[InstCombine] Teach foldSelectICmpAndOr to recognize (select (icmp slt (trunc...

[InstCombine] Teach foldSelectICmpAndOr to recognize (select (icmp slt (trunc (X)), 0), Y, (or Y, C2))

Summary:
InstCombine likes to turn (icmp eq (and X, C1), 0) into (icmp slt (trunc (X)), 0) sometimes. This breaks foldSelectICmpAndOr's ability to recognize (select (icmp eq (and X, C1), 0), Y, (or Y, C2))->(or (shl (and X, C1), C3), y).

This patch tries to recover this. I had to flip around some of the early out checks so that I could create a new And instruction during the compare processing without it possibly never getting used.

Reviewers: spatel, majnemer, davide

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D34184

llvm-svn: 306029