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llvm-6502/lib/Transforms/IPO/GlobalOpt.cpp
Bill Wendling 8e47daf285 Remove some introspection functions. 
The 'getSlot' function and its ilk allow introspection into the AttributeSet
class. However, that class should be opaque. Allow access through accessor
methods instead.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173522 91177308-0d34-0410-b5e6-96231b3b80d8
2013-01-25 23:09:36 +00:00

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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/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Support/CallSite.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/Target/TargetLibraryInfo.h"
#include <algorithm>
using namespace llvm;
STATISTIC(NumMarked , "Number of globals marked constant");
STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr");
STATISTIC(NumSRA , "Number of aggregate globals broken into scalars");
STATISTIC(NumHeapSRA , "Number of heap objects SRA'd");
STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
STATISTIC(NumDeleted , "Number of globals deleted");
STATISTIC(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");
STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
namespace {
struct GlobalStatus;
struct GlobalOpt : public ModulePass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetLibraryInfo>();
}
static char ID; // Pass identification, replacement for typeid
GlobalOpt() : ModulePass(ID) {
initializeGlobalOptPass(*PassRegistry::getPassRegistry());
}
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 ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI,
const SmallPtrSet<const PHINode*, 16> &PHIUsers,
const GlobalStatus &GS);
bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn);
DataLayout *TD;
TargetLibraryInfo *TLI;
};
}
char GlobalOpt::ID = 0;
INITIALIZE_PASS_BEGIN(GlobalOpt, "globalopt",
"Global Variable Optimizer", false, false)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
INITIALIZE_PASS_END(GlobalOpt, "globalopt",
"Global Variable Optimizer", false, false)
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 GlobalStatus {
/// isCompared - True if the global's address is used in a comparison.
bool isCompared;
/// 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.
const 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;
/// AtomicOrdering - Set to the strongest atomic ordering requirement.
AtomicOrdering Ordering;
GlobalStatus() : isCompared(false), isLoaded(false), StoredType(NotStored),
StoredOnceValue(0), AccessingFunction(0),
HasMultipleAccessingFunctions(false),
HasNonInstructionUser(false), Ordering(NotAtomic) {}
};
}
/// StrongerOrdering - Return the stronger of the two ordering. If the two
/// orderings are acquire and release, then return AcquireRelease.
///
static AtomicOrdering StrongerOrdering(AtomicOrdering X, AtomicOrdering Y) {
if (X == Acquire && Y == Release) return AcquireRelease;
if (Y == Acquire && X == Release) return AcquireRelease;
return (AtomicOrdering)std::max(X, Y);
}
/// 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(const Constant *C) {
if (isa<GlobalValue>(C)) return false;
for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E;
++UI)
if (const 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(const Value *V, GlobalStatus &GS,
SmallPtrSet<const PHINode*, 16> &PHIUsers) {
for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
++UI) {
const User *U = *UI;
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
GS.HasNonInstructionUser = true;
// If the result of the constantexpr isn't pointer type, then we won't
// know to expect it in various places. Just reject early.
if (!isa<PointerType>(CE->getType())) return true;
if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
} else if (const Instruction *I = dyn_cast<Instruction>(U)) {
if (!GS.HasMultipleAccessingFunctions) {
const Function *F = I->getParent()->getParent();
if (GS.AccessingFunction == 0)
GS.AccessingFunction = F;
else if (GS.AccessingFunction != F)
GS.HasMultipleAccessingFunctions = true;
}
if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
GS.isLoaded = true;
// Don't hack on volatile loads.
if (LI->isVolatile()) return true;
GS.Ordering = StrongerOrdering(GS.Ordering, LI->getOrdering());
} else if (const 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;
// Don't hack on volatile stores.
if (SI->isVolatile()) return true;
GS.Ordering = StrongerOrdering(GS.Ordering, SI->getOrdering());
// 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 (const GlobalVariable *GV = dyn_cast<GlobalVariable>(
SI->getOperand(1))) {
Value *StoredVal = SI->getOperand(0);
if (Constant *C = dyn_cast<Constant>(StoredVal)) {
if (C->isThreadDependent()) {
// The stored value changes between threads; don't track it.
return true;
}
}
if (StoredVal == GV->getInitializer()) {
if (GS.StoredType < GlobalStatus::isInitializerStored)
GS.StoredType = GlobalStatus::isInitializerStored;
} else if (isa<LoadInst>(StoredVal) &&
cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
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<BitCastInst>(I)) {
if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
} 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 (const 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;
} else if (isa<CmpInst>(I)) {
GS.isCompared = true;
} else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) {
if (MTI->isVolatile()) return true;
if (MTI->getArgOperand(0) == V)
GS.StoredType = GlobalStatus::isStored;
if (MTI->getArgOperand(1) == V)
GS.isLoaded = true;
} else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) {
assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!");
if (MSI->isVolatile()) return true;
GS.StoredType = GlobalStatus::isStored;
} else {
return true; // Any other non-load instruction might take address!
}
} else if (const Constant *C = dyn_cast<Constant>(U)) {
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;
}
/// isLeakCheckerRoot - Is this global variable possibly used by a leak checker
/// as a root? If so, we might not really want to eliminate the stores to it.
static bool isLeakCheckerRoot(GlobalVariable *GV) {
// A global variable is a root if it is a pointer, or could plausibly contain
// a pointer. There are two challenges; one is that we could have a struct
// the has an inner member which is a pointer. We recurse through the type to
// detect these (up to a point). The other is that we may actually be a union
// of a pointer and another type, and so our LLVM type is an integer which
// gets converted into a pointer, or our type is an [i8 x #] with a pointer
// potentially contained here.
if (GV->hasPrivateLinkage())
return false;
SmallVector<Type *, 4> Types;
Types.push_back(cast<PointerType>(GV->getType())->getElementType());
unsigned Limit = 20;
do {
Type *Ty = Types.pop_back_val();
switch (Ty->getTypeID()) {
default: break;
case Type::PointerTyID: return true;
case Type::ArrayTyID:
case Type::VectorTyID: {
SequentialType *STy = cast<SequentialType>(Ty);
Types.push_back(STy->getElementType());
break;
}
case Type::StructTyID: {
StructType *STy = cast<StructType>(Ty);
if (STy->isOpaque()) return true;
for (StructType::element_iterator I = STy->element_begin(),
E = STy->element_end(); I != E; ++I) {
Type *InnerTy = *I;
if (isa<PointerType>(InnerTy)) return true;
if (isa<CompositeType>(InnerTy))
Types.push_back(InnerTy);
}
break;
}
}
if (--Limit == 0) return true;
} while (!Types.empty());
return false;
}
/// Given a value that is stored to a global but never read, determine whether
/// it's safe to remove the store and the chain of computation that feeds the
/// store.
static bool IsSafeComputationToRemove(Value *V, const TargetLibraryInfo *TLI) {
do {
if (isa<Constant>(V))
return true;
if (!V->hasOneUse())
return false;
if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) ||
isa<GlobalValue>(V))
return false;
if (isAllocationFn(V, TLI))
return true;
Instruction *I = cast<Instruction>(V);
if (I->mayHaveSideEffects())
return false;
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
if (!GEP->hasAllConstantIndices())
return false;
} else if (I->getNumOperands() != 1) {
return false;
}
V = I->getOperand(0);
} while (1);
}
/// CleanupPointerRootUsers - This GV is a pointer root. Loop over all users
/// of the global and clean up any that obviously don't assign the global a
/// value that isn't dynamically allocated.
///
static bool CleanupPointerRootUsers(GlobalVariable *GV,
const TargetLibraryInfo *TLI) {
// A brief explanation of leak checkers. The goal is to find bugs where
// pointers are forgotten, causing an accumulating growth in memory
// usage over time. The common strategy for leak checkers is to whitelist the
// memory pointed to by globals at exit. This is popular because it also
// solves another problem where the main thread of a C++ program may shut down
// before other threads that are still expecting to use those globals. To
// handle that case, we expect the program may create a singleton and never
// destroy it.
bool Changed = false;
// If Dead[n].first is the only use of a malloc result, we can delete its
// chain of computation and the store to the global in Dead[n].second.
SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
// Constants can't be pointers to dynamically allocated memory.
for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
UI != E;) {
User *U = *UI++;
if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
Value *V = SI->getValueOperand();
if (isa<Constant>(V)) {
Changed = true;
SI->eraseFromParent();
} else if (Instruction *I = dyn_cast<Instruction>(V)) {
if (I->hasOneUse())
Dead.push_back(std::make_pair(I, SI));
}
} else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) {
if (isa<Constant>(MSI->getValue())) {
Changed = true;
MSI->eraseFromParent();
} else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) {
if (I->hasOneUse())
Dead.push_back(std::make_pair(I, MSI));
}
} else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) {
GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource());
if (MemSrc && MemSrc->isConstant()) {
Changed = true;
MTI->eraseFromParent();
} else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) {
if (I->hasOneUse())
Dead.push_back(std::make_pair(I, MTI));
}
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
if (CE->use_empty()) {
CE->destroyConstant();
Changed = true;
}
} else if (Constant *C = dyn_cast<Constant>(U)) {
if (SafeToDestroyConstant(C)) {
C->destroyConstant();
// This could have invalidated UI, start over from scratch.
Dead.clear();
CleanupPointerRootUsers(GV, TLI);
return true;
}
}
}
for (int i = 0, e = Dead.size(); i != e; ++i) {
if (IsSafeComputationToRemove(Dead[i].first, TLI)) {
Dead[i].second->eraseFromParent();
Instruction *I = Dead[i].first;
do {
if (isAllocationFn(I, TLI))
break;
Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
if (!J)
break;
I->eraseFromParent();
I = J;
} while (1);
I->eraseFromParent();
}
}
return Changed;
}
/// 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,
DataLayout *TD, TargetLibraryInfo *TLI) {
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, TD, TLI);
} else if (CE->getOpcode() == Instruction::BitCast &&
CE->getType()->isPointerTy()) {
// Pointer cast, delete any stores and memsets to the global.
Changed |= CleanupConstantGlobalUsers(CE, 0, TD, TLI);
}
if (CE->use_empty()) {
CE->destroyConstant();
Changed = true;
}
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
// Do not transform "gepinst (gep constexpr (GV))" here, because forming
// "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
// and will invalidate our notion of what Init is.
Constant *SubInit = 0;
if (!isa<ConstantExpr>(GEP->getOperand(0))) {
ConstantExpr *CE =
dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, TD, TLI));
if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
// If the initializer is an all-null value and we have an inbounds GEP,
// we already know what the result of any load from that GEP is.
// TODO: Handle splats.
if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
SubInit = Constant::getNullValue(GEP->getType()->getElementType());
}
Changed |= CleanupConstantGlobalUsers(GEP, SubInit, TD, TLI);
if (GEP->use_empty()) {
GEP->eraseFromParent();
Changed = true;
}
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
if (MI->getRawDest() == V) {
MI->eraseFromParent();
Changed = true;
}
} else if (Constant *C = dyn_cast<Constant>(U)) {
// If we have a chain of dead constantexprs or other things dangling from
// us, and if they are all dead, nuke them without remorse.
if (SafeToDestroyConstant(C)) {
C->destroyConstant();
// This could have invalidated UI, start over from scratch.
CleanupConstantGlobalUsers(V, Init, TD, TLI);
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 (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
uint64_t NumElements = AT->getNumElements();
ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
// Check to make sure that index falls within the array. If not,
// something funny is going on, so we won't do the optimization.
//
if (Idx->getZExtValue() >= NumElements)
return false;
// We cannot scalar repl this level of the array unless any array
// sub-indices are in-range constants. In particular, consider:
// A[0][i]. We cannot know that the user isn't doing invalid things like
// allowing i to index an out-of-range subscript that accesses A[1].
//
// Scalar replacing *just* the outer index of the array is probably not
// going to be a win anyway, so just give up.
for (++GEPI; // Skip array index.
GEPI != E;
++GEPI) {
uint64_t NumElements;
if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
NumElements = SubArrayTy->getNumElements();
else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
NumElements = SubVectorTy->getNumElements();
else {
assert((*GEPI)->isStructTy() &&
"Indexed GEP type is not array, vector, or struct!");
continue;
}
ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
return false;
}
}
for (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 DataLayout &TD) {
// 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();
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 (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 = Init->getAggregateElement(i);
assert(In && "Couldn't get element of initializer?");
GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
GlobalVariable::InternalLinkage,
In, GV->getName()+"."+Twine(i),
GV->getThreadLocalMode(),
GV->getType()->getAddressSpace());
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 (SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
unsigned NumElements = 0;
if (ArrayType *ATy = dyn_cast<ArrayType>(STy))
NumElements = ATy->getNumElements();
else
NumElements = cast<VectorType>(STy)->getNumElements();
if (NumElements > 16 && GV->hasNUsesOrMore(16))
return 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 = Init->getAggregateElement(i);
assert(In && "Couldn't get element of initializer?");
GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
GlobalVariable::InternalLinkage,
In, GV->getName()+"."+Twine(i),
GV->getThreadLocalMode(),
GV->getType()->getAddressSpace());
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;
DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV);
Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
// Loop over all of the uses of the global, replacing the constantexpr geps,
// with smaller constantexpr geps or direct references.
while (!GV->use_empty()) {
User *GEP = GV->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);
} 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,
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(const Value *V,
SmallPtrSet<const PHINode*, 8> &PHIs) {
for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
++UI) {
const User *U = *UI;
if (isa<LoadInst>(U)) {
// Will trap.
} else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
if (SI->getOperand(0) == V) {
//cerr << "NONTRAPPING USE: " << *U;
return false; // Storing the value.
}
} else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
if (CI->getCalledValue() != V) {
//cerr << "NONTRAPPING USE: " << *U;
return false; // Not calling the ptr
}
} else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
if (II->getCalledValue() != V) {
//cerr << "NONTRAPPING USE: " << *U;
return false; // Not calling the ptr
}
} else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
} else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
} else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
// If we've already seen this phi node, ignore it, it has already been
// checked.
if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
return false;
} else if (isa<ICmpInst>(U) &&
isa<ConstantPointerNull>(UI->getOperand(1))) {
// Ignore icmp X, null
} else {
//cerr << "NONTRAPPING USE: " << *U;
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(const GlobalVariable *GV) {
for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
UI != E; ++UI) {
const User *U = *UI;
if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
SmallPtrSet<const PHINode*, 8> PHIs;
if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
return false;
} else if (isa<StoreInst>(U)) {
// Ignore stores to the global.
} else {
// We don't know or understand this user, bail out.
//cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
return false;
}
}
return true;
}
static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
bool Changed = false;
for (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)) {
CallSite CS(I);
if (CS.getCalledValue() == V) {
// Calling through the pointer! Turn into a direct call, but be careful
// that the pointer is not also being passed as an argument.
CS.setCalledFunction(NewV);
Changed = true;
bool PassedAsArg = false;
for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
if (CS.getArgument(i) == V) {
PassedAsArg = true;
CS.setArgument(i, NewV);
}
if (PassedAsArg) {
// Being passed as an argument also. Be careful to not invalidate UI!
UI = V->use_begin();
}
}
} else if (CastInst *CI = dyn_cast<CastInst>(I)) {
Changed |= OptimizeAwayTrappingUsesOfValue(CI,
ConstantExpr::getCast(CI->getOpcode(),
NewV, CI->getType()));
if (CI->use_empty()) {
Changed = true;
CI->eraseFromParent();
}
} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
// Should handle GEP here.
