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llvm-mirror/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.
//
// Order relation is defined on set of functions. It was made through
// special function comparison procedure that returns
// 0 when functions are equal,
// -1 when Left function is less than right function, and
// 1 for opposite case. We need total-ordering, so we need to maintain
// four properties on the functions set:
// a <= a (reflexivity)
// if a <= b and b <= a then a = b (antisymmetry)
// if a <= b and b <= c then a <= c (transitivity).
// for all a and b: a <= b or b <= a (totality).
//
// Comparison iterates through each instruction in each basic block.
// Functions are kept on binary tree. For each new function F we perform
// lookup in binary tree.
// In practice it works the following way:
// -- We define Function* container class with custom "operator<" (FunctionPtr).
// -- "FunctionPtr" instances are stored in std::set collection, so every
// std::set::insert operation will give you result in log(N) time.
//
// As an optimization, a hash of the function structure is calculated first, and
// two functions are only compared if they have the same hash. This hash is
// cheap to compute, and has the property that if function F == G according to
// the comparison function, then hash(F) == hash(G). This consistency property
// is critical to ensuring all possible merging opportunities are exploited.
// Collisions in the hash affect the speed of the pass but not the correctness
// or determinism of the resulting transformation.
//
// 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.
//
// * 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.
//
// * Compare complex types with pointer types inside.
// * Compare cross-reference cases.
// * Compare complex expressions.
//
// All the three issues above could be described as ability to prove that
// fA == fB == fC == fE == fF == fG in example below:
//
// void fA() {
// fB();
// }
// void fB() {
// fA();
// }
//
// void fE() {
// fF();
// }
// void fF() {
// fG();
// }
// void fG() {
// fE();
// }
//
// Simplest cross-reference case (fA <--> fB) was implemented in previous
// versions of MergeFunctions, though it presented only in two function pairs
// in test-suite (that counts >50k functions)
// Though possibility to detect complex cross-referencing (e.g.: A->B->C->D->A)
// could cover much more cases.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/IR/ValueMap.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/Utils/FunctionComparator.h"
#include <algorithm>
#include <cassert>
#include <iterator>
#include <set>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "mergefunc"
STATISTIC(NumFunctionsMerged, "Number of functions merged");
STATISTIC(NumThunksWritten, "Number of thunks generated");
STATISTIC(NumDoubleWeak, "Number of new functions created");
static cl::opt<unsigned> NumFunctionsForSanityCheck(
"mergefunc-sanity",
cl::desc("How many functions in module could be used for "
"MergeFunctions pass sanity check. "
"'0' disables this check. Works only with '-debug' key."),
cl::init(0), cl::Hidden);
// Under option -mergefunc-preserve-debug-info we:
// - Do not create a new function for a thunk.
// - Retain the debug info for a thunk's parameters (and associated
// instructions for the debug info) from the entry block.
// Note: -debug will display the algorithm at work.
// - Create debug-info for the call (to the shared implementation) made by
// a thunk and its return value.
// - Erase the rest of the function, retaining the (minimally sized) entry
// block to create a thunk.
// - Preserve a thunk's call site to point to the thunk even when both occur
// within the same translation unit, to aid debugability. Note that this
// behaviour differs from the underlying -mergefunc implementation which
// modifies the thunk's call site to point to the shared implementation
// when both occur within the same translation unit.
static cl::opt<bool>
MergeFunctionsPDI("mergefunc-preserve-debug-info", cl::Hidden,
cl::init(false),
cl::desc("Preserve debug info in thunk when mergefunc "
"transformations are made."));
namespace {
class FunctionNode {
mutable AssertingVH<Function> F;
FunctionComparator::FunctionHash Hash;
public:
// Note the hash is recalculated potentially multiple times, but it is cheap.
