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

[Eugene Rozenfeld <Eugene.Rozenfeld@microsoft.com>]

Yes, -gstatement-frontiers is the root cause here but the new approach to discriminators is especially prone to this. I added the workaround to pr85213.c in my original discriminator patch but now two more -fcompare-debug bugs were opened (PR107231 and PR107169). I suspect we'll keep getting more. So I'd like to disable printing discriminators in -fcompare-debug dums until -gstatement-frontier issue is fixed.

Eugene

-----Original Message-----
From: Richard Biener <richard.guenther@gmail.com> 
Sent: Monday, October 17, 2022 12:06 AM
To: Eugene Rozenfeld <Eugene.Rozenfeld@microsoft.com>
Cc: gcc-patches@gcc.gnu.org; Jason Merrill <jason@redhat.com>
Subject: [EXTERNAL] Re: [PATCH] Don't print discriminators for -fcompare-debug.

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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fbugzilla%2Fshow_bug.cgi%3Fid%3D100733&amp;data=05%7C01%7CEugene.Rozenfeld%40microsoft.com%7C5d3df88ec7e14f5eec2708dab00e0440%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C638015871510301049%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=2JjQHAgDi6%2Fet1vowA1IRcdInJMkkjuva9DbM5rHawc%3D&amp;reserved=0 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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fbugzilla%2Fshow_bug.cgi%3Fid%3D100733&amp;data=05%7C01%7CEugene.Rozenfeld%40microsoft.com%7C5d3df88ec7e14f5eec2708dab00e0440%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C638015871510301049%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=2JjQHAgDi6%2Fet1vowA1IRcdInJMkkjuva9DbM5rHawc%3D&amp;reserved=0 :
> -   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