[llvm] r255123 - Change hasUniqueInitializer() to call isStrongDefinitionForLinker() instead of !isWeakForLinker()

[Mehdi Amini via llvm-commits]

Author: mehdi_amini
Date: Wed Dec  9 10:17:07 2015
New Revision: 255123

URL: http://llvm.org/viewvc/llvm-project?rev=255123&view=rev
Log:
Change hasUniqueInitializer() to call isStrongDefinitionForLinker() instead of !isWeakForLinker()

Summary:
Available_externally global variable with initializer were considered "hasInitializer()",
while obviously it can't match the description:

    Whether the global variable has an initializer, and any changes made to the
    initializer will turn up in the final executable.

since modifying the initializer of an externally available variable does not make sense.

Reviewers: pcc, rafael

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15351

From: Mehdi Amini <mehdi.amini at apple.com>

Added:
    llvm/trunk/test/Transforms/GlobalOpt/available_externally_global_ctors.ll
Modified:
    llvm/trunk/include/llvm/IR/GlobalVariable.h

Modified: llvm/trunk/include/llvm/IR/GlobalVariable.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/GlobalVariable.h?rev=255123&r1=255122&r2=255123&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/GlobalVariable.h (original)
+++ llvm/trunk/include/llvm/IR/GlobalVariable.h Wed Dec  9 10:17:07 2015
@@ -105,18 +105,13 @@ public:
   /// 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() &&
-      // It is not safe to modify initializers of global variables with the
-      // external_initializer marker since the value may be changed at runtime
-      // before C++ initializers are evaluated.
-      !isExternallyInitialized();
+    return
+        // We need to be sure this is the definition that will actually be used
+        isStrongDefinitionForLinker() &&
+        // It is not safe to modify initializers of global variables with the
+        // external_initializer marker since the value may be changed at runtime
+        // before C++ initializers are evaluated.
+        !isExternallyInitialized();
   }
 
   /// getInitializer - Return the initializer for this global variable.  It is

Added: llvm/trunk/test/Transforms/GlobalOpt/available_externally_global_ctors.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GlobalOpt/available_externally_global_ctors.ll?rev=255123&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/GlobalOpt/available_externally_global_ctors.ll (added)
+++ llvm/trunk/test/Transforms/GlobalOpt/available_externally_global_ctors.ll Wed Dec  9 10:17:07 2015
@@ -0,0 +1,22 @@
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+; RUN: opt -S -globalopt < %s | FileCheck %s
+
+; Verify that the initialization of the available_externally global is not eliminated
+; CHECK: @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @foo_static_init, i8* null }]
+
+ at llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @foo_static_init, i8* null }]
+ at foo_external = available_externally global void ()* null
+
+define internal void @foo_static_init() {
+entry:
+  store void ()* @foo_impl, void ()** @foo_external
+  ret void
+}
+
+define internal void @foo_impl() {
+entry:
+  ret void
+}
+