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target/arm: Improve gen_top_byte_ignore

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

Backports 2169b5c6f7a791ef9c43c72412efaafae3245114
This commit is contained in:
Richard Henderson 2021-03-04 18:39:21 -05:00 committed by Lioncash
parent ab07f048d8
commit de982a8346
1 changed files with 14 additions and 11 deletions
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25
qemu/target/arm/translate-a64.c
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@ -318,17 +318,20 @@ static void gen_top_byte_ignore(DisasContext *s, TCGv_i64 dst,
/* Sign-extend from bit 55. */
tcg_gen_sextract_i64(tcg_ctx, dst, src, 0, 56);
if (tbi != 3) {
TCGv_i64 tcg_zero = tcg_const_i64(tcg_ctx, 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(tcg_ctx, tbi == 1 ? TCG_COND_GE : TCG_COND_LT,
dst, dst, tcg_zero, dst, src);
tcg_temp_free_i64(tcg_ctx, tcg_zero);
switch (tbi) {
case 1:
/* tbi0 but !tbi1: only use the extension if positive */
tcg_gen_and_i64(tcg_ctx, dst, dst, src);
break;
case 2:
/* !tbi0 but tbi1: only use the extension if negative */
tcg_gen_or_i64(tcg_ctx, dst, dst, src);
break;
case 3:
/* tbi0 and tbi1: always use the extension */
break;
default:
g_assert_not_reached();
}
}
}