#include <stdio.h>

#if 0

peter@daintree[10:28AM]~-1051> cc -O1 -o bar bar.c
peter@daintree[10:28AM]~-1052> ./bar
Test foo1bar2foo3bar

peter@daintree[10:28AM]~-1053> cc -O2 -o bar bar.c
peter@daintree[10:28AM]~-1054> ./bar              
Test foo1bar2foo3bar
zsh: bus error (core dumped)  ./bar

If you look at assembler output, with -O1, the constant string appears
twice. One has .align 16 constraint, due to SSE use, the other does not.

With -O2, both strings are merged, and the alignment constraint is lost.

With -O1 the assembler output is:
...
foo:                                    # @foo
	movaps  foo.id(%rip), %xmm0
...
	.section	.rodata.str1.16,"aMS",@progbits,1
.align	16
foo.id:
	.asciz	 "foo1bar2foo3bar"
.section	.rodata.str1.1,"aMS",@progbits,1
.L.str:
	.asciz	 "Test %s\n"
.L.str1:
	.asciz	 "foo1bar2foo3bar"


With -O2:
...
foo:                                    # @foo
	movaps  .L.str1(%rip), %xmm0
...
	.section	.rodata.str1.1,"aMS",@progbits,1
.L.str:
	.asciz	 "Test %s\n"
.L.str1:
	.asciz	 "foo1bar2foo3bar"

Note missing ".align 16".  Luck will determine if it is aligned for the SSE data copy.

#endif

int foo(int a)
{
	char id[] = "foo1bar2foo3bar";
	id[0] += a;
	for (a = 0; id[a] != 0; a++) 
		;
	return a;
}

int main(void)
{
	printf("Test %s\n", "foo1bar2foo3bar");
	return foo(1);
	return 0;
}