Added fibonacci example

src/build/core/CompileCall.go

@@ -29,6 +29,12 @@ func (f *Function) CompileCall(root *expression.Expression) error {
 		registers = f.cpu.Syscall[:len(parameters)]
 	}
 
+	for _, register := range f.cpu.Input {
+		if f.cpu.IsUsed(register) {
+			f.SaveRegister(register)
+		}
+	}
+
 	err := f.ExpressionsToRegisters(parameters, registers)
 
 	if err != nil {
@@ -37,7 +43,7 @@ func (f *Function) CompileCall(root *expression.Expression) error {
 
 	// Push
 	for _, register := range f.cpu.General {
-		if !f.cpu.IsFree(register) {
+		if f.cpu.IsUsed(register) {
 			f.assembler.Register(asm.PUSH, register)
 		}
 	}
@@ -53,7 +59,7 @@ func (f *Function) CompileCall(root *expression.Expression) error {
 	for i := len(f.cpu.General) - 1; i >= 0; i-- {
 		register := f.cpu.General[i]
 
-		if !f.cpu.IsFree(register) {
+		if f.cpu.IsUsed(register) {
 			f.assembler.Register(asm.POP, register)
 		}
 	}

src/build/core/CompileDefinition.go

@@ -47,6 +47,7 @@ func (f *Function) AddVariable(variable *Variable) {
 	}
 
 	f.variables[variable.Name] = variable
+	f.cpu.Reserve(variable.Register)
 	f.cpu.Use(variable.Register)
 }
 
@@ -85,6 +86,7 @@ func (f *Function) storeVariableInRegister(name string, value *expression.Expres
 		panic("no free registers")
 	}
 
+	f.cpu.Reserve(reg)
 	err := f.ExpressionToRegister(value, reg)
 
 	f.AddVariable(&Variable{

src/build/core/ExpressionToRegister.go

@@ -36,6 +36,7 @@ func (f *Function) ExpressionToRegister(node *expression.Expression, register cp
 		register = f.cpu.MustFindFree(f.cpu.General)
 	}
 
+	f.cpu.Reserve(register)
 	err := f.ExpressionToRegister(left, register)
 
 	if err != nil {
@@ -47,8 +48,8 @@ func (f *Function) ExpressionToRegister(node *expression.Expression, register cp
 
 	if register != final {
 		f.assembler.RegisterRegister(asm.MOVE, final, register)
+		f.cpu.Free(register)
 	}
 
-	f.cpu.Free(register)
 	return err
 }

src/build/core/Function.go

@@ -31,6 +31,7 @@ func NewFunction(name string, file *fs.File, body token.List) *Function {
 				Instructions: make([]asm.Instruction, 0, 32),
 			},
 			cpu: cpu.CPU{
+				All:     x64.AllRegisters,
 				Input:   x64.CallRegisters,
 				General: x64.GeneralRegisters,
 				Syscall: x64.SyscallRegisters,

src/build/core/SaveRegister.go

@@ -0,0 +1,37 @@
+package core
+
+import (
+	"fmt"
+
+	"git.akyoto.dev/cli/q/src/build/asm"
+	"git.akyoto.dev/cli/q/src/build/config"
+	"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) {
+	var variable *Variable
+
+	for _, v := range f.variables {
+		if v.Register == register {
+			variable = v
+			break
+		}
+	}
+
+	if variable == nil || variable.Alive == 0 {
+		return
+	}
+
+	newRegister := f.cpu.MustFindFree(f.cpu.General)
+	f.cpu.Reserve(newRegister)
+	f.cpu.Use(newRegister)
+
+	if config.Comments {
+		f.assembler.Comment(fmt.Sprintf("save %s to %s", register, newRegister))
+	}
+
+	f.assembler.RegisterRegister(asm.MOVE, newRegister, register)
+	f.cpu.Free(register)
+	variable.Register = newRegister
+}