[11u] RFR 8257561 Some code is not vectorized after 8251925 and 8250607

[Roland Westrelin]

Hi,
 
Original bug:
  https://bugs.openjdk.java.net/browse/JDK-8257561
  https://github.com/openjdk/jdk/commit/6c9482ee
 
Original patch does not apply cleanly to 11u, because the change to
src/hotspot/share/opto/cfgnode.cpp is specific to jdk 16. Change is
otherwise identical to upstream change.
 
11u webrev:
  https://cr.openjdk.java.net/~roland/8257561.11u/webrev.00/
 
Testing: x86_64 build, tier1, manually verified with superword tests
that vectorization happens now

Roland.