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llvm / llvm / refs/heads/release_26 / . / 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "globalopt"
#include "llvm/Transforms/IPO.h"
#include "llvm/CallingConv.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
using namespace llvm;
STATISTIC(NumMarked , "Number of globals marked constant");
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(NumFnDeleted , "Number of functions 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");
namespace {
struct VISIBILITY_HIDDEN GlobalOpt : public ModulePass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
}
static char ID; // Pass identification, replacement for typeid
GlobalOpt() : ModulePass(&ID) {}
bool runOnModule(Module &M);
private:
GlobalVariable *FindGlobalCtors(Module &M);
bool OptimizeFunctions(Module &M);
bool OptimizeGlobalVars(Module &M);
bool OptimizeGlobalAliases(Module &M);
bool OptimizeGlobalCtorsList(GlobalVariable *&GCL);
bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
};
}
char GlobalOpt::ID = 0;
static RegisterPass<GlobalOpt> X("globalopt", "Global Variable Optimizer");
ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
namespace {
/// GlobalStatus - As we analyze each global, keep track of some information
/// about it. If we find out that the address of the global is taken, none of
/// this info will be accurate.
struct VISIBILITY_HIDDEN GlobalStatus {
/// isLoaded - True if the global is ever loaded. If the global isn't ever
/// loaded it can be deleted.
bool isLoaded;
/// StoredType - Keep track of what stores to the global look like.
///
enum StoredType {
/// NotStored - There is no store to this global. It can thus be marked
/// constant.
NotStored,
/// isInitializerStored - This global is stored to, but the only thing
/// stored is the constant it was initialized with. This is only tracked
/// for scalar globals.
isInitializerStored,
/// isStoredOnce - This global is stored to, but only its initializer and
/// one other value is ever stored to it. If this global isStoredOnce, we
/// track the value stored to it in StoredOnceValue below. This is only
/// tracked for scalar globals.
isStoredOnce,
/// isStored - This global is stored to by multiple values or something else
/// that we cannot track.
isStored
} StoredType;
/// StoredOnceValue - If only one value (besides the initializer constant) is
/// ever stored to this global, keep track of what value it is.
Value *StoredOnceValue;
/// AccessingFunction/HasMultipleAccessingFunctions - These start out
/// null/false. When the first accessing function is noticed, it is recorded.
/// When a second different accessing function is noticed,
/// HasMultipleAccessingFunctions is set to true.
Function *AccessingFunction;
bool HasMultipleAccessingFunctions;
/// HasNonInstructionUser - Set to true if this global has a user that is not
/// an instruction (e.g. a constant expr or GV initializer).
bool HasNonInstructionUser;
/// HasPHIUser - Set to true if this global has a user that is a PHI node.
bool HasPHIUser;
GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0),
AccessingFunction(0), HasMultipleAccessingFunctions(false),
HasNonInstructionUser(false), HasPHIUser(false) {}
};
}
// SafeToDestroyConstant - It is safe to destroy a constant iff it is only used
// by constants itself. Note that constants cannot be cyclic, so this test is
// pretty easy to implement recursively.
//
static bool SafeToDestroyConstant(Constant *C) {
if (isa<GlobalValue>(C)) return false;
for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI)
if (Constant *CU = dyn_cast<Constant>(*UI)) {
if (!SafeToDestroyConstant(CU)) return false;
} else
return false;
return true;
}
/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
/// structure. If the global has its address taken, return true to indicate we
/// can't do anything with it.
///
static bool AnalyzeGlobal(Value *V, GlobalStatus &GS,
SmallPtrSet<PHINode*, 16> &PHIUsers) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
GS.HasNonInstructionUser = true;
if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
} else if (Instruction *I = dyn_cast<Instruction>(*UI)) {
if (!GS.HasMultipleAccessingFunctions) {
Function *F = I->getParent()->getParent();
if (GS.AccessingFunction == 0)
GS.AccessingFunction = F;
else if (GS.AccessingFunction != F)
GS.HasMultipleAccessingFunctions = true;
}
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
GS.isLoaded = true;
if (LI->isVolatile()) return true; // Don't hack on volatile loads.
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
// Don't allow a store OF the address, only stores TO the address.
if (SI->getOperand(0) == V) return true;
if (SI->isVolatile()) return true; // Don't hack on volatile stores.
// If this is a direct store to the global (i.e., the global is a scalar
// value, not an aggregate), keep more specific information about
// stores.
if (GS.StoredType != GlobalStatus::isStored) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))){
Value *StoredVal = SI->getOperand(0);
if (StoredVal == GV->getInitializer()) {
if (GS.StoredType < GlobalStatus::isInitializerStored)
GS.StoredType = GlobalStatus::isInitializerStored;
} else if (isa<LoadInst>(StoredVal) &&
cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
// G = G
if (GS.StoredType < GlobalStatus::isInitializerStored)
GS.StoredType = GlobalStatus::isInitializerStored;
} else if (GS.StoredType < GlobalStatus::isStoredOnce) {
GS.StoredType = GlobalStatus::isStoredOnce;
GS.StoredOnceValue = StoredVal;
} else if (GS.StoredType == GlobalStatus::isStoredOnce &&
GS.StoredOnceValue == StoredVal) {
// noop.
} else {
GS.StoredType = GlobalStatus::isStored;
}
} else {
GS.StoredType = GlobalStatus::isStored;
}
}
} else if (isa<GetElementPtrInst>(I)) {
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
} else if (isa<SelectInst>(I)) {
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
} else if (PHINode *PN = dyn_cast<PHINode>(I)) {
// PHI nodes we can check just like select or GEP instructions, but we
// have to be careful about infinite recursion.
if (PHIUsers.insert(PN)) // Not already visited.
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
GS.HasPHIUser = true;
} else if (isa<CmpInst>(I)) {
} else if (isa<MemTransferInst>(I)) {
if (I->getOperand(1) == V)
GS.StoredType = GlobalStatus::isStored;
if (I->getOperand(2) == V)
GS.isLoaded = true;
} else if (isa<MemSetInst>(I)) {
assert(I->getOperand(1) == V && "Memset only takes one pointer!");
GS.StoredType = GlobalStatus::isStored;
} else {
return true; // Any other non-load instruction might take address!
