RFR: 8270366: C2: Add associative rule to add/sub node [v4]

[Zhengyu Gu]

> Please review this small patch that add associative rule to add/sub node, that eliminates a multiply instruction.
> 
> e.g.
> 
> private static int assocInt(int a, int b, int c) {
>   return a * c + b * c;
> }
> 
> 
> x86_64:
> Before:
> 
>   0x00007fda1506152c:   imul   %ecx,%esi
>   0x00007fda1506152f:   imul   %ecx,%edx
>   0x00007fda15061532:   mov    %esi,%eax
>   0x00007fda15061534:   add    %edx,%eax                    ;*iadd {reexecute=0 rethrow=0 return_oop=0}
>                                                             ; - TestAssoc::assocInt at 6 (line 9)
> 
> 
> After:
> 
>   0x00007fc1c078d52c:   add    %edx,%esi
>   0x00007fc1c078d52e:   mov    %ecx,%eax
>   0x00007fc1c078d530:   imul   %esi,%eax                    ;*iadd {reexecute=0 rethrow=0 return_oop=0}
>                                                             ; - TestAssoc::assocInt at 6 (line 9)

Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:

  @vnkozlov's suggestion

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4765/files
  - new: https://git.openjdk.java.net/jdk/pull/4765/files/f95996a2..14cca145

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4765&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4765&range=02-03

  Stats: 88 lines in 2 files changed: 52 ins; 0 del; 36 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4765.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4765/head:pull/4765

PR: https://git.openjdk.java.net/jdk/pull/4765