RFR: 8334228: C2 SuperWord: fix JDK-24 regression in VPointer::cmp_for_sort after JDK-8325155 [v2]

[Emanuel Peter]

> This is a small regression from https://git.openjdk.org/jdk/pull/18822.
> 
> An overflow in the subtraction between the offsets means that the offsets are not correctly sorted. This has no correctness impact, but hit a verification assert that checked if the offsets were correctly sorted.
> 
> I now removed the subtractions, and replaced it with two comparisons.
> 
> Just out of an abundance of caution, I also converted all other subtractions into comparisons - even though I could probably make an argument that the values would be guaranteed in ranges that would not underflow the subtraction.

Emanuel Peter 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 three additional commits since the last revision:

 - Merge branch 'master' into JDK-8334228-bad-offset-sorting
 - widen the fix
 - JDK-8334228

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19696/files
  - new: https://git.openjdk.org/jdk/pull/19696/files/676b86ff..03658959

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19696&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19696&range=00-01

  Stats: 207 lines in 14 files changed: 153 ins; 18 del; 36 mod
  Patch: https://git.openjdk.org/jdk/pull/19696.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19696/head:pull/19696

PR: https://git.openjdk.org/jdk/pull/19696