r344957 - Give Multiversion-inline functions linkonce linkage

[David Blaikie via cfe-commits]

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> 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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