[Bug c++/33514] New: Inconsistent warning for compile-time integer overflow

[Bug c++/33514] New: Inconsistent warning for compile-time integer overflow

[mec at google dot com]

This is with gcc 4.3-20070914 snapshot.

The attached program has four sites with compile-time integer overflow: the
initializations of h4, h8, bp_i:h, and bp_lli:h.  Only the last of these draws
a warning.

mec@hollerith:~/exp-integer-overflow$ cat z5.cc
#include <stdio.h>

int l4 = 0x01010101;
int h4 = l4 * 0x80;

long long int l8 = 0x0101010101010101ll;
long long int h8 = l8 * 0x80;

template <class T> struct BitPattern {
  // For int32:
  //   half_ones = 0x00001111
  //   l         = 0x01010101
  //   h         = 0x80808080
  static const T half_ones = (static_cast<T>(1) << (sizeof(T)*4)) - 1;
  static const T l = (sizeof(T) == 1) ? 1 : (half_ones / 0xff * (half_ones +
2));
  static const T h = l * 0x80;
};

BitPattern<int> bp_i;
BitPattern<long long int> bp_lli;

int main() {
  printf("%16.16llx\n", bp_lli.half_ones);
  printf("%16.16llx\n", bp_lli.l);
  printf("%16.16llx\n", bp_lli.h);
  return 0;
}

mec@hollerith:~/exp-integer-overflow$
/home/mec/gcc-4.3-20070914/install/bin/g++ -Wall -S z5.cc
z5.cc: In instantiation of 'const long long int BitPattern<long long int>::h':
z5.cc:25:   instantiated from here
z5.cc:16: warning: integer overflow in expression


-- 
           Summary: Inconsistent warning for compile-time integer overflow
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mec at google dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33514

[Bug c++/33514] Inconsistent warning for compile-time integer overflow

[mec at google dot com]

------- Comment #1 from mec at google dot com  2007-09-21 05:28 -------
Created an attachment (id=14235)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14235&action=view)
Test program

Compile with: gcc -Wall -S z5.cc


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33514

[Bug c++/33514] Inconsistent warning for compile-time integer overflow in struct compared to toplevel

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2008-12-31 18:07 -------
This happens also with non templates:
s/template <class T> struct BitPattern {/typedef long long T; struct BitPattern
{/

:).

Note 4.1.1 did not warn in either place.  I don't know if we should be warning
in both or none so I am not going to mark this as a regression.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
  GCC build triplet|i686-pc-linux-gnu           |
   GCC host triplet|i686-pc-linux-gnu           |
 GCC target triplet|i686-pc-linux-gnu           |
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2008-12-31 18:07:33
               date|                            |
            Summary|Inconsistent warning for    |Inconsistent warning for
                   |compile-time integer        |compile-time integer
                   |overflow                    |overflow in struct compared
                   |                            |to toplevel


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33514