[Bug c++/104507] New: internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[Bug c++/104507] New: internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[junk at sigpwr dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

            Bug ID: 104507
           Summary: internal compiler error: unexpected expression
                    ‘(int)(__ret)’ of kind cast_expr
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: junk at sigpwr dot com
  Target Milestone: ---

Created attachment 52423
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52423&action=edit
repro ii file

Observed on multiple builds of GCC 11.2 (originally on a couple
cross-compilers, then reproduced on debian)

GCC details:

COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 11.2.0-14'
--with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-11-lKfaJs/gcc-11-11.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-lKfaJs/gcc-11-11.2.0/debian/tmp-gcn/usr
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=8
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (Debian 11.2.0-14)

Command line to reproduce:

gcc -save-temps repro.cc -c -o repro.o
repro.cc: In function ‘int DoFoo()’:
repro.cc:11:89: internal compiler error: unexpected expression ‘(int)(__ret)’
of kind cast_expr
   11 |   const char *n = s_errmsg(__ret);
      |                                                                        
                ^
0x7fce4df477ec __libc_start_main
        ../csu/libc-start.c:332
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-11/README.Bugs> for instructions.

Contents of repro.cc (.ii file attached):

#define ERR_MAX -20

#define s_errmsg(r)          \
        _k_errmsg[(((int)r) <= 0 && ((int)r) > ERR_MAX) ? -(r) : -ERR_MAX]

extern const char *_k_errmsg[];

template <int size>
inline int DoFoo() {
  int __ret = 0;
  const char *n = s_errmsg(__ret);
  return __ret;
}

[Bug c++/104507] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code,
                   |                            |needs-bisection

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Looks to be fixed on the trunk.

[Bug c++/104507] [10/11 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |10.1.0, 9.3.0, 9.4.0
            Summary|internal compiler error:    |[10/11 Regression] internal
                   |unexpected expression       |compiler error: unexpected
                   |‘(int)(__ret)’ of kind      |expression ‘(int)(__ret)’
                   |cast_expr                   |of kind cast_expr
      Known to fail|                            |10.2.0, 10.3.0, 11.1.0
   Target Milestone|---                         |10.4

[Bug c++/104507] [10/11 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[junk at sigpwr dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

--- Comment #2 from Daniel Nelson <junk at sigpwr dot com> ---
Had a few moments to do some testing/bisecting, and found the commit that fixed
this in mainline.

commit 9927ecbb42d5be48fa933adc26f8601fab5007ca
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Oct 28 10:05:14 2021 -0400

    c++: quadratic constexpr behavior for left-assoc logical exprs [PR102780]

    In the testcase below the two left fold expressions each expand into a
    constant logical expression with 1024 terms, for which potential_const_expr
    takes more than a minute to return true.  This happens because p_c_e_1
    performs trial evaluation of the first operand of a &&/|| in order to
    determine whether to consider the potentiality of the second operand.
    And because the expanded expression is left-associated, this trial
    evaluation causes p_c_e_1 to be quadratic in the number of terms of the
    expression.

    This patch fixes this quadratic behavior by making p_c_e_1 preemptively
    compute potentiality of the second operand of a &&/||, and perform trial
    evaluation of the first operand only if the second operand isn't
    potentially constant.  We must be careful to avoid emitting bogus
    diagnostics during the preemptive computation; to that end, we perform
    this shortcut only when tf_error is cleared, and when tf_error is set we
    now first check potentiality of the whole expression quietly and replay
    the check noisily for diagnostics.

    Apart from fixing the quadraticness for left-associated logical exprs,
    this change also reduces compile time for the libstdc++ testcase
    20_util/variant/87619.cc by about 15% even though our <variant> uses
    right folds instead of left folds.  Likewise for the testcase in the PR,
    for which compile time is reduced by 30%.  The reason for these speedups
    is that p_c_e_1 no longer performs expensive trial evaluation of each term
    of large constant logical expressions when determining their potentiality.

