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llvm-6502/lib/Transforms/IPO/GlobalOpt.cpp
Chris Lattner 30ba5690cf This patch implements two things (sorry). 
First, it allows SRA of globals that have embedded arrays, implementing
GlobalOpt/globalsra-partial.llx.  This comes up infrequently, but does allow,
for example, deleting several stores to dead parts of globals in dhrystone.

Second, this implements GlobalOpt/malloc-promote-*.llx, which is the
following nifty transformation:

Basically if a global pointer is initialized with malloc, and we can tell
that the program won't notice, we transform this:

struct foo *FooPtr;
...
  FooPtr = malloc(sizeof(struct foo));
...
  FooPtr->A   FooPtr->B

Into:

struct foo FooPtrBody;
...
   FooPtrBody.A  FooPtrBody.B

This comes up occasionally, for example, the 'disp' global in 183.equake (where
the xform speeds the CBE version of the program up from 56.16s to 52.40s (7%)
on apoc), and the 'desired_accept', 'fixLRBT', 'macroArray', & 'key_queue'
globals in 300.twolf (speeding it up from 22.29s to 21.55s (3.4%)).

The nice thing about this xform is that it exposes the resulting global to
global variable optimization and makes alias analysis easier in addition to
eliminating a few loads.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16916 91177308-0d34-0410-b5e6-96231b3b80d8
2004-10-11 05:54:41 +00:00

833 lines
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//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and 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/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include <set>
#include <algorithm>
using namespace llvm;
namespace {
Statistic<> NumMarked ("globalopt", "Number of globals marked constant");
Statistic<> NumSRA ("globalopt", "Number of aggregate globals broken "
"into scalars");
Statistic<> NumDeleted ("globalopt", "Number of globals deleted");
Statistic<> NumFnDeleted("globalopt", "Number of functions deleted");
Statistic<> NumGlobUses ("globalopt", "Number of global uses devirtualized");
struct GlobalOpt : public ModulePass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetData>();
}
bool runOnModule(Module &M);
private:
bool ProcessInternalGlobal(GlobalVariable *GV, Module::giterator &GVI);
};
RegisterOpt<GlobalOpt> X("globalopt", "Global Variable Optimizer");
}
ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
/// 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 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;
/// isNotSuitableForSRA - Keep track of whether any SRA preventing users of
/// the global exist. Such users include GEP instruction with variable
/// indexes, and non-gep/load/store users like constant expr casts.
bool isNotSuitableForSRA;
GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0),
isNotSuitableForSRA(false) {}
};
/// ConstantIsDead - Return true if the specified constant is (transitively)
/// dead. The constant may be used by other constants (e.g. constant arrays and
/// constant exprs) as long as they are dead, but it cannot be used by anything
/// else.
static bool ConstantIsDead(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 (!ConstantIsDead(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,
std::set<PHINode*> &PHIUsers) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
if (CE->getOpcode() != Instruction::GetElementPtr)
GS.isNotSuitableForSRA = true;
else if (!GS.isNotSuitableForSRA) {
// 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.
if (CE->getNumOperands() < 3 || !CE->getOperand(1)->isNullValue())
GS.isNotSuitableForSRA = true;
else {
for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
if (!isa<ConstantInt>(CE->getOperand(i))) {
GS.isNotSuitableForSRA = true;
break;
}
}
}
} else if (Instruction *I = dyn_cast<Instruction>(*UI)) {
if (isa<LoadInst>(I)) {
GS.isLoaded = true;
} 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 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))){
if (SI->getOperand(0) == GV->getInitializer()) {
if (GS.StoredType < GlobalStatus::isInitializerStored)
GS.StoredType = GlobalStatus::isInitializerStored;
} else if (GS.StoredType < GlobalStatus::isStoredOnce) {
GS.StoredType = GlobalStatus::isStoredOnce;
GS.StoredOnceValue = SI->getOperand(0);
} else if (GS.StoredType == GlobalStatus::isStoredOnce &&
GS.StoredOnceValue == SI->getOperand(0)) {
// noop.
