reflect: implement support for array types

compiler/interface.go

@@ -54,6 +54,7 @@ func (c *Compiler) getTypeCode(typ types.Type) llvm.Value {
 		// element types. Store it directly in the typecode global to make
 		// reflect lowering simpler.
 		var references llvm.Value
+		var length int64
 		switch typ := typ.(type) {
 		case *types.Named:
 			references = c.getTypeCode(typ.Underlying())
@@ -63,6 +64,9 @@ func (c *Compiler) getTypeCode(typ types.Type) llvm.Value {
 			references = c.getTypeCode(typ.Elem())
 		case *types.Slice:
 			references = c.getTypeCode(typ.Elem())
+		case *types.Array:
+			references = c.getTypeCode(typ.Elem())
+			length = typ.Len()
 		case *types.Struct:
 			// Take a pointer to the typecodeID of the first field (if it exists).
 			structGlobal := c.makeStructTypeFields(typ)
@@ -72,6 +76,10 @@ func (c *Compiler) getTypeCode(typ types.Type) llvm.Value {
 			// Set the 'references' field of the runtime.typecodeID struct.
 			globalValue := c.getZeroValue(global.Type().ElementType())
 			globalValue = llvm.ConstInsertValue(globalValue, references, []uint32{0})
+			if length != 0 {
+				lengthValue := llvm.ConstInt(c.uintptrType, uint64(length), false)
+				globalValue = llvm.ConstInsertValue(globalValue, lengthValue, []uint32{1})
+			}
 			global.SetInitializer(globalValue)
 			global.SetLinkage(llvm.PrivateLinkage)
 		}

compiler/reflect.go

@@ -89,6 +89,11 @@ type typeCodeAssignmentState struct {
 	namedBasicTypes    map[string]int
 	namedNonBasicTypes map[string]int
 
+	// Map of array types to their type code.
+	arrayTypes               map[string]int
+	arrayTypesSidetable      []byte
+	needsArrayTypesSidetable bool
+
 	// Map of struct types to their type code.
 	structTypes               map[string]int
 	structTypesSidetable      []byte
@@ -137,11 +142,13 @@ func (c *Compiler) assignTypeCodes(typeSlice typeInfoSlice) {
 		uintptrLen:                       c.uintptrType.IntTypeWidth(),
 		namedBasicTypes:                  make(map[string]int),
 		namedNonBasicTypes:               make(map[string]int),
+		arrayTypes:                       make(map[string]int),
 		structTypes:                      make(map[string]int),
 		structNames:                      make(map[string]int),
 		needsNamedNonBasicTypesSidetable: len(getUses(c.mod.NamedGlobal("reflect.namedNonBasicTypesSidetable"))) != 0,
 		needsStructTypesSidetable:        len(getUses(c.mod.NamedGlobal("reflect.structTypesSidetable"))) != 0,
 		needsStructNamesSidetable:        len(getUses(c.mod.NamedGlobal("reflect.structNamesSidetable"))) != 0,
+		needsArrayTypesSidetable:         len(getUses(c.mod.NamedGlobal("reflect.arrayTypesSidetable"))) != 0,
 	}
 	for _, t := range typeSlice {
 		num := state.getTypeCodeNum(t.typecode)
@@ -161,6 +168,11 @@ func (c *Compiler) assignTypeCodes(typeSlice typeInfoSlice) {
 		global.SetLinkage(llvm.InternalLinkage)
 		global.SetUnnamedAddr(true)
 	}
+	if state.needsArrayTypesSidetable {
+		global := c.replaceGlobalIntWithArray("reflect.arrayTypesSidetable", state.arrayTypesSidetable)
+		global.SetLinkage(llvm.InternalLinkage)
+		global.SetUnnamedAddr(true)
+	}
 	if state.needsStructTypesSidetable {
 		global := c.replaceGlobalIntWithArray("reflect.structTypesSidetable", state.structTypesSidetable)
 		global.SetLinkage(llvm.InternalLinkage)
@@ -268,6 +280,10 @@ func (state *typeCodeAssignmentState) getNonBasicTypeCode(class string, typecode
 		// Prefix-style type kinds. The upper bits contain the element type.
 		sub := llvm.ConstExtractValue(typecode.Initializer(), []uint32{0})
 		return state.getTypeCodeNum(sub)
+	case "array":
+		// An array is basically a pair of (typecode, length) stored in a
+		// sidetable.
+		return big.NewInt(int64(state.getArrayTypeNum(typecode)))
 	case "struct":
 		// More complicated type kind. The upper bits contain the index to the
 		// struct type in the struct types sidetable.
@@ -312,6 +328,43 @@ func (state *typeCodeAssignmentState) getBasicNamedTypeNum(name string) int {
 	return num
 }
 
