Implemented return values

examples/hello/hello.q

@@ -1,19 +1,8 @@
-// Comment
 main() {
-	address := 4194304 + 1
-	length := (0 + 50 - 20) * 10 / 100
-
-	loop {
-		print(address, length)
-	}
+	x := f(2, 3)
+	syscall(60, x)
 }
 
-// Comment
-print(address, length) {
-	write(length-2, address, length)
-}
-
-// Comment
-write(fd, address, length) {
-	syscall(1, fd, address, length)
+f(x, y) {
+	return (x + y) * (x + y)
 }

src/build/Execute.go

@@ -3,7 +3,6 @@ package build
 import (
 	"strconv"
 
-	"git.akyoto.dev/cli/q/src/build/arch/x64"
 	"git.akyoto.dev/cli/q/src/build/asm"
 	"git.akyoto.dev/cli/q/src/build/cpu"
 	"git.akyoto.dev/cli/q/src/build/expression"
@@ -17,11 +16,18 @@ func (f *Function) Execute(operation token.Token, register cpu.Register, value *
 		return f.ExecuteLeaf(operation, register, value.Token)
 	}
 
-	temporary, found := f.cpu.FindFree(f.cpu.General)
+	var temporary cpu.Register
+
+	if isFunctionCall(value) {
+		temporary = f.cpu.Return[0]
+	} else {
+		found := false
+		temporary, found = f.cpu.FindFree(f.cpu.General)
 
 		if !found {
 			panic("no free registers")
 		}
+	}
 
 	f.cpu.Use(temporary)
 	defer f.cpu.Free(temporary)
@@ -122,6 +128,20 @@ func (f *Function) ExpressionToRegister(root *expression.Expression, register cp
 		return f.TokenToRegister(operation, register)
 	}
 
+	if isFunctionCall(root) {
+		err := f.CompileFunctionCall(root)
+
+		if err != nil {
+			return err
+		}
+
+		if register != f.cpu.Return[0] {
+			f.assembler.RegisterRegister(asm.MOVE, register, f.cpu.Return[0])
+		}
+
+		return nil
+	}
+
 	left := root.Children[0]
 	right := root.Children[1]
 
@@ -131,46 +151,21 @@ func (f *Function) ExpressionToRegister(root *expression.Expression, register cp
 		return err
 	}
 
+	f.SaveRegister(register)
 	return f.Execute(operation, register, right)
 }
 
 // ExpressionsToRegisters moves multiple expressions into the specified registers.
 func (f *Function) ExpressionsToRegisters(expressions []*expression.Expression, registers []cpu.Register) error {
-	var destinations []cpu.Register
-
 	for i := len(expressions) - 1; i >= 0; i-- {
-		original := registers[i]
 		expression := expressions[i]
-
-		if expression.IsLeaf() {
-			variable, exists := f.variables[expression.Token.Text()]
-
-			if exists && variable.Register == original {
-				continue
-			}
-		}
-
-		register := original
-		save := !f.cpu.IsFree(register)
-
-		if save {
-			register = x64.RAX
-		}
+		register := registers[i]
 
 		err := f.ExpressionToRegister(expression, register)
 
 		if err != nil {
 			return err
 		}
-
-		if save {
-			destinations = append(destinations, original)
-			f.assembler.Register(asm.PUSH, x64.RAX)
-		}
-	}
-
-	for i := len(destinations) - 1; i >= 0; i-- {
-		f.assembler.Register(asm.POP, destinations[i])
 	}
 
 	return nil

src/build/FunctionCall.go

@@ -1,17 +1,38 @@
 package build
 
-import "git.akyoto.dev/cli/q/src/build/expression"
+import (
+	"git.akyoto.dev/cli/q/src/build/cpu"
+	"git.akyoto.dev/cli/q/src/build/expression"
+)
 
 // CompileFunctionCall executes a function call.
 func (f *Function) CompileFunctionCall(expr *expression.Expression) error {
-	funcName := expr.Children[0].Token.Text()
-	parameters := expr.Children[1:]
+	var (
+		funcName   = expr.Children[0].Token.Text()
+		parameters = expr.Children[1:]
+		isSyscall  = funcName == "syscall"
+		registers  []cpu.Register
+	)
 
-	if funcName == "syscall" {
-		defer f.assembler.Syscall()
-		return f.ExpressionsToRegisters(parameters, f.cpu.Syscall)
+	if isSyscall {
+		registers = f.cpu.Syscall
+	} else {
+		registers = f.cpu.Call
 	}
 
-	defer f.assembler.Call(funcName)
-	return f.ExpressionsToRegisters(parameters, f.cpu.Call)
+	registers = registers[:len(parameters)]
+
+	for _, register := range registers {
+		f.SaveRegister(register)
+	}
+
+	err := f.ExpressionsToRegisters(parameters, registers)
+
+	if isSyscall {
+		f.assembler.Syscall()
+	} else {
+		f.assembler.Call(funcName)
+	}
+
+	return err
 }

src/build/Return.go

@@ -7,12 +7,18 @@ import (
 
 // CompileReturn compiles a return instruction.
 func (f *Function) CompileReturn(tokens token.List) error {
-	if len(tokens) > 1 {
-		value := expression.Parse(tokens[1:])
-		defer value.Close()
-		// TODO: Set the return value
+	defer f.assembler.Return()
+
+	if len(tokens) == 1 {
+		return nil
 	}
 
-	f.assembler.Return()
+	value := expression.Parse(tokens[1:])
+
+	if value == nil {
 		return nil
+	}
+
+	defer value.Close()
+	return f.ExpressionToRegister(value, f.cpu.Return[0])
 }

src/build/SaveRegister.go

@@ -0,0 +1,37 @@
+package build
+
+import (
+	"git.akyoto.dev/cli/q/src/build/asm"
+	"git.akyoto.dev/cli/q/src/build/cpu"
+)
+
+// SaveRegister attempts to move a variable occupying this register to another register.
+func (f *Function) SaveRegister(register cpu.Register) {
+	if f.cpu.IsFree(register) {
+		return
+	}
+
+	var variable *Variable
+
+	for _, v := range f.variables {
+		if v.Register == register {
+			variable = v
+			break
+		}
+	}
+
+	if variable == nil || variable.UsesRemaining == 0 {
+		return
+	}
+
+	newRegister, exists := f.cpu.FindFree(f.cpu.General)
+
+	if !exists {
+		panic("no free registers")
+	}
+
+	f.assembler.RegisterRegister(asm.MOVE, newRegister, register)
+	f.cpu.Free(register)
+	f.cpu.Use(newRegister)
+	variable.Register = newRegister
+}

src/build/arch/x64/Registers.go

@@ -22,7 +22,7 @@ const (
 )
 
 var (
-	CallRegisters        = []cpu.Register{RDI, RSI, RDX, RCX, R8, R9}
+	CallRegisters        = SyscallRegisters
 	GeneralRegisters     = []cpu.Register{RBX, RBP, R12, R13, R14, R15}
 	SyscallRegisters     = []cpu.Register{RAX, RDI, RSI, RDX, R10, R8, R9}
 	ReturnValueRegisters = []cpu.Register{RAX, RCX, R11}

src/build/asm/Instructions.go

@@ -66,6 +66,10 @@ func (a *Assembler) Jump(name string) {
 
 // Return returns back to the caller.
 func (a *Assembler) Return() {
+	if len(a.Instructions) > 0 && a.Instructions[len(a.Instructions)-1].Mnemonic == RETURN {
+		return
+	}
+
 	a.Instructions = append(a.Instructions, Instruction{Mnemonic: RETURN})
 }