} else {
GS.StoredType = GlobalStatus::isStored;
}
} else {
GS.StoredType = GlobalStatus::isStored;
}
} else if (I->getOpcode() == Instruction::GetElementPtr) {
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
// If the first two indices are constants, this can be SRA'd.
if (isa<GlobalVariable>(I->getOperand(0))) {
if (I->getNumOperands() < 3 || !isa<Constant>(I->getOperand(1)) ||
!cast<Constant>(I->getOperand(1))->isNullValue() ||
!isa<ConstantInt>(I->getOperand(2)))
GS.isNotSuitableForSRA = true;
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(I->getOperand(0))){
if (CE->getOpcode() != Instruction::GetElementPtr ||
CE->getNumOperands() < 3 || I->getNumOperands() < 2 ||
!isa<Constant>(I->getOperand(0)) ||
!cast<Constant>(I->getOperand(0))->isNullValue())
GS.isNotSuitableForSRA = true;
} else {
GS.isNotSuitableForSRA = true;
}
} else if (I->getOpcode() == Instruction::Select) {
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
GS.isNotSuitableForSRA = 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).second) // Not already visited.
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
GS.isNotSuitableForSRA = true;
} else if (isa<SetCondInst>(I)) {
GS.isNotSuitableForSRA = true;
} else {
return true; // Any other non-load instruction might take address!
}
} else if (Constant *C = dyn_cast<Constant>(*UI)) {
// We might have a dead and dangling constant hanging off of here.
if (!ConstantIsDead(C))
return true;
} else {
// Otherwise must be a global or some other user.
return true;
}
return false;
}
static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) {
ConstantInt *CI = dyn_cast<ConstantInt>(Idx);
if (!CI) return 0;
uint64_t IdxV = CI->getRawValue();
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 (ConstantPacked *CP = dyn_cast<ConstantPacked>(Agg)) {
if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV);
} else if (ConstantAggregateZero *CAZ =
dyn_cast<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());
}
}
return 0;
}
static Constant *TraverseGEPInitializer(User *GEP, Constant *Init) {
if (GEP->getNumOperands() == 1 ||
!isa<Constant>(GEP->getOperand(1)) ||
!cast<Constant>(GEP->getOperand(1))->isNullValue())
return 0;
for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) {
ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(i));
if (!Idx) return 0;
Init = getAggregateConstantElement(Init, Idx);
if (Init == 0) return 0;
}
return Init;
}
/// 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) {
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)) {
// Replace the load with the initializer.
LI->replaceAllUsesWith(Init);
LI->getParent()->getInstList().erase(LI);
Changed = true;
} else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
// Store must be unreachable or storing Init into the global.
SI->getParent()->getInstList().erase(SI);
Changed = true;
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
if (CE->getOpcode() == Instruction::GetElementPtr) {
if (Constant *SubInit = TraverseGEPInitializer(CE, Init))
Changed |= CleanupConstantGlobalUsers(CE, SubInit);
if (CE->use_empty()) {
CE->destroyConstant();
Changed = true;
}
}
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
if (Constant *SubInit = TraverseGEPInitializer(GEP, Init))
Changed |= CleanupConstantGlobalUsers(GEP, SubInit);
else {
// If this GEP has variable indexes, we should still be able to delete
// any stores through it.