+// getArrayTypeNum returns the array type number, which is an index into the
+// reflect.arrayTypesSidetable or a unique number for this type if this table is
+// not used.
+func (state *typeCodeAssignmentState) getArrayTypeNum(typecode llvm.Value) int {
+	name := typecode.Name()
+	if num, ok := state.arrayTypes[name]; ok {
+		// This array type already has an entry in the sidetable. Don't store
+		// it twice.
+		return num
+	}
+
+	if !state.needsArrayTypesSidetable {
+		// We don't need array sidetables, so we can just assign monotonically
+		// increasing numbers to each array type.
+		num := len(state.arrayTypes)
+		state.arrayTypes[name] = num
+		return num
+	}
+
+	elemTypeCode := llvm.ConstExtractValue(typecode.Initializer(), []uint32{0})
+	elemTypeNum := state.getTypeCodeNum(elemTypeCode)
+	if elemTypeNum.BitLen() > state.uintptrLen || !elemTypeNum.IsUint64() {
+		// TODO: make this a regular error
+		panic("array element type has a type code that is too big")
+	}
+
+	// The array side table is a sequence of {element type, array length}.
+	arrayLength := llvm.ConstExtractValue(typecode.Initializer(), []uint32{1}).ZExtValue()
+	buf := makeVarint(elemTypeNum.Uint64())
+	buf = append(buf, makeVarint(arrayLength)...)
+
+	index := len(state.arrayTypesSidetable)
+	state.arrayTypes[name] = index
+	state.arrayTypesSidetable = append(state.arrayTypesSidetable, buf...)
+	return index
+}
+
 // getStructTypeNum returns the struct type number, which is an index into
 // reflect.structTypesSidetable or an unique number for every struct if this
 // sidetable is not needed in the to-be-compiled program.

src/reflect/sidetables.go

@@ -16,6 +16,9 @@ var structTypesSidetable byte
 //go:extern reflect.structNamesSidetable
 var structNamesSidetable byte
 
+//go:extern reflect.arrayTypesSidetable
+var arrayTypesSidetable byte
+
 // readStringSidetable reads a string from the given table (like
 // structNamesSidetable) and returns this string. No heap allocation is
 // necessary because it makes the string point directly to the raw bytes of the

src/reflect/type.go

@@ -142,11 +142,17 @@ func (t Type) Kind() Kind {
 	}
 }
 
+// Elem returns the element type for channel, slice and array types, the
+// pointed-to value for pointer types, and the key type for map types.
 func (t Type) Elem() Type {
 	switch t.Kind() {
 	case Chan, Ptr, Slice:
 		return t.stripPrefix()
-	default: // not implemented: Array, Map
+	case Array:
+		index := t.stripPrefix()
+		elem, _ := readVarint(unsafe.Pointer(uintptr(unsafe.Pointer(&arrayTypesSidetable)) + uintptr(index)))
+		return Type(elem)
+	default: // not implemented: Map
 		panic("unimplemented: (reflect.Type).Elem()")
 	}
 }
@@ -254,8 +260,20 @@ func (t Type) Bits() int {
 	panic(TypeError{"Bits"})
 }
 
