[Bug tree-optimization/95118] New: gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[Bug tree-optimization/95118] New: gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[slyfox at inbox dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

            Bug ID: 95118
           Summary: gcc-10 and master -O3 -fopt-info-vec causes gcc to
                    hang
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at inbox dot ru
  Target Milestone: ---

The bug originally reported by Adrien Dessemond as
https://bugs.gentoo.org/722774 where gzip-1.10's ./configure CFLAGS="-O3 -pipe
-march=native -fomit-frame-pointer -fopt-info-vec -mindirect-branch=thunk
-mindirect-branch-register" makes gcc hang.

Minimal reproducer against gcc-10.1.0 anf gcc-master is:

  // $ cat bug.c
  void a();
  void b() {
    union {
      int c[4];
      long double d;
    } e = {{0, 0, 4}};
    a(e.d);
  }

$ /usr/bin/x86_64-pc-linux-gnu-gcc-10.1.0 -o conftest -O3 -fopt-info-vec -c
bug.c
<hung>

Reproducible on the following gcc config against master:

Reading specs from /home/slyfox/dev/git/gcc-native-quick/gcc/specs
COLLECT_GCC=/home/slyfox/dev/git/gcc-native-quick/gcc/xgcc
COLLECT_LTO_WRAPPER=/home/slyfox/dev/git/gcc-native-quick/gcc/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc/configure --enable-languages=c,c++ --disable-bootstrap
--with-multilib-list=m64
--prefix=/home/slyfox/dev/git/gcc-native-quick/../gcc-native-quick-installed
--disable-nls --without-isl --disable-libsanitizer --disable-libvtv
--disable-libgomp --disable-libstdcxx-pch --disable-libunwind-exceptions
CFLAGS='-O1 ' CXXFLAGS='-O1 ' --with-sysroot=/usr/x86_64-HEAD-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.0.0 20200513 (experimental) (GCC)

[Bug tree-optimization/95118] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[slyfox at inbox dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

--- Comment #1 from Sergei Trofimovich <slyfox at inbox dot ru> ---
Created attachment 48528
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48528&action=edit
bug.c

[Bug tree-optimization/95118] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[slyfox at inbox dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

--- Comment #2 from Sergei Trofimovich <slyfox at inbox dot ru> ---
Seems to be a regression since gcc-9.3.0.

[Bug tree-optimization/95118] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[slyfox at inbox dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

Sergei Trofimovich <slyfox at inbox dot ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #3 from Sergei Trofimovich <slyfox at inbox dot ru> ---
Bisect points to an old revision. Might be a coincidence?

38988cbf9ebaa96fb1e891a46aa063f0c298a2e2 is the first bad commit
commit 38988cbf9ebaa96fb1e891a46aa063f0c298a2e2
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Jul 8 07:09:24 2019 +0000

    re PR tree-optimization/83518 (Missing optimization: useless instructions
should be dropped)

    2019-07-08  Richard Biener  <rguenther@suse.de>

            PR tree-optimization/83518
            * tree-ssa-sccvn.c: Include splay-tree.h.
            (struct pd_range, struct pd_data): New.
            (struct vn_walk_cb_data): Add data to track partial definitions.
            (vn_walk_cb_data::~vn_walk_cb_data): New.
            (vn_walk_cb_data::push_partial_def): New.
            (pd_tree_alloc, pd_tree_dealloc, pd_range_compare): New.
            (vn_reference_lookup_2): When partial defs are registered give up.
            (vn_reference_lookup_3): Track partial defs for memset and
            constructor zeroing and for defs from constants.

            * gcc.dg/tree-ssa/ssa-fre-73.c: New testcase.
            * gcc.dg/tree-ssa/ssa-fre-74.c: Likewise.
            * gcc.dg/tree-ssa/ssa-fre-75.c: Likewise.
            * gcc.dg/tree-ssa/ssa-fre-76.c: Likewise.
            * g++.dg/tree-ssa/pr83518.C: Likewise.

    From-SVN: r273194

 gcc/ChangeLog                              |  13 +
 gcc/testsuite/ChangeLog                    |   9 +
 gcc/testsuite/g++.dg/tree-ssa/pr83518.C    |  27 ++
 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-73.c |  14 ++
 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-74.c |  16 ++
 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-75.c |  34 +++
 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-76.c |  16 ++
 gcc/tree-ssa-sccvn.c                       | 389 +++++++++++++++++++++++++----
 8 files changed, 469 insertions(+), 49 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr83518.C
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-73.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-74.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-75.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-76.c

[Bug tree-optimization/95118] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[admnd at protonmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

--- Comment #4 from Adrien Dessemond <admnd at protonmail dot com> ---
The hang also happens with "-O2 -ftree-vectorize -fopt-info-vec" 
I confirm that removing "-fopt-info-vec" avoids the hang.

