llvm-6502/lib/Transforms/IPO/MergeFunctions.cpp

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//===- MergeFunctions.cpp - Merge identical functions ---------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass looks for equivalent functions that are mergable and folds them.
//
// A hash is computed from the function, based on its type and number of
// basic blocks.
//
// Once all hashes are computed, we perform an expensive equality comparison
// on each function pair. This takes n^2/2 comparisons per bucket, so it's
// important that the hash function be high quality. The equality comparison
// iterates through each instruction in each basic block.
//
// When a match is found, the functions are folded. We can only fold two
// functions when we know that the definition of one of them is not
// overridable.
//
//===----------------------------------------------------------------------===//
//
// Future work:
//
// * fold vector<T*>::push_back and vector<S*>::push_back.
//
// These two functions have different types, but in a way that doesn't matter
// to us. As long as we never see an S or T itself, using S* and S** is the
// same as using a T* and T**.
//
// * virtual functions.
//
// Many functions have their address taken by the virtual function table for
// the object they belong to. However, as long as it's only used for a lookup
// and call, this is irrelevant, and we'd like to fold such implementations.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "mergefunc"
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Constants.h"
#include "llvm/InlineAsm.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include <map>
#include <vector>
using namespace llvm;
STATISTIC(NumFunctionsMerged, "Number of functions merged");
namespace {
struct VISIBILITY_HIDDEN MergeFunctions : public ModulePass {
static char ID; // Pass identification, replacement for typeid
MergeFunctions() : ModulePass((intptr_t)&ID) {}
bool runOnModule(Module &M);
};
}
char MergeFunctions::ID = 0;
static RegisterPass<MergeFunctions>
X("mergefunc", "Merge Functions");
ModulePass *llvm::createMergeFunctionsPass() {
return new MergeFunctions();
}
// ===----------------------------------------------------------------------===
// Comparison of functions
// ===----------------------------------------------------------------------===
static unsigned long hash(const Function *F) {
const FunctionType *FTy = F->getFunctionType();
FoldingSetNodeID ID;
ID.AddInteger(F->size());
ID.AddInteger(F->getCallingConv());
ID.AddBoolean(F->hasGC());
ID.AddBoolean(FTy->isVarArg());
ID.AddInteger(FTy->getReturnType()->getTypeID());
for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
ID.AddInteger(FTy->getParamType(i)->getTypeID());
return ID.ComputeHash();
}
/// IgnoreBitcasts - given a bitcast, returns the first non-bitcast found by
/// walking the chain of cast operands. Otherwise, returns the argument.
static Value* IgnoreBitcasts(Value *V) {
while (BitCastInst *BC = dyn_cast<BitCastInst>(V))
V = BC->getOperand(0);
return V;
}
/// isEquivalentType - any two pointers are equivalent. Otherwise, standard
/// type equivalence rules apply.
static bool isEquivalentType(const Type *Ty1, const Type *Ty2) {
if (Ty1 == Ty2)
return true;
if (Ty1->getTypeID() != Ty2->getTypeID())
return false;
switch(Ty1->getTypeID()) {
case Type::VoidTyID:
case Type::FloatTyID:
case Type::DoubleTyID:
case Type::X86_FP80TyID:
case Type::FP128TyID:
case Type::PPC_FP128TyID:
case Type::LabelTyID:
case Type::MetadataTyID:
return true;
case Type::IntegerTyID:
case Type::OpaqueTyID:
// Ty1 == Ty2 would have returned true earlier.
return false;
default:
assert(0 && "Unknown type!");
return false;
case Type::PointerTyID: {
const PointerType *PTy1 = cast<PointerType>(Ty1);
const PointerType *PTy2 = cast<PointerType>(Ty2);
return PTy1->getAddressSpace() == PTy2->getAddressSpace();
}
case Type::StructTyID: {
const StructType *STy1 = cast<StructType>(Ty1);
const StructType *STy2 = cast<StructType>(Ty2);
if (STy1->getNumElements() != STy2->getNumElements())
return false;
if (STy1->isPacked() != STy2->isPacked())
return false;
for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) {
if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i)))
return false;
}
return true;
}
case Type::FunctionTyID: {
const FunctionType *FTy1 = cast<FunctionType>(Ty1);
const FunctionType *FTy2 = cast<FunctionType>(Ty2);
if (FTy1->getNumParams() != FTy2->getNumParams() ||
FTy1->isVarArg() != FTy2->isVarArg())
return false;
if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType()))
return false;
for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) {
if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i)))
return false;
}
return true;
}
case Type::ArrayTyID:
case Type::VectorTyID: {
const SequentialType *STy1 = cast<SequentialType>(Ty1);
const SequentialType *STy2 = cast<SequentialType>(Ty2);
return isEquivalentType(STy1->getElementType(), STy2->getElementType());
}
}
}
/// isEquivalentOperation - determine whether the two operations are the same
/// except that pointer-to-A and pointer-to-B are equivalent. This should be
/// kept in sync with Instruction::isSameOperationAs.
static bool
isEquivalentOperation(const Instruction *I1, const Instruction *I2) {
if (I1->getOpcode() != I2->getOpcode() ||
I1->getNumOperands() != I2->getNumOperands() ||
!isEquivalentType(I1->getType(), I2->getType()))
return false;
// We have two instructions of identical opcode and #operands. Check to see
// if all operands are the same type
for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i)
if (!isEquivalentType(I1->getOperand(i)->getType(),
I2->getOperand(i)->getType()))
return false;
// Check special state that is a part of some instructions.
if (const LoadInst *LI = dyn_cast<LoadInst>(I1))
return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() &&
LI->getAlignment() == cast<LoadInst>(I2)->getAlignment();
if (const StoreInst *SI = dyn_cast<StoreInst>(I1))
return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() &&
SI->getAlignment() == cast<StoreInst>(I2)->getAlignment();
if (const CmpInst *CI = dyn_cast<CmpInst>(I1))
return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate();
if (const CallInst *CI = dyn_cast<CallInst>(I1))
return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() &&
CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() &&
CI->getAttributes().getRawPointer() ==
cast<CallInst>(I2)->getAttributes().getRawPointer();
if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1))
return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() &&
CI->getAttributes().getRawPointer() ==
cast<InvokeInst>(I2)->getAttributes().getRawPointer();
if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) {
if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices())
return false;
for (unsigned i = 0, e = IVI->getNumIndices(); i != e; ++i)
if (IVI->idx_begin()[i] != cast<InsertValueInst>(I2)->idx_begin()[i])
return false;
return true;
}
if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) {
if (EVI->getNumIndices() != cast<ExtractValueInst>(I2)->getNumIndices())
return false;
for (unsigned i = 0, e = EVI->getNumIndices(); i != e; ++i)
if (EVI->idx_begin()[i] != cast<ExtractValueInst>(I2)->idx_begin()[i])
return false;
return true;
}
return true;
}
static bool compare(const Value *V, const Value *U) {
assert(!isa<BasicBlock>(V) && !isa<BasicBlock>(U) &&
"Must not compare basic blocks.");
assert(isEquivalentType(V->getType(), U->getType()) &&
"Two of the same operation have operands of different type.");
// TODO: If the constant is an expression of F, we should accept that it's
// equal to the same expression in terms of G.
if (isa<Constant>(V))
return V == U;
// The caller has ensured that ValueMap[V] != U. Since Arguments are
// pre-loaded into the ValueMap, and Instructions are added as we go, we know
// that this can only be a mis-match.
if (isa<Instruction>(V) || isa<Argument>(V))
return false;
if (isa<InlineAsm>(V) && isa<InlineAsm>(U)) {
const InlineAsm *IAF = cast<InlineAsm>(V);
const InlineAsm *IAG = cast<InlineAsm>(U);
return IAF->getAsmString() == IAG->getAsmString() &&
IAF->getConstraintString() == IAG->getConstraintString();
}
return false;
}
static bool equals(const BasicBlock *BB1, const BasicBlock *BB2,
DenseMap<const Value *, const Value *> &ValueMap,
DenseMap<const Value *, const Value *> &SpeculationMap) {
// Speculatively add it anyways. If it's false, we'll notice a difference
// later, and this won't matter.
