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nir/dce: fix DCE of loops with a halt or return instruction in the pre-header

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If there is a halt or return instruction right before a loop with a single
continue, we would have taken the fast path intended for loops without
continues.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Tested-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 71a985d80b ("nir/dce: perform DCE for unlooped instructions in a single pass")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10284>
(cherry picked from commit 2fe13aa2ad)
This commit is contained in:
Rhys Perry 2021-04-16 13:18:33 +01:00 • committed by Eric Engestrom
parent ae0988b09c
commit 87bab07750
2 changed files with 8 additions and 5 deletions
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2
.pick_status.json
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@ -193,7 +193,7 @@
"description": "nir/dce: fix DCE of loops with a halt or return instruction in the pre-header",
"nominated": true,
"nomination_type": 1,
"resolution": 0,
"resolution": 1,
"main_sha": null,
"because_sha": "71a985d80b1c29cced979b3c8d16f74463d1170b"
},

11
src/compiler/nir/nir_opt_dce.c
View file

@ -166,18 +166,21 @@ dce_cf_list(struct exec_list *cf_list, BITSET_WORD *defs_live,
case nir_cf_node_loop: {
nir_loop *loop = nir_cf_node_as_loop(cf_node);
struct loop_state inner_state;
inner_state.preheader = nir_cf_node_as_block(nir_cf_node_prev(cf_node));
inner_state.header_phis_changed = false;
/* Fast path if the loop has no continues: we can remove instructions
* as we mark the others live.
*/
if (nir_loop_first_block(loop)->predecessors->entries == 1) {
struct set *predecessors = nir_loop_first_block(loop)->predecessors;
if (predecessors->entries == 1 &&
_mesa_set_next_entry(predecessors, NULL)->key == inner_state.preheader) {
progress |= dce_cf_list(&loop->body, defs_live, parent_loop);
break;
}
/* Mark instructions as live until there is no more progress. */
struct loop_state inner_state;
inner_state.preheader = nir_cf_node_as_block(nir_cf_node_prev(cf_node));
inner_state.header_phis_changed = false;
do {
/* dce_cf_list() resets inner_state.header_phis_changed itself, so
* it doesn't have to be done here.