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ConstantFold: Zero-sized globals might land on top of another global 

A zero sized array is zero sized and might share its address with
another global.

llvm-svn: 223684
This commit is contained in:
David Majnemer 2014-12-08 19:35:31 +00:00
parent 970ac60573
commit 770fd82f39
2 changed files with 21 additions and 3 deletions
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18
llvm/lib/IR/ConstantFold.cpp
View File

@ -1348,12 +1348,24 @@ static FCmpInst::Predicate evaluateFCmpRelation(Constant *V1, Constant *V2) {
static ICmpInst::Predicate areGlobalsPotentiallyEqual(const GlobalValue *GV1,
const GlobalValue *GV2) {
auto isLinkageUnsafeForEquality = [](const GlobalValue *GV) {
return GV->hasExternalWeakLinkage() || GV->hasWeakAnyLinkage();
auto isGlobalUnsafeForEquality = [](const GlobalValue *GV) {
if (GV->hasExternalWeakLinkage() || GV->hasWeakAnyLinkage())
return true;
if (const auto *GVar = dyn_cast<GlobalVariable>(GV)) {
Type *Ty = GVar->getType()->getPointerElementType();
// A global with opaque type might end up being zero sized.
if (!Ty->isSized())
return true;
// A global with an empty type might lie at the address of any other
// global.
if (Ty->isEmptyTy())
return true;
}
return false;
};
// Don't try to decide equality of aliases.
if (!isa<GlobalAlias>(GV1) && !isa<GlobalAlias>(GV2))
if (!isLinkageUnsafeForEquality(GV1) && !isLinkageUnsafeForEquality(GV2))
if (!isGlobalUnsafeForEquality(GV1) && !isGlobalUnsafeForEquality(GV2))
return ICmpInst::ICMP_NE;
return ICmpInst::BAD_ICMP_PREDICATE;
}

6
llvm/test/Assembler/ConstantExprNoFold.ll
View File

@ -36,6 +36,12 @@ target datalayout = "p:32:32"
@F = global i1 icmp eq (i32* @weakany, i32* @glob)
@weakany = weak global i32 0
; Empty globals might end up anywhere, even on top of another global.
; CHECK: @empty.cmp = global i1 icmp eq ([0 x i8]* @empty.1, [0 x i8]* @empty.2)
@empty.1 = external global [0 x i8], align 1
@empty.2 = external global [0 x i8], align 1
@empty.cmp = global i1 icmp eq ([0 x i8]* @empty.1, [0 x i8]* @empty.2)
; Don't add an inbounds on @glob.a3, since it's not inbounds.
; CHECK: @glob.a3 = alias getelementptr (i32* @glob.a2, i32 1)
@glob = global i32 0