[InstSimplify] fold implied null ptr check (PR35790)

This extends rL322327 to handle the pointer cast and should solve:
https://bugs.llvm.org/show_bug.cgi?id=35790

Name: or_eq_zero
  %isnull = icmp eq i64* %p, null
  %x = ptrtoint i64* %p to i64
  %somebits = and i64 %x, %y
  %somebits_are_zero = icmp eq i64 %somebits, 0
  %or = or i1 %somebits_are_zero, %isnull
  =>
  %or = %somebits_are_zero

Name: and_ne_zero
  %isnotnull = icmp ne i64* %p, null
  %x = ptrtoint i64* %p to i64
  %somebits = and i64 %x, %y
  %somebits_are_not_zero = icmp ne i64 %somebits, 0
  %and = and i1 %somebits_are_not_zero, %isnotnull
  =>
  %and = %somebits_are_not_zero

https://rise4fun.com/Alive/CQ3

llvm-svn: 322439