RFR: 8373343: C2: verify AddP base input only set for heap addresses [v4]

[Roland Westrelin]

> The base input of `AddP` is expected to only be set for heap accesses
> but I noticed some inconsistencies so I added an assert in the `AddP`
> constructor and fixed issues that it caught. AFAFICT, the
> inconsistencies shouldn't create issues.

Roland Westrelin 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 13 additional commits since the last revision:

 - more
 - more
 - review
 - Merge branch 'master' into JDK-8373343
 - review
 - review
 - review
 - merge
 - more
 - more
 - ... and 3 more: https://git.openjdk.org/jdk/compare/695159e3...b20f41db

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28769/files
  - new: https://git.openjdk.org/jdk/pull/28769/files/007e73cd..b20f41db

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28769&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28769&range=02-03

  Stats: 16548 lines in 2404 files changed: 8811 ins; 2140 del; 5597 mod
  Patch: https://git.openjdk.org/jdk/pull/28769.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28769/head:pull/28769

PR: https://git.openjdk.org/jdk/pull/28769