[Bug c/31083] New: for (int i = 1; i != 0; i++); hangs for 32-bit ints with -O2 or above. Should wrap quickly.

[Bug c/31083] New: for (int i = 1; i != 0; i++); hangs for 32-bit ints with -O2 or above. Should wrap quickly.

[niklas at cadence dot com]

The following code hangs for -O2 or -O3. I am running on a 32-bit machine, and
with -O1 it terminates after a few seconds:

    for (int i = 1; i != 0; i++);

You can replace 'i = 1' with 'i = (1<<30)' for faster testing.

I am running Gentoo Linux 64-bit. 'gcc --version' says: gcc (GCC) 4.1.1 (Gentoo
4.1.1).


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           Summary: for (int i = 1; i != 0; i++); hangs for 32-bit ints with
                    -O2 or above. Should wrap quickly.
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: niklas at cadence dot com
 GCC build triplet: What is this? How about an explanation in "bug writing
                    guideline
  GCC host triplet: What is this? How about an explanation in "bug writing
                    guideline
GCC target triplet: What is this? How about an explanation in "bug writing
                    guideline


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31083

[Bug c/31083] for (int i = 1; i != 0; i++); hangs for 32-bit ints with -O2 or above. Should wrap quickly.

[niklas at cadence dot com]

------- Comment #1 from niklas at cadence dot com  2007-03-08 14:17 -------
I am running on a 64-bit machine, not 32-bit as stated in the first line. Typo,
sorry.


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niklas at cadence dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |niklas at cadence dot com
           Keywords|                            |wrong-code


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31083

[Bug c/31083] for (int i = 1; i != 0; i++); hangs for 32-bit ints with -O2 or above. Should wrap quickly.

[manu at gcc dot gnu dot org]

------- Comment #2 from manu at gcc dot gnu dot org  2007-03-08 14:38 -------
I think you are relying on the fact that signed overflow wraps, when in
standard C it is actually undefined (it may wrap, it may not). To make integers
wrap on overflow you use unsigned or -fwrapv.

Thus, I think this is a duplicate of PR 30475.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31083

[Bug c/31083] for (int i = 1; i != 0; i++); hangs for 32-bit ints with -O2 or above. Should wrap quickly.

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2007-03-08 14:41 -------
*** Bug 31082 has been marked as a duplicate of this bug. ***


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31083

[Bug c/31083] for (int i = 1; i != 0; i++); hangs for 32-bit ints with -O2 or above. Should wrap quickly.

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2007-03-08 15:33 -------
Integer overflow is undefined.


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rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31083

[Bug c/31083] for (int i = 1; i != 0; i++); hangs for 32-bit ints with -O2 or above. Should wrap quickly.

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2007-03-09 00:50 -------
In reference to the triplets question, refer next time to
http://gcc.gnu.org/bugs.html

Which tells you how to file a bug report.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31083