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Date: Thu, 26 Jan 2006 23:13:00 -0000
Subject: [Bug c/25985]  New: with optimization integer math fails
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From: "jurka at ejurka dot com" <gcc-bugzilla@gcc.gnu.org>
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gcc version 4.2.0 20060121

With optimzation the following code skips the last loop iteration:

#include <stdio.h>

int main(void)
{
        int bits = 25;
        while (bits) {
                printf("bits=%d\n",bits);
                if (bits >= 8) {
                        bits -= 8;
                } else {
                        bits = 0;
                }

        }
        return 0;
}

jurka@fred:~/pg/test$ ~/gcc/42/bin/gcc  ip2.c 
jurka@fred:~/pg/test$ ./a.out 
bits=25
bits=17
bits=9
bits=1
jurka@fred:~/pg/test$ ~/gcc/42/bin/gcc -O ip2.c 
jurka@fred:~/pg/test$ ./a.out 
bits=25
bits=17
bits=9
jurka@fred:~/pg/test$


-- 
           Summary: with optimization integer math fails
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jurka at ejurka 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=25985