RFR: 8273454: C2: Transform (-a)*(-b) into a*b [v4]

[Zhengyu Gu]

On Tue, 14 Sep 2021 07:05:40 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix node in place instead of creating new node
>
> test/hotspot/jtreg/compiler/integerArithmetic/TestNegMultiply.java line 45:
> 
>> 43:     private static void testInt(int a, int b) {
>> 44:         int expected = (-a) * (-b);
>> 45:         for (int i = 0; i < 20_000; i++) {
> 
> Why do you need a second loop in here? It's sufficient to set `TEST_COUNT` high enough to trigger compilation. I would suggest something like this:
> 
> 
> private static int testInt(int a, int b) {
>     return (-a) * (-b);
> }
> 
> private static void runIntTests() {
>     for (int i = 0; i < TEST_COUNT; i++) {
>         int a = random.nextInt();
>         int b = random.nextInt();
>         int res = testInt(a, b);
>         Asserts.assertEQ(a * b, res);
>     }
> }
> 
> 
> And then run with `-XX:CompileCommand=dontinline,TestNegMultiply::test*`. No need to disable OnStackReplacement.

The inner loop ensures that all tests hit JIT-ed version. If the transformation is broken, I would prefer the test fails for the very first iteration, instead of somewhere in the middle.

I refactored the code to remove inner loop.

Also, fixed command option.

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