target/riscv: Properly check SEW in amo_op

We're currently assuming SEW <= 3, and the "else" from
the SEW == 3 must be less.  Use a switch and explicitly
bound both SEW and SEQ for all cases.

Reviewed-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20211020031709.359469-8-richard.henderson@linaro.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/insn_trans/trans_rvv.c.inc

@@ -704,18 +704,20 @@ static bool amo_op(DisasContext *s, arg_rwdvm *a, uint8_t seq)
         gen_helper_exit_atomic(cpu_env);
         s->base.is_jmp = DISAS_NORETURN;
         return true;
-    } else {
-        if (s->sew == 3) {
-            if (!is_32bit(s)) {
-                fn = fnsd[seq];
-            } else {
-                /* Check done in amo_check(). */
-                g_assert_not_reached();
-            }
-        } else {
-            assert(seq < ARRAY_SIZE(fnsw));
-            fn = fnsw[seq];
-        }
+    }
+
+    switch (s->sew) {
+    case 0 ... 2:
+        assert(seq < ARRAY_SIZE(fnsw));
+        fn = fnsw[seq];
+        break;
+    case 3:
+        /* XLEN check done in amo_check(). */
+        assert(seq < ARRAY_SIZE(fnsd));
+        fn = fnsd[seq];
+        break;
+    default:
+        g_assert_not_reached();
     }
 
     data = FIELD_DP32(data, VDATA, MLEN, s->mlen);