ValueMap[BB1] = BB2;
BasicBlock::const_iterator FI = BB1->begin(), FE = BB1->end();
BasicBlock::const_iterator GI = BB2->begin(), GE = BB2->end();
do {
if (isa<BitCastInst>(FI)) {
++FI;
continue;
}
if (isa<BitCastInst>(GI)) {
++GI;
continue;
}
if (!isEquivalentOperation(FI, GI))
return false;
if (isa<GetElementPtrInst>(FI)) {
const GetElementPtrInst *GEPF = cast<GetElementPtrInst>(FI);
const GetElementPtrInst *GEPG = cast<GetElementPtrInst>(GI);
if (GEPF->hasAllZeroIndices() && GEPG->hasAllZeroIndices()) {
// It's effectively a bitcast.
++FI, ++GI;
continue;
}
// TODO: we only really care about the elements before the index
if (FI->getOperand(0)->getType() != GI->getOperand(0)->getType())
return false;
}
if (ValueMap[FI] == GI) {
++FI, ++GI;
continue;
}
if (ValueMap[FI] != NULL)
return false;
for (unsigned i = 0, e = FI->getNumOperands(); i != e; ++i) {
Value *OpF = IgnoreBitcasts(FI->getOperand(i));
Value *OpG = IgnoreBitcasts(GI->getOperand(i));
if (ValueMap[OpF] == OpG)
continue;
if (ValueMap[OpF] != NULL)
return false;
if (OpF->getValueID() != OpG->getValueID() ||
!isEquivalentType(OpF->getType(), OpG->getType()))
return false;
if (isa<PHINode>(FI)) {
if (SpeculationMap[OpF] == NULL)
SpeculationMap[OpF] = OpG;
else if (SpeculationMap[OpF] != OpG)
return false;
continue;
} else if (isa<BasicBlock>(OpF)) {
assert(isa<TerminatorInst>(FI) &&
"BasicBlock referenced by non-Terminator non-PHI");
// This call changes the ValueMap, hence we can't use
// Value *& = ValueMap[...]
if (!equals(cast<BasicBlock>(OpF), cast<BasicBlock>(OpG), ValueMap,
SpeculationMap))
return false;
} else {
if (!compare(OpF, OpG))
return false;
}
ValueMap[OpF] = OpG;
}
ValueMap[FI] = GI;
++FI, ++GI;
} while (FI != FE && GI != GE);
return FI == FE && GI == GE;
}
static bool equals(const Function *F, const Function *G) {
// We need to recheck everything, but check the things that weren't included
// in the hash first.
if (F->getAttributes() != G->getAttributes())
return false;
if (F->hasGC() != G->hasGC())
return false;
if (F->hasGC() && F->getGC() != G->getGC())
return false;
if (F->hasSection() != G->hasSection())
return false;
if (F->hasSection() && F->getSection() != G->getSection())
return false;
if (F->isVarArg() != G->isVarArg())
return false;
// TODO: if it's internal and only used in direct calls, we could handle this
// case too.
