From: Peter Collingbourne <peter@pcc.me.uk>
Date: Wed, 1 Jul 2015 02:10:26 +0000 (+0000)
Subject: CodeGen: Do not give local-linkage functions externally available linkage, even tempo... 
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=cbbee9496cc7535e78f4b864812326495c98d779;p=clang

CodeGen: Do not give local-linkage functions externally available linkage, even temporarily.

When an internal-linkage thunk is code gen'd, CodeGenVTables::emitThunk
will first be called with ForVTable=true (which incorrectly set the
thunk's linkage to available_externally under the Itanium ABI) and later
with ForVTable=false (which reset it to internal). Because we will always
see a call with ForVTable=false, this incorrect linkage never ended up in
the final IR. However, the temporary presence of this linkage caused us
to give such functions a comdat as a result of code introduced in r241102.
To avoid this, check that the thunk is externally visible before giving it
available_externally linkage.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@241136 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/ItaniumCXXABI.cpp b/lib/CodeGen/ItaniumCXXABI.cpp
index d7dfe8bfa2..fa86e52ec8 100644
--- a/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/lib/CodeGen/ItaniumCXXABI.cpp
@@ -219,7 +219,7 @@ public:
                        bool ReturnAdjustment) override {
     // Allow inlining of thunks by emitting them with available_externally
     // linkage together with vtables when needed.
-    if (ForVTable)
+    if (ForVTable && !Thunk->hasLocalLinkage())
       Thunk->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage);
   }
 
diff --git a/test/CodeGenCXX/thunks.cpp b/test/CodeGenCXX/thunks.cpp
index 2287d65a28..0e97255cc6 100644
--- a/test/CodeGenCXX/thunks.cpp
+++ b/test/CodeGenCXX/thunks.cpp
@@ -365,6 +365,7 @@ namespace Test15 {
 
 // This is from Test5:
 // CHECK-LABEL: define internal void @_ZThn8_N6Test4B12_GLOBAL__N_11C1fEv(
+// CHECK-NOT: comdat
 // CHECK-LABEL: define linkonce_odr void @_ZTv0_n24_N5Test51B1fEv
 
 // This is from Test10: