--- /dev/null
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ssa
+
+// This file defines synthesis of Functions that delegate to declared
+// methods; they come in three kinds:
+//
+// (1) wrappers: methods that wrap declared methods, performing
+// implicit pointer indirections and embedded field selections.
+//
+// (2) thunks: funcs that wrap declared methods. Like wrappers,
+// thunks perform indirections and field selections. The thunk's
+// first parameter is used as the receiver for the method call.
+//
+// (3) bounds: funcs that wrap declared methods. The bound's sole
+// free variable, supplied by a closure, is used as the receiver
+// for the method call. No indirections or field selections are
+// performed since they can be done before the call.
+
+import (
+ "fmt"
+
+ "go/types"
+)
+
+// -- wrappers -----------------------------------------------------------
+
+// makeWrapper returns a synthetic method that delegates to the
+// declared method denoted by meth.Obj(), first performing any
+// necessary pointer indirections or field selections implied by meth.
+//
+// The resulting method's receiver type is meth.Recv().
+//
+// This function is versatile but quite subtle! Consider the
+// following axes of variation when making changes:
+// - optional receiver indirection
+// - optional implicit field selections
+// - meth.Obj() may denote a concrete or an interface method
+// - the result may be a thunk or a wrapper.
+//
+// EXCLUSIVE_LOCKS_REQUIRED(prog.methodsMu)
+//
+func makeWrapper(prog *Program, sel *types.Selection) *Function {
+ obj := sel.Obj().(*types.Func) // the declared function
+ sig := sel.Type().(*types.Signature) // type of this wrapper
+
+ var recv *types.Var // wrapper's receiver or thunk's params[0]
+ name := obj.Name()
+ var description string
+ var start int // first regular param
+ if sel.Kind() == types.MethodExpr {
+ name += "$thunk"
+ description = "thunk"
+ recv = sig.Params().At(0)
+ start = 1
+ } else {
+ description = "wrapper"
+ recv = sig.Recv()
+ }
+
+ description = fmt.Sprintf("%s for %s", description, sel.Obj())
+ if prog.mode&LogSource != 0 {
+ defer logStack("make %s to (%s)", description, recv.Type())()
+ }
+ fn := &Function{
+ name: name,
+ method: sel,
+ object: obj,
+ Signature: sig,
+ Synthetic: description,
+ Prog: prog,
+ pos: obj.Pos(),
+ }
+ fn.startBody()
+ fn.addSpilledParam(recv)
+ createParams(fn, start)
+
+ indices := sel.Index()
+
+ var v Value = fn.Locals[0] // spilled receiver
+ if isPointer(sel.Recv()) {
+ v = emitLoad(fn, v)
+
+ // For simple indirection wrappers, perform an informative nil-check:
+ // "value method (T).f called using nil *T pointer"
+ if len(indices) == 1 && !isPointer(recvType(obj)) {
+ var c Call
+ c.Call.Value = &Builtin{
+ name: "ssa:wrapnilchk",
+ sig: types.NewSignature(nil,
+ types.NewTuple(anonVar(sel.Recv()), anonVar(tString), anonVar(tString)),
+ types.NewTuple(anonVar(sel.Recv())), false),
+ }
+ c.Call.Args = []Value{
+ v,
+ stringConst(deref(sel.Recv()).String()),
+ stringConst(sel.Obj().Name()),
+ }
+ c.setType(v.Type())
+ v = fn.emit(&c)
+ }
+ }
+
+ // Invariant: v is a pointer, either
+ // value of *A receiver param, or
+ // address of A spilled receiver.
+
+ // We use pointer arithmetic (FieldAddr possibly followed by
+ // Load) in preference to value extraction (Field possibly
+ // preceded by Load).
+
+ v = emitImplicitSelections(fn, v, indices[:len(indices)-1])
+
+ // Invariant: v is a pointer, either
+ // value of implicit *C field, or
+ // address of implicit C field.
+
+ var c Call
+ if r := recvType(obj); !isInterface(r) { // concrete method
+ if !isPointer(r) {
+ v = emitLoad(fn, v)
+ }
+ c.Call.Value = prog.declaredFunc(obj)
+ c.Call.Args = append(c.Call.Args, v)
+ } else {
+ c.Call.Method = obj
+ c.Call.Value = emitLoad(fn, v)
+ }
+ for _, arg := range fn.Params[1:] {
+ c.Call.Args = append(c.Call.Args, arg)
+ }
+ emitTailCall(fn, &c)
+ fn.finishBody()
+ return fn
+}
+
+// createParams creates parameters for wrapper method fn based on its
+// Signature.Params, which do not include the receiver.
+// start is the index of the first regular parameter to use.
