[Mesa-dev] [PATCH] nir/spirv: short-circuit when conditional branch contains end block

[Juan A. Suarez Romero]

This fixes the case when the SPIR-V code has two nested conditional
branches, but only one selection merge:

[...]
%1 = OpLabel
     OpSelectionMerge %2 None
     OpBranchConditional %3 %4 %2
%4 = OpLabel
     OpBranchConditional %3 %5 %2
%5 = OpLabel
     OpBranch %2
%2 = OpLabel
[...]

In the second OpBranchConditional, as the else-part is the end
block (started in the first OpBranchConditional) we can just follow the
then-part.

This fixes dEQP-VK.vkrunner.controlflow.2-obc-triangle-triangle

CC: Jason Ekstrand <jason at jlekstrand.net>
---
 src/compiler/spirv/vtn_cfg.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/compiler/spirv/vtn_cfg.c b/src/compiler/spirv/vtn_cfg.c
index 7868eeb60bc..f749118efbe 100644
--- a/src/compiler/spirv/vtn_cfg.c
+++ b/src/compiler/spirv/vtn_cfg.c
@@ -605,7 +605,16 @@ vtn_cfg_walk_blocks(struct vtn_builder *b, struct list_head *cf_list,
             }
          } else if (if_stmt->then_type == vtn_branch_type_none &&
                     if_stmt->else_type == vtn_branch_type_none) {
-            /* Neither side of the if is something we can short-circuit. */
+            /* Neither side of the if is something we can short-circuit,
+             * unless one of the blocks is the end block. */
+            if (then_block == end) {
+               block = else_block;
+               continue;
+            } else if (else_block == end) {
+               block = then_block;
+               continue;
+            }
+
             vtn_assert((*block->merge & SpvOpCodeMask) == SpvOpSelectionMerge);
             struct vtn_block *merge_block =
                vtn_value(b, block->merge[1], vtn_value_type_block)->block;
-- 
2.20.1