<div dir="ltr">It looks like this breaks building base.dll in the Chromium project: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__code.google.com_p_chromium_issues_detail-3Fid-3D505916&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=BSqEv9KvKMW_Ob8SyngJ70KdZISM_ASROnREeq0cCxk&m=xMs8ZfUT3Nr56mKZ3nzNq6i9AgCksncaZXGExWByvQw&s=V2e1HC-R6Rj5m2hsvEgALDeW3EWdUrTblb9wTESzXXI&e=">http://code.google.com/p/chromium/issues/detail?id=505916</a></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jun 30, 2015 at 12:07 PM, Peter Collingbourne <span dir="ltr"><<a href="mailto:peter@pcc.me.uk" target="_blank">peter@pcc.me.uk</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: pcc<br>
Date: Tue Jun 30 14:07:26 2015<br>
New Revision: 241102<br>
<br>
URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D241102-26view-3Drev&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=BSqEv9KvKMW_Ob8SyngJ70KdZISM_ASROnREeq0cCxk&m=xMs8ZfUT3Nr56mKZ3nzNq6i9AgCksncaZXGExWByvQw&s=W-bxDk6mVHIOyu5_RvuIMZmQ1crcB-hLexRtkNFIfac&e=" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=241102&view=rev</a><br>
Log:<br>
CodeGen: Assign an appropriate comdat to thunks.<br>
<br>
Previously we were not assigning a comdat to thunks in the Microsoft ABI,<br>
which would have required us to emit these functions outside of a comdat.<br>
(Due to an inconsistency in how we were emitting objects, we were getting this<br>
right most of the time, but only when compiling with function sections.) This<br>
code generator change causes us to create a comdat for each thunk.<br>
<br>
Differential Revision: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_D10829&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=BSqEv9KvKMW_Ob8SyngJ70KdZISM_ASROnREeq0cCxk&m=xMs8ZfUT3Nr56mKZ3nzNq6i9AgCksncaZXGExWByvQw&s=omqx13XGdidA26637vSwu92d84sdfuPmECyQwUkyjxg&e=" rel="noreferrer" target="_blank">http://reviews.llvm.org/D10829</a><br>
<br>
Modified:<br>
cfe/trunk/lib/CodeGen/CGVTables.cpp<br>
cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp<br>
<br>
Modified: cfe/trunk/lib/CodeGen/CGVTables.cpp<br>
URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_cfe_trunk_lib_CodeGen_CGVTables.cpp-3Frev-3D241102-26r1-3D241101-26r2-3D241102-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=BSqEv9KvKMW_Ob8SyngJ70KdZISM_ASROnREeq0cCxk&m=xMs8ZfUT3Nr56mKZ3nzNq6i9AgCksncaZXGExWByvQw&s=nCfcMuT95AaDm9I430qhBJfznQ0XshuLejDS20oECV4&e=" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGVTables.cpp?rev=241102&r1=241101&r2=241102&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/lib/CodeGen/CGVTables.cpp (original)<br>
+++ cfe/trunk/lib/CodeGen/CGVTables.cpp Tue Jun 30 14:07:26 2015<br>
@@ -378,9 +378,6 @@ void CodeGenFunction::GenerateThunk(llvm<br>
// Set the right linkage.<br>
CGM.setFunctionLinkage(GD, Fn);<br>
<br>
- if (CGM.supportsCOMDAT() && Fn->isWeakForLinker())<br>
- Fn->setComdat(CGM.getModule().getOrInsertComdat(Fn->getName()));<br>
-<br>
// Set the right visibility.<br>
const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());<br>
setThunkVisibility(CGM, MD, Thunk, Fn);<br>
@@ -450,17 +447,18 @@ void CodeGenVTables::emitThunk(GlobalDec<br>
// expensive/sucky at the moment, so don't generate the thunk unless<br>
// we have to.<br>
// FIXME: Do something better here; GenerateVarArgsThunk is extremely ugly.<br>
- if (!UseAvailableExternallyLinkage) {<br>
- CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);<br>
- CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,<br>
- !Thunk.Return.isEmpty());<br>
- }<br>
+ if (UseAvailableExternallyLinkage)<br>
+ return;<br>
+ CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, Thunk);<br>
} else {<br>
// Normal thunk body generation.<br>
CodeGenFunction(CGM).GenerateThunk(ThunkFn, FnInfo, GD, Thunk);<br>
- CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,<br>
- !Thunk.Return.isEmpty());<br>
}<br>
+<br>
+ CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,<br>
+ !Thunk.Return.isEmpty());<br>
+ if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())<br>
+ ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(ThunkFn->getName()));<br>
}<br>
<br>
void CodeGenVTables::maybeEmitThunkForVTable(GlobalDecl GD,<br>
<br>
Modified: cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp<br>
URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_cfe_trunk_test_CodeGenCXX_microsoft-2Dabi-2Dthunks.cpp-3Frev-3D241102-26r1-3D241101-26r2-3D241102-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=BSqEv9KvKMW_Ob8SyngJ70KdZISM_ASROnREeq0cCxk&m=xMs8ZfUT3Nr56mKZ3nzNq6i9AgCksncaZXGExWByvQw&s=Zb0Qzta2L0rQXq4XO_e_OPuJXBlrOEV3yCV50PnVx2M&e=" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp?rev=241102&r1=241101&r2=241102&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp (original)<br>
+++ cfe/trunk/test/CodeGenCXX/microsoft-abi-thunks.cpp Tue Jun 30 14:07:26 2015<br>
@@ -91,7 +91,7 @@ struct E : D {<br>
<br>
E::E() {} // Emits vftable and forces thunk generation.<br>
<br>
-// CODEGEN-LABEL: define weak_odr x86_thiscallcc %struct.C* @"\01?goo@E@@QAEPAUB@@XZ"<br>
+// CODEGEN-LABEL: define weak_odr x86_thiscallcc %struct.C* @"\01?goo@E@@QAEPAUB@@XZ"{{.*}} comdat<br>
// CODEGEN: call x86_thiscallcc %struct.C* @"\01?goo@E@@UAEPAUC@@XZ"<br>
// CODEGEN: getelementptr inbounds i8, i8* {{.*}}, i32 4<br>
// CODEGEN: ret<br>
@@ -124,7 +124,7 @@ struct I : D {<br>
<br>
I::I() {} // Emits vftable and forces thunk generation.<br>
<br>
-// CODEGEN-LABEL: define weak_odr x86_thiscallcc %struct.{{[BF]}}* @"\01?goo@I@@QAEPAUB@@XZ"<br>
+// CODEGEN-LABEL: define weak_odr x86_thiscallcc %struct.{{[BF]}}* @"\01?goo@I@@QAEPAUB@@XZ"{{.*}} comdat<br>
// CODEGEN: %[[ORIG_RET:.*]] = call x86_thiscallcc %struct.F* @"\01?goo@I@@UAEPAUF@@XZ"<br>
// CODEGEN: %[[ORIG_RET_i8:.*]] = bitcast %struct.F* %[[ORIG_RET]] to i8*<br>
// CODEGEN: %[[VBPTR_i8:.*]] = getelementptr inbounds i8, i8* %[[ORIG_RET_i8]], i32 4<br>
<br>
<br>
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</blockquote></div><br></div>