diff --git a/ssa/builder.go b/ssa/builder.go
index cd79e543..9c8f3b66 100644
--- a/ssa/builder.go
+++ b/ssa/builder.go
@@ -49,8 +49,8 @@ type opaqueType struct {
 func (t *opaqueType) String() string { return t.name }
 
 var (
-	varOk    = types.NewVar(token.NoPos, nil, "ok", tBool)
-	varIndex = types.NewVar(token.NoPos, nil, "index", tInt)
+	varOk    = newVar("ok", tBool)
+	varIndex = newVar("index", tInt)
 
 	// Type constants.
 	tBool       = types.Typ[types.Bool]
@@ -236,7 +236,7 @@ func (b *builder) exprN(fn *Function, e ast.Expr) Value {
 	tuple.(interface {
 		setType(types.Type)
 	}).setType(types.NewTuple(
-		types.NewVar(token.NoPos, nil, "value", typ),
+		newVar("value", typ),
 		varOk,
 	))
 	return tuple
@@ -616,7 +616,7 @@ func (b *builder) expr0(fn *Function, e ast.Expr) Value {
 		// Universal built-in or nil?
 		switch obj := obj.(type) {
 		case *types.Builtin:
-			return fn.Prog.builtins[obj]
+			return &Builtin{object: obj, sig: fn.Pkg.typeOf(e).(*types.Signature)}
 		case *types.Nil:
 			return nilConst(fn.Pkg.typeOf(e))
 		}
@@ -756,7 +756,6 @@ func (b *builder) receiver(fn *Function, e ast.Expr, wantAddr, escaping bool, se
 //
 func (b *builder) setCallFunc(fn *Function, e *ast.CallExpr, c *CallCommon) {
 	c.pos = e.Lparen
-	c.HasEllipsis = e.Ellipsis != 0
 
 	// Is this a method call?
 	if selector, ok := unparen(e.Fun).(*ast.SelectorExpr); ok {
@@ -1442,7 +1441,7 @@ func (b *builder) selectStmt(fn *Function, s *ast.SelectStmt, label *lblock) {
 	for _, st := range states {
 		if st.Dir == types.RecvOnly {
 			tElem := st.Chan.Type().Underlying().(*types.Chan).Elem()
-			vars = append(vars, types.NewVar(token.NoPos, nil, "", tElem))
+			vars = append(vars, newVar("", tElem))
 		}
 	}
 	sel.setType(types.NewTuple(vars...))
@@ -1610,7 +1609,7 @@ func (b *builder) rangeIndexed(fn *Function, x Value, tv types.Type) (k, v Value
 	} else {
 		// length = len(x).
 		var c Call
-		c.Call.Value = fn.Prog.builtins[types.Universe.Lookup("len").(*types.Builtin)]
+		c.Call.Value = makeLen(x.Type())
 		c.Call.Args = []Value{x}
 		c.setType(tInt)
 		length = fn.emit(&c)
@@ -1714,8 +1713,8 @@ func (b *builder) rangeIter(fn *Function, x Value, tk, tv types.Type, pos token.
 	}
 	okv.setType(types.NewTuple(
 		varOk,
-		types.NewVar(token.NoPos, nil, "k", tk),
-		types.NewVar(token.NoPos, nil, "v", tv),
+		newVar("k", tk),
+		newVar("v", tv),
 	))
 	fn.emit(okv)
 
@@ -1761,7 +1760,7 @@ func (b *builder) rangeChan(fn *Function, x Value, tk types.Type, pos token.Pos)
 	}
 	recv.setPos(pos)
 	recv.setType(types.NewTuple(
-		types.NewVar(token.NoPos, nil, "k", x.Type().Underlying().(*types.Chan).Elem()),
+		newVar("k", x.Type().Underlying().(*types.Chan).Elem()),
 		varOk,
 	))
 	ko := fn.emit(recv)
diff --git a/ssa/create.go b/ssa/create.go
index 60677514..d8b04838 100644
--- a/ssa/create.go
+++ b/ssa/create.go
@@ -39,24 +39,14 @@ const (
 // mode controls diagnostics and checking during SSA construction.
 //
 func NewProgram(fset *token.FileSet, mode BuilderMode) *Program {
-	prog := &Program{
+	return &Program{
 		Fset:                fset,
 		imported:            make(map[string]*Package),
 		packages:            make(map[*types.Package]*Package),
-		builtins:            make(map[*types.Builtin]*Builtin),
 		boundMethodWrappers: make(map[*types.Func]*Function),
 		ifaceMethodWrappers: make(map[*types.Func]*Function),
 		mode:                mode,
 	}
-
-	// Create Values for built-in functions.
-	for _, name := range types.Universe.Names() {
-		if obj, ok := types.Universe.Lookup(name).(*types.Builtin); ok {
-			prog.builtins[obj] = &Builtin{obj}
-		}
-	}
-
-	return prog
 }
 
 // memberFromObject populates package pkg with a member for the
diff --git a/ssa/emit.go b/ssa/emit.go
index 95bf5713..5319064d 100644
--- a/ssa/emit.go
+++ b/ssa/emit.go
@@ -297,7 +297,7 @@ func emitTypeTest(f *Function, x Value, t types.Type, pos token.Pos) Value {
 	}
 	a.setPos(pos)
 	a.setType(types.NewTuple(
-		types.NewVar(token.NoPos, nil, "value", t),
+		newVar("value", t),
 		varOk,
 	))
 	return f.emit(a)
diff --git a/ssa/example_test.go b/ssa/example_test.go
index 4532d4ca..1a92dfc7 100644
--- a/ssa/example_test.go
+++ b/ssa/example_test.go
@@ -106,6 +106,6 @@ func main() {
 	// 	t2 = make interface{} <- string ("Hello, World!":string)    interface{}
 	// 	*t1 = t2
 	// 	t3 = slice t0[:]                                          []interface{}
-	// 	t4 = fmt.Println(t3)                                 (n int, err error)
+	// 	t4 = fmt.Println(t3...)                              (n int, err error)
 	// 	return
 }
diff --git a/ssa/print.go b/ssa/print.go
index 4738068c..a64f9c93 100644
--- a/ssa/print.go
+++ b/ssa/print.go
@@ -120,7 +120,7 @@ func printCall(v *CallCommon, prefix string, instr Instruction) string {
 		}
 		b.WriteString(relName(arg, instr))
 	}
-	if v.HasEllipsis {
+	if v.Signature().IsVariadic() {
 		b.WriteString("...")
 	}
 	b.WriteString(")")
diff --git a/ssa/promote.go b/ssa/promote.go
index 8adb38f2..936ac650 100644
--- a/ssa/promote.go
+++ b/ssa/promote.go
@@ -216,7 +216,7 @@ func findMethod(prog *Program, meth *types.Selection) *Function {
 func makeWrapper(prog *Program, typ types.Type, meth *types.Selection) *Function {
 	obj := meth.Obj().(*types.Func)
 	oldsig := obj.Type().(*types.Signature)
-	recv := types.NewVar(token.NoPos, nil, "recv", typ)
+	recv := newVar("recv", typ)
 
 	description := fmt.Sprintf("wrapper for %s", obj)
 	if prog.mode&LogSource != 0 {
diff --git a/ssa/sanity.go b/ssa/sanity.go
index 21de3d02..5368242d 100644
--- a/ssa/sanity.go
+++ b/ssa/sanity.go
@@ -179,6 +179,12 @@ func (s *sanity) checkInstr(idx int, instr Instruction) {
 		panic(fmt.Sprintf("Unknown instruction type: %T", instr))
 	}
 
+	if call, ok := instr.(CallInstruction); ok {
+		if call.Common().Signature() == nil {
+			s.errorf("nil signature: %s", call)
+		}
+	}
+
 	// Check that value-defining instructions have valid types.
 	if v, ok := instr.(Value); ok {
 		t := v.Type()
diff --git a/ssa/ssa.go b/ssa/ssa.go
index a0dfb527..70386946 100644
--- a/ssa/ssa.go
+++ b/ssa/ssa.go
@@ -25,7 +25,6 @@ type Program struct {
 	Fset     *token.FileSet              // position information for the files of this Program
 	imported map[string]*Package         // all importable Packages, keyed by import path
 	packages map[*types.Package]*Package // all loaded Packages, keyed by object
-	builtins map[*types.Builtin]*Builtin // all built-in functions, keyed by typechecker objects.
 	mode     BuilderMode                 // set of mode bits for SSA construction
 
 	methodsMu           sync.Mutex                // guards the following maps:
@@ -413,19 +412,19 @@ type Global struct {
 	Pkg *Package
 }
 
-// A Builtin represents a built-in function, e.g. len.
+// A Builtin represents a specific use of a built-in function, e.g. len.
 //
 // Builtins are immutable values.  Builtins do not have addresses.
 // Builtins can only appear in CallCommon.Func.
 //
 // Object() returns a *types.Builtin.
 //
-// Type() returns types.Typ[types.Invalid], since built-in functions
-// may have polymorphic or variadic types that are not expressible in
-// Go's type system.
+// Type() returns a *types.Signature representing the effective
+// signature of the built-in for this call.
 //
 type Builtin struct {
 	object *types.Builtin // canonical types.Universe object for this built-in
+	sig    *types.Signature
 }
 
 // Value-defining instructions  ----------------------------------------
@@ -842,7 +841,7 @@ type SelectState struct {
 	DebugNode ast.Node      // ast.SendStmt or ast.UnaryExpr(<-) [debug mode]
 }
 