}
} else if (Constant *C = dyn_cast<Constant>(*UI)) {
GS.HasNonInstructionUser = true;
// We might have a dead and dangling constant hanging off of here.
if (!SafeToDestroyConstant(C))
return true;
} else {
GS.HasNonInstructionUser = true;
// Otherwise must be some other user.
return true;
}
return false;
}
static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx,
LLVMContext &Context) {
ConstantInt *CI = dyn_cast<ConstantInt>(Idx);
if (!CI) return 0;
unsigned IdxV = CI->getZExtValue();
if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) {
if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV);
} else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) {
if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV);
} else if (ConstantVector *CP = dyn_cast<ConstantVector>(Agg)) {
if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV);
} else if (isa<ConstantAggregateZero>(Agg)) {
if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) {
if (IdxV < STy->getNumElements())
return Constant::getNullValue(STy->getElementType(IdxV));
} else if (const SequentialType *STy =
dyn_cast<SequentialType>(Agg->getType())) {
return Constant::getNullValue(STy->getElementType());
}
} else if (isa<UndefValue>(Agg)) {
if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) {
if (IdxV < STy->getNumElements())
return UndefValue::get(STy->getElementType(IdxV));
} else if (const SequentialType *STy =
dyn_cast<SequentialType>(Agg->getType())) {
return UndefValue::get(STy->getElementType());
}
}
return 0;
}
/// CleanupConstantGlobalUsers - 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,
LLVMContext &Context) {
bool Changed = false;
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) {
User *U = *UI++;
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 = 0;
if (Init)
SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE, Context);
Changed |= CleanupConstantGlobalUsers(CE, SubInit, Context);
} else if (CE->getOpcode() == Instruction::BitCast &&
isa<PointerType>(CE->getType())) {
// Pointer cast, delete any stores and memsets to the global.
Changed |= CleanupConstantGlobalUsers(CE, 0, Context);
}
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 = 0;
if (!isa<ConstantExpr>(GEP->getOperand(0))) {
ConstantExpr *CE =
dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, Context));
if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE, Context);
}
Changed |= CleanupConstantGlobalUsers(GEP, SubInit, Context);
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 (SafeToDestroyConstant(C)) {
C->destroyConstant();
// This could have invalidated UI, start over from scratch.
CleanupConstantGlobalUsers(V, Init, Context);
return true;
}
}
}
return Changed;
}
/// isSafeSROAElementUse - 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 SafeToDestroyConstant(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 == 0) return false;
if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
!cast<Constant>(GEPI->getOperand(1))->isNullValue())
return false;
for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end();
I != E; ++I)
if (!isSafeSROAElementUse(*I))
return false;
return true;
}
/// IsUserOfGlobalSafeForSRA - 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 (const 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 (const ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
NumElements = SubArrayTy->getNumElements();
else if (const VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
NumElements = SubVectorTy->getNumElements();
else {
assert(isa<StructType>(*GEPI) &&
"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 (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I)
if (!isSafeSROAElementUse(*I))
return false;
return true;
}
/// GlobalUsersSafeToSRA - 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 (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
UI != E; ++UI) {
if (!IsUserOfGlobalSafeForSRA(*UI, GV))
return false;
}
return true;
}
/// SRAGlobal - 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 TargetData &TD,
LLVMContext &Context) {
// Make sure this global only has simple uses that we can SRA.
if (!GlobalUsersSafeToSRA(GV))
return 0;
assert(GV->hasLocalLinkage() && !GV->isConstant());
Constant *Init = GV->getInitializer();
const 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 = TD.getABITypeAlignment(GV->getType());
if (const StructType *STy = dyn_cast<StructType>(Ty)) {
NewGlobals.reserve(STy->getNumElements());
const StructLayout &Layout = *TD.getStructLayout(STy);
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
Constant *In = getAggregateConstantElement(Init,
ConstantInt::get(Type::getInt32Ty(Context), i),
Context);
assert(In && "Couldn't get element of initializer?");
GlobalVariable *NGV = new GlobalVariable(Context,
STy->getElementType(i), false,
GlobalVariable::InternalLinkage,
In, GV->getName()+"."+Twine(i),
GV->isThreadLocal(),
GV->getType()->getAddressSpace());
Globals.insert(GV, 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 > TD.getABITypeAlignment(STy->getElementType(i)))
NGV->setAlignment(NewAlign);
}
} else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
unsigned NumElements = 0;
if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
NumElements = ATy->getNumElements();
else
NumElements = cast<VectorType>(STy)->getNumElements();
if (NumElements > 16 && GV->hasNUsesOrMore(16))
return 0; // It's not worth it.
NewGlobals.reserve(NumElements);
uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType());
unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType());
for (unsigned i = 0, e = NumElements; i != e; ++i) {
Constant *In = getAggregateConstantElement(Init,
ConstantInt::get(Type::getInt32Ty(Context), i),
Context);
assert(In && "Couldn't get element of initializer?");
GlobalVariable *NGV = new GlobalVariable(Context,
STy->getElementType(), false,
GlobalVariable::InternalLinkage,
In, GV->getName()+"."+Twine(i),
GV->isThreadLocal(),
GV->getType()->getAddressSpace());
Globals.insert(GV, 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 0;
DOUT << "PERFORMING GLOBAL SRA ON: " << *GV;
Constant *NullInt = Constant::getNullValue(Type::getInt32Ty(Context));
// 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->use_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];
// 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(cast<Constant>(NewPtr),
&Idxs[0], Idxs.size());
} 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(NewPtr, Idxs.begin(), Idxs.end(),
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] : 0;
}
/// AllUsesOfValueWillTrapIfNull - 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(Value *V,
SmallPtrSet<PHINode*, 8> &PHIs) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
if (isa<LoadInst>(*UI)) {
// Will trap.
} else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
if (SI->getOperand(0) == V) {
//cerr << "NONTRAPPING USE: " << **UI;
return false; // Storing the value.
}
} else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
if (CI->getOperand(0) != V) {
//cerr << "NONTRAPPING USE: " << **UI;
return false; // Not calling the ptr
}
} else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
if (II->getOperand(0) != V) {
//cerr << "NONTRAPPING USE: " << **UI;
return false; // Not calling the ptr
}
} else if (BitCastInst *CI = dyn_cast<BitCastInst>(*UI)) {
if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) {
if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
} else if (PHINode *PN = dyn_cast<PHINode>(*UI)) {
// If we've already seen this phi node, ignore it, it has already been
// checked.
if (PHIs.insert(PN))
return AllUsesOfValueWillTrapIfNull(PN, PHIs);
} else if (isa<ICmpInst>(*UI) &&
isa<ConstantPointerNull>(UI->getOperand(1))) {
// Ignore setcc X, null
} else {
//cerr << "NONTRAPPING USE: " << **UI;
return false;
}
return true;
}
/// AllUsesOfLoadedValueWillTrapIfNull - 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(GlobalVariable *GV) {
for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI!=E; ++UI)
if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
SmallPtrSet<PHINode*, 8> PHIs;
if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
return false;
} else if (isa<StoreInst>(*UI)) {
// Ignore stores to the global.
