[Mesa-dev] [PATCH] st/mesa: kill instruction if writemask=0 in eliminate_dead_code_advanced()

[Brian Paul]

On 10/09/2011 12:50 PM, Bryan Cain wrote:
> 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.

For the failing case, inst->dead_mask=0xf and inst->dst.writemask=0x8.
So the 'continue' clause isn't taken.  And dead_mask != writemask so 
the existing iter.remove() clause isn't taken either.

The else if test could be changed from:

     else if (inst->dead_mask == inst->dst.writemask) {

to read:

     else if ((inst->dst.writemask & ~inst->dead_mask) == 0) {

That works here.  Patch attached.  Look OK?

-Brian