cmd/compile/internal/types2: use []*TypeParam rather than []*TypeName for type param lists

This is a port of CL 343932 from go/types, with the necessary adjustments
to the compiler.

This change improves type safety slightly, avoids many internal type
assertions, and simplifies some code paths.

Change-Id: Ie9c4734814f49cd248927152d7b3264d3578428c
Reviewed-on: https://go-review.googlesource.com/c/go/+/344614
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dan Scales <danscales@google.com>

17 files changed, 79 insertions, 81 deletions

diff --git a/src/cmd/compile/internal/importer/iimport.go b/src/cmd/compile/internal/importer/iimport.go
index 4384e59c30..a46971d0a7 100644
--- a/src/cmd/compile/internal/importer/iimport.go
+++ b/src/cmd/compile/internal/importer/iimport.go
@@ -309,7 +309,7 @@ func (r *importReader) obj(name string) {
 		r.declare(types2.NewConst(pos, r.currPkg, name, typ, val))
 
 	case 'F', 'G':
-		var tparams []*types2.TypeName
+		var tparams []*types2.TypeParam
 		if tag == 'G' {
 			tparams = r.tparamList()
 		}
@@ -318,7 +318,7 @@ func (r *importReader) obj(name string) {
 		r.declare(types2.NewFunc(pos, r.currPkg, name, sig))
 
 	case 'T', 'U':
-		var tparams []*types2.TypeName
+		var tparams []*types2.TypeParam
 		if tag == 'U' {
 			tparams = r.tparamList()
 		}
@@ -347,9 +347,9 @@ func (r *importReader) obj(name string) {
 				// typeparams being used in the method sig/body).
 				targs := baseType(msig.Recv().Type()).TArgs()
 				if len(targs) > 0 {
-					rparams := make([]*types2.TypeName, len(targs))
+					rparams := make([]*types2.TypeParam, len(targs))
 					for i, targ := range targs {
-						rparams[i] = types2.AsTypeParam(targ).Obj()
+						rparams[i] = types2.AsTypeParam(targ)
 					}
 					msig.SetRParams(rparams)
 				}
@@ -690,15 +690,15 @@ func (r *importReader) signature(recv *types2.Var) *types2.Signature {
 	return types2.NewSignature(recv, params, results, variadic)
 }
 
-func (r *importReader) tparamList() []*types2.TypeName {
+func (r *importReader) tparamList() []*types2.TypeParam {
 	n := r.uint64()
 	if n == 0 {
 		return nil
 	}
-	xs := make([]*types2.TypeName, n)
+	xs := make([]*types2.TypeParam, n)
 	for i := range xs {
 		typ := r.typ()
-		xs[i] = types2.AsTypeParam(typ).Obj()
+		xs[i] = types2.AsTypeParam(typ)
 	}
 	return xs
 }
diff --git a/src/cmd/compile/internal/noder/decl.go b/src/cmd/compile/internal/noder/decl.go
index 6b55ce1453..ffcfc103a6 100644
--- a/src/cmd/compile/internal/noder/decl.go
+++ b/src/cmd/compile/internal/noder/decl.go
@@ -191,7 +191,7 @@ func (g *irgen) typeDecl(out *ir.Nodes, decl *syntax.TypeDecl) {
 	if n := tparams.Len(); n > 0 {
 		rparams := make([]*types.Type, n)
 		for i := range rparams {
-			rparams[i] = g.typ(tparams.At(i).Type())
+			rparams[i] = g.typ(tparams.At(i))
 		}
 		// This will set hasTParam flag if any rparams are not concrete types.
 		ntyp.SetRParams(rparams)
diff --git a/src/cmd/compile/internal/noder/reader2.go b/src/cmd/compile/internal/noder/reader2.go
index e72a6737ed..8f3f0a50e9 100644
--- a/src/cmd/compile/internal/noder/reader2.go
+++ b/src/cmd/compile/internal/noder/reader2.go
@@ -396,7 +396,7 @@ func (pr *pkgReader2) objIdx(idx int) (*types2.Package, string) {
 		case objType:
 			pos := r.pos()
 
-			return types2.NewTypeNameLazy(pos, objPkg, objName, func(named *types2.Named) (tparams []*types2.TypeName, underlying types2.Type, methods []*types2.Func) {
+			return types2.NewTypeNameLazy(pos, objPkg, objName, func(named *types2.Named) (tparams []*types2.TypeParam, underlying types2.Type, methods []*types2.Func) {
 				tparams = r.typeParamNames()
 
 				// TODO(mdempsky): Rewrite receiver types to underlying is an
@@ -453,7 +453,7 @@ func (pr *pkgReader2) objDictIdx(idx int) *reader2Dict {
 	return &dict
 }
 
-func (r *reader2) typeParamNames() []*types2.TypeName {
+func (r *reader2) typeParamNames() []*types2.TypeParam {
 	r.sync(syncTypeParamNames)
 
 	// Note: This code assumes it only processes objects without
@@ -470,21 +470,20 @@ func (r *reader2) typeParamNames() []*types2.TypeName {
 	// create all the TypeNames and TypeParams, then we construct and
 	// set the bound type.
 
