[Mesa-dev] [PATCH 19/22 v3] i965/fs: Merge CMP and SEL into CSEL on Gen8+
Ian Romanick
idr at freedesktop.org
Wed Feb 28 20:20:28 UTC 2018
From: Ian Romanick <ian.d.romanick at intel.com>
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).
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: Ian Romanick <ian.d.romanick at intel.com>
---
src/intel/compiler/brw_fs.cpp | 104 ++++++++++++++++++++++++++++++++++++++++++
src/intel/compiler/brw_fs.h | 1 +
2 files changed, 105 insertions(+)
diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index accae1b..865e02e 100644
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -2813,6 +2813,104 @@ mask_relative_to(const fs_reg &r, const fs_reg &s, unsigned ds)
}
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)
+ inst->remove(block);
+
+ break;
+ }
+ }
+ }
+
+ return progress;
+}
+
+bool
fs_visitor::compute_to_mrf()
{
bool progress = false;
@@ -5970,6 +6068,12 @@ 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;
diff --git a/src/intel/compiler/brw_fs.h b/src/intel/compiler/brw_fs.h
index 6337358..774288b 100644
--- a/src/intel/compiler/brw_fs.h
+++ b/src/intel/compiler/brw_fs.h
@@ -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();
--
2.9.5
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