rework bytecode and stacks

Instructions now take their static arguments in the bytecode directly
instead of from the stack. The return address is now moved into a
separate frame stack. That means the only thing in the main stack is now
variable references. That means we can mark every variable which is
currently on the stack during a GC; even variables which aren't referred
to from a namespace.

As a result, a GC can happen before or after any instruction without
having to worry. The VM should also be faster, and the bytecode should
be smaller, due to fewer instructions.

include/lang2/bytecode.h

@@ -11,19 +11,6 @@ enum l2_opcode {
 	 */
 	L2_OP_NOP,
 
-	/*
-	 * Push a value to the stack.
-	 * Push <word>
-	 */
-	L2_OP_PUSH,
-
-	/*
-	 * Push a value to the stack.
-	 * Push <word1>
-	 * Push <word2>
-	 */
-	L2_OP_PUSH_2,
-
 	/*
 	 * Discard the top element from the stack.
 	 * Pop <word>
@@ -53,94 +40,80 @@ enum l2_opcode {
 	L2_OP_ADD,
 
 	/*
-	 * Call a function.
-	 * Pop <argc>
-	 * Pop argc times
+	 * Call a function; func_call <argc>
+	 * Pop <argc> times
 	 * Pop <func>
-	 * Push <iptr> + 1
 	 * Push array with args
 	 * Call <func>
+	 * (Before returning, the function will push a return value onto the stack)
 	 */
 	L2_OP_FUNC_CALL,
 
 	/*
-	 * Jump relative.
-	 * Pop <word>
-	 * Jump <word> words forwards
+	 * Jump relative; rjmp <count>
+	 * Jump <count> words forwards
 	 */
 	L2_OP_RJMP,
 
 	/*
-	 * Look up a value from the current stack frame.
-	 * Pop <word>
-	 * Find <val> in stack frame using <word>
+	 * Look up a value from the current stack frame; stack_frame_lookup <key>
+	 * Find <val> in stack frame using <key>
 	 * Push <val>
 	 */
 	L2_OP_STACK_FRAME_LOOKUP,
 
 	/*
-	 * Set a value in the current stack frame.
-	 * Pop <key>
+	 * Set a value in the current stack frame; stack_frame_set <key>
 	 * Read <val>
-	 * Assign <val> to stack frame
+	 * Assign <val> to stack frame at <key>
 	 */
 	L2_OP_STACK_FRAME_SET,
 
 	/*
-	 * Replace a value on the stack.
-	 * Pop <key>
+	 * Replace a value on the stack; stack_frame_replace <key>
 	 * Read <val>
-	 * Assign <val> to stack frame
+	 * Assign <val> to stack frame at <key>
 	 */
 	L2_OP_STACK_FRAME_REPLACE,
 
 	/*
 	 * Return from a function.
-	 * NSPop
+	 * FSPop
 	 * Pop (discard args array)
-	 * Pop <word>
-	 * Jump to <word>
+	 * Jump to <return address>
 	 */
 	L2_OP_RET,
 
 	/*
-	 * Allocate an atom from one word.
-	 * Pop <word>
-	 * Alloc integer <var> from <word>
+	 * Put a reference to none at the top of the stack.
+	 * Push 0
+	 */
+	L2_OP_ALLOC_NONE,
+
+	/*
+	 * Allocate an atom from one word; alloc_atom <word>
+	 * Alloc atom <var> from <word>
 	 * Push <var>
 	 */
 	L2_OP_ALLOC_ATOM,
 
 	/*
-	 * Allocate a real from two words.
-	 * Pop <high>
-	 * Pop <low>
+	 * Allocate a real from two words; alloc_real <high> <low>
 	 * Alloc real <var> from <high> << 32 | <low>
 	 * Push <var>
 	 */
 	L2_OP_ALLOC_REAL,
 
 	/*
-	 * Allocate a buffer from static data.
-	 * Pop <word1>
-	 * Pop <word2>
-	 * Alloc buffer <var> with length=<word1>, offset=<word2>
+	 * Allocate a buffer from static data; alloc_buffer_static <length> <offset>
+	 * Alloc buffer <var> with <length> and <offset>
 	 * Push <var>
 	 */
 	L2_OP_ALLOC_BUFFER_STATIC,
 
 	/*
-	 * Allocate a zeroed buffer.
-	 * Pop <word>
-	 * Alloc buffer <var> with length=<word>
-	 * Push <var>
-	 */
-	L2_OP_ALLOC_BUFFER_ZERO,
-
-	/*
-	 * Allocate an array.
-	 * Pop <count>
-	 * Pop count times
+	 * Allocate an array; <count>
+	 * Pop <count> times
 	 * Alloc array <var>
 	 * Push <var>
 	 */
@@ -154,16 +127,14 @@ enum l2_opcode {
 	L2_OP_ALLOC_NAMESPACE,
 
