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go/types,types2: externalize used objects

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The 'used' field on Var and PkgName is fundamentally an aspect of the
type checking pass: it records when objects are used, for the purposes
of reporting errors for unused variables or package names. While
expedient and performant, recording this information in the types.Object
instances themselves increases the memory footprint of type-checked
packages, and (as we saw in golang/go#71817) can lead to data races when
Objects are reused in follow-up type checking, such as is done with the
CheckExpr and Eval APIs.

Fix this by externalizing the 'used' information into two maps (one for
variables and one for packages) on the types.Checker, so that they are
garbage-collected after type checking, and cannot be a source of data
races.

Benchmarks showed essentially no change in performance.

Fixes golang/go#71817

Change-Id: I40daeabe4ecaca3bcb494e2f1c62a04232098e49
Reviewed-on: https://go-review.googlesource.com/c/go/+/650796
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
This commit is contained in:
Rob Findley 2025-02-19 22:07:09 +00:00 committed by Gopher Robot
parent f7204d76bc
commit 9189921e47
16 changed files with 77 additions and 58 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/cmd/compile/internal/types2/assignments.go
View File

@ -204,7 +204,7 @@ func (check *Checker) lhsVar(lhs syntax.Expr) Type {
// dot-imported variables.
if w, _ := obj.(*Var); w != nil && w.pkg == check.pkg {
v = w
v_used = v.used
v_used = check.usedVars[v]
}
}
}
@ -213,7 +213,7 @@ func (check *Checker) lhsVar(lhs syntax.Expr) Type {
check.expr(nil, &x, lhs)
if v != nil {
v.used = v_used // restore v.used
check.usedVars[v] = v_used // restore v.used
}
if x.mode == invalid || !isValid(x.typ) {

6
src/cmd/compile/internal/types2/call.go
View File

@ -686,7 +686,7 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr, def *TypeName
if pname, _ := obj.(*PkgName); pname != nil {
assert(pname.pkg == check.pkg)
check.recordUse(ident, pname)
pname.used = true
check.usedPkgNames[pname] = true
pkg := pname.imported
var exp Object
@ -971,13 +971,13 @@ func (check *Checker) use1(e syntax.Expr, lhs bool) bool {
// dot-imported variables.
if w, _ := obj.(*Var); w != nil && w.pkg == check.pkg {
v = w
v_used = v.used
v_used = check.usedVars[v]
}
}
}
check.exprOrType(&x, n, true)
if v != nil {
v.used = v_used // restore v.used
check.usedVars[v] = v_used // restore v.used
}
case *syntax.ListExpr:
return check.useN(n.ElemList, lhs)

21
src/cmd/compile/internal/types2/check.go
View File

@ -162,6 +162,8 @@ type Checker struct {
dotImportMap map[dotImportKey]*PkgName // maps dot-imported objects to the package they were dot-imported through
brokenAliases map[*TypeName]bool // set of aliases with broken (not yet determined) types
unionTypeSets map[*Union]*_TypeSet // computed type sets for union types
usedVars map[*Var]bool // set of used variables
usedPkgNames map[*PkgName]bool // set of used package names
mono monoGraph // graph for detecting non-monomorphizable instantiation loops
firstErr error // first error encountered
@ -285,12 +287,14 @@ func NewChecker(conf *Config, pkg *Package, info *Info) *Checker {
// (previously, pkg.goVersion was mutated here: go.dev/issue/61212)
return &Checker{
conf: conf,
ctxt: conf.Context,
pkg: pkg,
Info: info,
objMap: make(map[Object]*declInfo),
impMap: make(map[importKey]*Package),
conf: conf,
ctxt: conf.Context,
pkg: pkg,
Info: info,
objMap: make(map[Object]*declInfo),
impMap: make(map[importKey]*Package),
usedVars: make(map[*Var]bool),
usedPkgNames: make(map[*PkgName]bool),
}
}
@ -298,6 +302,8 @@ func NewChecker(conf *Config, pkg *Package, info *Info) *Checker {
// The provided files must all belong to the same package.
func (check *Checker) initFiles(files []*syntax.File) {
// start with a clean slate (check.Files may be called multiple times)
// TODO(gri): what determines which fields are zeroed out here, vs at the end
// of checkFiles?
check.files = nil
check.imports = nil
check.dotImportMap = nil
@ -482,8 +488,11 @@ func (check *Checker) checkFiles(files []*syntax.File) {
check.seenPkgMap = nil
check.brokenAliases = nil
check.unionTypeSets = nil
check.usedVars = nil
check.usedPkgNames = nil
check.ctxt = nil
// TODO(gri): shouldn't the cleanup above occur after the bailout?
// TODO(gri) There's more memory we should release at this point.
}

