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Do more to modernize MergeFunctions. Refactor in response to Chris' code review.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110538 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2010-08-08 05:04:23 +00:00
parent 652eb506a7
commit be04fdeb6c
1 changed files with 81 additions and 91 deletions
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172
lib/Transforms/IPO/MergeFunctions.cpp
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@ -29,18 +29,17 @@
//
// 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.
// and call, this is irrelevant, and we'd like to fold such functions.
//
// * switch from n^2 pair-wise comparisons to an n-way comparison for each
// bucket.
//
// * be smarter about bitcast.
// * be smarter about bitcasts.
//
// In order to fold functions, we will sometimes add either bitcast instructions
// or bitcast constant expressions. Unfortunately, this can confound further
// analysis since the two functions differ where one has a bitcast and the
// other doesn't. We should learn to peer through bitcasts without imposing bad
// performance properties.
// other doesn't. We should learn to look through bitcasts.
//
//===----------------------------------------------------------------------===//
@ -59,6 +58,7 @@
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetData.h"
#include <map>
@ -73,11 +73,28 @@ namespace {
/// MergeFunctions will fold them by replacing a call to one to a call to a
/// bitcast of the other.
///
struct MergeFunctions : public ModulePass {
static char ID; // Pass identification, replacement for typeid
class MergeFunctions : public ModulePass {
public:
static char ID;
MergeFunctions() : ModulePass(ID) {}
bool runOnModule(Module &M);
private:
/// PairwiseCompareAndMerge - Given a list of functions, compare each pair
/// and merge the pairs of equivalent functions.
bool PairwiseCompareAndMerge(std::vector<Function *> &FnVec);
/// MergeTwoFunctions - Merge two equivalent functions. Upon completion,
/// FnVec[j] should never be visited again.
void MergeTwoFunctions(std::vector<Function *> &FnVec,
unsigned i, unsigned j) const;
/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also
/// replace direct uses of G with bitcast(F).
void WriteThunk(Function *F, Function *G) const;
TargetData *TD;
};
}
@ -88,42 +105,42 @@ ModulePass *llvm::createMergeFunctionsPass() {
return new MergeFunctions();
}
// ===----------------------------------------------------------------------===
// Comparison of functions
// ===----------------------------------------------------------------------===
namespace {
/// FunctionComparator - Compares two functions to determine whether or not
/// they will generate machine code with the same behaviour. TargetData is
/// used if available. The comparator always fails conservatively (erring on the
/// side of claiming that two functions are different).
class FunctionComparator {
public:
FunctionComparator(TargetData *TD, Function *F1, Function *F2)
: F1(F1), F2(F2), TD(TD), IDMap1Count(0), IDMap2Count(0) {}
// Compare - test whether the two functions have equivalent behaviour.
/// Compare - test whether the two functions have equivalent behaviour.
bool Compare();
private:
// Compare - test whether two basic blocks have equivalent behaviour.
/// Compare - test whether two basic blocks have equivalent behaviour.
bool Compare(const BasicBlock *BB1, const BasicBlock *BB2);
// Enumerate - Assign or look up previously assigned numbers for the two
// values, and return whether the numbers are equal. Numbers are assigned in
// the order visited.
/// Enumerate - Assign or look up previously assigned numbers for the two
/// values, and return whether the numbers are equal. Numbers are assigned in
/// the order visited.
bool Enumerate(const Value *V1, const Value *V2);
// isEquivalentOperation - Compare two Instructions for equivalence, similar
// to Instruction::isSameOperationAs but with modifications to the type
// comparison.
/// isEquivalentOperation - Compare two Instructions for equivalence, similar
/// to Instruction::isSameOperationAs but with modifications to the type
/// comparison.
bool isEquivalentOperation(const Instruction *I1,
const Instruction *I2) const;
// isEquivalentGEP - Compare two GEPs for equivalent pointer arithmetic.