-	names := make([]*types2.TypeName, len(r.dict.bounds))
 	r.dict.tparams = make([]*types2.TypeParam, len(r.dict.bounds))
 	for i := range r.dict.bounds {
 		pos := r.pos()
 		pkg, name := r.localIdent()
 
-		names[i] = types2.NewTypeName(pos, pkg, name, nil)
-		r.dict.tparams[i] = r.p.check.NewTypeParam(names[i], nil)
+		tname := types2.NewTypeName(pos, pkg, name, nil)
+		r.dict.tparams[i] = r.p.check.NewTypeParam(tname, nil)
 	}
 
 	for i, bound := range r.dict.bounds {
 		r.dict.tparams[i].SetConstraint(r.p.typIdx(bound, r.dict))
 	}
 
-	return names
+	return r.dict.tparams
 }
 
 func (r *reader2) method() *types2.Func {
diff --git a/src/cmd/compile/internal/noder/syncmarker_string.go b/src/cmd/compile/internal/noder/syncmarker_string.go
index 14747b7c10..655cafc950 100644
--- a/src/cmd/compile/internal/noder/syncmarker_string.go
+++ b/src/cmd/compile/internal/noder/syncmarker_string.go
@@ -140,11 +140,12 @@ func _() {
 	_ = x[syncTypeParamNames-130]
 	_ = x[syncTypeParamBounds-131]
 	_ = x[syncImplicitTypes-132]
+	_ = x[syncObjectName-133]
 }
 
-const _syncMarker_name = "NodeBoolInt64Uint64StringPosPkgSymSelectorKindTypeTypePkgSignatureParamOpObjectExprStmtDeclConstDeclFuncDeclTypeDeclVarDeclPragmaValueEOFMethodFuncBodyUseUseObjObjectIdxTypeIdxBOFEntryOpenScopeCloseScopeGlobalLocalDefineDefLocalUseLocalDefGlobalUseGlobalTypeParamsUseLabelDefLabelFuncLitCommonFuncBodyRefLinksymExtHackSetlinenoNameImportDeclDeclNamesDeclNameExprListExprsWrapnameTypeExprTypeExprOrNilChanDirParamsCloseAnotherScopeSumUnOpBinOpStructTypeInterfaceTypePacknameEmbeddedStmtsStmtsFallStmtFallBlockStmtIfStmtForStmtSwitchStmtRangeStmtCaseClauseCommClauseSelectStmtDeclsLabeledStmtCompLit1234NDefImplicitUseNameUseObjLocalAddLocalBothSignatureSetUnderlyingLinknameStmt1StmtsEndDeclareTopDeclsTopConstDeclTopFuncDeclTopTypeDeclTopVarDeclObject1AddBodyLabelFuncExtMethExtOptLabelScalarStmtDeclsDeclLocalObjLocalObjLocal1DeclareLocalPublicPrivateRelocsRelocUseRelocVarExtPkgDefTypeExtValCodeObjPosBaseLocalIdentTypeParamNamesTypeParamBoundsImplicitTypes"
+const _syncMarker_name = "NodeBoolInt64Uint64StringPosPkgSymSelectorKindTypeTypePkgSignatureParamOpObjectExprStmtDeclConstDeclFuncDeclTypeDeclVarDeclPragmaValueEOFMethodFuncBodyUseUseObjObjectIdxTypeIdxBOFEntryOpenScopeCloseScopeGlobalLocalDefineDefLocalUseLocalDefGlobalUseGlobalTypeParamsUseLabelDefLabelFuncLitCommonFuncBodyRefLinksymExtHackSetlinenoNameImportDeclDeclNamesDeclNameExprListExprsWrapnameTypeExprTypeExprOrNilChanDirParamsCloseAnotherScopeSumUnOpBinOpStructTypeInterfaceTypePacknameEmbeddedStmtsStmtsFallStmtFallBlockStmtIfStmtForStmtSwitchStmtRangeStmtCaseClauseCommClauseSelectStmtDeclsLabeledStmtCompLit1234NDefImplicitUseNameUseObjLocalAddLocalBothSignatureSetUnderlyingLinknameStmt1StmtsEndDeclareTopDeclsTopConstDeclTopFuncDeclTopTypeDeclTopVarDeclObject1AddBodyLabelFuncExtMethExtOptLabelScalarStmtDeclsDeclLocalObjLocalObjLocal1DeclareLocalPublicPrivateRelocsRelocUseRelocVarExtPkgDefTypeExtValCodeObjPosBaseLocalIdentTypeParamNamesTypeParamBoundsImplicitTypesObjectName"
 
