optimization/2847: GCC 2.96 with -O2 incorrectly compile if(var==0) break; else printf("test\n"); inside a while

[yannick.koehler@colubris.com]

>Number:         2847
>Category:       optimization
>Synopsis:       GCC 2.96 with -O2 incorrectly compile if(var==0) break; else printf("test\n"); inside a while
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Wed May 16 13:26:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Yannick Koehler
>Release:        gcc version 2.96 20000731 (Linux-Mandrake 8.0 2.96-0.48mdk)
>Organization:
>Environment:
Mandrake 7.2 updated to Mandrake 8.0
>Description:
I'm compiling this code with this command:

gcc -O2 ./bug.c

running ./a.out doesn't output the word "Wonderful!" as it should...

CODE:
#include <stdio.h>

int main(int argc, char *argv)
{
	int iNbr = 1;
	int test = 0;
	while(test == 0) {
		printf("iNbr = %d\n", iNbr);
		if (iNbr == 0)
			break;
		else {
			printf("Wonderful\n");
			iNbr--;
		}			
		test = 1;
	}
	return 0;
}

Instead if display nothing.  But if I replace the condition if (iNbr==0) with if (0) things work.  Even optimized that code should print Wonderful.

This code works with -O1 -O3 and with 2.95.3
>How-To-Repeat:
take the attachment and compile with 2.96 and option -O2 or -Os
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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