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From: Richard Biener <richard.guenther@gmail.com>
To: Alexandre Oliva <aoliva@redhat.com>
Cc: Jeff Law <law@redhat.com>, GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: bootstrap-debug-lean + flags in producer vs compare
Date: Mon, 13 Nov 2017 10:16:00 -0000	[thread overview]
Message-ID: <CAFiYyc2QdJ4fQbJEUuQGYjSeb+rs8xHzD0orttDEw1n3Tp3n0w@mail.gmail.com> (raw)
In-Reply-To: <ortvy11xi6.fsf@lxoliva.fsfla.org>

On Sat, Nov 11, 2017 at 1:15 AM, Alexandre Oliva <aoliva@redhat.com> wrote:
> On Oct 30, 2017, Jeff Law <law@redhat.com> wrote:
>
>> I'd support either or both.  Your call.
>
> Thanks.  I think I'll go with both, then.
>
> Ok to install as follows? (edited the comments and added a ChangeLog)

Ok.

>
> Use compare-debug for bootstrap-debug-lean to ignore != DW_AT_producer
>
> Unlike bootstrap-debug, bootstrap-debug-lean used to pass compare using
> the traditional compare command, because it compiled both stage2 and
> stage3 with options that used to generate identical output
> (-fcompare-debug= in stage2 vs -fcompare-debug in stage3).
>
> Since we started adding relevant command-line flags to DW_AT_producer,
> this is no longer the case, and stages 2 and 3 object files that differ
> in nothing but the DW_AT_producer strings.
>
>
> -fcompare-debug is short for -fcompare-debug=-gtoggle, so stage3
> compiles twice, once with the normal options, once with toggled -g, to
> then compare the temporary final dumps.  When enabled, both compilations
> get from the driver an additional -frandom-seed flag (if none is given
> explicitly).
>
> -fcompare-debug= is short for -fno-compare-debug, disabling the second
> compilation.
>
>
> The difference between the DW_AT_producer lines are the different
> -fcompare-debug flags, and the presence of the -frandom-seed flag in the
> stage3 compilation.
>
> It is easy and sensible enough to filter the -fcompare-debug flags out
> of the DW_AT_producer string.  This option should never affect the
> compilation output, it just determines whether or not to perform an
> additional compilation that should produce the same executable output.
>
> However, dropping -frandom-seed is not quite correct, in that it might
> have other consequences on the compilation.  So, it makes little sense
> to make the effort to drop it when it's implicit; for those comparing
> compiler output differences, it might even hint at what causes, and
> could fix, difficult to explain differences, namely, explicitly
> supplying -frandom-seed options.
>
> They don't seem to matter for compiler bootstraps, though, at least
> for now, so we can safely refrain from issuing -frandom-seed (or maybe
> we already issue it where needed :-), and then, for
> bootstrap-debug-lean, use the compare-debug script, that strips out
> debug information before comparing the object files.
>
>
> for  config/ChangeLog
>
>         * bootstrap-debug-lean.mk (do-compare): Use the
>         contrib/compare-debug script.
>
> for  gcc/ChangeLog
>
>         * dwarf2out.c (gen_producer_string): Discard
>         OPT_fcompare_debug.
>
> ---
>  config/bootstrap-debug-lean.mk |    1 +
>  gcc/dwarf2out.c                |    1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/config/bootstrap-debug-lean.mk b/config/bootstrap-debug-lean.mk
> index e215280b09f3..5f2db80687fa 100644
> --- a/config/bootstrap-debug-lean.mk
> +++ b/config/bootstrap-debug-lean.mk
> @@ -9,3 +9,4 @@
>
>  STAGE2_CFLAGS += -fcompare-debug=
>  STAGE3_CFLAGS += -fcompare-debug
> +do-compare = $(SHELL) $(srcdir)/contrib/compare-debug $$f1 $$f2
> diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
> index b8f4e4888f1b..01d90808fd3b 100644
> --- a/gcc/dwarf2out.c
> +++ b/gcc/dwarf2out.c
> @@ -23403,6 +23403,7 @@ gen_producer_string (void)
>        case OPT_fltrans_output_list_:
>        case OPT_fresolution_:
>        case OPT_fdebug_prefix_map_:
> +      case OPT_fcompare_debug:
>         /* Ignore these.  */
>         continue;
>        default:
>
>
> --
> Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
> You must be the change you wish to see in the world. -- Gandhi
> Be Free! -- http://FSFLA.org/   FSF Latin America board member
> Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer

      reply	other threads:[~2017-11-13  8:46 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-06  1:15 Alexandre Oliva
2017-10-31  1:20 ` Jeff Law
2017-11-11  1:00   ` Alexandre Oliva
2017-11-13 10:16     ` Richard Biener [this message]

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