} else {
// We don't know or understand this user, bail out.
//cerr << "UNKNOWN USER OF GLOBAL!: " << **UI;
return false;
}
return true;
}
static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV,
LLVMContext &Context) {
bool Changed = false;
for (Value::use_iterator UI = V->use_begin(), E = V->use_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)) {
if (I->getOperand(0) == V) {
// Calling through the pointer! Turn into a direct call, but be careful
// that the pointer is not also being passed as an argument.
I->setOperand(0, NewV);
Changed = true;
bool PassedAsArg = false;
for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i)
if (I->getOperand(i) == V) {
PassedAsArg = true;
I->setOperand(i, NewV);
}
if (PassedAsArg) {
// Being passed as an argument also. Be careful to not invalidate UI!
UI = V->use_begin();
}
}
} else if (CastInst *CI = dyn_cast<CastInst>(I)) {
Changed |= OptimizeAwayTrappingUsesOfValue(CI,
ConstantExpr::getCast(CI->getOpcode(),
NewV, CI->getType()), Context);
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(NewV, &Idxs[0],
Idxs.size()), Context);
if (GEPI->use_empty()) {
Changed = true;
GEPI->eraseFromParent();
}
}
}
return Changed;
}
/// OptimizeAwayTrappingUsesOfLoads - 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,
LLVMContext &Context) {
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::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){
User *GlobalUser = *GUI++;
if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV, Context);
// 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)) && "Only expect load and stores!");
}
}
if (Changed) {
DOUT << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV;
++NumGlobUses;
}
// If we nuked all of the loads, then none of the stores are needed either,
// nor is the global.
if (AllNonStoreUsesGone) {
DOUT << " *** GLOBAL NOW DEAD!\n";
CleanupConstantGlobalUsers(GV, 0, Context);
if (GV->use_empty()) {
GV->eraseFromParent();
++NumDeleted;
}
Changed = true;
}
return Changed;
}
/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
/// instructions that are foldable.
static void ConstantPropUsersOf(Value *V, LLVMContext &Context) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; )
if (Instruction *I = dyn_cast<Instruction>(*UI++))
if (Constant *NewC = ConstantFoldInstruction(I, Context)) {
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();
}
}
/// OptimizeGlobalAddressOfMalloc - 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,
MallocInst *MI,
LLVMContext &Context) {
DOUT << "PROMOTING MALLOC GLOBAL: " << *GV << " MALLOC = " << *MI;
ConstantInt *NElements = cast<ConstantInt>(MI->getArraySize());
if (NElements->getZExtValue() != 1) {
// If we have an array allocation, transform it to a single element
// allocation to make the code below simpler.
Type *NewTy = ArrayType::get(MI->getAllocatedType(),
NElements->getZExtValue());
MallocInst *NewMI =
new MallocInst(NewTy, Constant::getNullValue(Type::getInt32Ty(Context)),
MI->getAlignment(), MI->getName(), MI);
Value* Indices[2];
Indices[0] = Indices[1] = Constant::getNullValue(Type::getInt32Ty(Context));
Value *NewGEP = GetElementPtrInst::Create(NewMI, Indices, Indices + 2,
NewMI->getName()+".el0", MI);
MI->replaceAllUsesWith(NewGEP);
MI->eraseFromParent();
MI = NewMI;
}
// Create the new global variable. The contents of the malloc'd memory is
// undefined, so initialize with an undef value.
// FIXME: This new global should have the alignment returned by malloc. Code
// could depend on malloc returning large alignment (on the mac, 16 bytes) but
// this would only guarantee some lower alignment.
Constant *Init = UndefValue::get(MI->getAllocatedType());
GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(),
MI->getAllocatedType(), false,
GlobalValue::InternalLinkage, Init,
GV->getName()+".body",
GV,
GV->isThreadLocal());
// Anything that used the malloc now uses the global directly.
MI->replaceAllUsesWith(NewGV);
Constant *RepValue = NewGV;
if (NewGV->getType() != GV->getType()->getElementType())
RepValue = ConstantExpr::getBitCast(RepValue,
GV->getType()->getElementType());
// 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(Context, Type::getInt1Ty(Context), false,
GlobalValue::InternalLinkage,
ConstantInt::getFalse(Context), GV->getName()+".init",
GV->isThreadLocal());
bool InitBoolUsed = false;
// Loop over all uses of GV, processing them in turn.
std::vector<StoreInst*> Stores;
while (!GV->use_empty())
if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) {
while (!LI->use_empty()) {
Use &LoadUse = LI->use_begin().getUse();
if (!isa<ICmpInst>(LoadUse.getUser()))
LoadUse = RepValue;
else {
ICmpInst *CI = cast<ICmpInst>(LoadUse.getUser());
// Replace the cmp X, 0 with a use of the bool value.
Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", CI);
InitBoolUsed = true;
switch (CI->getPredicate()) {
default: llvm_unreachable("Unknown ICmp Predicate!");
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_SLT:
LV = ConstantInt::getFalse(Context); // X < null -> always false
break;
case ICmpInst::ICMP_ULE:
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_EQ:
LV = BinaryOperator::CreateNot(LV, "notinit", CI);
break;
case ICmpInst::ICMP_NE:
case ICmpInst::ICMP_UGE:
case ICmpInst::ICMP_SGE:
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_SGT:
break; // no change.
}
CI->replaceAllUsesWith(LV);
CI->eraseFromParent();
}
}
LI->eraseFromParent();
} else {
StoreInst *SI = cast<StoreInst>(GV->use_back());
// The global is initialized when the store to it occurs.
new StoreInst(ConstantInt::getTrue(Context), InitBool, SI);
SI->eraseFromParent();
}
// If the initialization boolean was used, insert it, otherwise delete it.
if (!InitBoolUsed) {
while (!InitBool->use_empty()) // Delete initializations
cast<Instruction>(InitBool->use_back())->eraseFromParent();
delete InitBool;
} else
GV->getParent()->getGlobalList().insert(GV, InitBool);
// Now the GV is dead, nuke it and the malloc.
GV->eraseFromParent();
MI->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, Context);
if (RepValue != NewGV)
ConstantPropUsersOf(RepValue, Context);
return NewGV;
}
/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - 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(Instruction *V,
GlobalVariable *GV,
SmallPtrSet<PHINode*, 8> &PHIs) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
Instruction *Inst = cast<Instruction>(*UI);
if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
continue; // Fine, ignore.
}
if (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.
