Re: [PATCH] Make sure SCALAR_INT_MODE_P before invoke try_const_anchors

[Richard Biener <rguenther@suse.de>]

On Fri, 9 Jun 2023, Richard Sandiford wrote:

> guojiufu <guojiufu@linux.ibm.com> writes:
> > Hi,
> >
> > On 2023-06-09 16:00, Richard Biener wrote:
> >> On Fri, 9 Jun 2023, Jiufu Guo wrote:
> >> 
> >>> Hi,
> >>> 
> >>> As checking the code, there is a "gcc_assert (SCALAR_INT_MODE_P 
> >>> (mode))"
> >>> in "try_const_anchors".
> >>> This assert seems correct because the function try_const_anchors cares
> >>> about integer values currently, and modes other than SCALAR_INT_MODE_P
> >>> are not needed to support.
> >>> 
> >>> This patch makes sure SCALAR_INT_MODE_P when calling 
> >>> try_const_anchors.
> >>> 
> >>> This patch is raised when drafting below one.
> >>> https://gcc.gnu.org/pipermail/gcc-patches/2022-October/603530.html.
> >>> With that patch, "{[%1:DI]=0;} stack_tie" with BLKmode runs into
> >>> try_const_anchors, and hits the assert/ice.
> >>> 
> >>> Boostrap and regtest pass on ppc64{,le} and x86_64.
> >>> Is this ok for trunk?
> >> 
> >> Iff the correct fix at all (how can a CONST_INT have BLKmode?) then
> >> I suggest to instead fix try_const_anchors to change
> >> 
> >>   /* CONST_INT is used for CC modes, but we should leave those alone.  
> >> */
> >>   if (GET_MODE_CLASS (mode) == MODE_CC)
> >>     return NULL_RTX;
> >> 
> >>   gcc_assert (SCALAR_INT_MODE_P (mode));
> >> 
> >> to
> >> 
> >>   /* CONST_INT is used for CC modes, leave any non-scalar-int mode 
> >> alone.  */
> >>   if (!SCALAR_INT_MODE_P (mode))
> >>     return NULL_RTX;
> >> 
> >
> > This is also able to fix this issue.  there is a "Punt on CC modes" 
> > patch
> > to return NULL_RTX in try_const_anchors.
> >
> >> but as said I wonder how we arrive at a BLKmode CONST_INT and whether
> >> we should have fended this off earlier.  Can you share more complete
> >> RTL of that stack_tie?
> >
> >
> > (insn 15 14 16 3 (parallel [
> >              (set (mem/c:BLK (reg/f:DI 1 1) [1  A8])
> >                  (const_int 0 [0]))
> >          ]) "/home/guojiufu/temp/gdb.c":13:3 922 {stack_tie}
> >       (nil))
> >
> > It is "set (mem/c:BLK (reg/f:DI 1 1) (const_int 0 [0])".
> 
> I'm not convinced this is correct RTL.  (unspec:BLK [(const_int 0)] ...)
> would be though.  It's arguably more accurate too, since the effect
> on the stack locations is unspecified rather than predictable.

powerpc seems to be the only port with a stack_tie that's not
using an UNSPEC RHS.

> Thanks,
> Richard