[Mesa-dev] [PATCH 1/2] i965/fs: Emit MADs from (x + -(y * z)).

[Kristian Høgsberg]

On Tue, Jan 13, 2015 at 3:00 PM, Matt Turner <mattst88 at gmail.com> wrote:
> Just use the negation source modifier on one of the multiplicand
> arguments.
>
> total instructions in shared programs: 5889529 -> 5880016 (-0.16%)
> instructions in affected programs:     600846 -> 591333 (-1.58%)

Reviewed-by: Kristian Høgsberg <krh at bitplanet.net>

> ---
>  src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> index bd9345e..dd4beff 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> @@ -426,10 +426,21 @@ fs_visitor::try_emit_mad(ir_expression *ir)
>     ir_rvalue *nonmul = ir->operands[1];
>     ir_expression *mul = ir->operands[0]->as_expression();
>
> +   bool mul_negate = false;
> +   if (mul && mul->operation == ir_unop_neg) {
> +      mul = mul->operands[0]->as_expression();
> +      mul_negate = true;
> +   }
> +
>     if (!mul || mul->operation != ir_binop_mul) {
>        nonmul = ir->operands[0];
>        mul = ir->operands[1]->as_expression();
>
> +      if (mul && mul->operation == ir_unop_neg) {
> +         mul = mul->operands[0]->as_expression();
> +         mul_negate = true;
> +      }
> +
>        if (!mul || mul->operation != ir_binop_mul)
>           return false;
>     }
> @@ -444,6 +455,7 @@ fs_visitor::try_emit_mad(ir_expression *ir)
>
>     mul->operands[0]->accept(this);
>     fs_reg src1 = this->result;
> +   src1.negate ^= mul_negate;
>
>     mul->operands[1]->accept(this);
>     fs_reg src2 = this->result;
> --
> 2.0.4
>
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