vm1: improve function calling (#6)

The "Enter" instruction has been removed and the frame pointer is
now saved by the "Call" instruction.

The "Return" instruction now takes the number of function input
parameters as the second operand. It's used to return the output
values at the correct place in the caller frame, no matter the
number of input parameters.

The tests and the code generator have been updated accordingly.

6 files changed, 76 insertions, 68 deletions

diff --git a/.gitignore b/.gitignore
index 385d6a8..9529633 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 *.out
 *.test
+gint
diff --git a/codegen/codegen.go b/codegen/codegen.go
index 048b20f..d7702cd 100644
--- a/codegen/codegen.go
+++ b/codegen/codegen.go
@@ -41,8 +41,7 @@ func (c *Compiler) CodeGen(node *parser.Node) (err error) {
 		switch n.Kind {
 		case parser.FuncDecl:
 			fname := n.Child[0].Content()
-			i := c.Emit(n, vm1.Enter)
-			c.AddSym(i, scope+fname, false)
+			c.AddSym(len(c.Code), scope+fname, false)
 			scope = pushScope(scope, fname)
 			frameNode = append(frameNode, n)
 			fnote = notes[n]
@@ -124,7 +123,8 @@ func (c *Compiler) CodeGen(node *parser.Node) (err error) {
 			}
 
 		case parser.ReturnStmt:
-			c.Emit(n, vm1.Return, int64(len(n.Child)))
+			fun := frameNode[len(frameNode)-1]
+			c.Emit(n, vm1.Return, int64(len(n.Child)), int64(len(fun.Child[1].Child)))
 
 		case parser.StmtBloc:
 			nd.ipend = len(c.Code)
@@ -144,7 +144,7 @@ func (c *Compiler) CodeGen(node *parser.Node) (err error) {
 		// TODO: Fix this temporary hack to compute an entry point
 		if c.Entry < 0 && len(scope) == 0 && n.Kind != parser.FuncDecl {
 			c.Entry = len(c.Code) - 1
-			if c.Code[c.Entry][1] == vm1.Return {
+			if c.Entry >= 0 && len(c.Code) > c.Entry && c.Code[c.Entry][1] == vm1.Return {
 				c.Entry++
 			}
 		}
diff --git a/codegen/codegen_test.go b/codegen/codegen_test.go
index d2f8033..7262ddc 100644
--- a/codegen/codegen_test.go
+++ b/codegen/codegen_test.go
@@ -16,7 +16,7 @@ func TestCodeGen(t *testing.T) {
 		test := test
 		t.Run("", func(t *testing.T) {
 			c := New()
-			c.AddSym(fmt.Println, "println")
+			c.AddSym(fmt.Println, "println", false)
 			n := &parser.Node{}
 			var err error
 			if n.Child, err = golang.GoParser.Parse(test.src); err != nil {
@@ -31,6 +31,9 @@ func TestCodeGen(t *testing.T) {
 			}
 			t.Log("data:", c.Data)
 			t.Log("code:", vm1.Disassemble(c.Code))
+			if s := vm1.Disassemble(c.Code); s != test.asm {
+				t.Errorf("got error %#v, want error %#v", s, test.asm)
+			}
 		})
 	}
 }
@@ -45,7 +48,11 @@ var tests = []struct {
 	asm: "Dup 0\nDup 1\nCallX 1\n",
 }, { // #02
 	src: `a := 2; println(a)`,
-	asm: "Push 2\nAssign 1\nDup 0\nDup 1\nCallX 1",
+	asm: "Push 2\nAssign 1\nDup 0\nDup 1\nCallX 1\n",
 }, { // #03
 	src: `a := 2; if a < 3 {println(a)}; println("bye")`,
-}}
+	asm: "Push 2\nAssign 1\nDup 1\nPush 3\nLower\nJumpFalse 4\nDup 0\nDup 1\nCallX 1\nDup 0\nDup 2\nCallX 1\n",
+}, { // #04
+	src: "func add(a int, b int) int { return a + b }",
+	asm: "Fdup -2\nFdup -3\nAdd\nReturn 1 2\n",
+}, {}}
diff --git a/samples/fib b/samples/fib
index 03545d3..654c5c0 100644
--- a/samples/fib
+++ b/samples/fib
@@ -3,4 +3,4 @@ func fib(i int) int {
 	return fib(i-2) + fib(i-1)
 }
 
