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llvm/lib/Transforms/IPO/MergeFunctions.cpp
Stepan Dyatkovskiy ab35f3fd0c First patch of patch series that improves MergeFunctions performance time from O(N*N) to 
O(N*log(N)). The idea is to introduce total ordering among functions set.
That allows to build binary tree and perform function look-up procedure in O(log(N)) time. 

This patch description:
Introduced total ordering among Type instances. Actually it is improvement for existing
isEquivalentType.
0. Coerce pointer of 0 address space to integer.
1. If left and right types are equal (the same Type* value), return 0 (means equal).
2. If types are of different kind (different type IDs). Return result of type IDs
comparison, treating them as numbers.
3. If types are vectors or integers, return result of its
pointers comparison (casted to numbers).
4. Check whether type ID belongs to the next group: 
* Void 
* Float 
* Double 
* X86_FP80 
* FP128 
* PPC_FP128 
* Label 
* Metadata 
If so, return 0.
5. If left and right are pointers, return result of address space
comparison (numbers comparison).
6. If types are complex.
Then both LEFT and RIGHT will be expanded and their element types will be checked with
the same way. If we get Res != 0 on some stage, return it. Otherwise return 0.
7. For all other cases put llvm_unreachable.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203788 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-13 11:54:50 +00:00

967 lines
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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. If both functions are
// overridable, we move the functionality into a new internal function and
// leave two overridable thunks to it.
//
//===----------------------------------------------------------------------===//
//
// Future work:
//
// * 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 functions.
//
// * switch from n^2 pair-wise comparisons to an n-way comparison for each
// bucket.
//
// * 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 look through bitcasts.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "mergefunc"
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InlineAsm.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <vector>
using namespace llvm;
STATISTIC(NumFunctionsMerged, "Number of functions merged");
STATISTIC(NumThunksWritten, "Number of thunks generated");
STATISTIC(NumAliasesWritten, "Number of aliases generated");
STATISTIC(NumDoubleWeak, "Number of new functions created");
/// Returns the type id for a type to be hashed. We turn pointer types into
/// integers here because the actual compare logic below considers pointers and
/// integers of the same size as equal.
static Type::TypeID getTypeIDForHash(Type *Ty) {
if (Ty->isPointerTy())
return Type::IntegerTyID;
return Ty->getTypeID();
}
/// Creates a hash-code for the function which is the same for any two
/// functions that will compare equal, without looking at the instructions
/// inside the function.
static unsigned profileFunction(const Function *F) {
FunctionType *FTy = F->getFunctionType();
FoldingSetNodeID ID;
ID.AddInteger(F->size());
ID.AddInteger(F->getCallingConv());
ID.AddBoolean(F->hasGC());
ID.AddBoolean(FTy->isVarArg());
ID.AddInteger(getTypeIDForHash(FTy->getReturnType()));
for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
ID.AddInteger(getTypeIDForHash(FTy->getParamType(i)));
return ID.ComputeHash();
}
namespace {
/// ComparableFunction - A struct that pairs together functions with a
/// DataLayout so that we can keep them together as elements in the DenseSet.
class ComparableFunction {
public:
static const ComparableFunction EmptyKey;
static const ComparableFunction TombstoneKey;
static DataLayout * const LookupOnly;
ComparableFunction(Function *Func, const DataLayout *DL)
: Func(Func), Hash(profileFunction(Func)), DL(DL) {}
Function *getFunc() const { return Func; }
unsigned getHash() const { return Hash; }
const DataLayout *getDataLayout() const { return DL; }
// Drops AssertingVH reference to the function. Outside of debug mode, this
// does nothing.
void release() {
assert(Func &&
"Attempted to release function twice, or release empty/tombstone!");
Func = NULL;
}
private:
explicit ComparableFunction(unsigned Hash)
: Func(NULL), Hash(Hash), DL(NULL) {}
AssertingVH<Function> Func;
unsigned Hash;
const DataLayout *DL;
};
const ComparableFunction ComparableFunction::EmptyKey = ComparableFunction(0);
const ComparableFunction ComparableFunction::TombstoneKey =
ComparableFunction(1);
DataLayout *const ComparableFunction::LookupOnly = (DataLayout*)(-1);
}
namespace llvm {
template <>
struct DenseMapInfo<ComparableFunction> {
static ComparableFunction getEmptyKey() {
return ComparableFunction::EmptyKey;
}
static ComparableFunction getTombstoneKey() {
return ComparableFunction::TombstoneKey;
}
static unsigned getHashValue(const ComparableFunction &CF) {
return CF.getHash();
}
static bool isEqual(const ComparableFunction &LHS,
const ComparableFunction &RHS);
};
}
namespace {
/// FunctionComparator - Compares two functions to determine whether or not
/// they will generate machine code with the same behaviour. DataLayout is
/// used if available. The comparator always fails conservatively (erring on the
/// side of claiming that two functions are different).