-var _syncMarker_index = [...]uint16{0, 4, 8, 13, 19, 25, 28, 31, 34, 42, 46, 50, 57, 66, 71, 73, 79, 83, 87, 91, 100, 108, 116, 123, 129, 134, 137, 143, 151, 154, 160, 169, 176, 179, 184, 193, 203, 209, 214, 220, 228, 236, 245, 254, 264, 272, 280, 287, 297, 304, 314, 318, 327, 331, 341, 350, 358, 366, 371, 379, 387, 400, 407, 413, 430, 433, 437, 442, 452, 465, 473, 481, 486, 495, 503, 512, 518, 525, 535, 544, 554, 564, 574, 579, 590, 597, 598, 599, 600, 601, 602, 613, 620, 631, 639, 652, 665, 673, 678, 686, 693, 701, 713, 724, 735, 745, 752, 759, 764, 771, 778, 786, 792, 801, 810, 818, 827, 839, 845, 852, 858, 863, 871, 877, 883, 890, 893, 900, 907, 917, 931, 946, 959}
+var _syncMarker_index = [...]uint16{0, 4, 8, 13, 19, 25, 28, 31, 34, 42, 46, 50, 57, 66, 71, 73, 79, 83, 87, 91, 100, 108, 116, 123, 129, 134, 137, 143, 151, 154, 160, 169, 176, 179, 184, 193, 203, 209, 214, 220, 228, 236, 245, 254, 264, 272, 280, 287, 297, 304, 314, 318, 327, 331, 341, 350, 358, 366, 371, 379, 387, 400, 407, 413, 430, 433, 437, 442, 452, 465, 473, 481, 486, 495, 503, 512, 518, 525, 535, 544, 554, 564, 574, 579, 590, 597, 598, 599, 600, 601, 602, 613, 620, 631, 639, 652, 665, 673, 678, 686, 693, 701, 713, 724, 735, 745, 752, 759, 764, 771, 778, 786, 792, 801, 810, 818, 827, 839, 845, 852, 858, 863, 871, 877, 883, 890, 893, 900, 907, 917, 931, 946, 959, 969}
 
 func (i syncMarker) String() string {
 	i -= 1
diff --git a/src/cmd/compile/internal/noder/types.go b/src/cmd/compile/internal/noder/types.go
index 8d596e599e..dd1fdcf96b 100644
--- a/src/cmd/compile/internal/noder/types.go
+++ b/src/cmd/compile/internal/noder/types.go
@@ -306,7 +306,7 @@ func (g *irgen) fillinMethods(typ *types2.Named, ntyp *types.Type) {
 					rparams := types2.AsSignature(m.Type()).RParams()
 					tparams := make([]*types.Type, rparams.Len())
 					for i := range tparams {
-						tparams[i] = g.typ1(rparams.At(i).Type())
+						tparams[i] = g.typ1(rparams.At(i))
 					}
 					assert(len(tparams) == len(targs))
 					ts := typecheck.Tsubster{
@@ -338,7 +338,7 @@ func (g *irgen) signature(recv *types.Field, sig *types2.Signature) *types.Type
 	tparams2 := sig.TParams()
 	tparams := make([]*types.Field, tparams2.Len())
 	for i := range tparams {
-		tp := tparams2.At(i)
+		tp := tparams2.At(i).Obj()
 		tparams[i] = types.NewField(g.pos(tp), g.sym(tp), g.typ1(tp.Type()))
 	}
 
