[FFmpeg-devel] [PATCH] Ticket #7124: Fixes compiler bug - replace vec_lvsl/vec_perm with vec_xl

[ckerchne]

On 2019-07-23 08:51, ckerchne wrote:
> A bug exist with the gcc compilers for Power in versions 6.x and 7.x
> (verified with 6.3 and 7.4). It was fixed in version 8.x (verified
> with 8.3). I was using a Power 9 ppc64le machine for building and
> testing.
> 
> It appears the compiler is generating the wrong code for little endian
> machines for the vec_lvsl/vec_perm instruction combos in some cases.
> If these instructions are replaced with vec_xl, the problem goes away
> for all versions of the compilers.
> 
> ---
>  libswscale/ppc/yuv2rgb_altivec.c | 24 ++++--------------------
>  1 file changed, 4 insertions(+), 20 deletions(-)
> 
> diff --git a/libswscale/ppc/yuv2rgb_altivec.c 
> b/libswscale/ppc/yuv2rgb_altivec.c
> index c1e2852adb..536545293d 100644
> --- a/libswscale/ppc/yuv2rgb_altivec.c
> +++ b/libswscale/ppc/yuv2rgb_altivec.c
> @@ -305,9 +305,6 @@ static int altivec_ ## name(SwsContext *c, const
> unsigned char **in,          \
>      vector signed short R1, G1, B1;                                    
>        \
>      vector unsigned char R, G, B;                                      
>        \
>                                                                         
>        \
> -    const vector unsigned char *y1ivP, *y2ivP, *uivP, *vivP;           
>        \
> -    vector unsigned char align_perm;                                   
>        \
> -                                                                       
>        \
>      vector signed short lCY       = c->CY;                             
>        \
>      vector signed short lOY       = c->OY;                             
>        \
>      vector signed short lCRV      = c->CRV;                            
>        \
> @@ -338,26 +335,13 @@ static int altivec_ ## name(SwsContext *c, const
> unsigned char **in,          \
>          vec_dstst(oute, (0x02000002 | (((w * 3 + 32) / 32) << 16)), 
> 1);       \
>                                                                         
>        \
>          for (j = 0; j < w / 16; j++) {                                 
>        \
> -            y1ivP = (const vector unsigned char *) y1i;                
>        \
> -            y2ivP = (const vector unsigned char *) y2i;                
>        \
> -            uivP  = (const vector unsigned char *) ui;                 
>        \
> -            vivP  = (const vector unsigned char *) vi;                 
>        \
> -                                                                       
>        \
> -            align_perm = vec_lvsl(0, y1i);                             
>        \
> -            y0 = (vector unsigned char)                                
>        \
> -                     vec_perm(y1ivP[0], y1ivP[1], align_perm);         
>        \
> +            y0 = vec_xl(0, y1i);                                       
>        \
>                                                                         
>        \
> -            align_perm = vec_lvsl(0, y2i);                             
>        \
> -            y1 = (vector unsigned char)                                
>        \
> -                     vec_perm(y2ivP[0], y2ivP[1], align_perm);         
>        \
> +            y1 = vec_xl(0, y2i);                                       
>        \
>                                                                         
>        \
> -            align_perm = vec_lvsl(0, ui);                              
>        \
> -            u = (vector signed char)                                   
>        \
> -                    vec_perm(uivP[0], uivP[1], align_perm);            
>        \
> +            u = (vector signed char) vec_xl(0, ui);                    
>        \
>                                                                         
>        \
> -            align_perm = vec_lvsl(0, vi);                              
>        \
> -            v = (vector signed char)                                   
>        \
> -                    vec_perm(vivP[0], vivP[1], align_perm);            
>        \
> +            v = (vector signed char) vec_xl(0, vi);                    
>        \
>                                                                         
>        \
>              u = (vector signed char)                                   
>        \
>                      vec_sub(u,                                         
>        \
> --
> 2.17.1
> 
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Could someone please engage on this issue?  It's been almost 10 days.

Chip Kerchner