FunctionNode(Function *F)
: F(F), Hash(FunctionComparator::functionHash(*F)) {}
Function *getFunc() const { return F; }
FunctionComparator::FunctionHash getHash() const { return Hash; }
/// Replace the reference to the function F by the function G, assuming their
/// implementations are equal.
void replaceBy(Function *G) const {
F = G;
}
void release() { F = nullptr; }
};
/// 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), FnTree(FunctionNodeCmp(&GlobalNumbers)) {
initializeMergeFunctionsPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
private:
// The function comparison operator is provided here so that FunctionNodes do
// not need to become larger with another pointer.
class FunctionNodeCmp {
GlobalNumberState* GlobalNumbers;
public:
FunctionNodeCmp(GlobalNumberState* GN) : GlobalNumbers(GN) {}
bool operator()(const FunctionNode &LHS, const FunctionNode &RHS) const {
// Order first by hashes, then full function comparison.
if (LHS.getHash() != RHS.getHash())
return LHS.getHash() < RHS.getHash();
FunctionComparator FCmp(LHS.getFunc(), RHS.getFunc(), GlobalNumbers);
return FCmp.compare() == -1;
}
};
using FnTreeType = std::set<FunctionNode, FunctionNodeCmp>;
GlobalNumberState GlobalNumbers;
/// A work queue of functions that may have been modified and should be
/// analyzed again.
std::vector<WeakTrackingVH> Deferred;
#ifndef NDEBUG
/// Checks the rules of order relation introduced among functions set.
/// Returns true, if sanity check has been passed, and false if failed.
bool doSanityCheck(std::vector<WeakTrackingVH> &Worklist);
#endif
/// Insert a ComparableFunction into the FnTree, or merge it away if it's
/// equal to one that's already present.
bool insert(Function *NewFunction);
/// Remove a Function from the FnTree 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 FnTree 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);
/// Fill PDIUnrelatedWL with instructions from the entry block that are
/// unrelated to parameter related debug info.
void filterInstsUnrelatedToPDI(BasicBlock *GEntryBlock,
std::vector<Instruction *> &PDIUnrelatedWL);
/// Erase the rest of the CFG (i.e. barring the entry block).
void eraseTail(Function *G);
/// Erase the instructions in PDIUnrelatedWL as they are unrelated to the
/// parameter debug info, from the entry block.
void eraseInstsUnrelatedToPDI(std::vector<Instruction *> &PDIUnrelatedWL);
/// Replace G with a simple tail call to bitcast(F). Also (unless
/// MergeFunctionsPDI holds) replace direct uses of G with bitcast(F),
/// delete G.
void writeThunk(Function *F, Function *G);
/// Replace function F with function G in the function tree.
void replaceFunctionInTree(const FunctionNode &FN, Function *G);
/// The set of all distinct functions. Use the insert() and remove() methods
/// to modify it. The map allows efficient lookup and deferring of Functions.
FnTreeType FnTree;
// Map functions to the iterators of the FunctionNode which contains them
// in the FnTree. This must be updated carefully whenever the FnTree is
// modified, i.e. in insert(), remove(), and replaceFunctionInTree(), to avoid
// dangling iterators into FnTree. The invariant that preserves this is that
// there is exactly one mapping F -> FN for each FunctionNode FN in FnTree.
ValueMap<Function*, FnTreeType::iterator> FNodesInTree;
};
} // end anonymous namespace
char MergeFunctions::ID = 0;
INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false)
ModulePass *llvm::createMergeFunctionsPass() {
return new MergeFunctions();
}
#ifndef NDEBUG
bool MergeFunctions::doSanityCheck(std::vector<WeakTrackingVH> &Worklist) {
if (const unsigned Max = NumFunctionsForSanityCheck) {
unsigned TripleNumber = 0;
bool Valid = true;
dbgs() << "MERGEFUNC-SANITY: Started for first " << Max << " functions.\n";
unsigned i = 0;
for (std::vector<WeakTrackingVH>::iterator I = Worklist.begin(),
E = Worklist.end();
I != E && i < Max; ++I, ++i) {
unsigned j = i;
for (std::vector<WeakTrackingVH>::iterator J = I; J != E && j < Max;
++J, ++j) {
Function *F1 = cast<Function>(*I);
Function *F2 = cast<Function>(*J);
int Res1 = FunctionComparator(F1, F2, &GlobalNumbers).compare();
int Res2 = FunctionComparator(F2, F1, &GlobalNumbers).compare();
// If F1 <= F2, then F2 >= F1, otherwise report failure.