diff --git a/src/cmd/compile/internal/noder/writer.go b/src/cmd/compile/internal/noder/writer.go
index a33b24e50c..02df9a43de 100644
--- a/src/cmd/compile/internal/noder/writer.go
+++ b/src/cmd/compile/internal/noder/writer.go
@@ -618,7 +618,7 @@ func (w *writer) objDict(obj types2.Object, dict *writerDict) {
 	ntparams := tparams.Len()
 	w.len(ntparams)
 	for i := 0; i < ntparams; i++ {
-		w.typ(tparams.At(i).Type().(*types2.TypeParam).Constraint())
+		w.typ(tparams.At(i).Constraint())
 	}
 
 	nderived := len(dict.derived)
@@ -647,7 +647,7 @@ func (w *writer) typeParamNames(tparams *types2.TParamList) {
 
 	ntparams := tparams.Len()
 	for i := 0; i < ntparams; i++ {
-		tparam := tparams.At(i)
+		tparam := tparams.At(i).Obj()
 		w.pos(tparam)
 		w.localIdent(tparam)
 	}
@@ -1479,7 +1479,7 @@ func (c *declCollector) withTParams(obj types2.Object) *declCollector {
 	copy := *c
 	copy.implicits = copy.implicits[:len(copy.implicits):len(copy.implicits)]
 	for i := 0; i < n; i++ {
-		copy.implicits = append(copy.implicits, tparams.At(i))
+		copy.implicits = append(copy.implicits, tparams.At(i).Obj())
 	}
 	return &copy
 }
diff --git a/src/cmd/compile/internal/types2/decl.go b/src/cmd/compile/internal/types2/decl.go
index aa9710788a..342e1090de 100644
--- a/src/cmd/compile/internal/types2/decl.go
+++ b/src/cmd/compile/internal/types2/decl.go
@@ -582,7 +582,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *syntax.TypeDecl, def *Named
 }
 
 func (check *Checker) collectTypeParams(list []*syntax.Field) *TParamList {
-	tparams := make([]*TypeName, len(list))
+	tparams := make([]*TypeParam, len(list))
 
 	// Declare type parameters up-front.
 	// The scope of type parameters starts at the beginning of the type parameter
@@ -599,16 +599,16 @@ func (check *Checker) collectTypeParams(list []*syntax.Field) *TParamList {
 		if i == 0 || f.Type != list[i-1].Type {
 			bound = check.boundType(f.Type)
 		}
-		tparams[i].typ.(*TypeParam).bound = bound
+		tparams[i].bound = bound
 	}
 
 	return bindTParams(tparams)
 }
 
-func (check *Checker) declareTypeParam(name *syntax.Name) *TypeName {
-	tpar := NewTypeName(name.Pos(), check.pkg, name.Value, nil)
-	check.NewTypeParam(tpar, nil)                           // assigns type to tpar as a side-effect
-	check.declare(check.scope, name, tpar, check.scope.pos) // TODO(gri) check scope position
+func (check *Checker) declareTypeParam(name *syntax.Name) *TypeParam {
+	tname := NewTypeName(name.Pos(), check.pkg, name.Value, nil)
+	tpar := check.NewTypeParam(tname, nil)                   // assigns type to tname as a side-effect
+	check.declare(check.scope, name, tname, check.scope.pos) // TODO(gri) check scope position
 	return tpar
 }
 
diff --git a/src/cmd/compile/internal/types2/infer.go b/src/cmd/compile/internal/types2/infer.go
index 7bf507471d..6e4fe502b6 100644
--- a/src/cmd/compile/internal/types2/infer.go
+++ b/src/cmd/compile/internal/types2/infer.go
@@ -28,7 +28,7 @@ const useConstraintTypeInference = true
 //
 // Constraint type inference is used after each step to expand the set of type arguments.
 //
-func (check *Checker) infer(pos syntax.Pos, tparams []*TypeName, targs []Type, params *Tuple, args []*operand, report bool) (result []Type) {
+func (check *Checker) infer(pos syntax.Pos, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand, report bool) (result []Type) {
 	if debug {
 		defer func() {
 			assert(result == nil || len(result) == len(tparams))
@@ -122,7 +122,7 @@ func (check *Checker) infer(pos syntax.Pos, tparams []*TypeName, targs []Type, p
 				}
 			}
 			if allFailed {
-				check.errorf(arg, "%s %s of %s does not match %s (cannot infer %s)", kind, targ, arg.expr, tpar, typeNamesString(tparams))
+				check.errorf(arg, "%s %s of %s does not match %s (cannot infer %s)", kind, targ, arg.expr, tpar, typeParamsString(tparams))
 				return
 			}
 		}
@@ -222,23 +222,23 @@ func (check *Checker) infer(pos syntax.Pos, tparams []*TypeName, targs []Type, p
 	assert(targs != nil && index >= 0 && targs[index] == nil)
 	tpar := tparams[index]
 	if report {
-		check.errorf(pos, "cannot infer %s (%s) (%s)", tpar.name, tpar.pos, targs)
+		check.errorf(pos, "cannot infer %s (%s) (%s)", tpar.obj.name, tpar.obj.pos, targs)
 	}
 	return nil
 }
 
