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Copy pathwrappers.go
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357 lines (319 loc) · 10.5 KB
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// 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 ir
// 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 -----------------------------------------------------------
// createWrapper 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
// - optional method type arguments
// - meth.Obj() may denote a concrete or an interface method
// - the result may be a thunk or a wrapper.
func createWrapper(prog *Program, sel *selection, targs []types.Type) *Function {
obj := sel.obj.(*types.Func) // the declared function
name, sig := maybeInstance(prog, obj.Name(), sel.typ.(*types.Signature), targs)
var recv *types.Var // wrapper's receiver or thunk's params[0]
var description string
if sel.kind == types.MethodExpr {
name += "$thunk"
description = "thunk"
recv = sig.Params().At(0)
} else {
description = "wrapper"
recv = sig.Recv()
}
description = fmt.Sprintf("%s for %s", description, obj)
if prog.mode&LogSource != 0 {
defer logStack("create %s to (%s)", description, recv.Type())()
}
/* method wrapper */
return &Function{
name: name,
method: sel,
object: obj,
Signature: sig,
Synthetic: description,
Prog: prog,
pos: obj.Pos(),
typeargs: targs,
// wrappers have no syntax
build: (*builder).buildWrapper,
info: nil,
goversion: "",
}
}
// maybeInstance returns name and sig instantiated to reflect any type arguments in targs.
func maybeInstance(prog *Program, name string, sig *types.Signature, targs []types.Type) (string, *types.Signature) {
if len(targs) > 0 {
name = fmt.Sprintf("%s%s", name, targstr(targs))
instSig, err := types.Instantiate(prog.ctxt, sig, targs, false)
if err != nil {
// validate was false, we should never get an error
panic(err)
}
sig = prog.canon.Type(instSig).(*types.Signature)
}
return name, sig
}
// buildWrapper builds fn.Body for a method wrapper.
func (b *builder) buildWrapper(fn *Function) {
var recv *types.Var // wrapper's receiver or thunk's params[0]
var start int // first regular param
if fn.method.kind == types.MethodExpr {
recv = fn.Signature.Params().At(0)
start = 1
} else {
recv = fn.Signature.Recv()
}
fn.startBody()
fn.addSpilledParam(recv, nil)
createParams(fn, start)
indices := fn.method.index
var v Value = fn.Locals[0] // spilled receiver
if isPointer(fn.method.recv) {
v = emitLoad(fn, v, nil)
// For simple indirection wrappers, perform an informative nil-check:
// "value method (T).f called using nil *T pointer"
if len(indices) == 1 && !isPointer(recvType(fn.object)) {
var c Call
c.Call.Value = &Builtin{
name: "ssa:wrapnilchk",
sig: types.NewSignatureType(nil, nil, nil, types.NewTuple(anonVar(fn.method.recv), anonVar(tString), anonVar(tString)), types.NewTuple(anonVar(fn.method.recv)), false),
}
c.Call.Args = []Value{
v,
stringConst(deref(fn.method.recv).String(), nil),
stringConst(fn.method.obj.Name(), nil),
}
c.setType(v.Type())
v = fn.emit(&c, nil)
}
}
// 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], nil)
// Invariant: v is a pointer, either
// value of implicit *C field, or
// address of implicit C field.
var c Call
if r := recvType(fn.object); !types.IsInterface(r) { // concrete method
if !isPointer(r) {
v = emitLoad(fn, v, nil)
}
c.Call.Value = fn.Prog.objectMethod(fn.object, fn.typeargs, b)
c.Call.Args = append(c.Call.Args, v)
} else {
c.Call.Method = fn.object
c.Call.Value = emitLoad(fn, v, nil) // interface (possibly a typeparam)
}
for _, arg := range fn.Params[1:] {
c.Call.Args = append(c.Call.Args, arg)
}
emitTailCall(fn, &c, nil)
fn.finishBody()
}
// 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.addParamVar(tparams.At(i), nil)
}
}
// -- bounds -----------------------------------------------------------
// createBound 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 createWrapper, createBound need perform no indirection or field
// selections because that can be done before the closure is
// constructed.
