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peers.go
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/
peers.go
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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 oracle
import (
"fmt"
"go/ast"
"go/token"
"sort"
"code.google.com/p/go.tools/go/ssa"
"code.google.com/p/go.tools/go/ssa/ssautil"
"code.google.com/p/go.tools/go/types"
"code.google.com/p/go.tools/oracle/serial"
)
// peers enumerates, for a given channel send (or receive) operation,
// the set of possible receives (or sends) that correspond to it.
//
// TODO(adonovan): support reflect.{Select,Recv,Send}.
// TODO(adonovan): permit the user to query based on a MakeChan (not send/recv),
// or the implicit receive in "for v := range ch".
//
func peers(o *Oracle, qpos *QueryPos) (queryResult, error) {
arrowPos := findArrow(qpos)
if arrowPos == token.NoPos {
return nil, fmt.Errorf("there is no send/receive here")
}
buildSSA(o)
var queryOp chanOp // the originating send or receive operation
var ops []chanOp // all sends/receives of opposite direction
// Look at all send/receive instructions in the whole ssa.Program.
// Build a list of those of same type to query.
allFuncs := ssautil.AllFunctions(o.prog)
for fn := range allFuncs {
for _, b := range fn.Blocks {
for _, instr := range b.Instrs {
for _, op := range chanOps(instr) {
ops = append(ops, op)
if op.pos == arrowPos {
queryOp = op // we found the query op
}
}
}
}
}
if queryOp.ch == nil {
return nil, fmt.Errorf("ssa.Instruction for send/receive not found")
}
// Discard operations of wrong channel element type.
// Build set of channel ssa.Values as query to pointer analysis.
// We compare channels by element types, not channel types, to
// ignore both directionality and type names.
queryType := queryOp.ch.Type()
queryElemType := queryType.Underlying().(*types.Chan).Elem()
o.ptaConfig.AddQuery(queryOp.ch)
i := 0
for _, op := range ops {
if types.Identical(op.ch.Type().Underlying().(*types.Chan).Elem(), queryElemType) {
o.ptaConfig.AddQuery(op.ch)
ops[i] = op
i++
}
}
ops = ops[:i]
// Run the pointer analysis.
ptares := ptrAnalysis(o)
// Find the points-to set.
queryChanPtr := ptares.Queries[queryOp.ch]
// Ascertain which make(chan) labels the query's channel can alias.
var makes []token.Pos
for _, label := range queryChanPtr.PointsTo().Labels() {
makes = append(makes, label.Pos())
}
sort.Sort(byPos(makes))
// Ascertain which send/receive operations can alias the same make(chan) labels.
var sends, receives []token.Pos
for _, op := range ops {
if ptr, ok := ptares.Queries[op.ch]; ok && ptr.MayAlias(queryChanPtr) {
if op.dir == types.SendOnly {
sends = append(sends, op.pos)
} else {
receives = append(receives, op.pos)
}
}
}
sort.Sort(byPos(sends))
sort.Sort(byPos(receives))
return &peersResult{
queryPos: arrowPos,
queryType: queryType,
makes: makes,
sends: sends,
receives: receives,
}, nil
}
// findArrow returns the position of the enclosing send/receive op
// (<-) for the query position, or token.NoPos if not found.
//
func findArrow(qpos *QueryPos) token.Pos {
for _, n := range qpos.path {
switch n := n.(type) {
case *ast.UnaryExpr:
if n.Op == token.ARROW {
return n.OpPos
}
case *ast.SendStmt:
return n.Arrow
}
}
return token.NoPos
}
// chanOp abstracts an ssa.Send, ssa.Unop(ARROW), or a SelectState.
type chanOp struct {
ch ssa.Value
dir types.ChanDir // SendOnly or RecvOnly
pos token.Pos
}
// chanOps returns a slice of all the channel operations in the instruction.
func chanOps(instr ssa.Instruction) []chanOp {
// TODO(adonovan): handle calls to reflect.{Select,Recv,Send} too.
var ops []chanOp
switch instr := instr.(type) {
case *ssa.UnOp:
if instr.Op == token.ARROW {
ops = append(ops, chanOp{instr.X, types.RecvOnly, instr.Pos()})
}
case *ssa.Send:
ops = append(ops, chanOp{instr.Chan, types.SendOnly, instr.Pos()})
case *ssa.Select:
for _, st := range instr.States {
ops = append(ops, chanOp{st.Chan, st.Dir, st.Pos})
}
}
return ops
}
type peersResult struct {
queryPos token.Pos // of queried '<-' token
queryType types.Type // type of queried channel
makes, sends, receives []token.Pos // positions of alisaed makechan/send/receive instrs
}
func (r *peersResult) display(printf printfFunc) {
if len(r.makes) == 0 {
printf(r.queryPos, "This channel can't point to anything.")
return
}
printf(r.queryPos, "This channel of type %s may be:", r.queryType)
for _, alloc := range r.makes {
printf(alloc, "\tallocated here")
}
for _, send := range r.sends {
printf(send, "\tsent to, here")
}
for _, receive := range r.receives {
printf(receive, "\treceived from, here")
}
}
func (r *peersResult) toSerial(res *serial.Result, fset *token.FileSet) {
peers := &serial.Peers{
Pos: fset.Position(r.queryPos).String(),
Type: r.queryType.String(),
}
for _, alloc := range r.makes {
peers.Allocs = append(peers.Allocs, fset.Position(alloc).String())
}
for _, send := range r.sends {
peers.Sends = append(peers.Sends, fset.Position(send).String())
}
for _, receive := range r.receives {
peers.Receives = append(peers.Receives, fset.Position(receive).String())
}
res.Peers = peers
}
// -------- utils --------
type byPos []token.Pos
func (p byPos) Len() int { return len(p) }
func (p byPos) Less(i, j int) bool { return p[i] < p[j] }
func (p byPos) Swap(i, j int) { p[i], p[j] = p[j], p[i] }