From 770fd82f390b14f0f245b33d19167ec32727c5d2 Mon Sep 17 00:00:00 2001 From: David Majnemer Date: Mon, 8 Dec 2014 19:35:31 +0000 Subject: [PATCH] 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 --- llvm/lib/IR/ConstantFold.cpp | 18 +++++++++++++++--- llvm/test/Assembler/ConstantExprNoFold.ll | 6 ++++++ 2 files changed, 21 insertions(+), 3 deletions(-) diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp index 719a3a4..4cb22bc 100644 --- a/llvm/lib/IR/ConstantFold.cpp +++ b/llvm/lib/IR/ConstantFold.cpp @@ -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(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(GV1) && !isa(GV2)) - if (!isLinkageUnsafeForEquality(GV1) && !isLinkageUnsafeForEquality(GV2)) + if (!isGlobalUnsafeForEquality(GV1) && !isGlobalUnsafeForEquality(GV2)) return ICmpInst::ICMP_NE; return ICmpInst::BAD_ICMP_PREDICATE; } diff --git a/llvm/test/Assembler/ConstantExprNoFold.ll b/llvm/test/Assembler/ConstantExprNoFold.ll index bed58c5..83236d5 100644 --- a/llvm/test/Assembler/ConstantExprNoFold.ll +++ b/llvm/test/Assembler/ConstantExprNoFold.ll @@ -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 -- 2.7.4