if (Res1 != -Res2) {
dbgs() << "MERGEFUNC-SANITY: Non-symmetric; triple: " << TripleNumber
<< "\n";
dbgs() << *F1 << '\n' << *F2 << '\n';
Valid = false;
}
if (Res1 == 0)
continue;
unsigned k = j;
for (std::vector<WeakTrackingVH>::iterator K = J; K != E && k < Max;
++k, ++K, ++TripleNumber) {
if (K == J)
continue;
Function *F3 = cast<Function>(*K);
int Res3 = FunctionComparator(F1, F3, &GlobalNumbers).compare();
int Res4 = FunctionComparator(F2, F3, &GlobalNumbers).compare();
bool Transitive = true;
if (Res1 != 0 && Res1 == Res4) {
// F1 > F2, F2 > F3 => F1 > F3
Transitive = Res3 == Res1;
} else if (Res3 != 0 && Res3 == -Res4) {
// F1 > F3, F3 > F2 => F1 > F2
Transitive = Res3 == Res1;
} else if (Res4 != 0 && -Res3 == Res4) {
// F2 > F3, F3 > F1 => F2 > F1
Transitive = Res4 == -Res1;
}
if (!Transitive) {
dbgs() << "MERGEFUNC-SANITY: Non-transitive; triple: "
<< TripleNumber << "\n";
dbgs() << "Res1, Res3, Res4: " << Res1 << ", " << Res3 << ", "
<< Res4 << "\n";
dbgs() << *F1 << '\n' << *F2 << '\n' << *F3 << '\n';
Valid = false;
}
}
}
}
dbgs() << "MERGEFUNC-SANITY: " << (Valid ? "Passed." : "Failed.") << "\n";
return Valid;
}
return true;
}
#endif
bool MergeFunctions::runOnModule(Module &M) {
if (skipModule(M))
return false;
bool Changed = false;
// All functions in the module, ordered by hash. Functions with a unique
// hash value are easily eliminated.
std::vector<std::pair<FunctionComparator::FunctionHash, Function *>>
HashedFuncs;
for (Function &Func : M) {
if (!Func.isDeclaration() && !Func.hasAvailableExternallyLinkage()) {
HashedFuncs.push_back({FunctionComparator::functionHash(Func), &Func});
}
}
std::stable_sort(
HashedFuncs.begin(), HashedFuncs.end(),
[](const std::pair<FunctionComparator::FunctionHash, Function *> &a,
const std::pair<FunctionComparator::FunctionHash, Function *> &b) {
return a.first < b.first;
});
auto S = HashedFuncs.begin();
for (auto I = HashedFuncs.begin(), IE = HashedFuncs.end(); I != IE; ++I) {
// If the hash value matches the previous value or the next one, we must
// consider merging it. Otherwise it is dropped and never considered again.
if ((I != S && std::prev(I)->first == I->first) ||
(std::next(I) != IE && std::next(I)->first == I->first) ) {
Deferred.push_back(WeakTrackingVH(I->second));
}
}
do {
std::vector<WeakTrackingVH> Worklist;
Deferred.swap(Worklist);
DEBUG(doSanityCheck(Worklist));
DEBUG(dbgs() << "size of module: " << M.size() << '\n');
DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n');
// Insert functions and merge them.
for (WeakTrackingVH &I : Worklist) {
if (!I)
continue;
Function *F = cast<Function>(I);
if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage()) {
Changed |= insert(F);
}
}
DEBUG(dbgs() << "size of FnTree: " << FnTree.size() << '\n');
} while (!Deferred.empty());
FnTree.clear();
GlobalNumbers.clear();
return Changed;
}
// 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)) {
// Transfer the called function's attributes to the call site. Due to the
// bitcast we will 'lose' ABI changing attributes because the 'called
// function' is no longer a Function* but the bitcast. Code that looks up
// the attributes from the called function will fail.
