GlobalOpt: EvaluateFunction() must not evaluate stores to weak_odr globals.

Fixes PR8389.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116812 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 28 insertions, 1 deletions

diff --git a/include/llvm/GlobalVariable.h b/include/llvm/GlobalVariable.h
index a8a2bd6a52..597583b2ce 100644
--- a/include/llvm/GlobalVariable.h
+++ b/include/llvm/GlobalVariable.h
@@ -80,7 +80,21 @@ public:
   inline bool hasInitializer() const { return !isDeclaration(); }
 
   /// hasDefinitiveInitializer - Whether the global variable has an initializer,
-  /// and this is the initializer that will be used in the final executable.
+  /// and any other instances of the global (this can happen due to weak
+  /// linkage) are guaranteed to have the same initializer.
+  ///
+  /// Note that if you want to transform a global, you must use
+  /// hasUniqueInitializer() instead, because of the *_odr linkage type.
+  ///
+  /// Example:
+  ///
+  /// @a = global SomeType* null - Initializer is both definitive and unique.
+  ///
+  /// @b = global weak SomeType* null - Initializer is neither definitive nor
+  /// unique.
+  ///
+  /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
+  /// unique.
   inline bool hasDefinitiveInitializer() const {
     return hasInitializer() &&
       // The initializer of a global variable with weak linkage may change at
@@ -88,6 +102,19 @@ public:
       !mayBeOverridden();
   }
 
+  /// hasUniqueInitializer - Whether the global variable has an initializer, and
+  /// any changes made to the initializer will turn up in the final executable.
+  inline bool hasUniqueInitializer() const {
+    return hasInitializer() &&
+      // It's not safe to modify initializers of global variables with weak
+      // linkage, because the linker might choose to discard the initializer and
+      // use the initializer from another instance of the global variable
+      // instead. It is wrong to modify the initializer of a global variable
+      // with *_odr linkage because then different instances of the global may
+      // have different initializers, breaking the One Definition Rule.
+      !isWeakForLinker();
+  }
+
   /// getInitializer - Return the initializer for this global variable.  It is
   /// illegal to call this method if the global is external, because we cannot
   /// tell what the value is initialized to!