[cfe-dev] preserving type signatures

[Victor Zverovich]

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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