[cfe-dev] preserving type signatures

[Naoya Maruyama]

Victor, thanks for pointing out the discussion, though unfortunately
there is no way to work around the ABI issue.

Thanks,
Naoya

On Wed, Mar 24, 2010 at 11:09 PM, Victor Zverovich
<victor.zverovich at googlemail.com> wrote:
> It has been discussed on the list recently:
> http://old.nabble.com/64bit-MRV-problem:-{-float,-float,-float}-->-{-double,-float-}-td27304830.html
>
> Best regards,
> Victor
> On 24 March 2010 13:24, Naoya Maruyama <naoya.maruyama at gmail.com> wrote:
>>
>> Renato,
>>
>> Here's a sample code that is compiled as I wrote:
>>
>> -------------------------------------------------
>> struct dim2
>> {
>>    float x;
>>    float y;
>> };
>>
>> struct dim2 kernel(struct dim2 *g)
>> {
>>    return *g;
>> }
>> -------------------------------------------------
>>
>> When this code is compiled with the clang command in the LLVM/Clang
>> 2.6 binary tarball:
>>
>> -------------------------------------------------
>> $ clang --version
>> clang version 1.0
>> (https://llvm.org/svn/llvm-project/cfe/branches/release_26 exported)
>> Target: x86_64-unknown-linux-gnu
>> Thread model: posix
>> $ clang -Wall -emit-llvm -S test.c -o -
>> ; ModuleID = 'test.c'
>> target datalayout =
>>
>> "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
>> target triple = "x86_64-unknown-linux-gnu"
>>
>> %struct.dim2 = type { float, float }
>>
>> define double @kernel(%struct.dim2* %g) nounwind {
>> entry:
>>  %retval = alloca %struct.dim2                   ; <%struct.dim2*>
>> [#uses=2]
>>  %g.addr = alloca %struct.dim2*                  ; <%struct.dim2**>
>> [#uses=2]
>>  store %struct.dim2* %g, %struct.dim2** %g.addr
>>  %tmp = load %struct.dim2** %g.addr              ; <%struct.dim2*>
>> [#uses=1]
>>  %tmp1 = bitcast %struct.dim2* %retval to i8*    ; <i8*> [#uses=1]
>>  %tmp2 = bitcast %struct.dim2* %tmp to i8*       ; <i8*> [#uses=1]
>>  call void @llvm.memcpy.i64(i8* %tmp1, i8* %tmp2, i64 8, i32 4)
>>  %0 = bitcast %struct.dim2* %retval to double*   ; <double*> [#uses=1]
>>  %1 = load double* %0, align 1                   ; <double> [#uses=1]
>>  ret double %1
>> }
>>
>> declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32)
>> nounwind
>> -------------------------------------------------
>>
>> What I want to see is the exactly same signature of the function named
>> "kernel" as in the source code.
>>
>> Let me know if I'm doing anything wrong.
>>
>> Thanks,
>> Naoya
>>
>> On Wed, Mar 24, 2010 at 8:58 PM, Renato Golin <rengolin at systemcall.org>
>> wrote:
>> > On 24 March 2010 07:34, Naoya Maruyama <naoya.maruyama at gmail.com> wrote:
>> >> However, for example, with Clang, if a function
>> >> returns struct {float, float}, then the compiled function in the llvm
>> >> bitcode returns a double that aggregates the two floats.
>> >
>> > It's completely wrong to convert { float, float } into double. Just
>> > because they have the same size doesn't mean they're identical.
>> >
>> > Can you give us a simple example where this occurs?
>> >
>> >
>> > --
>> > cheers,
>> > --renato
>> >
>> > http://systemcall.org/
>> >
>> > Reclaim your digital rights, eliminate DRM, learn more at
>> > http://www.defectivebydesign.org/what_is_drm
>> >
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>