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llvm-6502/lib/Transforms/IPO/GlobalOpt.cpp
Nate Begeman 14b0529532 Add support alignment of allocation instructions. 
Add support for specifying alignment and size of setjmp jmpbufs.

No targets currently do anything with this information, nor is it presrved
in the bytecode representation.  That's coming up next.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24196 91177308-0d34-0410-b5e6-96231b3b80d8
2005-11-05 09:21:28 +00:00

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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/CallingConv.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.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<> NumSubstitute("globalopt",
"Number of globals with initializers stored into them");
Statistic<> NumDeleted ("globalopt", "Number of globals deleted");
Statistic<> NumFnDeleted("globalopt", "Number of functions deleted");
Statistic<> NumGlobUses ("globalopt", "Number of global uses devirtualized");
Statistic<> NumLocalized("globalopt", "Number of globals localized");
Statistic<> NumShrunkToBool("globalopt",
"Number of global vars shrunk to booleans");
Statistic<> NumFastCallFns("globalopt",
"Number of functions converted to fastcc");
Statistic<> NumCtorsEvaluated("globalopt","Number of static ctors evaluated");
struct GlobalOpt : public ModulePass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetData>();
}
bool runOnModule(Module &M);
private:
GlobalVariable *FindGlobalCtors(Module &M);
bool OptimizeFunctions(Module &M);
bool OptimizeGlobalVars(Module &M);
bool OptimizeGlobalCtorsList(GlobalVariable *&GCL);
bool ProcessInternalGlobal(GlobalVariable *GV, Module::global_iterator &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;
// 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;
/// 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),
AccessingFunction(0), HasMultipleAccessingFunctions(false),
HasNonInstructionUser(false), 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)) {
GS.HasNonInstructionUser = true;
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 (!GS.HasMultipleAccessingFunctions) {
Function *F = I->getParent()->getParent();
if (GS.AccessingFunction == 0)
GS.AccessingFunction = F;
else if (GS.AccessingFunction != F)
GS.HasMultipleAccessingFunctions = true;
}
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))){
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;
// 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 (isa<SelectInst>(I)) {
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 if (isa<MemCpyInst>(I) || isa<MemMoveInst>(I)) {
if (I->getOperand(1) == V)
GS.StoredType = GlobalStatus::isStored;
if (I->getOperand(2) == V)
GS.isLoaded = true;
GS.isNotSuitableForSRA = true;
} else if (isa<MemSetInst>(I)) {
assert(I->getOperand(1) == V && "Memset only takes one pointer!");
GS.StoredType = GlobalStatus::isStored;
GS.isNotSuitableForSRA = true;
} 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 (!ConstantIsDead(C))
return true;
} else {
GS.HasNonInstructionUser = true;
// Otherwise must be some other user.
return true;
}
return false;
}
static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) {
ConstantInt *CI = dyn_cast<ConstantInt>(Idx);
if (!CI) return 0;
unsigned IdxV = (unsigned)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 (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) {
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);
Changed |= CleanupConstantGlobalUsers(CE, SubInit);
} else if (CE->getOpcode() == Instruction::Cast &&
isa<PointerType>(CE->getType())) {
// Pointer cast, delete any stores and memsets to the global.
Changed |= CleanupConstantGlobalUsers(CE, 0);
}
if (CE->use_empty()) {
CE->destroyConstant();
Changed = true;
}
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
Constant *SubInit = 0;
ConstantExpr *CE =
dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP));
if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
Changed |= CleanupConstantGlobalUsers(GEP, SubInit);
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 (ConstantIsDead(C)) {
C->destroyConstant();
// This could have invalidated UI, start over from scratch.
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->hasNUsesOrMore(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 =
(unsigned)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->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.