-// typeNamesString produces a string containing all the
-// type names in list suitable for human consumption.
-func typeNamesString(list []*TypeName) string {
+// typeParamsString produces a string of the type parameter names
+// in list suitable for human consumption.
+func typeParamsString(list []*TypeParam) string {
 	// common cases
 	n := len(list)
 	switch n {
 	case 0:
 		return ""
 	case 1:
-		return list[0].name
+		return list[0].obj.name
 	case 2:
-		return list[0].name + " and " + list[1].name
+		return list[0].obj.name + " and " + list[1].obj.name
 	}
 
 	// general case (n > 2)
@@ -248,15 +248,15 @@ func typeNamesString(list []*TypeName) string {
 		if i > 0 {
 			b.WriteString(", ")
 		}
-		b.WriteString(tname.name)
+		b.WriteString(tname.obj.name)
 	}
 	b.WriteString(", and ")
-	b.WriteString(list[n-1].name)
+	b.WriteString(list[n-1].obj.name)
 	return b.String()
 }
 
 // IsParameterized reports whether typ contains any of the type parameters of tparams.
-func isParameterized(tparams []*TypeName, typ Type) bool {
+func isParameterized(tparams []*TypeParam, typ Type) bool {
 	w := tpWalker{
 		seen:    make(map[Type]bool),
 		tparams: tparams,
@@ -266,7 +266,7 @@ func isParameterized(tparams []*TypeName, typ Type) bool {
 
 type tpWalker struct {
 	seen    map[Type]bool
-	tparams []*TypeName
+	tparams []*TypeParam
 }
 
 func (w *tpWalker) isParameterized(typ Type) (res bool) {
@@ -339,7 +339,7 @@ func (w *tpWalker) isParameterized(typ Type) (res bool) {
 
 	case *TypeParam:
 		// t must be one of w.tparams
-		return t.index < len(w.tparams) && w.tparams[t.index].typ == t
+		return t.index < len(w.tparams) && w.tparams[t.index] == t
 
 	default:
 		unreachable()
@@ -365,7 +365,7 @@ func (w *tpWalker) isParameterizedTypeList(list []Type) bool {
 // first type argument in that list that couldn't be inferred (and thus is nil). If all
 // type arguments were inferred successfully, index is < 0. The number of type arguments
 // provided may be less than the number of type parameters, but there must be at least one.
-func (check *Checker) inferB(tparams []*TypeName, targs []Type, report bool) (types []Type, index int) {
+func (check *Checker) inferB(tparams []*TypeParam, targs []Type, report bool) (types []Type, index int) {
 	assert(len(tparams) >= len(targs) && len(targs) > 0)
 
 	// Setup bidirectional unification between those structural bounds
@@ -383,12 +383,12 @@ func (check *Checker) inferB(tparams []*TypeName, targs []Type, report bool) (ty
 
 	// Unify type parameters with their structural constraints, if any.
 	for _, tpar := range tparams {
-		typ := tpar.typ.(*TypeParam)
+		typ := tpar
 		sbound := typ.structuralType()
 		if sbound != nil {
 			if !u.unify(typ, sbound) {
 				if report {
-					check.errorf(tpar, "%s does not match %s", tpar, sbound)
+					check.errorf(tpar.obj, "%s does not match %s", tpar.obj, sbound)
 				}
 				return nil, 0
 			}
diff --git a/src/cmd/compile/internal/types2/instantiate.go b/src/cmd/compile/internal/types2/instantiate.go
index 9d60021667..06cbcda58e 100644
--- a/src/cmd/compile/internal/types2/instantiate.go
+++ b/src/cmd/compile/internal/types2/instantiate.go
@@ -54,7 +54,7 @@ func Instantiate(env *Environment, typ Type, targs []Type, validate bool) (Type,
 
 	var err error
 	if validate {
-		var tparams []*TypeName
+		var tparams []*TypeParam
 		switch t := typ.(type) {
 		case *Named:
 			tparams = t.TParams().list()
@@ -96,7 +96,7 @@ func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, posLis
 	check.later(func() {
 		// Collect tparams again because lazily loaded *Named types may not have
 		// had tparams set up above.
-		var tparams []*TypeName
+		var tparams []*TypeParam
 		switch t := typ.(type) {
 		case *Named:
 			tparams = t.TParams().list()
@@ -192,11 +192,11 @@ func (check *Checker) validateTArgLen(pos syntax.Pos, tparams *TParamList, targs
 	return true
 }
 