}
if (isa<GetElementPtrInst>(Inst)) {
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
return false;
continue;
}
if (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))
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
return false;
continue;
}
if (BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
return false;
continue;
}
return false;
}
return true;
}
/// ReplaceUsesOfMallocWithGlobal - 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->use_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->use_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);
}
}
/// LoadUsesSimpleEnoughForHeapSRA - 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(Value *V,
SmallPtrSet<PHINode*, 32> &LoadUsingPHIs,
SmallPtrSet<PHINode*, 32> &LoadUsingPHIsPerLoad) {
// We permit two users of the load: setcc comparing against the null
// pointer, and a getelementptr of a specific form.
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
Instruction *User = cast<Instruction>(*UI);
// Comparison against null is ok.
if (ICmpInst *ICI = dyn_cast<ICmpInst>(User)) {
if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
return false;
continue;
}
// getelementptr is also ok, but only a simple form.
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
// Must index into the array and into the struct.
if (GEPI->getNumOperands() < 3)
return false;
// Otherwise the GEP is ok.
continue;
}
if (PHINode *PN = dyn_cast<PHINode>(User)) {
if (!LoadUsingPHIsPerLoad.insert(PN))
// This means some phi nodes are dependent on each other.
// Avoid infinite looping!
return false;
if (!LoadUsingPHIs.insert(PN))
// 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;
}
/// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from
/// GV are simple enough to perform HeapSRA, return true.
static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(GlobalVariable *GV,
MallocInst *MI) {
SmallPtrSet<PHINode*, 32> LoadUsingPHIs;
SmallPtrSet<PHINode*, 32> LoadUsingPHIsPerLoad;
for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;
++UI)
if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
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 (SmallPtrSet<PHINode*, 32>::iterator I = LoadUsingPHIs.begin(),
E = LoadUsingPHIs.end(); I != E; ++I) {
PHINode *PN = *I;
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 == MI) continue;
if (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 (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,
LLVMContext &Context) {
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, Context),
LI->getName()+".f"+Twine(FieldNo), LI);
} else if (PHINode *PN = dyn_cast<PHINode>(V)) {
// PN's type is pointer to struct. Make a new PHI of pointer to struct
// field.
const StructType *ST =
cast<StructType>(cast<PointerType>(PN->getType())->getElementType());
Result =
PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)),
PN->getName()+".f"+Twine(FieldNo), PN);
PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
} else {
llvm_unreachable("Unknown usable value");
Result = 0;
}
return FieldVals[FieldNo] = Result;
}
/// RewriteHeapSROALoadUser - 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,
LLVMContext &Context) {
// 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,
Context);
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,
Context);
// 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(NewPtr,
GEPIdx.begin(), GEPIdx.end(),
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);
bool Inserted;
DenseMap<Value*, std::vector<Value*> >::iterator InsertPos;
tie(InsertPos, Inserted) =
InsertedScalarizedValues.insert(std::make_pair(PN, std::vector<Value*>()));
if (!Inserted) return;
// If this is the first time we've seen this PHI, recursively process all
// users.
for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) {
Instruction *User = cast<Instruction>(*UI++);
RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite,
Context);
}
}
/// RewriteUsesOfLoadForHeapSRoA - 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,
LLVMContext &Context) {
for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end();
UI != E; ) {
Instruction *User = cast<Instruction>(*UI++);
RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite,
Context);
}
if (Load->use_empty()) {
Load->eraseFromParent();
InsertedScalarizedValues.erase(Load);
}
}
/// PerformHeapAllocSRoA - MI is an allocation of an array of structures. Break
/// it up into multiple allocations of arrays of the fields.
static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, MallocInst *MI,
LLVMContext &Context){
DOUT << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *MI;
const StructType *STy = cast<StructType>(MI->getAllocatedType());
// 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(MI, GV);
// Okay, at this point, there are no users of the malloc. Insert N
// new mallocs at the same place as MI, and N globals.
std::vector<Value*> FieldGlobals;
std::vector<MallocInst*> FieldMallocs;
for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
const Type *FieldTy = STy->getElementType(FieldNo);
const Type *PFieldTy = PointerType::getUnqual(FieldTy);
GlobalVariable *NGV =
new GlobalVariable(*GV->getParent(),
PFieldTy, false, GlobalValue::InternalLinkage,
Constant::getNullValue(PFieldTy),
GV->getName() + ".f" + Twine(FieldNo), GV,
GV->isThreadLocal());
FieldGlobals.push_back(NGV);
MallocInst *NMI = new MallocInst(FieldTy, MI->getArraySize(),
MI->getName() + ".f" + Twine(FieldNo), MI);
FieldMallocs.push_back(NMI);
new StoreInst(NMI, NGV, MI);
}
// 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; }
// }
Value *RunningOr = 0;
for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
Value *Cond = new ICmpInst(MI, ICmpInst::ICMP_EQ, FieldMallocs[i],
Constant::getNullValue(FieldMallocs[i]->getType()),
"isnull");
if (!RunningOr)
RunningOr = Cond; // First seteq
else
RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", MI);
}
// Split the basic block at the old malloc.
BasicBlock *OrigBB = MI->getParent();
BasicBlock *ContBB = OrigBB->splitBasicBlock(MI, "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(Context, "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()),
"tmp");
BasicBlock *FreeBlock = BasicBlock::Create(Context, "free_it",
OrigBB->getParent());
BasicBlock *NextBlock = BasicBlock::Create(Context, "next",
OrigBB->getParent());
BranchInst::Create(FreeBlock, NextBlock, Cmp, NullPtrBlock);
// Fill in FreeBlock.
new FreeInst(GVVal, FreeBlock);
new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
FreeBlock);
BranchInst::Create(NextBlock, FreeBlock);
NullPtrBlock = NextBlock;
}
BranchInst::Create(ContBB, NullPtrBlock);
// MI is no longer needed, remove it.
MI->eraseFromParent();
/// InsertedScalarizedLoads - 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 (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) {
Instruction *User = cast<Instruction>(*UI++);
if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite,
Context);
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) {
const PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType());
Constant *Null = Constant::getNullValue(PT->getElementType());
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, Context);
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]);
}
/// TryToOptimizeStoreOfMallocToGlobal - 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,
MallocInst *MI,
Module::global_iterator &GVI,
TargetData *TD,
LLVMContext &Context) {
// If this is a malloc of an abstract type, don't touch it.
if (!MI->getAllocatedType()->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 setcc'd, and
// GEP'd. These are all things we could transform to using the global
// for.