// FIXME: This is not actually true, at least not anymore. The callsite
// will always have the same ABI affecting attributes as the callee,
// because otherwise the original input has UB. Note that Old and New
// always have matching ABI, so no attributes need to be changed.
// Transferring other attributes may help other optimizations, but that
// should be done uniformly and not in this ad-hoc way.
auto &Context = New->getContext();
auto NewPAL = New->getAttributes();
SmallVector<AttributeSet, 4> NewArgAttrs;
for (unsigned argIdx = 0; argIdx < CS.arg_size(); argIdx++)
NewArgAttrs.push_back(NewPAL.getParamAttributes(argIdx));
// Don't transfer attributes from the function to the callee. Function
// attributes typically aren't relevant to the calling convention or ABI.
CS.setAttributes(AttributeList::get(Context, /*FnAttrs=*/AttributeSet(),
NewPAL.getRetAttributes(),
NewArgAttrs));
remove(CS.getInstruction()->getParent()->getParent());
U->set(BitcastNew);
}
}
}
// Helper for writeThunk,
// Selects proper bitcast operation,
// but a bit simpler then CastInst::getCastOpcode.
static Value *createCast(IRBuilder<> &Builder, Value *V, Type *DestTy) {
Type *SrcTy = V->getType();
if (SrcTy->isStructTy()) {
assert(DestTy->isStructTy());
assert(SrcTy->getStructNumElements() == DestTy->getStructNumElements());
Value *Result = UndefValue::get(DestTy);
for (unsigned int I = 0, E = SrcTy->getStructNumElements(); I < E; ++I) {
Value *Element = createCast(
Builder, Builder.CreateExtractValue(V, makeArrayRef(I)),
DestTy->getStructElementType(I));
Result =
Builder.CreateInsertValue(Result, Element, makeArrayRef(I));
}
return Result;
}
assert(!DestTy->isStructTy());
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);
}
// Erase the instructions in PDIUnrelatedWL as they are unrelated to the
// parameter debug info, from the entry block.
void MergeFunctions::eraseInstsUnrelatedToPDI(
std::vector<Instruction *> &PDIUnrelatedWL) {
DEBUG(dbgs() << " Erasing instructions (in reverse order of appearance in "
"entry block) unrelated to parameter debug info from entry "
"block: {\n");
while (!PDIUnrelatedWL.empty()) {
Instruction *I = PDIUnrelatedWL.back();
DEBUG(dbgs() << " Deleting Instruction: ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << "\n");
I->eraseFromParent();
PDIUnrelatedWL.pop_back();
}
DEBUG(dbgs() << " } // Done erasing instructions unrelated to parameter "
"debug info from entry block. \n");
}
// Reduce G to its entry block.
void MergeFunctions::eraseTail(Function *G) {
std::vector<BasicBlock *> WorklistBB;
for (Function::iterator BBI = std::next(G->begin()), BBE = G->end();
BBI != BBE; ++BBI) {
BBI->dropAllReferences();
WorklistBB.push_back(&*BBI);
}
while (!WorklistBB.empty()) {
BasicBlock *BB = WorklistBB.back();
BB->eraseFromParent();
WorklistBB.pop_back();
}
}
// We are interested in the following instructions from the entry block as being
// related to parameter debug info:
// - @llvm.dbg.declare
// - stores from the incoming parameters to locations on the stack-frame
// - allocas that create these locations on the stack-frame
// - @llvm.dbg.value
// - the entry block's terminator
// The rest are unrelated to debug info for the parameters; fill up
// PDIUnrelatedWL with such instructions.