SmallVector<Constant*, 8> Idxs;
Idxs.reserve(GEPI->getNumOperands()-1);
for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
i != e; ++i)
if (Constant *C = dyn_cast<Constant>(*i))
Idxs.push_back(C);
else
break;
if (Idxs.size() == GEPI->getNumOperands()-1)
Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
ConstantExpr::getGetElementPtr(NewV, Idxs));
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,
DataLayout *TD,
TargetLibraryInfo *TLI) {
bool Changed = false;
// Keep track of whether we are able to remove all the uses of the global
// other than the store that defines it.
bool AllNonStoreUsesGone = true;
// Replace all uses of loads with uses of uses of the stored value.
for (Value::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);
// If we were able to delete all uses of the loads
if (LI->use_empty()) {
LI->eraseFromParent();
Changed = true;
} else {
AllNonStoreUsesGone = false;
}
} else if (isa<StoreInst>(GlobalUser)) {
// Ignore the store that stores "LV" to the global.
assert(GlobalUser->getOperand(1) == GV &&
"Must be storing *to* the global");
} else {
AllNonStoreUsesGone = false;
// If we get here we could have other crazy uses that are transitively
// loaded.
assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) ||
isa<BitCastInst>(GlobalUser) ||
isa<GetElementPtrInst>(GlobalUser)) &&
"Only expect load and stores!");
}
}
if (Changed) {
DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV);
++NumGlobUses;
}
// If we nuked all of the loads, then none of the stores are needed either,
// nor is the global.
if (AllNonStoreUsesGone) {
if (isLeakCheckerRoot(GV)) {
Changed |= CleanupPointerRootUsers(GV, TLI);
} else {
Changed = true;
CleanupConstantGlobalUsers(GV, 0, TD, TLI);
}
if (GV->use_empty()) {
DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
Changed = true;
GV->eraseFromParent();
++NumDeleted;
}
}
return Changed;
}
/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
/// instructions that are foldable.
static void ConstantPropUsersOf(Value *V,
DataLayout *TD, TargetLibraryInfo *TLI) {
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, TD, TLI)) {
I->replaceAllUsesWith(NewC);
// Advance UI to the next non-I use to avoid invalidating it!
// Instructions could multiply use V.
while (UI != E && *UI == I)
++UI;
I->eraseFromParent();
}
}
/// 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,
CallInst *CI,
Type *AllocTy,
ConstantInt *NElements,
DataLayout *TD,
TargetLibraryInfo *TLI) {
DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n');
Type *GlobalType;
if (NElements->getZExtValue() == 1)
GlobalType = AllocTy;
else
// If we have an array allocation, the global variable is of an array.
GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
// Create the new global variable. The contents of the malloc'd memory is
// undefined, so initialize with an undef value.
GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(),
GlobalType, false,
GlobalValue::InternalLinkage,
UndefValue::get(GlobalType),
GV->getName()+".body",
GV,
GV->getThreadLocalMode());
// If there are bitcast users of the malloc (which is typical, usually we have
// a malloc + bitcast) then replace them with uses of the new global. Update
// other users to use the global as well.
BitCastInst *TheBC = 0;
while (!CI->use_empty()) {
Instruction *User = cast<Instruction>(CI->use_back());
if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
if (BCI->getType() == NewGV->getType()) {
BCI->replaceAllUsesWith(NewGV);
BCI->eraseFromParent();
} else {
BCI->setOperand(0, NewGV);
}
} else {
if (TheBC == 0)
TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
User->replaceUsesOfWith(CI, TheBC);
}
}
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(Type::getInt1Ty(GV->getContext()), false,
GlobalValue::InternalLinkage,
ConstantInt::getFalse(GV->getContext()),
GV->getName()+".init", GV->getThreadLocalMode());
bool InitBoolUsed = false;
// Loop over all uses of GV, processing them in turn.
while (!GV->use_empty()) {
if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) {
// The global is initialized when the store to it occurs.
new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
SI->getOrdering(), SI->getSynchScope(), SI);
SI->eraseFromParent();
continue;
}
LoadInst *LI = cast<LoadInst>(GV->use_back());
while (!LI->use_empty()) {
Use &LoadUse = LI->use_begin().getUse();
if (!isa<ICmpInst>(LoadUse.getUser())) {
LoadUse = RepValue;
continue;
}
ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser());
// Replace the cmp X, 0 with a use of the bool value.
// Sink the load to where the compare was, if atomic rules allow us to.
Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
LI->getOrdering(), LI->getSynchScope(),
LI->isUnordered() ? (Instruction*)ICI : LI);
InitBoolUsed = true;
switch (ICI->getPredicate()) {
default: llvm_unreachable("Unknown ICmp Predicate!");
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_SLT: // X < null -> always false
LV = ConstantInt::getFalse(GV->getContext());
break;
case ICmpInst::ICMP_ULE:
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_EQ:
LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
break;
case ICmpInst::ICMP_NE:
case ICmpInst::ICMP_UGE:
case ICmpInst::ICMP_SGE:
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_SGT:
break; // no change.
}
ICI->replaceAllUsesWith(LV);
ICI->eraseFromParent();
}
LI->eraseFromParent();
}
// If the initialization boolean was used, insert it, otherwise delete it.
if (!InitBoolUsed) {
while (!InitBool->use_empty()) // Delete initializations
cast<StoreInst>(InitBool->use_back())->eraseFromParent();
delete InitBool;
} else
GV->getParent()->getGlobalList().insert(GV, InitBool);
// Now the GV is dead, nuke it and the malloc..
GV->eraseFromParent();
CI->eraseFromParent();
// To further other optimizations, loop over all users of NewGV and try to
// constant prop them. This will promote GEP instructions with constant
// indices into GEP constant-exprs, which will allow global-opt to hack on it.
ConstantPropUsersOf(NewGV, TD, TLI);
if (RepValue != NewGV)
ConstantPropUsersOf(RepValue, TD, TLI);
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(const Instruction *V,
const GlobalVariable *GV,
SmallPtrSet<const PHINode*, 8> &PHIs) {
for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end();
UI != E; ++UI) {
const Instruction *Inst = cast<Instruction>(*UI);
if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
continue; // Fine, ignore.
}
if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
return false; // Storing the pointer itself... bad.
continue; // Otherwise, storing through it, or storing into GV... fine.
}
// Must index into the array and into the struct.
if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
return false;
continue;
}
if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
// PHIs are ok if all uses are ok. Don't infinitely recurse through PHI
// cycles.
if (PHIs.insert(PN))
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
return false;
continue;
}
if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
return false;
continue;
}
return false;
}
return true;
}
/// 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(const Value *V,
SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs,
SmallPtrSet<const 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::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
++UI) {
const Instruction *User = cast<Instruction>(*UI);
// Comparison against null is ok.
if (const 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 (const 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 (const 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(const GlobalVariable *GV,
Instruction *StoredVal) {
SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
UI != E; ++UI)
if (const 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<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin()
, E = LoadUsingPHIs.end(); I != E; ++I) {
const 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 == StoredVal) continue;
if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
// One of the PHIs in our set is (optimistically) ok.
if (LoadUsingPHIs.count(InPN))
continue;
return false;
}
// Load from GV is ok.
if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
if (LI->getOperand(0) == GV)
continue;
// UNDEF? NULL?
// Anything else is rejected.
return false;
}
}
return true;
}
static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
if (FieldNo >= FieldVals.size())
FieldVals.resize(FieldNo+1);
// If we already have this value, just reuse the previously scalarized
// version.
if (Value *FieldVal = FieldVals[FieldNo])
return FieldVal;
// Depending on what instruction this is, we have several cases.
Value *Result;
if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
// This is a scalarized version of the load from the global. Just create
// a new Load of the scalarized global.
Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
InsertedScalarizedValues,
PHIsToRewrite),
LI->getName()+".f"+Twine(FieldNo), LI);
} else if (PHINode *PN = dyn_cast<PHINode>(V)) {
// PN's type is pointer to struct. Make a new PHI of pointer to struct
// field.
StructType *ST =
cast<StructType>(cast<PointerType>(PN->getType())->getElementType());
PHINode *NewPN =
PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)),
PN->getNumIncomingValues(),
PN->getName()+".f"+Twine(FieldNo), PN);
Result = NewPN;
PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
} else {
llvm_unreachable("Unknown usable value");
}
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) {
// If this is a comparison against null, handle it.
if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
// If we have a setcc of the loaded pointer, we can use a setcc of any
// field.
Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
InsertedScalarizedValues, PHIsToRewrite);
Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
Constant::getNullValue(NPtr->getType()),
SCI->getName());
SCI->replaceAllUsesWith(New);
SCI->eraseFromParent();
return;
}
// Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
&& "Unexpected GEPI!");
// Load the pointer for this field.
unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
InsertedScalarizedValues, PHIsToRewrite);
// Create the new GEP idx vector.
SmallVector<Value*, 8> GEPIdx;
GEPIdx.push_back(GEPI->getOperand(1));
GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
Value *NGEPI = GetElementPtrInst::Create(NewPtr, GEPIdx,
GEPI->getName(), GEPI);
GEPI->replaceAllUsesWith(NGEPI);
GEPI->eraseFromParent();
return;
}
// Recursively transform the users of PHI nodes. This will lazily create the
// PHIs that are needed for individual elements. Keep track of what PHIs we
// see in InsertedScalarizedValues so that we don't get infinite loops (very
// antisocial). If the PHI is already in InsertedScalarizedValues, it has
// already been seen first by another load, so its uses have already been
// processed.
PHINode *PN = cast<PHINode>(LoadUser);
if (!InsertedScalarizedValues.insert(std::make_pair(PN,
std::vector<Value*>())).second)
return;
// If this is the first time we've seen this PHI, recursively process all
// users.
for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) {
Instruction *User = cast<Instruction>(*UI++);
RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
}
}
/// 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) {
for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end();
UI != E; ) {
Instruction *User = cast<Instruction>(*UI++);
RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
}
if (Load->use_empty()) {
Load->eraseFromParent();
InsertedScalarizedValues.erase(Load);
}
}
/// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break
/// it up into multiple allocations of arrays of the fields.
static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
Value *NElems, DataLayout *TD,
const TargetLibraryInfo *TLI) {
DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n');
Type *MAT = getMallocAllocatedType(CI, TLI);
StructType *STy = cast<StructType>(MAT);
// There is guaranteed to be at least one use of the malloc (storing
// it into GV). If there are other uses, change them to be uses of
// the global to simplify later code. This also deletes the store
// into GV.
ReplaceUsesOfMallocWithGlobal(CI, GV);
// Okay, at this point, there are no users of the malloc. Insert N
// new mallocs at the same place as CI, and N globals.
std::vector<Value*> FieldGlobals;
std::vector<Value*> FieldMallocs;
for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
Type *FieldTy = STy->getElementType(FieldNo);
PointerType *PFieldTy = PointerType::getUnqual(FieldTy);
GlobalVariable *NGV =
new GlobalVariable(*GV->getParent(),
PFieldTy, false, GlobalValue::InternalLinkage,
Constant::getNullValue(PFieldTy),
GV->getName() + ".f" + Twine(FieldNo), GV,
GV->getThreadLocalMode());
FieldGlobals.push_back(NGV);
unsigned TypeSize = TD->getTypeAllocSize(FieldTy);
if (StructType *ST = dyn_cast<StructType>(FieldTy))
TypeSize = TD->getStructLayout(ST)->getSizeInBytes();
Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
ConstantInt::get(IntPtrTy, TypeSize),
NElems, 0,
CI->getName() + ".f" + Twine(FieldNo));
FieldMallocs.push_back(NMI);
new StoreInst(NMI, NGV, CI);
}
// The tricky aspect of this transformation is handling the case when malloc
// fails. In the original code, malloc failing would set the result pointer
// of malloc to null. In this case, some mallocs could succeed and others
// could fail. As such, we emit code that looks like this:
// F0 = malloc(field0)
// F1 = malloc(field1)
// F2 = malloc(field2)
// if (F0 == 0 || F1 == 0 || F2 == 0) {
// if (F0) { free(F0); F0 = 0; }
// if (F1) { free(F1); F1 = 0; }
// if (F2) { free(F2); F2 = 0; }
// }
// The malloc can also fail if its argument is too large.
Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
ConstantZero, "isneg");
for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
Constant::getNullValue(FieldMallocs[i]->getType()),
"isnull");
RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
}
// Split the basic block at the old malloc.
BasicBlock *OrigBB = CI->getParent();
BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont");
// Create the block to check the first condition. Put all these blocks at the
// end of the function as they are unlikely to be executed.
BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
"malloc_ret_null",
OrigBB->getParent());
// Remove the uncond branch from OrigBB to ContBB, turning it into a cond
// branch on RunningOr.
OrigBB->getTerminator()->eraseFromParent();
BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
// Within the NullPtrBlock, we need to emit a comparison and branch for each
// pointer, because some may be null while others are not.
for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
Constant::getNullValue(GVVal->getType()));
BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
OrigBB->getParent());
BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
OrigBB->getParent());
Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
Cmp, NullPtrBlock);
// Fill in FreeBlock.
CallInst::CreateFree(GVVal, BI);
new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
FreeBlock);
BranchInst::Create(NextBlock, FreeBlock);
NullPtrBlock = NextBlock;
}
BranchInst::Create(ContBB, NullPtrBlock);
// CI is no longer needed, remove it.
CI->eraseFromParent();
/// 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);
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) {
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);
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,
CallInst *CI,
Type *AllocTy,
AtomicOrdering Ordering,
Module::global_iterator &GVI,
DataLayout *TD,
TargetLibraryInfo *TLI) {
if (!TD)
return false;
// If this is a malloc of an abstract type, don't touch it.
if (!AllocTy->isSized())
return false;
// We can't optimize this global unless all uses of it are *known* to be
// of the malloc value, not of the null initializer value (consider a use
// that compares the global's value against zero to see if the malloc has
// been reached). To do this, we check to see if all uses of the global
// would trap if the global were null: this proves that they must all
// happen after the malloc.
if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
return false;
// We can't optimize this if the malloc itself is used in a complex way,
// for example, being stored into multiple globals. This allows the
// malloc to be stored into the specified global, loaded icmp'd, and
// GEP'd. These are all things we could transform to using the global
// for.
SmallPtrSet<const PHINode*, 8> PHIs;
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
return false;
// If we have a global that is only initialized with a fixed size malloc,
// transform the program to use global memory instead of malloc'd memory.
// This eliminates dynamic allocation, avoids an indirection accessing the
// data, and exposes the resultant global to further GlobalOpt.
// We cannot optimize the malloc if we cannot determine malloc array size.
Value *NElems = getMallocArraySize(CI, TD, TLI, true);
if (!NElems)
return false;
if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
// Restrict this transformation to only working on small allocations
// (2048 bytes currently), as we don't want to introduce a 16M global or
// something.
if (NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) {
GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD, TLI);
return true;
}
// If the allocation is an array of structures, consider transforming this
// into multiple malloc'd arrays, one for each field. This is basically
// SRoA for malloc'd memory.
if (Ordering != NotAtomic)
return false;
// If this is an allocation of a fixed size array of structs, analyze as a
// variable size array. malloc [100 x struct],1 -> malloc struct, 100
if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
AllocTy = AT->getElementType();
StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
if (!AllocSTy)
return false;
// This the structure has an unreasonable number of fields, leave it
// alone.
if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
// If this is a fixed size array, transform the Malloc to be an alloc of
// structs. malloc [100 x struct],1 -> malloc struct, 100
if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) {
Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes();
Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy,
AllocSize, NumElements,
0, CI->getName());
Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
CI->replaceAllUsesWith(Cast);
CI->eraseFromParent();
if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc))
CI = cast<CallInst>(BCI->getOperand(0));
else
CI = cast<CallInst>(Malloc);
}
GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, TLI, true),
TD, TLI);
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,
AtomicOrdering Ordering,
Module::global_iterator &GVI,
DataLayout *TD, TargetLibraryInfo *TLI) {
// Ignore no-op GEPs and bitcasts.
