reflect: implement New function

This is very important for some use cases, for example for Vecty.

src/reflect/type.go

@@ -322,6 +322,9 @@ func TypeOf(i interface{}) Type {
 }
 
 func PtrTo(t Type) Type {
+	if t.Kind() == Ptr {
+		panic("reflect: cannot make **T type")
+	}
 	ptrType := t.(rawType)<<5 | 5 // 0b0101 == 5
 	if ptrType>>5 != t {
 		panic("reflect: PtrTo type does not fit")

src/reflect/value.go

@@ -724,8 +724,14 @@ func Zero(typ Type) Value {
 	panic("unimplemented: reflect.Zero()")
 }
 
+// New is the reflect equivalent of the new(T) keyword, returning a pointer to a
+// new value of the given type.
 func New(typ Type) Value {
-	panic("unimplemented: reflect.New()")
+	return Value{
+		typecode: PtrTo(typ).(rawType),
+		value:    alloc(typ.Size()),
+		flags:    valueFlagExported,
+	}
 }
 
 type funcHeader struct {
@@ -756,6 +762,9 @@ func (e *ValueError) Error() string {
 // llvm.memcpy.p0i8.p0i8.i32().
 func memcpy(dst, src unsafe.Pointer, size uintptr)
 
+//go:linkname alloc runtime.alloc
+func alloc(size uintptr) unsafe.Pointer
+
 // Copy copies the contents of src into dst until either
 // dst has been filled or src has been exhausted.
 func Copy(dst, src Value) int {

src/runtime/interface.go

@@ -112,6 +112,11 @@ type typecodeID struct {
 	length uintptr
 
 	methodSet *interfaceMethodInfo // nil or a GEP of an array
+
+	// The type that's a pointer to this type, nil if it is already a pointer.
+	// Keeping the type struct alive here is important so that values from
+	// reflect.New (which uses reflect.PtrTo) can be used in type asserts etc.
+	ptrTo *typecodeID
 }
 
 // structField is used by the compiler to pass information to the interface