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.
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