func createBound(prog *Program, obj *types.Func, targs []types.Type) *Function {
description := fmt.Sprintf("bound method wrapper for %s", obj)
if prog.mode&LogSource != 0 {
defer logStack("%s", description)()
}
name, sig := maybeInstance(prog, obj.Name(), obj.Type().(*types.Signature), targs)
/* bound method wrapper */
fn := &Function{
name: name + "$bound",
object: obj,
Signature: changeRecv(sig, nil), // drop receiver
Synthetic: description,
Prog: prog,
pos: obj.Pos(),
typeargs: targs,
// wrappers have no syntax
build: (*builder).buildBound,
info: nil,
goversion: "",
}
fn.FreeVars = []*FreeVar{{name: "recv", typ: recvType(obj), parent: fn}} // (cyclic)
return fn
}
// buildBound builds fn.Body for a bound method closure.
func (b *builder) buildBound(fn *Function) {
fn.startBody()
createParams(fn, 0)
var c Call
recv := fn.FreeVars[0]
if !types.IsInterface(recvType(fn.object)) { // concrete
c.Call.Value = fn.Prog.objectMethod(fn.object, fn.typeargs, b)
c.Call.Args = []Value{recv}
} else {
c.Call.Method = fn.object
c.Call.Value = recv // interface (possibly a typeparam)
}
for _, arg := range fn.Params {
c.Call.Args = append(c.Call.Args, arg)
}
emitTailCall(fn, &c, nil)
fn.finishBody()
}
// -- thunks -----------------------------------------------------------
// createThunk 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() }
func createThunk(prog *Program, sel *selection, targs []types.Type) *Function {
if sel.kind != types.MethodExpr {
panic(sel)
}
fn := createWrapper(prog, sel, targs)
if fn.Signature.Recv() != nil {
panic(fn) // unexpected receiver
}
return fn
}
func changeRecv(s *types.Signature, recv *types.Var) *types.Signature {
return types.NewSignatureType(recv, nil, nil, s.Params(), s.Results(), s.Variadic())
}
// A local version of *types.Selection.
// Needed for some additional control, such as creating a MethodExpr for an instantiation.
type selection struct {
kind types.SelectionKind
recv types.Type
typ types.Type
obj types.Object
index []int
indirect bool
}
func toSelection(sel *types.Selection) *selection {
return &selection{
kind: sel.Kind(),
recv: sel.Recv(),
typ: sel.Type(),
obj: sel.Obj(),
index: sel.Index(),
indirect: sel.Indirect(),
}
}
// -- instantiations --------------------------------------------------
// buildInstantiationWrapper builds the body of an instantiation
// wrapper fn. The body calls the original generic function,
// bracketed by ChangeType conversions on its arguments and results.
func (b *builder) buildInstantiationWrapper(fn *Function) {
orig := fn.topLevelOrigin
sig := fn.Signature
fn.startBody()
if sig.Recv() != nil {
fn.addParamVar(sig.Recv(), nil)
}
createParams(fn, 0)
// Create body. Add a call to origin generic function
// and make type changes between argument and parameters,
// as well as return values.
var c Call
c.Call.Value = orig
if res := orig.Signature.Results(); res.Len() == 1 {
c.typ = res.At(0).Type()
} else {
c.typ = res
}
// parameter of instance becomes an argument to the call
// to the original generic function.
argOffset := 0
for i, arg := range fn.Params {
var typ types.Type
if i == 0 && sig.Recv() != nil {
typ = orig.Signature.Recv().Type()
argOffset = 1
} else {
typ = orig.Signature.Params().At(i - argOffset).Type()
}
c.Call.Args = append(c.Call.Args, emitTypeCoercion(fn, arg, typ, nil))
}
results := fn.emit(&c, nil)
var ret Return
switch res := sig.Results(); res.Len() {
case 0:
// no results, do nothing.
case 1:
ret.Results = []Value{emitTypeCoercion(fn, results, res.At(0).Type(), nil)}
default:
for i := 0; i < sig.Results().Len(); i++ {
v := emitExtract(fn, results, i, nil)
ret.Results = append(ret.Results, emitTypeCoercion(fn, v, res.At(i).Type(), nil))
}
}
fn.emit(&ret, nil)
fn.currentBlock = nil
fn.finishBody()
}