nir: Give end_block its own index

Since there's no particular reason for the index to be 0, choose an
index that is not used by other block.  This is convenient when we
store "per-block" data in an array AND look for the successors
data (e.g. any kind of backwards data-flow analysis).

v2: Add a note about end_block's index. (Jason)

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

diff --git a/src/compiler/nir/nir.c b/src/compiler/nir/nir.c
index e12aa5d80f56ef6aa5c981211c3bd27f29736f65..7ae468451914ae96fb9625208382e925b466502a 100644 (file)
--- a/src/compiler/nir/nir.c
+++ b/src/compiler/nir/nir.c
@@ -1641,7 +1641,10 @@ nir_index_blocks(nir_function_impl *impl)
       block->index = index++;
    }
 
-   impl->num_blocks = index;
+   /* The end_block isn't really part of the program, which is why its index
+    * is >= num_blocks.
+    */
+   impl->num_blocks = impl->end_block->index = index;
 }
 
 static bool