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Host colectable GC references #55

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5ebcc5a
feat: store Wasm GC references as Java Objects in the interpreter
andreaTP Jun 2, 2026
4465b16
feat: add Object-based API (callGc/applyGc) for GC reference support
andreaTP Jun 3, 2026
51ab0e0
feat: remove GcRefStore — Java GC handles all Wasm GC references
andreaTP Jun 3, 2026
ad207f4
fix: interpreter GC ref handling — all 62,144 runtime tests green
andreaTP Jun 5, 2026
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180 changes: 139 additions & 41 deletions compiler/src/main/java/run/endive/compiler/internal/Compiler.java
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72 changes: 63 additions & 9 deletions compiler/src/main/java/run/endive/compiler/internal/CompilerUtil.java
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Original file line number Diff line number Diff line change
Expand Up @@ -54,10 +54,11 @@ private CompilerUtil() {}
public static Class<?> jvmType(ValType type) {
switch (type.opcode()) {
case ValType.ID.I32:
case ValType.ID.Ref:
case ValType.ID.RefNull:
case ValType.ID.ExnRef:
return int.class;
case ValType.ID.Ref:
case ValType.ID.RefNull:
return type.isGcReference() ? Object.class : int.class;
case ValType.ID.I64:
return long.class;
case ValType.ID.F32:
Expand All @@ -69,13 +70,16 @@ public static Class<?> jvmType(ValType type) {
}
}

private static final Type OBJECT_ASM_TYPE = Type.getType(Object.class);

public static Type asmType(ValType type) {
switch (type.opcode()) {
case ValType.ID.I32:
case ValType.ID.Ref:
case ValType.ID.RefNull:
case ValType.ID.ExnRef:
return INT_TYPE;
case ValType.ID.Ref:
case ValType.ID.RefNull:
return type.isGcReference() ? OBJECT_ASM_TYPE : INT_TYPE;
case ValType.ID.I64:
return LONG_TYPE;
case ValType.ID.F32:
Expand All @@ -98,9 +102,16 @@ public static ValType localType(FunctionType type, FunctionBody body, int localI
public static void emitLongToJvm(MethodVisitor asm, ValType type) {
switch (type.opcode()) {
case ValType.ID.I32:
case ValType.ID.ExnRef:
asm.visitInsn(Opcodes.L2I);
return;
case ValType.ID.Ref:
case ValType.ID.RefNull:
case ValType.ID.ExnRef:
if (type.isGcReference()) {
// GC refs are Objects - this conversion should not be called for them
// when unboxing from long[]. They come from Object[] instead.
return;
}
asm.visitInsn(Opcodes.L2I);
return;
case ValType.ID.I64:
Expand All @@ -119,9 +130,16 @@ public static void emitLongToJvm(MethodVisitor asm, ValType type) {
public static void emitJvmToLong(MethodVisitor asm, ValType type) {
switch (type.opcode()) {
case ValType.ID.I32:
case ValType.ID.ExnRef:
asm.visitInsn(Opcodes.I2L);
return;
case ValType.ID.Ref:
case ValType.ID.RefNull:
case ValType.ID.ExnRef:
if (type.isGcReference()) {
// GC refs are Objects - this conversion should not be called for them
// when boxing into long[]. They go into Object[] instead.
return;
}
asm.visitInsn(Opcodes.I2L);
return;
case ValType.ID.I64:
Expand All @@ -138,7 +156,9 @@ public static void emitJvmToLong(MethodVisitor asm, ValType type) {
}

public static MethodType valueMethodType(List<ValType> types) {
return methodType(long[].class, jvmTypes(types));
boolean hasGcRef = types.stream().anyMatch(t -> t.isGcReference());
Class<?> returnType = hasGcRef ? Object[].class : long[].class;
return methodType(returnType, jvmTypes(types));
}

public static MethodType callIndirectMethodType(FunctionType functionType) {
Expand All @@ -161,7 +181,7 @@ public static MethodType rawMethodTypeFor(FunctionType type) {
}

public static Class<?>[] jvmTypes(List<ValType> types) {
return types.stream().map(CompilerUtil::jvmType).toArray(Class[]::new);
return types.stream().map(t -> jvmType(t)).toArray(Class[]::new);
}

public static Class<?>[] jvmParameterTypes(FunctionType type) {
Expand All @@ -175,10 +195,28 @@ public static Class<?> jvmReturnType(FunctionType type) {
case 1:
return jvmType(type.returns().get(0));
default:
// If any return value is a GC ref (Object), use Object[] instead of long[]
for (ValType ret : type.returns()) {
if (ret.isGcReference()) {
return Object[].class;
}
}
return long[].class;
}
}

/**
* Returns true if a multi-value return contains any GC references.
*/
public static boolean hasGcRefReturns(FunctionType type) {
for (ValType ret : type.returns()) {
if (ret.isGcReference()) {
return true;
}
}
return false;
}

public static Object defaultValue(ValType type) {
switch (type.opcode()) {
case ValType.ID.I32:
Expand All @@ -191,13 +229,25 @@ public static Object defaultValue(ValType type) {
return 0.0d;
case ValType.ID.Ref:
case ValType.ID.RefNull:
if (type.isGcReference()) {
return null; // GC refs use null as their default
}
return REF_NULL_VALUE;
case ValType.ID.ExnRef:
return REF_NULL_VALUE;
default:
throw new IllegalArgumentException("Unsupported ValType: " + type);
}
}

/**
* Returns true if the given ValType is a GC reference type (struct/array/i31/anyref/eqref),
* which is represented as Object on the JVM.
*/
public static boolean isGcRef(ValType type) {
return type.isGcReference();
}

public static int slotCount(ValType type) {
return slotCount(type.id());
}
Expand All @@ -220,7 +270,11 @@ public static int slotCount(long valTypeId) {
}

public static void emitPop(MethodVisitor asm, ValType type) {
asm.visitInsn(slotCount(type) == 1 ? Opcodes.POP : Opcodes.POP2);
if (type.isGcReference()) {
asm.visitInsn(Opcodes.POP); // Object refs are always 1 slot
} else {
asm.visitInsn(slotCount(type) == 1 ? Opcodes.POP : Opcodes.POP2);
}
}

public static void emitInvokeStatic(MethodVisitor asm, Method method) {
Expand Down
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