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callee.go
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callee.go
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// Copyright 2023 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 inline
// This file defines the analysis of the callee function.
import (
"bytes"
"encoding/gob"
"fmt"
"go/ast"
"go/parser"
"go/token"
"go/types"
"strings"
"cuelang.org/go/internal/golangorgx/tools/typeparams"
"golang.org/x/tools/go/ast/astutil"
"golang.org/x/tools/go/types/typeutil"
)
// A Callee holds information about an inlinable function. Gob-serializable.
type Callee struct {
impl gobCallee
}
func (callee *Callee) String() string { return callee.impl.Name }
type gobCallee struct {
Content []byte // file content, compacted to a single func decl
// results of type analysis (does not reach go/types data structures)
PkgPath string // package path of declaring package
Name string // user-friendly name for error messages
Unexported []string // names of free objects that are unexported
FreeRefs []freeRef // locations of references to free objects
FreeObjs []object // descriptions of free objects
ValidForCallStmt bool // function body is "return expr" where expr is f() or <-ch
NumResults int // number of results (according to type, not ast.FieldList)
Params []*paramInfo // information about parameters (incl. receiver)
Results []*paramInfo // information about result variables
Effects []int // order in which parameters are evaluated (see calleefx)
HasDefer bool // uses defer
HasBareReturn bool // uses bare return in non-void function
TotalReturns int // number of return statements
TrivialReturns int // number of return statements with trivial result conversions
Labels []string // names of all control labels
Falcon falconResult // falcon constraint system
}
// A freeRef records a reference to a free object. Gob-serializable.
// (This means free relative to the FuncDecl as a whole, i.e. excluding parameters.)
type freeRef struct {
Offset int // byte offset of the reference relative to the FuncDecl
Object int // index into Callee.freeObjs
}
// An object abstracts a free types.Object referenced by the callee. Gob-serializable.
type object struct {
Name string // Object.Name()
Kind string // one of {var,func,const,type,pkgname,nil,builtin}
PkgPath string // path of object's package (or imported package if kind="pkgname")
PkgName string // name of object's package (or imported package if kind="pkgname")
// TODO(rfindley): should we also track LocalPkgName here? Do we want to
// preserve the local package name?
ValidPos bool // Object.Pos().IsValid()
Shadow map[string]bool // names shadowed at one of the object's refs
}
// AnalyzeCallee analyzes a function that is a candidate for inlining
// and returns a Callee that describes it. The Callee object, which is
// serializable, can be passed to one or more subsequent calls to
// Inline, each with a different Caller.
//
// This design allows separate analysis of callers and callees in the
// golang.org/x/tools/go/analysis framework: the inlining information
// about a callee can be recorded as a "fact".
//
// The content should be the actual input to the compiler, not the
// apparent source file according to any //line directives that
// may be present within it.
func AnalyzeCallee(logf func(string, ...any), fset *token.FileSet, pkg *types.Package, info *types.Info, decl *ast.FuncDecl, content []byte) (*Callee, error) {
checkInfoFields(info)
// The client is expected to have determined that the callee
// is a function with a declaration (not a built-in or var).
fn := info.Defs[decl.Name].(*types.Func)
sig := fn.Type().(*types.Signature)
logf("analyzeCallee %v @ %v", fn, fset.PositionFor(decl.Pos(), false))
// Create user-friendly name ("pkg.Func" or "(pkg.T).Method")
var name string
if sig.Recv() == nil {
name = fmt.Sprintf("%s.%s", fn.Pkg().Name(), fn.Name())
} else {
name = fmt.Sprintf("(%s).%s", types.TypeString(sig.Recv().Type(), (*types.Package).Name), fn.Name())
}
if decl.Body == nil {
return nil, fmt.Errorf("cannot inline function %s as it has no body", name)
}
// TODO(adonovan): support inlining of instantiated generic
// functions by replacing each occurrence of a type parameter
// T by its instantiating type argument (e.g. int). We'll need
// to wrap the instantiating type in parens when it's not an
// ident or qualified ident to prevent "if x == struct{}"
// parsing ambiguity, or "T(x)" where T = "*int" or "func()"
// from misparsing.
if funcHasTypeParams(decl) {
return nil, fmt.Errorf("cannot inline generic function %s: type parameters are not yet supported", name)
}
// Record the location of all free references in the FuncDecl.