-func (check *Checker) verify(pos syntax.Pos, tparams []*TypeName, targs []Type) (int, error) {
+func (check *Checker) verify(pos syntax.Pos, tparams []*TypeParam, targs []Type) (int, error) {
 	smap := makeSubstMap(tparams, targs)
-	for i, tname := range tparams {
+	for i, tpar := range tparams {
 		// stop checking bounds after the first failure
-		if err := check.satisfies(pos, targs[i], tname.typ.(*TypeParam), smap); err != nil {
+		if err := check.satisfies(pos, targs[i], tpar, smap); err != nil {
 			return i, err
 		}
 	}
diff --git a/src/cmd/compile/internal/types2/named.go b/src/cmd/compile/internal/types2/named.go
index 87b5716f7c..db12b08e67 100644
--- a/src/cmd/compile/internal/types2/named.go
+++ b/src/cmd/compile/internal/types2/named.go
@@ -24,7 +24,7 @@ type Named struct {
 	targs      []Type      // type arguments (after instantiation), or nil
 	methods    []*Func     // methods declared for this type (not the method set of this type); signatures are type-checked lazily
 
-	resolve func(*Named) ([]*TypeName, Type, []*Func)
+	resolve func(*Named) ([]*TypeParam, Type, []*Func)
 	once    sync.Once
 }
 
@@ -126,7 +126,7 @@ func (t *Named) Orig() *Named { return t.orig }
 func (t *Named) TParams() *TParamList { return t.load().tparams }
 
 // SetTParams sets the type parameters of the named type t.
-func (t *Named) SetTParams(tparams []*TypeName) { t.load().tparams = bindTParams(tparams) }
+func (t *Named) SetTParams(tparams []*TypeParam) { t.load().tparams = bindTParams(tparams) }
 
 // TArgs returns the type arguments after instantiation of the named type t, or nil if not instantiated.
 func (t *Named) TArgs() []Type { return t.targs }
diff --git a/src/cmd/compile/internal/types2/object.go b/src/cmd/compile/internal/types2/object.go
index 8263ccae0c..c1466f24ed 100644
--- a/src/cmd/compile/internal/types2/object.go
+++ b/src/cmd/compile/internal/types2/object.go
@@ -278,7 +278,7 @@ func NewTypeName(pos syntax.Pos, pkg *Package, name string, typ Type) *TypeName
 
 // NewTypeNameLazy returns a new defined type like NewTypeName, but it
 // lazily calls resolve to finish constructing the Named object.
-func NewTypeNameLazy(pos syntax.Pos, pkg *Package, name string, resolve func(named *Named) (tparams []*TypeName, underlying Type, methods []*Func)) *TypeName {
+func NewTypeNameLazy(pos syntax.Pos, pkg *Package, name string, resolve func(named *Named) (tparams []*TypeParam, underlying Type, methods []*Func)) *TypeName {
 	obj := NewTypeName(pos, pkg, name, nil)
 	NewNamed(obj, nil, nil).resolve = resolve
 	return obj
diff --git a/src/cmd/compile/internal/types2/predicates.go b/src/cmd/compile/internal/types2/predicates.go
index 3c883e1ab5..ed62743f6d 100644
--- a/src/cmd/compile/internal/types2/predicates.go
+++ b/src/cmd/compile/internal/types2/predicates.go
@@ -349,13 +349,13 @@ func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
 	return false
 }
 
-func identicalTParams(x, y []*TypeName, cmpTags bool, p *ifacePair) bool {
+func identicalTParams(x, y []*TypeParam, cmpTags bool, p *ifacePair) bool {
 	if len(x) != len(y) {
 		return false
 	}
 	for i, x := range x {
 		y := y[i]
-		if !identical(x.typ.(*TypeParam).bound, y.typ.(*TypeParam).bound, cmpTags, p) {
+		if !identical(x.bound, y.bound, cmpTags, p) {
 			return false
 		}
 	}
diff --git a/src/cmd/compile/internal/types2/signature.go b/src/cmd/compile/internal/types2/signature.go
index e319e65211..f1bf60ae8e 100644
--- a/src/cmd/compile/internal/types2/signature.go
+++ b/src/cmd/compile/internal/types2/signature.go
@@ -57,13 +57,13 @@ func (s *Signature) Recv() *Var { return s.recv }
 func (s *Signature) TParams() *TParamList { return s.tparams }
 
