// 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)
}
// TODO(adonovan): opt: canonicalize the recv Type to avoid
// construct unnecessary duplicate thunks.
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()
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
}
// EXCLUSIVE_LOCKS_REQUIRED(prog.methodsMu)
func (prog *Program) addMethod(mset *methodSet, sel *types.Selection) *Function {
if sel.Kind() == types.MethodExpr {
panic(sel)
}
id := sel.Obj().Id()
fn := mset.mapping[id]
if fn == nil {
obj := sel.Obj().(*types.Func)
needsPromotion := len(sel.Index()) > 1
needsIndirection := !isPointer(recvType(obj)) && isPointer(sel.Recv())
if needsPromotion || needsIndirection {
fn = makeWrapper(prog, sel)
} else {
fn = prog.declaredFunc(obj)
}
if fn.Signature.Recv() == nil {
panic(fn) // missing receiver
}
mset.mapping[id] = fn
}
return fn
}
// 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, meth *types.Selection) *Function {
obj := meth.Obj().(*types.Func) // the declared function
sig := meth.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 meth.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, meth.Obj())
if prog.mode&LogSource != 0 {
defer logStack("make %s to (%s)", description, recv.Type())()
}
fn := &Function{
name: name,
method: meth,
object: obj,
Signature: sig,
Synthetic: description,
Prog: prog,
pos: obj.Pos(),
}
fn.startBody()
fn.addSpilledParam(recv)
createParams(fn, start)
indices := meth.Index()
var v Value = fn.Locals[0] // spilled receiver
if isPointer(meth.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, nil,
types.NewTuple(anonVar(meth.Recv()), anonVar(tString), anonVar(tString)),
types.NewTuple(anonVar(meth.Recv())), false),
}
c.Call.Args = []Value{
v,
stringConst(deref(meth.Recv()).String()),
stringConst(meth.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
}