reflect: StructOf set abi.TFlagRegularMemory

Complete a TODO.

Change-Id: I791d27266ccee69c371524e298120765f5736cf8
GitHub-Last-Rev: 8878003efa2f9f3d8609b88073c982d21ece774b
GitHub-Pull-Request: golang/go#64617
Reviewed-on: https://go-review.googlesource.com/c/go/+/548435
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

3 files changed, 91 insertions, 1 deletions

diff --git a/src/reflect/export_test.go b/src/reflect/export_test.go
index 1648eb3624..55eb50a425 100644
--- a/src/reflect/export_test.go
+++ b/src/reflect/export_test.go
@@ -166,3 +166,5 @@ func SetArgRegs(ints, floats int, floatSize uintptr) (oldInts, oldFloats int, ol
 var MethodValueCallCodePtr = methodValueCallCodePtr
 
 var InternalIsZero = isZero
+
+var IsRegularMemory = isRegularMemory
diff --git a/src/reflect/type.go b/src/reflect/type.go
index 89c5015530..dfa2ff6ddf 100644
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@@ -2152,6 +2152,47 @@ func isValidFieldName(fieldName string) bool {
 	return len(fieldName) > 0
 }
 
+// This must match cmd/compile/internal/compare.IsRegularMemory
+func isRegularMemory(t Type) bool {
+	switch t.Kind() {
+	case Array:
+		return isRegularMemory(t.Elem())
+	case Int8, Int16, Int32, Int64, Int, Uint8, Uint16, Uint32, Uint64, Uint, Uintptr, Chan, Pointer, Bool, UnsafePointer:
+		return true
+	case Struct:
+		num := t.NumField()
+		switch num {
+		case 0:
+			return true
+		case 1:
+			field := t.Field(0)
+			if field.Name == "_" {
+				return false
+			}
+			return isRegularMemory(field.Type)
+		default:
+			for i := range num {
+				field := t.Field(i)
+				if field.Name == "_" || !isRegularMemory(field.Type) || isPaddedField(t, i) {
+					return false
+				}
+			}
+			return true
+		}
+	}
+	return false
+}
+
+// isPaddedField reports whether the i'th field of struct type t is followed
+// by padding.
+func isPaddedField(t Type, i int) bool {
+	field := t.Field(i)
+	if i+1 < t.NumField() {
+		return field.Offset+field.Type.Size() != t.Field(i+1).Offset
+	}
+	return field.Offset+field.Type.Size() != t.Size()
+}
+
 // StructOf returns the struct type containing fields.
 // The Offset and Index fields are ignored and computed as they would be
 // by the compiler.
@@ -2445,7 +2486,11 @@ func StructOf(fields []StructField) Type {
 	}
 
 	typ.Str = resolveReflectName(newName(str, "", false, false))
-	typ.TFlag = 0 // TODO: set tflagRegularMemory
+	if isRegularMemory(toType(&typ.Type)) {
+		typ.TFlag = abi.TFlagRegularMemory
+	} else {
+		typ.TFlag = 0
+	}
 	typ.Hash = hash
 	typ.Size_ = size
 	typ.PtrBytes = typeptrdata(&typ.Type)
diff --git a/src/reflect/type_test.go b/src/reflect/type_test.go
index 9e124273a2..d53bbe553d 100644
--- a/src/reflect/type_test.go
+++ b/src/reflect/type_test.go
@@ -57,3 +57,46 @@ func TestStructOfEmbeddedIfaceMethodCall(t *testing.T) {
 		_ = x.Name()
 	})
 }
+
+func TestIsRegularMemory(t *testing.T) {
+	type args struct {
+		t reflect.Type
+	}
+	type S struct {
+		int
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{"struct{i int}", args{reflect.TypeOf(struct{ i int }{})}, true},
+		{"struct{}", args{reflect.TypeOf(struct{}{})}, true},
+		{"struct{i int; s S}", args{reflect.TypeOf(struct {
+			i int
+			s S
+		}{})}, true},
+		{"map[int][int]", args{reflect.TypeOf(map[int]int{})}, false},
+		{"[4]chan int", args{reflect.TypeOf([4]chan int{})}, true},
+		{"struct{i int; _ S}", args{reflect.TypeOf(struct {
+			i int
+			_ S
+		}{})}, false},
+		{"struct{a int16; b int32}", args{reflect.TypeOf(struct {
+			a int16
+			b int32
+		}{})}, false},
+		{"struct {x int32; y int16}", args{reflect.TypeOf(struct {
+			x int32
+			y int16
+		}{})}, false},
+		{"struct {_ int32 }", args{reflect.TypeOf(struct{ _ int32 }{})}, false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := reflect.IsRegularMemory(tt.args.t); got != tt.want {
+				t.Errorf("isRegularMemory() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}