Make load->store deletion a bit smarter. This allows us to compile this:

Make load->store deletion a bit smarter.  This allows us to compile this:

void test(long long *P) { *P ^= 1; }

into just:

_test:
	movl	4(%esp), %eax
	xorl	$1, (%eax)
	ret

instead of code like this:

_test:
	movl	4(%esp), %ecx
        xorl    $1, (%ecx)
	movl	4(%ecx), %edx
	movl	%edx, 4(%ecx)
	ret

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45762 91177308-0d34-0410-b5e6-96231b3b80d8