go.tools/ssa: opt: create elements of method sets lazily.

Reduces by 94% the number of wrappers created during the tests.
(No appreciable difference in running time, sadly.)

R=gri
CC=golang-dev
https://golang.org/cl/11619043

ssa/builder.go

@@ -686,9 +686,7 @@ func (b *builder) expr(fn *Function, e ast.Expr) Value {
 		// (*T).f or T.f, the method f from the method-set of type T.
 		if fn.Pkg.info.IsType(e.X) {
 			typ := fn.Pkg.typeOf(e.X)
-			// TODO(adonovan): opt: it's overkill to
-			// generate the entire method set here.
-			if m := fn.Prog.MethodSet(typ)[id]; m != nil {
+			if m := fn.Prog.LookupMethod(typ, id); m != nil {
 				return emitConv(fn, m, fn.Pkg.typeOf(e))
 			}
 
@@ -776,9 +774,7 @@ func (b *builder) findMethod(fn *Function, base ast.Expr, id string) (*Function,
 	typ := fn.Pkg.typeOf(base)
 
 	// Consult method-set of X.
-	// TODO(adonovan): opt: it's overkill to generate the entire
-	// method set here.
-	if m := fn.Prog.MethodSet(typ)[id]; m != nil {
+	if m := fn.Prog.LookupMethod(typ, id); m != nil {
 		aptr := isPointer(typ)
 		fptr := isPointer(m.Signature.Recv().Type())
 		if aptr == fptr {
@@ -791,9 +787,7 @@ func (b *builder) findMethod(fn *Function, base ast.Expr, id string) (*Function,
 	}
 	if !isPointer(typ) {
 		// Consult method-set of *X.
-		// TODO(adonovan): opt: it's overkill to generate the
-		// entire method set here.
-		if m := fn.Prog.MethodSet(types.NewPointer(typ))[id]; m != nil {
+		if m := fn.Prog.LookupMethod(types.NewPointer(typ), id); m != nil {
 			// A method found only in MS(*X) must have a
 			// pointer formal receiver; but the actual
 			// value is not a pointer.

ssa/promote.go

@@ -23,14 +23,20 @@ import (
 // *T receiver types, etc.
 // A nil result indicates an empty set.
 //
-// TODO(adonovan): opt: most uses of MethodSet() only access one
-// member; only generation of object code for MakeInterface needs them
-// all.  Build it incrementally.
-//
 // Thread-safe.
 //
 func (prog *Program) MethodSet(typ types.Type) MethodSet {
-	if typ.MethodSet().Len() == 0 {
+	return prog.populateMethodSet(typ, "")
+}
+
+// populateMethodSet returns the method set for typ, ensuring that it
+// contains at least key id.  If id is empty, the entire method set is
+// populated.
+//
+func (prog *Program) populateMethodSet(typ types.Type, id string) MethodSet {
+	tmset := typ.MethodSet()
+	n := tmset.Len()
+	if n == 0 {
 		return nil
 	}
 	if _, ok := deref(typ).Underlying().(*types.Interface); ok {
@@ -38,31 +44,55 @@ func (prog *Program) MethodSet(typ types.Type) MethodSet {
 		// has no methods---yet go/types says it has!
 		return nil
 	}
-	if !canHaveConcreteMethods(typ, true) {
-		return nil
-	}
 
 	if prog.mode&LogSource != 0 {
-		defer logStack("MethodSet %s", typ)()
+		defer logStack("MethodSet %s id=%s", typ, id)()
 	}
 
 	prog.methodsMu.Lock()
 	defer prog.methodsMu.Unlock()
 
-	if mset := prog.methodSets.At(typ); mset != nil {
-		return mset.(MethodSet) // cache hit
+	mset, _ := prog.methodSets.At(typ).(MethodSet)
+	if mset == nil {
+		mset = make(MethodSet)
+		prog.methodSets.Set(typ, mset)
 	}
 
-	mset := make(MethodSet)
-	tmset := typ.MethodSet()
-	for i, n := 0, tmset.Len(); i < n; i++ {
-		obj := tmset.At(i)
-		mset[obj.Func.Id()] = makeMethod(prog, typ, obj)
+	if len(mset) < n {
+		if id != "" { // single method
+			// tmset.Lookup() is no use to us with only an Id string.
+			if mset[id] == nil {
+				for i := 0; i < n; i++ {
+					obj := tmset.At(i)
+					if obj.Id() == id {
+						mset[id] = makeMethod(prog, typ, obj)
+						return mset
+					}
+				}
+			}
+		}
+
+		// complete set
+		for i := 0; i < n; i++ {
+			obj := tmset.At(i)
+			if id := obj.Id(); mset[id] == nil {
+				mset[id] = makeMethod(prog, typ, obj)
+			}
+		}
 	}
-	prog.methodSets.Set(typ, mset)
+
 	return mset
 }
 
+// LookupMethod returns the method id of type typ, building wrapper
+// methods on demand.  It returns nil if the typ has no such method.
+//
+// Thread-safe.
+//
+func (prog *Program) LookupMethod(typ types.Type, id string) *Function {
+	return prog.populateMethodSet(typ, id)[id]
+}
+
 // makeMethod returns the concrete Function for the method obj,
 // adapted if necessary so that its receiver type is typ.
 //

ssa/util.go

@@ -106,26 +106,6 @@ outer:
 	return true
 }
 
-// canHaveConcreteMethods returns true iff typ may have concrete
-// methods associated with it.  Callers must supply allowPtr=true.
-//
-// TODO(gri): consider putting this in go/types.  It's surprisingly subtle.
-func canHaveConcreteMethods(typ types.Type, allowPtr bool) bool {
-	switch typ := typ.(type) {
-	case *types.Pointer:
-		return allowPtr && canHaveConcreteMethods(typ.Elem(), false)
-	case *types.Named:
-		switch typ.Underlying().(type) {
-		case *types.Pointer, *types.Interface:
-			return false
-		}
-		return true
-	case *types.Struct:
-		return true
-	}
-	return false
-}
-
 // DefaultType returns the default "typed" type for an "untyped" type;
 // it returns the incoming type for all other types.  The default type
 // for untyped nil is untyped nil.