for (Value::use_iterator GUI = GEP->use_begin(), E = GEP->use_end();
GUI != E;)
if (StoreInst *SI = dyn_cast<StoreInst>(*GUI++)) {
SI->getParent()->getInstList().erase(SI);
Changed = true;
}
}
if (GEP->use_empty()) {
GEP->getParent()->getInstList().erase(GEP);
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 (ConstantIsDead(C)) {
C->destroyConstant();
// This could have incalidated UI, start over from scratch.x
CleanupConstantGlobalUsers(V, Init);
return true;
}
}
}
return Changed;
}
/// 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) {
assert(GV->hasInternalLinkage() && !GV->isConstant());
Constant *Init = GV->getInitializer();
const Type *Ty = Init->getType();
std::vector<GlobalVariable*> NewGlobals;
Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
if (const StructType *STy = dyn_cast<StructType>(Ty)) {
NewGlobals.reserve(STy->getNumElements());
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
Constant *In = getAggregateConstantElement(Init,
ConstantUInt::get(Type::UIntTy, i));
assert(In && "Couldn't get element of initializer?");
GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
GlobalVariable::InternalLinkage,
In, GV->getName()+"."+utostr(i));
Globals.insert(GV, NGV);
NewGlobals.push_back(NGV);
}
} else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
unsigned NumElements = 0;
if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
NumElements = ATy->getNumElements();
else if (const PackedType *PTy = dyn_cast<PackedType>(STy))
NumElements = PTy->getNumElements();
else
assert(0 && "Unknown aggregate sequential type!");
if (NumElements > 16 && GV->use_size() > 16) return 0; // It's not worth it.
NewGlobals.reserve(NumElements);
for (unsigned i = 0, e = NumElements; i != e; ++i) {
Constant *In = getAggregateConstantElement(Init,
ConstantUInt::get(Type::UIntTy, i));
assert(In && "Couldn't get element of initializer?");
GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
GlobalVariable::InternalLinkage,
In, GV->getName()+"."+utostr(i));
Globals.insert(GV, NGV);
NewGlobals.push_back(NGV);
}
}
if (NewGlobals.empty())
return 0;
DEBUG(std::cerr << "PERFORMING GLOBAL SRA ON: " << *GV);
Constant *NullInt = Constant::getNullValue(Type::IntTy);
// 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))->getRawValue();
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)) {
std::vector<Constant*> 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);
} else {
GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
std::vector<Value*> Idxs;
Idxs.push_back(NullInt);
for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
Idxs.push_back(GEPI->getOperand(i));
NewPtr = new GetElementPtrInst(NewPtr, Idxs,
GEPI->getName()+"."+utostr(Val), GEPI);
}
GEP->replaceAllUsesWith(NewPtr);
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
GEPI->getParent()->getInstList().erase(GEPI);
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.
static bool AllUsesOfValueWillTrapIfNull(Value *V) {
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) {
//std::cerr << "NONTRAPPING USE: " << **UI;
return false; // Storing the value.
}
} else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
if (CI->getOperand(0) != V) {
//std::cerr << "NONTRAPPING USE: " << **UI;
return false; // Not calling the ptr
}
} else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
if (II->getOperand(0) != V) {
//std::cerr << "NONTRAPPING USE: " << **UI;
return false; // Not calling the ptr
}
} else if (CastInst *CI = dyn_cast<CastInst>(*UI)) {
if (!AllUsesOfValueWillTrapIfNull(CI)) return false;
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) {
if (!AllUsesOfValueWillTrapIfNull(GEPI)) return false;
} else {
//std::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.
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)) {
if (!AllUsesOfValueWillTrapIfNull(LI))
return false;
} else if (isa<StoreInst>(*UI)) {
// Ignore stores to the global.
} else {
// We don't know or understand this user, bail out.
//std::cerr << "UNKNOWN USER OF GLOBAL!: " << **UI;
return false;
}
return true;
}
static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
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(NewV, CI->getType()));
if (CI->use_empty()) {
Changed = true;
CI->getParent()->getInstList().erase(CI);
}
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
// Should handle GEP here.
