LTO: Don't internalize available_externally globals.

This breaks C and C++ semantics because it can cause the address
of the global inside the module to differ from the address outside
of the module.

Differential Revision: https://reviews.llvm.org/D55237

Change-Id: I84f5d3860beed2953078b3bd9ea0c6d2c334e3cb
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@348321 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 20 insertions, 1 deletions

diff --git a/lib/LTO/LTO.cpp b/lib/LTO/LTO.cpp
index 6b11f690ef3..d8e5d6ed6be 100644
--- a/lib/LTO/LTO.cpp
+++ b/lib/LTO/LTO.cpp
@@ -356,7 +356,10 @@ static void thinLTOInternalizeAndPromoteGUID(
                // Ignore local and appending linkage values since the linker
                // doesn't resolve them.
                !GlobalValue::isLocalLinkage(S->linkage()) &&
-               !GlobalValue::isAppendingLinkage(S->linkage()))
+               S->linkage() != GlobalValue::AppendingLinkage &&
+               // We can't internalize available_externally globals because this
+               // can break function pointer equality.
+               S->linkage() != GlobalValue::AvailableExternallyLinkage)
       S->setLinkage(GlobalValue::InternalLinkage);
   }
 }
diff --git a/test/LTO/Resolution/X86/available-externally.ll b/test/LTO/Resolution/X86/available-externally.ll
new file mode 100644
index 00000000000..eb17693c0a9
--- /dev/null
+++ b/test/LTO/Resolution/X86/available-externally.ll
@@ -0,0 +1,16 @@
+; RUN: opt -module-summary -o %t.bc %s
+; RUN: llvm-lto2 run %t.bc -r %t.bc,foo,px -r %t.bc,bar, -o %t2
+; RUN: llvm-nm %t2.1 | FileCheck %s
+
+; CHECK: U bar
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void ()* @foo() {
+  ret void ()* @bar
+}
+
+define available_externally void @bar() {
+  ret void
+}