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Implement a FIXME by checking to make sure that a malloc is not being used

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in scary and unknown ways before we promote it.  This fixes the miscompilation
of 188.ammp that has been plauging us since a globalopt patch went in.

Thanks a ton to Tanya for helping me diagnose the problem!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@18418 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-12-02 07:11:07 +00:00
parent bc965b97ad
commit fa07e4fc30
1 changed files with 25 additions and 3 deletions
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28
lib/Transforms/IPO/GlobalOpt.cpp
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@ -738,6 +738,29 @@ static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
return NewGV;
}
/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking
/// to make sure that there are no complex uses of V. We permit simple things
/// like dereferencing the pointer, but not storing through the address, unless
/// it is to the specified global.
static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Instruction *V,
GlobalVariable *GV) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI)
if (isa<LoadInst>(*UI) || isa<SetCondInst>(*UI)) {
// Fine, ignore.
} else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
return false; // Storing the pointer itself... bad.
// Otherwise, storing through it, or storing into GV... fine.
} else if (isa<GetElementPtrInst>(*UI) || isa<SelectInst>(*UI)) {
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(cast<Instruction>(*UI),GV))
return false;
} else {
return false;
}
return true;
}
// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
// that only one value (besides its initializer) is ever stored to the global.
static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
@ -783,9 +806,8 @@ static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
if (MI->getAllocatedType()->isSized() &&
NElements->getRawValue()*
TD.getTypeSize(MI->getAllocatedType()) < 2048 &&
AllUsesOfLoadedValueWillTrapIfNull(GV)) {
// FIXME: do more correctness checking to make sure the result of the
// malloc isn't squirrelled away somewhere.
AllUsesOfLoadedValueWillTrapIfNull(GV) &&
ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, GV)) {
GVI = OptimizeGlobalAddressOfMalloc(GV, MI);
return true;
}