[Bug c++/65075] New: [5 Regression] constexpr regression

[Bug c++/65075] New: [5 Regression] constexpr regression

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65075

            Bug ID: 65075
           Summary: [5 Regression] constexpr regression
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org

typedef void (*E) ();
template <class T>
constexpr E
bar ()
{
  return []() {};
}
void
foo ()
{
  (bar<int> ()) ();
}

is rejected since r215954 aka PR55250 with -std=c++11:
error: body of constexpr function ‘constexpr void (* bar())() [with T = int; E
= void (*)()]’ not a return-statement
The body is a return statement, just perhaps with some extra artificial
statements created for the lambda.
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Subject: [Bug tree-optimization/64992] More optimize opportunity
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd992

Marc Glisse <glisse at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW

--- Comment #5 from Marc Glisse <glisse at gcc dot gnu.org> ---
We do not sink the code that computes d into the branch c==-1. If we did, the
second comparison would simplify to a constant. VRP is not clever enough to
"backport" new assertions to already computed values.

We could also simplify N*x==0 to x==0 even for unsigned when VRP information
tells us that overflow/wrap cannot happen (here N is 2 and x is in [0,1]).

[Bug c++/65075] [5 Regression] constexpr regression

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65075

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-02-16
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |paolo at gcc dot gnu.org
   Target Milestone|---                         |5.0
     Ever confirmed|0                           |1

[Bug c++/65075] [5 Regression] constexpr regression

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65075

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
           Priority|P3                          |P1

[Bug c++/65075] [5 Regression] constexpr regression

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65075

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Hi Jakub. Something like the below passes testing and works for the testcase:

Index: constexpr.c
===================================================================
--- constexpr.c    (revision 220731)
+++ constexpr.c    (working copy)
@@ -415,8 +415,8 @@ check_constexpr_bind_expr_vars (tree t)
   gcc_assert (TREE_CODE (t) == BIND_EXPR);

   for (tree var = BIND_EXPR_VARS (t); var; var = DECL_CHAIN (var))
-    if (TREE_CODE (var) == TYPE_DECL
-    && DECL_IMPLICIT_TYPEDEF_P (var))
+    if (DECL_IMPLICIT_TYPEDEF_P (var)
+    && !LAMBDA_TYPE_P (TREE_TYPE (var)))
       return false;
   return true;
 }

Note that I will be traveling for a week or so, thus I'm not be able to fully
handle the issue. If we rather resolve the regression immediately, please feel
free to pick up the above / double check if it makes sense to Jason.

[Bug c++/65075] [5 Regression] constexpr regression

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65075

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Yeah, makes sense, I've just been looking for what the flag is for the lambda
types.  I can add the testcase and bootstrap/regtest it.

[Bug c++/65075] [5 Regression] constexpr regression

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65075

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Tue Feb 17 08:25:30 2015
New Revision: 220748

URL: https://gcc.gnu.org/viewcvs?rev=220748&root=gcc&view=rev
Log:
    PR c++/65075
    * constexpr.c (check_constexpr_bind_expr_vars): Allow
    implicit typedefs for lambda types.

    * g++.dg/cpp0x/pr65075.C: New test.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/pr65075.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/constexpr.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/65075] [5 Regression] constexpr regression

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65075

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed.