implement some more logical compares with constants, so that:

int foo1(int x, int y) {
  int t1 = x >= 0;
  int t2 = y >= 0;
  return t1 & t2;
}
int foo2(int x, int y) {
  int t1 = x == -1;
  int t2 = y == -1;
  return t1 & t2;
}

produces:

_foo1:
        or r2, r4, r3
        srwi r2, r2, 31
        xori r3, r2, 1
        blr
_foo2:
        and r2, r4, r3
        addic r2, r2, 1
        li r2, 0
        addze r3, r2
        blr

instead of:

_foo1:
        srwi r2, r4, 31
        xori r2, r2, 1
        srwi r3, r3, 31
        xori r3, r3, 1
        and r3, r2, r3
        blr
_foo2:
        addic r2, r4, 1
        li r2, 0
        addze r2, r2
        addic r3, r3, 1
        li r3, 0
        addze r3, r3
        and r3, r2, r3
        blr

llvm-svn: 21547