RFR: 8347997: assert(false) failed: EA: missing memory path

[Alan Bateman]

On Fri, 24 Jan 2025 00:07:43 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> C2's Escape Analysis does not recognize pattern where one input of memory `Phi` node is `MergeMem` node and an other is RAW store. This pattern is created by Continuation pinning intrinsic. As result EA complains about strange memory graph.
> 
> I suggest to add second `MergeMem` between Store and Phi nodes by calling `reset_memory()`. EA recognize such patter and removes allocations.
> 
> I checked generated assembler pinning code and it is the same as before. The only difference in the test is eliminated allocations.
> 
> I moved Uncommon code up to avoid resetting memory - it is already done at the beginning of this intrinsic code.
> 
> We should not use `uncommon_trap_exact()` for `Deoptimization::Action_none` - It is used for other actions to prevent changing them to `Action_none`.
> 
> Tested tier1-5, hs-xcomp, hs-comp-stress
> Added new regression test based on reproducer from bug report.

If you want, the reproducer can be simplified to just invoke pin/unpin, avoids needing the method handle code to invoke them reflectively, e.g.


import jdk.internal.vm.Continuation;

    static class FailsEA {
        final Object o;

        public FailsEA() throws Throwable {
            o = new Object();
            Continuation.pin();
            Continuation.unpin();
        }
    }

    static class Crashes {
        final Object o;

        public Crashes() throws Throwable {
            Continuation.pin();
            Continuation.unpin();
            o = new Object();
        }
    }


If you add `@modules java.base/jdk.internal.vm` to the test description then jtreg will compile and run the test with this package exported, no need be open the package with the `@run` tag.

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PR Comment: https://git.openjdk.org/jdk/pull/23284#issuecomment-2611857331