[Bug c++/52026] New: [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[Bug c++/52026] New: [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[cheesear at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

             Bug #: 52026
           Summary: [c++0x] g++: Constexpr Variable Appears Uninitialized
                    in Lambda
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: cheesear@gmail.com


Created attachment 26487
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26487
The code sample exhibiting the suspected bug.

Hello everyone,

In the code fragment below, g++ (4.6.1 on Linux Mint 64-bit) complains that x
is uninitialized in the lambda function, and prints out an initialized value
from the stack for the last three lines of the program's output. I'd except all
four lines of the output to be '5', so I suspect that this may be a compiler
bug.

Also, even without the reference-capture in the lambda function, the code still
compiles. Below follows the command used to compile the code, along with one
possible output.

# g++ -Wall -std=c++0x c.cpp
c.cpp: In lambda function:
c.cpp:25:4: warning: ‘x’ is used uninitialized in this function
[-Wuninitialized]

# ./a.out
5
32535
32535
32535

[Bug c++/52026] [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-01-28
     Ever Confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-01-28 04:34:34 UTC ---
Confirmed.

[Bug c++/52026] [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[slipstreamdrive at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

--- Comment #2 from TbR <slipstreamdrive at hotmail dot com> 2012-08-08 08:57:49 UTC ---
Created attachment 27958
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27958
Code example to trigger the supposed bug.

only the "bug" function triggers the bug, while "nobug1" and "nobug2" don't.

[Bug c++/52026] [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[slipstreamdrive at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

TbR <slipstreamdrive at hotmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |slipstreamdrive at hotmail
                   |                            |dot com

--- Comment #3 from TbR <slipstreamdrive at hotmail dot com> 2012-08-08 09:01:39 UTC ---
Sorry, to make two comments. The bug is indeed not only showing a warning, but
the variable is uninitialized when executing the code.

[Bug c++/52026] [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[jpalecek at web dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

Jiří Paleček <jpalecek at web dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jpalecek at web dot de

--- Comment #4 from Jiří Paleček <jpalecek at web dot de> 2012-08-17 15:35:22 UTC ---
Could it be a duplicate of <a
href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53488">53488</a>?

[Bug c++/52026] [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[jpalecek at web dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

--- Comment #5 from Jiří Paleček <jpalecek at web dot de> 2012-08-19 14:04:34 UTC ---
*** Bug 53488 has been marked as a duplicate of this bug. ***

[Bug c++/52026] [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[jpalecek at web dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

--- Comment #6 from Jiří Paleček <jpalecek at web dot de> 2012-08-19 14:13:44 UTC ---
BTW I have proposed a patch that fixes this problem here:
http://gcc.gnu.org/ml/gcc-patches/2012-08/msg01252.html. Please take a look at
it.

[Bug c++/52026] [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-08-19 14:38:36 UTC ---
Do you have a copyright assignment on file?

[Bug c++/52026] [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[jpalecek at web dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

--- Comment #8 from Jiří Paleček <jpalecek at web dot de> 2012-08-19 15:38:33 UTC ---
(In reply to comment #7)
> Do you have a copyright assignment on file?

I don't know what you're talking about, so probably no. (BTW which file?)

[Bug c++/52026] [c++0x] g++: Constexpr Variable Appears Uninitialized in Lambda

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

--- Comment #9 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-08-20 09:07:26 UTC ---
That's a big problem if you are serious about contributing to gcc. See: 
http://gcc.gnu.org/contribute.html 

In short, if you don't want to waste time, make sure to obtain, fill and return
the forms before sending patches.

[Bug c++/52026] [c++0x] Constexpr Variable Appears Uninitialized in Lambda

[matt at godbolt dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

Matt Godbolt <matt at godbolt dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matt at godbolt dot org

--- Comment #10 from Matt Godbolt <matt at godbolt dot org> 2013-01-29 13:31:01 UTC ---
I have a smaller reproduction case, and some extra information:

References to non-explicitly captured constant values in template functions
generate invalid code.

An empty capture list fails to error, and generates invalid code.  A catch-all
capture list ([=] or [&]) correctly compiles, but generates invalid code.

A capture list that explicitly captures the constant value by reference or
value compiles and generates correct code.

With -Wall -Wextra, the constant is flagged as "uninitialized".

The code compiles and works correctly on GCC 4.5.2, but fails on GCC 4.6.3 and
GCC 4.7.2.

template<bool B>
int func() {
  const int constVal = B ? 100 : -100;
  return [] { return constVal; }();
}

int main(int, const char* []) {
  return func<true>();  // Returns 100 in -O0, but 0 in -O1 and above
}

[Bug c++/52026] [4.6/4.7/4.8 Regression] Constexpr Variable Appears Uninitialized in Lambda

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
            Summary|[c++0x] Constexpr Variable  |[4.6/4.7/4.8 Regression]
                   |Appears Uninitialized in    |Constexpr Variable Appears
                   |Lambda                      |Uninitialized in Lambda

--- Comment #11 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-02-14 23:53:43 UTC ---
Seems indeed a regression.

[Bug c++/52026] [4.6/4.7/4.8 Regression] Constexpr Variable Appears Uninitialized in Lambda

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

--- Comment #12 from Jason Merrill <jason at gcc dot gnu.org> 2013-02-15 16:17:31 UTC ---
Author: jason
Date: Fri Feb 15 16:17:25 2013
New Revision: 196081

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196081
Log:
    PR c++/52026
    * semantics.c (finish_id_expression): In a template, return
    the identifier for a constant variable.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-const2.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/semantics.c

[Bug c++/52026] [4.6/4.7/4.8 Regression] Constexpr Variable Appears Uninitialized in Lambda

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

--- Comment #13 from Jason Merrill <jason at gcc dot gnu.org> 2013-02-15 18:32:25 UTC ---
Author: jason
Date: Fri Feb 15 18:32:12 2013
New Revision: 196087

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196087
Log:
    PR c++/52026
    * semantics.c (finish_id_expression): In a template, return
    the identifier for a constant variable.

Added:
    branches/gcc-4_7-branch/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-const2.C
Modified:
    branches/gcc-4_7-branch/gcc/cp/ChangeLog
    branches/gcc-4_7-branch/gcc/cp/semantics.c

[Bug c++/52026] [4.6/4.7/4.8 Regression] Constexpr Variable Appears Uninitialized in Lambda

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |
   Target Milestone|---                         |4.7.3

--- Comment #14 from Jason Merrill <jason at gcc dot gnu.org> 2013-02-15 18:39:10 UTC ---
Fixed for 4.7.3.

[Bug c++/52026] [4.6/4.7/4.8 Regression] Constexpr Variable Appears Uninitialized in Lambda

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52026
Bug 52026 depends on bug 56947, which changed state.

Bug 56947 Summary: [4.7 Regression] Bogus 'XX' was not declared in this scope
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56947

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