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nir/opt_if: merge IFs which have phis between them

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The phi-uses are rewritten on each side of the following if-stmt,
so that register pressure is kept the same.

Totals from 719 (0.91% of 79395) affected shaders: (Navi31)
MaxWaves: 18531 -> 18527 (-0.02%); split: +0.02%, -0.04%
Instrs: 4683616 -> 4621920 (-1.32%); split: -1.32%, +0.00%
CodeSize: 24154608 -> 23811472 (-1.42%); split: -1.42%, +0.00%
VGPRs: 46020 -> 46140 (+0.26%); split: -0.05%, +0.31%
SpillSGPRs: 1134 -> 1107 (-2.38%)
SpillVGPRs: 2221 -> 2202 (-0.86%)
Scratch: 603648 -> 602624 (-0.17%)
Latency: 30355976 -> 29516199 (-2.77%); split: -2.77%, +0.01%
InvThroughput: 7017283 -> 6878583 (-1.98%); split: -2.00%, +0.03%
VClause: 119826 -> 113392 (-5.37%); split: -5.37%, +0.00%
SClause: 100380 -> 93516 (-6.84%); split: -6.85%, +0.01%
Copies: 360589 -> 359154 (-0.40%); split: -1.13%, +0.73%
Branches: 146438 -> 138623 (-5.34%); split: -5.37%, +0.03%
PreSGPRs: 38237 -> 38317 (+0.21%); split: -0.52%, +0.72%
PreVGPRs: 37745 -> 37742 (-0.01%); split: -0.05%, +0.04%
VALU: 2594909 -> 2593667 (-0.05%); split: -0.12%, +0.07%
SALU: 572636 -> 554587 (-3.15%); split: -3.19%, +0.04%
VMEM: 203188 -> 201030 (-1.06%)
SMEM: 135731 -> 128683 (-5.19%)
VOPD: 1978 -> 1982 (+0.20%)

Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7710>
This commit is contained in:
Daniel Schürmann
2021-01-22 19:55:04 +01:00
committed by Marge Bot
parent 37881801c1
commit 51bb0e68b3
1 changed files with 96 additions and 51 deletions
Download Patch File Download Diff File Expand all files Collapse all files

147
src/compiler/nir/nir_opt_if.c
View File

@@ -1186,19 +1186,86 @@ opt_if_phi_src_unused(nir_builder *b, nir_if *nif)
return progress;
}
static void
rewrite_phi_uses(nir_phi_instr *phi, nir_if *prev_if, nir_if *next_if)
{
nir_def *then_src =
nir_phi_get_src_from_block(phi, nir_if_last_then_block(prev_if))->src.ssa;
nir_def *else_src =
nir_phi_get_src_from_block(phi, nir_if_last_else_block(prev_if))->src.ssa;
/* Rewrite all uses inside the next IF with either then_src or else_src. */
nir_foreach_use_including_if_safe(use, &phi->def) {
nir_cf_node *node = &nir_src_get_block(use)->cf_node;
/* Check if the node is inside the if-stmt. */
while (node) {
if (node->parent == &next_if->cf_node)
break;
node = node->parent;
if (node == prev_if->cf_node.parent)
node = NULL;
}
/* The node is outside of the IF. */
if (!node)
continue;
/* Get the first block. */
while (!nir_cf_node_is_first(node))
node = nir_cf_node_prev(node);
nir_block *block = nir_cf_node_as_block(node);
nir_src_rewrite(use, block == nir_if_first_then_block(next_if) ? then_src : else_src);
}
}
static bool
opt_if_merge(nir_if *nif)
{
bool progress = false;
nir_block *next_blk = nir_cf_node_cf_tree_next(&nif->cf_node);
if (!next_blk)
return false;
nir_if *next_if = nir_block_get_following_if(next_blk);
if (!next_if)
if (!next_if || !nir_srcs_equal(nif->condition, next_if->condition))
return false;
/* This optimization isn't made to work in this case and
* opt_if_evaluate_condition_use will optimize it later.
*/
if (nir_block_ends_in_jump(nir_if_last_then_block(nif)) ||
nir_block_ends_in_jump(nir_if_last_else_block(nif)))
return false;
/* This optimization is not prepared to handle updating phis other than
* immediately after the second if-statement.
*/
if (nir_block_ends_in_jump(nir_if_last_then_block(next_if)) ||
nir_block_ends_in_jump(nir_if_last_else_block(next_if)))
return false;
/* Ensure that there is nothing but phis between the IFs */
if (!exec_list_is_empty(&next_blk->instr_list)) {
if (nir_block_last_instr(next_blk)->type != nir_instr_type_phi)
return false;
/* If there are phis, then the next IF must not contain any jump. */
nir_foreach_block_in_cf_node(block, &next_if->cf_node) {
if (nir_block_ends_in_jump(block))
return false;
}
}
nir_foreach_phi(phi, next_blk) {
/* Rewrite the phi uses in each branch leg of the following IF
* with the phi source from the respective branch leg of the
* previous IF.
*/
rewrite_phi_uses(phi, nif, next_if);
}
/* Here we merge two consecutive ifs that have the same condition e.g:
*
* if ssa_12 {
@@ -1213,62 +1280,40 @@ opt_if_merge(nir_if *nif)
* }
*
* Note: This only merges if-statements when the block between them is
* empty. The reason we don't try to merge ifs that just have phis between
* them is because this can result in increased register pressure. For
* example when merging if ladders created by indirect indexing.
* empty except for phis.
*/
if (nif->condition.ssa == next_if->condition.ssa &&
exec_list_is_empty(&next_blk->instr_list)) {
simple_merge_if(nif, next_if, true, true);
simple_merge_if(nif, next_if, false, false);
/* This optimization isn't made to work in this case and
* opt_if_evaluate_condition_use will optimize it later.
*/
if (nir_block_ends_in_jump(nir_if_last_then_block(nif)) ||
nir_block_ends_in_jump(nir_if_last_else_block(nif)))
return false;
nir_block *new_then_block = nir_if_last_then_block(nif);
nir_block *new_else_block = nir_if_last_else_block(nif);
/* This optimization is not prepared to handle updating phis other than
* immediately after the second if-statement.
*/
if (nir_block_ends_in_jump(nir_if_last_then_block(next_if)) ||
nir_block_ends_in_jump(nir_if_last_else_block(next_if)))
return false;
nir_block *old_then_block = nir_if_last_then_block(next_if);
nir_block *old_else_block = nir_if_last_else_block(next_if);
simple_merge_if(nif, next_if, true, true);
simple_merge_if(nif, next_if, false, false);
/* Rewrite the predecessor block for any phis following the second
* if-statement.
*/
rewrite_phi_predecessor_blocks(next_if, old_then_block,
old_else_block,
new_then_block,
new_else_block);
nir_block *new_then_block = nir_if_last_then_block(nif);
nir_block *new_else_block = nir_if_last_else_block(nif);
/* Move phis after merged if to avoid them being deleted when we remove
* the merged if-statement.
*/
nir_block *after_next_if_block =
nir_cf_node_as_block(nir_cf_node_next(&next_if->cf_node));
nir_block *old_then_block = nir_if_last_then_block(next_if);
nir_block *old_else_block = nir_if_last_else_block(next_if);
/* Rewrite the predecessor block for any phis following the second
* if-statement.
*/
rewrite_phi_predecessor_blocks(next_if, old_then_block,
old_else_block,
new_then_block,
new_else_block);
/* Move phis after merged if to avoid them being deleted when we remove
* the merged if-statement.
*/
nir_block *after_next_if_block =
nir_cf_node_as_block(nir_cf_node_next(&next_if->cf_node));
nir_foreach_phi_safe(phi, after_next_if_block) {
exec_node_remove(&phi->instr.node);
exec_list_push_tail(&next_blk->instr_list, &phi->instr.node);
phi->instr.block = next_blk;
}
nir_cf_node_remove(&next_if->cf_node);
progress = true;
nir_foreach_phi_safe(phi, after_next_if_block) {
exec_node_remove(&phi->instr.node);
exec_list_push_tail(&next_blk->instr_list, &phi->instr.node);
phi->instr.block = next_blk;
}
return progress;
nir_cf_node_remove(&next_if->cf_node);
return true;
}
static bool