compiler: implement []byte(str)

compiler.go

@@ -2414,6 +2414,20 @@ func (c *Compiler) parseConvert(typeFrom, typeTo types.Type, value llvm.Value) (
 
 		return llvm.Value{}, errors.New("todo: convert: basic non-integer type: " + typeFrom.String() + " -> " + typeTo.String())
 
+	case *types.Slice:
+		if basic, ok := typeFrom.(*types.Basic); !ok || basic.Kind() != types.String {
+			panic("can only convert from a string to a slice")
+		}
+
+		elemType := typeTo.Elem().Underlying().(*types.Basic) // must be byte or rune
+		switch elemType.Kind() {
+		case types.Byte:
+			fn := c.mod.NamedFunction("runtime.stringToBytes")
+			return c.builder.CreateCall(fn, []llvm.Value{value}, ""), nil
+		default:
+			return llvm.Value{}, errors.New("todo: convert from string: " + elemType.String())
+		}
+
 	default:
 		return llvm.Value{}, errors.New("todo: convert " + typeTo.String() + " <- " + typeFrom.String())
 	}

src/runtime/string.go

@@ -42,12 +42,28 @@ func stringConcat(x, y _string) _string {
 }
 
 // Create a string from a []byte slice.
-func stringFromBytes(x []byte) _string {
-	buf := alloc(uintptr(len(x)))
-	for i, c := range x {
-		*(*byte)(unsafe.Pointer(uintptr(buf) + uintptr(i))) = c
+func stringFromBytes(x struct {
+	ptr *byte
+	len lenType
+	cap lenType
+}) _string {
+	buf := alloc(uintptr(x.len))
+	memcpy(buf, unsafe.Pointer(x.ptr), uintptr(x.len))
+	return _string{lenType(x.len), (*byte)(buf)}
 }
-	return _string{lenType(len(x)), (*byte)(buf)}
+
+// Convert a string to a []byte slice.
+func stringToBytes(x _string) (slice struct {
+	ptr *byte
+	len lenType
+	cap lenType
+}) {
+	buf := alloc(uintptr(x.length))
+	memcpy(buf, unsafe.Pointer(x.ptr), uintptr(x.length))
+	slice.ptr = (*byte)(buf)
+	slice.len = x.length
+	slice.cap = x.length
+	return
 }
 
 // Create a string from a Unicode code point.