From 892c7e4a2337fc017418b83f2543bddc11359ff2 Mon Sep 17 00:00:00 2001
From: Duncan Sands <baldrick@free.fr>
Date: Wed, 19 Sep 2007 10:10:31 +0000
Subject: [PATCH] A global variable with external weak linkage can be null,
while an alias could alias such a global variable.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42130 91177308-0d34-0410-b5e6-96231b3b80d8
---
lib/Transforms/Scalar/InstructionCombining.cpp | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 55ef0a80985..07eb2528c45 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -8936,8 +8936,12 @@ static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI) {
/// specified pointer, we do a quick local scan of the basic block containing
/// ScanFrom, to determine if the address is already accessed.
static bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom) {
- // If it is an alloca or global variable, it is always safe to load from.
- if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true;
+ // If it is an alloca it is always safe to load from.
+ if (isa<AllocaInst>(V)) return true;
+
+ // Don't try to evaluate aliases. External weak GV can be null.
+ if (const GlobalValue *GV = dyn_cast<GlobalVariable>(V))
+ return !isa<GlobalAlias>(GV) && !GV->hasExternalWeakLinkage();
// Otherwise, be a little bit agressive by scanning the local block where we
// want to check to see if the pointer is already being loaded or stored