diff options
| author | Paolo Bonzini <pbonzini@redhat.com> | 2023-10-27 04:12:59 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2023-12-29 22:02:48 +0100 |
| commit | 6032627f07a1632114f09612c80cf806ba03de4a (patch) | |
| tree | f98465b4837ad70a2b112d792cfd8e70e2a6ebe7 /target/i386/tcg | |
| parent | 007531586aa8ef6dccdadd927b89a50af62288d1 (diff) | |
target/i386: optimize computation of JL and JLE from flags
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.
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'target/i386/tcg')
| -rw-r--r-- | target/i386/tcg/translate.c | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c index 037bc47e7c..8fb80011a2 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; |