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llvm-project/llvm/lib/Transforms/IPO/GlobalOpt.cpp

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//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass transforms simple global variables that never have their address
// taken. If obviously true, it marks read/write globals as constant, deletes
// variables only stored to, etc.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.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/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/CtorUtils.h"
#include "llvm/Transforms/Utils/Evaluator.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
#include <algorithm>
#include <deque>
using namespace llvm;
#define DEBUG_TYPE "globalopt"
STATISTIC(NumMarked , "Number of globals marked constant");
STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr");
STATISTIC(NumSRA , "Number of aggregate globals broken into scalars");
STATISTIC(NumHeapSRA , "Number of heap objects SRA'd");
STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
STATISTIC(NumDeleted , "Number of globals deleted");
STATISTIC(NumGlobUses , "Number of global uses devirtualized");
STATISTIC(NumLocalized , "Number of globals localized");
STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans");
STATISTIC(NumFastCallFns , "Number of functions converted to fastcc");
STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");
STATISTIC(NumNestRemoved , "Number of nest attributes removed");
STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
namespace {
struct GlobalOpt : public ModulePass {
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
}
static char ID; // Pass identification, replacement for typeid
GlobalOpt() : ModulePass(ID) {
initializeGlobalOptPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override;
private:
bool OptimizeFunctions(Module &M);
bool OptimizeGlobalVars(Module &M);
bool OptimizeGlobalAliases(Module &M);
bool deleteIfDead(GlobalValue &GV);
bool processGlobal(GlobalValue &GV);
bool processInternalGlobal(GlobalVariable *GV, const GlobalStatus &GS);
bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn);
bool isPointerValueDeadOnEntryToFunction(const Function *F,
GlobalValue *GV);
TargetLibraryInfo *TLI;
SmallSet<const Comdat *, 8> NotDiscardableComdats;
};
}
char GlobalOpt::ID = 0;
INITIALIZE_PASS_BEGIN(GlobalOpt, "globalopt",
"Global Variable Optimizer", false, false)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_END(GlobalOpt, "globalopt",
"Global Variable Optimizer", false, false)
ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
/// Is this global variable possibly used by a leak checker as a root? If so,
/// we might not really want to eliminate the stores to it.
static bool isLeakCheckerRoot(GlobalVariable *GV) {
// A global variable is a root if it is a pointer, or could plausibly contain
// a pointer. There are two challenges; one is that we could have a struct
// the has an inner member which is a pointer. We recurse through the type to
// detect these (up to a point). The other is that we may actually be a union
// of a pointer and another type, and so our LLVM type is an integer which
// gets converted into a pointer, or our type is an [i8 x #] with a pointer
// potentially contained here.
if (GV->hasPrivateLinkage())
return false;
SmallVector<Type *, 4> Types;
Types.push_back(GV->getValueType());
unsigned Limit = 20;
do {
Type *Ty = Types.pop_back_val();
switch (Ty->getTypeID()) {
default: break;
case Type::PointerTyID: return true;
case Type::ArrayTyID:
case Type::VectorTyID: {
SequentialType *STy = cast<SequentialType>(Ty);
Types.push_back(STy->getElementType());
break;
}
case Type::StructTyID: {
StructType *STy = cast<StructType>(Ty);
if (STy->isOpaque()) return true;
for (StructType::element_iterator I = STy->element_begin(),
E = STy->element_end(); I != E; ++I) {
Type *InnerTy = *I;
if (isa<PointerType>(InnerTy)) return true;
if (isa<CompositeType>(InnerTy))
Types.push_back(InnerTy);
}
break;
}
}
if (--Limit == 0) return true;
} while (!Types.empty());
return false;
}
/// Given a value that is stored to a global but never read, determine whether
/// it's safe to remove the store and the chain of computation that feeds the
/// store.
static bool IsSafeComputationToRemove(Value *V, const TargetLibraryInfo *TLI) {
do {
if (isa<Constant>(V))
return true;
if (!V->hasOneUse())
return false;
if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) ||
isa<GlobalValue>(V))
return false;
if (isAllocationFn(V, TLI))
return true;
Instruction *I = cast<Instruction>(V);
if (I->mayHaveSideEffects())
return false;
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
if (!GEP->hasAllConstantIndices())
return false;
} else if (I->getNumOperands() != 1) {
return false;
}
V = I->getOperand(0);
} while (1);
}
/// This GV is a pointer root. Loop over all users of the global and clean up
/// any that obviously don't assign the global a value that isn't dynamically
/// allocated.
static bool CleanupPointerRootUsers(GlobalVariable *GV,
const TargetLibraryInfo *TLI) {
// A brief explanation of leak checkers. The goal is to find bugs where
// pointers are forgotten, causing an accumulating growth in memory
// usage over time. The common strategy for leak checkers is to whitelist the
// memory pointed to by globals at exit. This is popular because it also
// solves another problem where the main thread of a C++ program may shut down
// before other threads that are still expecting to use those globals. To
// handle that case, we expect the program may create a singleton and never
// destroy it.
bool Changed = false;
// If Dead[n].first is the only use of a malloc result, we can delete its
// chain of computation and the store to the global in Dead[n].second.
SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
// Constants can't be pointers to dynamically allocated memory.
for (Value::user_iterator UI = GV->user_begin(), E = GV->user_end();
UI != E;) {
User *U = *UI++;
if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
Value *V = SI->getValueOperand();
if (isa<Constant>(V)) {
Changed = true;
SI->eraseFromParent();
} else if (Instruction *I = dyn_cast<Instruction>(V)) {
if (I->hasOneUse())
Dead.push_back(std::make_pair(I, SI));
}
} else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
if (isa<Constant>(MSI->getValue())) {
Changed = true;
MSI->eraseFromParent();
} else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
if (I->hasOneUse())
Dead.push_back(std::make_pair(I, MSI));
}
} else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
if (MemSrc && MemSrc->isConstant()) {
Changed = true;
MTI->eraseFromParent();
} else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) {
if (I->hasOneUse())
Dead.push_back(std::make_pair(I, MTI));
}
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
if (CE->use_empty()) {
CE->destroyConstant();
Changed = true;
}
} else if (Constant *C = dyn_cast<Constant>(U)) {
if (isSafeToDestroyConstant(C)) {
C->destroyConstant();
// This could have invalidated UI, start over from scratch.
Dead.clear();
CleanupPointerRootUsers(GV, TLI);
return true;
}
}
}
for (int i = 0, e = Dead.size(); i != e; ++i) {
if (IsSafeComputationToRemove(Dead[i].first, TLI)) {
Dead[i].second->eraseFromParent();
Instruction *I = Dead[i].first;
do {
if (isAllocationFn(I, TLI))
break;
Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
if (!J)
break;
I->eraseFromParent();
I = J;
} while (1);
I->eraseFromParent();
}
}
return Changed;
}
/// We just marked GV constant. Loop over all users of the global, cleaning up
/// the obvious ones. This is largely just a quick scan over the use list to
/// clean up the easy and obvious cruft. This returns true if it made a change.
static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
const DataLayout &DL,
TargetLibraryInfo *TLI) {
bool Changed = false;
// Note that we need to use a weak value handle for the worklist items. When
// we delete a constant array, we may also be holding pointer to one of its
// elements (or an element of one of its elements if we're dealing with an
// array of arrays) in the worklist.
SmallVector<WeakVH, 8> WorkList(V->user_begin(), V->user_end());
while (!WorkList.empty()) {
Value *UV = WorkList.pop_back_val();
if (!UV)
continue;
User *U = cast<User>(UV);
if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
if (Init) {
// Replace the load with the initializer.
LI->replaceAllUsesWith(Init);
LI->eraseFromParent();
Changed = true;
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
// Store must be unreachable or storing Init into the global.
SI->eraseFromParent();
Changed = true;
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
if (CE->getOpcode() == Instruction::GetElementPtr) {
Constant *SubInit = nullptr;
if (Init)
SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
Changed |= CleanupConstantGlobalUsers(CE, SubInit, DL, TLI);
} else if ((CE->getOpcode() == Instruction::BitCast &&
CE->getType()->isPointerTy()) ||
CE->getOpcode() == Instruction::AddrSpaceCast) {
// Pointer cast, delete any stores and memsets to the global.
Changed |= CleanupConstantGlobalUsers(CE, nullptr, DL, TLI);
}
if (CE->use_empty()) {
CE->destroyConstant();
Changed = true;
}
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
// Do not transform "gepinst (gep constexpr (GV))" here, because forming
// "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
// and will invalidate our notion of what Init is.
Constant *SubInit = nullptr;
if (!isa<ConstantExpr>(GEP->getOperand(0))) {
ConstantExpr *CE = dyn_cast_or_null<ConstantExpr>(
ConstantFoldInstruction(GEP, DL, TLI));
if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
// If the initializer is an all-null value and we have an inbounds GEP,
// we already know what the result of any load from that GEP is.
