from FnSet. If it was already in FnSet, add it to Deferred
846 // so that we'll look at it in the next round.
847 void MergeFunctions::remove(Function *F) {
848 // We need to make sure we remove F, not a function "equal" to F per the
849 // function equality comparator.
851 // The special "lookup only" ComparableFunction bypasses the expensive
852 // function comparison in favour of a pointer comparison on the underlying
854 ComparableFunction CF = ComparableFunction(F, ComparableFunction::LookupOnly);
855 if (FnSet.erase(CF)) {
856 DEBUG(dbgs() << "Removed " << F->getName() << " from set and deferred it.\n");
857 Deferred.push_back(F);
861 // For each instruction used by the value, remove() the function that contains
862 // the instruction. This should happen right before a call to RAUW.
863 void MergeFunctions::removeUsers(Value *V) {
864 std::vector<Value *> Worklist;
865 Worklist.push_back(V);
866 while (!Worklist.empty()) {
867 Value *V = Worklist.back();
870 for (Value::use_iterator UI = V->use_begin(), UE = V->use_end();
872 Use &U = UI.getUse();
873 if (Instruction *I = dyn_cast<Instruction>(U.getUser())) {
874 remove(I->getParent()->getParent());
875 } else if (isa<GlobalValue>(U.getUser())) {
877 } else if (Constant *C = dyn_cast<Constant>(U.getUser())) {
878 for (Value::use_iterator CUI = C->use_begin(), CUE = C->use_end();
880 Worklist.push_back(*CUI);