10
src/cmd/compile/internal/types2/object.go
View File

@ -242,13 +242,12 @@ func (a *object) cmp(b *object) int {
type PkgName struct {
object
imported *Package
used bool // set if the package was used
}
// NewPkgName returns a new PkgName object representing an imported package.
// The remaining arguments set the attributes found with all Objects.
func NewPkgName(pos syntax.Pos, pkg *Package, name string, imported *Package) *PkgName {
return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, black, nopos}, imported, false}
return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, black, nopos}, imported}
}
// Imported returns the package that was imported.
@ -331,10 +330,9 @@ func (obj *TypeName) IsAlias() bool {
// A Variable represents a declared variable (including function parameters and results, and struct fields).
type Var struct {
object
origin *Var // if non-nil, the Var from which this one was instantiated
kind VarKind
embedded bool // if set, the variable is an embedded struct field, and name is the type name
used bool // set if the variable was used
origin *Var // if non-nil, the Var from which this one was instantiated
}
// A VarKind discriminates the various kinds of variables.
@ -403,9 +401,7 @@ func NewField(pos syntax.Pos, pkg *Package, name string, typ Type, embedded bool
// newVar returns a new variable.
// The arguments set the attributes found with all Objects.
func newVar(kind VarKind, pos syntax.Pos, pkg *Package, name string, typ Type) *Var {
// Function parameters are always 'used'.
used := kind == RecvVar || kind == ParamVar || kind == ResultVar
return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}, kind: kind, used: used}
return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}, kind: kind}
}
// Anonymous reports whether the variable is an embedded field.

4
src/cmd/compile/internal/types2/resolver.go
View File

@ -295,7 +295,7 @@ func (check *Checker) collectObjects() {
if imp.fake {
// match 1.17 cmd/compile (not prescribed by spec)
pkgName.used = true
check.usedPkgNames[pkgName] = true
}
// add import to file scope
@ -715,7 +715,7 @@ func (check *Checker) unusedImports() {
// (initialization), use the blank identifier as explicit package name."
for _, obj := range check.imports {
if !obj.used && obj.name != "_" {
if obj.name != "_" && !check.usedPkgNames[obj] {
check.errorUnusedPkg(obj)
}
}

2
src/cmd/compile/internal/types2/sizeof_test.go
View File

@ -36,7 +36,7 @@ func TestSizeof(t *testing.T) {
{term{}, 12, 24},
// Objects
{PkgName{}, 64, 104},
{PkgName{}, 60, 96},
{Const{}, 64, 104},
{TypeName{}, 56, 88},
{Var{}, 64, 104},

11
src/cmd/compile/internal/types2/stmt.go
View File

@ -55,10 +55,13 @@ func (check *Checker) funcBody(decl *declInfo, name string, sig *Signature, body
}
func (check *Checker) usage(scope *Scope) {
needUse := func(kind VarKind) bool {
return !(kind == RecvVar || kind == ParamVar || kind == ResultVar)
}
var unused []*Var
for name, elem := range scope.elems {
elem = resolve(name, elem)
if v, _ := elem.(*Var); v != nil && !v.used {
if v, _ := elem.(*Var); v != nil && needUse(v.kind) && !check.usedVars[v] {
unused = append(unused, v)
}
}
@ -812,10 +815,10 @@ func (check *Checker) typeSwitchStmt(inner stmtContext, s *syntax.SwitchStmt, gu
if lhs != nil {
var used bool
for _, v := range lhsVars {
if v.used {
if check.usedVars[v] {
used = true
}
v.used = true // avoid usage error when checking entire function
check.usedVars[v] = true // avoid usage error when checking entire function
}
if !used {
check.softErrorf(lhs, UnusedVar, "%s declared and not used", lhs.Value)
@ -921,7 +924,7 @@ func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *s
if typ == nil || typ == Typ[Invalid] {
// typ == Typ[Invalid] can happen if allowVersion fails.
obj.typ = Typ[Invalid]
obj.used = true // don't complain about unused variable
check.usedVars[obj] = true // don't complain about unused variable
continue
}

6
src/cmd/compile/internal/types2/typexpr.go
View File

@ -55,7 +55,7 @@ func (check *Checker) ident(x *operand, e *syntax.Name, def *TypeName, wantType
// avoid "declared but not used" errors
// (don't use Checker.use - we don't want to evaluate too much)
if v, _ := obj.(*Var); v != nil && v.pkg == check.pkg /* see Checker.use1 */ {
v.used = true
check.usedVars[v] = true
}
return
}
@ -83,7 +83,7 @@ func (check *Checker) ident(x *operand, e *syntax.Name, def *TypeName, wantType
// (This code is only needed for dot-imports. Without them,
// we only have to mark variables, see *Var case below).
if pkgName := check.dotImportMap[dotImportKey{scope, obj.Name()}]; pkgName != nil {
pkgName.used = true
check.usedPkgNames[pkgName] = true
}
switch obj := obj.(type) {
@ -120,7 +120,7 @@ func (check *Checker) ident(x *operand, e *syntax.Name, def *TypeName, wantType
// from other packages to avoid potential race conditions with
// dot-imported variables.
if obj.pkg == check.pkg {
obj.used = true
check.usedVars[obj] = true
}
check.addDeclDep(obj)
if !isValid(typ) {

