cmd/compile/internal/types2: refactor the Context type map to accept arbitrary types

This CL is a clean port of CL 362799 from go/types to types2.

Change-Id: Id670aa4b1ca0b568a79bb6e4855747807dcf00f3
Reviewed-on: https://go-review.googlesource.com/c/go/+/364154
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/context.go

@@ -17,15 +17,21 @@ import (
 // It is safe for concurrent use.
 type Context struct {
 	mu      sync.Mutex
-	typeMap map[string][]*Named // type hash -> instances
+	typeMap map[string][]ctxtEntry // type hash -> instances entries
-	nextID  int                 // next unique ID
+	nextID  int                    // next unique ID
-	seen    map[*Named]int      // assigned unique IDs
+	seen    map[*Named]int         // assigned unique IDs
+}
+
+type ctxtEntry struct {
+	orig     Type
+	targs    []Type
+	instance Type // = orig[targs]
 }
 
 // NewContext creates a new Context.
 func NewContext() *Context {
 	return &Context{
-		typeMap: make(map[string][]*Named),
+		typeMap: make(map[string][]ctxtEntry),
 		seen:    make(map[*Named]int),
 	}
 }
@@ -59,17 +65,17 @@ func (ctxt *Context) typeHash(typ Type, targs []Type) string {
 
 // lookup returns an existing instantiation of orig with targs, if it exists.
 // Otherwise, it returns nil.
-func (ctxt *Context) lookup(h string, orig *Named, targs []Type) *Named {
+func (ctxt *Context) lookup(h string, orig *Named, targs []Type) Type {
 	ctxt.mu.Lock()
 	defer ctxt.mu.Unlock()
 
 	for _, e := range ctxt.typeMap[h] {
-		if identicalInstance(orig, targs, e.orig, e.TypeArgs().list()) {
+		if identicalInstance(orig, targs, e.orig, e.targs) {
-			return e
+			return e.instance
 		}
 		if debug {
 			// Panic during development to surface any imperfections in our hash.
-			panic(fmt.Sprintf("non-identical instances: (orig: %s, targs: %v) and %s", orig, targs, e))
+			panic(fmt.Sprintf("non-identical instances: (orig: %s, targs: %v) and %s", orig, targs, e.instance))
 		}
 	}
 
@@ -80,24 +86,28 @@ func (ctxt *Context) lookup(h string, orig *Named, targs []Type) *Named {
 // identical type is found with the type hash h, the previously seen type is
 // returned. Otherwise, n is returned, and recorded in the Context for the hash
 // h.
-func (ctxt *Context) update(h string, n *Named) *Named {
+func (ctxt *Context) update(h string, orig Type, targs []Type, inst Type) Type {
-	assert(n != nil)
+	assert(inst != nil)
-
 	ctxt.mu.Lock()
 	defer ctxt.mu.Unlock()
 
 	for _, e := range ctxt.typeMap[h] {
-		if n == nil || Identical(n, e) {
+		if inst == nil || Identical(inst, e.instance) {
-			return e
+			return e.instance
 		}
 		if debug {
 			// Panic during development to surface any imperfections in our hash.
-			panic(fmt.Sprintf("%s and %s are not identical", n, e))
+			panic(fmt.Sprintf("%s and %s are not identical", inst, e.instance))
 		}
 	}
 
-	ctxt.typeMap[h] = append(ctxt.typeMap[h], n)
+	ctxt.typeMap[h] = append(ctxt.typeMap[h], ctxtEntry{
-	return n
+		orig:     orig,
+		targs:    targs,
+		instance: inst,
+	})
+
+	return inst
 }
 
 // idForType returns a unique ID for the pointer n.

