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[dev.typeparams] cmd/compile/internal/types2: clean up type set/union intersection

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- Eliminate the need for bottom type: This is now represented by
  an empty union (denoting the set of no types).

- Clean up type set intersection and incorporate tilde information
  in intersection operation and satisfaction tests.

- Minor cleanups along the way.

- Note: The intersection algorithm does not always compute the
        largest possible intersection. To be addressed in a follow-up CL.

Change-Id: I7fa19df5996da36a4d8f29300d30a0aa4d8a3e5c
Reviewed-on: https://go-review.googlesource.com/c/go/+/323354
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
This commit is contained in:
Robert Griesemer 2021-05-27 19:03:16 -07:00
parent 97cb0113a3
commit 848b58e473
10 changed files with 118 additions and 78 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
src/cmd/compile/internal/types2/interface.go
View File

@ -109,16 +109,6 @@ func flattenUnion(list []syntax.Expr, x syntax.Expr) []syntax.Expr {
return append(list, x)
}
// includes reports whether typ is in list
func includes(list []Type, typ Type) bool {
for _, e := range list {
if Identical(typ, e) {
return true
}
}
return false
}
func (check *Checker) completeInterface(pos syntax.Pos, ityp *Interface) {
if ityp.allMethods != nil {
return

11
src/cmd/compile/internal/types2/predicates.go
View File

@ -97,9 +97,9 @@ func comparable(T Type, seen map[Type]bool) bool {
seen[T] = true
// If T is a type parameter not constrained by any type
// list (i.e., it's underlying type is the top type),
// list (i.e., it's operational type is the top type),
// T is comparable if it has the == method. Otherwise,
// the underlying type "wins". For instance
// the operational type "wins". For instance
//
// interface{ comparable; type []byte }
//
@ -370,10 +370,9 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
// case *instance:
// unreachable since types are expanded
case *bottom, *top:
// Either both types are theBottom, or both are theTop in which
// case the initial x == y check will have caught them. Otherwise
// they are not identical.
case *top:
// Either both types are theTop in which case the initial x == y check
// will have caught them. Otherwise they are not identical.
case nil:
// avoid a crash in case of nil type

2
src/cmd/compile/internal/types2/sanitize.go
View File

@ -77,7 +77,7 @@ func (s sanitizer) typ(typ Type) Type {
s[typ] = typ
switch t := typ.(type) {
case *Basic, *bottom, *top:
case *Basic, *top:
// nothing to do
case *Array:

1
src/cmd/compile/internal/types2/sizeof_test.go
View File

@ -34,7 +34,6 @@ func TestSizeof(t *testing.T) {
{Named{}, 68, 136},
{TypeParam{}, 28, 48},
{instance{}, 52, 96},
{bottom{}, 0, 0},
{top{}, 0, 0},
// Objects

4
src/cmd/compile/internal/types2/subst.go
View File

@ -206,7 +206,7 @@ func (check *Checker) satisfies(pos syntax.Pos, targ Type, tpar *TypeParam, smap
// Otherwise, targ's type or underlying type must also be one of the interface types listed, if any.
if !iface.isSatisfiedBy(targ) {
check.softErrorf(pos, "%s does not satisfy %s (%s not found in %s)", targ, tpar.bound, under(targ), iface.allTypes)
check.softErrorf(pos, "%s does not satisfy %s (%s not found in %s)", targ, tpar.bound, targ, iface.allTypes)
return false
}
@ -249,7 +249,7 @@ func (subst *subster) typ(typ Type) Type {
// Call typOrNil if it's possible that typ is nil.
panic("nil typ")
case *Basic, *bottom, *top:
case *Basic, *top:
// nothing to do
case *Array:

2
src/cmd/compile/internal/types2/testdata/check/issues.go2 vendored
View File

@ -234,7 +234,7 @@ func _[T interface{ type func() }](f T) {
type sliceOf[E any] interface{ type []E }
func append[T interface{}, S sliceOf[T], T2 interface{ type T }](s S, t ...T2) S
func append[T interface{}, S sliceOf[T], T2 interface{ T }](s S, t ...T2) S
var f func()
var cancelSlice []context.CancelFunc

14
src/cmd/compile/internal/types2/testdata/examples/constraints.go2 vendored
View File

