Summary:
If the register has a negative value then unsigned overflow will occur;
this case is sometimes even created intentionally by LSR. For now
disable GA+reg folding. Fixes PR29127
Differential Revision: https://reviews.llvm.org/D24053
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280285 91177308-0d34-0410-b5e6-96231b3b80d8