Implemented jumps and jump related optimizations

src/asm/Assembler.go

@@ -17,9 +17,18 @@ type Assembler struct {
 
 // Append adds another instruction.
 func (a *Assembler) Append(instr Instruction) {
+	if a.Skip(instr) {
+		return
+	}
+
 	a.Instructions = append(a.Instructions, instr)
 }
 
+// Last returns the last instruction.
+func (a *Assembler) Last() Instruction {
+	return a.Instructions[len(a.Instructions)-1]
+}
+
 // Compile compiles the instructions to machine code.
 func (a *Assembler) Compile(b *build.Build) (code []byte, data []byte) {
 	data, dataLabels := a.Data.Finalize()
@@ -65,7 +74,10 @@ func (a *Assembler) Compile(b *build.Build) (code []byte, data []byte) {
 // Merge combines the contents of this assembler with another one.
 func (a *Assembler) Merge(b *Assembler) {
 	maps.Copy(a.Data, b.Data)
-	a.Instructions = append(a.Instructions, b.Instructions...)
+
+	for _, instr := range b.Instructions {
+		a.Append(instr)
+	}
 }
 
 // SetData sets the data for the given label.
@@ -76,3 +88,60 @@ func (a *Assembler) SetData(label string, bytes []byte) {
 
 	a.Data.Insert(label, bytes)
 }
+
+// SetLast sets the last instruction.
+func (a *Assembler) SetLast(instr Instruction) {
+	a.Instructions[len(a.Instructions)-1] = instr
+}
+
+// Skip returns true if appending the instruction can be skipped.
+func (a *Assembler) Skip(instr Instruction) bool {
+	if len(a.Instructions) == 0 {
+		return false
+	}
+
+	switch instr := instr.(type) {
+	case *FunctionEnd:
+		// Call + FunctionEnd can be replaced by a single Jump
+		call, isCall := a.Last().(*Call)
+
+		if isCall {
+			a.SetLast(&Jump{Label: call.Label})
+			return true
+		}
+
+	case *Label:
+		// Jump + Label can be replaced by just the Label if both addresses are equal
+		jump, isJump := a.Last().(*Jump)
+
+		if isJump && jump.Label == instr.Name {
+			a.SetLast(instr)
+			return true
+		}
+
+	case *Return:
+		// Call + Return can be replaced by a single Jump
+		call, isCall := a.Last().(*Call)
+
+		if isCall {
+			a.SetLast(&Jump{Label: call.Label})
+			return true
+		}
+
+		// Jump + Return is unnecessary
+		_, isJump := a.Last().(*Jump)
+
+		if isJump {
+			return true
+		}
+
+		// Return + Return is unnecessary
+		_, isReturn := a.Last().(*Return)
+
+		if isReturn {
+			return true
+		}
+	}
+
+	return false
+}

src/asm/Instruction.go

@@ -11,6 +11,10 @@ type Call struct {
 type FunctionStart struct{}
 type FunctionEnd struct{}
 
+type Jump struct {
+	Label string
+}
+
 type Label struct {
 	Name string
 }

src/asm/compilerARM.go

@@ -30,6 +30,25 @@ func (c *compilerARM) Compile(instr Instruction) {
 			offset := (address - start) / 4
 			binary.LittleEndian.PutUint32(c.code[start:start+4], arm.Call(offset))
 		})
+	case *Jump:
+		start := len(c.code)
+		c.append(arm.Jump(0))
+
+		c.Defer(func() {
+			address, exists := c.labels[instr.Label]
+
+			if !exists {
+				panic("unknown label: " + instr.Label)
+			}
+
+			offset := (address - start) / 4
+
+			if offset != (offset & 0b11_11111111_11111111_11111111) {
+				panic("not implemented: long jumps")
+			}
+
+			binary.LittleEndian.PutUint32(c.code[start:start+4], arm.Jump(offset))
+		})
 	case *FunctionStart:
 		c.append(arm.StorePair(arm.FP, arm.LR, arm.SP, -16))
 		c.append(arm.MoveRegisterRegister(arm.FP, arm.SP))
@@ -59,5 +78,7 @@ func (c *compilerARM) Compile(instr Instruction) {
 		c.append(arm.Return())
 	case *Syscall:
 		c.append(arm.Syscall())
+	default:
+		panic("unknown instruction")
 	}
 }

src/asm/compilerX86.go

@@ -3,6 +3,7 @@ package asm
 import (
 	"encoding/binary"
 
+	"git.urbach.dev/cli/q/src/sizeof"
 	"git.urbach.dev/cli/q/src/x86"
 )
 
@@ -26,6 +27,27 @@ func (c *compilerX86) Compile(instr Instruction) {
 			offset := address - end
 			binary.LittleEndian.PutUint32(c.code[end-4:end], uint32(offset))
 		})
+	case *FunctionStart:
+	case *FunctionEnd:
+	case *Jump:
+		c.code = x86.Jump8(c.code, 0)
+		end := len(c.code)
+
+		c.Defer(func() {
+			address, exists := c.labels[instr.Label]
+
+			if !exists {
+				panic("unknown label: " + instr.Label)
+			}
+
+			offset := address - end
+
+			if sizeof.Signed(offset) > 1 {
+				panic("not implemented: long jumps")
+			}
+
+			c.code[end-1] = byte(offset)
+		})
 	case *Label:
 		c.labels[instr.Name] = len(c.code)
 	case *MoveRegisterLabel:
@@ -50,5 +72,7 @@ func (c *compilerX86) Compile(instr Instruction) {
 		c.code = x86.Return(c.code)
 	case *Syscall:
 		c.code = x86.Syscall(c.code)
+	default:
+		panic("unknown instruction")
 	}
 }

src/core/Compile.go

@@ -93,11 +93,7 @@ func (f *Function) Compile() {
 	}
 
 	if f.UniqueName != "core.exit" {
-		switch f.Assembler.Instructions[len(f.Assembler.Instructions)-1].(type) {
-		case *asm.Return:
-		default:
-			f.Assembler.Append(&asm.Return{})
-		}
+		f.Assembler.Append(&asm.Return{})
 	}
 }