void MergeFunctions::filterInstsUnrelatedToPDI(
BasicBlock *GEntryBlock, std::vector<Instruction *> &PDIUnrelatedWL) {
std::set<Instruction *> PDIRelated;
for (BasicBlock::iterator BI = GEntryBlock->begin(), BIE = GEntryBlock->end();
BI != BIE; ++BI) {
if (auto *DVI = dyn_cast<DbgValueInst>(&*BI)) {
DEBUG(dbgs() << " Deciding: ");
DEBUG(BI->print(dbgs()));
DEBUG(dbgs() << "\n");
DILocalVariable *DILocVar = DVI->getVariable();
if (DILocVar->isParameter()) {
DEBUG(dbgs() << " Include (parameter): ");
DEBUG(BI->print(dbgs()));
DEBUG(dbgs() << "\n");
PDIRelated.insert(&*BI);
} else {
DEBUG(dbgs() << " Delete (!parameter): ");
DEBUG(BI->print(dbgs()));
DEBUG(dbgs() << "\n");
}
} else if (auto *DDI = dyn_cast<DbgDeclareInst>(&*BI)) {
DEBUG(dbgs() << " Deciding: ");
DEBUG(BI->print(dbgs()));
DEBUG(dbgs() << "\n");
DILocalVariable *DILocVar = DDI->getVariable();
if (DILocVar->isParameter()) {
DEBUG(dbgs() << " Parameter: ");
DEBUG(DILocVar->print(dbgs()));
AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
if (AI) {
DEBUG(dbgs() << " Processing alloca users: ");
DEBUG(dbgs() << "\n");
for (User *U : AI->users()) {
if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
if (Value *Arg = SI->getValueOperand()) {
if (dyn_cast<Argument>(Arg)) {
DEBUG(dbgs() << " Include: ");
DEBUG(AI->print(dbgs()));
DEBUG(dbgs() << "\n");
PDIRelated.insert(AI);
DEBUG(dbgs() << " Include (parameter): ");
DEBUG(SI->print(dbgs()));
DEBUG(dbgs() << "\n");
PDIRelated.insert(SI);
DEBUG(dbgs() << " Include: ");
DEBUG(BI->print(dbgs()));
DEBUG(dbgs() << "\n");
PDIRelated.insert(&*BI);
} else {
DEBUG(dbgs() << " Delete (!parameter): ");
DEBUG(SI->print(dbgs()));
DEBUG(dbgs() << "\n");
}
}
} else {
DEBUG(dbgs() << " Defer: ");
DEBUG(U->print(dbgs()));
DEBUG(dbgs() << "\n");
}
}
} else {
DEBUG(dbgs() << " Delete (alloca NULL): ");
DEBUG(BI->print(dbgs()));
DEBUG(dbgs() << "\n");
}
} else {
DEBUG(dbgs() << " Delete (!parameter): ");
DEBUG(BI->print(dbgs()));
DEBUG(dbgs() << "\n");
}
} else if (dyn_cast<TerminatorInst>(BI) == GEntryBlock->getTerminator()) {
DEBUG(dbgs() << " Will Include Terminator: ");
DEBUG(BI->print(dbgs()));
DEBUG(dbgs() << "\n");
PDIRelated.insert(&*BI);
} else {
DEBUG(dbgs() << " Defer: ");
DEBUG(BI->print(dbgs()));
DEBUG(dbgs() << "\n");
}
}
DEBUG(dbgs()
<< " Report parameter debug info related/related instructions: {\n");
for (BasicBlock::iterator BI = GEntryBlock->begin(), BE = GEntryBlock->end();
BI != BE; ++BI) {
Instruction *I = &*BI;
if (PDIRelated.find(I) == PDIRelated.end()) {
DEBUG(dbgs() << " !PDIRelated: ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << "\n");
PDIUnrelatedWL.push_back(I);
} else {
DEBUG(dbgs() << " PDIRelated: ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << "\n");
}
}
DEBUG(dbgs() << " }\n");
}
// Replace G with a simple tail call to bitcast(F). Also (unless
// MergeFunctionsPDI holds) replace direct uses of G with bitcast(F),
// delete G. Under MergeFunctionsPDI, we use G itself for creating
// the thunk as we preserve the debug info (and associated instructions)
// from G's entry block pertaining to G's incoming arguments which are
// passed on as corresponding arguments in the call that G makes to F.
