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....@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)
>
> > + && 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