class FunctionComparator {
public:
FunctionComparator(const DataLayout *DL, const Function *F1,
const Function *F2)
: F1(F1), F2(F2), DL(DL) {}
/// Test whether the two functions have equivalent behaviour.
bool compare();
private:
/// Test whether two basic blocks have equivalent behaviour.
bool compare(const BasicBlock *BB1, const BasicBlock *BB2);
/// 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);
/// 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;
/// Compare two GEPs for equivalent pointer arithmetic.
bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2);
bool isEquivalentGEP(const GetElementPtrInst *GEP1,
const GetElementPtrInst *GEP2) {
return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2));
}
/// cmpType - compares two types,
/// defines total ordering among the types set.
///
/// Return values:
/// 0 if types are equal,
/// -1 if Left is less than Right,
/// +1 if Left is greater than Right.
///
/// Description:
/// Comparison is broken onto stages. Like in lexicographical comparison
/// stage coming first has higher priority.
/// On each explanation stage keep in mind total ordering properties.
///
/// 0. Before comparison we coerce pointer types of 0 address space to integer.
/// We also don't bother with same type at left and right, so
/// just return 0 in this case.
///
/// 1. If types are of different kind (different type IDs).
/// Return result of type IDs comparison, treating them as numbers.
/// 2. If types are vectors or integers, compare Type* values as numbers.
/// 3. Types has same ID, so check whether they belongs to the next group:
/// * Void
/// * Float
/// * Double
/// * X86_FP80
/// * FP128
/// * PPC_FP128
/// * Label
/// * Metadata
/// If so - return 0, yes - we can treat these types as equal only because
/// their IDs are same.
/// 4. If Left and Right are pointers, return result of address space
/// comparison (numbers comparison). We can treat pointer types of same
/// address space as equal.
/// 5. If types are complex.
/// Then both Left and Right are to be expanded and their element types will
/// be checked with the same way. If we get Res != 0 on some stage, return it.
/// Otherwise return 0.
/// 6. For all other cases put llvm_unreachable.
int cmpType(Type *TyL, Type *TyR) const;
bool isEquivalentType(Type *Ty1, Type *Ty2) const {
return cmpType(Ty1, Ty2) == 0;
}
int cmpNumbers(uint64_t L, uint64_t R) const;
// The two functions undergoing comparison.
const Function *F1, *F2;
const DataLayout *DL;
DenseMap<const Value *, const Value *> id_map;
DenseSet<const Value *> seen_values;
};
}
int FunctionComparator::cmpNumbers(uint64_t L, uint64_t R) const {
if (L < R) return -1;
if (L > R) return 1;
return 0;
}
/// cmpType - compares two types,
/// defines total ordering among the types set.
/// See method declaration comments for more details.
int FunctionComparator::cmpType(Type *TyL, Type *TyR) const {
PointerType *PTy1 = dyn_cast<PointerType>(TyL);
PointerType *PTy2 = dyn_cast<PointerType>(TyR);
if (DL) {
if (PTy1 && PTy1->getAddressSpace() == 0) TyL = DL->getIntPtrType(TyL);
if (PTy2 && PTy2->getAddressSpace() == 0) TyR = DL->getIntPtrType(TyR);
}
if (TyL == TyR)
return 0;
if (int Res = cmpNumbers(TyL->getTypeID(), TyR->getTypeID()))
return Res;
switch (TyL->getTypeID()) {
default:
llvm_unreachable("Unknown type!");
// Fall through in Release mode.
case Type::IntegerTyID:
case Type::VectorTyID:
// TyL == TyR would have returned true earlier.
