[DAGCombiner] Fold (zext (and/or/xor (shl/shr (load x), cst), cst))

[DAGCombiner] Fold (zext (and/or/xor (shl/shr (load x), cst), cst))

In our real world application, we found the following optimization is missed in DAGCombiner

(zext (and/or/xor (shl/shr (load x), cst), cst)) -> (and/or/xor (shl/shr (zextload x), (zext cst)), (zext cst))

If the user of original zext is an add, it may enable further lea optimization on x86.

This patch add a new function CombineZExtLogicopShiftLoad to do this optimization.

Differential Revision: https://reviews.llvm.org/D44402

llvm-svn: 329516