StoredOnceVal = StoredOnceVal->stripPointerCasts();
// If we are dealing with a pointer global that is initialized to null and
// only has one (non-null) value stored into it, then we can optimize any
// users of the loaded value (often calls and loads) that would trap if the
// value was null.
if (GV->getInitializer()->getType()->isPointerTy() &&
GV->getInitializer()->isNullValue()) {
if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
if (GV->getInitializer()->getType() != SOVC->getType())
SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
// Optimize away any trapping uses of the loaded value.
if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, TD, TLI))
return true;
} else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) {
Type *MallocType = getMallocAllocatedType(CI, TLI);
if (MallocType &&
TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, Ordering, GVI,
TD, TLI))
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) {
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(GV->getContext()) ||
GVElType->isFloatingPointTy() ||
GVElType->isPointerTy() || GVElType->isVectorTy())
return false;
// Walk the use list of the global seeing if all the uses are load or store.
// If there is anything else, bail out.
for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){
User *U = *I;
if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
return false;
}
DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV);
// Create the new global, initializing it to false.
GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
false,
GlobalValue::InternalLinkage,
ConstantInt::getFalse(GV->getContext()),
GV->getName()+".b",
GV->getThreadLocalMode(),
GV->getType()->getAddressSpace());
GV->getParent()->getGlobalList().insert(GV, NewGV);
Constant *InitVal = GV->getInitializer();
assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
"No reason to shrink to bool!");
// If initialized to zero and storing one into the global, we can use a cast
// instead of a select to synthesize the desired value.
bool IsOneZero = false;
if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
IsOneZero = InitVal->isNullValue() && CI->isOne();
while (!GV->use_empty()) {
Instruction *UI = cast<Instruction>(GV->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(GV->getContext()),
StoringOther);
else {
// Otherwise, we are storing a previously loaded copy. To do this,
// change the copy from copying the original value to just copying the
// bool.
Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
// If we've already replaced the input, StoredVal will be a cast or
// select instruction. If not, it will be a load of the original
// global.
if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
assert(LI->getOperand(0) == GV && "Not a copy!");
// Insert a new load, to preserve the saved value.
StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
LI->getOrdering(), LI->getSynchScope(), LI);
} else {
assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
"This is not a form that we understand!");
StoreVal = StoredVal->getOperand(0);
assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
}
}
new StoreInst(StoreVal, NewGV, false, 0,
SI->getOrdering(), SI->getSynchScope(), SI);
} else {
// Change the load into a load of bool then a select.
LoadInst *LI = cast<LoadInst>(UI);
LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
LI->getOrdering(), LI->getSynchScope(), LI);
Value *NSI;
if (IsOneZero)
NSI = new ZExtInst(NLI, LI->getType(), "", LI);
else
NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
NSI->takeName(LI);
LI->replaceAllUsesWith(NSI);
}
UI->eraseFromParent();
}
GV->eraseFromParent();
return true;
}
/// ProcessGlobal - Analyze the specified global variable and optimize it if
/// possible. If we make a change, return true.
bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
Module::global_iterator &GVI) {
if (!GV->isDiscardableIfUnused())
return false;
// Do more involved optimizations if the global is internal.
GV->removeDeadConstantUsers();
if (GV->use_empty()) {
DEBUG(dbgs() << "GLOBAL DEAD: " << *GV);
GV->eraseFromParent();
++NumDeleted;
return true;
}
if (!GV->hasLocalLinkage())
return false;
SmallPtrSet<const PHINode*, 16> PHIUsers;
GlobalStatus GS;
if (AnalyzeGlobal(GV, GS, PHIUsers))
return false;
if (!GS.isCompared && !GV->hasUnnamedAddr()) {
GV->setUnnamedAddr(true);
NumUnnamed++;
}
if (GV->isConstant() || !GV->hasInitializer())
return false;
return ProcessInternalGlobal(GV, GVI, PHIUsers, GS);
}
/// 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,
const SmallPtrSet<const PHINode*, 16> &PHIUsers,
const GlobalStatus &GS) {
// 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) {
DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV);
Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction
->getEntryBlock().begin());
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(dbgs() << "GLOBAL NEVER LOADED: " << *GV);
bool Changed;
if (isLeakCheckerRoot(GV)) {
// Delete any constant stores to the global.
Changed = CleanupPointerRootUsers(GV, TLI);
} else {
// Delete any stores we can find to the global. We may not be able to
// make it completely dead though.
Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
}
// If the global is dead now, delete it.
if (GV->use_empty()) {
GV->eraseFromParent();
++NumDeleted;
Changed = true;
}
return Changed;
} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n");
GV->setConstant(true);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer(), TD, TLI);
// If the global is dead now, just nuke it.
if (GV->use_empty()) {
DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
<< "all users and delete global!\n");
GV->eraseFromParent();
++NumDeleted;
}
++NumMarked;
return true;
} else if (!GV->getInitializer()->getType()->isSingleValueType()) {
if (DataLayout *TD = getAnalysisIfAvailable<DataLayout>())
if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) {
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(), TD, TLI);
if (GV->use_empty()) {
DEBUG(dbgs() << " *** 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, GS.Ordering, GVI,
TD, TLI))
return true;
// Otherwise, if the global was not a boolean, we can shrink it to be a
// boolean.
if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
++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){
if (isa<BlockAddress>(*UI))
continue;
CallSite User(cast<Instruction>(*UI));
User.setCallingConv(CallingConv::Fast);
}
}
static AttributeSet StripNest(LLVMContext &C, const AttributeSet &Attrs) {
for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
unsigned Index = Attrs.getSlotIndex(i);
if (!Attrs.getSlotAttributes(i).hasAttribute(Index, Attribute::Nest))
continue;
// There can be only one.
return Attrs.removeAttribute(C, Index, Attribute::Nest);
}
return Attrs;
}
static void RemoveNestAttribute(Function *F) {
F->setAttributes(StripNest(F->getContext(), F->getAttributes()));
for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
if (isa<BlockAddress>(*UI))
continue;
CallSite User(cast<Instruction>(*UI));
User.setAttributes(StripNest(F->getContext(), 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->isDefTriviallyDead()) {
F->eraseFromParent();
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);
// Simplify the initializer.
if (GV->hasInitializer())
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
Constant *New = ConstantFoldConstantExpression(CE, TD, TLI);
if (New && New != CE)
GV->setInitializer(New);
}
Changed |= ProcessGlobal(GV, GVI);
}
return Changed;
}
/// FindGlobalCtors - Find the llvm.global_ctors list, verifying that all
/// initializers have an init priority of 65535.
GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) {
GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
if (GV == 0) return 0;
// Verify that the initializer is simple enough for us to handle. We are
// only allowed to optimize the initializer if it is unique.
if (!GV->hasUniqueInitializer()) return 0;
if (isa<ConstantAggregateZero>(GV->getInitializer()))
return GV;
ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
if (isa<ConstantAggregateZero>(*i))
continue;
ConstantStruct *CS = 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 = cast<ConstantInt>(CS->getOperand(0));
if (CI->getZExtValue() != 65535)
return 0;
}
return GV;
}
/// 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) {
if (GV->getInitializer()->isNullValue())
return std::vector<Function*>();
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) {
// If we made a change, reassemble the initializer list.
