pan/bi: Add helpers to get vertex/instance ID

These are preloaded in different places across Bifrost and Valhall. Abstract
that away so code using the builder isn't littered with "is Valhall?" checks.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15461>

src/panfrost/bifrost/compiler.h

@@ -1277,6 +1277,23 @@ bi_word_node(bi_index idx)
         return (idx.value << 2) | idx.offset;
 }
 
+/*
+ * Vertex ID and Instance ID are preloaded registers. Where they are preloaded
+ * changed from Bifrost to Valhall. Provide helpers that smooth over the
+ * architectural difference.
+ */
+static inline bi_index
+bi_vertex_id(bi_builder *b)
+{
+        return bi_register((b->shader->arch >= 9) ? 60 : 61);
+}
+
+static inline bi_index
+bi_instance_id(bi_builder *b)
+{
+        return bi_register((b->shader->arch >= 9) ? 61 : 62);
+}
+
 /* NIR passes */
 
 bool bi_lower_divergent_indirects(nir_shader *shader, unsigned lanes);