Debug blockchain reference test 455

[gauravahuja]

Steps to reproduce the OOM error:

1. Checkout this branch
2. ./gradlew generateBlockchainReferenceTests
3. In BlockchainReferenceTest_455.java set private static final String[] TEST_CONFIG_FILE_DIR_PATH = { "BlockchainTests/GeneralStateTests/stTimeConsuming/static_Call50000_sha256.json" };
4. Run BlockchainReferenceTest_455 in the IDE or in terminal ./gradlew reference-tests:referenceBlockchainTests --tests "BlockchainReferenceTest_455"

The test case static_Call50000_sha256_* in BlockchainReferenceTest_455 causes the JVM to run out of heap space. Increasing the heap to 24G worked for me.

In this test ZkTracer.traceContextEnter is invoked 50000 times (Don't know why), and inside this method this.hub.traceContextEnter(frame) consumes up all the heap.

[ahamlat]

Most of the objects in memory are related to the MMU module, which is coherent with SHA256 test, but I see also that Optional takes non negligible amount of memory (almost 5 GiB), and we should get rid of them.
Here are some fields that we need change and remove Optional (From the heap dump)

In MmuCall.java

  private Optional<Bytes> sourceRamBytes = Optional.empty();
  private Optional<Bytes> targetRamBytes = Optional.empty();
  private Optional<Bytes> exoBytes = Optional.empty();

In CallSection.java

  public Optional<Address> precompileAddress;

in AccountFragment.java

  private final Optional<Bytes> addressToTrim;