Commit 52c7df16 authored by Ian Romanick's avatar Ian Romanick

i965/fs: Merge CMP and SEL into CSEL on Gen8+

v2: Fix several problems handling inverted predicates.  Add a much
bigger comment around the BRW_CONDITIONAL_NZ case.

v3: Allow uniforms and shader inputs as sources for the original SEL and
CMP instructions.  This enables a LOT more shaders to receive CSEL
merging (5816 vs 8564 on SKL).

v4: Report progress.

Broadwell and Skylake had similar results. (Broadwell shown)
helped: 8527
HURT: 0
helped stats (abs) min: 1 max: 27 x̄: 2.44 x̃: 1
helped stats (rel) min: 0.03% max: 17.80% x̄: 1.12% x̃: 0.70%
95% mean confidence interval for instructions value: -2.51 -2.36
95% mean confidence interval for instructions %-change: -1.15% -1.10%
Instructions are helped.

total cycles in shared programs: 559442317 -> 558288357 (-0.21%)
cycles in affected programs: 372699860 -> 371545900 (-0.31%)
helped: 6748
HURT: 1450
helped stats (abs) min: 1 max: 32000 x̄: 182.41 x̃: 12
helped stats (rel) min: <.01% max: 66.08% x̄: 3.42% x̃: 0.70%
HURT stats (abs)   min: 1 max: 2538 x̄: 53.08 x̃: 14
HURT stats (rel)   min: <.01% max: 96.72% x̄: 3.32% x̃: 0.90%
95% mean confidence interval for cycles value: -179.01 -102.51
95% mean confidence interval for cycles %-change: -2.37% -2.08%
Cycles are helped.

LOST:   0
GAINED: 6

No changes on earlier platforms.
Signed-off-by: default avatarIan Romanick <ian.d.romanick@intel.com>
Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com> [v1]
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> [v3]
Reviewed-by: Matt Turner's avatarMatt Turner <mattst88@gmail.com>
parent 70de6159
......@@ -2843,6 +2843,106 @@ mask_relative_to(const fs_reg &r, const fs_reg &s, unsigned ds)
return ((1 << n) - 1) << shift;
}
bool
fs_visitor::opt_peephole_csel()
{
if (devinfo->gen < 8)
return false;
bool progress = false;
foreach_block_reverse(block, cfg) {
int ip = block->end_ip + 1;
foreach_inst_in_block_reverse_safe(fs_inst, inst, block) {
ip--;
if (inst->opcode != BRW_OPCODE_SEL ||
inst->predicate != BRW_PREDICATE_NORMAL ||
(inst->dst.type != BRW_REGISTER_TYPE_F &&
inst->dst.type != BRW_REGISTER_TYPE_D &&
inst->dst.type != BRW_REGISTER_TYPE_UD))
continue;
/* Because it is a 3-src instruction, CSEL cannot have an immediate
* value as a source, but we can sometimes handle zero.
*/
if ((inst->src[0].file != VGRF && inst->src[0].file != ATTR &&
inst->src[0].file != UNIFORM) ||
(inst->src[1].file != VGRF && inst->src[1].file != ATTR &&
inst->src[1].file != UNIFORM && !inst->src[1].is_zero()))
continue;
foreach_inst_in_block_reverse_starting_from(fs_inst, scan_inst, inst) {
if (!scan_inst->flags_written())
continue;
if ((scan_inst->opcode != BRW_OPCODE_CMP &&
scan_inst->opcode != BRW_OPCODE_MOV) ||
scan_inst->predicate != BRW_PREDICATE_NONE ||
(scan_inst->src[0].file != VGRF &&
scan_inst->src[0].file != ATTR &&
scan_inst->src[0].file != UNIFORM) ||
scan_inst->src[0].type != BRW_REGISTER_TYPE_F)
break;
if (scan_inst->opcode == BRW_OPCODE_CMP && !scan_inst->src[1].is_zero())
break;
const brw::fs_builder ibld(this, block, inst);
const enum brw_conditional_mod cond =
inst->predicate_inverse
? brw_negate_cmod(scan_inst->conditional_mod)
: scan_inst->conditional_mod;
fs_inst *csel_inst = NULL;
if (inst->src[1].file != IMM) {
csel_inst = ibld.CSEL(inst->dst,
inst->src[0],
inst->src[1],
scan_inst->src[0],
cond);
} else if (cond == BRW_CONDITIONAL_NZ) {
/* Consider the sequence
*
* cmp.nz.f0 null<1>F g3<8,8,1>F 0F
* (+f0) sel g124<1>UD g2<8,8,1>UD 0x00000000UD
*
* The sel will pick the immediate value 0 if r0 is ±0.0.
* Therefore, this sequence is equivalent:
*
* cmp.nz.f0 null<1>F g3<8,8,1>F 0F
* (+f0) sel g124<1>F g2<8,8,1>F (abs)g3<8,8,1>F
*
* The abs is ensures that the result is 0UD when g3 is -0.0F.
* By normal cmp-sel merging, this is also equivalent:
*
* csel.nz g124<1>F g2<4,4,1>F (abs)g3<4,4,1>F g3<4,4,1>F
*/
csel_inst = ibld.CSEL(inst->dst,
inst->src[0],
scan_inst->src[0],
scan_inst->src[0],
cond);
csel_inst->src[1].abs = true;
}
if (csel_inst != NULL) {
progress = true;
inst->remove(block);
}
break;
}
}
}
return progress;
}
bool
fs_visitor::compute_to_mrf()
{
......@@ -6078,6 +6178,12 @@ fs_visitor::optimize()
OPT(compact_virtual_grfs);
} while (progress);
/* Do this after cmod propagation has had every possible opportunity to
* propagate results into SEL instructions.
*/
if (OPT(opt_peephole_csel))
OPT(dead_code_eliminate);
progress = false;
pass_num = 0;
......
......@@ -191,6 +191,7 @@ public:
fs_reg resolve_source_modifiers(const fs_reg &src);
void emit_discard_jump();
bool opt_peephole_sel();
bool opt_peephole_csel();
bool opt_peephole_predicated_break();
bool opt_saturate_propagation();
bool opt_cmod_propagation();
......
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