+//
+func createParams(fn *Function, start int) {
+ tparams := fn.Signature.Params()
+ for i, n := start, tparams.Len(); i < n; i++ {
+ fn.addParamObj(tparams.At(i))
+ }
+}
+
+// -- bounds -----------------------------------------------------------
+
+// makeBound returns a bound method wrapper (or "bound"), a synthetic
+// function that delegates to a concrete or interface method denoted
+// by obj. The resulting function has no receiver, but has one free
+// variable which will be used as the method's receiver in the
+// tail-call.
+//
+// Use MakeClosure with such a wrapper to construct a bound method
+// closure. e.g.:
+//
+// type T int or: type T interface { meth() }
+// func (t T) meth()
+// var t T
+// f := t.meth
+// f() // calls t.meth()
+//
+// f is a closure of a synthetic wrapper defined as if by:
+//
+// f := func() { return t.meth() }
+//
+// Unlike makeWrapper, makeBound need perform no indirection or field
+// selections because that can be done before the closure is
+// constructed.
+//
+// EXCLUSIVE_LOCKS_ACQUIRED(meth.Prog.methodsMu)
+//
+func makeBound(prog *Program, obj *types.Func) *Function {
+ prog.methodsMu.Lock()
+ defer prog.methodsMu.Unlock()
+ fn, ok := prog.bounds[obj]
+ if !ok {
+ description := fmt.Sprintf("bound method wrapper for %s", obj)
+ if prog.mode&LogSource != 0 {
+ defer logStack("%s", description)()
+ }
+ fn = &Function{
+ name: obj.Name() + "$bound",
+ object: obj,
+ Signature: changeRecv(obj.Type().(*types.Signature), nil), // drop receiver
+ Synthetic: description,
+ Prog: prog,
+ pos: obj.Pos(),
+ }
+
+ fv := &FreeVar{name: "recv", typ: recvType(obj), parent: fn}
+ fn.FreeVars = []*FreeVar{fv}
+ fn.startBody()
+ createParams(fn, 0)
+ var c Call
+
+ if !isInterface(recvType(obj)) { // concrete
+ c.Call.Value = prog.declaredFunc(obj)
+ c.Call.Args = []Value{fv}
+ } else {
+ c.Call.Value = fv
+ c.Call.Method = obj
+ }
+ for _, arg := range fn.Params {
+ c.Call.Args = append(c.Call.Args, arg)
+ }
+ emitTailCall(fn, &c)
+ fn.finishBody()
+
+ prog.bounds[obj] = fn
+ }
+ return fn
+}
+
+// -- thunks -----------------------------------------------------------
+
+// makeThunk returns a thunk, a synthetic function that delegates to a
+// concrete or interface method denoted by sel.Obj(). The resulting
+// function has no receiver, but has an additional (first) regular
+// parameter.
+//
+// Precondition: sel.Kind() == types.MethodExpr.
+//
+// type T int or: type T interface { meth() }
+// func (t T) meth()
+// f := T.meth
+// var t T
+// f(t) // calls t.meth()
+//
+// f is a synthetic wrapper defined as if by:
+//
+// f := func(t T) { return t.meth() }
+//
+// TODO(adonovan): opt: currently the stub is created even when used
+// directly in a function call: C.f(i, 0). This is less efficient
+// than inlining the stub.
+//
+// EXCLUSIVE_LOCKS_ACQUIRED(meth.Prog.methodsMu)
+//
+func makeThunk(prog *Program, sel *types.Selection) *Function {
+ if sel.Kind() != types.MethodExpr {
+ panic(sel)
+ }
+
+ key := selectionKey{
+ kind: sel.Kind(),
+ recv: sel.Recv(),
+ obj: sel.Obj(),
+ index: fmt.Sprint(sel.Index()),
+ indirect: sel.Indirect(),
+ }
+
+ prog.methodsMu.Lock()
+ defer prog.methodsMu.Unlock()
+
+ // Canonicalize key.recv to avoid constructing duplicate thunks.
+ canonRecv, ok := prog.canon.At(key.recv).(types.Type)
+ if !ok {
+ canonRecv = key.recv
+ prog.canon.Set(key.recv, canonRecv)
+ }
+ key.recv = canonRecv
+
+ fn, ok := prog.thunks[key]
+ if !ok {
+ fn = makeWrapper(prog, sel)
+ if fn.Signature.Recv() != nil {
+ panic(fn) // unexpected receiver
+ }
+ prog.thunks[key] = fn
+ }
+ return fn
+}
+
+func changeRecv(s *types.Signature, recv *types.Var) *types.Signature {
+ return types.NewSignature(recv, s.Params(), s.Results(), s.Variadic())
+}
+
+// selectionKey is like types.Selection but a usable map key.
+type selectionKey struct {
+ kind types.SelectionKind
+ recv types.Type // canonicalized via Program.canon
+ obj types.Object
+ index string
+ indirect bool
+}
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