 // SetTParams sets the type parameters of signature s.
-func (s *Signature) SetTParams(tparams []*TypeName) { s.tparams = bindTParams(tparams) }
+func (s *Signature) SetTParams(tparams []*TypeParam) { s.tparams = bindTParams(tparams) }
 
 // RParams returns the receiver type parameters of signature s, or nil.
 func (s *Signature) RParams() *TParamList { return s.rparams }
 
 // SetRParams sets the receiver type params of signature s.
-func (s *Signature) SetRParams(rparams []*TypeName) { s.rparams = bindTParams(rparams) }
+func (s *Signature) SetRParams(rparams []*TypeParam) { s.rparams = bindTParams(rparams) }
 
 // Params returns the parameters of signature s, or nil.
 func (s *Signature) Params() *Tuple { return s.params }
@@ -119,14 +119,14 @@ func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []
 				// blank identifiers were found => use rewritten receiver type
 				recvTyp = isubst(recvPar.Type, smap)
 			}
-			rlist := make([]*TypeName, len(rparams))
+			rlist := make([]*TypeParam, len(rparams))
 			for i, rparam := range rparams {
 				rlist[i] = check.declareTypeParam(rparam)
 			}
 			sig.rparams = bindTParams(rlist)
 			// determine receiver type to get its type parameters
 			// and the respective type parameter bounds
-			var recvTParams []*TypeName
+			var recvTParams []*TypeParam
 			if rname != nil {
 				// recv should be a Named type (otherwise an error is reported elsewhere)
 				// Also: Don't report an error via genericType since it will be reported
@@ -142,19 +142,19 @@ func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []
 				// We have a list of *TypeNames but we need a list of Types.
 				list := make([]Type, sig.RParams().Len())
 				for i, t := range sig.RParams().list() {
-					list[i] = t.typ
+					list[i] = t
 				}
 				smap := makeSubstMap(recvTParams, list)
-				for i, tname := range sig.RParams().list() {
-					bound := recvTParams[i].typ.(*TypeParam).bound
+				for i, tpar := range sig.RParams().list() {
+					bound := recvTParams[i].bound
 					// bound is (possibly) parameterized in the context of the
 					// receiver type declaration. Substitute parameters for the
 					// current context.
 					// TODO(gri) should we assume now that bounds always exist?
 					//           (no bound == empty interface)
 					if bound != nil {
-						bound = check.subst(tname.pos, bound, smap, nil)
-						tname.typ.(*TypeParam).bound = bound
+						bound = check.subst(tpar.obj.pos, bound, smap, nil)
+						tpar.bound = bound
 					}
 				}
 			}
diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index edbbdb4758..467066cc69 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -15,11 +15,11 @@ type substMap map[*TypeParam]Type
 
 // makeSubstMap creates a new substitution map mapping tpars[i] to targs[i].
 // If targs[i] is nil, tpars[i] is not substituted.
-func makeSubstMap(tpars []*TypeName, targs []Type) substMap {
+func makeSubstMap(tpars []*TypeParam, targs []Type) substMap {
 	assert(len(tpars) == len(targs))
 	proj := make(substMap, len(tpars))
 	for i, tpar := range tpars {
-		proj[tpar.typ.(*TypeParam)] = targs[i]
+		proj[tpar] = targs[i]
 	}
 	return proj
 }
diff --git a/src/cmd/compile/internal/types2/typeparam.go b/src/cmd/compile/internal/types2/typeparam.go
index f666fae7ed..0d76dd1a6e 100644
--- a/src/cmd/compile/internal/types2/typeparam.go
+++ b/src/cmd/compile/internal/types2/typeparam.go
@@ -84,7 +84,7 @@ func (t *TypeParam) Underlying() Type { return t }
 func (t *TypeParam) String() string   { return TypeString(t, nil) }
 
 // TParamList holds a list of type parameters bound to a type.
-type TParamList struct{ tparams []*TypeName }
+type TParamList struct{ tparams []*TypeParam }
 
 // Len returns the number of type parameters in the list.
 // It is safe to call on a nil receiver.
@@ -93,23 +93,22 @@ func (tps *TParamList) Len() int {
 }
 
