llvm/test/CFrontend/2002-08-02-UnionTest.c

/* In this testcase, the return value of foo() is being promotedto a register
 * which breaks stuff
 */
#include <stdio.h>

union X { char X; void *B; int a, b, c, d;};

union X foo() {
	union X Global;
        Global.B = (void*)123;   /* Interesting part */
	return Global;
}

void main() {
	union X test = foo();
	printf("0x%p", test.B);
}