TryToSimplifyUncondBranchFromEmptyBlock was checking that any common
predecessors of the two blocks it is attempting to merge supply the
same incoming values to any phi in the successor block.  This change
allows merging in the case where there is one or more incoming values
that are undef.  The undef values are rewritten to match the non-undef
value that flows from the other edge.  Patch by Mark Lacey.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186069 91177308-0d34-0410-b5e6-96231b3b80d8
[SystemZ] Allow 8-bit operands to RISBG

RISBG has three 8-bit operands (I3, I4 and I5).  I'd originally
restricted all three to 6 bits, since that's the only range we intended
to use at the time.  However, the top bit of I4 acts as a "zero" flag for
RISBG, while the top bit of I3 acts as a "test" flag for RNSBG & co.
This patch therefore allows them to have the full 8-bit range.
I've left the fifth operand as a 6-bit value for now since the
upper 2 bits have no defined meaning.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186070 91177308-0d34-0410-b5e6-96231b3b80d8