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Revert r160602.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160603 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2012-07-21 09:03:15 +00:00
parent 61e2ff8f82
commit c7088c9a9c
3 changed files with 9 additions and 198 deletions
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185
lib/Transforms/IPO/GlobalOpt.cpp
View File

@ -296,165 +296,6 @@ static bool AnalyzeGlobal(const Value *V, GlobalStatus &GS,
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) {
do {
if (isa<Constant>(V))
return true;
if (!V->hasOneUse())
return false;
if (isa<LoadInst>(V) || isa<Argument>(V) || isa<GlobalValue>(V))
return false;
if (isAllocationFn(V))
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) {
// 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);
return true;
}
}
}
for (int i = 0, e = Dead.size(); i != e; ++i) {
if (IsSafeComputationToRemove(Dead[i].first)) {
Dead[i].second->eraseFromParent();
Instruction *I = Dead[i].first;
do {
Instruction *J = dyn_cast<Instruction>(I->getOperand(0));
I->eraseFromParent();
if (!J)
break;
I = J;
} while (!isAllocationFn(I));
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
@ -971,18 +812,13 @@ static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV,
// 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);
} else {
Changed = true;
CleanupConstantGlobalUsers(GV, 0, TD, TLI);
}
DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
CleanupConstantGlobalUsers(GV, 0, TD, TLI);
if (GV->use_empty()) {
DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
Changed = true;
GV->eraseFromParent();
++NumDeleted;
}
Changed = true;
}
return Changed;
}
@ -1958,15 +1794,10 @@ bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
if (!GS.isLoaded) {
DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV);
bool Changed;
if (isLeakCheckerRoot(GV)) {
// Delete any constant stores to the global.
Changed = CleanupPointerRootUsers(GV);
} 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);
}
// Delete any stores we can find to the global. We may not be able to
// make it completely dead though.
bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(),
TD, TLI);
// If the global is dead now, delete it.
if (GV->use_empty()) {
@ -2014,7 +1845,7 @@ bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
if (GV->use_empty()) {
DEBUG(dbgs() << " *** Substituting initializer allowed us to "
<< "simplify all users and delete global!\n");
<< "simplify all users and delete global!\n");
GV->eraseFromParent();
++NumDeleted;
} else {

2
test/Transforms/GlobalOpt/2009-11-16-BrokenPerformHeapAllocSRoA.ll
View File

@ -17,7 +17,7 @@ define void @test() nounwind ssp {
%2 = sext i32 %1 to i64 ; <i64> [#uses=1]
%3 = mul i64 %2, ptrtoint (%struct.strchartype* getelementptr (%struct.strchartype* null, i64 1) to i64) ; <i64> [#uses=1]
%4 = tail call i8* @malloc(i64 %3) ; <i8*> [#uses=1]
; CHECK-NOT: call i8* @malloc(i64
; CHECK: call i8* @malloc(i64
%5 = bitcast i8* %4 to %struct.strchartype* ; <%struct.strchartype*> [#uses=1]
store %struct.strchartype* %5, %struct.strchartype** @chartypes, align 8
ret void

20
test/Transforms/GlobalOpt/cleanup-pointer-root-users.ll
View File

@ -1,20 +0,0 @@
; RUN: opt -globalopt -S -o - < %s | FileCheck %s
@test1 = internal global i8* null
define void @test1a() {
; CHECK: @test1a
; CHECK-NOT: store
; CHECK-NEXT: ret void
store i8* null, i8** @test1
ret void
}
define void @test1b(i8* %p) {
; CHECK: @test1b
; CHECK-NEXT: store
; CHECK-NEXT: ret void
store i8* %p, i8** @test1
ret void
}