@ -23,3 +23,17 @@ type (
_ interface{~ /* ERROR cannot use interface */ interface{}}
_ interface{int|interface /* ERROR cannot use interface */ {}}
)
// Multiple embedded union elements are intersected. The order in which they
// appear in the interface doesn't matter since intersection is a symmetric
// operation.
type myInt1 int
type myInt2 int
func _[T interface{ myInt1|myInt2; ~int }]() T { return T(0) }
func _[T interface{ ~int; myInt1|myInt2 }]() T { return T(0) }
// Here the intersections are empty - there's no type that's in the type set of T.
func _[T interface{ myInt1|myInt2; int }]() T { return T(0 /* ERROR cannot convert */ ) }
func _[T interface{ int; myInt1|myInt2 }]() T { return T(0 /* ERROR cannot convert */ ) }

40
src/cmd/compile/internal/types2/type.go
View File

@ -376,7 +376,6 @@ func (t *Interface) Method(i int) *Func { t.Complete(); return t.allMethods[i] }
// Empty reports whether t is the empty interface.
func (t *Interface) Empty() bool {
t.Complete()
// A non-nil allTypes may still have length 0 but represents the bottom type.
return len(t.allMethods) == 0 && t.allTypes == nil
}
@ -431,11 +430,15 @@ func (t *Interface) iterate(f func(*Interface) bool, seen map[*Interface]bool) b
// "implements" predicate.
func (t *Interface) isSatisfiedBy(typ Type) bool {
t.Complete()
if t.allTypes == nil {
return true
switch t := t.allTypes.(type) {
case nil:
return true // no type restrictions
case *Union:
r, _ := t.intersect(typ, false)
return r != nil
default:
return Identical(t, typ)
}
types := unpack(t.allTypes)
return includes(types, typ) || includes(types, under(typ))
}
// Complete computes the interface's method set. It must be called by users of
@ -654,13 +657,11 @@ func (t *TypeParam) Bound() *Interface {
return iface
}
// optype returns a type's operational type. Except for
// type parameters, the operational type is the same
// as the underlying type (as returned by under). For
// Type parameters, the operational type is determined
// by the corresponding type bound's type list. The
// result may be the bottom or top type, but it is never
// the incoming type parameter.
// optype returns a type's operational type. Except for type parameters,
// the operational type is the same as the underlying type (as returned
// by under). For Type parameters, the operational type is determined
// by the corresponding type constraint. The result may be the top type,
// but it is never the incoming type parameter.
func optype(typ Type) Type {
if t := asTypeParam(typ); t != nil {
// If the optype is typ, return the top type as we have
@ -733,20 +734,11 @@ var expandf func(Type) Type
func init() { expandf = expand }
// bottom represents the bottom of the type lattice.
// It is the underlying type of a type parameter that
// cannot be satisfied by any type, usually because
// the intersection of type constraints left nothing).
type bottom struct{}
// theBottom is the singleton bottom type.
var theBottom = &bottom{}
// top represents the top of the type lattice.
// It is the underlying type of a type parameter that
// can be satisfied by any type (ignoring methods),
// usually because the type constraint has no type
// list.
// because its type constraint contains no restrictions
// besides methods.
type top struct{}
// theTop is the singleton top type.
@ -766,7 +758,6 @@ func (t *Chan) Underlying() Type { return t }
func (t *Named) Underlying() Type { return t.underlying }
func (t *TypeParam) Underlying() Type { return t }
func (t *instance) Underlying() Type { return t }
func (t *bottom) Underlying() Type { return t }
func (t *top) Underlying() Type { return t }
// Type-specific implementations of String.
@ -783,7 +774,6 @@ func (t *Chan) String() string { return TypeString(t, nil) }
func (t *Named) String() string { return TypeString(t, nil) }
func (t *TypeParam) String() string { return TypeString(t, nil) }
func (t *instance) String() string { return TypeString(t, nil) }
func (t *bottom) String() string { return TypeString(t, nil) }
func (t *top) String() string { return TypeString(t, nil) }
// under returns the true expanded underlying type.

7
src/cmd/compile/internal/types2/typestring.go
View File

@ -158,6 +158,10 @@ func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
writeSignature(buf, t, qf, visited)
case *Union:
if t.IsEmpty() {
buf.WriteString("⊥")
break
}
for i, e := range t.types {
if i > 0 {
buf.WriteString("|")
@ -294,9 +298,6 @@ func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
writeTypeList(buf, t.targs, qf, visited)
buf.WriteByte(']')
case *bottom:
buf.WriteString("⊥")
case *top:
buf.WriteString("⊤")