Constant *CSVals[2];
CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 65535);
CSVals[1] = 0;
StructType *StructTy =
cast <StructType>(
cast<ArrayType>(GCL->getType()->getElementType())->getElementType());
// 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 {
Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()),
false);
PointerType *PFTy = PointerType::getUnqual(FTy);
CSVals[1] = Constant::getNullValue(PFTy);
CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()),
0x7fffffff);
}
CAList.push_back(ConstantStruct::get(StructTy, CSVals));
}
// Create the array initializer.
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->getThreadLocalMode());
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 inline bool
isSimpleEnoughValueToCommit(Constant *C,
SmallPtrSet<Constant*, 8> &SimpleConstants,
const DataLayout *TD);
/// isSimpleEnoughValueToCommit - Return true if the specified constant can be
/// handled by the code generator. We don't want to generate something like:
/// void *X = &X/42;
/// because the code generator doesn't have a relocation that can handle that.
///
/// This function should be called if C was not found (but just got inserted)
/// in SimpleConstants to avoid having to rescan the same constants all the
/// time.
static bool isSimpleEnoughValueToCommitHelper(Constant *C,
SmallPtrSet<Constant*, 8> &SimpleConstants,
const DataLayout *TD) {
// Simple integer, undef, constant aggregate zero, global addresses, etc are
// all supported.
if (C->getNumOperands() == 0 || isa<BlockAddress>(C) ||
isa<GlobalValue>(C))
return true;
// Aggregate values are safe if all their elements are.
if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) ||
isa<ConstantVector>(C)) {
for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
Constant *Op = cast<Constant>(C->getOperand(i));
if (!isSimpleEnoughValueToCommit(Op, SimpleConstants, TD))
return false;
}
return true;
}
// We don't know exactly what relocations are allowed in constant expressions,
// so we allow &global+constantoffset, which is safe and uniformly supported
// across targets.
ConstantExpr *CE = cast<ConstantExpr>(C);
switch (CE->getOpcode()) {
case Instruction::BitCast:
// Bitcast is fine if the casted value is fine.
return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
case Instruction::IntToPtr:
case Instruction::PtrToInt:
// int <=> ptr is fine if the int type is the same size as the
// pointer type.
if (!TD || TD->getTypeSizeInBits(CE->getType()) !=
TD->getTypeSizeInBits(CE->getOperand(0)->getType()))
return false;
return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
// GEP is fine if it is simple + constant offset.
case Instruction::GetElementPtr:
for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
if (!isa<ConstantInt>(CE->getOperand(i)))
return false;
return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
case Instruction::Add:
// We allow simple+cst.
if (!isa<ConstantInt>(CE->getOperand(1)))
return false;
return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, TD);
}
return false;
}
static inline bool
isSimpleEnoughValueToCommit(Constant *C,
SmallPtrSet<Constant*, 8> &SimpleConstants,
const DataLayout *TD) {
// If we already checked this constant, we win.
if (!SimpleConstants.insert(C)) return true;
// Check the constant.
return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, TD);
}
/// isSimpleEnoughPointerToCommit - Return true if this constant is simple
/// enough for us to understand. In particular, if it is a cast to anything
/// other than from one pointer type to another pointer type, 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) {
// Conservatively, avoid aggregate types. This is because we don't
// want to worry about them partially overlapping other stores.
if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
return false;
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
// Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
// external globals.
return GV->hasUniqueInitializer();
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
// Handle a constantexpr gep.
if (CE->getOpcode() == Instruction::GetElementPtr &&
isa<GlobalVariable>(CE->getOperand(0)) &&
cast<GEPOperator>(CE)->isInBounds()) {
GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
// Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
// external globals.
if (!GV->hasUniqueInitializer())
return false;
// The first index must be zero.
ConstantInt *CI = dyn_cast<ConstantInt>(*llvm::next(CE->op_begin()));
if (!CI || !CI->isZero()) return false;
// The remaining indices must be compile-time known integers within the
// notional bounds of the corresponding static array types.
if (!CE->isGEPWithNoNotionalOverIndexing())
return false;
return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
// A constantexpr bitcast from a pointer to another pointer is a no-op,
// and we know how to evaluate it by moving the bitcast from the pointer
// operand to the value operand.
} else if (CE->getOpcode() == Instruction::BitCast &&
isa<GlobalVariable>(CE->getOperand(0))) {
// Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
// external globals.
return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
}
}
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;
}
SmallVector<Constant*, 32> Elts;
if (StructType *STy = dyn_cast<StructType>(Init->getType())) {
// Break up the constant into its elements.
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
Elts.push_back(Init->getAggregateElement(i));
// Replace the element that we are supposed to.
ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
unsigned Idx = CU->getZExtValue();
assert(Idx < STy->getNumElements() && "Struct index out of range!");
Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
// Return the modified struct.
return ConstantStruct::get(STy, Elts);
}
ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
SequentialType *InitTy = cast<SequentialType>(Init->getType());
uint64_t NumElts;
if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
NumElts = ATy->getNumElements();
else
NumElts = InitTy->getVectorNumElements();
// Break up the array into elements.
for (uint64_t i = 0, e = NumElts; i != e; ++i)
Elts.push_back(Init->getAggregateElement(i));
assert(CI->getZExtValue() < NumElts);
Elts[CI->getZExtValue()] =
EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
if (Init->getType()->isArrayTy())
return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
return ConstantVector::get(Elts);
}
/// 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));
GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
}
namespace {
/// Evaluator - This class evaluates LLVM IR, producing the Constant
/// representing each SSA instruction. Changes to global variables are stored
/// in a mapping that can be iterated over after the evaluation is complete.
/// Once an evaluation call fails, the evaluation object should not be reused.
class Evaluator {
public:
Evaluator(const DataLayout *TD, const TargetLibraryInfo *TLI)
: TD(TD), TLI(TLI) {
ValueStack.push_back(new DenseMap<Value*, Constant*>);
}
~Evaluator() {
DeleteContainerPointers(ValueStack);
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;
}
}
/// 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.
bool EvaluateFunction(Function *F, Constant *&RetVal,
const SmallVectorImpl<Constant*> &ActualArgs);
/// EvaluateBlock - Evaluate all instructions in block BB, returning true if
/// successful, false if we can't evaluate it. NewBB returns the next BB that
/// control flows into, or null upon return.
bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB);
Constant *getVal(Value *V) {
if (Constant *CV = dyn_cast<Constant>(V)) return CV;
Constant *R = ValueStack.back()->lookup(V);
assert(R && "Reference to an uncomputed value!");
return R;
}
void setVal(Value *V, Constant *C) {
ValueStack.back()->operator[](V) = C;
}
const DenseMap<Constant*, Constant*> &getMutatedMemory() const {
return MutatedMemory;
}
const SmallPtrSet<GlobalVariable*, 8> &getInvariants() const {
return Invariants;
}
private:
Constant *ComputeLoadResult(Constant *P);
/// ValueStack - As we compute SSA register values, we store their contents
/// here. The back of the vector contains the current function and the stack
/// contains the values in the calling frames.
SmallVector<DenseMap<Value*, Constant*>*, 4> ValueStack;
/// CallStack - This is used to detect recursion. In pathological situations
/// we could hit exponential behavior, but at least there is nothing
/// unbounded.
SmallVector<Function*, 4> CallStack;
/// 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.
SmallVector<GlobalVariable*, 32> AllocaTmps;
/// Invariants - These global variables have been marked invariant by the
/// static constructor.
SmallPtrSet<GlobalVariable*, 8> Invariants;
/// SimpleConstants - These are constants we have checked and know to be
/// simple enough to live in a static initializer of a global.
SmallPtrSet<Constant*, 8> SimpleConstants;
const DataLayout *TD;
const TargetLibraryInfo *TLI;
};
} // anonymous namespace
/// 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.
Constant *Evaluator::ComputeLoadResult(Constant *P) {
// 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 = MutatedMemory.find(P);
if (I != MutatedMemory.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);
}
return 0; // don't know how to evaluate.
