RFR: 8369435: C2: transform (LShiftX (SubX con0 a), con1) into (SubX con0<<con1 (LShiftX a con1)) [v3]

[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 incrementally with two additional commits since the last revision:

 - 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>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27842/files
  - new: https://git.openjdk.org/jdk/pull/27842/files/8b581911..e2533202

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27842&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27842&range=01-02

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 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