Re: [PATCH] Don't print discriminators for -fcompare-debug.

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

On Sun, Oct 16, 2022 at 10:25 PM Eugene Rozenfeld via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> With -gstatement-frontiers we may end up with different IR
> coming from the front end with and without debug information turned on.
> See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100733 for details.
> That may result in differences in discriminator values and -fcompare-debug
> failures.
>
> This patch disables printing of discriminators when the dump is intended
> for -fcompare-debug comparison and reverses the workaround in a test.

I don't think this is the correct approach.  -gstatement-frontiers is
known to be
prone to these issues and is the one to blame here.  I think the bugs should be
SUSPENDED until -gstatement-frontiers is fixed or at least disabled by default
(IIRC Jakub tried that but failed last time)

> Tested on x86_64-pc-linux-gnu.
>
> gcc/ChangeLog:
>         PR debug/107231
>         PR debug/107169
>         * print-rtl.cc (print_rtx_operand_code_i): Don't print discriminators
>         for -fdebug-compare.
>
> gcc/testsuite/ChangeLog:
>
>         * c-c++-common/ubsan/pr85213.c: Reverse the workaround for discriminators.
> ---
>  gcc/print-rtl.cc                           | 13 ++++++++++---
>  gcc/testsuite/c-c++-common/ubsan/pr85213.c |  7 +------
>  2 files changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/gcc/print-rtl.cc b/gcc/print-rtl.cc
> index e115f987173..0476f3d7e79 100644
> --- a/gcc/print-rtl.cc
> +++ b/gcc/print-rtl.cc
> @@ -453,10 +453,17 @@ rtx_writer::print_rtx_operand_code_i (const_rtx in_rtx, int idx)
>           expanded_location xloc = insn_location (in_insn);
>           fprintf (m_outfile, " \"%s\":%i:%i", xloc.file, xloc.line,
>                    xloc.column);
> -         int discriminator = insn_discriminator (in_insn);
> -           if (discriminator)
> -             fprintf (m_outfile, " discrim %d", discriminator);
>
> +         /* Don't print discriminators for -fcompare-debug since the IR
> +            coming from the front end may be different with and without
> +            debug information turned on. That may result in different
> +            discriminator values. */
> +         if (!(dump_flags & TDF_COMPARE_DEBUG))
> +           {
> +             int discriminator = insn_discriminator (in_insn);
> +             if (discriminator)
> +               fprintf (m_outfile, " discrim %d", discriminator);
> +           }
>         }
>  #endif
>      }
> diff --git a/gcc/testsuite/c-c++-common/ubsan/pr85213.c b/gcc/testsuite/c-c++-common/ubsan/pr85213.c
> index e903e976f2c..8a6be81d20f 100644
> --- a/gcc/testsuite/c-c++-common/ubsan/pr85213.c
> +++ b/gcc/testsuite/c-c++-common/ubsan/pr85213.c
> @@ -1,11 +1,6 @@
>  /* PR sanitizer/85213 */
>  /* { dg-do compile } */
> -/* Pass -gno-statement-frontiers to work around
> -   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100733 :
> -   without it the IR coming from the front end may be different with and without
> -   debug information turned on. That may cause e.g., different discriminator values
> -   and -fcompare-debug failures. */
> -/* { dg-options "-O1 -fsanitize=undefined -fcompare-debug -gno-statement-frontiers" } */
> +/* { dg-options "-O1 -fsanitize=undefined -fcompare-debug" } */
>
>  int
>  foo (int x)
> --
> 2.25.1