[X86] Prevent constant hoisting for a couple compare immediates that the...

[X86] Prevent constant hoisting for a couple compare immediates that the selection DAG knows how to optimize into a shift.

This allows "icmp ugt %a, 4294967295" and "icmp uge %a, 4294967296" to be optimized into right shifts by 32 which can fold the immediate into the shift instruction. These patterns show up with some regularity in real code.

Unfortunately, since getImmCost can't see the icmp predicate we can't be tell if we're only catching these specific cases.

llvm-svn: 256126