{
SmallPtrSet<PHINode*, 8> PHIs;
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, 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.
if (ConstantInt *NElements = dyn_cast<ConstantInt>(MI->getArraySize())) {
// 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 (TD &&
NElements->getZExtValue()*
TD->getTypeAllocSize(MI->getAllocatedType()) < 2048) {
GVI = OptimizeGlobalAddressOfMalloc(GV, MI, Context);
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.
const Type *AllocTy = MI->getAllocatedType();
// 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 (!MI->isArrayAllocation())
if (const ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
AllocTy = AT->getElementType();
if (const StructType *AllocSTy = dyn_cast<StructType>(AllocTy)) {
// This the structure has an unreasonable number of fields, leave it
// alone.
if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, MI)) {
// 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 (const ArrayType *AT = dyn_cast<ArrayType>(MI->getAllocatedType())) {
MallocInst *NewMI =
new MallocInst(AllocSTy,
ConstantInt::get(Type::getInt32Ty(Context),
AT->getNumElements()),
"", MI);
NewMI->takeName(MI);
Value *Cast = new BitCastInst(NewMI, MI->getType(), "tmp", MI);
MI->replaceAllUsesWith(Cast);
MI->eraseFromParent();
MI = NewMI;
}
GVI = PerformHeapAllocSRoA(GV, MI, Context);
return true;
}
}
return false;
}
// OptimizeOnceStoredGlobal - 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,
Module::global_iterator &GVI,
TargetData *TD, LLVMContext &Context) {
// 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 (isa<PointerType>(GV->getInitializer()->getType()) &&
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, Context))
return true;
} else if (MallocInst *MI = dyn_cast<MallocInst>(StoredOnceVal)) {
if (TryToOptimizeStoreOfMallocToGlobal(GV, MI, GVI, TD, Context))
return true;
}
}
return false;
}
/// TryToShrinkGlobalToBoolean - 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,
LLVMContext &Context) {
const Type *GVElType = GV->getType()->getElementType();
// 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(Context) || GVElType->isFloatingPoint() ||
isa<PointerType>(GVElType) || isa<VectorType>(GVElType))
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 (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I)
if (!isa<LoadInst>(I) && !isa<StoreInst>(I))
return false;
DOUT << " *** SHRINKING TO BOOL: " << *GV;
// Create the new global, initializing it to false.
GlobalVariable *NewGV = new GlobalVariable(Context,
Type::getInt1Ty(Context), false,
GlobalValue::InternalLinkage, ConstantInt::getFalse(Context),
GV->getName()+".b",
GV->isThreadLocal());
GV->getParent()->getGlobalList().insert(GV, NewGV);
Constant *InitVal = GV->getInitializer();
assert(InitVal->getType() != Type::getInt1Ty(Context) &&
"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->use_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(Context), 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're 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", 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, 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", 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();
}
GV->eraseFromParent();
return true;
}
/// ProcessInternalGlobal - Analyze the specified global variable and optimize
/// it if possible. If we make a change, return true.
bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
Module::global_iterator &GVI) {
SmallPtrSet<PHINode*, 16> PHIUsers;
GlobalStatus GS;
GV->removeDeadConstantUsers();
if (GV->use_empty()) {
DOUT << "GLOBAL DEAD: " << *GV;
GV->eraseFromParent();
++NumDeleted;
return true;
}
if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
#if 0
cerr << "Global: " << *GV;
cerr << " isLoaded = " << GS.isLoaded << "\n";
cerr << " StoredType = ";
switch (GS.StoredType) {
case GlobalStatus::NotStored: cerr << "NEVER STORED\n"; break;
case GlobalStatus::isInitializerStored: cerr << "INIT STORED\n"; break;
case GlobalStatus::isStoredOnce: cerr << "STORED ONCE\n"; break;
case GlobalStatus::isStored: cerr << "stored\n"; break;
}
if (GS.StoredType == GlobalStatus::isStoredOnce && GS.StoredOnceValue)
cerr << " StoredOnceValue = " << *GS.StoredOnceValue << "\n";
if (GS.AccessingFunction && !GS.HasMultipleAccessingFunctions)
cerr << " AccessingFunction = " << GS.AccessingFunction->getName()
<< "\n";
cerr << " HasMultipleAccessingFunctions = "
<< GS.HasMultipleAccessingFunctions << "\n";
cerr << " HasNonInstructionUser = " << GS.HasNonInstructionUser<<"\n";
cerr << "\n";
#endif
// If this is a first class global and has only one accessing function
// and this function is main (which we know is not recursive we can make
// this global a local variable) 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 && !GS.HasNonInstructionUser &&
GV->getType()->getElementType()->isSingleValueType() &&
GS.AccessingFunction->getName() == "main" &&
GS.AccessingFunction->hasExternalLinkage() &&
GV->getType()->getAddressSpace() == 0) {
DOUT << "LOCALIZING GLOBAL: " << *GV;
Instruction* FirstI = GS.AccessingFunction->getEntryBlock().begin();
const Type* ElemTy = GV->getType()->getElementType();
// FIXME: Pass Global's alignment when globals have alignment
AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), FirstI);
if (!isa<UndefValue>(GV->getInitializer()))
new StoreInst(GV->getInitializer(), Alloca, FirstI);
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) {
DOUT << "GLOBAL NEVER LOADED: " << *GV;
// Delete any stores we can find to the global. We may not be able to
// make it completely dead though.
bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(),
GV->getContext());
// If the global is dead now, delete it.
if (GV->use_empty()) {
GV->eraseFromParent();
++NumDeleted;
Changed = true;
}
return Changed;
} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
DOUT << "MARKING CONSTANT: " << *GV;
GV->setConstant(true);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer(), GV->getContext());
// If the global is dead now, just nuke it.
if (GV->use_empty()) {
DOUT << " *** Marking constant allowed us to simplify "
<< "all users and delete global!\n";
GV->eraseFromParent();
++NumDeleted;
}
++NumMarked;
return true;
} else if (!GV->getInitializer()->getType()->isSingleValueType()) {
if (TargetData *TD = getAnalysisIfAvailable<TargetData>())
if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD,
GV->getContext())) {
GVI = FirstNewGV; // Don't skip the newly produced globals!
return true;
}
} else if (GS.StoredType == GlobalStatus::isStoredOnce) {
// 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(),
GV->getContext());
if (GV->use_empty()) {
DOUT << " *** Substituting initializer allowed us to "
<< "simplify all users and delete global!\n";
GV->eraseFromParent();
++NumDeleted;
} else {
GVI = GV;
}
++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, GVI,
getAnalysisIfAvailable<TargetData>(),
GV->getContext()))
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 (TryToShrinkGlobalToBoolean(GV, SOVConstant, GV->getContext())) {
++NumShrunkToBool;
return true;
}
}
}
return false;
}
/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified
/// function, changing them to FastCC.
static void ChangeCalleesToFastCall(Function *F) {
for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
CallSite User(cast<Instruction>(*UI));
User.setCallingConv(CallingConv::Fast);
}
}
static AttrListPtr StripNest(const AttrListPtr &Attrs) {
for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0)
continue;
// There can be only one.
