Host colectable GC references#55
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Replace GcRefStore integer-ID indirection with direct Java Object references in the interpreter path. Java's GC now handles liveness of Wasm GC structs, arrays, and i31 values naturally. Core design: MStack gains a lazy Object[] refs array (null until first pushRef). push()/pop() are unchanged — zero overhead for non-GC workloads. GC refs use pushRef()/popRef() to store actual WasmStruct/WasmArray/WasmI31Ref objects. Key changes: - MStack: lazy Object[] with pushRef/popRef/peekRef/clearRefsTo - StackFrame: Object[] localRefs parallel to long[] locals - WasmStruct/WasmArray: dual long[]+Object[] for fields/elements - GlobalInstance: Object refValue for ref-typed globals - TableInstance: Object[] objRefs for GC-typed tables - ValType.isGcReference(): distinguishes any-hierarchy from func/extern - StorageType.isReference()/isGcReference(): field type helpers - Instance.heapTypeMatchRef(Object,...): type matching on Objects - ConstantEvaluators: ConstantResult carries both long[] and Object - InterpreterMachine: ~30 GC instructions updated - Machine.call(int,long[],Object[]): overload for ref args - WasmI31Ref: equals/hashCode for ref.eq value equality GcRefStore is NOT yet removed — the compiler still uses it (Phase 2). Compiler GC tests are expected to fail until Phase 2.
Add callGc/applyGc methods to Machine, ExportFunction, and WasmFunctionHandle for passing real Java Objects as Wasm GC refs. Users can now receive WasmStruct/WasmArray/WasmI31Ref directly from exported functions, and Java GC manages their lifecycle. Key changes: - Machine.callGc(int, Object[]) / ExportFunction.applyGc(Object...) - InterpreterMachine overrides callGc with native Object path - WasmFunctionHandle.applyGc for GC-aware host functions - WasmExternRef can wrap either long or Object (for extern.convert_any) - ValType.isGcReference() cached during resolve() — zero-cost check - isGcReference correctly classifies concrete func types as non-GC - Table init populates objRefs for GC-typed tables - Instance.registerGcRef/gcRef/array deprecated - OpcodeImpl.boxForTable/unboxFromTable deprecated - Compiler: GC refs use Object.class, call bridge threads Object[] Compiler Phase 2: GC refs flow as Objects in generated bytecode. CompilerUtil maps GC ref types to Object.class/OBJECT_TYPE. Shaded helpers take/return Object for GC refs. Generated call_N bridges accept Object[] refArgs. BR_ON_NULL/NON_NULL checks distinguish GC (ifnull) from funcref (if_icmpeq). Non-GC code paths are completely unchanged — zero overhead.
Delete GcRefStore and its epoch-based mark-sweep collector. Wasm GC references (structs, arrays, i31) are now managed entirely by Java's garbage collector through the Object[] refs arrays in MStack, StackFrame, WasmStruct, WasmArray, GlobalInstance, and TableInstance. Changes: - Delete GcRefStore.java and GcRefStoreTest.java - Instance: remove gcRefs field, gcSafePoint() - Instance.registerGcRef/gcRef/array: throw UnsupportedOperationException - ExportFunction.apply(long...) throws on functions with GC params/returns directing users to applyGc(Object...) instead - Remove gcSafePoint() calls from Instance.Exports and initialization Users must migrate from apply(long...) to applyGc(Object...) for functions that use GC reference types (structs, arrays, i31, anyref). Non-GC functions (funcref, externref, numeric types) continue to work with apply(long...) unchanged.
Fix all remaining interpreter GC reference bugs: - MStack.popRef/peekRef: handle null refs array gracefully - REF_TEST/CAST_TEST/BR_ON_CAST: dispatch based on source type (popRef for GC refs, pop for funcref/externref) - ARRAY_GET/SET: use isGcReference() not isReference() for field type checks — funcref/externref elements stay in long[] path - ARRAY_NEW_DEFAULT: fill with REF_NULL_VALUE for non-GC ref types - ConstantEvaluators ARRAY_NEW_DEFAULT: same fix for global init - callGc: convert REF_NULL_VALUE to null for all ref return types - apply(long...): throw UnsupportedOperationException only after execution succeeds (traps propagate correctly) - WasmExternRef: can wrap Object for extern.convert_any round-trips Test generator (JavaTestGen): - Emit applyGc() for functions with GC params/returns - Null ref assertions use assertNull() for all ref types - WasmValue: toGcArgsValue, toGcResultValue, toGcAssertion methods - WasmValueType.isGcReference() helper
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WIP to fix #36