Mesa (main): nir/lower_shader_calls: don't insert code after break/continue

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Module: Mesa
Branch: main
Commit: 9cf986dcff3c4364aacea5f36afdae7c3d3957f5
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=9cf986dcff3c4364aacea5f36afdae7c3d3957f5

Author: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Date:   Wed Apr 20 10:54:36 2022 +0300

nir/lower_shader_calls: don't insert code after break/continue

When moving code from below to the insertion cursor point, if the
cursor points to a jump instruction, don't bother inserting the code.
It would break the break/continue assumptions of NIR and would not be
executed anyway.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Fixes: 8dfb240b1f06 ("nir: Add raytracing shader call lowering pass.")
Reviewed-by: Jason Ekstrand <jason.ekstrand at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16036>

---

 src/compiler/nir/nir_lower_shader_calls.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/compiler/nir/nir_lower_shader_calls.c b/src/compiler/nir/nir_lower_shader_calls.c
index 4a2f36b2c89..155ba35e932 100644
--- a/src/compiler/nir/nir_lower_shader_calls.c
+++ b/src/compiler/nir/nir_lower_shader_calls.c
@@ -729,6 +729,21 @@ rewrite_phis_to_pred(nir_block *block, nir_block *pred)
    }
 }
 
+static bool
+cursor_is_after_jump(nir_cursor cursor)
+{
+   switch (cursor.option) {
+   case nir_cursor_before_instr:
+   case nir_cursor_before_block:
+      return false;
+   case nir_cursor_after_instr:
+      return cursor.instr->type == nir_instr_type_jump;
+   case nir_cursor_after_block:
+      return nir_block_ends_in_jump(cursor.block);;
+   }
+   unreachable("Invalid cursor option");
+}
+
 /** Flattens if ladders leading up to a resume
  *
  * Given a resume_instr, this function flattens any if ladders leading to the
@@ -948,7 +963,18 @@ found_resume:
       nir_cf_extract(&cf_list, nir_after_instr(resume_instr),
                                nir_after_cf_list(child_list));
    }
-   b->cursor = nir_cf_reinsert(&cf_list, b->cursor);
+
+   if (cursor_is_after_jump(b->cursor)) {
+      /* If the resume instruction is in a loop, it's possible cf_list ends
+       * in a break or continue instruction, in which case we don't want to
+       * insert anything.  It's also possible we have an early return if
+       * someone hasn't lowered those yet.  In either case, nothing after that
+       * point executes in this context so we can delete it.
+       */
+      nir_cf_delete(&cf_list);
+   } else {
+      b->cursor = nir_cf_reinsert(&cf_list, b->cursor);
+   }
 
    if (!resume_node) {
       /* We want the resume to be the first "interesting" instruction */