 	/*
-	 * Allocate a function.
-	 * Pop <word>
+	 * Allocate a function; alloc_function <pos>
 	 * Alloc function <var> pointing to location <word>
 	 * Push <var>
 	 */
 	L2_OP_ALLOC_FUNCTION,
 
 	/*
-	 * Set a namespace's name to a value.
-	 * Pop <key>
+	 * Set a namespace's name to a value; namespace_set <key>
 	 * Read <val>
 	 * Read <ns>
 	 * Assign <val> to <ns[<key>]>
@@ -171,29 +142,26 @@ enum l2_opcode {
 	L2_OP_NAMESPACE_SET,
 
 	/*
-	 * Lookup a value from a namespace.
-	 * Pop <key>
+	 * Lookup a value from a namespace; namespace_lookup <key>
 	 * Pop <ns>
 	 * Push <ns[<key>]>
 	 */
 	L2_OP_NAMESPACE_LOOKUP,
 
 	/*
-	 * Look up a value from an array.
-	 * Pop <key>
-	 * Read <val>
-	 * Read <arr>
+	 * Look up a value from an array; direct_array_lookup <key>
+	 * Pop <val>
+	 * Pop <arr>
 	 * Assign <val> to <arr[<key>]>
 	 */
-	L2_OP_DIRECT_ARRAY_LOOKUP,
+	L2_OP_ARRAY_LOOKUP,
 
 	/*
-	 * Set a value in an array.
-	 * Pop <key>
+	 * Set a value in an array; direct_array_set <key>
 	 * Read <arr>
 	 * Push <arr[<key>]>
 	 */
-	L2_OP_DIRECT_ARRAY_SET,
+	L2_OP_ARRAY_SET,
 
 	/*
 	 * Halt execution.

include/lang2/gen/gen.h

@@ -26,8 +26,8 @@ void l2_gen_halt(struct l2_generator *gen);
 void l2_gen_rjmp(struct l2_generator *gen, l2_word len);
 void l2_gen_pop(struct l2_generator *gen);
 void l2_gen_swap_pop(struct l2_generator *gen);
-void l2_gen_push(struct l2_generator *gen, l2_word word);
 void l2_gen_ret(struct l2_generator *gen);
+void l2_gen_none(struct l2_generator *gen);
 void l2_gen_number(struct l2_generator *gen, double num);
 void l2_gen_string(struct l2_generator *gen, char **str);
 void l2_gen_atom(struct l2_generator *gen, char **ident);
@@ -36,11 +36,11 @@ void l2_gen_array(struct l2_generator *gen, l2_word count);
 void l2_gen_namespace(struct l2_generator *gen);
 void l2_gen_namespace_set(struct l2_generator *gen, char **ident);
 void l2_gen_namespace_lookup(struct l2_generator *gen, char **ident);
-void l2_gen_direct_array_lookup(struct l2_generator *gen, int number);
-void l2_gen_direct_array_set(struct l2_generator *gen, int number);
+void l2_gen_array_lookup(struct l2_generator *gen, int number);
+void l2_gen_array_set(struct l2_generator *gen, int number);
 void l2_gen_stack_frame_lookup(struct l2_generator *gen, char **ident);
 void l2_gen_stack_frame_set(struct l2_generator *gen, char **ident);
 void l2_gen_stack_frame_replace(struct l2_generator *gen, char **ident);
-void l2_gen_func_call(struct l2_generator *gen);
+void l2_gen_func_call(struct l2_generator *gen, l2_word argc);
 
 #endif

include/lang2/vm/print.h

@@ -7,7 +7,7 @@ void l2_vm_print_val(struct l2_vm_value *val);
 void l2_vm_print_state(struct l2_vm *vm);
 void l2_vm_print_heap(struct l2_vm *vm);
 void l2_vm_print_stack(struct l2_vm *vm);
-void l2_vm_print_nstack(struct l2_vm *vm);
+void l2_vm_print_fstack(struct l2_vm *vm);
 
 void l2_vm_print_op(l2_word *ops, size_t opcount, size_t *ptr);
 void l2_vm_print_bytecode(l2_word *ops, size_t opcount);

include/lang2/vm/vm.h

@@ -75,6 +75,11 @@ struct l2_vm_namespace {
 	l2_word data[];
 };
 
+struct l2_vm_stack_frame {
+	l2_word namespace;
+	l2_word retptr;
+};
+
 l2_word l2_vm_namespace_get(struct l2_vm *vm, struct l2_vm_value *ns, l2_word key);
 void l2_vm_namespace_set(struct l2_vm_value *ns, l2_word key, l2_word val);
 int l2_vm_namespace_replace(struct l2_vm *vm, struct l2_vm_value *ns, l2_word key, l2_word val);
@@ -94,8 +99,8 @@ struct l2_vm {
 	l2_word stack[1024];
 	l2_word sptr;
 
