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nir: detect more induction variables

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This allows loop analysis to detect inductions variables that
are incremented in both branches of an if rather than in a main
loop block. For example:

   loop {
      block block_1:
      /* preds: block_0 block_7 */
      vec1 32 ssa_8 = phi block_0: ssa_4, block_7: ssa_20
      vec1 32 ssa_9 = phi block_0: ssa_0, block_7: ssa_4
      vec1 32 ssa_10 = phi block_0: ssa_1, block_7: ssa_4
      vec1 32 ssa_11 = phi block_0: ssa_2, block_7: ssa_21
      vec1 32 ssa_12 = phi block_0: ssa_3, block_7: ssa_22
      vec4 32 ssa_13 = vec4 ssa_12, ssa_11, ssa_10, ssa_9
      vec1 32 ssa_14 = ige ssa_8, ssa_5
      /* succs: block_2 block_3 */
      if ssa_14 {
         block block_2:
         /* preds: block_1 */
         break
         /* succs: block_8 */
      } else {
         block block_3:
         /* preds: block_1 */
         /* succs: block_4 */
      }
      block block_4:
      /* preds: block_3 */
      vec1 32 ssa_15 = ilt ssa_6, ssa_8
      /* succs: block_5 block_6 */
      if ssa_15 {
         block block_5:
         /* preds: block_4 */
         vec1 32 ssa_16 = iadd ssa_8, ssa_7
         vec1 32 ssa_17 = load_const (0x3f800000 /* 1.000000*/)
         /* succs: block_7 */
      } else {
         block block_6:
         /* preds: block_4 */
         vec1 32 ssa_18 = iadd ssa_8, ssa_7
         vec1 32 ssa_19 = load_const (0x3f800000 /* 1.000000*/)
         /* succs: block_7 */
      }
      block block_7:
      /* preds: block_5 block_6 */
      vec1 32 ssa_20 = phi block_5: ssa_16, block_6: ssa_18
      vec1 32 ssa_21 = phi block_5: ssa_17, block_6: ssa_4
      vec1 32 ssa_22 = phi block_5: ssa_4, block_6: ssa_19
      /* succs: block_1 */
   }

Unfortunatly GCM could move the addition out of the if for us
(making this patch unrequired) but we still cannot enable the GCM
pass without regressions.

This unrolls a loop in Rise of The Tomb Raider.

vkpipeline-db results (VEGA):

Totals from affected shaders:
SGPRS: 88 -> 96 (9.09 %)
VGPRS: 56 -> 52 (-7.14 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 2168 -> 4560 (110.33 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 4 -> 4 (0.00 %)
Wait states: 0 -> 0 (0.00 %)

Reviewed-by: Thomas Helland <thomashelland90@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=32211
This commit is contained in:
Timothy Arceri
2018-11-26 12:05:00 +11:00
parent c03d6e61cc
commit 9e6b39e1d5
1 changed files with 36 additions and 0 deletions
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36
src/compiler/nir/nir_loop_analyze.c
View File

@@ -245,6 +245,42 @@ compute_induction_information(loop_info_state *state)
if (src_var->in_if_branch || src_var->in_nested_loop)
break;
/* Detect inductions variables that are incremented in both branches
* of an unnested if rather than in a loop block.
*/
if (is_var_phi(src_var)) {
nir_phi_instr *src_phi =
nir_instr_as_phi(src_var->def->parent_instr);
nir_op alu_op;
nir_ssa_def *alu_srcs[2] = {0};
nir_foreach_phi_src(src2, src_phi) {
nir_loop_variable *src_var2 =
get_loop_var(src2->src.ssa, state);
if (!src_var2->in_if_branch || !is_var_alu(src_var2))
break;
nir_alu_instr *alu =
nir_instr_as_alu(src_var2->def->parent_instr);
if (nir_op_infos[alu->op].num_inputs != 2)
break;
if (alu->src[0].src.ssa == alu_srcs[0] &&
alu->src[1].src.ssa == alu_srcs[1] &&
alu->op == alu_op) {
/* Both branches perform the same calculation so we can use
* one of them to find the induction variable.
*/
src_var = src_var2;
} else {
alu_srcs[0] = alu->src[0].src.ssa;
alu_srcs[1] = alu->src[1].src.ssa;
alu_op = alu->op;
}
}
}
if (!src_var->in_loop) {
biv->def_outside_loop = src_var;
} else if (is_var_alu(src_var)) {