4
src/go/types/assignments.go
View File

@ -207,7 +207,7 @@ func (check *Checker) lhsVar(lhs ast.Expr) Type {
// dot-imported variables.
if w, _ := obj.(*Var); w != nil && w.pkg == check.pkg {
v = w
v_used = v.used
v_used = check.usedVars[v]
}
}
}
@ -216,7 +216,7 @@ func (check *Checker) lhsVar(lhs ast.Expr) Type {
check.expr(nil, &x, lhs)
if v != nil {
v.used = v_used // restore v.used
check.usedVars[v] = v_used // restore v.used
}
if x.mode == invalid || !isValid(x.typ) {

6
src/go/types/call.go
View File

@ -688,7 +688,7 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr, def *TypeName, w
if pname, _ := obj.(*PkgName); pname != nil {
assert(pname.pkg == check.pkg)
check.recordUse(ident, pname)
pname.used = true
check.usedPkgNames[pname] = true
pkg := pname.imported
var exp Object
@ -1019,13 +1019,13 @@ func (check *Checker) use1(e ast.Expr, lhs bool) bool {
// dot-imported variables.
if w, _ := obj.(*Var); w != nil && w.pkg == check.pkg {
v = w
v_used = v.used
v_used = check.usedVars[v]
}
}
}
check.exprOrType(&x, n, true)
if v != nil {
v.used = v_used // restore v.used
check.usedVars[v] = v_used // restore v.used
}
default:
check.rawExpr(nil, &x, e, nil, true)

25
src/go/types/check.go
View File

@ -182,6 +182,8 @@ type Checker struct {
dotImportMap map[dotImportKey]*PkgName // maps dot-imported objects to the package they were dot-imported through
brokenAliases map[*TypeName]bool // set of aliases with broken (not yet determined) types
unionTypeSets map[*Union]*_TypeSet // computed type sets for union types
usedVars map[*Var]bool // set of used variables
usedPkgNames map[*PkgName]bool // set of used package names
mono monoGraph // graph for detecting non-monomorphizable instantiation loops
firstErr error // first error encountered
@ -308,13 +310,15 @@ func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Ch
conf._EnableAlias = gotypesalias.Value() != "0"
return &Checker{
conf: conf,
ctxt: conf.Context,
fset: fset,
pkg: pkg,
Info: info,
objMap: make(map[Object]*declInfo),
impMap: make(map[importKey]*Package),
conf: conf,
ctxt: conf.Context,
fset: fset,
pkg: pkg,
Info: info,
objMap: make(map[Object]*declInfo),
impMap: make(map[importKey]*Package),
usedVars: make(map[*Var]bool),
usedPkgNames: make(map[*PkgName]bool),
}
}
@ -322,6 +326,8 @@ func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Ch
// The provided files must all belong to the same package.
func (check *Checker) initFiles(files []*ast.File) {
// start with a clean slate (check.Files may be called multiple times)
// TODO(gri): what determines which fields are zeroed out here, vs at the end
// of checkFiles?
check.files = nil
check.imports = nil
check.dotImportMap = nil
@ -507,9 +513,12 @@ func (check *Checker) checkFiles(files []*ast.File) {
check.seenPkgMap = nil
check.brokenAliases = nil
check.unionTypeSets = nil
check.usedVars = nil
check.usedPkgNames = nil
check.ctxt = nil
// TODO(rFindley) There's more memory we should release at this point.
// TODO(gri): shouldn't the cleanup above occur after the bailout?
// TODO(gri) There's more memory we should release at this point.
}
// processDelayed processes all delayed actions pushed after top.

