On Wed, Mar 11, 2015 at 1:44 PM, Ian Romanick <i...@freedesktop.org> wrote:
> From: Ian Romanick <ian.d.roman...@intel.com>
>
> Espically on platforms that do not natively generate 0u and ~0u for
> Boolean results, we generate a lot of sequences where a CMP is
> followed by an AND with 1. emit_bool_to_cond_code does this, for
> example. On ILK, this results in a sequence like:
>
> add(8) g3<1>F g8<8,8,1>F -g4<0,1,0>F
> cmp.l.f0(8) g3<1>D g3<8,8,1>F 0F
> and.nz.f0(8) null g3<8,8,1>D 1D
> (+f0) iff(8) Jump: 6
>
> The AND.nz is obviously redundant. By propagating the cmod, we can
> instead generate
>
> add.l.f0(8) null g8<8,8,1>F -g4<0,1,0>F
> (+f0) iff(8) Jump: 6
>
> Existing code already handles the propagation from the CMP to the ADD.
>
> Shader-db results:
>
> GM45 (0x2A42):
> total instructions in shared programs: 3550829 -> 3550788 (-0.00%)
> instructions in affected programs: 10028 -> 9987 (-0.41%)
> helped: 24
>
> Iron Lake (0x0046):
> total instructions in shared programs: 4993146 -> 4993105 (-0.00%)
> instructions in affected programs: 9675 -> 9634 (-0.42%)
> helped: 24
>
> Ivy Bridge (0x0166):
> total instructions in shared programs: 6291870 -> 6291794 (-0.00%)
> instructions in affected programs: 17914 -> 17838 (-0.42%)
> helped: 48
>
> Haswell (0x0426):
> total instructions in shared programs: 5779256 -> 5779180 (-0.00%)
> instructions in affected programs: 16694 -> 16618 (-0.46%)
> helped: 48
>
> Broadwell (0x162E):
> total instructions in shared programs: 6823088 -> 6823014 (-0.00%)
> instructions in affected programs: 15824 -> 15750 (-0.47%)
> helped: 46
>
> No chage on Sandy Bridge or on any platform when NIR is used.
typo: change
>
> Signed-off-by: Ian Romanick <ian.d.roman...@intel.com>
> Cc: Matt Turner <matts...@gmail.com>
> ---
> .../drivers/dri/i965/brw_fs_cmod_propagation.cpp | 32
> +++++++++++++++++++++-
> 1 file changed, 31 insertions(+), 1 deletion(-)
>
> 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 d0ca2f9..6df3d45 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
> @@ -57,7 +57,8 @@ opt_cmod_propagation_local(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_AND &&
> + inst->opcode != BRW_OPCODE_CMP &&
> inst->opcode != BRW_OPCODE_MOV) ||
> inst->predicate != BRW_PREDICATE_NONE ||
> !inst->dst.is_null() ||
> @@ -65,6 +66,19 @@ opt_cmod_propagation_local(bblock_t *block)
> inst->src[0].abs)
> continue;
>
> + /* Only an AND.NZ can be propagated. Many AND.Z instructions are
> + * generated (for ir_unop_not in fs_visitor::emit_bool_to_cond_code).
> + * Propagating those would require inverting the condition on the CMP.
> + * This changes both the flag value and the register destination of the
> + * CMP. That result may be used elsewhere, so we can't change its
> value
> + * on a whim.
> + */
> + if (inst->opcode == BRW_OPCODE_AND &&
> + !(inst->src[1].is_one() &&
> + inst->conditional_mod == BRW_CONDITIONAL_NZ &&
> + !inst->src[0].negate))
I had a hard time reading this condition, but I think it is right.
> + continue;
> +
> if (inst->opcode == BRW_OPCODE_CMP && !inst->src[1].is_zero())
> continue;
>
> @@ -80,6 +94,22 @@ opt_cmod_propagation_local(bblock_t *block)
> scan_inst->dst.reg_offset != inst->src[0].reg_offset)
> break;
>
> + /* This must be done before the dst.type check because the result
> + * type of the AND will always be D, but the result of the CMP
> + * could be anything. The assumption is that the AND is just
> + * figuring out what the result of the previous comparison was
> + * instead of doing a new comparison with a different type.
> + */
> + if (inst->opcode == BRW_OPCODE_AND) {
> + if (scan_inst->opcode == BRW_OPCODE_CMP &&
> + scan_inst->writes_flag()) {
CMPs will always writes the flag, so no need to check that. I guess
you could assert it or something if you wanted.
This looks good... we just need some additional unit tests :)
- Test that you can remove the AND.NZ after a CMP null
- Test that AND.Z isn't removed
I don't think there's any other interesting case to test?
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