With the following C code, the loop is completely eliminated, thanks to loop
unrolling and constant propagation.
The resulting LLVM code just calls printf with 20.

#include <stdio.h>
#include <stddef.h>

int main()
{
	int v = 0;

	size_t i;
	for(i=0; i<5; i++)
	{
		v += i*2;
	}

	printf("%d\n", v);
}


However, if 5 is replaced by 100, loop unrolling doesn't occur, and for some
reason constant propagation doesn't work anymore.
The resulting code just needs to call printf with 9900, there is no need for any
loop.