On Mon, Sep 13, 2021 at 8:26 AM Hongtao Liu <crazy...@gmail.com> wrote:
>
> On Mon, Sep 13, 2021 at 2:11 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))
> > > + && 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);
> >
> > That would be equivalent to use gen_lowpart_if_possible?
> No, target will be changed to NULL_RTX.
> But it does avoid ICE since maybe_expand_insn can legitimate operands,
> but I doubt it will introduce other bugs since the target has been
> changed here.
>
> I think the validate_subreg solution is plain and straightforward,
> just like it's done in
> r11-7515-g0ad6de3883a1641f7ec0bd9cf56d41fa5b313dae.
That guards an explicit gen_rtx_SUBREG, here we're using gen_lowpart.
It's not an obvious match to validate gen_lowpart with validate_subreg,
I thought that gen_lowpart_if_possible would be prefered. You obviously
have to adjust the code, like
rtx tem;
if (...
&& (tem = gen_lowpart_if_possible (ext_mode, target))
{
target = tem;
...
Richard.
>
> >
> > > if (partial_subreg_p (GET_MODE (spec_target), ext_mode))
> > > --
> > > 2.27.0
> > >
>
>
>
> --
> BR,
> Hongtao