            PR c++/102780

    gcc/cp/ChangeLog:

            * constexpr.c (potential_constant_expression_1) <case
TRUTH_*_EXPR>:
            When tf_error isn't set, preemptively check potentiality of the
            second operand before performing trial evaluation of the first
            operand.
            (potential_constant_expression_1): When tf_error is set, first
check
            potentiality quietly and return true if successful, otherwise
            proceed noisily to give errors.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1z/fold13.C: New test.

 gcc/cp/constexpr.c                  | 26 +++++++++++++++++++++-----
 gcc/testsuite/g++.dg/cpp1z/fold13.C | 29 +++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/fold13.C

[Bug c++/104507] [10/11 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=102780
                 CC|                            |ppalka at gcc dot gnu.org
           Keywords|needs-bisection             |

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Daniel Nelson from comment #2)
> Had a few moments to do some testing/bisecting, and found the commit that
> fixed this in mainline.

I kinda of see how that might help here but not really. I wonder if there is
another testcase which might shows the issue on the trunk still.

[Bug c++/104507] [10/11 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[junk at sigpwr dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

--- Comment #4 from Daniel Nelson <junk at sigpwr dot com> ---
Yeah, that was my thought as well (though I'm 99% unfamiliar with the GCC
codebase).

Some more bisecting reveals that this was introduced with
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95508

ae2ebf011fec926e003645c33c07a03619ea216a is the first bad commit
commit ae2ebf011fec926e003645c33c07a03619ea216a
Author: Marek Polacek <polacek@redhat.com>
Date:   Wed Jun 17 09:19:02 2020 -0400

    c++: ICE with IMPLICIT_CONV_EXPR in array subscript [PR95508]
...

[Bug c++/104507] [10/11 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/104507] [10/11 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

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

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

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Yeah, I confirm it doesn't ICE starting with
r12-4769-g9927ecbb42d5be48fa933adc26f8601fab5007ca
and ICE started with r11-1449-gae2ebf011fec926e003645c33c07a03619ea216a
which has been backported to 10 in
r10-8315-g1bab254fd30c2b94a675b9057349fc80946375b1

[Bug c++/104507] [10/11/12 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
            Summary|[10/11 Regression] internal |[10/11/12 Regression]
                   |compiler error: unexpected  |internal compiler error:
                   |expression ‘(int)(__ret)’   |unexpected expression
                   |of kind cast_expr           |‘(int)(__ret)’ of kind
                   |                            |cast_expr
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-02-14
      Known to fail|                            |12.0

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #3)
> (In reply to Daniel Nelson from comment #2)
> > Had a few moments to do some testing/bisecting, and found the commit that
> > fixed this in mainline.
> 
> I kinda of see how that might help here but not really. I wonder if there is
> another testcase which might shows the issue on the trunk still.

trunk crashes on this version:

#define ERR_MAX -20

#define s_errmsg(r)          \
        _k_errmsg[(((int)r) <= 0 && r) ? -(r) : -ERR_MAX]

extern const char *_k_errmsg[];

template <int size>
inline int DoFoo() {
  int __ret = 0;
  const char *n = s_errmsg(__ret);
  return __ret;
}

[Bug c++/104507] [10/11/12 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

Patrick Palka <ppalka at gcc dot gnu.org> changed:

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

[Bug c++/104507] [10/11/12 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:c19f317a78c0e4c1b51d0e5a8e4c0a3b985b7a8e

commit r12-7264-gc19f317a78c0e4c1b51d0e5a8e4c0a3b985b7a8e
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Feb 16 12:41:35 2022 -0500

    c++: treat NON_DEPENDENT_EXPR as not potentially constant [PR104507]

    Here we're crashing from potential_constant_expression because it tries
    to perform trial evaluation of the first operand '(bool)__r' of the
    conjunction (which is overall wrapped in a NON_DEPENDENT_EXPR), but
    cxx_eval_constant_expression ICEs on unsupported trees (of which CAST_EXPR
    is one).  The sequence of events is:

      1. build_non_dependent_expr for the array subscript yields
         NON_DEPENDENT_EXPR<<<(bool)__r && __s>>> ? 1 : 2
      2. cp_build_array_ref calls fold_non_dependent_expr on this subscript
         (after this point, processing_template_decl is cleared)
      3. during which, the COND_EXPR case of tsubst_copy_and_build calls
         fold_non_dependent_expr on the first operand
      4. during which, we crash from p_c_e_1 because it attempts trial
         evaluation of the CAST_EXPR '(bool)__r'.

