RFR: 8273454: C2: Transform (-a)*(-b) into a*b [v6]

[Zhengyu Gu]

> The transformation reduce instructions in generated code.
> 
> ### x86_64:
> 
> Before:
> ```  
>   0x00007fb92c78b3ac:   neg    %esi
>   0x00007fb92c78b3ae:   neg    %edx
>   0x00007fb92c78b3b0:   mov    %esi,%eax
>   0x00007fb92c78b3b2:   imul   %edx,%eax                    ;*imul {reexecute=0 rethrow=0 return_oop=0}
>                                                             ; - TestSub::runSub at 4 (line 9)
> 
> After:
> 
>                                                            ; - TestSub::runSub at -1 (line 9)
>   0x00007fc8c05b74ac:   mov    %esi,%eax
>   0x00007fc8c05b74ae:   imul   %edx,%eax                    ;*imul {reexecute=0 rethrow=0 return_oop=0}
>                                                             ; - TestSub::runSub at 4 (line 9)
> 
> 
> 
> ### AArch64:
> Before:
> 
>  0x0000ffff814b4a70:   neg     w11, w1
>  0x0000ffff814b4a74:   mneg    w0, w2, w11                 ;*imul {reexecute=0 rethrow=0 return_oop=0}
>                                                             ; - TestSub::runSub at 4 (line 9)
> 
> 
> After:
> 
>  0x0000ffff794a67f0:   mul     w0, w1, w2                  ;*imul {reexecute=0 rethrow=0 return_oop=0}
>                                                             ; - TestSub::runSub at 4 (line 9)

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

  Trailing space

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5403/files
  - new: https://git.openjdk.java.net/jdk/pull/5403/files/f9d7d612..3f3eeb01

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5403&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5403&range=04-05

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5403.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5403/head:pull/5403

PR: https://git.openjdk.java.net/jdk/pull/5403