+// Len returns the number of elements in this array. It panics of the type kind
+// is not Array.
 func (t Type) Len() int {
-	panic("unimplemented: (reflect.Type).Len()")
+	if t.Kind() != Array {
+		panic(TypeError{"Len"})
+	}
+
+	// skip past the element type
+	arrayIdentifier := t.stripPrefix()
+	_, p := readVarint(unsafe.Pointer(uintptr(unsafe.Pointer(&arrayTypesSidetable)) + uintptr(arrayIdentifier)))
+
+	// Read the array length.
+	arrayLen, _ := readVarint(p)
+	return int(arrayLen)
 }
 
 // NumField returns the number of fields of a struct type. It panics for other
@@ -301,6 +319,8 @@ func (t Type) Size() uintptr {
 		return unsafe.Sizeof(SliceHeader{})
 	case Interface:
 		return unsafe.Sizeof(interfaceHeader{})
+	case Array:
+		return t.Elem().Size() * uintptr(t.Len())
 	case Struct:
 		numField := t.NumField()
 		if numField == 0 {

src/reflect/value.go

@@ -302,6 +302,8 @@ func (v Value) Slice(i, j int) Value {
 	panic("unimplemented: (reflect.Value).Slice()")
 }
 
+// Len returns the length of this value for slices, strings, arrays, channels,
+// and maps. For oter types, it panics.
 func (v Value) Len() int {
 	t := v.Type()
 	switch t.Kind() {
@@ -309,7 +311,9 @@ func (v Value) Len() int {
 		return int((*SliceHeader)(v.value).Len)
 	case String:
 		return int((*StringHeader)(v.value).Len)
-	default: // Array, Chan, Map
+	case Array:
+		return v.Type().Len()
+	default: // Chan, Map
 		panic("unimplemented: (reflect.Value).Len()")
 	}
 }
@@ -392,27 +396,21 @@ func (v Value) Field(i int) Value {
 		// afterwards, so load the value (from the correct offset) and return
 		// it.
 		ptr := unsafe.Pointer(uintptr(v.value) + structField.Offset)
-		loadedValue := uintptr(0)
-		shift := uintptr(0)
-		for i := uintptr(0); i < fieldSize; i++ {
-			loadedValue |= uintptr(*(*byte)(ptr)) << shift
-			shift += 8
-			ptr = unsafe.Pointer(uintptr(ptr) + 1)
-		}
+		value := unsafe.Pointer(loadValue(ptr, fieldSize))
 		return Value{
 			flags:    0,
 			typecode: structField.Type,
-			value:    unsafe.Pointer(loadedValue),
+			value:    value,
 		}
 	}
 
 	// The value was already stored directly in the interface and it still
 	// is. Cut out the part of the value that we need.
-	mask := ^uintptr(0) >> ((unsafe.Sizeof(uintptr(0)) - fieldSize) * 8)
+	value := maskAndShift(uintptr(v.value), structField.Offset, fieldSize)
 	return Value{
 		flags:    flags,
 		typecode: structField.Type,
-		value:    unsafe.Pointer((uintptr(v.value) >> (structField.Offset * 8)) & mask),
+		value:    unsafe.Pointer(value),
 	}
 }
 
@@ -444,12 +442,75 @@ func (v Value) Index(i int) Value {
 			value:    unsafe.Pointer(uintptr(*(*uint8)(unsafe.Pointer(s.Data + uintptr(i))))),
 		}
 	case Array:
-		panic("unimplemented: (reflect.Value).Index()")
+		// Extract an element from the array.
+		elemType := v.Type().Elem()
+		elemSize := elemType.Size()
+		size := v.Type().Size()
+		if size == 0 {
+			// The element size is 0 and/or the length of the array is 0.
+			return Value{
+				typecode: v.Type().Elem(),
+				flags:    v.flags,
+			}
+		}
+		if elemSize > unsafe.Sizeof(uintptr(0)) {
+			// The resulting value doesn't fit in a pointer so must be
+			// indirect. Also, because size != 0 this implies that the array
+			// length must be != 0, and thus that the total size is at least
+			// elemSize.
+			addr := uintptr(v.value) + elemSize*uintptr(i) // pointer to new value
+			return Value{
+				typecode: v.Type().Elem(),
+				flags:    v.flags,
+				value:    unsafe.Pointer(addr),
+			}
+		}
+
+		if size > unsafe.Sizeof(uintptr(0)) {
+			// The element fits in a pointer, but the array does not.
+			// Load the value from the pointer.
+			addr := uintptr(v.value) + elemSize*uintptr(i) // pointer to new value
+			return Value{
+				typecode: v.Type().Elem(),
+				flags:    v.flags,
+				value:    unsafe.Pointer(loadValue(unsafe.Pointer(addr), elemSize)),
+			}
+		}
+
+		// The value fits in a pointer, so extract it with some shifting and
+		// masking.
+		offset := elemSize * uintptr(i)
+		value := maskAndShift(uintptr(v.value), offset, elemSize)
+		return Value{
+			typecode: v.Type().Elem(),
+			flags:    v.flags,
+			value:    unsafe.Pointer(value),
+		}
 	default:
 		panic(&ValueError{"Index"})
 	}
 }
 
