[Mesa-dev] [PATCH 14/16] i965/fs: Allow flipping cond mod for negated arguments.

[Ian Romanick]

On 01/20/2015 01:31 AM, Matt Turner wrote:
> @@ -73,10 +72,14 @@ opt_cmod_propagation_local(fs_visitor *v, bblock_t *block)
>               scan_inst->dst.reg == inst->src[0].reg &&
>               scan_inst->dst.reg_offset == inst->src[0].reg_offset &&
>               !scan_inst->is_partial_write()) {
> +            enum brw_conditional_mod cond =
> +               inst->src[0].negate ? brw_invert_cmod(inst->conditional_mod)
> +                                   : inst->conditional_mod;
> +
>              if (scan_inst->can_do_cmod() &&
>                  ((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
> -                 scan_inst->conditional_mod == inst->conditional_mod)) {
> -               scan_inst->conditional_mod = inst->conditional_mod;
> +                 scan_inst->conditional_mod == cond)) {
> +               scan_inst->conditional_mod = cond;

I've been adding support for AND.nz here, and a question came up.  Does
this work correctly if scan_inst is a CMP and the result register is
used elsewhere?  Won't this turn

cmp.l.f0(8)     g3<1>D          g3<8,8,1>F      g4<8,8,1>F
mov.z.f0(8)     null            g3<8,8,1>D
and(8)          g8<1>F          g3<8,8,1>UW     0x3f800000

into

cmp.ge.f0(8)    g3<1>D          g3<8,8,1>F      g4<8,8,1>F
and(8)          g8<1>F          g3<8,8,1>UW     0x3f800000

For AND, we generate a lot of and.z for ir_unop_not in
fs_visitor::emit_bool_to_cond_code.  I want to do the same cmod
inversion for that, but it doesn't seem safe.  I think I have another
way to deal with this for ir_unop_not, but either I don't really
understand this code or there's already a bug here.