// TODO: Handle splats.
if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
SubInit = Constant::getNullValue(GEP->getResultElementType());
}
Changed |= CleanupConstantGlobalUsers(GEP, SubInit, DL, TLI);
if (GEP->use_empty()) {
GEP->eraseFromParent();
Changed = true;
}
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
if (MI->getRawDest() == V) {
MI->eraseFromParent();
Changed = true;
}
} else if (Constant *C = dyn_cast<Constant>(U)) {
// If we have a chain of dead constantexprs or other things dangling from
// us, and if they are all dead, nuke them without remorse.
if (isSafeToDestroyConstant(C)) {
C->destroyConstant();
CleanupConstantGlobalUsers(V, Init, DL, TLI);
return true;
}
}
}
return Changed;
}
/// Return true if the specified instruction is a safe user of a derived
/// expression from a global that we want to SROA.
static bool isSafeSROAElementUse(Value *V) {
// We might have a dead and dangling constant hanging off of here.
if (Constant *C = dyn_cast<Constant>(V))
return isSafeToDestroyConstant(C);
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return false;
// Loads are ok.
if (isa<LoadInst>(I)) return true;
// Stores *to* the pointer are ok.
if (StoreInst *SI = dyn_cast<StoreInst>(I))
return SI->getOperand(0) != V;
// Otherwise, it must be a GEP.
GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
if (!GEPI) return false;
if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
!cast<Constant>(GEPI->getOperand(1))->isNullValue())
return false;
for (User *U : GEPI->users())
if (!isSafeSROAElementUse(U))
return false;
return true;
}
/// U is a direct user of the specified global value. Look at it and its uses
/// and decide whether it is safe to SROA this global.
static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
// The user of the global must be a GEP Inst or a ConstantExpr GEP.
if (!isa<GetElementPtrInst>(U) &&
(!isa<ConstantExpr>(U) ||
cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
return false;
// Check to see if this ConstantExpr GEP is SRA'able. In particular, we
// don't like < 3 operand CE's, and we don't like non-constant integer
// indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
// value of C.
if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
!cast<Constant>(U->getOperand(1))->isNullValue() ||
!isa<ConstantInt>(U->getOperand(2)))
return false;
gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
++GEPI; // Skip over the pointer index.
// If this is a use of an array allocation, do a bit more checking for sanity.
if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
uint64_t NumElements = AT->getNumElements();
ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
// Check to make sure that index falls within the array. If not,
// something funny is going on, so we won't do the optimization.
//
if (Idx->getZExtValue() >= NumElements)
return false;
// We cannot scalar repl this level of the array unless any array
// sub-indices are in-range constants. In particular, consider:
// A[0][i]. We cannot know that the user isn't doing invalid things like
// allowing i to index an out-of-range subscript that accesses A[1].
//
// Scalar replacing *just* the outer index of the array is probably not
// going to be a win anyway, so just give up.
for (++GEPI; // Skip array index.
GEPI != E;
++GEPI) {
uint64_t NumElements;
if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
NumElements = SubArrayTy->getNumElements();
else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
NumElements = SubVectorTy->getNumElements();
else {
assert((*GEPI)->isStructTy() &&
"Indexed GEP type is not array, vector, or struct!");
continue;
}
ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
return false;
}
}
for (User *UU : U->users())
if (!isSafeSROAElementUse(UU))
return false;
return true;
}
/// Look at all uses of the global and decide whether it is safe for us to
/// perform this transformation.
static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
for (User *U : GV->users())
if (!IsUserOfGlobalSafeForSRA(U, GV))
return false;
return true;
}
/// Perform scalar replacement of aggregates on the specified global variable.
/// This opens the door for other optimizations by exposing the behavior of the
/// program in a more fine-grained way. We have determined that this
/// transformation is safe already. We return the first global variable we
/// insert so that the caller can reprocess it.
static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) {
// Make sure this global only has simple uses that we can SRA.
if (!GlobalUsersSafeToSRA(GV))
return nullptr;
assert(GV->hasLocalLinkage() && !GV->isConstant());
Constant *Init = GV->getInitializer();
Type *Ty = Init->getType();
std::vector<GlobalVariable*> NewGlobals;
Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
// Get the alignment of the global, either explicit or target-specific.
unsigned StartAlignment = GV->getAlignment();
if (StartAlignment == 0)
StartAlignment = DL.getABITypeAlignment(GV->getType());
if (StructType *STy = dyn_cast<StructType>(Ty)) {
NewGlobals.reserve(STy->getNumElements());
const StructLayout &Layout = *DL.getStructLayout(STy);
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
Constant *In = Init->getAggregateElement(i);
assert(In && "Couldn't get element of initializer?");
GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
GlobalVariable::InternalLinkage,
In, GV->getName()+"."+Twine(i),
GV->getThreadLocalMode(),
GV->getType()->getAddressSpace());
NGV->setExternallyInitialized(GV->isExternallyInitialized());
NGV->copyAttributesFrom(GV);
Globals.push_back(NGV);
NewGlobals.push_back(NGV);
// Calculate the known alignment of the field. If the original aggregate
// had 256 byte alignment for example, something might depend on that:
// propagate info to each field.
uint64_t FieldOffset = Layout.getElementOffset(i);
unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
if (NewAlign > DL.getABITypeAlignment(STy->getElementType(i)))
NGV->setAlignment(NewAlign);
}
} else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
unsigned NumElements = 0;
if (ArrayType *ATy = dyn_cast<ArrayType>(STy))
NumElements = ATy->getNumElements();
else
NumElements = cast<VectorType>(STy)->getNumElements();
if (NumElements > 16 && GV->hasNUsesOrMore(16))
return nullptr; // It's not worth it.
NewGlobals.reserve(NumElements);
uint64_t EltSize = DL.getTypeAllocSize(STy->getElementType());
unsigned EltAlign = DL.getABITypeAlignment(STy->getElementType());
for (unsigned i = 0, e = NumElements; i != e; ++i) {
Constant *In = Init->getAggregateElement(i);
assert(In && "Couldn't get element of initializer?");
GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
GlobalVariable::InternalLinkage,
In, GV->getName()+"."+Twine(i),
GV->getThreadLocalMode(),
GV->getType()->getAddressSpace());
NGV->setExternallyInitialized(GV->isExternallyInitialized());
NGV->copyAttributesFrom(GV);
Globals.push_back(NGV);
NewGlobals.push_back(NGV);
// Calculate the known alignment of the field. If the original aggregate
// had 256 byte alignment for example, something might depend on that:
// propagate info to each field.
unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
if (NewAlign > EltAlign)
NGV->setAlignment(NewAlign);
}
}
if (NewGlobals.empty())
return nullptr;
DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV << "\n");
Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
// Loop over all of the uses of the global, replacing the constantexpr geps,
// with smaller constantexpr geps or direct references.
while (!GV->use_empty()) {
User *GEP = GV->user_back();
assert(((isa<ConstantExpr>(GEP) &&
cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
// Ignore the 1th operand, which has to be zero or else the program is quite
// broken (undefined). Get the 2nd operand, which is the structure or array
// index.
unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
Value *NewPtr = NewGlobals[Val];
Type *NewTy = NewGlobals[Val]->getValueType();
// Form a shorter GEP if needed.
if (GEP->getNumOperands() > 3) {
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
SmallVector<Constant*, 8> Idxs;
Idxs.push_back(NullInt);
for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
Idxs.push_back(CE->getOperand(i));
NewPtr =
ConstantExpr::getGetElementPtr(NewTy, cast<Constant>(NewPtr), Idxs);
} else {
GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
SmallVector<Value*, 8> Idxs;
Idxs.push_back(NullInt);
for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
Idxs.push_back(GEPI->getOperand(i));
NewPtr = GetElementPtrInst::Create(
NewTy, NewPtr, Idxs, GEPI->getName() + "." + Twine(Val), GEPI);
}
}
GEP->replaceAllUsesWith(NewPtr);
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
GEPI->eraseFromParent();
else
cast<ConstantExpr>(GEP)->destroyConstant();
}
// Delete the old global, now that it is dead.
Globals.erase(GV);
++NumSRA;
// Loop over the new globals array deleting any globals that are obviously
// dead. This can arise due to scalarization of a structure or an array that
// has elements that are dead.
unsigned FirstGlobal = 0;
for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
if (NewGlobals[i]->use_empty()) {
Globals.erase(NewGlobals[i]);
if (FirstGlobal == i) ++FirstGlobal;
}
return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : nullptr;
}
/// Return true if all users of the specified value will trap if the value is
/// dynamically null. PHIs keeps track of any phi nodes we've seen to avoid
/// reprocessing them.
static bool AllUsesOfValueWillTrapIfNull(const Value *V,
SmallPtrSetImpl<const PHINode*> &PHIs) {
for (const User *U : V->users())
if (isa<LoadInst>(U)) {
// Will trap.
} else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
if (SI->getOperand(0) == V) {
//cerr << "NONTRAPPING USE: " << *U;
return false; // Storing the value.
}
} else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
if (CI->getCalledValue() != V) {
//cerr << "NONTRAPPING USE: " << *U;
return false; // Not calling the ptr
}
} else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
if (II->getCalledValue() != V) {
//cerr << "NONTRAPPING USE: " << *U;
return false; // Not calling the ptr
}
} else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
} else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
} else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
// If we've already seen this phi node, ignore it, it has already been
// checked.
if (PHIs.insert(PN).second && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
return false;
} else if (isa<ICmpInst>(U) &&
isa<ConstantPointerNull>(U->getOperand(1))) {
// Ignore icmp X, null
} else {
//cerr << "NONTRAPPING USE: " << *U;
return false;
}
return true;
}
/// Return true if all uses of any loads from GV will trap if the loaded value
/// is null. Note that this also permits comparisons of the loaded value
/// against null, as a special case.
static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
for (const User *U : GV->users())
if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
SmallPtrSet<const PHINode*, 8> PHIs;
if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
return false;
} else if (isa<StoreInst>(U)) {
// Ignore stores to the global.