return cmpNumbers((uint64_t)TyL, (uint64_t)TyR);
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 0;
case Type::PointerTyID: {
assert(PTy1 && PTy2 && "Both types must be pointers here.");
return cmpNumbers(PTy1->getAddressSpace(), PTy2->getAddressSpace());
}
case Type::StructTyID: {
StructType *STy1 = cast<StructType>(TyL);
StructType *STy2 = cast<StructType>(TyR);
if (STy1->getNumElements() != STy2->getNumElements())
return cmpNumbers(STy1->getNumElements(), STy2->getNumElements());
if (STy1->isPacked() != STy2->isPacked())
return cmpNumbers(STy1->isPacked(), STy2->isPacked());
for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) {
if (int Res = cmpType(STy1->getElementType(i),
STy2->getElementType(i)))
return Res;
}
return 0;
}
case Type::FunctionTyID: {
FunctionType *FTy1 = cast<FunctionType>(TyL);
FunctionType *FTy2 = cast<FunctionType>(TyR);
if (FTy1->getNumParams() != FTy2->getNumParams())
return cmpNumbers(FTy1->getNumParams(), FTy2->getNumParams());
if (FTy1->isVarArg() != FTy2->isVarArg())
return cmpNumbers(FTy1->isVarArg(), FTy2->isVarArg());
if (int Res = cmpType(FTy1->getReturnType(), FTy2->getReturnType()))
return Res;
for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) {
if (int Res = cmpType(FTy1->getParamType(i), FTy2->getParamType(i)))
return Res;
}
return 0;
}
case Type::ArrayTyID: {
ArrayType *ATy1 = cast<ArrayType>(TyL);
ArrayType *ATy2 = cast<ArrayType>(TyR);
if (ATy1->getNumElements() != ATy2->getNumElements())
return cmpNumbers(ATy1->getNumElements(), ATy2->getNumElements());
return cmpType(ATy1->getElementType(), ATy2->getElementType());
}
}
}
// 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.
bool FunctionComparator::isEquivalentOperation(const Instruction *I1,
const Instruction *I2) const {
// Differences from Instruction::isSameOperationAs:
// * replace type comparison with calls to isEquivalentType.
// * we test for I->hasSameSubclassOptionalData (nuw/nsw/tail) at the top
// * because of the above, we don't test for the tail bit on calls later on
if (I1->getOpcode() != I2->getOpcode() ||
I1->getNumOperands() != I2->getNumOperands() ||
!isEquivalentType(I1->getType(), I2->getType()) ||
!I1->hasSameSubclassOptionalData(I2))
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() &&
LI->getOrdering() == cast<LoadInst>(I2)->getOrdering() &&
LI->getSynchScope() == cast<LoadInst>(I2)->getSynchScope();
if (const StoreInst *SI = dyn_cast<StoreInst>(I1))
return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() &&
SI->getAlignment() == cast<StoreInst>(I2)->getAlignment() &&
SI->getOrdering() == cast<StoreInst>(I2)->getOrdering() &&
SI->getSynchScope() == cast<StoreInst>(I2)->getSynchScope();
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->getCallingConv() == cast<CallInst>(I2)->getCallingConv() &&
CI->getAttributes() == cast<CallInst>(I2)->getAttributes();
if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1))
return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() &&
CI->getAttributes() == cast<InvokeInst>(I2)->getAttributes();
if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1))
return IVI->getIndices() == cast<InsertValueInst>(I2)->getIndices();
if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1))
return EVI->getIndices() == cast<ExtractValueInst>(I2)->getIndices();
if (const FenceInst *FI = dyn_cast<FenceInst>(I1))
return FI->getOrdering() == cast<FenceInst>(I2)->getOrdering() &&
FI->getSynchScope() == cast<FenceInst>(I2)->getSynchScope();
if (const AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(I1))
return CXI->isVolatile() == cast<AtomicCmpXchgInst>(I2)->isVolatile() &&
CXI->getSuccessOrdering() ==
cast<AtomicCmpXchgInst>(I2)->getSuccessOrdering() &&
CXI->getFailureOrdering() ==
cast<AtomicCmpXchgInst>(I2)->getFailureOrdering() &&
CXI->getSynchScope() == cast<AtomicCmpXchgInst>(I2)->getSynchScope();
if (const AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(I1))
return RMWI->getOperation() == cast<AtomicRMWInst>(I2)->getOperation() &&
RMWI->isVolatile() == cast<AtomicRMWInst>(I2)->isVolatile() &&
RMWI->getOrdering() == cast<AtomicRMWInst>(I2)->getOrdering() &&
RMWI->getSynchScope() == cast<AtomicRMWInst>(I2)->getSynchScope();
return true;
}
// Determine whether two GEP operations perform the same underlying arithmetic.
bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1,
const GEPOperator *GEP2) {
unsigned AS = GEP1->getPointerAddressSpace();
if (AS != GEP2->getPointerAddressSpace())
return false;
if (DL) {
// When we have target data, we can reduce the GEP down to the value in bytes
// added to the address.
unsigned BitWidth = DL ? DL->getPointerSizeInBits(AS) : 1;
APInt Offset1(BitWidth, 0), Offset2(BitWidth, 0);
if (GEP1->accumulateConstantOffset(*DL, Offset1) &&
GEP2->accumulateConstantOffset(*DL, Offset2)) {
return Offset1 == Offset2;
}
}
if (GEP1->getPointerOperand()->getType() !=
GEP2->getPointerOperand()->getType())
return false;
if (GEP1->getNumOperands() != GEP2->getNumOperands())
return false;
for (unsigned i = 0, e = GEP1->getNumOperands(); i != e; ++i) {
if (!enumerate(GEP1->getOperand(i), GEP2->getOperand(i)))
return false;
}
return true;
}
// Compare two values used by the two functions under pair-wise comparison. If
// this is the first time the values are seen, they're added to the mapping so
// that we will detect mismatches on next use.
bool FunctionComparator::enumerate(const Value *V1, const Value *V2) {
// Check for function @f1 referring to itself and function @f2 referring to
// itself, or referring to each other, or both referring to either of them.
// They're all equivalent if the two functions are otherwise equivalent.
if (V1 == F1 && V2 == F2)
return true;
if (V1 == F2 && V2 == F1)
return true;
if (const Constant *C1 = dyn_cast<Constant>(V1)) {
if (V1 == V2) return true;
const Constant *C2 = dyn_cast<Constant>(V2);
if (!C2) return false;
// TODO: constant expressions with GEP or references to F1 or F2.
if (C1->isNullValue() && C2->isNullValue() &&
isEquivalentType(C1->getType(), C2->getType()))
return true;
// Try bitcasting C2 to C1's type. If the bitcast is legal and returns C1
// then they must have equal bit patterns.
return C1->getType()->canLosslesslyBitCastTo(C2->getType()) &&
C1 == ConstantExpr::getBitCast(const_cast<Constant*>(C2), C1->getType());
}
if (isa<InlineAsm>(V1) || isa<InlineAsm>(V2))
return V1 == V2;
// Check that V1 maps to V2. If we find a value that V1 maps to then we simply
// check whether it's equal to V2. When there is no mapping then we need to
// ensure that V2 isn't already equivalent to something else. For this
// purpose, we track the V2 values in a set.
const Value *&map_elem = id_map[V1];
if (map_elem)
return map_elem == V2;
if (!seen_values.insert(V2).second)
return false;
map_elem = V2;
return true;
}
// 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();
do {
if (!enumerate(F1I, F2I))
return false;
if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(F1I)) {
const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(F2I);
if (!GEP2)
return false;
if (!enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand()))
return false;
if (!isEquivalentGEP(GEP1, GEP2))
return false;
} else {
if (!isEquivalentOperation(F1I, F2I))
return false;
assert(F1I->getNumOperands() == F2I->getNumOperands());
for (unsigned i = 0, e = F1I->getNumOperands(); i != e; ++i) {
Value *OpF1 = F1I->getOperand(i);
Value *OpF2 = F2I->getOperand(i);
if (!enumerate(OpF1, OpF2))
return false;
if (OpF1->getValueID() != OpF2->getValueID() ||
!isEquivalentType(OpF1->getType(), OpF2->getType()))
return false;
}
}
++F1I, ++F2I;
} while (F1I != F1E && F2I != F2E);
return F1I == F1E && F2I == F2E;
}
// 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.
