On Tue, Jan 20, 2015 at 3:31 PM, Matt Turner <matts...@gmail.com> wrote:
> On Tue, Jan 20, 2015 at 3:17 PM, Jason Ekstrand <ja...@jlekstrand.net>
> wrote:
> >
> >
> > On Tue, Jan 20, 2015 at 3:09 PM, Matt Turner <matts...@gmail.com> wrote:
> >>
> >> On Tue, Jan 20, 2015 at 2:58 PM, Jason Ekstrand <ja...@jlekstrand.net>
> >> wrote:
> >> > On Mon, Jan 19, 2015 at 3:31 PM, Matt Turner <matts...@gmail.com>
> wrote:
> >> >>
> >> >> For some reason, we occasionally write the flag register with a
> MOV.NZ
> >> >> instruction:
> >> >>
> >> >> add(8) g25<1>F -g6<0,1,0>F g15<8,8,1>F
> >> >> cmp.l.f0(8) g26<1>D g25<8,8,1>F 0F
> >> >> mov.nz.f0(8) null g26<8,8,1>D
> >> >>
> >> >> A MOV.NZ instruction on the result of a CMP is like comparing for
> >> >> equality with true in C. It's useless. Removing it allows us to
> >> >> generate:
> >> >>
> >> >> add.l.f0(8) null -g6<0,1,0>F g15<8,8,1>F
> >> >>
> >> >> total instructions in shared programs: 5955701 -> 5951657 (-0.07%)
> >> >> instructions in affected programs: 302910 -> 298866 (-1.34%)
> >> >> GAINED: 1
> >> >> LOST: 0
> >> >> ---
> >> >> .../drivers/dri/i965/brw_fs_cmod_propagation.cpp | 23
> >> >> ++++++++++++++--
> >> >> .../drivers/dri/i965/test_fs_cmod_propagation.cpp | 32
> >> >> ++++++++++++++++++++++
> >> >> 2 files changed, 52 insertions(+), 3 deletions(-)
> >> >>
> >> >> diff --git a/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
> >> >> b/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
> >> >> index b521350..dd89512 100644
> >> >> --- a/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
> >> >> +++ b/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
> >> >> @@ -57,12 +57,20 @@ opt_cmod_propagation_local(fs_visitor *v,
> bblock_t
> >> >> *block)
> >> >> foreach_inst_in_block_reverse_safe(fs_inst, inst, block) {
> >> >> ip--;
> >> >>
> >> >> - if (inst->opcode != BRW_OPCODE_CMP ||
> >> >> + if ((inst->opcode != BRW_OPCODE_CMP &&
> >> >> + inst->opcode != BRW_OPCODE_MOV) ||
> >> >> inst->predicate != BRW_PREDICATE_NONE ||
> >> >> !inst->dst.is_null() ||
> >> >> inst->src[0].file != GRF ||
> >> >> - inst->src[0].abs ||
> >> >> - !inst->src[1].is_zero())
> >> >> + inst->src[0].abs)
> >> >> + continue;
> >> >> +
> >> >> + if (inst->opcode == BRW_OPCODE_CMP && !inst->src[1].is_zero())
> >> >> + continue;
> >> >> +
> >> >> + if (inst->opcode == BRW_OPCODE_MOV &&
> >> >> + (inst->conditional_mod != BRW_CONDITIONAL_NZ ||
> >> >> + inst->src[0].negate))
> >> >
> >> >
> >> > I think negate is ok here. I'm not 100% sure on the symantics of
> >> > move.nz,
> >> > but if it's a "!= 0" then negation shouldn't matter. If it only
> >> > considers
> >> > the bottom bit then negation shouldn't matter there either.
> >>
> >> The instruction "mov.nz.f0 null src0" sets f0 if src0 != 0.
> >>
> >> Hmm, you're right. Since we're only allowing NZ conditional modifiers
> >> we can also allow negation. I don't think we'll ever generate that,
> >> but okay. I'll remove the inst->src[0].negate check.
> >
> >
> > Sure we will. When we do older gens in NIR, we'll emit one of those
> after
> > every cmp. Still have to deal with the and though...
>
> Emitting it after every comparison isn't what you want. We emit it
> from resolve_bool_comparison() before we need the integer
> representation of a bool for things like b2f. NIR -> FS should behave
> the same way.
>
Except typeless... We need some sort of assurance that the result of a NIR
comparison is always 0 or ~0. We may be able to pull similar stunts or
maybe do the cleanup in NIR, but I'm not sure if we can or not. It's going
to be a bit interesting.
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