} else {
// We don't know or understand this user, bail out.
//cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
return false;
}
return true;
}
static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
bool Changed = false;
for (auto UI = V->user_begin(), E = V->user_end(); UI != E; ) {
Instruction *I = cast<Instruction>(*UI++);
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
LI->setOperand(0, NewV);
Changed = true;
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
if (SI->getOperand(1) == V) {
SI->setOperand(1, NewV);
Changed = true;
}
} else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
CallSite CS(I);
if (CS.getCalledValue() == V) {
// Calling through the pointer! Turn into a direct call, but be careful
// that the pointer is not also being passed as an argument.
CS.setCalledFunction(NewV);
Changed = true;
bool PassedAsArg = false;
for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
if (CS.getArgument(i) == V) {
PassedAsArg = true;
CS.setArgument(i, NewV);
}
if (PassedAsArg) {
// Being passed as an argument also. Be careful to not invalidate UI!
UI = V->user_begin();
}
}
} else if (CastInst *CI = dyn_cast<CastInst>(I)) {
Changed |= OptimizeAwayTrappingUsesOfValue(CI,
ConstantExpr::getCast(CI->getOpcode(),
NewV, CI->getType()));
if (CI->use_empty()) {
Changed = true;
CI->eraseFromParent();
}
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
// Should handle GEP here.
SmallVector<Constant*, 8> Idxs;
Idxs.reserve(GEPI->getNumOperands()-1);
for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
i != e; ++i)
if (Constant *C = dyn_cast<Constant>(*i))
Idxs.push_back(C);
else
break;
if (Idxs.size() == GEPI->getNumOperands()-1)
Changed |= OptimizeAwayTrappingUsesOfValue(
GEPI, ConstantExpr::getGetElementPtr(nullptr, NewV, Idxs));
if (GEPI->use_empty()) {
Changed = true;
GEPI->eraseFromParent();
}
}
}
return Changed;
}
/// The specified global has only one non-null value stored into it. If there
/// are uses of the loaded value that would trap if the loaded value is
/// dynamically null, then we know that they cannot be reachable with a null
/// optimize away the load.
static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV,
const DataLayout &DL,
TargetLibraryInfo *TLI) {
bool Changed = false;
// Keep track of whether we are able to remove all the uses of the global
// other than the store that defines it.
bool AllNonStoreUsesGone = true;
// Replace all uses of loads with uses of uses of the stored value.
for (Value::user_iterator GUI = GV->user_begin(), E = GV->user_end(); GUI != E;){
User *GlobalUser = *GUI++;
if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
// If we were able to delete all uses of the loads
if (LI->use_empty()) {
LI->eraseFromParent();
Changed = true;
} else {
AllNonStoreUsesGone = false;
}
} else if (isa<StoreInst>(GlobalUser)) {
// Ignore the store that stores "LV" to the global.
assert(GlobalUser->getOperand(1) == GV &&
"Must be storing *to* the global");
} else {
AllNonStoreUsesGone = false;
// If we get here we could have other crazy uses that are transitively
// loaded.
assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) ||
isa<BitCastInst>(GlobalUser) ||
isa<GetElementPtrInst>(GlobalUser)) &&
"Only expect load and stores!");
}
}
if (Changed) {
DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV << "\n");
++NumGlobUses;
}
// If we nuked all of the loads, then none of the stores are needed either,
// nor is the global.
if (AllNonStoreUsesGone) {
if (isLeakCheckerRoot(GV)) {
Changed |= CleanupPointerRootUsers(GV, TLI);
} else {
Changed = true;
CleanupConstantGlobalUsers(GV, nullptr, DL, TLI);
}
if (GV->use_empty()) {
DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
Changed = true;
GV->eraseFromParent();
++NumDeleted;
}
}
return Changed;
}
/// Walk the use list of V, constant folding all of the instructions that are
/// foldable.
static void ConstantPropUsersOf(Value *V, const DataLayout &DL,
TargetLibraryInfo *TLI) {
for (Value::user_iterator UI = V->user_begin(), E = V->user_end(); UI != E; )
if (Instruction *I = dyn_cast<Instruction>(*UI++))
if (Constant *NewC = ConstantFoldInstruction(I, DL, TLI)) {
I->replaceAllUsesWith(NewC);
// Advance UI to the next non-I use to avoid invalidating it!
// Instructions could multiply use V.
while (UI != E && *UI == I)
++UI;
I->eraseFromParent();
}
}
/// This function takes the specified global variable, and transforms the
/// program as if it always contained the result of the specified malloc.
/// Because it is always the result of the specified malloc, there is no reason
/// to actually DO the malloc. Instead, turn the malloc into a global, and any
/// loads of GV as uses of the new global.
static GlobalVariable *
OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, CallInst *CI, Type *AllocTy,
ConstantInt *NElements, const DataLayout &DL,
TargetLibraryInfo *TLI) {
DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n');
Type *GlobalType;
if (NElements->getZExtValue() == 1)
GlobalType = AllocTy;
else
// If we have an array allocation, the global variable is of an array.
GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
// Create the new global variable. The contents of the malloc'd memory is
// undefined, so initialize with an undef value.
GlobalVariable *NewGV = new GlobalVariable(
*GV->getParent(), GlobalType, false, GlobalValue::InternalLinkage,
UndefValue::get(GlobalType), GV->getName() + ".body", nullptr,
GV->getThreadLocalMode());
// If there are bitcast users of the malloc (which is typical, usually we have
// a malloc + bitcast) then replace them with uses of the new global. Update
// other users to use the global as well.
BitCastInst *TheBC = nullptr;
while (!CI->use_empty()) {
Instruction *User = cast<Instruction>(CI->user_back());
if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
if (BCI->getType() == NewGV->getType()) {
BCI->replaceAllUsesWith(NewGV);
BCI->eraseFromParent();
} else {
BCI->setOperand(0, NewGV);
}
} else {
if (!TheBC)
TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
User->replaceUsesOfWith(CI, TheBC);
}
}
Constant *RepValue = NewGV;
if (NewGV->getType() != GV->getValueType())
RepValue = ConstantExpr::getBitCast(RepValue, GV->getValueType());
// If there is a comparison against null, we will insert a global bool to
// keep track of whether the global was initialized yet or not.
GlobalVariable *InitBool =
new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
GlobalValue::InternalLinkage,
ConstantInt::getFalse(GV->getContext()),
GV->getName()+".init", GV->getThreadLocalMode());
bool InitBoolUsed = false;
// Loop over all uses of GV, processing them in turn.
while (!GV->use_empty()) {
if (StoreInst *SI = dyn_cast<StoreInst>(GV->user_back())) {
// The global is initialized when the store to it occurs.
new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
SI->getOrdering(), SI->getSynchScope(), SI);
SI->eraseFromParent();
continue;
}
LoadInst *LI = cast<LoadInst>(GV->user_back());
while (!LI->use_empty()) {
Use &LoadUse = *LI->use_begin();
ICmpInst *ICI = dyn_cast<ICmpInst>(LoadUse.getUser());
if (!ICI) {
LoadUse = RepValue;
continue;
}
// Replace the cmp X, 0 with a use of the bool value.
// Sink the load to where the compare was, if atomic rules allow us to.
Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
LI->getOrdering(), LI->getSynchScope(),
LI->isUnordered() ? (Instruction*)ICI : LI);
InitBoolUsed = true;
switch (ICI->getPredicate()) {
default: llvm_unreachable("Unknown ICmp Predicate!");
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_SLT: // X < null -> always false
LV = ConstantInt::getFalse(GV->getContext());
break;
case ICmpInst::ICMP_ULE:
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_EQ:
LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
break;
case ICmpInst::ICMP_NE:
case ICmpInst::ICMP_UGE:
case ICmpInst::ICMP_SGE:
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_SGT:
break; // no change.
}
ICI->replaceAllUsesWith(LV);
ICI->eraseFromParent();
}
LI->eraseFromParent();
}
// If the initialization boolean was used, insert it, otherwise delete it.
if (!InitBoolUsed) {
while (!InitBool->use_empty()) // Delete initializations
cast<StoreInst>(InitBool->user_back())->eraseFromParent();
delete InitBool;
} else
GV->getParent()->getGlobalList().insert(GV->getIterator(), InitBool);
// Now the GV is dead, nuke it and the malloc..
GV->eraseFromParent();
CI->eraseFromParent();
// To further other optimizations, loop over all users of NewGV and try to
// constant prop them. This will promote GEP instructions with constant
// indices into GEP constant-exprs, which will allow global-opt to hack on it.
ConstantPropUsersOf(NewGV, DL, TLI);
if (RepValue != NewGV)
ConstantPropUsersOf(RepValue, DL, TLI);
return NewGV;
}
/// Scan the use-list of V checking to make sure that there are no complex uses
/// of V. We permit simple things like dereferencing the pointer, but not
/// storing through the address, unless it is to the specified global.
static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
const GlobalVariable *GV,
SmallPtrSetImpl<const PHINode*> &PHIs) {
for (const User *U : V->users()) {
const Instruction *Inst = cast<Instruction>(U);
if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
continue; // Fine, ignore.
}
if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
return false; // Storing the pointer itself... bad.
continue; // Otherwise, storing through it, or storing into GV... fine.
