[Bug debug/100303] New: [11/12 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[Bug debug/100303] New: [11/12 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

            Bug ID: 100303
           Summary: [11/12 Regression] -fcompare-debug failure (length)
                    with -O -fno-dce -ftracer
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
                CC: aoliva at gcc dot gnu.org
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu

Created attachment 50693
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50693&action=edit
auto-reduced testcase (from OpenTTD sources)

Compiler output:
$ x86_64-pc-linux-gnu-gcc -O -fno-dce -ftracer -fcompare-debug testcase.C -w
x86_64-pc-linux-gnu-gcc: error: testcase.C: '-fcompare-debug' failure (length)

$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r12-174-20210427141825-g37d2b98100c-checking-yes-rtl-df-extra-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--with-cloog --with-ppl --with-isl --build=x86_64-pc-linux-gnu
--host=x86_64-pc-linux-gnu --target=x86_64-pc-linux-gnu
--with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-r12-174-20210427141825-g37d2b98100c-checking-yes-rtl-df-extra-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20210427 (experimental) (GCC)

[Bug debug/100303] [11/12 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.2

[Bug debug/100303] [11/12 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
                 CC|                            |jakub at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-04-28

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r11-6188-g0b76990a9d75d97b84014e37519086b81824c307

[Bug debug/100303] [11/12 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rsandifo at gcc dot gnu.org

--- Comment #2 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Oops, I should have thought about this case.

[Bug debug/100303] [11/12 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.org>:

https://gcc.gnu.org/g:c97351c0cf4872cc0e99e73ed17fb16659fd38b3

commit r12-292-gc97351c0cf4872cc0e99e73ed17fb16659fd38b3
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Thu Apr 29 17:24:57 2021 +0100

    rtl-ssa: Fix -fcompare-debug failure [PR100303]

    This patch fixes an oversight in the handling of debug instructions
    in rtl-ssa.  At the moment (and whether this is a good idea or not
    remains to be seen), we maintain a linear RPO sequence of definitions
    and non-debug uses.  If a register is defined more than once, we use
    a degenerate phi to reestablish a previous definition where necessary.

    However, debug instructions shouldn't of course affect codegen,
    so we can't create a new definition just for them.  In those situations
    we instead hang the debug use off the real definition (meaning that
    debug uses do not follow a linear order wrt definitions).  Again,
    it remains to be seen whether that's a good idea.

    The problem in the PR was that we weren't taking this into account
    when increasing (or potentially increasing) the live range of an
    existing definition.  We'd create the phi even if it would only
    be used by debug instructions.

    The patch goes for the simple but inelegant approach of passing
    a bool to say whether the use is a debug use or not.  I imagine
    this area will need some tweaking based on experience in future.

    gcc/
            PR rtl-optimization/100303
            * rtl-ssa/accesses.cc (function_info::make_use_available): Take a
            boolean that indicates whether the use will only be used in
            debug instructions.  Treat it in the same way that existing
            cross-EBB debug references would be handled if so.
            (function_info::make_uses_available): Likewise.
            * rtl-ssa/functions.h (function_info::make_uses_available): Update
            prototype accordingly.
            (function_info::make_uses_available): Likewise.
            * fwprop.c (try_fwprop_subst): Update call accordingly.

[Bug debug/100303] [11 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11/12 Regression]          |[11 Regression]
                   |-fcompare-debug failure     |-fcompare-debug failure
                   |(length) with -O -fno-dce   |(length) with -O -fno-dce
                   |-ftracer                    |-ftracer

--- Comment #4 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Fixed on trunk so far.

[Bug debug/100303] [11 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.2                        |11.3

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 11.2 is being released, retargeting bugs to GCC 11.3

[Bug debug/100303] [11 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=100304

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 100304 has been marked as a duplicate of this bug. ***

[Bug debug/100303] [11 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.3                        |11.4

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 11.3 is being released, retargeting bugs to GCC 11.4.

[Bug debug/100303] [11 Regression] -fcompare-debug failure (length) with -O -fno-dce -ftracer

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100303

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.4                        |11.5

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 11.4 is being released, retargeting bugs to GCC 11.5.