<div dir="ltr"><br><br><div class="gmail_quote"><div dir="ltr">On Mon, Oct 29, 2018 at 11:30 AM Keane, Erich <<a href="mailto:erich.keane@intel.com">erich.keane@intel.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d">GCC actually doesn’t support function multiversioning in C mode, so this fix is part of our extension to support C with multiversioning.</span></p></div></div></blockquote><div><br>Ah, what's the motivation for that?<br> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div class="m_-2818023329972350043WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"> I perhaps wonder if
this is part of the reason GCC only supports it in C++ mode... </span></p></div></div></blockquote><div><br>Yeah... could be.<br><br>I mean I suppose using linkonce isn't making multiversioning any worse in C than it already is in C++ inline functions (which is where it's pretty easy to misuse, as I understand it - two files, one compiled with a CPU feature, one without, linkonce functions get linked together & the linker picks one - then code built without the feature calls code that uses the feature - but, I mean, that can happen even witohut multiversioning, if you compile some source files with a feature and some without) - I guess the main risk would be if it confuses users by making multiversioned C inline functions end up behaving too differently from non-multiversioned ones... <br><br>- Dave<br> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div class="m_-2818023329972350043WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"> <u></u><u></u></span></p>
<p class="MsoNormal"><a name="m_-2818023329972350043__MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></a></p>
<p class="MsoNormal"><a name="m_-2818023329972350043______replyseparator"></a><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> David Blaikie [mailto:<a href="mailto:dblaikie@gmail.com" target="_blank">dblaikie@gmail.com</a>]
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<b>Sent:</b> Monday, October 29, 2018 11:25 AM<br>
<b>To:</b> Keane, Erich <<a href="mailto:erich.keane@intel.com" target="_blank">erich.keane@intel.com</a>>; Eric Christopher <<a href="mailto:echristo@gmail.com" target="_blank">echristo@gmail.com</a>><br>
<b>Cc:</b> <a href="mailto:cfe-commits@lists.llvm.org" target="_blank">cfe-commits@lists.llvm.org</a><br>
<b>Subject:</b> Re: r344957 - Give Multiversion-inline functions linkonce linkage<u></u><u></u></span></p></div></div><div lang="EN-US" link="blue" vlink="purple"><div class="m_-2818023329972350043WordSection1">
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<p class="MsoNormal" style="margin-bottom:12.0pt">Does this match GCC's approach here?<br>
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(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)<u></u><u></u></p>
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<p class="MsoNormal">On Mon, Oct 22, 2018 at 2:22 PM Erich Keane via cfe-commits <<a href="mailto:cfe-commits@lists.llvm.org" target="_blank">cfe-commits@lists.llvm.org</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">Author: erichkeane<br>
Date: Mon Oct 22 14:20:45 2018<br>
New Revision: 344957<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=344957&view=rev" target="_blank">
http://llvm.org/viewvc/llvm-project?rev=344957&view=rev</a><br>
Log:<br>
Give Multiversion-inline functions linkonce linkage<br>
<br>
Since multiversion variant functions can be inline, in C they become<br>
available-externally linkage. This ends up causing the variants to not<br>
be emitted, and not available to the linker.<br>
<br>
The solution is to make sure that multiversion functions are always<br>
emitted by marking them linkonce.<br>
<br>
Change-Id: I897aa37c7cbba0c1eb2c57ee881d5000a2113b75<br>
<br>
Modified:<br>
cfe/trunk/lib/CodeGen/CodeGenModule.cpp<br>
cfe/trunk/test/CodeGen/attr-target-mv.c<br>
<br>
Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=344957&r1=344956&r2=344957&view=diff" target="_blank">
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=344957&r1=344956&r2=344957&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)<br>
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Mon Oct 22 14:20:45 2018<br>
@@ -3669,6 +3669,10 @@ llvm::GlobalValue::LinkageTypes CodeGenM<br>
return llvm::GlobalVariable::WeakAnyLinkage;<br>
}<br>
<br>
+ if (const auto *FD = D->getAsFunction())<br>
+ if (FD->isMultiVersion() && Linkage == GVA_AvailableExternally)<br>
+ return llvm::GlobalVariable::LinkOnceAnyLinkage;<br>
+<br>
// We are guaranteed to have a strong definition somewhere else,<br>
// so we can use available_externally linkage.<br>
if (Linkage == GVA_AvailableExternally)<br>
<br>
Modified: cfe/trunk/test/CodeGen/attr-target-mv.c<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/attr-target-mv.c?rev=344957&r1=344956&r2=344957&view=diff" target="_blank">
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/attr-target-mv.c?rev=344957&r1=344956&r2=344957&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/test/CodeGen/attr-target-mv.c (original)<br>
+++ cfe/trunk/test/CodeGen/attr-target-mv.c Mon Oct 22 14:20:45 2018<br>
@@ -88,19 +88,19 @@ void bar4() {<br>
<br>
// CHECK: declare i32 @foo.arch_sandybridge()<br>
<br>
-// CHECK: define available_externally i32 @foo_inline.sse4.2()<br>
+// CHECK: define linkonce i32 @foo_inline.sse4.2()<br>
// CHECK: ret i32 0<br>
<br>
// CHECK: declare i32 @foo_inline.arch_sandybridge()<br>
//<br>
-// CHECK: define available_externally i32 @foo_inline.arch_ivybridge()<br>
+// CHECK: define linkonce i32 @foo_inline.arch_ivybridge()<br>
// CHECK: ret i32 1<br>
-// CHECK: define available_externally i32 @foo_inline()<br>
+// CHECK: define linkonce i32 @foo_inline()<br>
// CHECK: ret i32 2<br>
<br>
-// CHECK: define available_externally void @foo_decls()<br>
-// CHECK: define available_externally void @foo_decls.sse4.2()<br>
+// CHECK: define linkonce void @foo_decls()<br>
+// CHECK: define linkonce void @foo_decls.sse4.2()<br>
<br>
-// CHECK: define available_externally void @foo_multi.avx_sse4.2()<br>
-// CHECK: define available_externally void @foo_multi.fma4_sse4.2()<br>
-// CHECK: define available_externally void @foo_multi.arch_ivybridge_fma4_sse4.2()<br>
+// CHECK: define linkonce void @foo_multi.avx_sse4.2()<br>
+// CHECK: define linkonce void @foo_multi.fma4_sse4.2()<br>
+// CHECK: define linkonce void @foo_multi.arch_ivybridge_fma4_sse4.2()<br>
<br>
<br>
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