+// loadValue loads a value that may or may not be word-aligned. The number of
+// bytes given in size are loaded. The biggest possible size it can load is that
+// of an uintptr.
+func loadValue(ptr unsafe.Pointer, size uintptr) uintptr {
+	loadedValue := uintptr(0)
+	shift := uintptr(0)
+	for i := uintptr(0); i < size; i++ {
+		loadedValue |= uintptr(*(*byte)(ptr)) << shift
+		shift += 8
+		ptr = unsafe.Pointer(uintptr(ptr) + 1)
+	}
+	return loadedValue
+}
+
+// maskAndShift cuts out a part of a uintptr. Note that the offset may not be 0.
+func maskAndShift(value, offset, size uintptr) uintptr {
+	mask := ^uintptr(0) >> ((unsafe.Sizeof(uintptr(0)) - size) * 8)
+	return (uintptr(value) >> (offset * 8)) & mask
+}
+
 func (v Value) MapKeys() []Value {
 	panic("unimplemented: (reflect.Value).MapKeys()")
 }

src/runtime/interface.go

@@ -49,10 +49,13 @@ type typecodeID struct {
 	// * basic types: null
 	// * named type: the underlying type
 	// * interface: null
-	// * chan/pointer/slice: the element type
-	// * struct: GEP of structField array (to typecode field)
-	// * array/func/map: TODO
+	// * chan/pointer/slice/array: the element type
+	// * struct: bitcast of global with structField array
+	// * func/map: TODO
 	references *typecodeID
+
+	// The array length, for array types.
+	length uintptr
 }
 
 // structField is used by the compiler to pass information to the interface

testdata/reflect.go

@@ -91,7 +91,8 @@ func main() {
 		[]complex128{1, 1.128 + 0.4i},
 		myslice{5, 3, 11},
 		// array
-		[4]int{1, 2, 3, 4},
+		[3]int64{5, 8, 2},
+		[2]uint8{3, 5},
 		// functions
 		zeroFunc,
 		emptyFunc,
@@ -287,7 +288,10 @@ func showValue(rv reflect.Value, indent string) {
 	case reflect.UnsafePointer:
 		println(indent+"  pointer:", rv.Pointer() != 0)
 	case reflect.Array:
-		println(indent + "  array")
+		println(indent+"  array:", rt.Len(), rt.Elem().Kind().String(), int(rt.Size()))
+		for i := 0; i < rv.Len(); i++ {
+			showValue(rv.Index(i), indent+"  ")
+		}
 	case reflect.Chan:
 		println(indent+"  chan:", rt.Elem().Kind().String())
 		println(indent+"  nil:", rv.IsNil())

testdata/reflect.txt

@@ -203,7 +203,19 @@ reflect type: slice
   reflect type: uint8 settable=true
     uint: 11
 reflect type: array
-  array
+  array: 3 int64 24
+  reflect type: int64
+    int: 5
+  reflect type: int64
+    int: 8
+  reflect type: int64
+    int: 2
+reflect type: array
+  array: 2 uint8 2
+  reflect type: uint8
+    uint: 3
+  reflect type: uint8
+    uint: 5
 reflect type: func
   func
   nil: true