-	l2_word nstack[1024];
-	l2_word nsptr;
+	struct l2_vm_stack_frame fstack[1024];
+	l2_word fsptr;
 };
 
 void l2_vm_init(struct l2_vm *vm, l2_word *ops, size_t opcount);

lib/gen/gen.c

@@ -36,9 +36,8 @@ void l2_gen_halt(struct l2_generator *gen) {
 }
 
 void l2_gen_rjmp(struct l2_generator *gen, l2_word len) {
-	put(gen, L2_OP_PUSH);
-	put(gen, len);
 	put(gen, L2_OP_RJMP);
+	put(gen, len);
 }
 
 void l2_gen_pop(struct l2_generator *gen) {
@@ -49,29 +48,26 @@ void l2_gen_swap_pop(struct l2_generator *gen) {
 	put(gen, L2_OP_SWAP_POP);
 }
 
-void l2_gen_push(struct l2_generator *gen, l2_word word) {
-	put(gen, L2_OP_PUSH);
-	put(gen, word);
-}
-
 void l2_gen_ret(struct l2_generator *gen) {
 	put(gen, L2_OP_RET);
 }
 
+void l2_gen_none(struct l2_generator *gen) {
+	put(gen, L2_OP_ALLOC_NONE);
+}
+
 void l2_gen_number(struct l2_generator *gen, double num) {
 	uint64_t n;
 	memcpy(&n, &num, sizeof(num));
-	put(gen, L2_OP_PUSH_2);
-	put(gen, n);
-	put(gen, n >> 32);
 	put(gen, L2_OP_ALLOC_REAL);
+	put(gen, n >> 32);
+	put(gen, n);
 }
 
 void l2_gen_atom(struct l2_generator *gen, char **str) {
 	size_t id = l2_strset_put(&gen->atomset, str);
-	put(gen, L2_OP_PUSH);
-	put(gen, id);
 	put(gen, L2_OP_ALLOC_ATOM);
+	put(gen, id);
 }
 
 void l2_gen_string(struct l2_generator *gen, char **str) {
@@ -83,9 +79,8 @@ void l2_gen_string(struct l2_generator *gen, char **str) {
 			aligned += sizeof(l2_word) - (aligned % sizeof(l2_word));
 		}
 
-		put(gen, L2_OP_PUSH);
-		put(gen, aligned / sizeof(l2_word));
 		put(gen, L2_OP_RJMP);
+		put(gen, aligned / sizeof(l2_word));
 		l2_word pos = gen->pos;
 
 		gen->pos += aligned / sizeof(l2_word);
@@ -99,30 +94,26 @@ void l2_gen_string(struct l2_generator *gen, char **str) {
 		gen->strings[id - 1].length = len;
 		gen->strings[id - 1].pos = pos;
 
-		put(gen, L2_OP_PUSH_2);
-		put(gen, pos);
-		put(gen, len);
 		put(gen, L2_OP_ALLOC_BUFFER_STATIC);
+		put(gen, len);
+		put(gen, pos);
 	} else {
 		free(*str);
 		struct l2_generator_string *s = &gen->strings[id - 1];
-		put(gen, L2_OP_PUSH_2);
-		put(gen, s->pos);
-		put(gen, s->length);
 		put(gen, L2_OP_ALLOC_BUFFER_STATIC);
+		put(gen, s->length);
+		put(gen, s->pos);
 	}
 }
 
 void l2_gen_function(struct l2_generator *gen, l2_word pos) {
-	put(gen, L2_OP_PUSH);
-	put(gen, pos);
 	put(gen, L2_OP_ALLOC_FUNCTION);
+	put(gen, pos);
 }
 
 void l2_gen_array(struct l2_generator *gen, l2_word count) {
-	put(gen, L2_OP_PUSH);
-	put(gen, count);
 	put(gen, L2_OP_ALLOC_ARRAY);
+	put(gen, count);
 }
 
 void l2_gen_namespace(struct l2_generator *gen) {
@@ -131,51 +122,45 @@ void l2_gen_namespace(struct l2_generator *gen) {
 
 void l2_gen_namespace_set(struct l2_generator *gen, char **ident) {
 	size_t atom_id = l2_strset_put(&gen->atomset, ident);
-	put(gen, L2_OP_PUSH);
-	put(gen, atom_id);
 	put(gen, L2_OP_NAMESPACE_SET);
+	put(gen, atom_id);
 }
 
 void l2_gen_namespace_lookup(struct l2_generator *gen, char **ident) {
 	size_t atom_id = l2_strset_put(&gen->atomset, ident);
-	put(gen, L2_OP_PUSH);
-	put(gen, atom_id);
 	put(gen, L2_OP_NAMESPACE_LOOKUP);
+	put(gen, atom_id);
 }
 
-void l2_gen_direct_array_lookup(struct l2_generator *gen, int number) {
-	put(gen, L2_OP_PUSH);
+void l2_gen_array_lookup(struct l2_generator *gen, int number) {
+	put(gen, L2_OP_ARRAY_LOOKUP);
 	put(gen, number);
-	put(gen, L2_OP_DIRECT_ARRAY_LOOKUP);
 }
 
