RFR: Remove redundant null checks [v8]

[Vicente Romero]

> some of the null checks javac generates are redundant and can be removed

Vicente Romero has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:

 - Merge branch 'bworld' into remove.redundant.null.checks
 - minor change
 - addressing review comments
 - adding test cases
 - adding more tests
 - adding more tests
 - minor change
 - another change
 - regression tests
 - remove redundant null checks
 - ... and 2 more: https://git.openjdk.org/valhalla/compare/ac608f6f...37939f06

-------------

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1947/files
  - new: https://git.openjdk.org/valhalla/pull/1947/files/1341ce04..37939f06

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1947&range=07
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1947&range=06-07

  Stats: 66205 lines in 3137 files changed: 31607 ins; 13541 del; 21057 mod
  Patch: https://git.openjdk.org/valhalla/pull/1947.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1947/head:pull/1947

PR: https://git.openjdk.org/valhalla/pull/1947