return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest);
}
return Attrs;
}
static void RemoveNestAttribute(Function *F) {
F->setAttributes(StripNest(F->getAttributes()));
for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
CallSite User(cast<Instruction>(*UI));
User.setAttributes(StripNest(User.getAttributes()));
}
}
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->setLinkage(GlobalValue::InternalLinkage);
F->removeDeadConstantUsers();
if (F->use_empty() && (F->hasLocalLinkage() ||
F->hasLinkOnceLinkage())) {
M.getFunctionList().erase(F);
Changed = true;
++NumFnDeleted;
} else if (F->hasLocalLinkage()) {
if (F->getCallingConv() == CallingConv::C && !F->isVarArg() &&
!F->hasAddressTaken()) {
// If this function has C calling conventions, 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->setLinkage(GlobalValue::InternalLinkage);
if (!GV->isConstant() && GV->hasLocalLinkage() &&
GV->hasInitializer())
Changed |= ProcessInternalGlobal(GV, GVI);
}
return Changed;
}
/// FindGlobalCtors - Find the llvm.globalctors list, verifying that all
/// initializers have an init priority of 65535.
GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) {
for (Module::global_iterator I = M.global_begin(), E = M.global_end();
I != E; ++I)
if (I->getName() == "llvm.global_ctors") {
// Found it, verify it's an array of { int, void()* }.
const ArrayType *ATy =dyn_cast<ArrayType>(I->getType()->getElementType());
if (!ATy) return 0;
const StructType *STy = dyn_cast<StructType>(ATy->getElementType());
if (!STy || STy->getNumElements() != 2 ||
STy->getElementType(0) != Type::getInt32Ty(M.getContext())) return 0;
const PointerType *PFTy = dyn_cast<PointerType>(STy->getElementType(1));
if (!PFTy) return 0;
const FunctionType *FTy = dyn_cast<FunctionType>(PFTy->getElementType());
if (!FTy || FTy->getReturnType() != Type::getVoidTy(M.getContext()) ||
FTy->isVarArg() || FTy->getNumParams() != 0)
return 0;
// Verify that the initializer is simple enough for us to handle.
if (!I->hasDefinitiveInitializer()) return 0;
ConstantArray *CA = dyn_cast<ConstantArray>(I->getInitializer());
if (!CA) return 0;
for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i)
if (ConstantStruct *CS = dyn_cast<ConstantStruct>(*i)) {
if (isa<ConstantPointerNull>(CS->getOperand(1)))
continue;
// Must have a function or null ptr.
if (!isa<Function>(CS->getOperand(1)))
return 0;
// Init priority must be standard.
ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0));
if (!CI || CI->getZExtValue() != 65535)
return 0;
} else {
return 0;
}
return I;
}
return 0;
}
/// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand,
/// return a list of the functions and null terminator as a vector.
static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) {
ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
std::vector<Function*> Result;
Result.reserve(CA->getNumOperands());
for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
ConstantStruct *CS = cast<ConstantStruct>(*i);
Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
}
return Result;
}
/// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the
/// specified array, returning the new global to use.
static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL,
const std::vector<Function*> &Ctors,
LLVMContext &Context) {
// If we made a change, reassemble the initializer list.
std::vector<Constant*> CSVals;
CSVals.push_back(ConstantInt::get(Type::getInt32Ty(Context), 65535));
CSVals.push_back(0);
// Create the new init list.
std::vector<Constant*> CAList;
for (unsigned i = 0, e = Ctors.size(); i != e; ++i) {
if (Ctors[i]) {
CSVals[1] = Ctors[i];
} else {
const Type *FTy = FunctionType::get(Type::getVoidTy(Context), false);
const PointerType *PFTy = PointerType::getUnqual(FTy);
CSVals[1] = Constant::getNullValue(PFTy);
CSVals[0] = ConstantInt::get(Type::getInt32Ty(Context), 2147483647);
}
CAList.push_back(ConstantStruct::get(Context, CSVals));
}
// Create the array initializer.
const Type *StructTy =
cast<ArrayType>(GCL->getType()->getElementType())->getElementType();
Constant *CA = ConstantArray::get(ArrayType::get(StructTy,
CAList.size()), CAList);
// If we didn't change the number of elements, don't create a new GV.
if (CA->getType() == GCL->getInitializer()->getType()) {
GCL->setInitializer(CA);
return GCL;
}
// Create the new global and insert it next to the existing list.
GlobalVariable *NGV = new GlobalVariable(Context, CA->getType(),
GCL->isConstant(),
GCL->getLinkage(), CA, "",
GCL->isThreadLocal());
GCL->getParent()->getGlobalList().insert(GCL, NGV);
NGV->takeName(GCL);
// Nuke the old list, replacing any uses with the new one.
if (!GCL->use_empty()) {
Constant *V = NGV;
if (V->getType() != GCL->getType())
V = ConstantExpr::getBitCast(V, GCL->getType());
GCL->replaceAllUsesWith(V);
}
GCL->eraseFromParent();
if (Ctors.size())
return NGV;
else
return 0;
}
static Constant *getVal(DenseMap<Value*, Constant*> &ComputedValues,
Value *V) {
if (Constant *CV = dyn_cast<Constant>(V)) return CV;
Constant *R = ComputedValues[V];
assert(R && "Reference to an uncomputed value!");
return R;
}
/// isSimpleEnoughPointerToCommit - Return true if this constant is simple
/// enough for us to understand. In particular, if it is a cast of something,
/// we punt. We basically just support direct accesses to globals and GEP's of
/// globals. This should be kept up to date with CommitValueTo.
static bool isSimpleEnoughPointerToCommit(Constant *C, LLVMContext &Context) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
if (!GV->hasExternalLinkage() && !GV->hasLocalLinkage())
return false; // do not allow weak/linkonce/dllimport/dllexport linkage.
return !GV->isDeclaration(); // reject external globals.