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 if (isa<SetCondInst>(*UI) &&
isa<ConstantPointerNull>(UI->getOperand(1))) {
// Ignore setcc X, null
} 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. 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)) {
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->eraseFromParent();
}
} 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->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) {
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->eraseFromParent();
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->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) {
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);
// 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 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(),
(unsigned)NElements->getRawValue());
MallocInst *NewMI =
new MallocInst(NewTy, Constant::getNullValue(Type::UIntTy),
MI->getAlignment(), 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->eraseFromParent();
MI = NewMI;
}
// Create the new global variable. The contents of the malloc'd memory is
// undefined, so initialize with an undef value.
Constant *Init = UndefValue::get(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);
Constant *RepValue = NewGV;
if (NewGV->getType() != GV->getType()->getElementType())
RepValue = ConstantExpr::getCast(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(Type::BoolTy, false, GlobalValue::InternalLinkage,
ConstantBool::False, GV->getName()+".init");
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<SetCondInst>(LoadUse.getUser()))
LoadUse = RepValue;
else {
// Replace the setcc X, 0 with a use of the bool value.
SetCondInst *SCI = cast<SetCondInst>(LoadUse.getUser());
Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", SCI);
InitBoolUsed = true;
switch (SCI->getOpcode()) {
default: assert(0 && "Unknown opcode!");
case Instruction::SetLT:
LV = ConstantBool::False; // X < null -> always false
break;
case Instruction::SetEQ:
case Instruction::SetLE:
LV = BinaryOperator::createNot(LV, "notinit", SCI);
break;
case Instruction::SetNE:
case Instruction::SetGE:
case Instruction::SetGT:
break; // no change.
}
SCI->replaceAllUsesWith(LV);
SCI->eraseFromParent();
}
}
LI->eraseFromParent();
} else {
StoreInst *SI = cast<StoreInst>(GV->use_back());
// The global is initialized when the store to it occurs.
new StoreInst(ConstantBool::True, 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);
if (RepValue != NewGV)
ConstantPropUsersOf(RepValue);
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) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI)
if (isa<LoadInst>(*UI) || isa<SetCondInst>(*UI)) {
// Fine, ignore.
} else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
return false; // Storing the pointer itself... bad.
// Otherwise, storing through it, or storing into GV... fine.
} else if (isa<GetElementPtrInst>(*UI) || isa<SelectInst>(*UI)) {
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(cast<Instruction>(*UI),GV))
return false;
} else {
return false;
}
return true;
}
// 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) {
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) &&
ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, GV)) {
GVI = OptimizeGlobalAddressOfMalloc(GV, MI);
return true;
}
}
}
return false;
}
/// ShrinkGlobalToBoolean - At this point, we have learned that the only two
/// values ever stored into GV are its initializer and OtherVal.
static void ShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
// Create the new global, initializing it to false.
GlobalVariable *NewGV = new GlobalVariable(Type::BoolTy, false,
GlobalValue::InternalLinkage, ConstantBool::False, GV->getName()+".b");
GV->getParent()->getGlobalList().insert(GV, NewGV);
Constant *InitVal = GV->getInitializer();
assert(InitVal->getType() != Type::BoolTy && "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->equalsInt(1);
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 = ConstantBool::get(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 if (!UI->use_empty()) {
// Change the load into a load of bool then a select.
LoadInst *LI = cast<LoadInst>(UI);
std::string Name = LI->getName(); LI->setName("");
LoadInst *NLI = new LoadInst(NewGV, Name+".b", LI);
Value *NSI;
if (IsOneZero)
NSI = new CastInst(NLI, LI->getType(), Name, LI);
else
NSI = new SelectInst(NLI, OtherVal, InitVal, Name, LI);
LI->replaceAllUsesWith(NSI);
}
UI->eraseFromParent();
}
GV->eraseFromParent();
}
/// 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) {
std::set<PHINode*> PHIUsers;
GlobalStatus GS;
GV->removeDeadConstantUsers();
if (GV->use_empty()) {
DEBUG(std::cerr << "GLOBAL DEAD: " << *GV);
GV->eraseFromParent();
++NumDeleted;
return true;
}
if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
// 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 first class types since we
// are just replacing static memory to stack memory.
