target/arm: Improve gen_top_byte_ignore

Use simple arithmetic instead of a conditional
move when tbi0 != tbi1.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210212184902.1251044-22-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 14 insertions, 11 deletions

diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index 1c4b8d02f3..b23a8975d5 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -183,17 +183,20 @@ static void gen_top_byte_ignore(DisasContext *s, TCGv_i64 dst,
         /* Sign-extend from bit 55.  */
         tcg_gen_sextract_i64(dst, src, 0, 56);
 
-        if (tbi != 3) {
-            TCGv_i64 tcg_zero = tcg_const_i64(0);
-
-            /*
-             * The two TBI bits differ.
-             * If tbi0, then !tbi1: only use the extension if positive.
-             * if !tbi0, then tbi1: only use the extension if negative.
-             */
-            tcg_gen_movcond_i64(tbi == 1 ? TCG_COND_GE : TCG_COND_LT,
-                                dst, dst, tcg_zero, dst, src);
-            tcg_temp_free_i64(tcg_zero);
+        switch (tbi) {
+        case 1:
+            /* tbi0 but !tbi1: only use the extension if positive */
+            tcg_gen_and_i64(dst, dst, src);
+            break;
+        case 2:
+            /* !tbi0 but tbi1: only use the extension if negative */
+            tcg_gen_or_i64(dst, dst, src);
+            break;
+        case 3:
+            /* tbi0 and tbi1: always use the extension */
+            break;
+        default:
+            g_assert_not_reached();
         }
     }
 }