On Fri, 11 Aug 2023 at 11:26, Peter Maydell <peter.mayd...@linaro.org> wrote:
>
> On Tue, 8 Aug 2023 at 04:13, Richard Henderson
> <richard.hender...@linaro.org> wrote:
> >
> > Add the parameter to avoid TEST and pass along to tgen_arithi.
> > All current users pass false.
> >
> > Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
> > ---
> > tcg/i386/tcg-target.c.inc | 16 ++++++++--------
> > 1 file changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
> > index b88fc14afd..56549ff2a0 100644
> > --- a/tcg/i386/tcg-target.c.inc
> > +++ b/tcg/i386/tcg-target.c.inc
> > @@ -1418,15 +1418,15 @@ static void tcg_out_jxx(TCGContext *s, int opc,
> > TCGLabel *l, bool small)
> > }
> > }
> >
> > -static void tcg_out_cmp(TCGContext *s, TCGArg arg1, TCGArg arg2,
> > - int const_arg2, int rexw)
> > +static void tcg_out_cmp(TCGContext *s, int rexw, TCGArg arg1, TCGArg arg2,
> > + int const_arg2, bool cf)
> > {
> > if (const_arg2) {
> > - if (arg2 == 0) {
> > + if (arg2 == 0 && !cf) {
> > /* test r, r */
> > tcg_out_modrm(s, OPC_TESTL + rexw, arg1, arg1);
> > } else {
> > - tgen_arithi(s, ARITH_CMP + rexw, arg1, arg2, 0);
> > + tgen_arithi(s, ARITH_CMP + rexw, arg1, arg2, cf);
> > }
> > } else {
> > tgen_arithr(s, ARITH_CMP + rexw, arg1, arg2);
>
> I don't really understand the motivation here.
> Why are some uses of this function fine with using the TEST
> insn, but some must avoid it? What does 'cf' stand for?
> A comment would help here if there isn't a clearer argument
> name available...
Looking at the following patch suggests perhaps:
/**
* tcg_out_cmp: Emit a compare, setting the X, Y, Z flags accordingly.
* @need_cf : true if the comparison must also set CF
*/
(fill in which XYZ flags you can rely on even if need_cf is false)
?
-- PMM