}
/// EvaluateBlock - Evaluate all instructions in block BB, returning true if
/// successful, false if we can't evaluate it. NewBB returns the next BB that
/// control flows into, or null upon return.
bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst,
BasicBlock *&NextBB) {
// This is the main evaluation loop.
while (1) {
Constant *InstResult = 0;
DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n");
if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
if (!SI->isSimple()) {
DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n");
return false; // no volatile/atomic accesses.
}
Constant *Ptr = getVal(SI->getOperand(1));
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr);
Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
DEBUG(dbgs() << "; To: " << *Ptr << "\n");
}
if (!isSimpleEnoughPointerToCommit(Ptr)) {
// If this is too complex for us to commit, reject it.
DEBUG(dbgs() << "Pointer is too complex for us to evaluate store.");
return false;
}
Constant *Val = getVal(SI->getOperand(0));
// If this might be too difficult for the backend to handle (e.g. the addr
// of one global variable divided by another) then we can't commit it.
if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, TD)) {
DEBUG(dbgs() << "Store value is too complex to evaluate store. " << *Val
<< "\n");
return false;
}
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
if (CE->getOpcode() == Instruction::BitCast) {
DEBUG(dbgs() << "Attempting to resolve bitcast on constant ptr.\n");
// If we're evaluating a store through a bitcast, then we need
// to pull the bitcast off the pointer type and push it onto the
// stored value.
Ptr = CE->getOperand(0);
Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType();
// In order to push the bitcast onto the stored value, a bitcast
// from NewTy to Val's type must be legal. If it's not, we can try
// introspecting NewTy to find a legal conversion.
while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
// If NewTy is a struct, we can convert the pointer to the struct
// into a pointer to its first member.
// FIXME: This could be extended to support arrays as well.
if (StructType *STy = dyn_cast<StructType>(NewTy)) {
NewTy = STy->getTypeAtIndex(0U);
IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32);
Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
Constant * const IdxList[] = {IdxZero, IdxZero};
Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList);
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
// If we can't improve the situation by introspecting NewTy,
// we have to give up.
} else {
DEBUG(dbgs() << "Failed to bitcast constant ptr, can not "
"evaluate.\n");
return false;
}
}
// If we found compatible types, go ahead and push the bitcast
// onto the stored value.
Val = ConstantExpr::getBitCast(Val, NewTy);
DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n");
}
}
MutatedMemory[Ptr] = Val;
} else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
InstResult = ConstantExpr::get(BO->getOpcode(),
getVal(BO->getOperand(0)),
getVal(BO->getOperand(1)));
DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: " << *InstResult
<< "\n");
} else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
InstResult = ConstantExpr::getCompare(CI->getPredicate(),
getVal(CI->getOperand(0)),
getVal(CI->getOperand(1)));
DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult
<< "\n");
} else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
InstResult = ConstantExpr::getCast(CI->getOpcode(),
getVal(CI->getOperand(0)),
CI->getType());
DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult
<< "\n");
} else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)),
getVal(SI->getOperand(1)),
getVal(SI->getOperand(2)));
DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult
<< "\n");
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
Constant *P = getVal(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(*i));
InstResult =
ConstantExpr::getGetElementPtr(P, GEPOps,
cast<GEPOperator>(GEP)->isInBounds());
DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult
<< "\n");
} else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
if (!LI->isSimple()) {
DEBUG(dbgs() << "Found a Load! Not a simple load, can not evaluate.\n");
return false; // no volatile/atomic accesses.
}
Constant *Ptr = getVal(LI->getOperand(0));
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) {
Ptr = ConstantFoldConstantExpression(CE, TD, TLI);
DEBUG(dbgs() << "Found a constant pointer expression, constant "
"folding: " << *Ptr << "\n");
}
InstResult = ComputeLoadResult(Ptr);
if (InstResult == 0) {
DEBUG(dbgs() << "Failed to compute load result. Can not evaluate load."
"\n");
return false; // Could not evaluate load.
}
DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n");
} else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
if (AI->isArrayAllocation()) {
DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n");
return false; // Cannot handle array allocs.
}
Type *Ty = AI->getType()->getElementType();
AllocaTmps.push_back(new GlobalVariable(Ty, false,
GlobalValue::InternalLinkage,
UndefValue::get(Ty),
AI->getName()));
InstResult = AllocaTmps.back();
DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n");
} else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) {
CallSite CS(CurInst);
// Debug info can safely be ignored here.
if (isa<DbgInfoIntrinsic>(CS.getInstruction())) {
DEBUG(dbgs() << "Ignoring debug info.\n");
++CurInst;
continue;
}
// Cannot handle inline asm.
if (isa<InlineAsm>(CS.getCalledValue())) {
DEBUG(dbgs() << "Found inline asm, can not evaluate.\n");
return false;
}
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) {
if (MSI->isVolatile()) {
DEBUG(dbgs() << "Can not optimize a volatile memset " <<
"intrinsic.\n");
return false;
}
Constant *Ptr = getVal(MSI->getDest());
Constant *Val = getVal(MSI->getValue());
Constant *DestVal = ComputeLoadResult(getVal(Ptr));
if (Val->isNullValue() && DestVal && DestVal->isNullValue()) {
// This memset is a no-op.
DEBUG(dbgs() << "Ignoring no-op memset.\n");
++CurInst;
continue;
}
}
if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
II->getIntrinsicID() == Intrinsic::lifetime_end) {
DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n");
++CurInst;
continue;
}
if (II->getIntrinsicID() == Intrinsic::invariant_start) {
// We don't insert an entry into Values, as it doesn't have a
// meaningful return value.
if (!II->use_empty()) {
DEBUG(dbgs() << "Found unused invariant_start. Cant evaluate.\n");
return false;
}
ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0));
Value *PtrArg = getVal(II->getArgOperand(1));
Value *Ptr = PtrArg->stripPointerCasts();
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
Type *ElemTy = cast<PointerType>(GV->getType())->getElementType();
if (!Size->isAllOnesValue() &&
Size->getValue().getLimitedValue() >=
TD->getTypeStoreSize(ElemTy)) {
Invariants.insert(GV);
DEBUG(dbgs() << "Found a global var that is an invariant: " << *GV
<< "\n");
} else {
DEBUG(dbgs() << "Found a global var, but can not treat it as an "
"invariant.\n");
}
}
// Continue even if we do nothing.
++CurInst;
continue;
}
DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n");
return false;
}
// Resolve function pointers.
Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue()));
if (!Callee || Callee->mayBeOverridden()) {
DEBUG(dbgs() << "Can not resolve function pointer.\n");
return false; // Cannot resolve.
}
SmallVector<Constant*, 8> Formals;
for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i)
Formals.push_back(getVal(*i));
if (Callee->isDeclaration()) {
// If this is a function we can constant fold, do it.
if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) {
InstResult = C;
DEBUG(dbgs() << "Constant folded function call. Result: " <<
*InstResult << "\n");
} else {
DEBUG(dbgs() << "Can not constant fold function call.\n");
return false;
}
} else {
if (Callee->getFunctionType()->isVarArg()) {
DEBUG(dbgs() << "Can not constant fold vararg function call.\n");
return false;
}
Constant *RetVal = 0;
// Execute the call, if successful, use the return value.
ValueStack.push_back(new DenseMap<Value*, Constant*>);
if (!EvaluateFunction(Callee, RetVal, Formals)) {
DEBUG(dbgs() << "Failed to evaluate function.\n");
return false;
}
delete ValueStack.pop_back_val();
InstResult = RetVal;
if (InstResult != NULL) {
DEBUG(dbgs() << "Successfully evaluated function. Result: " <<
InstResult << "\n\n");
} else {
DEBUG(dbgs() << "Successfully evaluated function. Result: 0\n\n");
}
}
} else if (isa<TerminatorInst>(CurInst)) {
DEBUG(dbgs() << "Found a terminator instruction.\n");
if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
if (BI->isUnconditional()) {
NextBB = BI->getSuccessor(0);
} else {
ConstantInt *Cond =
dyn_cast<ConstantInt>(getVal(BI->getCondition()));
if (!Cond) return false; // Cannot determine.
