i965/vec4: Propagate conditional modifiers from compares to adds

No changes on Broadwell or later as those platforms do not use the vec4
backend.

Ivy Bridge and Haswell had similar results. (Ivy Bridge shown)
total instructions in shared programs: 11682119 -> 11681056 (<.01%)
instructions in affected programs: 150403 -> 149340 (-0.71%)
helped: 950
HURT: 0
helped stats (abs) min: 1 max: 16 x̄: 1.12 x̃: 1
helped stats (rel) min: 0.23% max: 2.78% x̄: 0.82% x̃: 0.71%
95% mean confidence interval for instructions value: -1.19 -1.04
95% mean confidence interval for instructions %-change: -0.84% -0.79%
Instructions are helped.

total cycles in shared programs: 257495842 -> 257495238 (<.01%)
cycles in affected programs: 270302 -> 269698 (-0.22%)
helped: 271
HURT: 13
helped stats (abs) min: 2 max: 14 x̄: 2.42 x̃: 2
helped stats (rel) min: 0.06% max: 1.13% x̄: 0.32% x̃: 0.28%
HURT stats (abs)   min: 2 max: 12 x̄: 4.00 x̃: 4
HURT stats (rel)   min: 0.15% max: 1.18% x̄: 0.30% x̃: 0.26%
95% mean confidence interval for cycles value: -2.41 -1.84
95% mean confidence interval for cycles %-change: -0.31% -0.26%
Cycles are helped.

Sandy Bridge
total instructions in shared programs: 10430493 -> 10429727 (<.01%)
instructions in affected programs: 120860 -> 120094 (-0.63%)
helped: 766
HURT: 0
helped stats (abs) min: 1 max: 1 x̄: 1.00 x̃: 1
helped stats (rel) min: 0.30% max: 2.70% x̄: 0.78% x̃: 0.73%
95% mean confidence interval for instructions value: -1.00 -1.00
95% mean confidence interval for instructions %-change: -0.80% -0.75%
Instructions are helped.

total cycles in shared programs: 146138718 -> 146138446 (<.01%)
cycles in affected programs: 244114 -> 243842 (-0.11%)
helped: 132
HURT: 0
helped stats (abs) min: 2 max: 4 x̄: 2.06 x̃: 2
helped stats (rel) min: 0.03% max: 0.43% x̄: 0.16% x̃: 0.19%
95% mean confidence interval for cycles value: -2.12 -2.00
95% mean confidence interval for cycles %-change: -0.18% -0.15%
Cycles are helped.

GM45 and Iron Lake had identical results. (Iron Lake shown)
total instructions in shared programs: 7780251 -> 7780248 (<.01%)
instructions in affected programs: 175 -> 172 (-1.71%)
helped: 3
HURT: 0
helped stats (abs) min: 1 max: 1 x̄: 1.00 x̃: 1
helped stats (rel) min: 1.49% max: 2.44% x̄: 1.81% x̃: 1.49%

total cycles in shared programs: 177851584 -> 177851578 (<.01%)
cycles in affected programs: 9796 -> 9790 (-0.06%)
helped: 3
HURT: 0
helped stats (abs) min: 2 max: 2 x̄: 2.00 x̃: 2
helped stats (rel) min: 0.05% max: 0.08% x̄: 0.06% x̃: 0.05%

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

1 files changed, 65 insertions, 5 deletions

diff --git a/src/intel/compiler/brw_vec4_cmod_propagation.cpp b/src/intel/compiler/brw_vec4_cmod_propagation.cpp
index 7f1001b6d1..5205da4983 100644
--- a/src/intel/compiler/brw_vec4_cmod_propagation.cpp
+++ b/src/intel/compiler/brw_vec4_cmod_propagation.cpp
@@ -50,8 +50,14 @@ opt_cmod_propagation_local(bblock_t *block)
           inst->predicate != BRW_PREDICATE_NONE ||
           !inst->dst.is_null() ||
           (inst->src[0].file != VGRF && inst->src[0].file != ATTR &&
-           inst->src[0].file != UNIFORM) ||
-          inst->src[0].abs)
+           inst->src[0].file != UNIFORM))
+         continue;
+
+      /* An ABS source modifier can only be handled when processing a compare
+       * with a value other than zero.
+       */
+      if (inst->src[0].abs &&
+          (inst->opcode != BRW_OPCODE_CMP || inst->src[1].is_zero()))
          continue;
 
       if (inst->opcode == BRW_OPCODE_AND &&
@@ -60,15 +66,68 @@ opt_cmod_propagation_local(bblock_t *block)
             !inst->src[0].negate))
          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)
          continue;
 
       bool read_flag = false;
       foreach_inst_in_block_reverse_starting_from(vec4_instruction, scan_inst, inst) {
+         /* A CMP with a second source of zero can match with anything.  A CMP
+          * with a second source that is not zero can only match with an ADD
+          * instruction.
+          */
+         if (inst->opcode == BRW_OPCODE_CMP && !inst->src[1].is_zero()) {
+            bool negate;
+
+            if (scan_inst->opcode != BRW_OPCODE_ADD)
+               goto not_match;
+
+            /* A CMP is basically a subtraction.  The result of the
+             * subtraction must be the same as the result of the addition.
+             * This means that one of the operands must be negated.  So (a +
+             * b) vs (a == -b) or (a + -b) vs (a == b).
+             */
+            if ((inst->src[0].equals(scan_inst->src[0]) &&
+                 inst->src[1].negative_equals(scan_inst->src[1])) ||
+                (inst->src[0].equals(scan_inst->src[1]) &&
+                 inst->src[1].negative_equals(scan_inst->src[0]))) {
+               negate = false;
+            } else if ((inst->src[0].negative_equals(scan_inst->src[0]) &&
+                        inst->src[1].equals(scan_inst->src[1])) ||
+                       (inst->src[0].negative_equals(scan_inst->src[1]) &&
+                        inst->src[1].equals(scan_inst->src[0]))) {
+               negate = true;
+            } else {
+               goto not_match;
+            }
+
+            if (scan_inst->exec_size != inst->exec_size ||
+                scan_inst->group != inst->group)
+               goto not_match;
+
+            /* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
+             *
+             *    * Note that the [post condition signal] bits generated at
+             *      the output of a compute are before the .sat.
+             *
+             * So we don't have to bail if scan_inst has saturate.
+             */
+
+            /* Otherwise, try propagating the conditional. */
+            const enum brw_conditional_mod cond =
+               negate ? brw_swap_cmod(inst->conditional_mod)
+                      : inst->conditional_mod;
+
+            if (scan_inst->can_do_cmod() &&
+                ((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
+                 scan_inst->conditional_mod == cond)) {
+               scan_inst->conditional_mod = cond;
+               inst->remove(block);
+               progress = true;
+            }
+            break;
+         }
+
          if (regions_overlap(inst->src[0], inst->size_read(0),
                              scan_inst->dst, scan_inst->size_written)) {
             if ((scan_inst->predicate && scan_inst->opcode != BRW_OPCODE_SEL) ||
@@ -170,6 +229,7 @@ opt_cmod_propagation_local(bblock_t *block)
             break;
          }
 
+      not_match:
          if (scan_inst->writes_flag())
             break;