if (!GS.HasMultipleAccessingFunctions &&
GS.AccessingFunction && !GS.HasNonInstructionUser &&
GV->getType()->getElementType()->isFirstClassType() &&
GS.AccessingFunction->getName() == "main" &&
GS.AccessingFunction->hasExternalLinkage()) {
DEBUG(std::cerr << "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) {
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->eraseFromParent();
++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->eraseFromParent();
++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) {
// 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 an undef 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());
if (GV->use_empty()) {
DEBUG(std::cerr << " *** 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,
getAnalysis<TargetData>()))
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 (GV->getType()->getElementType() != Type::BoolTy &&
!GV->getType()->getElementType()->isFloatingPoint()) {
DEBUG(std::cerr << " *** SHRINKING TO BOOL: " << *GV);
ShrinkGlobalToBoolean(GV, SOVConstant);
++NumShrunkToBool;
return true;
}
}
}
return false;
}
/// OnlyCalledDirectly - Return true if the specified function is only called
/// directly. In other words, its address is never taken.
static bool OnlyCalledDirectly(Function *F) {
for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
Instruction *User = dyn_cast<Instruction>(*UI);
if (!User) return false;
if (!isa<CallInst>(User) && !isa<InvokeInst>(User)) return false;
// See if the function address is passed as an argument.
for (unsigned i = 1, e = User->getNumOperands(); i != e; ++i)
if (User->getOperand(i) == F) return false;
}
return true;
}
/// 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){
Instruction *User = cast<Instruction>(*UI);
if (CallInst *CI = dyn_cast<CallInst>(User))
CI->setCallingConv(CallingConv::Fast);
else
cast<InvokeInst>(User)->setCallingConv(CallingConv::Fast);
}
}
bool GlobalOpt::OptimizeFunctions(Module &M) {
bool Changed = false;
// Optimize functions.
for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
Function *F = FI++;
F->removeDeadConstantUsers();
if (F->use_empty() && (F->hasInternalLinkage() ||
F->hasLinkOnceLinkage())) {
M.getFunctionList().erase(F);
Changed = true;
++NumFnDeleted;
} else if (F->hasInternalLinkage() &&
F->getCallingConv() == CallingConv::C && !F->isVarArg() &&
OnlyCalledDirectly(F)) {
// 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;
}
}
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++;
if (!GV->isConstant() && GV->hasInternalLinkage() &&
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::IntTy) 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::VoidTy || FTy->isVarArg() ||
FTy->getNumParams() != 0)
return 0;
// Verify that the initializer is simple enough for us to handle.
if (!I->hasInitializer()) return 0;
ConstantArray *CA = dyn_cast<ConstantArray>(I->getInitializer());
if (!CA) return 0;
for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i)
if (ConstantStruct *CS = dyn_cast<ConstantStruct>(CA->getOperand(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->getRawValue() != 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 (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i) {
ConstantStruct *CS = cast<ConstantStruct>(CA->getOperand(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) {
// If we made a change, reassemble the initializer list.
std::vector<Constant*> CSVals;
CSVals.push_back(ConstantSInt::get(Type::IntTy, 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::VoidTy,
std::vector<const Type*>(), false);
const PointerType *PFTy = PointerType::get(FTy);
CSVals[1] = Constant::getNullValue(PFTy);
CSVals[0] = ConstantSInt::get(Type::IntTy, 2147483647);
}
CAList.push_back(ConstantStruct::get(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(CA->getType(), GCL->isConstant(),
GCL->getLinkage(), CA,
GCL->getName());
GCL->setName("");
GCL->getParent()->getGlobalList().insert(GCL, NGV);
// 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::getCast(V, GCL->getType());
GCL->replaceAllUsesWith(V);
}
GCL->eraseFromParent();
if (Ctors.size())
return NGV;
else
return 0;
}
static Constant *getVal(std::map<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) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
if (!GV->hasExternalLinkage() && !GV->hasInternalLinkage())
return false; // do not allow weak/linkonce linkage.
return !GV->isExternal(); // 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->hasInternalLinkage())
return false; // do not allow weak/linkonce linkage.
return GV->hasInitializer() &&
ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
}
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) {
// 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 (unsigned i = 0, e = CS->getNumOperands(); i != e; ++i)
Elts.push_back(CS->getOperand(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 {
assert(0 && "This code is out of sync with "
" ConstantFoldLoadThroughGEPConstantExpr");
}
// Replace the element that we are supposed to.
