r344957 - Give Multiversion-inline functions linkonce linkage

[Keane, Erich via cfe-commits]

GCC actually doesn’t support function multiversioning in C mode, so this fix is part of our extension to support C with multiversioning.  I perhaps wonder if this is part of the reason GCC only supports it in C++ mode...

From: David Blaikie [mailto:dblaikie at gmail.com]
Sent: Monday, October 29, 2018 11:25 AM
To: Keane, Erich <erich.keane at intel.com>; Eric Christopher <echristo at gmail.com>
Cc: cfe-commits at lists.llvm.org
Subject: Re: r344957 - Give Multiversion-inline functions linkonce linkage

Does this match GCC's approach here?

(I ask this sort of as throwaway/conversation starter - because the linkage/behavior around multiversion functions and their inlining is full of sharp corners/risks of code moving out of the areas appropriately restricted based on the cpu features)
On Mon, Oct 22, 2018 at 2:22 PM Erich Keane via cfe-commits <cfe-commits at lists.llvm.org<mailto:cfe-commits at lists.llvm.org>> wrote:
Author: erichkeane
Date: Mon Oct 22 14:20:45 2018
New Revision: 344957

URL: http://llvm.org/viewvc/llvm-project?rev=344957&view=rev
Log:
Give Multiversion-inline functions linkonce linkage

Since multiversion variant functions can be inline, in C they become
available-externally linkage.  This ends up causing the variants to not
be emitted, and not available to the linker.

The solution is to make sure that multiversion functions are always
emitted by marking them linkonce.

Change-Id: I897aa37c7cbba0c1eb2c57ee881d5000a2113b75

Modified:
    cfe/trunk/lib/CodeGen/CodeGenModule.cpp
    cfe/trunk/test/CodeGen/attr-target-mv.c

Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=344957&r1=344956&r2=344957&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Mon Oct 22 14:20:45 2018
@@ -3669,6 +3669,10 @@ llvm::GlobalValue::LinkageTypes CodeGenM
       return llvm::GlobalVariable::WeakAnyLinkage;
   }

+  if (const auto *FD = D->getAsFunction())
+    if (FD->isMultiVersion() && Linkage == GVA_AvailableExternally)
+      return llvm::GlobalVariable::LinkOnceAnyLinkage;
+
   // We are guaranteed to have a strong definition somewhere else,
   // so we can use available_externally linkage.
   if (Linkage == GVA_AvailableExternally)

Modified: cfe/trunk/test/CodeGen/attr-target-mv.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/attr-target-mv.c?rev=344957&r1=344956&r2=344957&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/attr-target-mv.c (original)
+++ cfe/trunk/test/CodeGen/attr-target-mv.c Mon Oct 22 14:20:45 2018
@@ -88,19 +88,19 @@ void bar4() {

 // CHECK: declare i32 @foo.arch_sandybridge()

-// CHECK: define available_externally i32 @foo_inline.sse4.2()
+// CHECK: define linkonce i32 @foo_inline.sse4.2()
 // CHECK: ret i32 0

 // CHECK: declare i32 @foo_inline.arch_sandybridge()
 //
-// CHECK: define available_externally i32 @foo_inline.arch_ivybridge()
+// CHECK: define linkonce i32 @foo_inline.arch_ivybridge()
 // CHECK: ret i32 1
-// CHECK: define available_externally i32 @foo_inline()
+// CHECK: define linkonce i32 @foo_inline()
 // CHECK: ret i32 2

-// CHECK: define available_externally void @foo_decls()
-// CHECK: define available_externally void @foo_decls.sse4.2()
+// CHECK: define linkonce void @foo_decls()
+// CHECK: define linkonce void @foo_decls.sse4.2()

-// CHECK: define available_externally void @foo_multi.avx_sse4.2()
-// CHECK: define available_externally void @foo_multi.fma4_sse4.2()
-// CHECK: define available_externally void @foo_multi.arch_ivybridge_fma4_sse4.2()
+// CHECK: define linkonce void @foo_multi.avx_sse4.2()
+// CHECK: define linkonce void @foo_multi.fma4_sse4.2()
+// CHECK: define linkonce void @foo_multi.arch_ivybridge_fma4_sse4.2()


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