[Mesa-dev] [PATCH 1/2] i965/fs: Handle negating immediates on MADs when propagating saturates

[Ian Romanick]

On 11/20/2017 02:33 PM, Matt Turner wrote:
> MADs don't take immediate sources, but we allow them in the IR since it
> simplifies a lot of things. I neglected to consider that case.
> 
> Fixes: 4009a9ead490 ("i965/fs: Allow saturate propagation to propagate
>                       negations into MADs.")
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103616
> Reported-and-Tested-by: Ruslan Kabatsayev <b7.10110111 at gmail.com>
> ---
>  src/intel/compiler/brw_fs_saturate_propagation.cpp | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/src/intel/compiler/brw_fs_saturate_propagation.cpp b/src/intel/compiler/brw_fs_saturate_propagation.cpp
> index 1c97a507d8..d6cfa79a61 100644
> --- a/src/intel/compiler/brw_fs_saturate_propagation.cpp
> +++ b/src/intel/compiler/brw_fs_saturate_propagation.cpp
> @@ -88,8 +88,14 @@ opt_saturate_propagation_local(fs_visitor *v, bblock_t *block)
>                          scan_inst->src[0].negate = !scan_inst->src[0].negate;
>                          inst->src[0].negate = false;
>                       } else if (scan_inst->opcode == BRW_OPCODE_MAD) {
> -                        scan_inst->src[0].negate = !scan_inst->src[0].negate;
> -                        scan_inst->src[1].negate = !scan_inst->src[1].negate;
> +                        for (int i = 0; i < 2; i++) {
> +                           if (scan_inst->src[i].file == IMM) {
> +                              brw_negate_immediate(scan_inst->src[i].type,
> +                                                   &scan_inst->src[i].as_brw_reg());
> +                           } else {
> +                              scan_inst->src[i].negate = !scan_inst->src[i].negate;
> +                           }
> +                        }

Is this going to affect the number of generated instructions if there
are multiple MADs using the same immediate value for a multiply source?
Would it be better to find a multiply source that isn't an immediate?

>                          inst->src[0].negate = false;
>                       } else if (scan_inst->opcode == BRW_OPCODE_ADD) {
>                          if (scan_inst->src[1].file == IMM) {
>