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target-s390: Optimize ADDC/SUBB

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Giving the proper mask to disas_jcc allows us to generate an inline
comparison generating the carry/borrow with setcond.

In the very worst case, when we must use the external helper to compute
a value for CC, we generate (cc > 1) instead of (cc >> 1), which is only
very slightly slower on common cpus.

In the very best case, when the CC comes from a COMPARE insn and the
compiler is using ALCG with zero, everything folds out to become just
the setcond that the compiler wanted.

Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Richard Henderson 2012-09-20 09:51:40 -07:00
parent a359b770c6
commit c95ec459c6
1 changed files with 37 additions and 19 deletions
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56
target-s390x/translate.c
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@ -1344,18 +1344,28 @@ static ExitStatus op_add(DisasContext *s, DisasOps *o)
static ExitStatus op_addc(DisasContext *s, DisasOps *o)
{
TCGv_i64 cc;
DisasCompare cmp;
TCGv_i64 carry;
tcg_gen_add_i64(o->out, o->in1, o->in2);
/* XXX possible optimization point */
gen_op_calc_cc(s);
cc = tcg_temp_new_i64();
tcg_gen_extu_i32_i64(cc, cc_op);
tcg_gen_shri_i64(cc, cc, 1);
/* The carry flag is the msb of CC, therefore the branch mask that would
create that comparison is 3. Feeding the generated comparison to
setcond produces the carry flag that we desire. */
disas_jcc(s, &cmp, 3);
carry = tcg_temp_new_i64();
if (cmp.is_64) {
tcg_gen_setcond_i64(cmp.cond, carry, cmp.u.s64.a, cmp.u.s64.b);
} else {
TCGv_i32 t = tcg_temp_new_i32();
tcg_gen_setcond_i32(cmp.cond, t, cmp.u.s32.a, cmp.u.s32.b);
tcg_gen_extu_i32_i64(carry, t);
tcg_temp_free_i32(t);
}
free_compare(&cmp);
tcg_gen_add_i64(o->out, o->out, cc);
tcg_temp_free_i64(cc);
tcg_gen_add_i64(o->out, o->out, carry);
tcg_temp_free_i64(carry);
return NO_EXIT;
}
@ -3397,19 +3407,27 @@ static ExitStatus op_sub(DisasContext *s, DisasOps *o)
static ExitStatus op_subb(DisasContext *s, DisasOps *o)
{
TCGv_i64 cc;
DisasCompare cmp;
TCGv_i64 borrow;
assert(!o->g_in2);
tcg_gen_not_i64(o->in2, o->in2);
tcg_gen_add_i64(o->out, o->in1, o->in2);
tcg_gen_sub_i64(o->out, o->in1, o->in2);
/* XXX possible optimization point */
gen_op_calc_cc(s);
cc = tcg_temp_new_i64();
tcg_gen_extu_i32_i64(cc, cc_op);
tcg_gen_shri_i64(cc, cc, 1);
tcg_gen_add_i64(o->out, o->out, cc);
tcg_temp_free_i64(cc);
/* The !borrow flag is the msb of CC. Since we want the inverse of
that, we ask for a comparison of CC=0 | CC=1 -> mask of 8 | 4. */
disas_jcc(s, &cmp, 8 | 4);
borrow = tcg_temp_new_i64();
if (cmp.is_64) {
tcg_gen_setcond_i64(cmp.cond, borrow, cmp.u.s64.a, cmp.u.s64.b);
} else {
TCGv_i32 t = tcg_temp_new_i32();
tcg_gen_setcond_i32(cmp.cond, t, cmp.u.s32.a, cmp.u.s32.b);
tcg_gen_extu_i32_i64(borrow, t);
tcg_temp_free_i32(t);
}
free_compare(&cmp);
tcg_gen_sub_i64(o->out, o->out, borrow);
tcg_temp_free_i64(borrow);
return NO_EXIT;
}