if (F1->getAttributes() != F2->getAttributes())
return false;
if (F1->hasGC() != F2->hasGC())
return false;
if (F1->hasGC() && F1->getGC() != F2->getGC())
return false;
if (F1->hasSection() != F2->hasSection())
return false;
if (F1->hasSection() && F1->getSection() != F2->getSection())
return false;
if (F1->isVarArg() != F2->isVarArg())
return false;
// TODO: if it's internal and only used in direct calls, we could handle this
// case too.
if (F1->getCallingConv() != F2->getCallingConv())
return false;
if (!isEquivalentType(F1->getFunctionType(), F2->getFunctionType()))
return false;
assert(F1->arg_size() == F2->arg_size() &&
"Identically typed functions have different numbers of args!");
// Visit the arguments so that they get enumerated in the order they're
// passed in.
for (Function::const_arg_iterator f1i = F1->arg_begin(),
f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) {
if (!enumerate(f1i, f2i))
llvm_unreachable("Arguments repeat!");
}
// 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;
SmallSet<const BasicBlock *, 128> VisitedBBs; // in terms of F1.
F1BBs.push_back(&F1->getEntryBlock());
F2BBs.push_back(&F2->getEntryBlock());
VisitedBBs.insert(F1BBs[0]);
while (!F1BBs.empty()) {
const BasicBlock *F1BB = F1BBs.pop_back_val();
const BasicBlock *F2BB = F2BBs.pop_back_val();
if (!enumerate(F1BB, F2BB) || !compare(F1BB, F2BB))
return false;
const TerminatorInst *F1TI = F1BB->getTerminator();
const TerminatorInst *F2TI = F2BB->getTerminator();
assert(F1TI->getNumSuccessors() == F2TI->getNumSuccessors());
for (unsigned i = 0, e = F1TI->getNumSuccessors(); i != e; ++i) {
if (!VisitedBBs.insert(F1TI->getSuccessor(i)))
continue;
F1BBs.push_back(F1TI->getSuccessor(i));
F2BBs.push_back(F2TI->getSuccessor(i));
}
}
return true;
}
namespace {
/// MergeFunctions finds functions which will generate identical machine code,
/// by considering all pointer types to be equivalent. Once identified,
/// MergeFunctions will fold them by replacing a call to one to a call to a
/// bitcast of the other.
///
class MergeFunctions : public ModulePass {
public:
static char ID;
MergeFunctions()
: ModulePass(ID), HasGlobalAliases(false) {
initializeMergeFunctionsPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
private:
typedef DenseSet<ComparableFunction> FnSetType;
/// A work queue of functions that may have been modified and should be
/// analyzed again.
std::vector<WeakVH> Deferred;
/// Insert a ComparableFunction into the FnSet, or merge it away if it's
/// equal to one that's already present.
bool insert(ComparableFunction &NewF);
/// Remove a Function from the FnSet and queue it up for a second sweep of
/// analysis.
void remove(Function *F);
/// Find the functions that use this Value and remove them from FnSet and
/// queue the functions.
void removeUsers(Value *V);
/// Replace all direct calls of Old with calls of New. Will bitcast New if
/// necessary to make types match.
void replaceDirectCallers(Function *Old, Function *New);
/// Merge two equivalent functions. Upon completion, G may be deleted, or may
/// be converted into a thunk. In either case, it should never be visited
/// again.
void mergeTwoFunctions(Function *F, Function *G);
/// Replace G with a thunk or an alias to F. Deletes G.
void writeThunkOrAlias(Function *F, Function *G);
/// Replace G with a simple tail call to bitcast(F). Also replace direct uses
/// of G with bitcast(F). Deletes G.
void writeThunk(Function *F, Function *G);
/// Replace G with an alias to F. Deletes G.
void writeAlias(Function *F, Function *G);
/// The set of all distinct functions. Use the insert() and remove() methods
/// to modify it.
