[NFC][InstCombine] R38708 - inefficient pattern for high-bits checking.

More complicated, canonical pattern:
https://rise4fun.com/Alive/uhA
https://godbolt.org/z/o4RB8D

Also, we need to be careful not to skip some patters...

https://bugs.llvm.org/show_bug.cgi?id=38708

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342074 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed