Mesa (staging/20.0): nir: Lower returns correctly inside nested loops

[GitLab Mirror]

Module: Mesa
Branch: staging/20.0
Commit: 5bbf4cc54e688805f77848bcdc118ddc80693916
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=5bbf4cc54e688805f77848bcdc118ddc80693916

Author: Arcady Goldmints-Orlov <agoldmints at igalia.com>
Date:   Thu Apr 16 16:28:12 2020 -0500

nir: Lower returns correctly inside nested loops

Inside nested flow control, nir_lower_returns inserts predicated breaks
in the outer block. However, it would omit doing this if the remainder
of the outer block (after the inner block) was empty. This is not
correct in the case of loops, as execution just wraps back around to the
start of the loop, so this change doesn't skip the predication inside
loops.

Fixes: 79dec93ead6e (nir: Add return lowering pass)
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2724

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4603>
(cherry picked from commit ec1b96fdc8bccaf2c1a4e1e3cca32b4aacbe4f7c)

---

 .pick_status.json                    | 2 +-
 src/compiler/nir/nir_lower_returns.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/.pick_status.json b/.pick_status.json
index 839d00f452c..4f3fd2dc2b9 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -193,7 +193,7 @@
         "description": "nir: Lower returns correctly inside nested loops",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": "79dec93ead6e3b95b1240a9d843d617a88ee9179"
     },
diff --git a/src/compiler/nir/nir_lower_returns.c b/src/compiler/nir/nir_lower_returns.c
index e166a7cc32a..ecbbf43da3b 100644
--- a/src/compiler/nir/nir_lower_returns.c
+++ b/src/compiler/nir/nir_lower_returns.c
@@ -50,7 +50,7 @@ predicate_following(nir_cf_node *node, struct lower_returns_state *state)
    nir_builder *b = &state->builder;
    b->cursor = nir_after_cf_node_and_phis(node);
 
-   if (nir_cursors_equal(b->cursor, nir_after_cf_list(state->cf_list)))
+   if (!state->loop && nir_cursors_equal(b->cursor, nir_after_cf_list(state->cf_list)))
       return; /* Nothing to predicate */
 
    assert(state->return_flag);