[llvm] r266856 - ThinLTO: never promote as external weak

[Mehdi Amini via llvm-commits]

> On Apr 19, 2016, at 9:36 PM, Teresa Johnson <tejohnson at google.com> wrote:
> 
> 
> 
> On Tue, Apr 19, 2016 at 9:18 PM, Mehdi Amini via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> Author: mehdi_amini
> Date: Tue Apr 19 23:18:11 2016
> New Revision: 266856
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=266856&view=rev <http://llvm.org/viewvc/llvm-project?rev=266856&view=rev>
> Log:
> ThinLTO: never promote as external weak
> 
> This linkage is *not* intended to express that a declaration refers
> to a weak symbol, but that the symbol might not be present at link
> time. I don't believe it was the intent.
> 
> In fact, this was the intent. WeakAny linkage is used for defined symbols with __attribute__((weak)), which may not have a definition. The corresponding declaration should be ExternalWeak.

It is not clear to me: how can you during the link be in a situation where you have a weak definition that will not be present?
I don't see a case where we *introduce* an external_weak that is not present in the original program.

CC Rafael.


-- 
Mehdi


> 
> 
> From: Mehdi Amini <mehdi.amini at apple.com <mailto:mehdi.amini at apple.com>>
> 
> Modified:
>     llvm/trunk/lib/Transforms/Utils/FunctionImportUtils.cpp
>     llvm/trunk/test/Linker/funcimport.ll
> 
> Modified: llvm/trunk/lib/Transforms/Utils/FunctionImportUtils.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/FunctionImportUtils.cpp?rev=266856&r1=266855&r2=266856&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/FunctionImportUtils.cpp?rev=266856&r1=266855&r2=266856&view=diff>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/FunctionImportUtils.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/FunctionImportUtils.cpp Tue Apr 19 23:18:11 2016
> @@ -132,7 +132,7 @@ FunctionImportGlobalProcessing::getLinka
>      // linker. The module linking caller needs to enforce this.
>      assert(!doImportAsDefinition(SGV));
>      // If imported as a declaration, it becomes external_weak.
> -    return GlobalValue::ExternalWeakLinkage;
> +    return SGV->getLinkage();
> 
>    case GlobalValue::WeakODRLinkage:
>      // For weak_odr linkage, there is a guarantee that all copies will be
> 
> Modified: llvm/trunk/test/Linker/funcimport.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Linker/funcimport.ll?rev=266856&r1=266855&r2=266856&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Linker/funcimport.ll?rev=266856&r1=266855&r2=266856&view=diff>
> ==============================================================================
> --- llvm/trunk/test/Linker/funcimport.ll (original)
> +++ llvm/trunk/test/Linker/funcimport.ll Tue Apr 19 23:18:11 2016
> @@ -98,7 +98,7 @@
>  ; reference should turned into an external_weak declaration.
>  ; RUN: llvm-link %t2.bc -summary-index=%t3.thinlto.bc -import=callweakfunc:%t.bc -import=weakfunc:%t.bc -S 2>&1 | FileCheck %s --check-prefix=IMPORTWEAKFUNC
>  ; IMPORTWEAKFUNC-DAG: Ignoring import request for weak-any function weakfunc
> -; IMPORTWEAKFUNC-DAG: declare extern_weak void @weakfunc
> +; IMPORTWEAKFUNC-DAG: declare void @weakfunc
>  ; IMPORTWEAKFUNC-DAG: define available_externally void @callweakfunc
>  ; IMPORTWEAKFUNC-NOT: @weakvar = extern_weak global i32, align 4
> 
> 
> 
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> 
> -- 
> Teresa Johnson |	 Software Engineer |	 tejohnson at google.com <mailto:tejohnson at google.com> |	 408-460-2413

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