}
// Must index into the array and into the struct.
if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
return false;
continue;
}
if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
// PHIs are ok if all uses are ok. Don't infinitely recurse through PHI
// cycles.
if (PHIs.insert(PN).second)
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
return false;
continue;
}
if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
return false;
continue;
}
return false;
}
return true;
}
/// The Alloc pointer is stored into GV somewhere. Transform all uses of the
/// allocation into loads from the global and uses of the resultant pointer.
/// Further, delete the store into GV. This assumes that these value pass the
/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc,
GlobalVariable *GV) {
while (!Alloc->use_empty()) {
Instruction *U = cast<Instruction>(*Alloc->user_begin());
Instruction *InsertPt = U;
if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
// If this is the store of the allocation into the global, remove it.
if (SI->getOperand(1) == GV) {
SI->eraseFromParent();
continue;
}
} else if (PHINode *PN = dyn_cast<PHINode>(U)) {
// Insert the load in the corresponding predecessor, not right before the
// PHI.
InsertPt = PN->getIncomingBlock(*Alloc->use_begin())->getTerminator();
} else if (isa<BitCastInst>(U)) {
// Must be bitcast between the malloc and store to initialize the global.
ReplaceUsesOfMallocWithGlobal(U, GV);
U->eraseFromParent();
continue;
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
// If this is a "GEP bitcast" and the user is a store to the global, then
// just process it as a bitcast.
if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse())
if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->user_back()))
if (SI->getOperand(1) == GV) {
// Must be bitcast GEP between the malloc and store to initialize
// the global.
ReplaceUsesOfMallocWithGlobal(GEPI, GV);
GEPI->eraseFromParent();
continue;
}
}
// Insert a load from the global, and use it instead of the malloc.
Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt);
U->replaceUsesOfWith(Alloc, NL);
}
}
/// Verify that all uses of V (a load, or a phi of a load) are simple enough to
/// perform heap SRA on. This permits GEP's that index through the array and
/// struct field, icmps of null, and PHIs.
static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
SmallPtrSetImpl<const PHINode*> &LoadUsingPHIs,
SmallPtrSetImpl<const PHINode*> &LoadUsingPHIsPerLoad) {
// We permit two users of the load: setcc comparing against the null
// pointer, and a getelementptr of a specific form.
for (const User *U : V->users()) {
const Instruction *UI = cast<Instruction>(U);
// Comparison against null is ok.
if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UI)) {
if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
return false;
continue;
}
// getelementptr is also ok, but only a simple form.
if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(UI)) {
// Must index into the array and into the struct.
if (GEPI->getNumOperands() < 3)
return false;
// Otherwise the GEP is ok.
continue;
}
if (const PHINode *PN = dyn_cast<PHINode>(UI)) {
if (!LoadUsingPHIsPerLoad.insert(PN).second)
// This means some phi nodes are dependent on each other.
// Avoid infinite looping!
return false;
if (!LoadUsingPHIs.insert(PN).second)
// If we have already analyzed this PHI, then it is safe.
continue;
// Make sure all uses of the PHI are simple enough to transform.
if (!LoadUsesSimpleEnoughForHeapSRA(PN,
LoadUsingPHIs, LoadUsingPHIsPerLoad))
return false;
continue;
}
// Otherwise we don't know what this is, not ok.
return false;
}
return true;
}
/// If all users of values loaded from GV are simple enough to perform HeapSRA,
/// return true.
static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
Instruction *StoredVal) {
SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
for (const User *U : GV->users())
if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
LoadUsingPHIsPerLoad))
return false;
LoadUsingPHIsPerLoad.clear();
}
// If we reach here, we know that all uses of the loads and transitive uses
// (through PHI nodes) are simple enough to transform. However, we don't know
// that all inputs the to the PHI nodes are in the same equivalence sets.
// Check to verify that all operands of the PHIs are either PHIS that can be
// transformed, loads from GV, or MI itself.
for (const PHINode *PN : LoadUsingPHIs) {
for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
Value *InVal = PN->getIncomingValue(op);
// PHI of the stored value itself is ok.
if (InVal == StoredVal) continue;
if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
// One of the PHIs in our set is (optimistically) ok.
if (LoadUsingPHIs.count(InPN))
continue;
return false;
}
// Load from GV is ok.
if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
if (LI->getOperand(0) == GV)
continue;
// UNDEF? NULL?
// Anything else is rejected.
return false;
}
}
return true;
}
static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
if (FieldNo >= FieldVals.size())
FieldVals.resize(FieldNo+1);
// If we already have this value, just reuse the previously scalarized
// version.
if (Value *FieldVal = FieldVals[FieldNo])
return FieldVal;
// Depending on what instruction this is, we have several cases.
Value *Result;
if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
// This is a scalarized version of the load from the global. Just create
// a new Load of the scalarized global.
Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
InsertedScalarizedValues,
PHIsToRewrite),
LI->getName()+".f"+Twine(FieldNo), LI);
} else {
PHINode *PN = cast<PHINode>(V);
// PN's type is pointer to struct. Make a new PHI of pointer to struct
// field.
PointerType *PTy = cast<PointerType>(PN->getType());
StructType *ST = cast<StructType>(PTy->getElementType());
unsigned AS = PTy->getAddressSpace();
PHINode *NewPN =
PHINode::Create(PointerType::get(ST->getElementType(FieldNo), AS),
PN->getNumIncomingValues(),
PN->getName()+".f"+Twine(FieldNo), PN);
Result = NewPN;
PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
}
return FieldVals[FieldNo] = Result;
}
/// Given a load instruction and a value derived from the load, rewrite the
/// derived value to use the HeapSRoA'd load.
static void RewriteHeapSROALoadUser(Instruction *LoadUser,
DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
// If this is a comparison against null, handle it.
if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
// If we have a setcc of the loaded pointer, we can use a setcc of any
// field.
Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
InsertedScalarizedValues, PHIsToRewrite);
Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
Constant::getNullValue(NPtr->getType()),
SCI->getName());
SCI->replaceAllUsesWith(New);
SCI->eraseFromParent();
return;
}
// Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
&& "Unexpected GEPI!");
// Load the pointer for this field.
unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
InsertedScalarizedValues, PHIsToRewrite);
// Create the new GEP idx vector.
SmallVector<Value*, 8> GEPIdx;
GEPIdx.push_back(GEPI->getOperand(1));
GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
Value *NGEPI = GetElementPtrInst::Create(GEPI->getResultElementType(), NewPtr, GEPIdx,
GEPI->getName(), GEPI);
GEPI->replaceAllUsesWith(NGEPI);
GEPI->eraseFromParent();
return;
}
// Recursively transform the users of PHI nodes. This will lazily create the
// PHIs that are needed for individual elements. Keep track of what PHIs we
// see in InsertedScalarizedValues so that we don't get infinite loops (very
// antisocial). If the PHI is already in InsertedScalarizedValues, it has
// already been seen first by another load, so its uses have already been
// processed.
PHINode *PN = cast<PHINode>(LoadUser);
if (!InsertedScalarizedValues.insert(std::make_pair(PN,
std::vector<Value*>())).second)
return;
// If this is the first time we've seen this PHI, recursively process all
// users.
for (auto UI = PN->user_begin(), E = PN->user_end(); UI != E;) {
Instruction *User = cast<Instruction>(*UI++);
RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
}
}
/// We are performing Heap SRoA on a global. Ptr is a value loaded from the
/// global. Eliminate all uses of Ptr, making them use FieldGlobals instead.
/// All uses of loaded values satisfy AllGlobalLoadUsesSimpleEnoughForHeapSRA.
static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
for (auto UI = Load->user_begin(), E = Load->user_end(); UI != E;) {
Instruction *User = cast<Instruction>(*UI++);
RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
}
if (Load->use_empty()) {
Load->eraseFromParent();
InsertedScalarizedValues.erase(Load);
}
}
/// CI is an allocation of an array of structures. Break it up into multiple
/// allocations of arrays of the fields.
static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
Value *NElems, const DataLayout &DL,
const TargetLibraryInfo *TLI) {
DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n');
Type *MAT = getMallocAllocatedType(CI, TLI);
StructType *STy = cast<StructType>(MAT);
// There is guaranteed to be at least one use of the malloc (storing
// it into GV). If there are other uses, change them to be uses of
// the global to simplify later code. This also deletes the store
// into GV.
ReplaceUsesOfMallocWithGlobal(CI, GV);
// Okay, at this point, there are no users of the malloc. Insert N
// new mallocs at the same place as CI, and N globals.
std::vector<Value*> FieldGlobals;
std::vector<Value*> FieldMallocs;
unsigned AS = GV->getType()->getPointerAddressSpace();
for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
Type *FieldTy = STy->getElementType(FieldNo);
PointerType *PFieldTy = PointerType::get(FieldTy, AS);
GlobalVariable *NGV = new GlobalVariable(
*GV->getParent(), PFieldTy, false, GlobalValue::InternalLinkage,
Constant::getNullValue(PFieldTy), GV->getName() + ".f" + Twine(FieldNo),
nullptr, GV->getThreadLocalMode());
NGV->copyAttributesFrom(GV);
FieldGlobals.push_back(NGV);
unsigned TypeSize = DL.getTypeAllocSize(FieldTy);
if (StructType *ST = dyn_cast<StructType>(FieldTy))
TypeSize = DL.getStructLayout(ST)->getSizeInBytes();
Type *IntPtrTy = DL.getIntPtrType(CI->getType());
Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
ConstantInt::get(IntPtrTy, TypeSize),
NElems, nullptr,
CI->getName() + ".f" + Twine(FieldNo));
FieldMallocs.push_back(NMI);
new StoreInst(NMI, NGV, CI);
}
// The tricky aspect of this transformation is handling the case when malloc
// fails. In the original code, malloc failing would set the result pointer
// of malloc to null. In this case, some mallocs could succeed and others
// could fail. As such, we emit code that looks like this:
// F0 = malloc(field0)
// F1 = malloc(field1)
// F2 = malloc(field2)
// if (F0 == 0 || F1 == 0 || F2 == 0) {
// if (F0) { free(F0); F0 = 0; }
// if (F1) { free(F1); F1 = 0; }
// if (F2) { free(F2); F2 = 0; }
// }
// The malloc can also fail if its argument is too large.
Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
ConstantZero, "isneg");
for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
Constant::getNullValue(FieldMallocs[i]->getType()),
"isnull");
RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
}
// Split the basic block at the old malloc.
BasicBlock *OrigBB = CI->getParent();
BasicBlock *ContBB =
OrigBB->splitBasicBlock(CI->getIterator(), "malloc_cont");
// Create the block to check the first condition. Put all these blocks at the
// end of the function as they are unlikely to be executed.
BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
"malloc_ret_null",
OrigBB->getParent());
// Remove the uncond branch from OrigBB to ContBB, turning it into a cond
// branch on RunningOr.
OrigBB->getTerminator()->eraseFromParent();
BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
// Within the NullPtrBlock, we need to emit a comparison and branch for each
// pointer, because some may be null while others are not.
for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
Constant::getNullValue(GVVal->getType()));
BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
OrigBB->getParent());
BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
OrigBB->getParent());
Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
Cmp, NullPtrBlock);
// Fill in FreeBlock.
CallInst::CreateFree(GVVal, BI);
new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
FreeBlock);
BranchInst::Create(NextBlock, FreeBlock);
NullPtrBlock = NextBlock;
}
BranchInst::Create(ContBB, NullPtrBlock);
// CI is no longer needed, remove it.
CI->eraseFromParent();
/// As we process loads, if we can't immediately update all uses of the load,
/// keep track of what scalarized loads are inserted for a given load.
DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues;
InsertedScalarizedValues[GV] = FieldGlobals;
std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite;
// Okay, the malloc site is completely handled. All of the uses of GV are now
// loads, and all uses of those loads are simple. Rewrite them to use loads
// of the per-field globals instead.
for (auto UI = GV->user_begin(), E = GV->user_end(); UI != E;) {
Instruction *User = cast<Instruction>(*UI++);
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
continue;
}
// Must be a store of null.
StoreInst *SI = cast<StoreInst>(User);
assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
"Unexpected heap-sra user!");
// Insert a store of null into each global.
for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
Type *ValTy = cast<GlobalValue>(FieldGlobals[i])->getValueType();
Constant *Null = Constant::getNullValue(ValTy);
new StoreInst(Null, FieldGlobals[i], SI);
}
// Erase the original store.
SI->eraseFromParent();
}
// While we have PHIs that are interesting to rewrite, do it.
while (!PHIsToRewrite.empty()) {
PHINode *PN = PHIsToRewrite.back().first;
unsigned FieldNo = PHIsToRewrite.back().second;
PHIsToRewrite.pop_back();
PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
// Add all the incoming values. This can materialize more phis.
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *InVal = PN->getIncomingValue(i);
InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
PHIsToRewrite);
FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
}
}
// Drop all inter-phi links and any loads that made it this far.
for (DenseMap<Value*, std::vector<Value*> >::iterator
I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
I != E; ++I) {
if (PHINode *PN = dyn_cast<PHINode>(I->first))
PN->dropAllReferences();
else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
LI->dropAllReferences();
}
// Delete all the phis and loads now that inter-references are dead.
for (DenseMap<Value*, std::vector<Value*> >::iterator
I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
I != E; ++I) {
if (PHINode *PN = dyn_cast<PHINode>(I->first))
PN->eraseFromParent();
else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
LI->eraseFromParent();
}
// The old global is now dead, remove it.
GV->eraseFromParent();
++NumHeapSRA;
return cast<GlobalVariable>(FieldGlobals[0]);
}
/// This function is called when we see a pointer global variable with a single
/// value stored it that is a malloc or cast of malloc.
static bool tryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, CallInst *CI,
Type *AllocTy,
AtomicOrdering Ordering,
const DataLayout &DL,
TargetLibraryInfo *TLI) {
// If this is a malloc of an abstract type, don't touch it.
if (!AllocTy->isSized())
return false;
// We can't optimize this global unless all uses of it are *known* to be
// of the malloc value, not of the null initializer value (consider a use
// that compares the global's value against zero to see if the malloc has
// been reached). To do this, we check to see if all uses of the global
// would trap if the global were null: this proves that they must all
// happen after the malloc.
if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
return false;
// We can't optimize this if the malloc itself is used in a complex way,
// for example, being stored into multiple globals. This allows the
// malloc to be stored into the specified global, loaded icmp'd, and
// GEP'd. These are all things we could transform to using the global
// for.
SmallPtrSet<const PHINode*, 8> PHIs;
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
return false;
// If we have a global that is only initialized with a fixed size malloc,
// transform the program to use global memory instead of malloc'd memory.
// This eliminates dynamic allocation, avoids an indirection accessing the
// data, and exposes the resultant global to further GlobalOpt.
// We cannot optimize the malloc if we cannot determine malloc array size.
Value *NElems = getMallocArraySize(CI, DL, TLI, true);
if (!NElems)
return false;
if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
// Restrict this transformation to only working on small allocations
// (2048 bytes currently), as we don't want to introduce a 16M global or
// something.
if (NElements->getZExtValue() * DL.getTypeAllocSize(AllocTy) < 2048) {
OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, DL, TLI);
return true;
}
// If the allocation is an array of structures, consider transforming this
// into multiple malloc'd arrays, one for each field. This is basically
// SRoA for malloc'd memory.
if (Ordering != NotAtomic)
return false;
// If this is an allocation of a fixed size array of structs, analyze as a
// variable size array. malloc [100 x struct],1 -> malloc struct, 100
if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
AllocTy = AT->getElementType();
StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
if (!AllocSTy)
return false;
// This the structure has an unreasonable number of fields, leave it
// alone.
if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
// If this is a fixed size array, transform the Malloc to be an alloc of
// structs. malloc [100 x struct],1 -> malloc struct, 100
if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) {
Type *IntPtrTy = DL.getIntPtrType(CI->getType());
unsigned TypeSize = DL.getStructLayout(AllocSTy)->getSizeInBytes();
Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy,
AllocSize, NumElements,
nullptr, CI->getName());
Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
CI->replaceAllUsesWith(Cast);
CI->eraseFromParent();
if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc))
CI = cast<CallInst>(BCI->getOperand(0));
else
CI = cast<CallInst>(Malloc);
}
PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, DL, TLI, true), DL,
TLI);
return true;
}
return false;
}
// Try to optimize globals based on the knowledge that only one value (besides
// its initializer) is ever stored to the global.
static bool optimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
AtomicOrdering Ordering,
const DataLayout &DL,
TargetLibraryInfo *TLI) {
// Ignore no-op GEPs and bitcasts.
StoredOnceVal = StoredOnceVal->stripPointerCasts();
// If we are dealing with a pointer global that is initialized to null and
// only has one (non-null) value stored into it, then we can optimize any
// users of the loaded value (often calls and loads) that would trap if the
// value was null.
if (GV->getInitializer()->getType()->isPointerTy() &&
GV->getInitializer()->isNullValue()) {
if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
if (GV->getInitializer()->getType() != SOVC->getType())
SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
// Optimize away any trapping uses of the loaded value.
if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, DL, TLI))
return true;
} else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) {
Type *MallocType = getMallocAllocatedType(CI, TLI);
if (MallocType && tryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType,
Ordering, DL, TLI))
return true;
}
}
return false;
}
/// At this point, we have learned that the only two values ever stored into GV
/// are its initializer and OtherVal. See if we can shrink the global into a
/// boolean and select between the two values whenever it is used. This exposes
/// the values to other scalar optimizations.
static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
Type *GVElType = GV->getValueType();
// If GVElType is already i1, it is already shrunk. If the type of the GV is
// an FP value, pointer or vector, don't do this optimization because a select
// between them is very expensive and unlikely to lead to later
// simplification. In these cases, we typically end up with "cond ? v1 : v2"
// where v1 and v2 both require constant pool loads, a big loss.
if (GVElType == Type::getInt1Ty(GV->getContext()) ||
GVElType->isFloatingPointTy() ||
GVElType->isPointerTy() || GVElType->isVectorTy())
return false;
// Walk the use list of the global seeing if all the uses are load or store.
// If there is anything else, bail out.
for (User *U : GV->users())
if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
return false;
DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV << "\n");
// Create the new global, initializing it to false.
GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
false,
GlobalValue::InternalLinkage,
ConstantInt::getFalse(GV->getContext()),
GV->getName()+".b",
GV->getThreadLocalMode(),
GV->getType()->getAddressSpace());
NewGV->copyAttributesFrom(GV);
GV->getParent()->getGlobalList().insert(GV->getIterator(), NewGV);
Constant *InitVal = GV->getInitializer();
assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
"No reason to shrink to bool!");
// If initialized to zero and storing one into the global, we can use a cast
// instead of a select to synthesize the desired value.
bool IsOneZero = false;
if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
IsOneZero = InitVal->isNullValue() && CI->isOne();
while (!GV->use_empty()) {
Instruction *UI = cast<Instruction>(GV->user_back());
if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
// Change the store into a boolean store.
bool StoringOther = SI->getOperand(0) == OtherVal;
// Only do this if we weren't storing a loaded value.
