The following code:
#include <stdio.h>
int main(int argc, char **argv) {
void *v = (void*) 1;
int *i = (int*) &v;
int intpos;
for (intpos = 0; intpos < (sizeof(void*) / sizeof(int)); intpos++)
if (i[intpos] == 1)
break;
printf("intpos = %d\n",intpos);
}
Produces:
intpos = 0
when compiled optimization of -O or less. When compiled with -O2, it produces:
intpos = 1
on x86 and:
intpos = 2
on x86_64.
Latest gcc tested is gcc version 4.1.0 20060512 (Red Hat 4.1.0-17)
This code is from LAM/MPI.
--
Summary: Optimized code gives incorrect result
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: orion at cora dot nwra dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27744