FnSetType FnSet;
/// DataLayout for more accurate GEP comparisons. May be NULL.
const DataLayout *DL;
/// Whether or not the target supports global aliases.
bool HasGlobalAliases;
};
} // end anonymous namespace
char MergeFunctions::ID = 0;
INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false)
ModulePass *llvm::createMergeFunctionsPass() {
return new MergeFunctions();
}
bool MergeFunctions::runOnModule(Module &M) {
bool Changed = false;
DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
DL = DLP ? &DLP->getDataLayout() : 0;
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage())
Deferred.push_back(WeakVH(I));
}
FnSet.resize(Deferred.size());
do {
std::vector<WeakVH> Worklist;
Deferred.swap(Worklist);
DEBUG(dbgs() << "size of module: " << M.size() << '\n');
DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n');
// Insert only strong functions and merge them. Strong function merging
// always deletes one of them.
for (std::vector<WeakVH>::iterator I = Worklist.begin(),
E = Worklist.end(); I != E; ++I) {
if (!*I) continue;
Function *F = cast<Function>(*I);
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
!F->mayBeOverridden()) {
ComparableFunction CF = ComparableFunction(F, DL);
Changed |= insert(CF);
}
}
// Insert only weak functions and merge them. By doing these second we
// create thunks to the strong function when possible. When two weak
// functions are identical, we create a new strong function with two weak
// weak thunks to it which are identical but not mergable.
for (std::vector<WeakVH>::iterator I = Worklist.begin(),
E = Worklist.end(); I != E; ++I) {
if (!*I) continue;
Function *F = cast<Function>(*I);
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() &&
F->mayBeOverridden()) {
ComparableFunction CF = ComparableFunction(F, DL);
Changed |= insert(CF);
}
}
DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n');
} while (!Deferred.empty());
FnSet.clear();
return Changed;
}
bool DenseMapInfo<ComparableFunction>::isEqual(const ComparableFunction &LHS,
const ComparableFunction &RHS) {
if (LHS.getFunc() == RHS.getFunc() &&
LHS.getHash() == RHS.getHash())
return true;
if (!LHS.getFunc() || !RHS.getFunc())
return false;
// One of these is a special "underlying pointer comparison only" object.
if (LHS.getDataLayout() == ComparableFunction::LookupOnly ||
RHS.getDataLayout() == ComparableFunction::LookupOnly)
return false;
assert(LHS.getDataLayout() == RHS.getDataLayout() &&
"Comparing functions for different targets");
return FunctionComparator(LHS.getDataLayout(), LHS.getFunc(),
RHS.getFunc()).compare();
}
// Replace direct callers of Old with New.
void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) {
Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType());
for (auto UI = Old->use_begin(), UE = Old->use_end(); UI != UE;) {
Use *U = &*UI;
++UI;
CallSite CS(U->getUser());
if (CS && CS.isCallee(U)) {
remove(CS.getInstruction()->getParent()->getParent());
U->set(BitcastNew);
}
}
}
// Replace G with an alias to F if possible, or else a thunk to F. Deletes G.
void MergeFunctions::writeThunkOrAlias(Function *F, Function *G) {
if (HasGlobalAliases && G->hasUnnamedAddr()) {
if (G->hasExternalLinkage() || G->hasLocalLinkage() ||
G->hasWeakLinkage()) {
writeAlias(F, G);
return;
}
}
writeThunk(F, G);
}
// Helper for writeThunk,
// Selects proper bitcast operation,
// but a bit simpler then CastInst::getCastOpcode.
static Value* createCast(IRBuilder<false> &Builder, Value *V, Type *DestTy) {
Type *SrcTy = V->getType();
if (SrcTy->isIntegerTy() && DestTy->isPointerTy())
return Builder.CreateIntToPtr(V, DestTy);
else if (SrcTy->isPointerTy() && DestTy->isIntegerTy())
return Builder.CreatePtrToInt(V, DestTy);
else
return Builder.CreateBitCast(V, DestTy);
}
// Replace G with a simple tail call to bitcast(F). Also replace direct uses
// of G with bitcast(F). Deletes G.
void MergeFunctions::writeThunk(Function *F, Function *G) {
if (!G->mayBeOverridden()) {
// Redirect direct callers of G to F.
replaceDirectCallers(G, F);
}
// If G was internal then we may have replaced all uses of G with F. If so,
// stop here and delete G. There's no need for a thunk.
