[Mesa-dev] [PATCH] nir: remove jump from two merging jump-ending blocks

[Juan A. Suarez Romero]

In opt_peel_initial_if optimization, when moving the continue list to
end of the continue block, before the jump, could happen that the
continue list itself also ends with a jump.

This would mean that we would have two jump instructions in a row: the
first one from the continue list and the second one from the contine
block.

As inserting an instruction after a jump is not allowed (and it does not
make sense, as it will not be executed), remove the jump from the
continue block and keep the one from continue list, as it will be
executed first.

CC: Jason Ekstrand <jason at jlekstrand.net>
---
 src/compiler/nir/nir_opt_if.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c
index 932af9e37ab..a011401b3b4 100644
--- a/src/compiler/nir/nir_opt_if.c
+++ b/src/compiler/nir/nir_opt_if.c
@@ -241,12 +241,29 @@ opt_peel_loop_initial_if(nir_loop *loop)
    nir_cf_reinsert(&header,
                    nir_after_block_before_jump(find_continue_block(loop)));
 
+   bool continue_list_jumps =
+      nir_block_ends_in_jump(exec_node_data(nir_block,
+                                            exec_list_get_tail(continue_list),
+                                            cf_node.node));
+
    nir_cf_extract(&tmp, nir_before_cf_list(continue_list),
                         nir_after_cf_list(continue_list));
 
-   /* Get continue block again as the previous reinsert might have removed the block. */
+   /* Get continue block again as the previous reinsert might have removed the
+    * block.  Also, if both the continue list and the continue block ends in
+    * jump instructions, removes the jump from the later, as it will not be
+    * executed if we insert the continue list before it */
+
+   nir_block *continue_block = find_continue_block(loop);
+
+   if (continue_list_jumps) {
+      nir_instr *last_instr = nir_block_last_instr(continue_block);
+      if (last_instr && last_instr->type == nir_instr_type_jump)
+         nir_instr_remove(last_instr);
+   }
+
    nir_cf_reinsert(&tmp,
-                   nir_after_block_before_jump(find_continue_block(loop)));
+                   nir_after_block_before_jump(continue_block));
 
    nir_cf_node_remove(&nif->cf_node);
 
-- 
2.20.1