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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 pointer
import (
// A Config formulates a pointer analysis problem for Analyze. It is
// only usable for a single invocation of Analyze and must not be
// reused.
type Config struct {
// Mains contains the set of 'main' packages to analyze
// Clients must provide the analysis with at least one
// package defining a main() function.
// Non-main packages in the ssa.Program that are not
// dependencies of any main package may still affect the
// analysis result, because they contribute runtime types and
// thus methods.
// TODO(adonovan): investigate whether this is desirable.
Mains []*ssa.Package
// Reflection determines whether to handle reflection
// operators soundly, which is currently rather slow since it
// causes constraint to be generated during solving
// proportional to the number of constraint variables, which
// has not yet been reduced by presolver optimisation.
Reflection bool
// BuildCallGraph determines whether to construct a callgraph.
// If enabled, the graph will be available in Result.CallGraph.
BuildCallGraph bool
// The client populates Queries[v] or IndirectQueries[v]
// for each ssa.Value v of interest, to request that the
// points-to sets pts(v) or pts(*v) be computed. If the
// client needs both points-to sets, v may appear in both
// maps.
// (IndirectQueries is typically used for Values corresponding
// to source-level lvalues, e.g. an *ssa.Global.)
// The analysis populates the corresponding
// Result.{Indirect,}Queries map when it creates the pointer
// variable for v or *v. Upon completion the client can
// inspect that map for the results.
// TODO(adonovan): this API doesn't scale well for batch tools
// that want to dump the entire solution. Perhaps optionally
// populate a map[*ssa.DebugRef]Pointer in the Result, one
// entry per source expression.
Queries map[ssa.Value]struct{}
IndirectQueries map[ssa.Value]struct{}
extendedQueries map[ssa.Value][]*extendedQuery
// If Log is non-nil, log messages are written to it.
// Logging is extremely verbose.
Log io.Writer
type track uint32
const (
trackChan track = 1 << iota // track 'chan' references
trackMap // track 'map' references
trackPtr // track regular pointers
trackSlice // track slice references
trackAll = ^track(0)
// AddQuery adds v to Config.Queries.
// Precondition: CanPoint(v.Type()).
func (c *Config) AddQuery(v ssa.Value) {
if !CanPoint(v.Type()) {
panic(fmt.Sprintf("%s is not a pointer-like value: %s", v, v.Type()))
if c.Queries == nil {
c.Queries = make(map[ssa.Value]struct{})
c.Queries[v] = struct{}{}
// AddQuery adds v to Config.IndirectQueries.
// Precondition: CanPoint(v.Type().Underlying().(*types.Pointer).Elem()).
func (c *Config) AddIndirectQuery(v ssa.Value) {
if c.IndirectQueries == nil {
c.IndirectQueries = make(map[ssa.Value]struct{})
if !CanPoint(mustDeref(v.Type())) {
panic(fmt.Sprintf("%s is not the address of a pointer-like value: %s", v, v.Type()))
c.IndirectQueries[v] = struct{}{}
// AddExtendedQuery adds an extended, AST-based query on v to the
// analysis. The query, which must be a single Go expression, allows
// destructuring the value.
// The query must operate on a variable named 'x', which represents
// the value, and result in a pointer-like object. Only a subset of
// Go expressions are permitted in queries, namely channel receives,
// pointer dereferences, field selectors, array/slice/map/tuple
// indexing and grouping with parentheses. The specific indices when
// indexing arrays, slices and maps have no significance. Indices used
// on tuples must be numeric and within bounds.
// All field selectors must be explicit, even ones usually elided
// due to promotion of embedded fields.
// The query 'x' is identical to using AddQuery. The query '*x' is
// identical to using AddIndirectQuery.
// On success, AddExtendedQuery returns a Pointer to the queried
// value. This Pointer will be initialized during analysis. Using it
// before analysis has finished has undefined behavior.
// Example:
// // given v, which represents a function call to 'fn() (int, []*T)', and
// // 'type T struct { F *int }', the following query will access the field F.
