[Bug c/63886] New: float will fit into int with abs - possible missing warning Wabsolute-value

[Bug c/63886] New: float will fit into int with abs - possible missing warning Wabsolute-value

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63886

            Bug ID: 63886
           Summary: float will fit into int with abs - possible missing
                    warning Wabsolute-value
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com

# include <stdlib.h>

extern void g(int);

void f( float qw)
{
    int n = abs(qw);    

    g(n);
}

$ ~/gcc/results/bin/gcc -c -g -O2 -Wall -Wextra -pedantic nov15z.c
$ ~/gcc/results/bin/gcc -v
gcc version 5.0.0 20141112 (experimental) (GCC) 
$ ~/llvm/results/bin/clang -c -g -O2 -Wall nov15z.c
nov15z.c:10:10: warning: using integer absolute value function 'abs' when
      argument is of floating point type [-Wabsolute-value]
        int n = abs(qw);        
                ^

[Bug c/63886] float will fit into int with abs - possible missing warning Wabsolute-value

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63886

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
warning: conversion to ‘int’ from ‘float’ may alter its value
[-Wfloat-conversion]
>From gcc-bugs-return-466854-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sat Nov 15 13:49:57 2014
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Subject: [Bug c/63886] float will fit into int with abs - possible missing warning Wabsolute-value
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63886

--- Comment #2 from David Binderman <dcb314 at hotmail dot com> ---
(In reply to Marc Glisse from comment #1)
> warning: conversion to ‘int’ from ‘float’ may alter its value
> [-Wfloat-conversion]

Thanks for that. 

Given the obscurity of -Wfloat-conversion, maybe it is time for it 
to be included in -Wall, where more folks will notice it ?
>From gcc-bugs-return-466855-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sat Nov 15 14:15:42 2014
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From: "dcb314 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/63886] float will fit into int with abs - possible missing warning Wabsolute-value
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63886

--- Comment #3 from David Binderman <dcb314 at hotmail dot com> ---
(In reply to David Binderman from comment #2)
> Given the obscurity of -Wfloat-conversion, maybe it is time for it 
> to be included in -Wall, where more folks will notice it ?

Scratch that. While -Wfloat-conversion does check fine for
int into double, it also does the "whole lot less useful, even
though technically accurate" double into float message.

Like

float f = 3.1;

warning: conversion to ‘float’ alters ‘double’ constant value
[-Wfloat-conversion]

I'll proceed with -Wfloat-conversion, but I'll be stripping out
(fgrep -v) these unwanted warnings.
>From gcc-bugs-return-466856-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sat Nov 15 14:20:48 2014
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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/63887] New: abi_tag confuses demangler
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc887

            Bug ID: 63887
           Summary: abi_tag confuses demangler
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
                CC: jason at gcc dot gnu.org

struct __attribute((abi_tag("cxx11"))) time_get
{
  ~time_get();
};

int main()
{
  time_get t;
}

/tmp/ccvqinyx.o: In function `main':
/tmp/t.cc:8: undefined reference to `time_get[abi:cxx11]::~cxx11()'
collect2: error: ld returned 1 exit status

Note that the destructor name is ~cxx11 not ~time_get

[Bug c/63886] float will fit into int with abs - possible missing warning Wabsolute-value

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63886

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |mpolacek at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Seems like there's nothing to do for this bug.

[Bug c/63886] float will fit into int with abs - possible missing warning Wabsolute-value

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63886

--- Comment #6 from David Binderman <dcb314 at hotmail dot com> ---
(In reply to Marek Polacek from comment #5)
> Seems like there's nothing to do for this bug.

Suggest there are two cases

1. double to float

2. double or float into any integer type.

The one warning, produced by -Wfloat-conversion, could be
split into two warnings, as per the two cases.

#1 isn't very useful, #2 seems useful to me.

Then put case #1 into -Wall.

[Bug c/63886] float will fit into int with abs - possible missing warning Wabsolute-value

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63886

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |---

--- Comment #7 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Reopening then.

[Bug c/63886] float will fit into int with abs - possible missing warning Wabsolute-value

[egall at gwmail dot gwu.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63886

Eric Gallager <egall at gwmail dot gwu.edu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |egall at gwmail dot gwu.edu

--- Comment #8 from Eric Gallager <egall at gwmail dot gwu.edu> ---
(In reply to Andreas Schwab from comment #4)
> float f = 3.1f;

Isn't there already -Wunsuffixed-float-constants for warnings with that kind of
fix?