Re: [PATCH v2] Return a NULL rtx when targets don't support cbranchcc4 or predicate check fails in prepare_cmp_insn

[Richard Biener <richard.guenther@gmail.com>]

On Mon, Dec 5, 2022 at 4:08 AM HAO CHEN GUI <guihaoc@linux.ibm.com> wrote:
>
> Hi,
>   It gets an assertion failure when targers don't support cbranchcc4 or
> predicate check fails in prepare_cmp_insn. prepare_cmp_insn is a help
> function to generate compare rtx, so it should not assume that cbranchcc4
> is existing or all sub-CC modes are supported on one target. I think it
> should return the NULL rtx when cbranchcc4 is not supported or predicate check
> fails, as its callers already check if the return value is null or not for CC
> mode. This patch just does the change.
>
>   Bootstrapped and tested on powerpc64-linux BE/LE and x86 with no regressions.
> Is this okay for trunk? Any recommendations? Thanks a lot.

I wonder if you have a testcase you can add showing this change is
worthwhile and
fixes a bug?

OK.

Thanks,
Richard.

>
> ChangeLog
> 2022-12-05  Haochen Gui <guihaoc@linux.ibm.com>
>
> gcc/
>         * optabs.cc (prepare_cmp_insn): Return a NULL rtx other than assertion
>         failure when targets don't have cbranch optab or predicate check
>         fails.
>
> patch.diff
> diff --git a/gcc/optabs.cc b/gcc/optabs.cc
> index 165f8d1fa22..f6d3242479b 100644
> --- a/gcc/optabs.cc
> +++ b/gcc/optabs.cc
> @@ -4484,10 +4484,14 @@ prepare_cmp_insn (rtx x, rtx y, enum rtx_code comparison, rtx size,
>      {
>        enum insn_code icode = optab_handler (cbranch_optab, CCmode);
>        test = gen_rtx_fmt_ee (comparison, VOIDmode, x, y);
> -      gcc_assert (icode != CODE_FOR_nothing
> -                  && insn_operand_matches (icode, 0, test));
> -      *ptest = test;
> -      return;
> +      if (icode != CODE_FOR_nothing
> +         && insn_operand_matches (icode, 0, test))
> +       {
> +         *ptest = test;
> +         return;
> +       }
> +      else
> +       goto fail;
>      }
>
>    mclass = GET_MODE_CLASS (mode);