-void l2_gen_direct_array_set(struct l2_generator *gen, int number) {
-	put(gen, L2_OP_PUSH);
+void l2_gen_array_set(struct l2_generator *gen, int number) {
+	put(gen, L2_OP_ARRAY_SET);
 	put(gen, number);
-	put(gen, L2_OP_DIRECT_ARRAY_SET);
 }
 
 void l2_gen_stack_frame_lookup(struct l2_generator *gen, char **ident) {
 	size_t atom_id = l2_strset_put(&gen->atomset, ident);
-	put(gen, L2_OP_PUSH);
-	put(gen, atom_id);
 	put(gen, L2_OP_STACK_FRAME_LOOKUP);
+	put(gen, atom_id);
 }
 
 void l2_gen_stack_frame_set(struct l2_generator *gen, char **ident) {
 	size_t atom_id = l2_strset_put(&gen->atomset, ident);
-	put(gen, L2_OP_PUSH);
-	put(gen, atom_id);
 	put(gen, L2_OP_STACK_FRAME_SET);
+	put(gen, atom_id);
 }
 
 void l2_gen_stack_frame_replace(struct l2_generator *gen, char **ident) {
 	size_t atom_id = l2_strset_put(&gen->atomset, ident);
-	put(gen, L2_OP_PUSH);
-	put(gen, atom_id);
 	put(gen, L2_OP_STACK_FRAME_REPLACE);
+	put(gen, atom_id);
 }
 
-void l2_gen_func_call(struct l2_generator *gen) {
+void l2_gen_func_call(struct l2_generator *gen, l2_word argc) {
 	put(gen, L2_OP_FUNC_CALL);
+	put(gen, argc);
 }

lib/parse/parse.c

@@ -101,7 +101,7 @@ static int parse_function_literal_impl(
 
 	// All functions must put _something_ on the stack
 	if (first) {
-		l2_gen_push(gen, 0);
+		l2_gen_none(gen);
 	}
 
 	l2_gen_ret(gen);
@@ -119,7 +119,7 @@ static int parse_function_literal(
 	w.w.write = l2_io_mem_write;
 	gen->writer.w = &w.w;
 
-	// Generates three words; PUSH, 0, RJMP
+	// Generates two words; RJMP, 0
 	l2_gen_rjmp(gen, 0);
 
 	l2_word pos = gen->pos;
@@ -138,8 +138,8 @@ static int parse_function_literal(
 
 	// Due to the earlier gen_rjmp, the second word will be the argument to RJMP.
 	// Need to set it properly to skip the function body.
-	// The '- 3' is because we don't skip the PUSH, <count>, RJMP sequence.
-	ops[1] = opcount - 3;
+	// The '- 2' is because we don't skip the RJMP, <count> sequence.
+	ops[1] = opcount - 2;
 
 	l2_bufio_put_n(&gen->writer, ops, opcount * sizeof(l2_word));
 	free(w.mem);
@@ -284,8 +284,7 @@ static int parse_arg_level_expression(
 			l2_lexer_consume(lexer); // '('
 			l2_lexer_consume(lexer); // ')'
 
-			l2_gen_push(gen, 0);
-			l2_gen_func_call(gen);
+			l2_gen_func_call(gen, 0);
 		} else if (
 				tok->kind == L2_TOK_PERIOD && tok2->kind == L2_TOK_IDENT &&
 				tok3->kind == L2_TOK_EQUALS) {
@@ -320,14 +319,14 @@ static int parse_arg_level_expression(
 				return -1;
 			}
 
-			l2_gen_direct_array_set(gen, number);
+			l2_gen_array_set(gen, number);
 			l2_gen_swap_pop(gen);
 		} else if (tok->kind == L2_TOK_DOT_NUMBER) {
 			l2_trace_scope("direct array lookup");
 			int number = tok->v.integer;
 			l2_lexer_consume(lexer); // dot-number
 
-			l2_gen_direct_array_lookup(gen, number);
+			l2_gen_array_lookup(gen, number);
 		} else {
 			break;
 		}
@@ -351,8 +350,7 @@ static int parse_func_call_after_base(
 	} while (!tok_is_end(l2_lexer_peek(lexer, 1)));
 
 	// The 'argc' previous expressions were arguments, the one before that was the function
-	l2_gen_push(gen, argc);
-	l2_gen_func_call(gen);
+	l2_gen_func_call(gen, argc);
 
 	return 0;
 }

lib/vm/print.c

@@ -78,8 +78,8 @@ void l2_vm_print_state(struct l2_vm *vm) {
 	l2_vm_print_stack(vm);
 	printf("Heap:\n");
 	l2_vm_print_heap(vm);
-	printf("Namespace Stack:\n");
-	l2_vm_print_nstack(vm);
+	printf("Frame Stack:\n");
+	l2_vm_print_fstack(vm);
 }
 
 void l2_vm_print_heap(struct l2_vm *vm) {
@@ -97,9 +97,9 @@ void l2_vm_print_stack(struct l2_vm *vm) {
 	}
 }
 
