[llvm] r260122 - [ThinLTO] Remove imported available externally defs from comdats.

Mon Feb 8 13:04:42 PST 2016

On Mon, Feb 8, 2016 at 11:27 AM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Mon, Feb 8, 2016 at 11:22 AM, Teresa Johnson <tejohnson at google.com>
> wrote:
>
>>
>>
>> On Mon, Feb 8, 2016 at 11:06 AM, David Blaikie <dblaikie at gmail.com>
>> wrote:
>>
>>> I couldn't quite follow the test - but wouldn't removing things (or in
>>> any way modifyidng) from a COMDAT cause problems? (the COMDAT would no
>>> longer match between objects, etc?)
>>>
>>
>> The comdat will not be emitted in the importing module if we import its
>> definitions as available_externally, since any such imported defs will be
>> removed from the comdat with this patch.  Any non-imported members remained
>> decls and are not part of a comdat in the importing module either.
>>
>
> Ah, right - thanks! (the available_externally helps me understand)
>
> Though perhaps we should remove the comdats, to be safe? Once we're
> adding/removing things from them they're no longer accurate anyway. Is
> there any benefit to keeping them? Seems like they're just likely to be a
> trap/misleading thing to keep them around.
>

I can do that. The empty comdats never get emitted but I am not sure where
they are ultimately removed/suppressed.
Teresa