 // At returns the i'th type parameter in the list.
-func (tps *TParamList) At(i int) *TypeName {
+func (tps *TParamList) At(i int) *TypeParam {
 	return tps.list()[i]
 }
 
-func (tps *TParamList) list() []*TypeName {
+func (tps *TParamList) list() []*TypeParam {
 	if tps == nil {
 		return nil
 	}
 	return tps.tparams
 }
 
-func bindTParams(list []*TypeName) *TParamList {
+func bindTParams(list []*TypeParam) *TParamList {
 	if len(list) == 0 {
 		return nil
 	}
-	for i, tp := range list {
-		typ := tp.Type().(*TypeParam)
+	for i, typ := range list {
 		if typ.index >= 0 {
 			panic("type parameter bound more than once")
 		}
diff --git a/src/cmd/compile/internal/types2/typestring.go b/src/cmd/compile/internal/types2/typestring.go
index cb7cf73a62..5759118c94 100644
--- a/src/cmd/compile/internal/types2/typestring.go
+++ b/src/cmd/compile/internal/types2/typestring.go
@@ -242,14 +242,13 @@ func writeTypeList(buf *bytes.Buffer, list []Type, qf Qualifier, visited []Type)
 	}
 }
 
-func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited []Type) {
+func writeTParamList(buf *bytes.Buffer, list []*TypeParam, qf Qualifier, visited []Type) {
 	buf.WriteString("[")
 	var prev Type
-	for i, p := range list {
+	for i, tpar := range list {
 		// Determine the type parameter and its constraint.
 		// list is expected to hold type parameter names,
 		// but don't crash if that's not the case.
-		tpar, _ := p.typ.(*TypeParam)
 		var bound Type
 		if tpar != nil {
 			bound = tpar.bound // should not be nil but we want to see it if it is
@@ -268,7 +267,7 @@ func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited
 		if tpar != nil {
 			writeType(buf, tpar, qf, visited)
 		} else {
-			buf.WriteString(p.name)
+			buf.WriteString(tpar.obj.name)
 		}
 	}
 	if prev != nil {
diff --git a/src/cmd/compile/internal/types2/unify.go b/src/cmd/compile/internal/types2/unify.go
index 710fc51b53..58f5c17e5f 100644
--- a/src/cmd/compile/internal/types2/unify.go
+++ b/src/cmd/compile/internal/types2/unify.go
@@ -62,7 +62,7 @@ func (u *unifier) unify(x, y Type) bool {
 // A tparamsList describes a list of type parameters and the types inferred for them.
 type tparamsList struct {
 	unifier *unifier
-	tparams []*TypeName
+	tparams []*TypeParam
 	// For each tparams element, there is a corresponding type slot index in indices.
 	// index  < 0: unifier.types[-index-1] == nil
 	// index == 0: no type slot allocated yet
@@ -77,11 +77,11 @@ type tparamsList struct {
 func (d *tparamsList) String() string {
 	var buf bytes.Buffer
 	buf.WriteByte('[')
-	for i, tname := range d.tparams {
+	for i, tpar := range d.tparams {
 		if i > 0 {
 			buf.WriteString(", ")
 		}
-		writeType(&buf, tname.typ, nil, nil)
+		writeType(&buf, tpar, nil, nil)
 		buf.WriteString(": ")
 		writeType(&buf, d.at(i), nil, nil)
 	}
@@ -92,13 +92,13 @@ func (d *tparamsList) String() string {
 // init initializes d with the given type parameters.
 // The type parameters must be in the order in which they appear in their declaration
 // (this ensures that the tparams indices match the respective type parameter index).
-func (d *tparamsList) init(tparams []*TypeName) {
+func (d *tparamsList) init(tparams []*TypeParam) {
 	if len(tparams) == 0 {
 		return
 	}
 	if debug {
 		for i, tpar := range tparams {
-			assert(i == tpar.typ.(*TypeParam).index)
+			assert(i == tpar.index)
 		}
 	}
 	d.tparams = tparams
@@ -158,8 +158,8 @@ func (d *tparamsList) index(typ Type) int {
 
 // If tpar is a type parameter in list, tparamIndex returns the type parameter index.
 // Otherwise, the result is < 0. tpar must not be nil.
-func tparamIndex(list []*TypeName, tpar *TypeParam) int {
-	if i := tpar.index; i < len(list) && list[i].typ == tpar {
+func tparamIndex(list []*TypeParam, tpar *TypeParam) int {
+	if i := tpar.index; i < len(list) && list[i] == tpar {
 		return i
 	}
 	return -1