[Mesa-dev] [PATCH 15/21] nir/cf: fix link_blocks() when there are no successors

[Connor Abbott]

When we insert a single basic block A into another basic block B, we
will split B into C and D, insert A in the middle, and then splice
together C, A, and D. When we splice together C and A, we need to move
the successors of A into C -- except A has no successors, since it
hasn't been inserted yet. So in move_successors(), we need to handle the
case where the block whose successors are to be moved doesn't have any
successors. Fixing link_blocks() here prevents a segfault and makes it
work correctly.

Signed-off-by: Connor Abbott <connor.w.abbott at intel.com>
---
 src/glsl/nir/nir_control_flow.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/glsl/nir/nir_control_flow.c b/src/glsl/nir/nir_control_flow.c
index 91788ad..9ae113f 100644
--- a/src/glsl/nir/nir_control_flow.c
+++ b/src/glsl/nir/nir_control_flow.c
@@ -57,7 +57,8 @@ static void
 link_blocks(nir_block *pred, nir_block *succ1, nir_block *succ2)
 {
    pred->successors[0] = succ1;
-   block_add_pred(succ1, pred);
+   if (succ1 != NULL)
+      block_add_pred(succ1, pred);
 
    pred->successors[1] = succ2;
    if (succ2 != NULL)
-- 
2.4.3