Initial commit

pkg/vm/compiler.go

@@ -0,0 +1,66 @@
+package vm
+
+import (
+	"fmt"
+)
+
+type Instruction struct {
+	Op   Opcode
+	Args []int64
+}
+
+type LabelledInstr struct {
+	Label  string
+	Instr  Instruction
+	Target string
+}
+
+func Compile(program []LabelledInstr) []byte {
+	labelAddrs := make(map[string]int)
+
+	type fixup struct {
+		offset int
+		op     Opcode
+		target string
+	}
+	var fixups []fixup
+	var bytecode []byte
+
+	for _, entry := range program {
+		if entry.Label != "" {
+			labelAddrs[entry.Label] = len(bytecode)
+		}
+
+		instr := entry.Instr
+		isJump := instr.Op == OpJmp || instr.Op == OpJz || instr.Op == OpJnz
+
+		if isJump && entry.Target != "" {
+			fixups = append(fixups, fixup{
+				offset: len(bytecode),
+				op:     instr.Op,
+				target: entry.Target,
+			})
+			ph := make([]byte, InstrSize(instr.Op))
+			ph[0] = encodeOp(instr.Op)
+			bytecode = append(bytecode, ph...)
+			continue
+		}
+
+		arg := int64(0)
+		if len(instr.Args) > 0 {
+			arg = instr.Args[0]
+		}
+		bytecode = append(bytecode, EncodeInstr(instr.Op, arg)...)
+	}
+
+	for _, f := range fixups {
+		addr, ok := labelAddrs[f.target]
+		if !ok {
+			panic(fmt.Sprintf("vm: undefined label %q", f.target))
+		}
+		enc := EncodeInstr(f.op, int64(addr))
+		copy(bytecode[f.offset:], enc)
+	}
+
+	return bytecode
+}