On Thu, Mar 7, 2024 at 10:56 AM Richard Biener <rguent...@suse.de> wrote:
>
> On Thu, 7 Mar 2024, Uros Bizjak wrote:
>
> > The compiler, configured with --enable-checking=yes,rtl,extra ICEs with:
> >
> > internal compiler error: RTL check: expected elt 0 type 'e' or 'u',
> > have 'E' (rtx unspec) in try_combine, at combine.cc:3237
> >
> > This is
> >
> > 3236 /* Just replace the CC reg with a new mode. */
> > 3237 SUBST (XEXP (*cc_use_loc, 0), newpat_dest);
> > 3238 undobuf.other_insn = cc_use_insn;
> >
> > in combine.cc, where *cc_use_loc is
> >
> > (unspec:DI [
> > (reg:CC 17 flags)
> > ] UNSPEC_PUSHFL)
> >
> > combine assumes CC must be used inside of a comparison and uses XEXP (...,
> > 0)
> > without checking on the RTX type of the argument.
> >
> > Undo the combination if *cc_use_loc is not COMPARISON_P.
> >
> > Also remove buggy and now redundant check for (const 0) RTX as part of
> > the comparison.
> >
> > PR rtl-optimization/112560
> >
> > gcc/ChangeLog:
> >
> > * combine.cc (try_combine): Reject the combination
> > if *cc_use_loc is not COMPARISON_P.
> >
> > Bootstrapped and regression tested on x86_64-pc-linux-gnu {,-m32}.
> >
> > OK for trunk?
>
> Since you CCed me - looking at the code I wonder why we fatally fail.
> The following might also fix the issue and preserve more of the
> rest of the flow of the function.
>
> If that works I'd prefer it. But I'll defer approval to the combine
> maintainer which is Segher.
Your patch is basically what v1 did [1], but it was suggested (in a
reply by you ;) ) that we should stop the attempt to combine if we
can't handle the use. So, the v2 patch undoes the combine and records
a nice message in this case.
Also, please note the removal of an existing crude hack that tries to
reject non-comparison uses by looking for (const_int 0) in the use
RTX, which is wrong as well.
[1] https://gcc.gnu.org/pipermail/gcc-patches/2023-November/638589.html
Uros.
>
> Thanks,
> Richard.
>
> diff --git a/gcc/combine.cc b/gcc/combine.cc
> index a4479f8d836..e280cd72ec7 100644
> --- a/gcc/combine.cc
> +++ b/gcc/combine.cc
> @@ -3182,7 +3182,8 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn
> *i1, rtx_insn *i0,
>
> if (undobuf.other_insn == 0
> && (cc_use_loc = find_single_use (SET_DEST (newpat), i3,
> - &cc_use_insn)))
> + &cc_use_insn))
> + && COMPARISON_P (*cc_use_loc))
> {
> compare_code = orig_compare_code = GET_CODE (*cc_use_loc);
> if (is_a <scalar_int_mode> (GET_MODE (i2dest), &mode))
> @@ -3200,7 +3201,7 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn
> *i1, rtx_insn *i0,
> the above simplify_compare_const() returned a new comparison
> operator. undobuf.other_insn is assigned the CC use insn
> when modifying it. */
> - if (cc_use_loc)
> + if (cc_use_loc && COMPARISON_P (*cc_use_loc))
> {
> #ifdef SELECT_CC_MODE
> machine_mode new_mode
>