10
src/go/types/object.go
View File

@ -245,13 +245,12 @@ func (a *object) cmp(b *object) int {
type PkgName struct {
object
imported *Package
used bool // set if the package was used
}
// NewPkgName returns a new PkgName object representing an imported package.
// The remaining arguments set the attributes found with all Objects.
func NewPkgName(pos token.Pos, pkg *Package, name string, imported *Package) *PkgName {
return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, black, nopos}, imported, false}
return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, black, nopos}, imported}
}
// Imported returns the package that was imported.
@ -334,10 +333,9 @@ func (obj *TypeName) IsAlias() bool {
// A Variable represents a declared variable (including function parameters and results, and struct fields).
type Var struct {
object
origin *Var // if non-nil, the Var from which this one was instantiated
kind VarKind
embedded bool // if set, the variable is an embedded struct field, and name is the type name
used bool // set if the variable was used
origin *Var // if non-nil, the Var from which this one was instantiated
}
// A VarKind discriminates the various kinds of variables.
@ -406,9 +404,7 @@ func NewField(pos token.Pos, pkg *Package, name string, typ Type, embedded bool)
// newVar returns a new variable.
// The arguments set the attributes found with all Objects.
func newVar(kind VarKind, pos token.Pos, pkg *Package, name string, typ Type) *Var {
// Function parameters are always 'used'.
used := kind == RecvVar || kind == ParamVar || kind == ResultVar
return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}, kind: kind, used: used}
return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), nopos}, kind: kind}
}
// Anonymous reports whether the variable is an embedded field.

4
src/go/types/resolver.go
View File

@ -310,7 +310,7 @@ func (check *Checker) collectObjects() {
if imp.fake {
// match 1.17 cmd/compile (not prescribed by spec)
pkgName.used = true
check.usedPkgNames[pkgName] = true
}
// add import to file scope
@ -710,7 +710,7 @@ func (check *Checker) unusedImports() {
// (initialization), use the blank identifier as explicit package name."
for _, obj := range check.imports {
if !obj.used && obj.name != "_" {
if obj.name != "_" && !check.usedPkgNames[obj] {
check.errorUnusedPkg(obj)
}
}

2
src/go/types/sizeof_test.go
View File

@ -35,7 +35,7 @@ func TestSizeof(t *testing.T) {
{term{}, 12, 24},
// Objects
{PkgName{}, 48, 88},
{PkgName{}, 44, 80},
{Const{}, 48, 88},
{TypeName{}, 40, 72},
{Var{}, 48, 88},

14
src/go/types/stmt.go
View File

@ -56,10 +56,13 @@ func (check *Checker) funcBody(decl *declInfo, name string, sig *Signature, body
}
func (check *Checker) usage(scope *Scope) {
needUse := func(kind VarKind) bool {
return !(kind == RecvVar || kind == ParamVar || kind == ResultVar)
}
var unused []*Var
for name, elem := range scope.elems {
elem = resolve(name, elem)
if v, _ := elem.(*Var); v != nil && !v.used {
if v, _ := elem.(*Var); v != nil && needUse(v.kind) && !check.usedVars[v] {
unused = append(unused, v)
}
}
@ -765,13 +768,16 @@ func (check *Checker) stmt(ctxt stmtContext, s ast.Stmt) {
}
// If lhs exists, we must have at least one lhs variable that was used.
// (We can't use check.usage because that only looks at one scope; and
// we don't want to use the same variable for all scopes and change the
// variable type underfoot.)
if lhs != nil {
var used bool
for _, v := range lhsVars {
if v.used {
if check.usedVars[v] {
used = true
}
v.used = true // avoid usage error when checking entire function
check.usedVars[v] = true // avoid usage error when checking entire function
}
if !used {
check.softErrorf(lhs, UnusedVar, "%s declared and not used", lhs.Name)
@ -939,7 +945,7 @@ func (check *Checker) rangeStmt(inner stmtContext, s *ast.RangeStmt) {
if typ == nil || typ == Typ[Invalid] {
// typ == Typ[Invalid] can happen if allowVersion fails.
obj.typ = Typ[Invalid]
obj.used = true // don't complain about unused variable
check.usedVars[obj] = true // don't complain about unused variable
continue
}

6
src/go/types/typexpr.go
View File

@ -54,7 +54,7 @@ func (check *Checker) ident(x *operand, e *ast.Ident, def *TypeName, wantType bo
// avoid "declared but not used" errors
// (don't use Checker.use - we don't want to evaluate too much)
if v, _ := obj.(*Var); v != nil && v.pkg == check.pkg /* see Checker.use1 */ {
v.used = true
check.usedVars[v] = true
}
return
}
@ -82,7 +82,7 @@ func (check *Checker) ident(x *operand, e *ast.Ident, def *TypeName, wantType bo
// (This code is only needed for dot-imports. Without them,
// we only have to mark variables, see *Var case below).
if pkgName := check.dotImportMap[dotImportKey{scope, obj.Name()}]; pkgName != nil {
pkgName.used = true
check.usedPkgNames[pkgName] = true
}
switch obj := obj.(type) {
@ -119,7 +119,7 @@ func (check *Checker) ident(x *operand, e *ast.Ident, def *TypeName, wantType bo
// from other packages to avoid potential race conditions with
// dot-imported variables.
if obj.pkg == check.pkg {
obj.used = true
check.usedVars[obj] = true
}
check.addDeclDep(obj)
if !isValid(typ) {