[X86][SSE] Lower ICMP EQ(AND(X,C),C) -> SRA(SHL(X,LOG2(C)),BW-1) iff C is power-of-2.

This replaces the MOVMSK combine introduced at D52121/rL342326

(movmsk (setne (and X, (1 << C)), 0)) -> (movmsk (X << C))

with the more general icmp lowering so it can pick up more cases through bitcasts - notably vXi8 cases which use vXi16 shifts+masks, this patch can remove the mask and use pcmpgtb(0,x) for the sra.

Differential Revision: https://reviews.llvm.org/D60625

llvm-svn: 358651