-void l2_vm_print_nstack(struct l2_vm *vm) {
-	for (l2_word i = 0; i < vm->nsptr; ++i) {
-		printf("  %i: %i\n", i, vm->nstack[i]);
+void l2_vm_print_fstack(struct l2_vm *vm) {
+	for (l2_word i = 0; i < vm->fsptr; ++i) {
+		printf("  %i: %i, ret %i\n", i, vm->fstack[i].namespace, vm->fstack[i].retptr);
 	}
 }
 
@@ -119,20 +119,6 @@ void l2_vm_print_op(l2_word *ops, size_t opcount, size_t *ptr) {
 		printf("NOP\n");
 		return;
 
-	case L2_OP_PUSH:
-		printf("PUSH ");
-		print_op_num(ops, opcount, (*ptr)++);
-		printf("\n");
-		return;
-
-	case L2_OP_PUSH_2:
-		printf("PUSH2 ");
-		print_op_num(ops, opcount, (*ptr)++);
-		printf(" ");
-		print_op_num(ops, opcount, (*ptr)++);
-		printf("\n");
-		return;
-
 	case L2_OP_POP:
 		printf("POP\n");
 		return;
@@ -150,47 +136,55 @@ void l2_vm_print_op(l2_word *ops, size_t opcount, size_t *ptr) {
 		return;
 
 	case L2_OP_FUNC_CALL:
-		printf("FUNC_CALL\n");
+		printf("FUNC_CALL %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_RJMP:
-		printf("RJMP\n");
+		printf("RJMP %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_STACK_FRAME_LOOKUP:
-		printf("STACK_FRAME_LOOKUP\n");
+		printf("STACK_FRAME_LOOKUP %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_STACK_FRAME_SET:
-		printf("STACK_FRAME_SET\n");
+		printf("STACK_FRAME_SET %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_STACK_FRAME_REPLACE:
-		printf("STACK_FRAME_REPLACE\n");
+		printf("STACK_FRAME_REPLACE %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_RET:
 		printf("RET\n");
 		return;
 
+	case L2_OP_ALLOC_NONE:
+		printf("ALLOC_NONE\n");
+		return;
+
 	case L2_OP_ALLOC_ATOM:
-		printf("ALLOC_ATOM\n");
+		printf("ALLOC_ATOM %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_ALLOC_REAL:
-		printf("ALLOC_REAL\n");
+		{
+			l2_word w1 = ops[(*ptr)++];
+			l2_word w2 = ops[(*ptr)++];
+			printf("ALLOC_REAL %08x %08x\n", w1, w2);
+		}
 		return;
 
 	case L2_OP_ALLOC_BUFFER_STATIC:
-		printf("ALLOC_BUFFER_STATIC\n");
-		return;
-
-	case L2_OP_ALLOC_BUFFER_ZERO:
-		printf("ALLOC_BUFFER_ZERO\n");
+		{
+			l2_word w1 = ops[(*ptr)++];
+			l2_word w2 = ops[(*ptr)++];
+			printf("ALLOC_BUFFER_STATIC %08x %08x\n", w1, w2);
+		}
 		return;
 
 	case L2_OP_ALLOC_ARRAY:
-		printf("ALLOC_ARRAY\n");
+		printf("ALLOC_ARRAY %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_ALLOC_NAMESPACE:
@@ -198,23 +192,23 @@ void l2_vm_print_op(l2_word *ops, size_t opcount, size_t *ptr) {
 		return;
 
 	case L2_OP_ALLOC_FUNCTION:
-		printf("ALLOC_FUNCTION\n");
+		printf("ALLOC_FUNCTION %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_NAMESPACE_SET:
-		printf("NAMESPACE_SET\n");
+		printf("NAMESPACE_SET %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_NAMESPACE_LOOKUP:
-		printf("NAMESPACE_LOOKUP\n");
+		printf("NAMESPACE_LOOKUP %08x\n", ops[(*ptr)++]);
 		return;
 
-	case L2_OP_DIRECT_ARRAY_LOOKUP:
-		printf("DIRECT_ARRAY_LOOKUP\n");
+	case L2_OP_ARRAY_LOOKUP:
+		printf("ARRAY_LOOKUP %08x\n", ops[(*ptr)++]);
 		return;
 
