pan/bi: Add discard flag to bi_index

Needed to model Valhall instructions. Should also be useful to RA if we
ever get around to doing something SSA based.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12026>

src/panfrost/bifrost/bi_printer.c.py

@@ -75,6 +75,9 @@ bir_passthrough_name(unsigned idx)
 static void
 bi_print_index(FILE *fp, bi_index index)
 {
+    if (index.discard)
+        fputs("`", fp);
+
     if (bi_is_null(index))
         fprintf(fp, "_");
     else if (index.type == BI_INDEX_CONSTANT)

src/panfrost/bifrost/compiler.h

@@ -83,6 +83,10 @@ typedef struct {
         bool abs : 1;
         bool neg : 1;
 
+        /* The last use of a value, should be purged from the register cache.
+         * Set by liveness analysis. */
+        bool discard : 1;
+
         /* For a source, the swizzle. For a destination, acts a bit like a
          * write mask. Identity for the full 32-bit, H00 for only caring about
          * the lower half, other values unused. */
@@ -207,6 +211,13 @@ bi_neg(bi_index idx)
         return idx;
 }
 
+static inline bi_index
+bi_discard(bi_index idx)
+{
+        idx.discard = true;
+        return idx;
+}
+
 /* Additive identity in IEEE 754 arithmetic */
 static inline bi_index
 bi_negzero()