[Mesa-dev] [PATCH] glsl_to_tgsi: Skip useless comparison instructions.

[Ilia Mirkin]

On Tue, Dec 1, 2015 at 8:12 PM, Matt Turner <mattst88 at gmail.com> wrote:
> ---
>  src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> index 7f58b44..89ad6cd 100644
> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> @@ -1655,7 +1655,13 @@ glsl_to_tgsi_visitor::visit(ir_expression *ir)
>              st_dst_reg temp_dst = st_dst_reg(temp);
>              st_src_reg temp1 = st_src_reg(temp), temp2 = st_src_reg(temp);
>
> -            emit_asm(ir, TGSI_OPCODE_SEQ, st_dst_reg(temp), op[0], op[1]);
> +            if (ir->operands[0]->type->is_boolean() &&
> +                ir->operands[1]->as_constant() &&
> +                ir->operands[1]->as_constant()->is_one()) {
> +               emit_asm(ir, TGSI_OPCODE_MOV, st_dst_reg(temp), op[0]);
> +            } else {
> +               emit_asm(ir, TGSI_OPCODE_SEQ, st_dst_reg(temp), op[0], op[1]);
> +            }
>
>              /* Emit 1-3 AND operations to combine the SEQ results. */
>              switch (ir->operands[0]->type->vector_elements) {
> @@ -1708,7 +1714,13 @@ glsl_to_tgsi_visitor::visit(ir_expression *ir)
>           st_src_reg temp = get_temp(native_integers ?
>                                      glsl_type::uvec4_type :
>                                      glsl_type::vec4_type);
> -         emit_asm(ir, TGSI_OPCODE_SNE, st_dst_reg(temp), op[0], op[1]);
> +         if (ir->operands[0]->type->is_boolean() &&
> +             ir->operands[1]->as_constant() &&
> +             ir->operands[1]->as_constant()->is_zero()) {
> +            emit_asm(ir, TGSI_OPCODE_MOV, st_dst_reg(temp), op[0]);
> +         } else {
> +            emit_asm(ir, TGSI_OPCODE_SNE, st_dst_reg(temp), op[0], op[1]);
> +         }
>
>           if (native_integers) {
>              st_dst_reg temp_dst = st_dst_reg(temp);

Reviewed-by: Ilia Mirkin <imirkin at alum.mit.edu>

I'd feel a little better if you double-checked that a shader_test that
hits this continues to pass with llvmpipe or softpipe.

Thanks,

  -ilia