oracle/graal · error · IOException

Unknown replay assumption kind

Error message

Unknown replay assumption kind

What it means

Thrown when decoding an ASSUMPTION_TAG payload: the nested assumption-kind int matches none of the known assumption kinds (leaf type, concrete subtype, concrete method, call site target, delayed-deserialization variants, ...). The codec cannot reconstruct the Assumptions.Assumption and throws IOException 'Unknown replay assumption kind'. Like other 'unknown replay kind' errors it points to version skew or corruption.

Source

Thrown at compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/hotspot/replaycomp/BinaryReplayCodec.java:935

            case ASSUMPTION_TAG -> switch (in.readPackedUnsignedInt()) {
                case ASSUMPTION_NO_FINALIZABLE_SUBCLASS ->
                    new Assumptions.NoFinalizableSubclass((ResolvedJavaType) readValue(in, state));
                case ASSUMPTION_CONCRETE_SUBTYPE -> {
                    ResolvedJavaType subtype = (ResolvedJavaType) readValue(in, state);
                    ResolvedJavaType context = (ResolvedJavaType) readValue(in, state);
                    yield new DelayedDeserializationObject.ConcreteSubtypeWithDelayedDeserialization(context, subtype);
                }
                case ASSUMPTION_LEAF_TYPE ->
                    new DelayedDeserializationObject.LeafTypeWithDelayedDeserialization((ResolvedJavaType) readValue(in, state));
                case ASSUMPTION_CONCRETE_METHOD -> {
                    ResolvedJavaType context = (ResolvedJavaType) readValue(in, state);
                    ResolvedJavaMethod method = (ResolvedJavaMethod) readValue(in, state);
                    ResolvedJavaMethod impl = (ResolvedJavaMethod) readValue(in, state);
                    yield new Assumptions.ConcreteMethod(method, context, impl);
                }
                case ASSUMPTION_CALL_SITE_TARGET_VALUE ->
                    new Assumptions.CallSiteTargetValue((JavaConstant) readValue(in, state), (JavaConstant) readValue(in, state));
                default -> throw new IOException("Unknown replay assumption kind");
            };
            case UNRESOLVED_JAVA_TYPE_TAG ->
                UnresolvedJavaType.create(requireNonNullString(readStringReference(in, state), "unresolved type name"));
            case UNRESOLVED_JAVA_METHOD_TAG ->
                new UnresolvedJavaMethod(requireNonNullString(readStringReference(in, state), "unresolved method name"),
                                (Signature) readValue(in, state), (JavaType) readValue(in, state));
            case UNRESOLVED_JAVA_FIELD_TAG -> {
                String name = requireNonNullString(readStringReference(in, state), "unresolved field name");
                JavaType type = (JavaType) readValue(in, state);
                JavaType holder = (JavaType) readValue(in, state);
                yield new UnresolvedJavaField(holder, name, type);
            }
            case PRIMITIVE_CONSTANT_TAG -> {
                long raw = in.readPackedSignedLong();
                JavaKind kind = (JavaKind) readValue(in, state);
                yield JavaConstant.forPrimitive(kind, raw);
            }
            case FOREIGN_CALL_DESCRIPTOR_TAG ->

View on GitHub (pinned to a66e9ccd1d)

Solutions

  1. Regenerate the replay file with the same build that will replay it
  2. If you added a new Assumptions.Assumption subtype, add both the writer kind constant and the reader case, and bump VERSION
  3. Validate the file version header before parsing to fail fast

Example fix

// before
case ASSUMPTION_TAG -> switch (in.readPackedUnsignedInt()) {
    ...
    default -> throw new IOException("Unknown replay assumption kind");
};

// after
// add the new kind symmetrically on write and read sides
case ASSUMPTION_MY_KIND -> new Assumptions.MyKind(...);
Defensive patterns

Strategy: try-catch

Try / catch

try {
    result = codec.readReplay(in);
} catch (IOException e) {
    if ("Unknown replay assumption kind".equals(e.getMessage())) {
        // reader older than writer: re-record or upgrade the reader build
    } else throw e;
}

Prevention

When it happens

Trigger: Replaying a file written by a build with new assumption kinds (the writer emitted a kind constant this reader does not define); corrupted stream misaligning the packed assumption-kind int.

Common situations: Cross-version replay between GraalVM builds whose Assumptions subclasses differ; extending the assumptions model without updating the binary codec.

Related errors

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/df47e3fddc597e28. Report an issue: GitHub.