-	case L2_OP_DIRECT_ARRAY_SET:
-		printf("DIRECT_ARRAY_SET\n");
+	case L2_OP_ARRAY_SET:
+		printf("ARRAY_SET %08x\n", ops[(*ptr)++]);
 		return;
 
 	case L2_OP_HALT:

lib/vm/vm.c

@@ -71,6 +71,10 @@ static void gc_mark_array(struct l2_vm *vm, struct l2_vm_value *val) {
 }
 
 static void gc_mark_namespace(struct l2_vm *vm, struct l2_vm_value *val) {
+	if (val->extra.ns_parent != 0) {
+		gc_mark(vm, val->extra.ns_parent);
+	}
+
 	if (val->ns == NULL) {
 		return;
 	}
@@ -83,10 +87,6 @@ static void gc_mark_namespace(struct l2_vm *vm, struct l2_vm_value *val) {
 
 		gc_mark(vm, val->ns->data[val->ns->size + i]);
 	}
-
-	if (val->extra.ns_parent != 0) {
-		gc_mark(vm, val->extra.ns_parent);
-	}
 }
 
 static void gc_free(struct l2_vm *vm, l2_word id) {
@@ -140,7 +140,7 @@ void l2_vm_init(struct l2_vm *vm, l2_word *ops, size_t opcount) {
 	vm->opcount = opcount;
 	vm->iptr = 0;
 	vm->sptr = 0;
-	vm->nsptr = 0;
+	vm->fsptr = 0;
 
 	vm->values = NULL;
 	vm->valuessize = 0;
@@ -156,14 +156,18 @@ void l2_vm_init(struct l2_vm *vm, l2_word *ops, size_t opcount) {
 	vm->values[builtins].extra.ns_parent = 0;
 	vm->values[builtins].ns = NULL; // Will be allocated on first insert
 	vm->values[builtins].flags = L2_VAL_TYPE_NAMESPACE;
-	vm->nstack[vm->nsptr++] = builtins;
+	vm->fstack[vm->fsptr].namespace = builtins;
+	vm->fstack[vm->fsptr].retptr = 0;
+	vm->fsptr += 1;
 
 	// Need to allocate a root namespace
 	l2_word root = alloc_val(vm);
 	vm->values[root].extra.ns_parent = builtins;
 	vm->values[root].ns = NULL;
 	vm->values[root].flags = L2_VAL_TYPE_NAMESPACE;
-	vm->nstack[vm->nsptr++] = root;
+	vm->fstack[vm->fsptr].namespace = root;
+	vm->fstack[vm->fsptr].retptr = 0;
+	vm->fsptr += 1;
 
 	// Define a C function variable for every builtin
 	l2_word id;
@@ -199,10 +203,12 @@ void l2_vm_free(struct l2_vm *vm) {
 }
 
 size_t l2_vm_gc(struct l2_vm *vm) {
-	for (l2_word nsptr = 0; nsptr < vm->nsptr; ++nsptr) {
-		struct l2_vm_value *val = &vm->values[vm->nstack[nsptr]];
-		val->flags |= L2_VAL_MARKED;
-		gc_mark_namespace(vm, val);
+	for (l2_word sptr = 0; sptr < vm->sptr; ++sptr) {
+		gc_mark(vm, vm->stack[sptr]);
+	}
+
+	for (l2_word fsptr = 0; fsptr < vm->fsptr; ++fsptr) {
+		gc_mark(vm, vm->fstack[fsptr].namespace);
 	}
 
 	return gc_sweep(vm);
@@ -222,19 +228,6 @@ void l2_vm_step(struct l2_vm *vm) {
 	case L2_OP_NOP:
 		break;
 
-	case L2_OP_PUSH:
-		vm->stack[vm->sptr] = vm->ops[vm->iptr];
-		vm->sptr += 1;
-		vm->iptr += 1;
-		break;
-
-	case L2_OP_PUSH_2:
-		vm->stack[vm->sptr] = vm->ops[vm->iptr];
-		vm->stack[vm->sptr + 1] = vm->ops[vm->iptr + 1];
-		vm->sptr += 2;
-		vm->iptr += 2;
-		break;
-
 	case L2_OP_POP:
 		vm->sptr -= 1;
 		break;
@@ -256,7 +249,7 @@ void l2_vm_step(struct l2_vm *vm) {
 
 	case L2_OP_FUNC_CALL:
 		{
-			l2_word argc = vm->stack[--vm->sptr];
+			l2_word argc = vm->ops[vm->iptr++];
 
 			l2_word arr_id = alloc_val(vm);
 			vm->values[arr_id].flags = L2_VAL_TYPE_ARRAY;
@@ -288,7 +281,6 @@ void l2_vm_step(struct l2_vm *vm) {
 				break;
 			}
 