src/cmd/compile/internal/types2/instantiate.go

@@ -52,20 +52,20 @@ func Instantiate(ctxt *Context, typ Type, targs []Type, validate bool) (Type, er
 // instance creates a type or function instance using the given original type
 // typ and arguments targs. For Named types the resulting instance will be
 // unexpanded.
-func (check *Checker) instance(pos syntax.Pos, typ Type, targs []Type, ctxt *Context) Type {
+func (check *Checker) instance(pos syntax.Pos, orig Type, targs []Type, ctxt *Context) Type {
-	switch t := typ.(type) {
+	switch orig := orig.(type) {
 	case *Named:
 		var h string
 		if ctxt != nil {
-			h = ctxt.typeHash(t, targs)
+			h = ctxt.typeHash(orig, targs)
 			// typ may already have been instantiated with identical type arguments. In
 			// that case, re-use the existing instance.
-			if named := ctxt.lookup(h, t, targs); named != nil {
+			if named := ctxt.lookup(h, orig, targs); named != nil {
 				return named
 			}
 		}
-		tname := NewTypeName(pos, t.obj.pkg, t.obj.name, nil)
+		tname := NewTypeName(pos, orig.obj.pkg, orig.obj.name, nil)
-		named := check.newNamed(tname, t, nil, nil, nil) // underlying, tparams, and methods are set when named is resolved
+		named := check.newNamed(tname, orig, nil, nil, nil) // underlying, tparams, and methods are set when named is resolved
 		named.targs = NewTypeList(targs)
 		named.resolver = func(ctxt *Context, n *Named) (*TypeParamList, Type, []*Func) {
 			return expandNamed(ctxt, n, pos)
@@ -73,23 +73,23 @@ func (check *Checker) instance(pos syntax.Pos, typ Type, targs []Type, ctxt *Con
 		if ctxt != nil {
 			// It's possible that we've lost a race to add named to the context.
 			// In this case, use whichever instance is recorded in the context.
-			named = ctxt.update(h, named)
+			named = ctxt.update(h, orig, targs, named).(*Named)
 		}
 		return named
 
 	case *Signature:
-		tparams := t.TypeParams()
+		tparams := orig.TypeParams()
 		if !check.validateTArgLen(pos, tparams.Len(), len(targs)) {
 			return Typ[Invalid]
 		}
 		if tparams.Len() == 0 {
-			return typ // nothing to do (minor optimization)
+			return orig // nothing to do (minor optimization)
 		}
-		sig := check.subst(pos, typ, makeSubstMap(tparams.list(), targs), ctxt).(*Signature)
+		sig := check.subst(pos, orig, makeSubstMap(tparams.list(), targs), ctxt).(*Signature)
 		// If the signature doesn't use its type parameters, subst
 		// will not make a copy. In that case, make a copy now (so
 		// we can set tparams to nil w/o causing side-effects).
-		if sig == t {
+		if sig == orig {
 			copy := *sig
 			sig = &copy
 		}
@@ -98,9 +98,8 @@ func (check *Checker) instance(pos syntax.Pos, typ Type, targs []Type, ctxt *Con
 		sig.tparams = nil
 		return sig
 	}
-
 	// only types and functions can be generic
-	panic(fmt.Sprintf("%v: cannot instantiate %v", pos, typ))
+	panic(fmt.Sprintf("%v: cannot instantiate %v", pos, orig))
 }
 
 // validateTArgLen verifies that the length of targs and tparams matches,

src/cmd/compile/internal/types2/named.go

@@ -253,7 +253,7 @@ func expandNamed(ctxt *Context, n *Named, instPos syntax.Pos) (tparams *TypePara
 		ctxt = check.bestContext(ctxt)
 		h := ctxt.typeHash(n.orig, n.targs.list())
 		// ensure that an instance is recorded for h to avoid infinite recursion.
-		ctxt.update(h, n)
+		ctxt.update(h, n.orig, n.TypeArgs().list(), n)
 
 		smap := makeSubstMap(n.orig.tparams.list(), n.targs.list())
 		underlying = n.check.subst(instPos, n.orig.underlying, smap, ctxt)

src/cmd/compile/internal/types2/typexpr.go

@@ -439,7 +439,7 @@ func (check *Checker) instantiatedType(x syntax.Expr, targsx []syntax.Expr, def
 	// create the instance
 	h := check.conf.Context.typeHash(orig, targs)
 	// targs may be incomplete, and require inference. In any case we should de-duplicate.
-	inst := check.conf.Context.lookup(h, orig, targs)
+	inst, _ := check.conf.Context.lookup(h, orig, targs).(*Named)
 	// If inst is non-nil, we can't just return here. Inst may have been
 	// constructed via recursive substitution, in which case we wouldn't do the
 	// validation below. Ensure that the validation (and resulting errors) runs
@@ -448,7 +448,7 @@ func (check *Checker) instantiatedType(x syntax.Expr, targsx []syntax.Expr, def
 		tname := NewTypeName(x.Pos(), orig.obj.pkg, orig.obj.name, nil)
 		inst = check.newNamed(tname, orig, nil, nil, nil) // underlying, methods and tparams are set when named is resolved
 		inst.targs = NewTypeList(targs)
-		inst = check.conf.Context.update(h, inst)
+		inst = check.conf.Context.update(h, orig, targs, inst).(*Named)
 	}
 	def.setUnderlying(inst)