// (Parameters are not free by this definition.)
var (
freeObjIndex = make(map[types.Object]int)
freeObjs []object
freeRefs []freeRef // free refs that may need renaming
unexported []string // free refs to unexported objects, for later error checks
)
var f func(n ast.Node) bool
visit := func(n ast.Node) { ast.Inspect(n, f) }
var stack []ast.Node
stack = append(stack, decl.Type) // for scope of function itself
f = func(n ast.Node) bool {
if n != nil {
stack = append(stack, n) // push
} else {
stack = stack[:len(stack)-1] // pop
}
switch n := n.(type) {
case *ast.SelectorExpr:
// Check selections of free fields/methods.
if sel, ok := info.Selections[n]; ok &&
!within(sel.Obj().Pos(), decl) &&
!n.Sel.IsExported() {
sym := fmt.Sprintf("(%s).%s", info.TypeOf(n.X), n.Sel.Name)
unexported = append(unexported, sym)
}
// Don't recur into SelectorExpr.Sel.
visit(n.X)
return false
case *ast.CompositeLit:
// Check for struct literals that refer to unexported fields,
// whether keyed or unkeyed. (Logic assumes well-typedness.)
litType := deref(info.TypeOf(n))
if s, ok := typeparams.CoreType(litType).(*types.Struct); ok {
if n.Type != nil {
visit(n.Type)
}
for i, elt := range n.Elts {
var field *types.Var
var value ast.Expr
if kv, ok := elt.(*ast.KeyValueExpr); ok {
field = info.Uses[kv.Key.(*ast.Ident)].(*types.Var)
value = kv.Value
} else {
field = s.Field(i)
value = elt
}
if !within(field.Pos(), decl) && !field.Exported() {
sym := fmt.Sprintf("(%s).%s", litType, field.Name())
unexported = append(unexported, sym)
}
// Don't recur into KeyValueExpr.Key.
visit(value)
}
return false
}
case *ast.Ident:
if obj, ok := info.Uses[n]; ok {
// Methods and fields are handled by SelectorExpr and CompositeLit.
if isField(obj) || isMethod(obj) {
panic(obj)
}
// Inv: id is a lexical reference.
// A reference to an unexported package-level declaration
// cannot be inlined into another package.
if !n.IsExported() &&
obj.Pkg() != nil && obj.Parent() == obj.Pkg().Scope() {
unexported = append(unexported, n.Name)
}
// Record free reference (incl. self-reference).
if obj == fn || !within(obj.Pos(), decl) {
objidx, ok := freeObjIndex[obj]
if !ok {
objidx = len(freeObjIndex)
var pkgpath, pkgname string
if pn, ok := obj.(*types.PkgName); ok {
pkgpath = pn.Imported().Path()
pkgname = pn.Imported().Name()
} else if obj.Pkg() != nil {
pkgpath = obj.Pkg().Path()
pkgname = obj.Pkg().Name()
}
freeObjs = append(freeObjs, object{
Name: obj.Name(),
Kind: objectKind(obj),
PkgName: pkgname,
PkgPath: pkgpath,
ValidPos: obj.Pos().IsValid(),
})
freeObjIndex[obj] = objidx
}
freeObjs[objidx].Shadow = addShadows(freeObjs[objidx].Shadow, info, obj.Name(), stack)
freeRefs = append(freeRefs, freeRef{
Offset: int(n.Pos() - decl.Pos()),
Object: objidx,
})
}
}
}
return true
}
visit(decl)
// Analyze callee body for "return expr" form,
// where expr is f() or <-ch. These forms are
// safe to inline as a standalone statement.