-// The Select instruction tests whether (or blocks until) one or more
+// The Select instruction tests whether (or blocks until) one
 // of the specified sent or received states is entered.
 //
 // Let n be the number of States for which Dir==RECV and T_i (0<=i<n)
@@ -874,7 +873,7 @@ type SelectState struct {
 // Pos() returns the ast.SelectStmt.Select.
 //
 // Example printed form:
-// 	t3 = select nonblocking [<-t0, t1<-t2, ...]
+// 	t3 = select nonblocking [<-t0, t1<-t2]
 // 	t4 = select blocking []
 //
 type Select struct {
@@ -1239,13 +1238,18 @@ type anInstruction struct {
 // which may be a *Builtin, a *Function or any other value of kind
 // 'func'.
 //
-// In the common case in which Value is a *Function, this indicates a
-// statically dispatched call to a package-level function, an
-// anonymous function, or a method of a named type.  Also statically
-// dispatched, but less common, Value may be a *MakeClosure, indicating
-// an immediately applied function literal with free variables.  Any
-// other value of Value indicates a dynamically dispatched function
-// call.  The StaticCallee method returns the callee in these cases.
+// Value may be one of:
+//    (a) a *Function, indicating a statically dispatched call
+//        to a package-level function, an anonymous function, or
+//        a method of a named type.
+//    (b) a *MakeClosure, indicating an immediately applied
+//        function literal with free variables.
+//    (c) a *Builtin, indicating a statically dispatched call
+//        to a built-in function.  StaticCallee returns nil.
+//    (d) any other value, indicating a dynamically dispatched
+//        function call.
+// StaticCallee returns the identity of the callee in cases
+// (a) and (b), nil otherwise.
 //
 // Args contains the arguments to the call.  If Value is a method,
 // Args[0] contains the receiver parameter.
@@ -1271,18 +1275,14 @@ type anInstruction struct {
 // 	go invoke t3.Run(t2)
 // 	defer invoke t4.Handle(...t5)
 //
-// In both modes, HasEllipsis is true iff the last element of Args is
-// a slice value containing zero or more arguments to a variadic
-// function.  (This is not semantically significant since the type of
-// the called function is sufficient to determine this, but it aids
-// readability of the printed form.)
+// For all calls to variadic functions (Signature().IsVariadic()),
+// the last element of Args is a slice.
 //
 type CallCommon struct {
-	Value       Value       // receiver (invoke mode) or func value (call mode)
-	Method      *types.Func // abstract method (invoke mode)
-	Args        []Value     // actual parameters (in static method call, includes receiver)
-	HasEllipsis bool        // true iff last Args is a slice of '...' args (needed?)
-	pos         token.Pos   // position of CallExpr.Lparen, iff explicit in source
+	Value  Value       // receiver (invoke mode) or func value (call mode)
+	Method *types.Func // abstract method (invoke mode)
+	Args   []Value     // actual parameters (in static method call, includes receiver)
+	pos    token.Pos   // position of CallExpr.Lparen, iff explicit in source
 }
 
 // IsInvoke returns true if this call has "invoke" (not "call") mode.
@@ -1300,18 +1300,15 @@ func (c *CallCommon) Pos() token.Pos { return c.pos }
 // In either "call" or "invoke" mode, if the callee is a method, its
 // receiver is represented by sig.Recv, not sig.Params().At(0).
 //
-// Signature returns nil for a call to a built-in function.
-//
 func (c *CallCommon) Signature() *types.Signature {
 	if c.Method != nil {
 		return c.Method.Type().(*types.Signature)
 	}
-	sig, _ := c.Value.Type().Underlying().(*types.Signature) // nil for *Builtin
-	return sig
+	return c.Value.Type().Underlying().(*types.Signature)
 }
 
-// StaticCallee returns the called function if this is a trivially
-// static "call"-mode call.
+// StaticCallee returns the callee if this is a trivially static
+// "call"-mode call to a function.
 func (c *CallCommon) StaticCallee() *Function {
 	switch fn := c.Value.(type) {
 	case *Function:
@@ -1360,7 +1357,7 @@ func (s *Call) Value() *Call  { return s }
 func (s *Defer) Value() *Call { return nil }
 func (s *Go) Value() *Call    { return nil }
 
-func (v *Builtin) Type() types.Type        { return v.object.Type() }
+func (v *Builtin) Type() types.Type        { return v.sig }
 func (v *Builtin) Name() string            { return v.object.Name() }
 func (*Builtin) Referrers() *[]Instruction { return nil }
 func (v *Builtin) Pos() token.Pos          { return token.NoPos }
diff --git a/ssa/util.go b/ssa/util.go
index 5978c942..a2bd9a76 100644
--- a/ssa/util.go
+++ b/ssa/util.go
@@ -9,6 +9,7 @@ package ssa
 import (
 	"fmt"
 	"go/ast"
+	"go/token"
 	"io"
 	"os"
 
@@ -117,3 +118,22 @@ func callsRecover(f *Function) bool {
 	}
 	return false
 }
+
+// newVar creates a 'var' for use in a types.Tuple.
+func newVar(name string, typ types.Type) *types.Var {
+	return types.NewParam(token.NoPos, nil, name, typ)
+}
+
+var (
+	lenObject  = types.Universe.Lookup("len").(*types.Builtin)
+	lenResults = types.NewTuple(newVar("", tInt))
+)
+
+// makeLen returns the len builtin specialized to type func(T)int.
+func makeLen(T types.Type) *Builtin {
+	lenParams := types.NewTuple(newVar("", T))
+	return &Builtin{
+		object: lenObject,
+		sig:    types.NewSignature(nil, nil, lenParams, lenResults, false),
+	}
+}