-println(fib(5))
+println(fib(6))
diff --git a/vm1/vm.go b/vm1/vm.go
index 54e5223..6b74e7a 100644
--- a/vm1/vm.go
+++ b/vm1/vm.go
@@ -16,7 +16,6 @@ const (
 	CallX            // f [a1 .. ai] -- [r1 .. rj] ; r1, ... = mem[f](a1, ...)
 	Dup              // addr -- value ; value = mem[addr]
 	Fdup             // addr -- value ; value = mem[addr]
-	Enter            // -- ; enter frame: push(fp), fp = sp
 	Exit             // -- ;
 	Jump             // -- ; ip += $1
 	JumpTrue         // cond -- ; if cond { ip += $1 }
@@ -38,7 +37,6 @@ var strop = [...]string{ // for VM tracing.
 	CallX:     "CallX",
 	Dup:       "Dup",
 	Fdup:      "Fdup",
-	Enter:     "Enter",
 	Exit:      "Exit",
 	Jump:      "Jump",
 	JumpTrue:  "JumpTrue",
@@ -67,11 +65,15 @@ func (m *Machine) Run() {
 	defer func() { m.mem, m.ip, m.fp = mem, ip, fp }()
 
 	trace := func() {
-		var op2 string
-		if len(code[ip]) > 2 {
-			op2 = strconv.Itoa(int(code[ip][2]))
+		var op2, op3 string
+		c := code[ip]
+		if l := len(c); l > 2 {
+			op2 = strconv.Itoa(int(c[2]))
+			if l > 3 {
+				op3 = strconv.Itoa(int(c[3]))
+			}
 		}
-		fmt.Printf("ip:%-4d sp:%-4d fp:%-4d op:[%-9s %-4s] mem:%v\n", ip, sp, fp, strop[code[ip][1]], op2, mem)
+		fmt.Printf("ip:%-4d sp:%-4d fp:%-4d op:[%-9s %-4s %-4s] mem:%v\n", ip, sp, fp, strop[c[1]], op2, op3, mem)
 	}
 	_ = trace
 
