Re: [PATCH 2/2] validate_subreg before call gen_lowpart to avoid ICE.

[Hongtao Liu <crazylht@gmail.com>]

On Fri, Sep 10, 2021 at 9:32 PM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On September 10, 2021 3:27:09 PM GMT+02:00, Hongtao Liu <crazylht@gmail.com> wrote:
> >On Fri, Sep 10, 2021 at 9:16 PM Richard Biener via Gcc-patches
> ><gcc-patches@gcc.gnu.org> wrote:
> >>
> >> On Fri, Sep 10, 2021 at 2:58 PM liuhongt <hongtao.liu@intel.com> wrote:
> >> >
> >> > gcc/ChangeLog:
> >> >
> >> >         * expmed.c (extract_bit_field_using_extv): validate_subreg
> >> >         before call gen_lowpart.
> >> > ---
> >> >  gcc/expmed.c | 6 +++++-
> >> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >> >
> >> > diff --git a/gcc/expmed.c b/gcc/expmed.c
> >> > index 3143f38e057..10d62d857a8 100644
> >> > --- a/gcc/expmed.c
> >> > +++ b/gcc/expmed.c
> >> > @@ -1571,12 +1571,16 @@ extract_bit_field_using_extv (const extraction_insn *extv, rtx op0,
> >> >
> >> >    if (GET_MODE (target) != ext_mode)
> >> >      {
> >> > +      machine_mode tmode = GET_MODE (target);
> >> >        /* Don't use LHS paradoxical subreg if explicit truncation is needed
> >> >          between the mode of the extraction (word_mode) and the target
> >> >          mode.  Instead, create a temporary and use convert_move to set
> >> >          the target.  */
> >> >        if (REG_P (target)
> >> > -         && TRULY_NOOP_TRUNCATION_MODES_P (GET_MODE (target), ext_mode))
> >>
> >> ^^^
> >>
> >> I wonder if herein lies the problem in that the HFmode "truncation" from SImode
> >> is considered noop?  Note the underlying target hook only looks at the mode
> >> precision and thus receives 16 and 32, and thus maybe that
> >> TRULY_NOOP_TRUNCATION_MODES_P query only makes sense for
> >> integer modes?  Though the documentation of the hook only talks about
> >> "conversion" of "values" ...
> >>
> >> So maybe a targetm.modes_tieable_p (GET_MODE (target), extmode) check
> >> is missing?
> >
> >According to document, it should be true for
> >targetm.modes_tieable_p(HFmode, SImode) since HFmode can be allocated
> >to gpr.
> >
> >----------------
> >This hook returns true if a value of mode mode1 is accessible in mode
> >mode2 without
> >copying
> >-------------------
> >
> >and also here gen_lowpart (SImode, HFmode, target) is called and hit
> >gcc_assert, not (subreg:HF (reg:SI) 0)
>
> I see. Of course that leads to a suggestion to allow the subreg based on modes_tieable_p, but then others will know why that's the wrong thing to do?
allowing subreg based on modes_tieable_p would be too strict， it even
disallows (subreg SF (reg:SI).
>
> Richard.
>
> >>
> >> > +         && TRULY_NOOP_TRUNCATION_MODES_P (tmode, ext_mode)
> >> > +         && validate_subreg (ext_mode, tmode,
> >> > +                             target,
> >> > +                             subreg_lowpart_offset (ext_mode, tmode)))
> >> >         {
> >> >           target = gen_lowpart (ext_mode, target);
> >> >           if (partial_subreg_p (GET_MODE (spec_target), ext_mode))
> >> > --
> >> > 2.27.0
> >> >
> >
> >
> >
>


-- 
BR,
Hongtao