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target/i386: optimize computation of ZF from CC_OP_DYNAMIC

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Most uses of CC_OP_DYNAMIC are for CMP/JB/JE or similar sequences.
We can optimize many of them to avoid computation of the flags.
This eliminates both TCG ops to set up the new cc_op, and helper
instructions because evaluating just ZF is much cheaper.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2024-06-20 10:34:28 +02:00
parent 1f7f72bdc4
commit ae14b33de8
3 changed files with 21 additions and 3 deletions
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1
target/i386/helper.h
View File

@ -1,5 +1,6 @@
DEF_HELPER_FLAGS_4(cc_compute_all, TCG_CALL_NO_RWG_SE, tl, tl, tl, tl, int)
DEF_HELPER_FLAGS_4(cc_compute_c, TCG_CALL_NO_RWG_SE, tl, tl, tl, tl, int)
DEF_HELPER_FLAGS_3(cc_compute_nz, TCG_CALL_NO_RWG_SE, tl, tl, tl, int)
DEF_HELPER_3(write_eflags, void, env, tl, i32)
DEF_HELPER_1(read_eflags, tl, env)

13
target/i386/tcg/cc_helper.c
View File

@ -95,6 +95,19 @@ static target_ulong compute_all_adcox(target_ulong dst, target_ulong src1,
return (src1 & ~(CC_C | CC_O)) | (dst * CC_C) | (src2 * CC_O);
}
target_ulong helper_cc_compute_nz(target_ulong dst, target_ulong src1,
int op)
{
if (CC_OP_HAS_EFLAGS(op)) {
return ~src1 & CC_Z;
} else {
MemOp size = cc_op_size(op);
target_ulong mask = MAKE_64BIT_MASK(0, 8 << size);
return dst & mask;
}
}
target_ulong helper_cc_compute_all(target_ulong dst, target_ulong src1,
target_ulong src2, int op)
{

10
target/i386/tcg/translate.c
View File

@ -1008,15 +1008,19 @@ static CCPrepare gen_prepare_eflags_o(DisasContext *s, TCGv reg)
static CCPrepare gen_prepare_eflags_z(DisasContext *s, TCGv reg)
{
switch (s->cc_op) {
case CC_OP_DYNAMIC:
gen_compute_eflags(s);
/* FALLTHRU */
case CC_OP_EFLAGS:
case CC_OP_ADCX:
case CC_OP_ADOX:
case CC_OP_ADCOX:
return (CCPrepare) { .cond = TCG_COND_TSTNE, .reg = cpu_cc_src,
.imm = CC_Z };
case CC_OP_DYNAMIC:
gen_update_cc_op(s);
if (!reg) {
reg = tcg_temp_new();
}
gen_helper_cc_compute_nz(reg, cpu_cc_dst, cpu_cc_src, cpu_cc_op);
return (CCPrepare) { .cond = TCG_COND_EQ, .reg = reg, .imm = 0 };
default:
{
MemOp size = cc_op_size(s->cc_op);