/// isEquivalentGEP - Compare two GEPs for equivalent pointer arithmetic.
bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2);
bool isEquivalentGEP(const GetElementPtrInst *GEP1,
const GetElementPtrInst *GEP2) {
const GetElementPtrInst *GEP2) {
return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2));
}
// isEquivalentType - Compare two Types, treating all pointer types as equal.
/// isEquivalentType - Compare two Types, treating all pointer types as equal.
bool isEquivalentType(const Type *Ty1, const Type *Ty2) const;
// The two functions undergoing comparison.
@ -137,9 +154,8 @@ private:
};
}
/// Compute a number which is guaranteed to be equal for two equivalent
/// functions, but is very likely to be different for different functions. This
/// needs to be computed as efficiently as possible.
/// Compute a hash guaranteed to be equal for two equivalent functions, but
/// very likely to be different for different functions.
static unsigned long ProfileFunction(const Function *F) {
const FunctionType *FTy = F->getFunctionType();
@ -208,7 +224,6 @@ bool FunctionComparator::isEquivalentType(const Type *Ty1,
const UnionType *UTy1 = cast<UnionType>(Ty1);
const UnionType *UTy2 = cast<UnionType>(Ty2);
// TODO: we could be fancy with union(A, union(A, B)) === union(A, B), etc.
if (UTy1->getNumElements() != UTy2->getNumElements())
return false;
@ -373,7 +388,7 @@ bool FunctionComparator::Enumerate(const Value *V1, const Value *V2) {
return ID1 == ID2;
}
// Compare - test whether two basic blocks have equivalent behaviour.
/// Compare - test whether two basic blocks have equivalent behaviour.
bool FunctionComparator::Compare(const BasicBlock *BB1, const BasicBlock *BB2) {
BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end();
BasicBlock::const_iterator F2I = BB2->begin(), F2E = BB2->end();
@ -416,6 +431,7 @@ bool FunctionComparator::Compare(const BasicBlock *BB1, const BasicBlock *BB2) {
return F1I == F1E && F2I == F2E;
}
/// Compare - test whether the two functions have equivalent behaviour.
bool FunctionComparator::Compare() {
// We need to recheck everything, but check the things that weren't included
// in the hash first.
@ -457,8 +473,8 @@ bool FunctionComparator::Compare() {
llvm_unreachable("Arguments repeat");
}
// We need to do an ordered walk since the actual ordering of the blocks in
// the linked list is immaterial. Our walk starts at the entry block for both
// We do a CFG-ordered walk since the actual ordering of the blocks in the
// linked list is immaterial. Our walk starts at the entry block for both
// functions, then takes each block from each terminator in order. As an
// artifact, this also means that unreachable blocks are ignored.
SmallVector<const BasicBlock *, 8> F1BBs, F2BBs;
@ -490,31 +506,9 @@ bool FunctionComparator::Compare() {
return true;
}
// ===----------------------------------------------------------------------===
// Folding of functions
// ===----------------------------------------------------------------------===
// Cases:
// * F is external strong, G is external strong:
// turn G into a thunk to F
// * F is external strong, G is external weak:
// turn G into a thunk to F
// * F is external weak, G is external weak:
// unfoldable
// * F is external strong, G is internal:
// turn G into a thunk to F
// * F is internal, G is external weak
// turn G into a thunk to F
// * F is internal, G is internal:
// turn G into a thunk to F
//
// external means 'externally visible' linkage != (internal,private)
// internal means linkage == (internal,private)
// weak means linkage mayBeOverridable
/// ThunkGToF - Replace G with a simple tail call to bitcast(F). Also replace
/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also replace
/// direct uses of G with bitcast(F).
static void ThunkGToF(Function *F, Function *G) {
void MergeFunctions::WriteThunk(Function *F, Function *G) const {
if (!G->mayBeOverridden()) {
// Redirect direct callers of G to F.
Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
@ -538,30 +532,24 @@ static void ThunkGToF(Function *F, Function *G) {
Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
G->getParent());
BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG);
IRBuilder<false> Builder(BB);
SmallVector<Value *, 16> 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 {
Args.push_back(new BitCastInst(AI, FFTy->getParamType(i), "", BB));
}
Args.push_back(Builder.CreateBitCast(AI, FFTy->getParamType(i)));
++i;
}
CallInst *CI = CallInst::Create(F, Args.begin(), Args.end(), "", BB);
CallInst *CI = Builder.CreateCall(F, Args.begin(), Args.end());
CI->setTailCall();
CI->setCallingConv(F->getCallingConv());
if (NewG->getReturnType()->isVoidTy()) {
ReturnInst::Create(F->getContext(), BB);
} else if (CI->getType() != NewG->getReturnType()) {
Value *BCI = new BitCastInst(CI, NewG->getReturnType(), "", BB);
ReturnInst::Create(F->getContext(), BCI, BB);
Builder.CreateRetVoid();
} else {
ReturnInst::Create(F->getContext(), CI, BB);
Builder.CreateRet(Builder.CreateBitCast(CI, NewG->getReturnType()));
}
NewG->copyAttributesFrom(G);
@ -570,7 +558,10 @@ static void ThunkGToF(Function *F, Function *G) {
G->eraseFromParent();
}
static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
/// MergeTwoFunctions - Merge two equivalent functions. Upon completion,
/// FnVec[j] should never be visited again.
void MergeFunctions::MergeTwoFunctions(std::vector<Function *> &FnVec,
unsigned i, unsigned j) const {
Function *F = FnVec[i];
Function *G = FnVec[j];
@ -589,22 +580,39 @@ static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
H->takeName(F);
F->replaceAllUsesWith(H);
ThunkGToF(F, G);
ThunkGToF(F, H);
WriteThunk(F, G);
WriteThunk(F, H);
F->setAlignment(std::max(G->getAlignment(), H->getAlignment()));
F->setLinkage(GlobalValue::InternalLinkage);
} else {
ThunkGToF(F, G);
WriteThunk(F, G);
}
++NumFunctionsMerged;
return true;
}
// ===----------------------------------------------------------------------===
// Pass definition
// ===----------------------------------------------------------------------===
/// PairwiseCompareAndMerge - Given a list of functions, compare each pair and
/// merge the pairs of equivalent functions.
bool MergeFunctions::PairwiseCompareAndMerge(std::vector<Function *> &FnVec) {
bool Changed = false;
for (int i = 0, e = FnVec.size(); i != e; ++i) {
for (int j = i + 1; j != e; ++j) {
bool isEqual = FunctionComparator(TD, FnVec[i], FnVec[j]).Compare();
DEBUG(dbgs() << " " << FnVec[i]->getName()
<< (isEqual ? " == " : " != ") << FnVec[j]->getName() << "\n");
if (isEqual) {
MergeTwoFunctions(FnVec, i, j);
Changed = true;
FnVec.erase(FnVec.begin() + j);
--j, --e;
}
}
}
return Changed;
}
bool MergeFunctions::runOnModule(Module &M) {
bool Changed = false;
@ -618,7 +626,7 @@ bool MergeFunctions::runOnModule(Module &M) {
FnMap[ProfileFunction(F)].push_back(F);
}
TargetData *TD = getAnalysisIfAvailable<TargetData>();
TD = getAnalysisIfAvailable<TargetData>();
bool LocalChanged;
do {
@ -628,25 +636,7 @@ bool MergeFunctions::runOnModule(Module &M) {
I = FnMap.begin(), E = FnMap.end(); I != E; ++I) {
std::vector<Function *> &FnVec = I->second;
DEBUG(dbgs() << "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 = FunctionComparator(TD, FnVec[i], FnVec[j]).Compare();
DEBUG(dbgs() << " " << FnVec[i]->getName()
<< (isEqual ? " == " : " != ")
<< FnVec[j]->getName() << "\n");
if (isEqual) {
if (fold(FnVec, i, j)) {
LocalChanged = true;
FnVec.erase(FnVec.begin() + j);
--j, --e;
}
}
}
}
LocalChanged |= PairwiseCompareAndMerge(FnVec);
}
Changed |= LocalChanged;
} while (LocalChanged);