// c.AddExtendedQuery(v, "x[1][0].F")
func (c *Config) AddExtendedQuery(v ssa.Value, query string) (*Pointer, error) {
ops, _, err := parseExtendedQuery(v.Type(), query)
if err != nil {
return nil, fmt.Errorf("invalid query %q: %s", query, err)
if c.extendedQueries == nil {
c.extendedQueries = make(map[ssa.Value][]*extendedQuery)
ptr := &Pointer{}
c.extendedQueries[v] = append(c.extendedQueries[v], &extendedQuery{ops: ops, ptr: ptr})
return ptr, nil
func (c *Config) prog() *ssa.Program {
for _, main := range c.Mains {
return main.Prog
panic("empty scope")
type Warning struct {
Pos token.Pos
Message string
// A Result contains the results of a pointer analysis.
// See Config for how to request the various Result components.
type Result struct {
CallGraph *callgraph.Graph // discovered call graph
Queries map[ssa.Value]Pointer // pts(v) for each v in Config.Queries.
IndirectQueries map[ssa.Value]Pointer // pts(*v) for each v in Config.IndirectQueries.
Warnings []Warning // warnings of unsoundness
// A Pointer is an equivalence class of pointer-like values.
// A Pointer doesn't have a unique type because pointers of distinct
// types may alias the same object.
type Pointer struct {
a *analysis
n nodeid
// A PointsToSet is a set of labels (locations or allocations).
type PointsToSet struct {
a *analysis // may be nil if pts is nil
pts *nodeset
func (s PointsToSet) String() string {
var buf bytes.Buffer
if s.pts != nil {
var space [50]int
for i, l := range s.pts.AppendTo(space[:0]) {
if i > 0 {
buf.WriteString(", ")
return buf.String()
// PointsTo returns the set of labels that this points-to set
// contains.
func (s PointsToSet) Labels() []*Label {
var labels []*Label
if s.pts != nil {
var space [50]int
for _, l := range s.pts.AppendTo(space[:0]) {
labels = append(labels, s.a.labelFor(nodeid(l)))
return labels
// If this PointsToSet came from a Pointer of interface kind
// or a reflect.Value, DynamicTypes returns the set of dynamic
// types that it may contain. (For an interface, they will
// always be concrete types.)
// The result is a mapping whose keys are the dynamic types to which
// it may point. For each pointer-like key type, the corresponding
// map value is the PointsToSet for pointers of that type.
// The result is empty unless CanHaveDynamicTypes(T).
func (s PointsToSet) DynamicTypes() *typeutil.Map {
var tmap typeutil.Map
if s.pts != nil {
var space [50]int
for _, x := range s.pts.AppendTo(space[:0]) {
ifaceObjId := nodeid(x)
if !s.a.isTaggedObject(ifaceObjId) {
continue // !CanHaveDynamicTypes(tDyn)
tDyn, v, indirect := s.a.taggedValue(ifaceObjId)
if indirect {
panic("indirect tagged object") // implement later
pts, ok := tmap.At(tDyn).(PointsToSet)
if !ok {
pts = PointsToSet{s.a, new(nodeset)}
tmap.Set(tDyn, pts)
return &tmap
// Intersects reports whether this points-to set and the
// argument points-to set contain common members.
func (x PointsToSet) Intersects(y PointsToSet) bool {
if x.pts == nil || y.pts == nil {
return false
// This takes Θ(|x|+|y|) time.
var z intsets.Sparse
z.Intersection(&x.pts.Sparse, &y.pts.Sparse)
return !z.IsEmpty()
func (p Pointer) String() string {
return fmt.Sprintf("n%d", p.n)
// PointsTo returns the points-to set of this pointer.
func (p Pointer) PointsTo() PointsToSet {
if p.n == 0 {
return PointsToSet{}
return PointsToSet{p.a, &p.a.nodes[p.n].solve.pts}
// MayAlias reports whether the receiver pointer may alias
// the argument pointer.
func (p Pointer) MayAlias(q Pointer) bool {
return p.PointsTo().Intersects(q.PointsTo())
// DynamicTypes returns p.PointsTo().DynamicTypes().
func (p Pointer) DynamicTypes() *typeutil.Map {
return p.PointsTo().DynamicTypes()