ConstantFold: an undef shift amount results in undef

X shifted by undef results in undef because the undef value can
represent values greater than the width of the operands.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223968 91177308-0d34-0410-b5e6-96231b3b80d8
ConstantFold, InstSimplify: undef >>a x can be either -1 or 0, choose 0

Zero is usually a nicer constant to have than -1.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223969 91177308-0d34-0410-b5e6-96231b3b80d8
ConstantFold: Clean up X * undef code

No functional change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223970 91177308-0d34-0410-b5e6-96231b3b80d8
[Hexagon] Adding combine ri/ir instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223971 91177308-0d34-0410-b5e6-96231b3b80d8