// For better debugability, under MergeFunctionsPDI, we do not modify G's
// call sites to point to F even when within the same translation unit.
void MergeFunctions::writeThunk(Function *F, Function *G) {
if (!G->isInterposable() && !MergeFunctionsPDI) {
if (G->hasGlobalUnnamedAddr()) {
// G might have been a key in our GlobalNumberState, and it's illegal
// to replace a key in ValueMap<GlobalValue *> with a non-global.
GlobalNumbers.erase(G);
// If G's address is not significant, replace it entirely.
Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
G->replaceAllUsesWith(BitcastF);
} else {
// Redirect direct callers of G to F. (See note on MergeFunctionsPDI
// above).
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. (See note on
// MergeFunctionsPDI above).
if (G->hasLocalLinkage() && G->use_empty() && !MergeFunctionsPDI) {
G->eraseFromParent();
return;
}
// Don't merge tiny functions using a thunk, since it can just end up
// making the function larger.
if (F->size() == 1) {
if (F->front().size() <= 2) {
DEBUG(dbgs() << "writeThunk: " << F->getName()
<< " is too small to bother creating a thunk for\n");
return;
}
}
BasicBlock *GEntryBlock = nullptr;
std::vector<Instruction *> PDIUnrelatedWL;
BasicBlock *BB = nullptr;
Function *NewG = nullptr;
if (MergeFunctionsPDI) {
DEBUG(dbgs() << "writeThunk: (MergeFunctionsPDI) Do not create a new "
"function as thunk; retain original: "
<< G->getName() << "()\n");
GEntryBlock = &G->getEntryBlock();
DEBUG(dbgs() << "writeThunk: (MergeFunctionsPDI) filter parameter related "
"debug info for "
<< G->getName() << "() {\n");
filterInstsUnrelatedToPDI(GEntryBlock, PDIUnrelatedWL);
GEntryBlock->getTerminator()->eraseFromParent();
BB = GEntryBlock;
} else {
NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
G->getParent());
BB = BasicBlock::Create(F->getContext(), "", NewG);
}
IRBuilder<> Builder(BB);
Function *H = MergeFunctionsPDI ? G : NewG;
SmallVector<Value *, 16> Args;
unsigned i = 0;
FunctionType *FFTy = F->getFunctionType();
for (Argument &AI : H->args()) {
Args.push_back(createCast(Builder, &AI, FFTy->getParamType(i)));
++i;
}
CallInst *CI = Builder.CreateCall(F, Args);
ReturnInst *RI = nullptr;
CI->setTailCall();
CI->setCallingConv(F->getCallingConv());
CI->setAttributes(F->getAttributes());
if (H->getReturnType()->isVoidTy()) {
RI = Builder.CreateRetVoid();
} else {
RI = Builder.CreateRet(createCast(Builder, CI, H->getReturnType()));
}
if (MergeFunctionsPDI) {
DISubprogram *DIS = G->getSubprogram();
if (DIS) {
DebugLoc CIDbgLoc = DebugLoc::get(DIS->getScopeLine(), 0, DIS);
DebugLoc RIDbgLoc = DebugLoc::get(DIS->getScopeLine(), 0, DIS);
CI->setDebugLoc(CIDbgLoc);
RI->setDebugLoc(RIDbgLoc);
} else {
DEBUG(dbgs() << "writeThunk: (MergeFunctionsPDI) No DISubprogram for "
<< G->getName() << "()\n");
}
eraseTail(G);
eraseInstsUnrelatedToPDI(PDIUnrelatedWL);
DEBUG(dbgs() << "} // End of parameter related debug info filtering for: "
<< G->getName() << "()\n");
} else {
NewG->copyAttributesFrom(G);
NewG->takeName(G);
removeUsers(G);
G->replaceAllUsesWith(NewG);
G->eraseFromParent();
}
DEBUG(dbgs() << "writeThunk: " << H->getName() << '\n');
++NumThunksWritten;
}
// Merge two equivalent functions. Upon completion, Function G is deleted.