}
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
// Handle a constantexpr gep.
if (CE->getOpcode() == Instruction::GetElementPtr &&
isa<GlobalVariable>(CE->getOperand(0))) {
GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
if (!GV->hasExternalLinkage() && !GV->hasLocalLinkage())
return false; // do not allow weak/linkonce/dllimport/dllexport linkage.
return GV->hasInitializer() &&
ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE,
Context);
}
return false;
}
/// EvaluateStoreInto - 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,
LLVMContext &Context) {
// Base case of the recursion.
if (OpNo == Addr->getNumOperands()) {
assert(Val->getType() == Init->getType() && "Type mismatch!");
return Val;
}
if (const StructType *STy = dyn_cast<StructType>(Init->getType())) {
std::vector<Constant*> Elts;
// Break up the constant into its elements.
if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) {
for (User::op_iterator i = CS->op_begin(), e = CS->op_end(); i != e; ++i)
Elts.push_back(cast<Constant>(*i));
} else if (isa<ConstantAggregateZero>(Init)) {
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
Elts.push_back(Constant::getNullValue(STy->getElementType(i)));
} else if (isa<UndefValue>(Init)) {
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
Elts.push_back(UndefValue::get(STy->getElementType(i)));
} else {
llvm_unreachable("This code is out of sync with "
" ConstantFoldLoadThroughGEPConstantExpr");
}
// 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, Context);
// Return the modified struct.
return ConstantStruct::get(Context, &Elts[0], Elts.size(), STy->isPacked());
} else {
ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
const ArrayType *ATy = cast<ArrayType>(Init->getType());
// Break up the array into elements.
std::vector<Constant*> Elts;
if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) {
for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i)
Elts.push_back(cast<Constant>(*i));
} else if (isa<ConstantAggregateZero>(Init)) {
Constant *Elt = Constant::getNullValue(ATy->getElementType());
Elts.assign(ATy->getNumElements(), Elt);
} else if (isa<UndefValue>(Init)) {
Constant *Elt = UndefValue::get(ATy->getElementType());
Elts.assign(ATy->getNumElements(), Elt);
} else {
llvm_unreachable("This code is out of sync with "
" ConstantFoldLoadThroughGEPConstantExpr");
}
assert(CI->getZExtValue() < ATy->getNumElements());
Elts[CI->getZExtValue()] =
EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1, Context);
return ConstantArray::get(ATy, Elts);
}
}
/// CommitValueTo - 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,
LLVMContext &Context) {
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));
Constant *Init = GV->getInitializer();
Init = EvaluateStoreInto(Init, Val, CE, 2, Context);
GV->setInitializer(Init);
}
/// ComputeLoadResult - Return the value that would be computed by a load from
/// P after the stores reflected by 'memory' have been performed. If we can't
/// decide, return null.
static Constant *ComputeLoadResult(Constant *P,
const DenseMap<Constant*, Constant*> &Memory,
LLVMContext &Context) {
// If this memory location has been recently stored, use the stored value: it
// is the most up-to-date.
DenseMap<Constant*, Constant*>::const_iterator I = Memory.find(P);
if (I != Memory.end()) return I->second;
// Access it.
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
if (GV->hasDefinitiveInitializer())
return GV->getInitializer();
return 0;
}
// Handle a constantexpr getelementptr.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
if (CE->getOpcode() == Instruction::GetElementPtr &&
isa<GlobalVariable>(CE->getOperand(0))) {
GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
if (GV->hasDefinitiveInitializer())
return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE,
Context);
}
return 0; // don't know how to evaluate.
}
/// EvaluateFunction - Evaluate a call to function F, returning true if
/// successful, false if we can't evaluate it. ActualArgs contains the formal
/// arguments for the function.
static bool EvaluateFunction(Function *F, Constant *&RetVal,
const SmallVectorImpl<Constant*> &ActualArgs,
std::vector<Function*> &CallStack,
DenseMap<Constant*, Constant*> &MutatedMemory,
std::vector<GlobalVariable*> &AllocaTmps) {
// Check to see if this function is already executing (recursion). If so,
// bail out. TODO: we might want to accept limited recursion.
if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
return false;
LLVMContext &Context = F->getContext();
CallStack.push_back(F);
/// Values - As we compute SSA register values, we store their contents here.
DenseMap<Value*, Constant*> Values;
// Initialize arguments to the incoming values specified.
unsigned ArgNo = 0;
for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
++AI, ++ArgNo)
Values[AI] = ActualArgs[ArgNo];
/// ExecutedBlocks - We only handle non-looping, non-recursive code. As such,
/// we can only evaluate any one basic block at most once. This set keeps
/// track of what we have executed so we can detect recursive cases etc.
SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
// CurInst - The current instruction we're evaluating.
BasicBlock::iterator CurInst = F->begin()->begin();
// This is the main evaluation loop.
while (1) {
Constant *InstResult = 0;
if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
if (SI->isVolatile()) return false; // no volatile accesses.
Constant *Ptr = getVal(Values, SI->getOperand(1));
if (!isSimpleEnoughPointerToCommit(Ptr, Context))
// If this is too complex for us to commit, reject it.
return false;
Constant *Val = getVal(Values, SI->getOperand(0));
MutatedMemory[Ptr] = Val;
} else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
InstResult = ConstantExpr::get(BO->getOpcode(),
getVal(Values, BO->getOperand(0)),
getVal(Values, BO->getOperand(1)));
} else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
InstResult = ConstantExpr::getCompare(CI->getPredicate(),
getVal(Values, CI->getOperand(0)),
getVal(Values, CI->getOperand(1)));
} else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
InstResult = ConstantExpr::getCast(CI->getOpcode(),
getVal(Values, CI->getOperand(0)),
CI->getType());
} else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
InstResult =
ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)),
getVal(Values, SI->getOperand(1)),
getVal(Values, SI->getOperand(2)));
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
Constant *P = getVal(Values, GEP->getOperand(0));
SmallVector<Constant*, 8> GEPOps;
for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
i != e; ++i)
GEPOps.push_back(getVal(Values, *i));
InstResult =
ConstantExpr::getGetElementPtr(P, &GEPOps[0], GEPOps.size());
} else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
if (LI->isVolatile()) return false; // no volatile accesses.
InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)),
MutatedMemory, Context);
if (InstResult == 0) return false; // Could not evaluate load.
} else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
if (AI->isArrayAllocation()) return false; // Cannot handle array allocs.
const Type *Ty = AI->getType()->getElementType();
AllocaTmps.push_back(new GlobalVariable(Context, Ty, false,
GlobalValue::InternalLinkage,
UndefValue::get(Ty),
AI->getName()));
InstResult = AllocaTmps.back();
} else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) {
// Debug info can safely be ignored here.
if (isa<DbgInfoIntrinsic>(CI)) {
++CurInst;
continue;
}
// Cannot handle inline asm.
if (isa<InlineAsm>(CI->getOperand(0))) return false;
// Resolve function pointers.
Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0)));
if (!Callee) return false; // Cannot resolve.
