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* [Bug c/26566]  New: Invalid code: loop optimization removes exit condition
@ 2006-03-05  9:55 steffen dot list dot account at gmail dot com
  2006-03-05 10:06 ` [Bug c/26566] " falk at debian dot org
  0 siblings, 1 reply; 2+ messages in thread
From: steffen dot list dot account at gmail dot com @ 2006-03-05  9:55 UTC (permalink / raw)
  To: gcc-bugs

With -O2 or higher, the following little C loop does not terminate:

   short i;
   for (i=-1; i; i--) ;

The generated assembler code is:

.L2:
        jmp     .L2

which means that the exit condition has been completely eliminated. 

The same loop works as expected (terminates after 0xffff iterations) with
gcc-4.0 or earlier, with -O1 or lower, and with unsigned types. 

This is an i386 style system with a P4 2.8 GHz, running Debian SID/i386 with
gcc-4.1 1:4.1.0-0 from Debian experimental.


-- 
           Summary: Invalid code: loop optimization removes exit condition
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steffen dot list dot account at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26566


^ permalink raw reply	[flat|nested] 2+ messages in thread
* [Bug c/26566] Invalid code: loop optimization removes exit condition
  2006-03-05  9:55 [Bug c/26566] New: Invalid code: loop optimization removes exit condition steffen dot list dot account at gmail dot com
@ 2006-03-05 10:06 ` falk at debian dot org
  0 siblings, 0 replies; 2+ messages in thread
From: falk at debian dot org @ 2006-03-05 10:06 UTC (permalink / raw)
  To: gcc-bugs



------- Comment #1 from falk at debian dot org  2006-03-05 10:06 -------
Signed integer overflow is undefined in C. Use -fwrapv to force twos-complement
semantics.


-- 

falk at debian dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26566


^ permalink raw reply	[flat|nested] 2+ messages in thread
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2006-03-05  9:55 [Bug c/26566] New: Invalid code: loop optimization removes exit condition steffen dot list dot account at gmail dot com
2006-03-05 10:06 ` [Bug c/26566] " falk at debian dot org

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