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[instsimplify] Clarify assumptions about disjoint memory regions [NFC]

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This commit is contained in:
Philip Reames 2022-02-18 08:51:18 -08:00
parent 5ecf218eca
commit bf296ea6bb
1 changed files with 22 additions and 16 deletions
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38
llvm/lib/Analysis/InstructionSimplify.cpp
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@ -2507,6 +2507,25 @@ static Value *ExtractEquivalentCondition(Value *V, CmpInst::Predicate Pred,
return nullptr;
}
/// Return true if the underlying object (storage) must be disjoint from
/// storage returned by any noalias return call.
static bool IsAllocDisjoint(const Value *V) {
// For allocas, we consider only static ones (dynamic
// allocas might be transformed into calls to malloc not simultaneously
// live with the compared-to allocation). For globals, we exclude symbols
// that might be resolve lazily to symbols in another dynamically-loaded
// library (and, thus, could be malloc'ed by the implementation).
if (const AllocaInst *AI = dyn_cast<AllocaInst>(V))
return AI->getParent() && AI->getFunction() && AI->isStaticAlloca();
if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
return (GV->hasLocalLinkage() || GV->hasHiddenVisibility() ||
GV->hasProtectedVisibility() || GV->hasGlobalUnnamedAddr()) &&
!GV->isThreadLocal();
if (const Argument *A = dyn_cast<Argument>(V))
return A->hasByValAttr();
return false;
}
/// Return true if V1 and V2 are each the base of some distict storage region
/// [V, object_size(V)] which do not overlap. Note that zero sized regions
/// *are* possible, and that zero sized regions do not overlap with any other.
@ -2666,23 +2685,10 @@ computePointerICmp(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
};
// Is the set of underlying objects all things which must be disjoint from
// noalias calls. For allocas, we consider only static ones (dynamic
// allocas might be transformed into calls to malloc not simultaneously
// live with the compared-to allocation). For globals, we exclude symbols
// that might be resolve lazily to symbols in another dynamically-loaded
// library (and, thus, could be malloc'ed by the implementation).
// noalias calls. We assume that indexing from such disjoint storage
// into the heap is undefined, and thus offsets can be safely ignored.
auto IsAllocDisjoint = [](ArrayRef<const Value *> Objects) {
return all_of(Objects, [](const Value *V) {
if (const AllocaInst *AI = dyn_cast<AllocaInst>(V))
return AI->getParent() && AI->getFunction() && AI->isStaticAlloca();
if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
return (GV->hasLocalLinkage() || GV->hasHiddenVisibility() ||
GV->hasProtectedVisibility() || GV->hasGlobalUnnamedAddr()) &&
!GV->isThreadLocal();
if (const Argument *A = dyn_cast<Argument>(V))
return A->hasByValAttr();
return false;
});
return all_of(Objects, ::IsAllocDisjoint);
};
if ((IsNAC(LHSUObjs) && IsAllocDisjoint(RHSUObjs)) ||