From 65ac598c7ba7e36f2ad611f2bb39cc957053be5d Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Tue, 1 Nov 2011 21:06:14 +0000
Subject: [PATCH] When constant-folding, don't look at the initializer of a
 global const variable if it's marked as weak: that definition may not end up
 being used.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@143496 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/AST/ExprConstant.cpp | 16 +++++++++++-----
 test/Sema/const-eval.c   |  4 ++++
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 4dd49c9125..781ffa6fb4 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -270,16 +270,17 @@ static bool IsLiteralLValue(const LValue &Value) {
          !isa<MaterializeTemporaryExpr>(Value.Base);
 }
 
-static bool IsWeakLValue(const LValue &Value) {
-  const ValueDecl *Decl = GetLValueBaseDecl(Value);
-  if (!Decl)
-    return false;
-
+static bool IsWeakDecl(const ValueDecl *Decl) {
   return Decl->hasAttr<WeakAttr>() ||
          Decl->hasAttr<WeakRefAttr>() ||
          Decl->isWeakImported();
 }
 
+static bool IsWeakLValue(const LValue &Value) {
+  const ValueDecl *Decl = GetLValueBaseDecl(Value);
+  return Decl && IsWeakDecl(Decl);
+}
+
 static bool EvalPointerValueAsBool(const LValue &Value, bool &Result) {
   const Expr* Base = Value.Base;
 
@@ -394,6 +395,11 @@ static bool EvaluateVarDeclInit(EvalInfo &Info, const VarDecl *VD,
     return true;
   }
 
+  // Never evaluate the initializer of a weak variable. We can't be sure that
+  // this is the definition which will be used.
+  if (IsWeakDecl(VD))
+    return false;
+
   const Expr *Init = VD->getAnyInitializer();
   if (!Init)
     return false;
diff --git a/test/Sema/const-eval.c b/test/Sema/const-eval.c
index df56b06e48..c984f5bf84 100644
--- a/test/Sema/const-eval.c
+++ b/test/Sema/const-eval.c
@@ -95,3 +95,7 @@ int intLvalue[*(int*)((long)&n ?: 1)] = { 1, 2 }; // expected-error {{variable l
 
 union u { int a; char b[4]; };
 char c = ((union u)(123456)).b[0]; // expected-error {{not a compile-time constant}}
+
+extern const int weak_int __attribute__((weak));
+const int weak_int = 42;
+int weak_int_test = weak_int; // expected-error {{not a compile-time constant}}
-- 
2.50.1