[Bug c/26566] New: Invalid code: loop optimization removes exit condition

[steffen dot list dot account at gmail dot com]

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