-			vm->stack[vm->sptr++] = vm->iptr;
 			vm->stack[vm->sptr++] = arr_id;
 
 			l2_word ns_id = alloc_val(vm);
@@ -296,40 +288,40 @@ void l2_vm_step(struct l2_vm *vm) {
 			vm->values[ns_id].extra.ns_parent = func->func.namespace;
 			vm->values[ns_id].ns = NULL;
 			vm->values[ns_id].flags = L2_VAL_TYPE_NAMESPACE;
-			vm->nstack[vm->nsptr++] = ns_id;
+			vm->fstack[vm->fsptr].namespace = ns_id;
+			vm->fstack[vm->fsptr].retptr = vm->iptr;
+			vm->fsptr += 1;
 
 			vm->iptr = func->func.pos;
 		}
 		break;
 
 	case L2_OP_RJMP:
-		word = vm->stack[vm->sptr - 1];
-		vm->sptr -= 1;
-		vm->iptr += word;
+		vm->iptr += vm->ops[vm->iptr++];
 		break;
 
 	case L2_OP_STACK_FRAME_LOOKUP:
 		{
-			l2_word key = vm->stack[vm->sptr - 1];
-			struct l2_vm_value *ns = &vm->values[vm->nstack[vm->nsptr - 1]];
-			vm->stack[vm->sptr - 1] = l2_vm_namespace_get(vm, ns, key);
+			l2_word key = vm->ops[vm->iptr++];
+			struct l2_vm_value *ns = &vm->values[vm->fstack[vm->fsptr - 1].namespace];
+			vm->stack[vm->sptr++] = l2_vm_namespace_get(vm, ns, key);
 		}
 		break;
 
 	case L2_OP_STACK_FRAME_SET:
 		{
-			l2_word key = vm->stack[--vm->sptr];
+			l2_word key = vm->ops[vm->iptr++];
 			l2_word val = vm->stack[vm->sptr - 1];
-			struct l2_vm_value *ns = &vm->values[vm->nstack[vm->nsptr - 1]];
+			struct l2_vm_value *ns = &vm->values[vm->fstack[vm->fsptr - 1].namespace];
 			l2_vm_namespace_set(ns, key, val);
 		}
 		break;
 
 	case L2_OP_STACK_FRAME_REPLACE:
 		{
-			l2_word key = vm->stack[--vm->sptr];
+			l2_word key = vm->ops[vm->iptr++];
 			l2_word val = vm->stack[vm->sptr - 1];
-			struct l2_vm_value *ns = &vm->values[vm->nstack[vm->nsptr - 1]];
+			struct l2_vm_value *ns = &vm->values[vm->fstack[vm->fsptr - 1].namespace];
 			l2_vm_namespace_replace(vm, ns, key, val); // TODO: error if returns -1
 		}
 		break;
@@ -338,34 +330,39 @@ void l2_vm_step(struct l2_vm *vm) {
 		{
 			l2_word retval = vm->stack[--vm->sptr];
 			vm->sptr -= 1; // Discard arguments array
-			l2_word retaddr = vm->stack[--vm->sptr];
+			l2_word retptr = vm->fstack[--vm->fsptr].retptr;
 			vm->stack[vm->sptr++] = retval;
-			vm->nsptr -= 1; // Pop function stack frame
-			vm->iptr = retaddr;
+			vm->iptr = retptr;
 		}
 		break;
 
+	case L2_OP_ALLOC_NONE:
+		vm->stack[vm->sptr++] = 0;
+		break;
+
 	case L2_OP_ALLOC_ATOM:
 		word = alloc_val(vm);
 		vm->values[word].flags = L2_VAL_TYPE_ATOM;
-		vm->values[word].atom= vm->stack[--vm->sptr];
+		vm->values[word].atom = vm->ops[vm->iptr++];
 		vm->stack[vm->sptr++] = word;
 		break;
 
 	case L2_OP_ALLOC_REAL:
-		word = alloc_val(vm);
-		vm->values[word].flags = L2_VAL_TYPE_REAL;
-		vm->values[word].real = u32s_to_double(vm->stack[vm->sptr - 1], vm->stack[vm->sptr - 2]);
-		vm->sptr -= 2;
-		vm->stack[vm->sptr] = word;
-		vm->sptr += 1;
+		{
+			word = alloc_val(vm);
+			l2_word high = vm->ops[vm->iptr++];
+			l2_word low = vm->ops[vm->iptr++];
+			vm->values[word].flags = L2_VAL_TYPE_REAL;
+			vm->values[word].real = u32s_to_double(high, low);
+			vm->stack[vm->sptr++] = word;
+		}
 		break;
 
 	case L2_OP_ALLOC_BUFFER_STATIC:
 		{
 			word = alloc_val(vm);
-			l2_word length = vm->stack[--vm->sptr];
-			l2_word offset = vm->stack[--vm->sptr];
+			l2_word length = vm->ops[vm->iptr++];
+			l2_word offset = vm->ops[vm->iptr++];
 			vm->values[word].flags = L2_VAL_TYPE_BUFFER;
 			vm->values[word].buffer = malloc(sizeof(struct l2_vm_buffer) + length);
 			vm->values[word].buffer->len = length;
@@ -377,21 +374,9 @@ void l2_vm_step(struct l2_vm *vm) {
 		}
 		break;
 
