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