std::vector<Constant*> Indices;
Indices.reserve(GEPI->getNumOperands()-1);
for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i)
if (Constant *C = dyn_cast<Constant>(GEPI->getOperand(i)))
Indices.push_back(C);
else
break;
if (Indices.size() == GEPI->getNumOperands()-1)
Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
ConstantExpr::getGetElementPtr(NewV, Indices));
if (GEPI->use_empty()) {
Changed = true;
GEPI->getParent()->getInstList().erase(GEPI);
}
}
}
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) {
std::vector<LoadInst*> Loads;
bool Changed = false;
// 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; ++GUI)
if (LoadInst *LI = dyn_cast<LoadInst>(*GUI)) {
Loads.push_back(LI);
Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
} else {
assert(isa<StoreInst>(*GUI) && "Only expect load and stores!");
}
if (Changed) {
DEBUG(std::cerr << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV);
++NumGlobUses;
}
// Delete all of the loads we can, keeping track of whether we nuked them all!
bool AllLoadsGone = true;
while (!Loads.empty()) {
LoadInst *L = Loads.back();
if (L->use_empty()) {
L->getParent()->getInstList().erase(L);
Changed = true;
} else {
AllLoadsGone = false;
}
Loads.pop_back();
}
// If we nuked all of the loads, then none of the stores are needed either,
// nor is the global.
if (AllLoadsGone) {
DEBUG(std::cerr << " *** GLOBAL NOW DEAD!\n");
CleanupConstantGlobalUsers(GV, 0);
if (GV->use_empty()) {
GV->getParent()->getGlobalList().erase(GV);
++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) {
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)) {
I->replaceAllUsesWith(NewC);
// Back up UI to avoid invalidating it!
bool AtBegin = false;
if (UI == V->use_begin())
AtBegin = true;
else
--UI;
I->getParent()->getInstList().erase(I);
if (AtBegin)
UI = V->use_begin();
else
++UI;
}
}
/// 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 laods of GV as uses of the new global.
static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
MallocInst *MI) {
DEBUG(std::cerr << "PROMOTING MALLOC GLOBAL: " << *GV << " MALLOC = " <<*MI);
ConstantInt *NElements = cast<ConstantInt>(MI->getArraySize());
if (NElements->getRawValue() != 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->getRawValue());
MallocInst *NewMI =
new MallocInst(NewTy, Constant::getNullValue(Type::UIntTy),
MI->getName(), MI);
std::vector<Value*> Indices;
Indices.push_back(Constant::getNullValue(Type::IntTy));
Indices.push_back(Indices[0]);
Value *NewGEP = new GetElementPtrInst(NewMI, Indices,
NewMI->getName()+".el0", MI);
MI->replaceAllUsesWith(NewGEP);
MI->getParent()->getInstList().erase(MI);
MI = NewMI;
}
// Create the new global variable.
Constant *Init = Constant::getNullValue(MI->getAllocatedType());
GlobalVariable *NewGV = new GlobalVariable(MI->getAllocatedType(), false,
GlobalValue::InternalLinkage, Init,
GV->getName()+".body");
GV->getParent()->getGlobalList().insert(GV, NewGV);
// Anything that used the malloc now uses the global directly.
MI->replaceAllUsesWith(NewGV);
MI->getParent()->getInstList().erase(MI);
Constant *RepValue = NewGV;
if (NewGV->getType() != GV->getType()->getElementType())
RepValue = ConstantExpr::getCast(RepValue, GV->getType()->getElementType());
// Loop over all uses of GV, processing them in turn.
while (!GV->use_empty())
if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) {
LI->replaceAllUsesWith(RepValue);
LI->getParent()->getInstList().erase(LI);
} else {
StoreInst *SI = cast<StoreInst>(GV->use_back());
SI->getParent()->getInstList().erase(SI);
}
// Now the GV is dead, nuke it.