>
>>
>>
>>> On Mon, Feb 8, 2016 at 10:47 AM, Teresa Johnson via llvm-commits <
>>> llvm-commits at lists.llvm.org> wrote:
>>>
>>>> Author: tejohnson
>>>> Date: Mon Feb  8 12:47:20 2016
>>>> New Revision: 260122
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=260122&view=rev
>>>> Log:
>>>> [ThinLTO] Remove imported available externally defs from comdats.
>>>>
>>>> Summary:
>>>> Available externally definitions are considered declarations for the
>>>> linker and eventually dropped. As such they are not allowed to be
>>>> in comdats. Remove any such imported functions from comdats.
>>>>
>>>> Reviewers: rafael
>>>>
>>>> Subscribers: davidxl, llvm-commits, joker.eph
>>>>
>>>> Differential Revision: http://reviews.llvm.org/D16120
>>>>
>>>> Added:
>>>>     llvm/trunk/test/Linker/Inputs/funcimport_comdat.ll
>>>>     llvm/trunk/test/Linker/funcimport_comdat.ll
>>>> Modified:
>>>>     llvm/trunk/lib/Linker/LinkModules.cpp
>>>>
>>>> Modified: llvm/trunk/lib/Linker/LinkModules.cpp
>>>> URL:
>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Linker/LinkModules.cpp?rev=260122&r1=260121&r2=260122&view=diff
>>>>
>>>> ==============================================================================
>>>> --- llvm/trunk/lib/Linker/LinkModules.cpp (original)
>>>> +++ llvm/trunk/lib/Linker/LinkModules.cpp Mon Feb  8 12:47:20 2016
>>>> @@ -722,9 +722,21 @@ void ThinLTOGlobalProcessing::processGlo
>>>>        GV.setVisibility(GlobalValue::HiddenVisibility);
>>>>      if (isModuleExporting())
>>>>        NewExportedValues.insert(&GV);
>>>> -    return;
>>>> +  } else
>>>> +    GV.setLinkage(getLinkage(&GV));
>>>> +
>>>> +  // Remove functions imported as available externally defs from
>>>> comdats,
>>>> +  // as this is a declaration for the linker, and will be dropped
>>>> eventually.
>>>> +  // It is illegal for comdats to contain declarations.
>>>> +  auto *GO = dyn_cast_or_null<GlobalObject>(&GV);
>>>> +  if (GO && GO->isDeclarationForLinker() && GO->hasComdat()) {
>>>> +    // The IRMover should not have placed any imported declarations in
>>>> +    // a comdat, so the only declaration that should be in a comdat
>>>> +    // at this point would be a definition imported as
>>>> available_externally.
>>>> +    assert(GO->hasAvailableExternallyLinkage() &&
>>>> +           "Expected comdat on definition (possibly available
>>>> external)");
>>>> +    GO->setComdat(nullptr);
>>>>    }
>>>> -  GV.setLinkage(getLinkage(&GV));
>>>>  }
>>>>
>>>>  void ThinLTOGlobalProcessing::processGlobalsForThinLTO() {
>>>>
>>>> Added: llvm/trunk/test/Linker/Inputs/funcimport_comdat.ll
>>>> URL:
>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Linker/Inputs/funcimport_comdat.ll?rev=260122&view=auto
>>>>
>>>> ==============================================================================
>>>> --- llvm/trunk/test/Linker/Inputs/funcimport_comdat.ll (added)
>>>> +++ llvm/trunk/test/Linker/Inputs/funcimport_comdat.ll Mon Feb  8
>>>> 12:47:20 2016
>>>> @@ -0,0 +1,4 @@
>>>> +define i32 @main() #0 {
>>>> +entry:
>>>> +  ret i32 0
>>>> +}
>>>>
>>>> Added: llvm/trunk/test/Linker/funcimport_comdat.ll
>>>> URL:
>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Linker/funcimport_comdat.ll?rev=260122&view=auto
>>>>
>>>> ==============================================================================
>>>> --- llvm/trunk/test/Linker/funcimport_comdat.ll (added)
>>>> +++ llvm/trunk/test/Linker/funcimport_comdat.ll Mon Feb  8 12:47:20 2016
>>>> @@ -0,0 +1,28 @@
>>>> +; Do setup work for all below tests: generate bitcode and combined
>>>> index
>>>> +; RUN: llvm-as -function-summary %s -o %t.bc
>>>> +; RUN: llvm-as -function-summary %p/Inputs/funcimport_comdat.ll -o
>>>> %t2.bc
>>>> +; RUN: llvm-lto -thinlto -o %t3 %t.bc %t2.bc
>>>> +
>>>> +; Ensure linking of comdat containing external linkage global and
>>>> function
>>>> +; removes the imported available_externally defs from comdat.
>>>> +; RUN: llvm-link %t2.bc -functionindex=%t3.thinlto.bc
>>>> -import=comdat1_func1:%t.bc -S | FileCheck %s --check-prefix=IMPORTCOMDAT
>>>> +; IMPORTCOMDAT-NOT: $comdat1 = comdat any
>>>> +; IMPORTCOMDAT-NOT: comdat($comdat1)
>>>> +
>>>> +; Ensure linking of comdat containing internal linkage function with
>>>> alias
>>>> +; removes the imported and promoted available_externally defs from
>>>> comdat.
>>>> +; RUN: llvm-link %t2.bc -functionindex=%t3.thinlto.bc
>>>> -import=comdat2_func1:%t.bc -S | FileCheck %s --check-prefix=IMPORTCOMDAT2
>>>> +; IMPORTCOMDAT2-NOT: $comdat2 = comdat any
>>>> +; IMPORTCOMDAT2-NOT: comdat($comdat2)
>>>> +
>>>> +$comdat1 = comdat any
>>>> + at comdat1_glob = global i32 0, comdat($comdat1)
>>>> +define void @comdat1_func1() comdat($comdat1) {
>>>> +  ret void
>>>> +}
>>>> +
>>>> +$comdat2 = comdat any
>>>> + at comdat2_alias = alias void (), void ()* @comdat2_func1
>>>> +define internal void @comdat2_func1() comdat($comdat2) {
>>>> +  ret void
>>>> +}
>>>>
>>>>
>>>> _______________________________________________
>>>> llvm-commits mailing list
>>>> llvm-commits at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>>>>
>>>
>>>
>>
>>
>> --
>> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>> 408-460-2413
>>
>
>

-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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