Value *StoreVal;
if (StoringOther || SI->getOperand(0) == InitVal) {
StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
StoringOther);
} else {
// Otherwise, we are storing a previously loaded copy. To do this,
// change the copy from copying the original value to just copying the
// bool.
Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
// If we've already replaced the input, StoredVal will be a cast or
// select instruction. If not, it will be a load of the original
// global.
if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
assert(LI->getOperand(0) == GV && "Not a copy!");
// Insert a new load, to preserve the saved value.
StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
LI->getOrdering(), LI->getSynchScope(), LI);
} else {
assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
"This is not a form that we understand!");
StoreVal = StoredVal->getOperand(0);
assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
}
}
new StoreInst(StoreVal, NewGV, false, 0,
SI->getOrdering(), SI->getSynchScope(), SI);
} else {
// Change the load into a load of bool then a select.
LoadInst *LI = cast<LoadInst>(UI);
LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
LI->getOrdering(), LI->getSynchScope(), LI);
Value *NSI;
if (IsOneZero)
NSI = new ZExtInst(NLI, LI->getType(), "", LI);
else
NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
NSI->takeName(LI);
LI->replaceAllUsesWith(NSI);
}
UI->eraseFromParent();
}
// Retain the name of the old global variable. People who are debugging their
// programs may expect these variables to be named the same.
NewGV->takeName(GV);
GV->eraseFromParent();
return true;
}
bool GlobalOpt::deleteIfDead(GlobalValue &GV) {
GV.removeDeadConstantUsers();
if (!GV.isDiscardableIfUnused())
return false;
if (const Comdat *C = GV.getComdat())
if (!GV.hasLocalLinkage() && NotDiscardableComdats.count(C))
return false;
bool Dead;
if (auto *F = dyn_cast<Function>(&GV))
Dead = F->isDefTriviallyDead();
else
Dead = GV.use_empty();
if (!Dead)
return false;
DEBUG(dbgs() << "GLOBAL DEAD: " << GV << "\n");
GV.eraseFromParent();
++NumDeleted;
return true;
}
/// Analyze the specified global variable and optimize it if possible. If we
/// make a change, return true.
bool GlobalOpt::processGlobal(GlobalValue &GV) {
// Do more involved optimizations if the global is internal.
if (!GV.hasLocalLinkage())
return false;
GlobalStatus GS;
if (GlobalStatus::analyzeGlobal(&GV, GS))
return false;
bool Changed = false;
if (!GS.IsCompared && !GV.hasUnnamedAddr()) {
GV.setUnnamedAddr(true);
NumUnnamed++;
Changed = true;
}
auto *GVar = dyn_cast<GlobalVariable>(&GV);
if (!GVar)
return Changed;
if (GVar->isConstant() || !GVar->hasInitializer())
return Changed;
return processInternalGlobal(GVar, GS) || Changed;
}
bool GlobalOpt::isPointerValueDeadOnEntryToFunction(const Function *F, GlobalValue *GV) {
// Find all uses of GV. We expect them all to be in F, and if we can't
// identify any of the uses we bail out.
//
// On each of these uses, identify if the memory that GV points to is
// used/required/live at the start of the function. If it is not, for example
// if the first thing the function does is store to the GV, the GV can
// possibly be demoted.
//
// We don't do an exhaustive search for memory operations - simply look
// through bitcasts as they're quite common and benign.
const DataLayout &DL = GV->getParent()->getDataLayout();
SmallVector<LoadInst *, 4> Loads;
SmallVector<StoreInst *, 4> Stores;
for (auto *U : GV->users()) {
if (Operator::getOpcode(U) == Instruction::BitCast) {
for (auto *UU : U->users()) {
if (auto *LI = dyn_cast<LoadInst>(UU))
Loads.push_back(LI);
else if (auto *SI = dyn_cast<StoreInst>(UU))
Stores.push_back(SI);
else
return false;
}
continue;
}
Instruction *I = dyn_cast<Instruction>(U);
if (!I)
return false;
assert(I->getParent()->getParent() == F);
if (auto *LI = dyn_cast<LoadInst>(I))
Loads.push_back(LI);
else if (auto *SI = dyn_cast<StoreInst>(I))
Stores.push_back(SI);
else
return false;
}
// We have identified all uses of GV into loads and stores. Now check if all
// of them are known not to depend on the value of the global at the function
// entry point. We do this by ensuring that every load is dominated by at
// least one store.
auto &DT = getAnalysis<DominatorTreeWrapperPass>(*const_cast<Function *>(F))
.getDomTree();
// The below check is quadratic. Check we're not going to do too many tests.
// FIXME: Even though this will always have worst-case quadratic time, we
// could put effort into minimizing the average time by putting stores that
// have been shown to dominate at least one load at the beginning of the
// Stores array, making subsequent dominance checks more likely to succeed
// early.
//
// The threshold here is fairly large because global->local demotion is a
// very powerful optimization should it fire.
const unsigned Threshold = 100;
if (Loads.size() * Stores.size() > Threshold)
return false;
for (auto *L : Loads) {
auto *LTy = L->getType();
if (!std::any_of(Stores.begin(), Stores.end(), [&](StoreInst *S) {
auto *STy = S->getValueOperand()->getType();
// The load is only dominated by the store if DomTree says so
// and the number of bits loaded in L is less than or equal to
// the number of bits stored in S.
return DT.dominates(S, L) &&
DL.getTypeStoreSize(LTy) <= DL.getTypeStoreSize(STy);
}))
return false;
}
// All loads have known dependences inside F, so the global can be localized.
return true;
}
/// C may have non-instruction users. Can all of those users be turned into
/// instructions?
static bool allNonInstructionUsersCanBeMadeInstructions(Constant *C) {
// We don't do this exhaustively. The most common pattern that we really need
// to care about is a constant GEP or constant bitcast - so just looking
// through one single ConstantExpr.
//
// The set of constants that this function returns true for must be able to be
// handled by makeAllConstantUsesInstructions.
for (auto *U : C->users()) {
if (isa<Instruction>(U))
continue;
if (!isa<ConstantExpr>(U))
// Non instruction, non-constantexpr user; cannot convert this.
return false;
for (auto *UU : U->users())
if (!isa<Instruction>(UU))
// A constantexpr used by another constant. We don't try and recurse any
// further but just bail out at this point.
return false;
}
return true;
}
/// C may have non-instruction users, and
/// allNonInstructionUsersCanBeMadeInstructions has returned true. Convert the
/// non-instruction users to instructions.
static void makeAllConstantUsesInstructions(Constant *C) {
SmallVector<ConstantExpr*,4> Users;
for (auto *U : C->users()) {
if (isa<ConstantExpr>(U))
Users.push_back(cast<ConstantExpr>(U));
else
// We should never get here; allNonInstructionUsersCanBeMadeInstructions
// should not have returned true for C.
assert(
isa<Instruction>(U) &&
"Can't transform non-constantexpr non-instruction to instruction!");
}
SmallVector<Value*,4> UUsers;
for (auto *U : Users) {
UUsers.clear();
for (auto *UU : U->users())
UUsers.push_back(UU);
for (auto *UU : UUsers) {
Instruction *UI = cast<Instruction>(UU);
Instruction *NewU = U->getAsInstruction();
NewU->insertBefore(UI);
UI->replaceUsesOfWith(U, NewU);
}
U->dropAllReferences();
}
}
/// Analyze the specified global variable and optimize
/// it if possible. If we make a change, return true.
bool GlobalOpt::processInternalGlobal(GlobalVariable *GV,
const GlobalStatus &GS) {
auto &DL = GV->getParent()->getDataLayout();
// If this is a first class global and has only one accessing function and
// this function is non-recursive, we replace the global with a local alloca
// in this function.
//
// NOTE: It doesn't make sense to promote non-single-value types since we
// are just replacing static memory to stack memory.
//
// If the global is in different address space, don't bring it to stack.
if (!GS.HasMultipleAccessingFunctions &&
GS.AccessingFunction &&
GV->getValueType()->isSingleValueType() &&
GV->getType()->getAddressSpace() == 0 &&
!GV->isExternallyInitialized() &&
allNonInstructionUsersCanBeMadeInstructions(GV) &&
GS.AccessingFunction->doesNotRecurse() &&
isPointerValueDeadOnEntryToFunction(GS.AccessingFunction, GV) ) {
DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV << "\n");
Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction
->getEntryBlock().begin());
Type *ElemTy = GV->getValueType();
// FIXME: Pass Global's alignment when globals have alignment
AllocaInst *Alloca = new AllocaInst(ElemTy, nullptr,
GV->getName(), &FirstI);
if (!isa<UndefValue>(GV->getInitializer()))
new StoreInst(GV->getInitializer(), Alloca, &FirstI);
makeAllConstantUsesInstructions(GV);
GV->replaceAllUsesWith(Alloca);
GV->eraseFromParent();
++NumLocalized;
return true;
}
// If the global is never loaded (but may be stored to), it is dead.
// Delete it now.
if (!GS.IsLoaded) {
DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV << "\n");
bool Changed;
if (isLeakCheckerRoot(GV)) {
// Delete any constant stores to the global.
Changed = CleanupPointerRootUsers(GV, TLI);
} else {
// Delete any stores we can find to the global. We may not be able to
// make it completely dead though.
Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
}
// If the global is dead now, delete it.
if (GV->use_empty()) {
GV->eraseFromParent();
++NumDeleted;
Changed = true;
}
return Changed;
} else if (GS.StoredType <= GlobalStatus::InitializerStored) {
DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n");
GV->setConstant(true);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
// If the global is dead now, just nuke it.
if (GV->use_empty()) {
DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
<< "all users and delete global!\n");
GV->eraseFromParent();
++NumDeleted;
}
++NumMarked;
return true;
} else if (!GV->getInitializer()->getType()->isSingleValueType()) {
const DataLayout &DL = GV->getParent()->getDataLayout();
if (SRAGlobal(GV, DL))
return true;
} else if (GS.StoredType == GlobalStatus::StoredOnce && GS.StoredOnceValue) {
// If the initial value for the global was an undef value, and if only
// one other value was stored into it, we can just change the
// initializer to be the stored value, then delete all stores to the
// global. This allows us to mark it constant.
if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
if (isa<UndefValue>(GV->getInitializer())) {
// Change the initial value here.
GV->setInitializer(SOVConstant);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI);
if (GV->use_empty()) {
DEBUG(dbgs() << " *** Substituting initializer allowed us to "
<< "simplify all users and delete global!\n");
GV->eraseFromParent();
++NumDeleted;
}
++NumSubstitute;
return true;
}
// Try to optimize globals based on the knowledge that only one value
// (besides its initializer) is ever stored to the global.
if (optimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, DL, TLI))
return true;
// Otherwise, if the global was not a boolean, we can shrink it to be a
// boolean.
if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) {
if (GS.Ordering == NotAtomic) {
if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
++NumShrunkToBool;
return true;
}
}
}
}
return false;
}
/// Walk all of the direct calls of the specified function, changing them to
/// FastCC.
static void ChangeCalleesToFastCall(Function *F) {
for (User *U : F->users()) {
if (isa<BlockAddress>(U))
continue;
CallSite CS(cast<Instruction>(U));
CS.setCallingConv(CallingConv::Fast);
}
}
static AttributeSet StripNest(LLVMContext &C, const AttributeSet &Attrs) {
for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
unsigned Index = Attrs.getSlotIndex(i);
if (!Attrs.getSlotAttributes(i).hasAttribute(Index, Attribute::Nest))
continue;
// There can be only one.
return Attrs.removeAttribute(C, Index, Attribute::Nest);
}
return Attrs;
}
static void RemoveNestAttribute(Function *F) {
F->setAttributes(StripNest(F->getContext(), F->getAttributes()));
for (User *U : F->users()) {
if (isa<BlockAddress>(U))
continue;
CallSite CS(cast<Instruction>(U));
CS.setAttributes(StripNest(F->getContext(), CS.getAttributes()));
}
}
/// Return true if this is a calling convention that we'd like to change. The
/// idea here is that we don't want to mess with the convention if the user
/// explicitly requested something with performance implications like coldcc,
/// GHC, or anyregcc.
static bool isProfitableToMakeFastCC(Function *F) {
CallingConv::ID CC = F->getCallingConv();
// FIXME: Is it worth transforming x86_stdcallcc and x86_fastcallcc?
return CC == CallingConv::C || CC == CallingConv::X86_ThisCall;
}
bool GlobalOpt::OptimizeFunctions(Module &M) {
bool Changed = false;
// Optimize functions.
for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
Function *F = &*FI++;
// Functions without names cannot be referenced outside this module.
if (!F->hasName() && !F->isDeclaration() && !F->hasLocalLinkage())
F->setLinkage(GlobalValue::InternalLinkage);
if (deleteIfDead(*F)) {
Changed = true;
continue;
}
Changed |= processGlobal(*F);
if (!F->hasLocalLinkage())
continue;
if (isProfitableToMakeFastCC(F) && !F->isVarArg() &&
!F->hasAddressTaken()) {
// If this function has a calling convention worth changing, is not a
// varargs function, and is only called directly, promote it to use the
// Fast calling convention.
F->setCallingConv(CallingConv::Fast);
ChangeCalleesToFastCall(F);
++NumFastCallFns;
Changed = true;
}
if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
!F->hasAddressTaken()) {
// The function is not used by a trampoline intrinsic, so it is safe
// to remove the 'nest' attribute.
RemoveNestAttribute(F);
++NumNestRemoved;
Changed = true;
}
}
return Changed;
}
bool GlobalOpt::OptimizeGlobalVars(Module &M) {
bool Changed = false;
for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
GVI != E; ) {
GlobalVariable *GV = &*GVI++;
// Global variables without names cannot be referenced outside this module.
if (!GV->hasName() && !GV->isDeclaration() && !GV->hasLocalLinkage())
GV->setLinkage(GlobalValue::InternalLinkage);
// Simplify the initializer.
if (GV->hasInitializer())
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
auto &DL = M.getDataLayout();
Constant *New = ConstantFoldConstantExpression(CE, DL, TLI);
if (New && New != CE)
GV->setInitializer(New);
}
if (deleteIfDead(*GV)) {
Changed = true;
continue;
}
Changed |= processGlobal(*GV);
}
return Changed;
}
/// Evaluate a piece of a constantexpr store into a global initializer. This
/// returns 'Init' modified to reflect 'Val' stored into it. At this point, the
/// GEP operands of Addr [0, OpNo) have been stepped into.
static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
ConstantExpr *Addr, unsigned OpNo) {
// Base case of the recursion.
if (OpNo == Addr->getNumOperands()) {
assert(Val->getType() == Init->getType() && "Type mismatch!");
return Val;
}
SmallVector<Constant*, 32> Elts;
if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
// Break up the constant into its elements.
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
Elts.push_back(Init->getAggregateElement(i));
// Replace the element that we are supposed to.
ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
unsigned Idx = CU->getZExtValue();
assert(Idx < STy->getNumElements() && "Struct index out of range!");
Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
// Return the modified struct.
return ConstantStruct::get(STy, Elts);
}
ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
SequentialType *InitTy = cast<SequentialType>(Init->getType());
uint64_t NumElts;
if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
NumElts = ATy->getNumElements();
else
NumElts = InitTy->getVectorNumElements();
// Break up the array into elements.
for (uint64_t i = 0, e = NumElts; i != e; ++i)
Elts.push_back(Init->getAggregateElement(i));
assert(CI->getZExtValue() < NumElts);
Elts[CI->getZExtValue()] =
EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
if (Init->getType()->isArrayTy())
return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
return ConstantVector::get(Elts);
}
/// We have decided that Addr (which satisfies the predicate
/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen.
static void CommitValueTo(Constant *Val, Constant *Addr) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
assert(GV->hasInitializer());
GV->setInitializer(Val);
return;
}
ConstantExpr *CE = cast<ConstantExpr>(Addr);
GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
}
/// Evaluate static constructors in the function, if we can. Return true if we
/// can, false otherwise.
static bool EvaluateStaticConstructor(Function *F, const DataLayout &DL,
const TargetLibraryInfo *TLI) {
// Call the function.
Evaluator Eval(DL, TLI);
Constant *RetValDummy;
bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy,
SmallVector<Constant*, 0>());
if (EvalSuccess) {
++NumCtorsEvaluated;
// We succeeded at evaluation: commit the result.
DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
<< F->getName() << "' to " << Eval.getMutatedMemory().size()
<< " stores.\n");
for (DenseMap<Constant*, Constant*>::const_iterator I =
Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end();
I != E; ++I)
CommitValueTo(I->second, I->first);
for (GlobalVariable *GV : Eval.getInvariants())
GV->setConstant(true);
}
return EvalSuccess;
}
static int compareNames(Constant *const *A, Constant *const *B) {
Value *AStripped = (*A)->stripPointerCastsNoFollowAliases();
Value *BStripped = (*B)->stripPointerCastsNoFollowAliases();
return AStripped->getName().compare(BStripped->getName());
}
static void setUsedInitializer(GlobalVariable &V,
const SmallPtrSet<GlobalValue *, 8> &Init) {
if (Init.empty()) {
V.eraseFromParent();
return;
}
// Type of pointer to the array of pointers.