SmallVector<Constant*, 8> Formals;
for (User::op_iterator i = CI->op_begin() + 1, e = CI->op_end();
i != e; ++i)
Formals.push_back(getVal(Values, *i));
if (Callee->isDeclaration()) {
// If this is a function we can constant fold, do it.
if (Constant *C = ConstantFoldCall(Callee, Formals.data(),
Formals.size())) {
InstResult = C;
} else {
return false;
}
} else {
if (Callee->getFunctionType()->isVarArg())
return false;
Constant *RetVal;
// Execute the call, if successful, use the return value.
if (!EvaluateFunction(Callee, RetVal, Formals, CallStack,
MutatedMemory, AllocaTmps))
return false;
InstResult = RetVal;
}
} else if (isa<TerminatorInst>(CurInst)) {
BasicBlock *NewBB = 0;
if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
if (BI->isUnconditional()) {
NewBB = BI->getSuccessor(0);
} else {
ConstantInt *Cond =
dyn_cast<ConstantInt>(getVal(Values, BI->getCondition()));
if (!Cond) return false; // Cannot determine.
NewBB = BI->getSuccessor(!Cond->getZExtValue());
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
ConstantInt *Val =
dyn_cast<ConstantInt>(getVal(Values, SI->getCondition()));
if (!Val) return false; // Cannot determine.
NewBB = SI->getSuccessor(SI->findCaseValue(Val));
} else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) {
if (RI->getNumOperands())
RetVal = getVal(Values, RI->getOperand(0));
CallStack.pop_back(); // return from fn.
return true; // We succeeded at evaluating this ctor!
} else {
// invoke, unwind, unreachable.
return false; // Cannot handle this terminator.
}
// Okay, we succeeded in evaluating this control flow. See if we have
// executed the new block before. If so, we have a looping function,
// which we cannot evaluate in reasonable time.
if (!ExecutedBlocks.insert(NewBB))
return false; // looped!
// Okay, we have never been in this block before. Check to see if there
// are any PHI nodes. If so, evaluate them with information about where
// we came from.
BasicBlock *OldBB = CurInst->getParent();
CurInst = NewBB->begin();
PHINode *PN;
for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB));
// Do NOT increment CurInst. We know that the terminator had no value.
continue;
} else {
// Did not know how to evaluate this!
return false;
}
if (!CurInst->use_empty())
Values[CurInst] = InstResult;
// Advance program counter.
++CurInst;
}
}
/// EvaluateStaticConstructor - Evaluate static constructors in the function, if
/// we can. Return true if we can, false otherwise.
static bool EvaluateStaticConstructor(Function *F) {
/// MutatedMemory - For each store we execute, we update this map. Loads
/// check this to get the most up-to-date value. If evaluation is successful,
/// this state is committed to the process.
DenseMap<Constant*, Constant*> MutatedMemory;
/// AllocaTmps - To 'execute' an alloca, we create a temporary global variable
/// to represent its body. This vector is needed so we can delete the
/// temporary globals when we are done.
std::vector<GlobalVariable*> AllocaTmps;
/// CallStack - This is used to detect recursion. In pathological situations
/// we could hit exponential behavior, but at least there is nothing
/// unbounded.
std::vector<Function*> CallStack;
// Call the function.
Constant *RetValDummy;
bool EvalSuccess = EvaluateFunction(F, RetValDummy,
SmallVector<Constant*, 0>(), CallStack,
MutatedMemory, AllocaTmps);
if (EvalSuccess) {
// We succeeded at evaluation: commit the result.
DEBUG(errs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
<< F->getName() << "' to " << MutatedMemory.size()
<< " stores.\n");
for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(),
E = MutatedMemory.end(); I != E; ++I)
CommitValueTo(I->second, I->first, F->getContext());
}
// At this point, we are done interpreting. If we created any 'alloca'
// temporaries, release them now.
while (!AllocaTmps.empty()) {
GlobalVariable *Tmp = AllocaTmps.back();
AllocaTmps.pop_back();
// If there are still users of the alloca, the program is doing something
// silly, e.g. storing the address of the alloca somewhere and using it
// later. Since this is undefined, we'll just make it be null.
if (!Tmp->use_empty())
Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
delete Tmp;
}
return EvalSuccess;
}
/// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible.
/// Return true if anything changed.
bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) {
std::vector<Function*> Ctors = ParseGlobalCtors(GCL);
bool MadeChange = false;
if (Ctors.empty()) return false;
// Loop over global ctors, optimizing them when we can.
for (unsigned i = 0; i != Ctors.size(); ++i) {
Function *F = Ctors[i];
// Found a null terminator in the middle of the list, prune off the rest of
// the list.
if (F == 0) {
if (i != Ctors.size()-1) {
Ctors.resize(i+1);
MadeChange = true;
}
break;
}
// We cannot simplify external ctor functions.
if (F->empty()) continue;
// If we can evaluate the ctor at compile time, do.
if (EvaluateStaticConstructor(F)) {
Ctors.erase(Ctors.begin()+i);
MadeChange = true;
--i;
++NumCtorsEvaluated;
continue;
}
}
if (!MadeChange) return false;
GCL = InstallGlobalCtors(GCL, Ctors, GCL->getContext());
return true;
}
bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
bool Changed = false;
for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
I != E;) {
Module::alias_iterator J = I++;
// Aliases without names cannot be referenced outside this module.
if (!J->hasName() && !J->isDeclaration())
J->setLinkage(GlobalValue::InternalLinkage);
// If the aliasee may change at link time, nothing can be done - bail out.
if (J->mayBeOverridden())
continue;
Constant *Aliasee = J->getAliasee();
GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
Target->removeDeadConstantUsers();
bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse();
// Make all users of the alias use the aliasee instead.
if (!J->use_empty()) {
J->replaceAllUsesWith(Aliasee);
++NumAliasesResolved;
Changed = true;
}
// 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(...)
if (!Target->hasLocalLinkage())
continue;
// The transform is only useful if the alias does not have internal linkage.
if (J->hasLocalLinkage())
continue;
// 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 (!hasOneUse)
continue;
// Give the aliasee the name, linkage and other attributes of the alias.
Target->takeName(J);
Target->setLinkage(J->getLinkage());
Target->GlobalValue::copyAttributesFrom(J);
// Delete the alias.
M.getAliasList().erase(J);
++NumAliasesRemoved;
Changed = true;
}
return Changed;
}
bool GlobalOpt::runOnModule(Module &M) {
bool Changed = false;
// Try to find the llvm.globalctors list.
GlobalVariable *GlobalCtors = FindGlobalCtors(M);
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
// Delete functions that are trivially dead, ccc -> fastcc
LocalChange |= OptimizeFunctions(M);
// Optimize global_ctors list.
if (GlobalCtors)
LocalChange |= OptimizeGlobalCtorsList(GlobalCtors);
// Optimize non-address-taken globals.
LocalChange |= OptimizeGlobalVars(M);
// Resolve aliases, when possible.
LocalChange |= OptimizeGlobalAliases(M);
Changed |= LocalChange;
}
// TODO: Move all global ctors functions to the end of the module for code
// layout.
return Changed;
}