[Bug tree-optimization/95118] [10/11 Regression] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
           Keywords|                            |compile-time-hog
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
   Target Milestone|---                         |10.2
            Summary|gcc-10 and master -O3       |[10/11 Regression] gcc-10
                   |-fopt-info-vec causes gcc   |and master -O3
                   |to hang                     |-fopt-info-vec causes gcc
                   |                            |to hang
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-05-14
      Known to work|                            |9.3.0

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
On the GCC 10 branch I see it not returning from

(gdb) fin
Run till exit from #0  0x000000000107148d in real_to_decimal_for_mode (
    str=0x7fffffffcd60 "\200", r_orig=0x7fffffffcd40, buf_size=100, digits=57, 
    crop_trailing_zeros=1, mode=E_VOIDmode)
    at /space/rguenther/src/gcc-10-branch/gcc/real.c:1718

we're in this loop:

      while (1)
        {
          /* Stop if we'd shift bits off the bottom.  */
          if (v.sig[0] & 7)
            break;

          do_multiply (&u, &v, ten);

          /* Stop if we're now >= 1.  */
          if (REAL_EXP (&u) > 0)
            break;

          v = u;
          dec_exp -= 1;
        }

(gdb) p u
$1 = {cl = 0, decimal = 0, sign = 0, signalling = 0, canonical = 0, uexp = 0, 
  sig = {0, 0, 0}}

and the original REAL_VALUE_TYPE is

(gdb) p *r_orig
$4 = {cl = 1, decimal = 0, sign = 0, signalling = 0, canonical = 0, 
  uexp = 67092486, sig = {0, 0, 0}}

so it's simply a weird not normalized constant zero ...

I have a patch to paper over this in real_to_decimal_for_mode which then
prints

  a (0.0e-8191);

for the specific number.

[Bug tree-optimization/95118] [10/11 Regression] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:568c985113b29574c4e25e1a016475668fc17c28

commit r11-383-g568c985113b29574c4e25e1a016475668fc17c28
Author: Richard Biener <rguenther@suse.de>
Date:   Thu May 14 08:53:03 2020 +0200

    middle-end/95118 - fix printing of denormal zero

    This fixes printing a REAL_CST generated from value-numbering
    punning some bits to a real which turns out as zero with big
    negative exponent.  This causes the loop in real_to_decimal_for_mode to
    never terminate.

    2020-05-14  Richard Biener  <rguenther@suse.de>

            PR middle-end/95118
            * real.c (real_to_decimal_for_mode): Make sure we handle
            a zero with nonzero exponent.

            * gcc.dg/pr95118.c: New testcase.

[Bug tree-optimization/95118] [10 Regression] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |11.0
            Summary|[10/11 Regression] gcc-10   |[10 Regression] gcc-10 and
                   |and master -O3              |master -O3 -fopt-info-vec
                   |-fopt-info-vec causes gcc   |causes gcc to hang
                   |to hang                     |
      Known to fail|                            |10.1.0

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed on trunk sofar.

[Bug tree-optimization/95118] [10 Regression] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:fe19d514ae915163b49fa344703ecfa1778a44d8

commit r10-8349-gfe19d514ae915163b49fa344703ecfa1778a44d8
Author: Richard Biener <rguenther@suse.de>
Date:   Thu May 14 08:53:03 2020 +0200

    middle-end/95118 - fix printing of denormal zero

    This fixes printing a REAL_CST generated from value-numbering
    punning some bits to a real which turns out as zero with big
    negative exponent.  This causes the loop in real_to_decimal_for_mode to
    never terminate.

    2020-05-14  Richard Biener  <rguenther@suse.de>

            PR middle-end/95118
            * real.c (real_to_decimal_for_mode): Make sure we handle
            a zero with nonzero exponent.

            * gcc.dg/pr95118.c: New testcase.

[Bug tree-optimization/95118] [10 Regression] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|                            |10.1.1
         Resolution|---                         |FIXED

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.

[Bug tree-optimization/95118] [10 Regression] gcc-10 and master -O3 -fopt-info-vec causes gcc to hang

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95118

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ch3root at openwall dot com

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 71533 has been marked as a duplicate of this bug. ***