PointerType *Int8PtrTy = Type::getInt8PtrTy(V.getContext(), 0);
SmallVector<llvm::Constant *, 8> UsedArray;
for (GlobalValue *GV : Init) {
Constant *Cast
= ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, Int8PtrTy);
UsedArray.push_back(Cast);
}
// Sort to get deterministic order.
array_pod_sort(UsedArray.begin(), UsedArray.end(), compareNames);
ArrayType *ATy = ArrayType::get(Int8PtrTy, UsedArray.size());
Module *M = V.getParent();
V.removeFromParent();
GlobalVariable *NV =
new GlobalVariable(*M, ATy, false, llvm::GlobalValue::AppendingLinkage,
llvm::ConstantArray::get(ATy, UsedArray), "");
NV->takeName(&V);
NV->setSection("llvm.metadata");
delete &V;
}
namespace {
/// An easy to access representation of llvm.used and llvm.compiler.used.
class LLVMUsed {
SmallPtrSet<GlobalValue *, 8> Used;
SmallPtrSet<GlobalValue *, 8> CompilerUsed;
GlobalVariable *UsedV;
GlobalVariable *CompilerUsedV;
public:
LLVMUsed(Module &M) {
UsedV = collectUsedGlobalVariables(M, Used, false);
CompilerUsedV = collectUsedGlobalVariables(M, CompilerUsed, true);
}
typedef SmallPtrSet<GlobalValue *, 8>::iterator iterator;
typedef iterator_range<iterator> used_iterator_range;
iterator usedBegin() { return Used.begin(); }
iterator usedEnd() { return Used.end(); }
used_iterator_range used() {
return used_iterator_range(usedBegin(), usedEnd());
}
iterator compilerUsedBegin() { return CompilerUsed.begin(); }
iterator compilerUsedEnd() { return CompilerUsed.end(); }
used_iterator_range compilerUsed() {
return used_iterator_range(compilerUsedBegin(), compilerUsedEnd());
}
bool usedCount(GlobalValue *GV) const { return Used.count(GV); }
bool compilerUsedCount(GlobalValue *GV) const {
return CompilerUsed.count(GV);
}
bool usedErase(GlobalValue *GV) { return Used.erase(GV); }
bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(GV); }
bool usedInsert(GlobalValue *GV) { return Used.insert(GV).second; }
bool compilerUsedInsert(GlobalValue *GV) {
return CompilerUsed.insert(GV).second;
}
void syncVariablesAndSets() {
if (UsedV)
setUsedInitializer(*UsedV, Used);
if (CompilerUsedV)
setUsedInitializer(*CompilerUsedV, CompilerUsed);
}
};
}
static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) {
if (GA.use_empty()) // No use at all.
return false;
assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) &&
"We should have removed the duplicated "
"element from llvm.compiler.used");
if (!GA.hasOneUse())
// Strictly more than one use. So at least one is not in llvm.used and
// llvm.compiler.used.
return true;
// Exactly one use. Check if it is in llvm.used or llvm.compiler.used.
return !U.usedCount(&GA) && !U.compilerUsedCount(&GA);
}
static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V,
const LLVMUsed &U) {
unsigned N = 2;
assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) &&
"We should have removed the duplicated "
"element from llvm.compiler.used");
if (U.usedCount(&V) || U.compilerUsedCount(&V))
++N;
return V.hasNUsesOrMore(N);
}
static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) {
if (!GA.hasLocalLinkage())
return true;
return U.usedCount(&GA) || U.compilerUsedCount(&GA);
}
static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
bool &RenameTarget) {
RenameTarget = false;
bool Ret = false;
if (hasUseOtherThanLLVMUsed(GA, U))
Ret = true;
// If the alias is externally visible, we may still be able to simplify it.
if (!mayHaveOtherReferences(GA, U))
return Ret;
// If the aliasee has internal linkage, give it the name and linkage
// of the alias, and delete the alias. This turns:
// define internal ... @f(...)
// @a = alias ... @f
// into:
// define ... @a(...)
Constant *Aliasee = GA.getAliasee();
GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
if (!Target->hasLocalLinkage())
return Ret;
// Do not perform the transform if multiple aliases potentially target the
// aliasee. This check also ensures that it is safe to replace the section
// and other attributes of the aliasee with those of the alias.
if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U))
return Ret;
RenameTarget = true;
return true;
}
bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
bool Changed = false;
LLVMUsed Used(M);
for (GlobalValue *GV : Used.used())
Used.compilerUsedErase(GV);
for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
I != E;) {
GlobalAlias *J = &*I++;
// Aliases without names cannot be referenced outside this module.
if (!J->hasName() && !J->isDeclaration() && !J->hasLocalLinkage())
J->setLinkage(GlobalValue::InternalLinkage);
if (deleteIfDead(*J)) {
Changed = true;
continue;
}
// If the aliasee may change at link time, nothing can be done - bail out.
if (J->mayBeOverridden())
continue;
Constant *Aliasee = J->getAliasee();
GlobalValue *Target = dyn_cast<GlobalValue>(Aliasee->stripPointerCasts());
// We can't trivially replace the alias with the aliasee if the aliasee is
// non-trivial in some way.
// TODO: Try to handle non-zero GEPs of local aliasees.
if (!Target)
continue;
Target->removeDeadConstantUsers();
// Make all users of the alias use the aliasee instead.
bool RenameTarget;
if (!hasUsesToReplace(*J, Used, RenameTarget))
continue;
J->replaceAllUsesWith(ConstantExpr::getBitCast(Aliasee, J->getType()));
++NumAliasesResolved;
Changed = true;
if (RenameTarget) {
// Give the aliasee the name, linkage and other attributes of the alias.
Target->takeName(&*J);
Target->setLinkage(J->getLinkage());
Target->setVisibility(J->getVisibility());
Target->setDLLStorageClass(J->getDLLStorageClass());
if (Used.usedErase(&*J))
Used.usedInsert(Target);
if (Used.compilerUsedErase(&*J))
Used.compilerUsedInsert(Target);
} else if (mayHaveOtherReferences(*J, Used))
continue;
// Delete the alias.
M.getAliasList().erase(J);
++NumAliasesRemoved;
Changed = true;
}
Used.syncVariablesAndSets();
return Changed;
}
static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) {
if (!TLI->has(LibFunc::cxa_atexit))
return nullptr;
Function *Fn = M.getFunction(TLI->getName(LibFunc::cxa_atexit));
if (!Fn)
return nullptr;
FunctionType *FTy = Fn->getFunctionType();
// Checking that the function has the right return type, the right number of
// parameters and that they all have pointer types should be enough.
if (!FTy->getReturnType()->isIntegerTy() ||
FTy->getNumParams() != 3 ||
!FTy->getParamType(0)->isPointerTy() ||
!FTy->getParamType(1)->isPointerTy() ||
!FTy->getParamType(2)->isPointerTy())
return nullptr;
return Fn;
}
/// Returns whether the given function is an empty C++ destructor and can
/// therefore be eliminated.
/// Note that we assume that other optimization passes have already simplified
/// the code so we only look for a function with a single basic block, where
/// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and
/// other side-effect free instructions.
static bool cxxDtorIsEmpty(const Function &Fn,
SmallPtrSet<const Function *, 8> &CalledFunctions) {
// FIXME: We could eliminate C++ destructors if they're readonly/readnone and
// nounwind, but that doesn't seem worth doing.
if (Fn.isDeclaration())
return false;
if (++Fn.begin() != Fn.end())
return false;
const BasicBlock &EntryBlock = Fn.getEntryBlock();
for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
I != E; ++I) {
if (const CallInst *CI = dyn_cast<CallInst>(I)) {
// Ignore debug intrinsics.
if (isa<DbgInfoIntrinsic>(CI))
continue;
const Function *CalledFn = CI->getCalledFunction();
if (!CalledFn)
return false;
SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
// Don't treat recursive functions as empty.
if (!NewCalledFunctions.insert(CalledFn).second)
return false;
if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
return false;
} else if (isa<ReturnInst>(*I))
return true; // We're done.
else if (I->mayHaveSideEffects())
return false; // Destructor with side effects, bail.
}
return false;
}
bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
/// Itanium C++ ABI p3.3.5:
///
/// After constructing a global (or local static) object, that will require
/// destruction on exit, a termination function is registered as follows:
///
/// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
///
/// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
/// call f(p) when DSO d is unloaded, before all such termination calls
/// registered before this one. It returns zero if registration is
/// successful, nonzero on failure.
// This pass will look for calls to __cxa_atexit where the function is trivial
// and remove them.
bool Changed = false;
for (auto I = CXAAtExitFn->user_begin(), E = CXAAtExitFn->user_end();
I != E;) {
// We're only interested in calls. Theoretically, we could handle invoke
// instructions as well, but neither llvm-gcc nor clang generate invokes
// to __cxa_atexit.
CallInst *CI = dyn_cast<CallInst>(*I++);
if (!CI)
continue;
Function *DtorFn =
dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
if (!DtorFn)
continue;
SmallPtrSet<const Function *, 8> CalledFunctions;
if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
continue;
// Just remove the call.
CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
CI->eraseFromParent();
++NumCXXDtorsRemoved;
Changed |= true;
}
return Changed;
}
bool GlobalOpt::runOnModule(Module &M) {
bool Changed = false;
auto &DL = M.getDataLayout();
TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
NotDiscardableComdats.clear();
for (const GlobalVariable &GV : M.globals())
if (const Comdat *C = GV.getComdat())
if (!GV.isDiscardableIfUnused() || !GV.use_empty())
NotDiscardableComdats.insert(C);
for (Function &F : M)
if (const Comdat *C = F.getComdat())
if (!F.isDefTriviallyDead())
NotDiscardableComdats.insert(C);
for (GlobalAlias &GA : M.aliases())
if (const Comdat *C = GA.getComdat())
if (!GA.isDiscardableIfUnused() || !GA.use_empty())
NotDiscardableComdats.insert(C);
// Delete functions that are trivially dead, ccc -> fastcc
LocalChange |= OptimizeFunctions(M);
// Optimize global_ctors list.
LocalChange |= optimizeGlobalCtorsList(M, [&](Function *F) {
return EvaluateStaticConstructor(F, DL, TLI);
});
// Optimize non-address-taken globals.
LocalChange |= OptimizeGlobalVars(M);
// Resolve aliases, when possible.
LocalChange |= OptimizeGlobalAliases(M);
// Try to remove trivial global destructors if they are not removed
// already.
Function *CXAAtExitFn = FindCXAAtExit(M, TLI);
if (CXAAtExitFn)
LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
Changed |= LocalChange;
}
// TODO: Move all global ctors functions to the end of the module for code
// layout.
return Changed;
}
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