GV->getParent()->getGlobalList().erase(GV);
// 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);
if (RepValue != NewGV)
ConstantPropUsersOf(RepValue);
return NewGV;
}
// 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::giterator &GVI, TargetData &TD) {
if (CastInst *CI = dyn_cast<CastInst>(StoredOnceVal))
StoredOnceVal = CI->getOperand(0);
else if (GetElementPtrInst *GEPI =dyn_cast<GetElementPtrInst>(StoredOnceVal)){
// "getelementptr Ptr, 0, 0, 0" is really just a cast.
bool IsJustACast = true;
for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i)
if (!isa<Constant>(GEPI->getOperand(i)) ||
!cast<Constant>(GEPI->getOperand(i))->isNullValue()) {
IsJustACast = false;
break;
}
if (IsJustACast)
StoredOnceVal = GEPI->getOperand(0);
}
// 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::getCast(SOVC, GV->getInitializer()->getType());
// Optimize away any trapping uses of the loaded value.
if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC))
return true;
} else if (MallocInst *MI = dyn_cast<MallocInst>(StoredOnceVal)) {
// If we have a global that is only initialized with a fixed size malloc,
// and if all users of the malloc trap, and if the malloc'd address is not
// put anywhere else, transform the program to use global memory instead
// of malloc'd memory. This eliminates dynamic allocation (good) and
// exposes the resultant global to further GlobalOpt (even better). Note
// that we 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 (ConstantInt *NElements = dyn_cast<ConstantInt>(MI->getArraySize()))
if (MI->getAllocatedType()->isSized() &&
NElements->getRawValue()*
TD.getTypeSize(MI->getAllocatedType()) < 2048 &&
AllUsesOfLoadedValueWillTrapIfNull(GV)) {
// FIXME: do more correctness checking to make sure the result of the
// malloc isn't squirrelled away somewhere.
GVI = OptimizeGlobalAddressOfMalloc(GV, MI);
return true;
}
}
}
return false;
}
/// ProcessInternalGlobal - Analyze the specified global variable and optimize
/// it if possible. If we make a change, return true.
bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
Module::giterator &GVI) {
std::set<PHINode*> PHIUsers;
GlobalStatus GS;
PHIUsers.clear();
GV->removeDeadConstantUsers();
if (GV->use_empty()) {
DEBUG(std::cerr << "GLOBAL DEAD: " << *GV);
GV->getParent()->getGlobalList().erase(GV);
++NumDeleted;
return true;
}
if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
// If the global is never loaded (but may be stored to), it is dead.
// Delete it now.
if (!GS.isLoaded) {
DEBUG(std::cerr << "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());
// If the global is dead now, delete it.
if (GV->use_empty()) {
GV->getParent()->getGlobalList().erase(GV);
++NumDeleted;
Changed = true;
}
return Changed;
} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
DEBUG(std::cerr << "MARKING CONSTANT: " << *GV);
GV->setConstant(true);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer());
// If the global is dead now, just nuke it.
if (GV->use_empty()) {
DEBUG(std::cerr << " *** Marking constant allowed us to simplify "
"all users and delete global!\n");
GV->getParent()->getGlobalList().erase(GV);
++NumDeleted;
}
++NumMarked;
return true;
} else if (!GS.isNotSuitableForSRA &&
!GV->getInitializer()->getType()->isFirstClassType()) {
if (GlobalVariable *FirstNewGV = SRAGlobal(GV)) {
GVI = FirstNewGV; // Don't skip the newly produced globals!
return true;
}
} else if (GS.StoredType == GlobalStatus::isStoredOnce) {
// 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,
getAnalysis<TargetData>()))
return true;
}
}
return false;
}
bool GlobalOpt::runOnModule(Module &M) {
bool Changed = false;
// As a prepass, delete functions that are trivially dead.
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
Function *F = FI++;
F->removeDeadConstantUsers();
if (F->use_empty() && (F->hasInternalLinkage() || F->hasWeakLinkage())) {
M.getFunctionList().erase(F);
LocalChange = true;
++NumFnDeleted;
}
}
Changed |= LocalChange;
}
LocalChange = true;
while (LocalChange) {
LocalChange = false;
for (Module::giterator GVI = M.gbegin(), E = M.gend(); GVI != E;) {
GlobalVariable *GV = GVI++;
if (!GV->isConstant() && GV->hasInternalLinkage() &&
GV->hasInitializer())
LocalChange |= ProcessInternalGlobal(GV, GVI);
}
Changed |= LocalChange;
}
return Changed;
}
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