[llvm-dev] Suspecting a frontend bug in LLVM compiler

[Christudasan D via llvm-dev]

Please give a remark on this.

Regards,
Christu

On Tue, Aug 30, 2016 at 10:21 AM, Christudasan D <xander.cd at gmail.com>
wrote:

> Greetings to all.
>
>
>
> I am facing a problem with LLVM 3.5 and suspect it is a bug. Here is my
> observation.
>
>
>
> I am trying to support a target specific function attribute for a
> particular target machine.
>
> Having followed the steps specified in the compiler documentation, I see
> the attribute is passed to the backend if we include the attribute in the
> function definition. But this attribute is not propagate to the backend if
> I include it only in the function’s prototype/declaration (in the C
> program).
>
>
>
> This virtual function (given below) invocation in
> clang/lib/CodeGen/CodeGenModule.cpp in clang is responsible for attaching
> the target specific attributes to the backend CodeGen objects (functions,
> variables etc.)
>
> getTargetCodeGenInfo().SetTargetAttributes(D, GO, *this)
>
>
>
> I found that this virtual function is getting invoked only for function
> definitions and not for function declarations.
>
>
>
> Actual requirement:
>
> Along with regular C functions we have special functions supported in the
> target and its definition and invocation will always come in different
> compilation units. There must be a way to recognize these special functions
> at the call-sites during codegen in the backend. By attaching some info in
> the function prototype, we can recognize these special functions at the
> call-site during backend codegen. That’s why I thought of a new target
> specific attribute to achieve this purpose.
>
>
>
> *Is it really a bug?*
>
> When I compile a program having function declarations/prototypes with
> generic attributes like __attribute__((*const*)), clang will add it to
> that function’s attributelist in the IR and it will be available in the
> backend.
>
>
>
> Similarly I expected the target specific attribute should also be added to
> the attributelist available in the backend and I should be able to identify
> it using *F.hasFnAttribute("XYZ")*, where XYZ is the new attribute name.
>
>
>
> Since I work with LLVM 3.5 code-base, I am not sure whether this issue (if
> it is really a bug) has already been fixed with recent compiler releases.
>
> Please write to me.
>
>
>
> Thanks,
>
> Christu
>
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