-	case L2_OP_ALLOC_BUFFER_ZERO:
-		{
-			word = alloc_val(vm);
-			l2_word length = vm->stack[--vm->sptr];
-			vm->values[word].flags = L2_VAL_TYPE_BUFFER;
-			vm->values[word].buffer = calloc(1, sizeof(struct l2_vm_buffer) + length);
-			vm->values[word].buffer->len = length;
-			vm->stack[vm->sptr] = word;
-			vm->sptr += 1;
-		}
-		break;
-
 	case L2_OP_ALLOC_ARRAY:
 		{
-			l2_word count = vm->stack[--vm->sptr];
+			l2_word count = vm->ops[vm->iptr++];
 			l2_word arr_id = alloc_val(vm);
 			struct l2_vm_value *arr = &vm->values[arr_id];
 			arr->flags = L2_VAL_TYPE_ARRAY;
@@ -424,15 +409,15 @@ void l2_vm_step(struct l2_vm *vm) {
 	case L2_OP_ALLOC_FUNCTION:
 		word = alloc_val(vm);
 		vm->values[word].flags = L2_VAL_TYPE_FUNCTION;
-		vm->values[word].func.pos = vm->stack[--vm->sptr];
-		vm->values[word].func.namespace = vm->nstack[vm->nsptr - 1];
+		vm->values[word].func.pos = vm->ops[vm->iptr++];
+		vm->values[word].func.namespace = vm->fstack[vm->fsptr - 1].namespace;
 		vm->stack[vm->sptr] = word;
 		vm->sptr += 1;
 		break;
 
 	case L2_OP_NAMESPACE_SET:
 		{
-			l2_word key = vm->stack[--vm->sptr];
+			l2_word key = vm->ops[vm->iptr++];
 			l2_word val = vm->stack[vm->sptr - 1];
 			l2_word ns = vm->stack[vm->sptr - 2];
 			l2_vm_namespace_set(&vm->values[ns], key, val);
@@ -441,24 +426,24 @@ void l2_vm_step(struct l2_vm *vm) {
 
 	case L2_OP_NAMESPACE_LOOKUP:
 		{
-			l2_word key = vm->stack[--vm->sptr];
+			l2_word key = vm->ops[vm->iptr++];
 			l2_word ns = vm->stack[--vm->sptr];
 			vm->stack[vm->sptr++] = l2_vm_namespace_get(vm, &vm->values[ns], key);
 		}
 		break;
 
-	case L2_OP_DIRECT_ARRAY_LOOKUP:
+	case L2_OP_ARRAY_LOOKUP:
 		{
-			l2_word key = vm->stack[--vm->sptr];
+			l2_word key = vm->ops[vm->iptr++];
 			l2_word arr = vm->stack[--vm->sptr];
 			// TODO: Error if out of bounds or incorrect type
 			vm->stack[vm->sptr++] = vm->values[arr].array->data[key];
 		}
 		break;
 
-	case L2_OP_DIRECT_ARRAY_SET:
+	case L2_OP_ARRAY_SET:
 		{
-			l2_word key = vm->stack[--vm->sptr];
+			l2_word key = vm->ops[vm->iptr++];
 			l2_word val = vm->stack[vm->sptr - 1];
 			l2_word arr = vm->stack[vm->sptr - 2];
 			// TODO: Error if out of bounds or incorrect type

test/src/eval.t.c

@@ -13,7 +13,7 @@ static struct l2_vm vm;
 
 static struct l2_vm_value *var_lookup(const char *name) {
 	l2_word atom_id = l2_strset_get(&gen.atomset, name);
-	l2_word id = l2_vm_namespace_get(&vm, &vm.values[vm.nstack[1]], atom_id);
+	l2_word id = l2_vm_namespace_get(&vm, &vm.values[vm.fstack[1].namespace], atom_id);
 	return &vm.values[id];
 }
 

test/src/examples.t.c

@@ -110,8 +110,11 @@ static void check_impl(const char *name) {
 	l2_vm_init(&vm, (l2_word *)bytecode.mem, bytecode.len / sizeof(l2_word));
 	vm.std_output = &output.w;
 
-	l2_vm_run(&vm);
-	l2_vm_gc(&vm);
+	// Run a GC after every instruction to uncover potential GC issues
+	while (vm.ops[vm.iptr] != L2_OP_HALT) {
+		l2_vm_step(&vm);
+		l2_vm_gc(&vm);
+	}
 
 	l2_vm_free(&vm);
 	free(bytecode.mem);
@@ -122,15 +125,13 @@ static void check_impl(const char *name) {
 
 #define check(name) do { \
 	snow_fail_update(); \
-	check_impl(name); \
+	test(name) { check_impl(name); } \
 } while (0)
 
 describe(exaples) {
-	test("examples") {
-		check("namespaces.l2");
-		check("arrays.l2");
-		check("functions.l2");
-	}
+	check("namespaces.l2");
+	check("arrays.l2");
+	check("functions.l2");
 
 	if (error_message != NULL) {
 		free(error_message);