    Note that even if this crash didn't happen, fold_non_dependent_expr
    from cp_build_array_ref would still ultimately be one big no-op here
    since neither constexpr evaluation nor tsubst handle NON_DEPENDENT_EXPR.

    In light of this and of the observation that we should never see
    NON_DEPENDENT_EXPR in a context where a constant expression is needed
    (it's used primarily in the build_x_* family of functions), it seems
    futile for p_c_e_1 to ever return true for NON_DEPENDENT_EXPR.  And the
    otherwise inconsistent handling of NON_DEPENDENT_EXPR between p_c_e_1,
    cxx_evaluate_constexpr_expression and tsubst apparently leads to weird
    bugs such as this one.

            PR c++/104507

    gcc/cp/ChangeLog:

            * constexpr.cc (potential_constant_expression_1)
            <case NON_DEPENDENT_EXPR>: Return false instead of recursing.
            Assert tf_error isn't set.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/non-dependent21.C: New test.

[Bug c++/104507] [10/11 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[10/11/12 Regression]       |[10/11 Regression] internal
                   |internal compiler error:    |compiler error: unexpected
                   |unexpected expression       |expression ‘(int)(__ret)’
                   |‘(int)(__ret)’ of kind      |of kind cast_expr
                   |cast_expr                   |

--- Comment #8 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12 so far.

[Bug c++/104507] [10/11 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:c8aaa9cca96207b5674048972c82a338ef81ce7e

commit r11-9843-gc8aaa9cca96207b5674048972c82a338ef81ce7e
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Feb 16 12:41:35 2022 -0500

    c++: treat NON_DEPENDENT_EXPR as not potentially constant [PR104507]

    Here we're crashing from potential_constant_expression because it tries
    to perform trial evaluation of the first operand '(bool)__r' of the
    conjunction (which is overall wrapped in a NON_DEPENDENT_EXPR), but
    cxx_eval_constant_expression ICEs on unsupported trees (of which CAST_EXPR
    is one).  The sequence of events is:

      1. build_non_dependent_expr for the array subscript yields
         NON_DEPENDENT_EXPR<<<(bool)__r && __s>>> ? 1 : 2
      2. cp_build_array_ref calls fold_non_dependent_expr on this subscript
         (after this point, processing_template_decl is cleared)
      3. during which, the COND_EXPR case of tsubst_copy_and_build calls
         fold_non_dependent_expr on the first operand
      4. during which, we crash from p_c_e_1 because it attempts trial
         evaluation of the CAST_EXPR '(bool)__r'.

    Note that even if this crash didn't happen, fold_non_dependent_expr
    from cp_build_array_ref would still ultimately be one big no-op here
    since neither constexpr evaluation nor tsubst handle NON_DEPENDENT_EXPR.

    In light of this and of the observation that we should never see
    NON_DEPENDENT_EXPR in a context where a constant expression is needed
    (it's used primarily in the build_x_* family of functions), it seems
    futile for p_c_e_1 to ever return true for NON_DEPENDENT_EXPR.  And the
    otherwise inconsistent handling of NON_DEPENDENT_EXPR between p_c_e_1,
    cxx_evaluate_constexpr_expression and tsubst apparently leads to weird
    bugs such as this one.

            PR c++/104507

    gcc/cp/ChangeLog:

            * constexpr.c (potential_constant_expression_1)
            <case NON_DEPENDENT_EXPR>: Return false instead of recursing.
            Assert tf_error isn't set.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/non-dependent21.C: New test.

    (cherry picked from commit c19f317a78c0e4c1b51d0e5a8e4c0a3b985b7a8e)

[Bug c++/104507] [10 Regression] internal compiler error: unexpected expression ‘(int)(__ret)’ of kind cast_expr

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104507

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |11.3
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #10 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 11.3/12, thanks for the bug report.