nir: Do not use continue block after removing it.

Reinserting code directly before a jump means the block gets split
and merged, removing the original block and replacing it in the
process.

Hence keeping a pointer to the continue block over a reinsert
causes issues.

This code changes nir_opt_if to simply look for the new continue
block.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107275
CC: 18.1 <mesa-stable@lists.freedesktop.org>

diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c
index a52de120ad624aec0a708299bf14755ee9bdc98b..49ba5de09e9a287030d28df0c51d9af1504912d9 100644 (file)
--- a/src/compiler/nir/nir_opt_if.c
+++ b/src/compiler/nir/nir_opt_if.c
@@ -26,6 +26,26 @@
 #include "nir_control_flow.h"
 #include "nir_loop_analyze.h"
 
+/**
+ * Gets the single block that jumps back to the loop header. Already assumes
+ * there is exactly one such block.
+ */
+static nir_block*
+find_continue_block(nir_loop *loop)
+{
+   nir_block *header_block = nir_loop_first_block(loop);
+   nir_block *prev_block =
+      nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
+
+   assert(header_block->predecessors->entries == 2);
+
+   struct set_entry *pred_entry;
+   set_foreach(header_block->predecessors, pred_entry) {
+      if (pred_entry->key != prev_block)
+         return (nir_block*)pred_entry->key;
+   }
+}
+
 /**
  * This optimization detects if statements at the tops of loops where the
  * condition is a phi node of two constants and moves half of the if to above
@@ -97,12 +117,7 @@ opt_peel_loop_initial_if(nir_loop *loop)
    if (header_block->predecessors->entries != 2)
       return false;
 
-   nir_block *continue_block = NULL;
-   struct set_entry *pred_entry;
-   set_foreach(header_block->predecessors, pred_entry) {
-      if (pred_entry->key != prev_block)
-         continue_block = (void *)pred_entry->key;
-   }
+   nir_block *continue_block = find_continue_block(loop);
 
    nir_cf_node *if_node = nir_cf_node_next(&header_block->cf_node);
    if (!if_node || if_node->type != nir_cf_node_if)
@@ -193,6 +208,10 @@ opt_peel_loop_initial_if(nir_loop *loop)
    nir_cf_reinsert(&tmp, nir_before_cf_node(&loop->cf_node));
 
    nir_cf_reinsert(&header, nir_after_block_before_jump(continue_block));
+
+   /* Get continue block again as the previous reinsert might have removed the block. */
+   continue_block = find_continue_block(loop);
+
    nir_cf_extract(&tmp, nir_before_cf_list(continue_list),
                         nir_after_cf_list(continue_list));
    nir_cf_reinsert(&tmp, nir_after_block_before_jump(continue_block));