From 107f41fad5f8df734c72cf39a016a7ea0d874388 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Wed, 19 Aug 2009 00:11:12 +0000
Subject: [PATCH] Fix SimplifyLibcalls and ValueTracking to check
 mayBeOverridden before performing optimizations based on constant string
 values.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79384 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ValueTracking.cpp                |  3 ++-
 lib/Transforms/Scalar/SimplifyLibCalls.cpp    |  3 ++-
 .../SimplifyLibCalls/weak-symbols.ll          | 26 +++++++++++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)
 create mode 100644 test/Transforms/SimplifyLibCalls/weak-symbols.ll

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 604d10c68b9..3ab10c55d81 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -1061,7 +1061,8 @@ bool llvm::GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset,
   // variable that is a constant and is initialized. The referenced constant
   // initializer is the array that we'll use for optimization.
   GlobalVariable* GV = dyn_cast<GlobalVariable>(V);
-  if (!GV || !GV->isConstant() || !GV->hasInitializer())
+  if (!GV || !GV->isConstant() || !GV->hasInitializer() ||
+      GV->mayBeOverridden())
     return false;
   Constant *GlobalInit = GV->getInitializer();
   
diff --git a/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index 02b26bdac2b..761c309c200 100644
--- a/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -438,7 +438,8 @@ static uint64_t GetStringLengthH(Value *V, SmallPtrSet<PHINode*, 32> &PHIs) {
   // variable that is a constant and is initialized. The referenced constant
   // initializer is the array that we'll use for optimization.
   GlobalVariable* GV = dyn_cast<GlobalVariable>(GEP->getOperand(0));
-  if (!GV || !GV->isConstant() || !GV->hasInitializer())
+  if (!GV || !GV->isConstant() || !GV->hasInitializer() ||
+      GV->mayBeOverridden())
     return 0;
   Constant *GlobalInit = GV->getInitializer();
   
diff --git a/test/Transforms/SimplifyLibCalls/weak-symbols.ll b/test/Transforms/SimplifyLibCalls/weak-symbols.ll
new file mode 100644
index 00000000000..970ee0ddf12
--- /dev/null
+++ b/test/Transforms/SimplifyLibCalls/weak-symbols.ll
@@ -0,0 +1,26 @@
+; RUN: llvm-as < %s | opt -simplify-libcalls | llvm-dis | FileCheck %s
+; PR4738
+
+; SimplifyLibcalls shouldn't assume anything about weak symbols.
+
+@real_init = weak_odr constant [2 x i8] c"y\00"
+@fake_init = weak constant [2 x i8] c"y\00"
+@.str = private constant [2 x i8] c"y\00"
+
+; CHECK: define i32 @foo
+; CHECK: call i32 @strcmp
+define i32 @foo() nounwind {
+entry:
+  %t0 = call i32 @strcmp(i8* getelementptr inbounds ([2 x i8]* @fake_init, i64 0, i64 0), i8* getelementptr inbounds ([2 x i8]* @.str, i64 0, i64 0)) nounwind readonly
+  ret i32 %t0
+}
+
+; CHECK: define i32 @bar
+; CHECK: ret i32 0
+define i32 @bar() nounwind {
+entry:
+  %t0 = call i32 @strcmp(i8* getelementptr inbounds ([2 x i8]* @real_init, i64 0, i64 0), i8* getelementptr inbounds ([2 x i8]* @.str, i64 0, i64 0)) nounwind readonly
+  ret i32 %t0
+}
+
+declare i32 @strcmp(i8*, i8*) nounwind readonly