NextBB = BI->getSuccessor(!Cond->getZExtValue());
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
ConstantInt *Val =
dyn_cast<ConstantInt>(getVal(SI->getCondition()));
if (!Val) return false; // Cannot determine.
NextBB = SI->findCaseValue(Val).getCaseSuccessor();
} else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
Value *Val = getVal(IBI->getAddress())->stripPointerCasts();
if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
NextBB = BA->getBasicBlock();
else
return false; // Cannot determine.
} else if (isa<ReturnInst>(CurInst)) {
NextBB = 0;
} else {
// invoke, unwind, resume, unreachable.
DEBUG(dbgs() << "Can not handle terminator.");
return false; // Cannot handle this terminator.
}
// We succeeded at evaluating this block!
DEBUG(dbgs() << "Successfully evaluated block.\n");
return true;
} else {
// Did not know how to evaluate this!
DEBUG(dbgs() << "Failed to evaluate block due to unhandled instruction."
"\n");
return false;
}
if (!CurInst->use_empty()) {
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
InstResult = ConstantFoldConstantExpression(CE, TD, TLI);
setVal(CurInst, InstResult);
}
// If we just processed an invoke, we finished evaluating the block.
if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {
NextBB = II->getNormalDest();
DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n");
return true;
}
// Advance program counter.
++CurInst;
}
}
/// 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.
bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal,
const SmallVectorImpl<Constant*> &ActualArgs) {
// 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);
// 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)
setVal(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;
// CurBB - The current basic block we're evaluating.
BasicBlock *CurBB = F->begin();
BasicBlock::iterator CurInst = CurBB->begin();
while (1) {
BasicBlock *NextBB = 0; // Initialized to avoid compiler warnings.
DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n");
if (!EvaluateBlock(CurInst, NextBB))
return false;
if (NextBB == 0) {
// Successfully running until there's no next block means that we found
// the return. Fill it the return value and pop the call stack.
ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator());
if (RI->getNumOperands())
RetVal = getVal(RI->getOperand(0));
CallStack.pop_back();
return true;
}
// 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(NextBB))
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.
PHINode *PN = 0;
for (CurInst = NextBB->begin();
(PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB)));
// Advance to the next block.
CurBB = NextBB;
}
}
/// EvaluateStaticConstructor - Evaluate static constructors in the function, if
/// we can. Return true if we can, false otherwise.
static bool EvaluateStaticConstructor(Function *F, const DataLayout *TD,
const TargetLibraryInfo *TLI) {
// Call the function.
Evaluator Eval(TD, TLI);
Constant *RetValDummy;
bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy,
SmallVector<Constant*, 0>());
if (EvalSuccess) {
// We succeeded at evaluation: commit the result.
DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
<< F->getName() << "' to " << Eval.getMutatedMemory().size()
<< " stores.\n");
for (DenseMap<Constant*, Constant*>::const_iterator I =
Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end();
I != E; ++I)
CommitValueTo(I->second, I->first);
for (SmallPtrSet<GlobalVariable*, 8>::const_iterator I =
Eval.getInvariants().begin(), E = Eval.getInvariants().end();
I != E; ++I)
(*I)->setConstant(true);
}
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;
}
DEBUG(dbgs() << "Optimizing Global Constructor: " << *F << "\n");
// We cannot simplify external ctor functions.
if (F->empty()) continue;
// If we can evaluate the ctor at compile time, do.
if (EvaluateStaticConstructor(F, TD, TLI)) {
Ctors.erase(Ctors.begin()+i);
MadeChange = true;
--i;
++NumCtorsEvaluated;
continue;
}
}
if (!MadeChange) return false;
GCL = InstallGlobalCtors(GCL, Ctors);
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 alias is externally visible, we may still be able to simplify it.
if (!J->hasLocalLinkage()) {
// 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;
// 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;
}
static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) {
if (!TLI->has(LibFunc::cxa_atexit))
return 0;
Function *Fn = M.getFunction(TLI->getName(LibFunc::cxa_atexit));
if (!Fn)
return 0;
FunctionType *FTy = Fn->getFunctionType();
// Checking that the function has the right return type, the right number of
// parameters and that they all have pointer types should be enough.
if (!FTy->getReturnType()->isIntegerTy() ||
FTy->getNumParams() != 3 ||
!FTy->getParamType(0)->isPointerTy() ||
!FTy->getParamType(1)->isPointerTy() ||
!FTy->getParamType(2)->isPointerTy())
return 0;
return Fn;
}
/// cxxDtorIsEmpty - Returns whether the given function is an empty C++
/// destructor and can therefore be eliminated.
/// Note that we assume that other optimization passes have already simplified
/// the code so we only look for a function with a single basic block, where
/// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and
/// other side-effect free instructions.
static bool cxxDtorIsEmpty(const Function &Fn,
SmallPtrSet<const Function *, 8> &CalledFunctions) {
// FIXME: We could eliminate C++ destructors if they're readonly/readnone and
// nounwind, but that doesn't seem worth doing.
if (Fn.isDeclaration())
return false;
if (++Fn.begin() != Fn.end())
return false;
const BasicBlock &EntryBlock = Fn.getEntryBlock();
for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end();
I != E; ++I) {
if (const CallInst *CI = dyn_cast<CallInst>(I)) {
// Ignore debug intrinsics.
if (isa<DbgInfoIntrinsic>(CI))
continue;
const Function *CalledFn = CI->getCalledFunction();
if (!CalledFn)
return false;
SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions);
// Don't treat recursive functions as empty.
if (!NewCalledFunctions.insert(CalledFn))
return false;
if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions))
return false;
} else if (isa<ReturnInst>(*I))
return true; // We're done.
else if (I->mayHaveSideEffects())
return false; // Destructor with side effects, bail.
}
return false;
}
bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) {
/// Itanium C++ ABI p3.3.5:
///
/// After constructing a global (or local static) object, that will require
/// destruction on exit, a termination function is registered as follows:
///
/// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
///
/// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
/// call f(p) when DSO d is unloaded, before all such termination calls
/// registered before this one. It returns zero if registration is
/// successful, nonzero on failure.
// This pass will look for calls to __cxa_atexit where the function is trivial
// and remove them.
bool Changed = false;
for (Function::use_iterator I = CXAAtExitFn->use_begin(),
E = CXAAtExitFn->use_end(); I != E;) {
// We're only interested in calls. Theoretically, we could handle invoke
// instructions as well, but neither llvm-gcc nor clang generate invokes
// to __cxa_atexit.
CallInst *CI = dyn_cast<CallInst>(*I++);
if (!CI)
continue;
Function *DtorFn =
dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts());
if (!DtorFn)
continue;
SmallPtrSet<const Function *, 8> CalledFunctions;
if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions))
continue;
// Just remove the call.
CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
CI->eraseFromParent();
++NumCXXDtorsRemoved;
Changed |= true;
}
return Changed;
}
bool GlobalOpt::runOnModule(Module &M) {
bool Changed = false;
TD = getAnalysisIfAvailable<DataLayout>();
TLI = &getAnalysis<TargetLibraryInfo>();
// Try to find the llvm.globalctors list.
GlobalVariable *GlobalCtors = FindGlobalCtors(M);
Function *CXAAtExitFn = FindCXAAtExit(M, TLI);
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);
// Try to remove trivial global destructors.
if (CXAAtExitFn)
LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn);
Changed |= LocalChange;
}
// TODO: Move all global ctors functions to the end of the module for code
// layout.
return Changed;
}
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