pan/bi: Add special op for exp2

Needs some extra help but basically exp2_fast

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4615>

src/panfrost/bifrost/bi_print.c

@@ -267,6 +267,7 @@ bi_special_op_name(enum bi_special_op op)
         switch (op) {
         case BI_SPECIAL_FRCP: return "frcp";
         case BI_SPECIAL_FRSQ: return "frsq";
+        case BI_SPECIAL_EXP2_LOW: return "exp2_low";
         default: return "invalid";
         }
 }

src/panfrost/bifrost/compiler.h

@@ -195,6 +195,11 @@ enum bi_table_op {
 enum bi_special_op {
         BI_SPECIAL_FRCP,
         BI_SPECIAL_FRSQ,
+
+        /* fp32 exp2() with low precision, suitable for half_exp2() in CL or
+         * exp2() in GL. In the first argument, it takes f2i_rte(x * 2^24). In
+         * the second, it takes x itself. */
+        BI_SPECIAL_EXP2_LOW,
 };
 
 typedef struct {