if (F->getCallingConv() != G->getCallingConv())
return false;
if (!isEquivalentType(F->getFunctionType(), G->getFunctionType()))
return false;
DenseMap<const Value *, const Value *> ValueMap;
DenseMap<const Value *, const Value *> SpeculationMap;
ValueMap[F] = G;
assert(F->arg_size() == G->arg_size() &&
"Identical functions have a different number of args.");
for (Function::const_arg_iterator fi = F->arg_begin(), gi = G->arg_begin(),
fe = F->arg_end(); fi != fe; ++fi, ++gi)
ValueMap[fi] = gi;
if (!equals(&F->getEntryBlock(), &G->getEntryBlock(), ValueMap,
SpeculationMap))
return false;
for (DenseMap<const Value *, const Value *>::iterator
I = SpeculationMap.begin(), E = SpeculationMap.end(); I != E; ++I) {
if (ValueMap[I->first] != I->second)
return false;
}
return true;
}
// ===----------------------------------------------------------------------===
// Folding of functions
// ===----------------------------------------------------------------------===
// Cases:
// * F is external strong, G is external strong:
// turn G into a thunk to F (1)
// * F is external strong, G is external weak:
// turn G into a thunk to F (1)
// * F is external weak, G is external weak:
// unfoldable
// * F is external strong, G is internal:
// address of G taken:
// turn G into a thunk to F (1)
// address of G not taken:
// make G an alias to F (2)
// * F is internal, G is external weak
// address of F is taken:
// turn G into a thunk to F (1)
// address of F is not taken:
// make G an alias of F (2)
// * F is internal, G is internal:
// address of F and G are taken:
// turn G into a thunk to F (1)
// address of G is not taken:
// make G an alias to F (2)
//
// alias requires linkage == (external,local,weak) fallback to creating a thunk
// external means 'externally visible' linkage != (internal,private)
// internal means linkage == (internal,private)
// weak means linkage mayBeOverridable
// being external implies that the address is taken
//
// 1. turn G into a thunk to F
// 2. make G an alias to F
enum LinkageCategory {
ExternalStrong,
ExternalWeak,
Internal
};
static LinkageCategory categorize(const Function *F) {
switch (F->getLinkage()) {
case GlobalValue::InternalLinkage:
case GlobalValue::PrivateLinkage:
return Internal;
case GlobalValue::WeakAnyLinkage:
case GlobalValue::WeakODRLinkage:
case GlobalValue::ExternalWeakLinkage:
return ExternalWeak;
case GlobalValue::ExternalLinkage:
case GlobalValue::AvailableExternallyLinkage:
case GlobalValue::LinkOnceAnyLinkage:
case GlobalValue::LinkOnceODRLinkage:
case GlobalValue::AppendingLinkage:
case GlobalValue::DLLImportLinkage:
case GlobalValue::DLLExportLinkage:
case GlobalValue::GhostLinkage:
case GlobalValue::CommonLinkage:
return ExternalStrong;
}
assert(0 && "Unknown LinkageType.");
return ExternalWeak;
}
static void ThunkGToF(Function *F, Function *G) {
Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
G->getParent());
BasicBlock *BB = BasicBlock::Create("", NewG);
std::vector<Value *> Args;
unsigned i = 0;
const FunctionType *FFTy = F->getFunctionType();
for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end();
AI != AE; ++AI) {
if (FFTy->getParamType(i) == AI->getType())
Args.push_back(AI);
else {
Value *BCI = new BitCastInst(AI, FFTy->getParamType(i), "", BB);
Args.push_back(BCI);
}
++i;
}
CallInst *CI = CallInst::Create(F, Args.begin(), Args.end(), "", BB);
CI->setTailCall();
CI->setCallingConv(F->getCallingConv());
if (NewG->getReturnType() == Type::VoidTy) {
ReturnInst::Create(BB);
} else if (CI->getType() != NewG->getReturnType()) {
Value *BCI = new BitCastInst(CI, NewG->getReturnType(), "", BB);
ReturnInst::Create(BCI, BB);
} else {
ReturnInst::Create(CI, BB);
}
NewG->copyAttributesFrom(G);
NewG->takeName(G);
G->replaceAllUsesWith(NewG);
G->eraseFromParent();
// TODO: look at direct callers to G and make them all direct callers to F.
