[Mesa-dev] [PATCH] nir/opcodes: Fix constant-folding of ufind_msb

[Bas Nieuwenhuizen]

Reviewed-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>

On Tue, Aug 29, 2017, at 00:10, Jason Ekstrand wrote:
> We didn't fold correctly in the case of 0x1 because we never let the
> loop counter hit 0.  Switching it to bit >= 0 solves this problem.
> 
> Cc: mesa-stable at lists.freedesktop.org
> ---
>  src/compiler/nir/nir_opcodes.py | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/compiler/nir/nir_opcodes.py
> b/src/compiler/nir/nir_opcodes.py
> index 39c01a7..a64a28e 100644
> --- a/src/compiler/nir/nir_opcodes.py
> +++ b/src/compiler/nir/nir_opcodes.py
> @@ -308,7 +308,7 @@ for (unsigned bit = 0; bit < 32; bit++) {
>  
>  unop_convert("ufind_msb", tint32, tuint32, """
>  dst = -1;
> -for (int bit = 31; bit > 0; bit--) {
> +for (int bit = 31; bit >= 0; bit--) {
>     if ((src0 >> bit) & 1) {
>        dst = bit;
>        break;
> -- 
> 2.5.0.400.gff86faf
> 
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