RFR: 8369435: C2: transform (LShiftX (SubX con0 a), con1) into (SubX con0<<con1 (LShiftX a con1)) [v4]

[Roland Westrelin]

> We already transform:
> 
> (LShiftX (AddX a con0), con1) into (AddX (LShiftX a con1) con0<<con1)
> 
> THis is a variant with SubX. I found that this helps RCE.

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 five additional commits since the last revision:

 - Merge branch 'master' into JDK-8369435
 - Update src/hotspot/share/opto/mulnode.cpp
   
   Co-authored-by: Benoît Maillard <benoit.maillard at protonmail.com>
 - Update src/hotspot/share/opto/mulnode.cpp
   
   Co-authored-by: Benoît Maillard <benoit.maillard at protonmail.com>
 - review
 - test & fix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27842/files
  - new: https://git.openjdk.org/jdk/pull/27842/files/e2533202..a5cce41e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27842&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27842&range=02-03

  Stats: 26386 lines in 704 files changed: 15428 ins; 6512 del; 4446 mod
  Patch: https://git.openjdk.org/jdk/pull/27842.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27842/head:pull/27842

PR: https://git.openjdk.org/jdk/pull/27842