[InstCombine] Fold x & (-1 >> y) == x to x u<= (-1 >> y)

Summary:
https://bugs.llvm.org/show_bug.cgi?id=38123

This pattern will be produced by Implicit Integer Truncation sanitizer,
https://reviews.llvm.org/D48958
https://bugs.llvm.org/show_bug.cgi?id=21530
in unsigned case, therefore it is probably a good idea to improve it.

https://rise4fun.com/Alive/Rny
^ there are more opportunities for folds, i will follow up with them afterwards.

Caveat: this somehow exposes a missing opportunities
in `test/Transforms/InstCombine/icmp-logical.ll`
It seems, the problem is in `foldLogOpOfMaskedICmps()` in `InstCombineAndOrXor.cpp`.
But i'm not quite sure what is wrong, because it calls `getMaskedTypeForICmpPair()`,
which calls `decomposeBitTestICmp()` which should already work for these cases...
As @spatel notes in https://reviews.llvm.org/D49179#1158760,
that code is a rather complex mess, so we'll let it slide.

Reviewers: spatel, craig.topper

Reviewed By: spatel

Subscribers: yamauchi, majnemer, t.p.northover, llvm-commits

Differential Revision: https://reviews.llvm.org/D49179

llvm-svn: 336834