[Bug c++/63283] New: constexpr function called by templated function is not treated as constexpr

[Bug c++/63283] New: constexpr function called by templated function is not treated as constexpr

[roc at ocallahan dot org]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63283

            Bug ID: 63283
           Summary: constexpr function called by templated function is not
                    treated as constexpr
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: roc at ocallahan dot org

[roc@eternity tmp]$ cat test.cc
#include <stdio.h>
constexpr int array_length(int (&array)[3]) { return 3; }
int a[] = { 1, 2, 3 };
template <typename T> int f() {
  struct { int e[array_length(a)]; } t;
  return sizeof(t);
}
int main() { printf("%d\n", f<void>()); }

[roc@eternity tmp]$ g++ -std=c++11 -o ~/tmp/test ~/tmp/test.cc && ~/tmp/test
/home/roc/tmp/test.cc: In function ‘int f()’:
/home/roc/tmp/test.cc:5:33: error: array bound is not an integer constant
before ‘]’ token
   struct { int e[array_length(a)]; } t;
                                 ^
[roc@eternity tmp]$ g++ -v
Using built-in specs.
COLLECT_GCC=/usr/bin/g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.3/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-isl=/builddir/build/BUILD/gcc-4.8.3-20140624/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.8.3-20140624/obj-x86_64-redhat-linux/cloog-install
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.8.3 20140624 (Red Hat 4.8.3-1) (GCC) 

My friend also sees this in g++ 4.9.1.

clang++ 3.4 compiles the code successfully. Removing "template <typename T>"
from f() (and changing main() to match) makes the problem go away.
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc281

Alan Modra <amodra at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amodra at gmail dot com

--- Comment #1 from Alan Modra <amodra at gmail dot com> ---
Created attachment 33503
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id3503&actioníit
stop the inline expansion

This forces constants requiring more than one extra instruction for an inline
evaluation as compared to a memory load, into the TOC.

[Bug c++/63283] constexpr function called by templated function is not treated as constexpr

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63283

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-09-17
             Blocks|                            |55004
     Ever confirmed|0                           |1

[Bug c++/63283] constexpr function called by templated function is not treated as constexpr

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63283

--- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Thu Jan 15 20:46:03 2015
New Revision: 219686

URL: https://gcc.gnu.org/viewcvs?rev=219686&root=gcc&view=rev
Log:
    PR c++/63283
    * constexpr.c (potential_constant_expression_1): Handle reference
    args in templates.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/constexpr-template8.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/constexpr.c
    trunk/gcc/testsuite/g++.dg/cpp0x/static_assert10.C

[Bug c++/63283] constexpr function called by templated function is not treated as constexpr

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63283

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |jason at gcc dot gnu.org
         Resolution|---                         |FIXED
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
   Target Milestone|---                         |5.0

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for GCC 5.

[Bug c++/63283] constexpr function called by templated function is not treated as constexpr

[roc at ocallahan dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63283

--- Comment #3 from roc at ocallahan dot org <roc at ocallahan dot org> ---
Thanks!!!