}
static void AliasGToF(Function *F, Function *G) {
if (!G->hasExternalLinkage() && !G->hasLocalLinkage() && !G->hasWeakLinkage())
return ThunkGToF(F, G);
GlobalAlias *GA = new GlobalAlias(
G->getType(), G->getLinkage(), "",
ConstantExpr::getBitCast(F, G->getType()), G->getParent());
F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
GA->takeName(G);
GA->setVisibility(G->getVisibility());
G->replaceAllUsesWith(GA);
G->eraseFromParent();
}
static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
Function *F = FnVec[i];
Function *G = FnVec[j];
LinkageCategory catF = categorize(F);
LinkageCategory catG = categorize(G);
if (catF == ExternalWeak || (catF == Internal && catG == ExternalStrong)) {
std::swap(FnVec[i], FnVec[j]);
std::swap(F, G);
std::swap(catF, catG);
}
switch (catF) {
case ExternalStrong:
switch (catG) {
case ExternalStrong:
case ExternalWeak:
ThunkGToF(F, G);
break;
case Internal:
if (G->hasAddressTaken())
ThunkGToF(F, G);
else
AliasGToF(F, G);
break;
}
break;
case ExternalWeak: {
assert(catG == ExternalWeak);
// Make them both thunks to the same internal function.
F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
F->getParent());
H->copyAttributesFrom(F);
H->takeName(F);
F->replaceAllUsesWith(H);
ThunkGToF(F, G);
ThunkGToF(F, H);
F->setLinkage(GlobalValue::InternalLinkage);
} break;
case Internal:
switch (catG) {
case ExternalStrong:
assert(0);
// fall-through
case ExternalWeak:
if (F->hasAddressTaken())
ThunkGToF(F, G);
else
AliasGToF(F, G);
break;
case Internal: {
bool addrTakenF = F->hasAddressTaken();
bool addrTakenG = G->hasAddressTaken();
if (!addrTakenF && addrTakenG) {
std::swap(FnVec[i], FnVec[j]);
std::swap(F, G);
std::swap(addrTakenF, addrTakenG);
}
if (addrTakenF && addrTakenG) {
ThunkGToF(F, G);
} else {
assert(!addrTakenG);
AliasGToF(F, G);
}
} break;
}
break;
}
++NumFunctionsMerged;
return true;
}
// ===----------------------------------------------------------------------===
// Pass definition
// ===----------------------------------------------------------------------===
bool MergeFunctions::runOnModule(Module &M) {
bool Changed = false;
std::map<unsigned long, std::vector<Function *> > FnMap;
for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
if (F->isDeclaration() || F->isIntrinsic())
continue;
FnMap[hash(F)].push_back(F);
}
// TODO: instead of running in a loop, we could also fold functions in
// callgraph order. Constructing the CFG probably isn't cheaper than just
// running in a loop, unless it happened to already be available.
bool LocalChanged;
do {
LocalChanged = false;
DOUT << "size: " << FnMap.size() << "\n";
for (std::map<unsigned long, std::vector<Function *> >::iterator
I = FnMap.begin(), E = FnMap.end(); I != E; ++I) {
std::vector<Function *> &FnVec = I->second;
DOUT << "hash (" << I->first << "): " << FnVec.size() << "\n";
for (int i = 0, e = FnVec.size(); i != e; ++i) {
for (int j = i + 1; j != e; ++j) {
bool isEqual = equals(FnVec[i], FnVec[j]);
DOUT << " " << FnVec[i]->getName()
<< (isEqual ? " == " : " != ")
<< FnVec[j]->getName() << "\n";
if (isEqual) {
if (fold(FnVec, i, j)) {
LocalChanged = true;
FnVec.erase(FnVec.begin() + j);
--j, --e;
}
}
}
}
}
Changed |= LocalChanged;
} while (LocalChanged);
return Changed;
}