void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
if (F->isInterposable()) {
assert(G->isInterposable());
// 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());
writeThunk(F, G);
writeThunk(F, H);
F->setAlignment(MaxAlignment);
F->setLinkage(GlobalValue::PrivateLinkage);
++NumDoubleWeak;
} else {
writeThunk(F, G);
}
++NumFunctionsMerged;
}
/// Replace function F by function G.
void MergeFunctions::replaceFunctionInTree(const FunctionNode &FN,
Function *G) {
Function *F = FN.getFunc();
assert(FunctionComparator(F, G, &GlobalNumbers).compare() == 0 &&
"The two functions must be equal");
auto I = FNodesInTree.find(F);
assert(I != FNodesInTree.end() && "F should be in FNodesInTree");
assert(FNodesInTree.count(G) == 0 && "FNodesInTree should not contain G");
FnTreeType::iterator IterToFNInFnTree = I->second;
assert(&(*IterToFNInFnTree) == &FN && "F should map to FN in FNodesInTree.");
// Remove F -> FN and insert G -> FN
FNodesInTree.erase(I);
FNodesInTree.insert({G, IterToFNInFnTree});
// Replace F with G in FN, which is stored inside the FnTree.
FN.replaceBy(G);
}
// Insert a ComparableFunction into the FnTree, or merge it away if equal to one
// that was already inserted.
bool MergeFunctions::insert(Function *NewFunction) {
std::pair<FnTreeType::iterator, bool> Result =
FnTree.insert(FunctionNode(NewFunction));
if (Result.second) {
assert(FNodesInTree.count(NewFunction) == 0);
FNodesInTree.insert({NewFunction, Result.first});
DEBUG(dbgs() << "Inserting as unique: " << NewFunction->getName() << '\n');
return false;
}
const FunctionNode &OldF = *Result.first;
// Impose a total order (by name) on the replacement of functions. This is
// important when operating on more than one module independently to prevent
// cycles of thunks calling each other when the modules are linked together.
//
// First of all, we process strong functions before weak functions.
if ((OldF.getFunc()->isInterposable() && !NewFunction->isInterposable()) ||
(OldF.getFunc()->isInterposable() == NewFunction->isInterposable() &&
OldF.getFunc()->getName() > NewFunction->getName())) {
// Swap the two functions.
Function *F = OldF.getFunc();
replaceFunctionInTree(*Result.first, NewFunction);
NewFunction = F;
assert(OldF.getFunc() != F && "Must have swapped the functions.");
}
DEBUG(dbgs() << " " << OldF.getFunc()->getName()
<< " == " << NewFunction->getName() << '\n');
Function *DeleteF = NewFunction;
mergeTwoFunctions(OldF.getFunc(), DeleteF);
return true;
}
// Remove a function from FnTree. If it was already in FnTree, add
// it to Deferred so that we'll look at it in the next round.
void MergeFunctions::remove(Function *F) {
auto I = FNodesInTree.find(F);
if (I != FNodesInTree.end()) {
DEBUG(dbgs() << "Deferred " << F->getName()<< ".\n");
FnTree.erase(I->second);
// I->second has been invalidated, remove it from the FNodesInTree map to
// preserve the invariant.
FNodesInTree.erase(I);
Deferred.emplace_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);
SmallSet<Value*, 8> Visited;
Visited.insert(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()) {
if (!Visited.insert(UU).second)
Worklist.push_back(UU);
}
}
}
}
}
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