pan/bi: Add helpers for working with singletons

Clauses with exactly one instruction (not canonical terminology to my
knowledge, but the notation is suggestive). Since these are isomorphic
to the instructions themselves, we want helpers to go between the forms.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7206>

src/panfrost/bifrost/bi_ra.c

@@ -229,6 +229,46 @@ bi_fill(unsigned node, uint64_t offset, unsigned channels)
         return load;
 }
 
+/* Get the single instruction in a singleton clause. Precondition: clause
+ * contains exactly 1 instruction.
+ *
+ * More complex scheduling implies tougher constraints on spilling. We'll cross
+ * that bridge when we get to it. For now, just grab the one and only
+ * instruction in the clause */
+
+static bi_instruction *
+bi_unwrap_singleton(bi_clause *clause)
+{
+       assert(clause->bundle_count == 1);
+       assert((clause->bundles[0].fma != NULL) ^ (clause->bundles[0].add != NULL));
+
+       return clause->bundles[0].fma ? clause->bundles[0].fma
+               : clause->bundles[0].add;
+}
+
+static inline void
+bi_insert_singleton(void *memctx, bi_clause *cursor, bi_block *block,
+                bi_instruction ins, bool before)
+{
+        bi_instruction *uins = rzalloc(memctx, bi_instruction);
+        memcpy(uins, &ins, sizeof(ins));
+
+        /* Get the instruction to pivot around. Should be first/last of clause
+         * depending on before setting, those coincide for singletons */
+        bi_instruction *cursor_ins = bi_unwrap_singleton(cursor);
+
+        bi_clause *clause = bi_make_singleton(memctx, uins,
+                        block, 0, (1 << 0), true);
+
+        if (before) {
+                list_addtail(&clause->link, &cursor->link);
+                list_addtail(&uins->link, &cursor_ins->link);
+        } else {
+                list_add(&clause->link, &cursor->link);
+                list_add(&uins->link, &cursor_ins->link);
+        }
+}
+
 /* If register allocation fails, find the best spill node */
 
 static signed