validForCallStmt := false
if len(decl.Body.List) != 1 {
// not just a return statement
} else if ret, ok := decl.Body.List[0].(*ast.ReturnStmt); ok && len(ret.Results) == 1 {
validForCallStmt = func() bool {
switch expr := astutil.Unparen(ret.Results[0]).(type) {
case *ast.CallExpr: // f(x)
callee := typeutil.Callee(info, expr)
if callee == nil {
return false // conversion T(x)
}
// The only non-void built-in functions that may be
// called as a statement are copy and recover
// (though arguably a call to recover should never
// be inlined as that changes its behavior).
if builtin, ok := callee.(*types.Builtin); ok {
return builtin.Name() == "copy" ||
builtin.Name() == "recover"
}
return true // ordinary call f()
case *ast.UnaryExpr: // <-x
return expr.Op == token.ARROW // channel receive <-ch
}
// No other expressions are valid statements.
return false
}()
}
// Record information about control flow in the callee
// (but not any nested functions).
var (
hasDefer = false
hasBareReturn = false
totalReturns = 0
trivialReturns = 0
labels []string
)
ast.Inspect(decl.Body, func(n ast.Node) bool {
switch n := n.(type) {
case *ast.FuncLit:
return false // prune traversal
case *ast.DeferStmt:
hasDefer = true
case *ast.LabeledStmt:
labels = append(labels, n.Label.Name)
case *ast.ReturnStmt:
totalReturns++
// Are implicit assignment conversions
// to result variables all trivial?
trivial := true
if len(n.Results) > 0 {
argType := func(i int) types.Type {
return info.TypeOf(n.Results[i])
}
if len(n.Results) == 1 && sig.Results().Len() > 1 {
// Spread return: return f() where f.Results > 1.
tuple := info.TypeOf(n.Results[0]).(*types.Tuple)
argType = func(i int) types.Type {
return tuple.At(i).Type()
}
}
for i := 0; i < sig.Results().Len(); i++ {
if !trivialConversion(argType(i), sig.Results().At(i)) {
trivial = false
break
}
}
} else if sig.Results().Len() > 0 {
hasBareReturn = true
}
if trivial {
trivialReturns++
}
}
return true
})
// Reject attempts to inline cgo-generated functions.
for _, obj := range freeObjs {
// There are others (iconst fconst sconst fpvar macro)
// but this is probably sufficient.
if strings.HasPrefix(obj.Name, "_Cfunc_") ||
strings.HasPrefix(obj.Name, "_Ctype_") ||
strings.HasPrefix(obj.Name, "_Cvar_") {
return nil, fmt.Errorf("cannot inline cgo-generated functions")
}
}
// Compact content to just the FuncDecl.
//
// As a space optimization, we don't retain the complete
// callee file content; all we need is "package _; func f() { ... }".
// This reduces the size of analysis facts.
//
// Offsets in the callee information are "relocatable"
// since they are all relative to the FuncDecl.
content = append([]byte("package _\n"),
content[offsetOf(fset, decl.Pos()):offsetOf(fset, decl.End())]...)
// Sanity check: re-parse the compacted content.
if _, _, err := parseCompact(content); err != nil {
return nil, err
}
params, results, effects, falcon := analyzeParams(logf, fset, info, decl)
return &Callee{gobCallee{
Content: content,
PkgPath: pkg.Path(),
Name: name,
Unexported: unexported,
FreeObjs: freeObjs,
FreeRefs: freeRefs,
ValidForCallStmt: validForCallStmt,
NumResults: sig.Results().Len(),
Params: params,
Results: results,
Effects: effects,
HasDefer: hasDefer,
HasBareReturn: hasBareReturn,
TotalReturns: totalReturns,
TrivialReturns: trivialReturns,
Labels: labels,
Falcon: falcon,
}}, nil
}
// parseCompact parses a Go source file of the form "package _\n func f() { ... }"
// and returns the sole function declaration.