103
src/cmd/compile/internal/types2/union.go
View File

@ -16,8 +16,12 @@ type Union struct {
tilde []bool // if tilde[i] is set, terms[i] is of the form ~T
}
func NewUnion(types []Type, tilde []bool) Type { return newUnion(types, tilde) }
// NewUnion returns a new Union type with the given terms (types[i], tilde[i]).
// The lengths of both arguments must match. An empty union represents the set
// of no types.
func NewUnion(types []Type, tilde []bool) *Union { return newUnion(types, tilde) }
func (u *Union) IsEmpty() bool { return len(u.types) == 0 }
func (u *Union) NumTerms() int { return len(u.types) }
func (u *Union) Term(i int) (Type, bool) { return u.types[i], u.tilde[i] }
@ -27,10 +31,12 @@ func (u *Union) String() string { return TypeString(u, nil) }
// ----------------------------------------------------------------------------
// Implementation
func newUnion(types []Type, tilde []bool) Type {
var emptyUnion = new(Union)
func newUnion(types []Type, tilde []bool) *Union {
assert(len(types) == len(tilde))
if types == nil {
return nil
if len(types) == 0 {
return emptyUnion
}
t := new(Union)
t.types = types
@ -40,7 +46,7 @@ func newUnion(types []Type, tilde []bool) Type {
// is reports whether f returned true for all terms (type, tilde) of u.
func (u *Union) is(f func(Type, bool) bool) bool {
if u == nil {
if u.IsEmpty() {
return false
}
for i, t := range u.types {
@ -53,7 +59,7 @@ func (u *Union) is(f func(Type, bool) bool) bool {
// is reports whether f returned true for the underlying types of all terms of u.
func (u *Union) underIs(f func(Type) bool) bool {
if u == nil {
if u.IsEmpty() {
return false
}
for _, t := range u.types {
@ -130,26 +136,24 @@ func parseTilde(check *Checker, x syntax.Expr) (Type, bool) {
return check.anyType(x), tilde
}
// intersect computes the intersection of the types x and y.
// Note: An incomming nil type stands for the top type. A top
// type result is returned as nil.
// intersect computes the intersection of the types x and y,
// A nil type stands for the set of all types; an empty union
// stands for the set of no types.
func intersect(x, y Type) (r Type) {
defer func() {
if r == theTop {
r = nil
}
}()
// If one of the types is nil (no restrictions)
// the result is the other type.
switch {
case x == theBottom || y == theBottom:
return theBottom
case x == nil || x == theTop:
case x == nil:
return y
case y == nil || x == theTop:
case y == nil:
return x
}
// Compute the terms which are in both x and y.
// TODO(gri) This is not correct as it may not always compute
// the "largest" intersection. For instance, for
// x = myInt|~int, y = ~int
// we get the result myInt but we should get ~int.
xu, _ := x.(*Union)
yu, _ := y.(*Union)
switch {
@ -158,23 +162,29 @@ func intersect(x, y Type) (r Type) {
// TODO(gri) fix asymptotic performance
var types []Type
var tilde []bool
for _, y := range yu.types {
if includes(xu.types, y) {
types = append(types, y)
tilde = append(tilde, true) // TODO(gri) fix this
for j, y := range yu.types {
yt := yu.tilde[j]
if r, rt := xu.intersect(y, yt); r != nil {
// Terms x[i] and y[j] match: Select the one that
// is not a ~t because that is the intersection
// type. If both are ~t, they are identical:
// T ∩ T = T
// T ∩ ~t = T
// ~t ∩ T = T
// ~t ∩ ~t = ~t
types = append(types, r)
tilde = append(tilde, rt)
}
}
if types != nil {
return newUnion(types, tilde)
}
case xu != nil:
if includes(xu.types, y) {
if r, _ := xu.intersect(y, false); r != nil {
return y
}
case yu != nil:
if includes(yu.types, x) {
if r, _ := yu.intersect(x, false); r != nil {
return x
}
@ -184,5 +194,42 @@ func intersect(x, y Type) (r Type) {
}
}
return theBottom
return emptyUnion
}
// includes reports whether typ is in list.
func includes(list []Type, typ Type) bool {
for _, e := range list {
if Identical(typ, e) {
return true
}
}
return false
}
// intersect computes the intersection of the union u and term (y, yt)
// and returns the intersection term, if any. Otherwise the result is
// (nil, false).
func (u *Union) intersect(y Type, yt bool) (Type, bool) {
under_y := under(y)
for i, x := range u.types {
xt := u.tilde[i]
// determine which types xx, yy to compare
xx := x
if yt {
xx = under(x)
}
yy := y
if xt {
yy = under_y
}
if Identical(xx, yy) {
// T ∩ T = T
// T ∩ ~t = T
// ~t ∩ T = T
// ~t ∩ ~t = ~t
return xx, xt && yt
}
}
return nil, false
}