I don't think there's any reason we can't eliminate a dead instruction
when the writemask is zero. I do wonder, though, why this patch
actually makes a difference. There's an "if (!inst->dead_mask ||
!inst->dst.writemask)" three lines before the code visible in the patch
that makes it not kill the instruction if the writemask is zero. I
don't remember why that's there, but if it weren't there, and the
writemask is zero, the dead_mask should also be zero, so it should be
handled by the "else if" block.
In short, I think that entire if/else if/else statement could use a look.
Bryan
On 10/07/2011 10:40 AM, Brian Paul wrote:
> From: Brian Paul <bri...@vmware.com>
>
> This fixes a bug where we'd wind up emitting an invalid instruction like
> MOVE R[0]., R[1]; - note the empty/zero writemask. If we don't write to
> any dest register channels, cull the instruction.
> ---
> src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 8 +++++++-
> 1 files changed, 7 insertions(+), 1 deletions(-)
>
> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> index d8ef8a3..44b1149 100644
> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> @@ -3776,8 +3776,14 @@
> glsl_to_tgsi_visitor::eliminate_dead_code_advanced(void)
> iter.remove();
> delete inst;
> removed++;
> - } else
> + } else {
> inst->dst.writemask &= ~(inst->dead_mask);
> + if (inst->dst.writemask == 0) {
> + iter.remove();
> + delete inst;
> + removed++;
> + }
> + }
> }
>
> ralloc_free(write_level);
_______________________________________________
mesa-dev mailing list
mesa-dev@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/mesa-dev
