ConstantFold: Don't optimize comparisons with weak linkage objects

Consider:
void f() {}
void __attribute__((weak)) g() {}
bool b = &f != &g;

It's possble for g to resolve to f if --defsym=g=f is passed on to the
linker.

llvm-svn: 223585

2 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index cdfb41f7dcc..719a3a4b4c8 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1348,9 +1348,12 @@ 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();
+  };
   // Don't try to decide equality of aliases.
   if (!isa<GlobalAlias>(GV1) && !isa<GlobalAlias>(GV2))
-    if (!GV1->hasExternalWeakLinkage() || !GV2->hasExternalWeakLinkage())
+    if (!isLinkageUnsafeForEquality(GV1) && !isLinkageUnsafeForEquality(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 8d03e7a320b..bed58c52ad9 100644
--- a/llvm/test/Assembler/ConstantExprNoFold.ll
+++ b/llvm/test/Assembler/ConstantExprNoFold.ll
@@ -31,6 +31,11 @@ target datalayout = "p:32:32"
 @weak.gep = global i32* getelementptr (i32* @weak, i32 1)
 @weak = extern_weak global i32
 
+; An object with weak linkage cannot have it's identity determined at compile time.
+; CHECK: @F = global i1 icmp eq (i32* @weakany, i32* @glob)
+@F = global i1 icmp eq (i32* @weakany, i32* @glob)
+@weakany = weak global i32 0
+
 ; 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