[Bug c++/65091] New: decltype(~arg) fails for template functions

["ptomulik at meil dot pw.edu.pl" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65091

            Bug ID: 65091
           Summary: decltype(~arg) fails for template functions
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ptomulik at meil dot pw.edu.pl

Created attachment 34790
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34790&action=edit
ii file generated by -save-temps

The following program does not compile with g++ (although it compiles with
clang++):

template<typename T>
auto foo(T x) -> decltype(~x)
{ return ~x; }

int bar()
{ return foo(10); }

ptomulik@tea:$ g++ -std=c++11 -g -O0 -Wall -Wextra -Werror -pedantic -c -o
test.o test.cpp
test.cpp: In function ‘int bar()’:
test.cpp:6:16: error: no matching function for call to ‘foo(int)’
 { return foo(10); }
                ^
test.cpp:6:16: note: candidate is:
test.cpp:2:6: note: template<class T> decltype (~ x) foo(T)
 auto foo(T x) -> decltype(~x)
      ^
test.cpp:2:6: note:   template argument deduction/substitution failed:
test.cpp: In substitution of ‘template<class T> decltype (~ x) foo(T) [with T =
int]’:
test.cpp:6:16:   required from here
test.cpp:2:6: error: ‘x’ was not declared in this scope
test.cpp:6:19: error: control reaches end of non-void function
[-Werror=return-type]
 { return foo(10); }
                   ^
cc1plus: all warnings being treated as errors


This is specific to the unary operator "~" and expression involving argument
name (not its type). All the following variants compile well for instance:

template<typename T>
auto foo(T x) -> decltype(!x)
{ return !x; }

template<typename T>
auto foo(T x) -> decltype(-x)
{ return -x; }

template<typename T>
auto foo(T x) -> decltype(+x)
{ return +x; }

template<typename T>
auto foo(T x) -> decltype(~T())
{ return ~x; }

My gcc is:

ptomulik@tea:$ g++ --version
g++-4.9.real (Debian 4.9.2-10) 4.9.2
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

My OS is Debian 8.0.
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From: "howarth at bromo dot med.uc.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/65084] Lack of type narrowing/widening inhibits good vectorization
Date: Tue, 17 Feb 2015 15:34:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ide084

howarth at bromo dot med.uc.edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |howarth at bromo dot med.uc.edu

--- Comment #3 from howarth at bromo dot med.uc.edu ---
I assume that https://gcc.gnu.org/bugzilla/show_bug.cgi?ide088 is a
duplicate?