return;
}
- /* In the case where begin points to an instruction in some basic block and
- * end points to the end of the same basic block, we rely on the fact that
- * splitting on an instruction moves earlier instructions into a new basic
- * block. If the later instructions were moved instead, then the end cursor
- * would be pointing to the same place that begin used to point to, which
- * is obviously not what we want.
- */
split_block_cursor(begin, &block_before, &block_begin);
+
+ /* Splitting a block twice with two cursors created before either split is
+ * tricky and there are a couple of places it can go wrong if both cursors
+ * point to the same block. One is if the second cursor is an block-based
+ * cursor and, thanks to the split above, it ends up pointing to the wrong
+ * block. If it's a before_block cursor and it's in the same block as
+ * begin, then begin must also be a before_block cursor and it should be
+ * caught by the nir_cursors_equal check above and we won't get here. If
+ * it's an after_block cursor, we need to re-adjust to ensure that it
+ * points to the second one of the split blocks, regardless of which it is.
+ */
+ if (end.option == nir_cursor_after_block && end.block == block_before)
+ end.block = block_begin;
+
split_block_cursor(end, &block_end, &block_after);
+ /* The second place this can all go wrong is that it could be that the
+ * second split places the original block after the new block in which case
+ * the block_begin pointer that we saved off above is pointing to the block
+ * at the end rather than the block in the middle like it's supposed to be.
+ * In this case, we have to re-adjust begin_block to point to the middle
+ * one.
+ */
+ if (block_begin == block_after)
+ block_begin = block_end;
+
extracted->impl = nir_cf_node_get_function(&block_begin->cf_node);
exec_list_make_empty(&extracted->list);