if (G->hasLocalLinkage() && G->use_empty()) {
G->eraseFromParent();
return;
}
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;
FunctionType *FFTy = F->getFunctionType();
for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end();
AI != AE; ++AI) {
Args.push_back(createCast(Builder, (Value*)AI, FFTy->getParamType(i)));
++i;
}
CallInst *CI = Builder.CreateCall(F, Args);
CI->setTailCall();
CI->setCallingConv(F->getCallingConv());
if (NewG->getReturnType()->isVoidTy()) {
Builder.CreateRetVoid();
} else {
Builder.CreateRet(createCast(Builder, CI, NewG->getReturnType()));
}
NewG->copyAttributesFrom(G);
NewG->takeName(G);
removeUsers(G);
G->replaceAllUsesWith(NewG);
G->eraseFromParent();
DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n');
++NumThunksWritten;
}
// Replace G with an alias to F and delete G.
void MergeFunctions::writeAlias(Function *F, Function *G) {
Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "",
BitcastF, G->getParent());
F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
GA->takeName(G);
GA->setVisibility(G->getVisibility());
removeUsers(G);
G->replaceAllUsesWith(GA);
G->eraseFromParent();
DEBUG(dbgs() << "writeAlias: " << GA->getName() << '\n');
++NumAliasesWritten;
}
// Merge two equivalent functions. Upon completion, Function G is deleted.
void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
if (F->mayBeOverridden()) {
assert(G->mayBeOverridden());
if (HasGlobalAliases) {
// Make them both thunks to the same internal function.
Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
F->getParent());
H->copyAttributesFrom(F);
H->takeName(F);
removeUsers(F);
F->replaceAllUsesWith(H);
unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment());
writeAlias(F, G);
writeAlias(F, H);
F->setAlignment(MaxAlignment);
F->setLinkage(GlobalValue::PrivateLinkage);
} else {
// We can't merge them. Instead, pick one and update all direct callers
// to call it and hope that we improve the instruction cache hit rate.
replaceDirectCallers(G, F);
}
++NumDoubleWeak;
} else {
writeThunkOrAlias(F, G);
}
++NumFunctionsMerged;
}
// Insert a ComparableFunction into the FnSet, or merge it away if equal to one
// that was already inserted.
bool MergeFunctions::insert(ComparableFunction &NewF) {
std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF);
if (Result.second) {
DEBUG(dbgs() << "Inserting as unique: " << NewF.getFunc()->getName() << '\n');
return false;
}
const ComparableFunction &OldF = *Result.first;
// Don't merge tiny functions, since it can just end up making the function
// larger.
// FIXME: Should still merge them if they are unnamed_addr and produce an
// alias.
if (NewF.getFunc()->size() == 1) {
if (NewF.getFunc()->front().size() <= 2) {
DEBUG(dbgs() << NewF.getFunc()->getName()
<< " is to small to bother merging\n");
return false;
}
}
// Never thunk a strong function to a weak function.
assert(!OldF.getFunc()->mayBeOverridden() ||
NewF.getFunc()->mayBeOverridden());
DEBUG(dbgs() << " " << OldF.getFunc()->getName() << " == "
<< NewF.getFunc()->getName() << '\n');
Function *DeleteF = NewF.getFunc();
NewF.release();
mergeTwoFunctions(OldF.getFunc(), DeleteF);
return true;
}
// Remove a function from FnSet. If it was already in FnSet, add it to Deferred
// so that we'll look at it in the next round.
void MergeFunctions::remove(Function *F) {
// We need to make sure we remove F, not a function "equal" to F per the
// function equality comparator.
//
// The special "lookup only" ComparableFunction bypasses the expensive
// function comparison in favour of a pointer comparison on the underlying
// Function*'s.
ComparableFunction CF = ComparableFunction(F, ComparableFunction::LookupOnly);
if (FnSet.erase(CF)) {
DEBUG(dbgs() << "Removed " << F->getName() << " from set and deferred it.\n");
Deferred.push_back(F);
}
}
// For each instruction used by the value, remove() the function that contains
// the instruction. This should happen right before a call to RAUW.
void MergeFunctions::removeUsers(Value *V) {
std::vector<Value *> Worklist;
Worklist.push_back(V);
while (!Worklist.empty()) {
Value *V = Worklist.back();
Worklist.pop_back();
for (User *U : V->users()) {
if (Instruction *I = dyn_cast<Instruction>(U)) {
remove(I->getParent()->getParent());
} else if (isa<GlobalValue>(U)) {
// do nothing
} else if (Constant *C = dyn_cast<Constant>(U)) {
for (User *UU : C->users())
Worklist.push_back(UU);
}
}
}
}
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