[Mesa-dev] [PATCH 01/13] i965/fs: Allow constant propagation into MACH.

[Kenneth Graunke]

On 03/20/2013 05:36 PM, Eric Anholt wrote:
> This happens quite a bit with varying-index uniform loads.  We could also
> do better by avoiding the MACH entirely, but there's no reason not to at
> least take this step.
> ---
>   src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp |    6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)

Okay, yeah, so we constant propagate the immediate into both the MUL and 
the MACH.  That makes sense...may free up a register.

It'd be nice to eliminate it if the constant is small enough, yeah.

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

> diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> index 194ed07..2d0391a 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> @@ -261,6 +261,7 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
>            progress = true;
>            break;
>
> +      case BRW_OPCODE_MACH:
>         case BRW_OPCODE_MUL:
>         case BRW_OPCODE_ADD:
>            if (i == 1) {
> @@ -268,10 +269,11 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
>               progress = true;
>            } else if (i == 0 && inst->src[1].file != IMM) {
>               /* Fit this constant in by commuting the operands.
> -             * Exception: we can't do this for 32-bit integer MUL
> +             * Exception: we can't do this for 32-bit integer MUL/MACH
>                * because it's asymmetric.
>                */
> -            if (inst->opcode == BRW_OPCODE_MUL &&
> +            if ((inst->opcode == BRW_OPCODE_MUL ||
> +                 inst->opcode == BRW_OPCODE_MACH) &&
>                   (inst->src[1].type == BRW_REGISTER_TYPE_D ||
>                    inst->src[1].type == BRW_REGISTER_TYPE_UD))
>                  break;