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// Copyright 2009 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 walk
import (
"cmd/compile/internal/base"
"cmd/compile/internal/ir"
"cmd/compile/internal/typecheck"
"cmd/compile/internal/types"
"cmd/internal/src"
)
// Closure is called in a separate phase after escape analysis.
// It transform closure bodies to properly reference captured variables.
func Closure(fn *ir.Func) {
lno := base.Pos
base.Pos = fn.Pos()
if fn.ClosureCalled() {
// If the closure is directly called, we transform it to a plain function call
// with variables passed as args. This avoids allocation of a closure object.
// Here we do only a part of the transformation. Walk of OCALLFUNC(OCLOSURE)
// will complete the transformation later.
// For illustration, the following closure:
// func(a int) {
// println(byval)
// byref++
// }(42)
// becomes:
// func(byval int, &byref *int, a int) {
// println(byval)
// (*&byref)++
// }(byval, &byref, 42)
// f is ONAME of the actual function.
f := fn.Nname
// We are going to insert captured variables before input args.
var params []*types.Field
var decls []*ir.Name
for _, v := range fn.ClosureVars {
if !v.Byval() {
// If v of type T is captured by reference,
// we introduce function param &v *T
// and v remains PAUTOHEAP with &v heapaddr
// (accesses will implicitly deref &v).
addr := typecheck.NewName(typecheck.Lookup("&" + v.Sym().Name))
addr.SetType(types.NewPtr(v.Type()))
v.Heapaddr = addr
v = addr
}
v.Class_ = ir.PPARAM
decls = append(decls, v)
fld := types.NewField(src.NoXPos, v.Sym(), v.Type())
fld.Nname = v
params = append(params, fld)
}
if len(params) > 0 {
// Prepend params and decls.
f.Type().Params().SetFields(append(params, f.Type().Params().FieldSlice()...))
fn.Dcl = append(decls, fn.Dcl...)
}
types.CalcSize(f.Type())
fn.Nname.SetType(f.Type()) // update type of ODCLFUNC
} else {
// The closure is not called, so it is going to stay as closure.
var body []ir.Node
offset := int64(types.PtrSize)
for _, v := range fn.ClosureVars {
// cv refers to the field inside of closure OSTRUCTLIT.
typ := v.Type()
if !v.Byval() {
typ = types.NewPtr(typ)
}
offset = types.Rnd(offset, int64(typ.Align))
cr := ir.NewClosureRead(typ, offset)
offset += typ.Width
if v.Byval() && v.Type().Width <= int64(2*types.PtrSize) {
// If it is a small variable captured by value, downgrade it to PAUTO.
v.Class_ = ir.PAUTO
fn.Dcl = append(fn.Dcl, v)
body = append(body, ir.NewAssignStmt(base.Pos, v, cr))
} else {
// Declare variable holding addresses taken from closure
// and initialize in entry prologue.
addr := typecheck.NewName(typecheck.Lookup("&" + v.Sym().Name))
addr.SetType(types.NewPtr(v.Type()))
addr.Class_ = ir.PAUTO
addr.SetUsed(true)
addr.Curfn = fn
fn.Dcl = append(fn.Dcl, addr)
v.Heapaddr = addr
var src ir.Node = cr
if v.Byval() {
src = typecheck.NodAddr(cr)
}
body = append(body, ir.NewAssignStmt(base.Pos, addr, src))
}
}
if len(body) > 0 {
typecheck.Stmts(body)
fn.Enter = body
fn.SetNeedctxt(true)
}
}
base.Pos = lno
}
func walkClosure(clo *ir.ClosureExpr, init *ir.Nodes) ir.Node {
fn := clo.Func
// If no closure vars, don't bother wrapping.
if ir.IsTrivialClosure(clo) {
if base.Debug.Closure > 0 {
base.WarnfAt(clo.Pos(), "closure converted to global")
}
return fn.Nname
}
ir.ClosureDebugRuntimeCheck(clo)
typ := typecheck.ClosureType(clo)
clos := ir.NewCompLitExpr(base.Pos, ir.OCOMPLIT, ir.TypeNode(typ), nil)
clos.SetEsc(clo.Esc())
clos.List = append([]ir.Node{ir.NewUnaryExpr(base.Pos, ir.OCFUNC, fn.Nname)}, closureArgs(clo)...)
addr := typecheck.NodAddr(clos)
addr.SetEsc(clo.Esc())
// Force type conversion from *struct to the func type.
cfn := typecheck.ConvNop(addr, clo.Type())
// non-escaping temp to use, if any.
if x := clo.Prealloc; x != nil {
if !types.Identical(typ, x.Type()) {
panic("closure type does not match order's assigned type")
}
addr.Prealloc = x
clo.Prealloc = nil
}
return walkExpr(cfn, init)
}
// closureArgs returns a slice of expressions that an be used to
// initialize the given closure's free variables. These correspond
// one-to-one with the variables in clo.Func.ClosureVars, and will be
// either an ONAME node (if the variable is captured by value) or an
// OADDR-of-ONAME node (if not).
func closureArgs(clo *ir.ClosureExpr) []ir.Node {
fn := clo.Func
args := make([]ir.Node, len(fn.ClosureVars))
for i, v := range fn.ClosureVars {
var outer ir.Node
outer = v.Outer
if !v.Byval() {
outer = typecheck.NodAddrAt(fn.Pos(), outer)
}
args[i] = typecheck.Expr(outer)
}
return args
}
func walkCallPart(n *ir.SelectorExpr, init *ir.Nodes) ir.Node {
// Create closure in the form of a composite literal.
// For x.M with receiver (x) type T, the generated code looks like:
//
// clos = &struct{F uintptr; R T}{T.M·f, x}
//
// Like walkclosure above.
if n.X.Type().IsInterface() {
// Trigger panic for method on nil interface now.
// Otherwise it happens in the wrapper and is confusing.
n.X = cheapExpr(n.X, init)
n.X = walkExpr(n.X, nil)
tab := typecheck.Expr(ir.NewUnaryExpr(base.Pos, ir.OITAB, n.X))
c := ir.NewUnaryExpr(base.Pos, ir.OCHECKNIL, tab)
c.SetTypecheck(1)
init.Append(c)
}
typ := typecheck.PartialCallType(n)
clos := ir.NewCompLitExpr(base.Pos, ir.OCOMPLIT, ir.TypeNode(typ), nil)
clos.SetEsc(n.Esc())
clos.List = []ir.Node{ir.NewUnaryExpr(base.Pos, ir.OCFUNC, typecheck.MethodValueWrapper(n).Nname), n.X}
addr := typecheck.NodAddr(clos)
addr.SetEsc(n.Esc())
// Force type conversion from *struct to the func type.
cfn := typecheck.ConvNop(addr, n.Type())
// non-escaping temp to use, if any.
if x := n.Prealloc; x != nil {
if !types.Identical(typ, x.Type()) {
panic("partial call type does not match order's assigned type")
}
addr.Prealloc = x
n.Prealloc = nil
}
return walkExpr(cfn, init)
}
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