RFR: 8271203: C2: assert(iff->Opcode() == Op_If || iff->Opcode() == Op_CountedLoopEnd || iff->Opcode() == Op_RangeCheck) failed: Check this code when new subtype is added [v3]

[Yi Yang]

On Fri, 13 Aug 2021 11:41:48 GMT, Yi Yang <yyang at openjdk.org> wrote:

>> Hi, I'm trying to fix [JDK-8271203](https://bugs.openjdk.java.net/browse/JDK-8271203). It's reasonable to unswitch LongCountedLoop, so relax it.
>> 
>> ![image](https://user-images.githubusercontent.com/5010047/127302280-0faa90bb-add7-4639-8c63-49668901f267.png)
>
> Yi Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   package

JTREG TEST:


public class Reduced {
    static int iArrFld[] = new int[400];

    public static void main(String[] strArr) {
        for (int i = 0; i < 10; i++) {
            test();
        }
    }

    static void test() {
        int i = 56, i2 = 22257;

        do {
            do {
                int i24 = 1;
                while (++i24 < 2) {
                }
                for (long l1 = i; l1 < 2; ++l1) {
                    iArrFld[0] += 5;
                }
            } while ((i2 -= 2) > 0);  //line 22
            for (long l3 = 8; l3 < 194; ++l3) { // line 23
            }
        } while (--i > 0);  //line25
    }
}

Well, the above CFG is corresponding to the last step(before beautify loops, [loop.xml.log](https://github.com/openjdk/jdk/files/6982404/loop.xml.log) ) before crash. I haven't learned about loopopts in C2 yet,  it looks like B9 and B19-22 are refer to the same loop(`do{...} while ((i2 -= 2) > 0); `), the above CFG looks like:

 static void test() {
        int i = 56, i2 = 22257;

        do {
             if (xx) {
               do{ ... } while ((i2 -= 2) > 0); 
             } else {
               do{ ... } while ((i2 -= 2) > 0); 
             }
            for (long l3 = 8; l3 < 194; ++l3) { // line 23
            }
        } while (--i > 0);  //line25
    }

...maybe that's not true.

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

PR: https://git.openjdk.java.net/jdk/pull/4920