ConstantUInt *CU = cast<ConstantUInt>(Addr->getOperand(OpNo));
assert(CU->getValue() < STy->getNumElements() &&
"Struct index out of range!");
unsigned Idx = (unsigned)CU->getValue();
Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
// Return the modified struct.
return ConstantStruct::get(Elts);
} 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 (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i)
Elts.push_back(CA->getOperand(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 {
assert(0 && "This code is out of sync with "
" ConstantFoldLoadThroughGEPConstantExpr");
}
assert((uint64_t)CI->getRawValue() < ATy->getNumElements());
Elts[(uint64_t)CI->getRawValue()] =
EvaluateStoreInto(Elts[(uint64_t)CI->getRawValue()], Val, Addr, OpNo+1);
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) {
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);
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 std::map<Constant*, Constant*> &Memory) {
// If this memory location has been recently stored, use the stored value: it
// is the most up-to-date.
std::map<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->hasInitializer())
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->hasInitializer())
return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
}
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 std::vector<Constant*> &ActualArgs,
std::vector<Function*> &CallStack,
std::map<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;
CallStack.push_back(F);
/// Values - As we compute SSA register values, we store their contents here.
std::map<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.
std::set<BasicBlock*> 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))
// 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 (ShiftInst *SI = dyn_cast<ShiftInst>(CurInst)) {
InstResult = ConstantExpr::get(SI->getOpcode(),
getVal(Values, SI->getOperand(0)),
getVal(Values, SI->getOperand(1)));
} else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
InstResult = ConstantExpr::getCast(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));
std::vector<Constant*> GEPOps;
for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
GEPOps.push_back(getVal(Values, GEP->getOperand(i)));
InstResult = ConstantExpr::getGetElementPtr(P, GEPOps);
} else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
if (LI->isVolatile()) return false; // no volatile accesses.
InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)),
MutatedMemory);
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(Ty, false,
GlobalValue::InternalLinkage,
UndefValue::get(Ty),
AI->getName()));
InstResult = AllocaTmps.back();
} else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) {
// Resolve function pointers.
Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0)));
if (!Callee) return false; // Cannot resolve.
std::vector<Constant*> Formals;
for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
Formals.push_back(getVal(Values, CI->getOperand(i)));
if (Callee->isExternal()) {
// If this is a function we can constant fold, do it.
if (Constant *C = ConstantFoldCall(Callee, Formals)) {
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 (TerminatorInst *TI = dyn_cast<TerminatorInst>(CurInst)) {
BasicBlock *NewBB = 0;
if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
if (BI->isUnconditional()) {
NewBB = BI->getSuccessor(0);
} else {
ConstantBool *Cond =
dyn_cast<ConstantBool>(getVal(Values, BI->getCondition()));
if (!Cond) return false; // Cannot determine.
NewBB = BI->getSuccessor(!Cond->getValue());
}
} 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).second)
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.
std::map<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, std::vector<Constant*>(),
CallStack, MutatedMemory, AllocaTmps);
if (EvalSuccess) {
// We succeeded at evaluation: commit the result.
DEBUG(std::cerr << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" <<
F->getName() << "' to " << MutatedMemory.size() << " stores.\n");
for (std::map<Constant*, Constant*>::iterator I = MutatedMemory.begin(),
E = MutatedMemory.end(); I != E; ++I)
CommitValueTo(I->second, I->first);
}
// 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);
return true;
}
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);
Changed |= LocalChange;
}
// TODO: Move all global ctors functions to the end of the module for code
// layout.
return Changed;
}
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