RFR: 8270366: C2: Add associative rule to add/sub node [v3]

[Vladimir Kozlov]

On Wed, 14 Jul 2021 17:30:42 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> 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:
> 
>   Add a test

I am fine with your selection of corner cases in the test.
You need second test file for `long` values.

test/hotspot/jtreg/compiler/integerArithmetic/TestIntegerAssociative.java line 99:

> 97:     // Method should run under interpreter mode
> 98:     private static int addInt(int a, int b, int c) {
> 99:         return a * b + a * c;

You need tests for all order variations you optimized.

test/hotspot/jtreg/compiler/integerArithmetic/TestIntegerAssociative.java line 104:

> 102:     private static int addComp(int a, int b, int c) {
> 103:         return a * b + a * c;
> 104:     }

You don't need separate method for compilation. First call will be executed in interpreter.

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