If we have a load of a global address that's not modified during the

If we have a load of a global address that's not modified during the
function, then go ahead and hoist it out of the loop. This is the result:

$ cat a.c
volatile int G;

int A(int N) {
  for (; N > 0; --N)
    G++;
}
$ llc -o - -relocation-model=pic
_A:
...
LBB1_2: # bb
        movl    L_G$non_lazy_ptr-"L1$pb"(%eax), %esi
        incl    (%esi)
        incl    %edx
        cmpl    %ecx, %edx
        jne     LBB1_2  # bb
...
$ llc -o - -relocation-model=pic -machine-licm
_A:
...
        movl    L_G$non_lazy_ptr-"L1$pb"(%eax), %eax
LBB1_2: # bb
        incl    (%eax)
        incl    %edx
        cmpl    %ecx, %edx
        jne     LBB1_2  # bb
...

I'm limiting this to the MOV32rm x86 instruction for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45444 91177308-0d34-0410-b5e6-96231b3b80d8