Only allow replacements of nodes that have a single user. This is better as
simple instructions (e.g. XGRK) are one cycle faster, and it helps in cases
where both inputs share a common node.
Review: Ulrich Weigand
The LIT test cases were migrated with the script provided by
Nikita Popov.
No manual changes were made. Committed without review since
no functional changes, after consultation with uweigand.
The zext handling added in r197802 wasn't right for RNSBG. This patch
restricts it to ROSBG, RXSBG and RISBG. (The tests for RISBG were added
in r197802 since RISBG was the motivating example.)
llvm-svn: 198862
