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

[Hongtao Liu <crazylht@gmail.com>]

On Mon, Sep 13, 2021 at 5:15 PM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Mon, Sep 13, 2021 at 8:26 AM Hongtao Liu <crazylht@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.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))
> > > > +         && 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))
>     {
Yes, update patch

  bootstrapped and regtested on x86_64-linux-gnu{-m32,}.
  Ok for trunk?
gcc/ChangeLog:

        * expmed.c (extract_bit_field_using_extv): Use
        gen_lowpart_if_possible instead of gen_lowpart to avoid ICE.
---
 gcc/expmed.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/gcc/expmed.c b/gcc/expmed.c
index 3143f38e057..59734d4841c 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -1571,14 +1571,16 @@ extract_bit_field_using_extv (const
extraction_insn *extv, rtx op0,

   if (GET_MODE (target) != ext_mode)
     {
+      rtx temp;
       /* 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 (GET_MODE (target), ext_mode)
+         && (temp = gen_lowpart_if_possible (ext_mode, target)))
        {
-         target = gen_lowpart (ext_mode, target);
+         target = temp;
          if (partial_subreg_p (GET_MODE (spec_target), ext_mode))
            spec_target_subreg = target;
        }
--
2.27.0

>        target = tem;
> ...
>
> Richard.
>
> >
> > >
> > > >           if (partial_subreg_p (GET_MODE (spec_target), ext_mode))
> > > > --
> > > > 2.27.0
> > > >
> >
> >
> >
> > --
> > BR,
> > Hongtao



-- 
BR,
Hongtao