@@ -86,7 +88,8 @@ func (m *Machine) Run() {
 			mem[op[2]] = mem[sp-1]
 			mem = mem[:sp-1]
 		case Call:
-			mem = append(mem, ip+1)
+			mem = append(mem, ip+1, fp)
+			fp = sp + 2
 			ip += int(op[2])
 			continue
 		case CallX: // Should be made optional.
@@ -102,9 +105,6 @@ func (m *Machine) Run() {
 			}
 		case Dup:
 			mem = append(mem, mem[int(op[2])])
-		case Enter:
-			mem = append(mem, fp)
-			fp = sp + 1
 		case Exit:
 			return
 		case Fdup:
@@ -139,7 +139,7 @@ func (m *Machine) Run() {
 			ip = mem[fp-2].(int)
 			ofp := fp
 			fp = mem[fp-1].(int)
-			mem = append(mem[:ofp-int(op[2])-2], mem[sp-int(op[2]):]...)
+			mem = append(mem[:ofp-int(op[2])-int(op[3])-1], mem[sp-int(op[2]):]...)
 			continue
 		case Sub:
 			mem[sp-2] = mem[sp-2].(int) - mem[sp-1].(int)
@@ -164,10 +164,13 @@ func (m *Machine) Pop() (v any)       { l := len(m.mem) - 1; v = m.mem[l]; m.mem
 // Disassemble returns the code as a readable string.
 func Disassemble(code [][]int64) (asm string) {
 	for _, op := range code {
-		if len(op) > 2 {
-			asm += fmt.Sprintf("%s %d\n", strop[op[1]], op[2])
-		} else {
+		switch len(op) {
+		case 2:
 			asm += strop[op[1]] + "\n"
+		case 3:
+			asm += fmt.Sprintf("%s %d\n", strop[op[1]], op[2])
+		case 4:
+			asm += fmt.Sprintf("%s %d %d\n", strop[op[1]], op[2], op[3])
 		}
 	}
 	return asm
diff --git a/vm1/vm_test.go b/vm1/vm_test.go
index 53b0d07..cea4f29 100644
--- a/vm1/vm_test.go
+++ b/vm1/vm_test.go
@@ -62,60 +62,57 @@ var tests = []struct {
 	start: 0, end: 2, mem: "[6 <nil>]",
 }, { // #02 -- Defining and calling a function in VM.
 	code: [][]int64{
-		{0, Jump, 4},   // 0
-		{0, Enter},     // 1
-		{0, Push, 3},   // 2
-		{0, Return, 1}, // 3
-		{0, Push, 1},   // 4
-		{0, Call, -4},  // 5
-		{0, Exit},      // 6
+		{0, Jump, 3},      // 0
+		{0, Push, 3},      // 1
+		{0, Return, 1, 1}, // 2
+		{0, Push, 1},      // 3
+		{0, Call, -3},     // 4
+		{0, Exit},         // 5
 	},
 	start: 0, end: 1, mem: "[3]",
 }, { // #03 -- Fibonacci numbers, hand written. Showcase recursivity.
 	code: [][]int64{
-		{0, Jump, 18},     // 0, goto 18
-		{0, Enter},        // 1,
-		{0, Fdup, -2},     // 2, [i]
-		{0, Push, 2},      // 3, [i 2]
-		{0, Lower},        // 4, [true/false]
-		{0, JumpTrue, 11}, // 5, [], goto 16
-		{0, Fdup, -2},     // 6  [i]
-		{0, Push, 2},      // 7  [i 2]
-		{0, Sub},          // 8  [(i-2)]
-		{0, Call, -8},     // 9  [fib(i-2)]
-		{0, Fdup, -2},     // 10 [fib(i-2) i]
-		{0, Push, 1},      // 11 [(i-2) i 1]
-		{0, Sub},          // 12 [(i-2) (i-1)]
-		{0, Call, -12},    // 13 [fib(i-2) fib(i-1)]
-		{0, Add},          // 14 [fib(i-2)+fib(i-1)]
-		{0, Return, 1},    // 15 return i
-		{0, Fdup, -2},     // 16 [i]
-		{0, Return, 1},    // 17 return i
-		{0, Push, 6},      // 18 [1]
-		{0, Call, -18},    // 19 [fib(*1)]
-		{0, Exit},         // 20
+		{0, Jump, 17},     // 0
+		{0, Fdup, -2},     // 1  [i]
+		{0, Push, 2},      // 2  [i 2]
+		{0, Lower},        // 3  [true/false]
+		{0, JumpTrue, 11}, // 4  [], goto 16
+		{0, Fdup, -2},     // 5  [i]
+		{0, Push, 2},      // 6  [i 2]
+		{0, Sub},          // 7  [(i-2)]
+		{0, Call, -7},     // 8  [fib(i-2)]
+		{0, Fdup, -2},     // 9  [fib(i-2) i]
+		{0, Push, 1},      // 10 [(i-2) i 1]
+		{0, Sub},          // 11 [(i-2) (i-1)]
+		{0, Call, -11},    // 12 [fib(i-2) fib(i-1)]
+		{0, Add},          // 13 [fib(i-2)+fib(i-1)]
+		{0, Return, 1, 1}, // 14 return i
+		{0, Fdup, -2},     // 15 [i]
+		{0, Return, 1, 1}, // 16 return i
+		{0, Push, 6},      // 17 [1]
+		{0, Call, -17},    // 18 [fib(*1)]
+		{0, Exit},         // 19
 	},
 	start: 0, end: 1, mem: "[8]",
 }, { // #04 -- Fibonacci with some immediate instructions.
 	code: [][]int64{
-		{0, Jump, 15},    // 0, goto 15
-		{0, Enter},       // 1,
-		{0, Fdup, -2},    // 2, [i]
-		{0, Loweri, 2},   // 3, [true/false]
-		{0, JumpTrue, 9}, // 4, [], goto 13
-		{0, Fdup, -2},    // 5  [i]
-		{0, Subi, 2},     // 6  [(i-2)]
-		{0, Call, -6},    // 7  [fib(i-2)]
-		{0, Fdup, -2},    // 8  [fib(i-2) i]
-		{0, Subi, 1},     // 9  [(i-2) (i-1)]
-		{0, Call, -9},    // 10 [fib(i-2) fib(i-1)], call 1
-		{0, Add},         // 11 [fib(i-2)+fib(i-1)]
-		{0, Return, 1},   // 12 return i
-		{0, Fdup, -2},    // 13 [i]
-		{0, Return, 1},   // 14 return i
-		{0, Push, 6},     // 15 [1]
-		{0, Call, -15},   // 16 [fib(*1)], call 1
-		{0, Exit},        // 17
+		{0, Jump, 14},     // 0
+		{0, Fdup, -2},     // 1  [i]
+		{0, Loweri, 2},    // 2  [true/false]
+		{0, JumpTrue, 9},  // 3  [], goto 13
+		{0, Fdup, -2},     // 4  [i]
+		{0, Subi, 2},      // 5  [(i-2)]
+		{0, Call, -5},     // 6  [fib(i-2)]
+		{0, Fdup, -2},     // 7  [fib(i-2) i]
+		{0, Subi, 1},      // 8  [(i-2) (i-1)]
+		{0, Call, -8},     // 9  [fib(i-2) fib(i-1)], call 1
+		{0, Add},          // 10 [fib(i-2)+fib(i-1)]
+		{0, Return, 1, 1}, // 11 return i
+		{0, Fdup, -2},     // 12 [i]
+		{0, Return, 1, 1}, // 13 return i
+		{0, Push, 6},      // 14 [1]
+		{0, Call, -14},    // 15 [fib(*1)], call 1
+		{0, Exit},         // 16
 	},
 	start: 0, end: 1, mem: "[8]",
 }}