Take advantage of the fact that there can be no 1 bits between SF and OF.
If they were adjacent, you could sum SF and get a carry only if SF was
already set. Then the value of OF in the sum is the XOR of OF itself,
the carry (which is SF) and 0 (the value of the OF bit in the addend):
this is OF^SF exactly.
Because OF and SF are not adjacent, just place more 1 bits to the
left so that the carry propagates, which means summing CC_O - CC_S.
Signed-off-by: Paolo Bonzini
---
target/i386/tcg/translate.c | 10 --
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
index 037bc47e7c2..8fb80011a22 100644
--- a/target/i386/tcg/translate.c
+++ b/target/i386/tcg/translate.c
@@ -1126,10 +1126,9 @@ static CCPrepare gen_prepare_cc(DisasContext *s, int b,
TCGv reg)
if (reg == cpu_cc_src) {
reg = s->tmp0;
}
-tcg_gen_shri_tl(reg, cpu_cc_src, 4); /* CC_O -> CC_S */
-tcg_gen_xor_tl(reg, reg, cpu_cc_src);
+tcg_gen_addi_tl(reg, cpu_cc_src, CC_O - CC_S);
cc = (CCPrepare) { .cond = TCG_COND_NE, .reg = reg,
- .mask = CC_S };
+ .mask = CC_O };
break;
default:
case JCC_LE:
@@ -1137,10 +1136,9 @@ static CCPrepare gen_prepare_cc(DisasContext *s, int b,
TCGv reg)
if (reg == cpu_cc_src) {
reg = s->tmp0;
}
-tcg_gen_shri_tl(reg, cpu_cc_src, 4); /* CC_O -> CC_S */
-tcg_gen_xor_tl(reg, reg, cpu_cc_src);
+tcg_gen_addi_tl(reg, cpu_cc_src, CC_O - CC_S);
cc = (CCPrepare) { .cond = TCG_COND_NE, .reg = reg,
- .mask = CC_S | CC_Z };
+ .mask = CC_O | CC_Z };
break;
}
break;
--
2.43.0
