[Mesa-dev] [PATCH 2/3] i965/fs: Fix comparisions with uint negation.

[Eric Anholt]

On Mon, 03 Oct 2011 16:34:28 -0700, Ian Romanick <idr at freedesktop.org> wrote:
> On 10/03/2011 03:41 PM, Eric Anholt wrote:

> > diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
> > index 2000180..555d26d 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> > @@ -1347,6 +1347,19 @@ fs_visitor::register_coalesce()
> >   	    interfered = true;
> >   	    break;
> >   	 }
> > +
> > +	 /* The accumulator result appears to get used for the
> > +	  * conditional modifier generation.  When negating a UD
> > +	  * value, there is a 33rd bit generated for the sign in the
> > +	  * accumulator value, so now you can't check, for example,
> > +	  * equality with a 32-bit value.  See piglit fs-op-neg-uint.
> > +	  */
> > +	 if (scan_inst->conditional_mod&&
> > +	     inst->src[0].negate&&
> > +	     inst->src[0].type == BRW_REGISTER_TYPE_UD) {
> > +	    interfered = true;
> > +	    break;
> > +	 }
> >         }
> >         if (interfered) {
> >   	 continue;

> >   }
> > +
> > +void
> > +fs_visitor::resolve_ud_negate(fs_reg *reg)
> > +{
> > +   if (reg->type != BRW_REGISTER_TYPE_UD ||
> > +       !reg->negate)
> > +      return;
> > +
> > +   fs_reg temp = fs_reg(this, glsl_type::uint_type);
> > +   emit(BRW_OPCODE_MOV, temp, *reg);
> > +   *reg = temp;
> > +}
> 
> I suspect I know the answer, but are we sure that a later optimization 
> pass won't copy propagate this extra move away?

That's what the hunk in the badly-named copy-propagation pass is about
(and the neg-uint test tested it specifically).
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