func parseCompact(content []byte) (*token.FileSet, *ast.FuncDecl, error) {
fset := token.NewFileSet()
const mode = parser.ParseComments | parser.SkipObjectResolution | parser.AllErrors
f, err := parser.ParseFile(fset, "callee.go", content, mode)
if err != nil {
return nil, nil, fmt.Errorf("internal error: cannot compact file: %v", err)
}
return fset, f.Decls[0].(*ast.FuncDecl), nil
}
// A paramInfo records information about a callee receiver, parameter, or result variable.
type paramInfo struct {
Name string // parameter name (may be blank, or even "")
Index int // index within signature
IsResult bool // false for receiver or parameter, true for result variable
Assigned bool // parameter appears on left side of an assignment statement
Escapes bool // parameter has its address taken
Refs []int // FuncDecl-relative byte offset of parameter ref within body
Shadow map[string]bool // names shadowed at one of the above refs
FalconType string // name of this parameter's type (if basic) in the falcon system
}
// analyzeParams computes information about parameters of function fn,
// including a simple "address taken" escape analysis.
//
// It returns two new arrays, one of the receiver and parameters, and
// the other of the result variables of function fn.
//
// The input must be well-typed.
func analyzeParams(logf func(string, ...any), fset *token.FileSet, info *types.Info, decl *ast.FuncDecl) (params, results []*paramInfo, effects []int, _ falconResult) {
fnobj, ok := info.Defs[decl.Name]
if !ok {
panic(fmt.Sprintf("%s: no func object for %q",
fset.PositionFor(decl.Name.Pos(), false), decl.Name)) // ill-typed?
}
paramInfos := make(map[*types.Var]*paramInfo)
{
sig := fnobj.Type().(*types.Signature)
newParamInfo := func(param *types.Var, isResult bool) *paramInfo {
info := ¶mInfo{
Name: param.Name(),
IsResult: isResult,
Index: len(paramInfos),
}
paramInfos[param] = info
return info
}
if sig.Recv() != nil {
params = append(params, newParamInfo(sig.Recv(), false))
}
for i := 0; i < sig.Params().Len(); i++ {
params = append(params, newParamInfo(sig.Params().At(i), false))
}
for i := 0; i < sig.Results().Len(); i++ {
results = append(results, newParamInfo(sig.Results().At(i), true))
}
}
// Search function body for operations &x, x.f(), and x = y
// where x is a parameter, and record it.
escape(info, decl, func(v *types.Var, escapes bool) {
if info := paramInfos[v]; info != nil {
if escapes {
info.Escapes = true
} else {
info.Assigned = true
}
}
})
// Record locations of all references to parameters.
// And record the set of intervening definitions for each parameter.
//
// TODO(adonovan): combine this traversal with the one that computes
// FreeRefs. The tricky part is that calleefx needs this one first.
var stack []ast.Node
stack = append(stack, decl.Type) // for scope of function itself
ast.Inspect(decl.Body, func(n ast.Node) bool {
if n != nil {
stack = append(stack, n) // push
} else {
stack = stack[:len(stack)-1] // pop
}
if id, ok := n.(*ast.Ident); ok {
if v, ok := info.Uses[id].(*types.Var); ok {
if pinfo, ok := paramInfos[v]; ok {
// Record location of ref to parameter/result
// and any intervening (shadowing) names.
offset := int(n.Pos() - decl.Pos())
pinfo.Refs = append(pinfo.Refs, offset)
pinfo.Shadow = addShadows(pinfo.Shadow, info, pinfo.Name, stack)
}
}
}
return true
})
// Compute subset and order of parameters that are strictly evaluated.
// (Depends on Refs computed above.)
effects = calleefx(info, decl.Body, paramInfos)
logf("effects list = %v", effects)
falcon := falcon(logf, fset, paramInfos, info, decl)
return params, results, effects, falcon
}
// -- callee helpers --
// addShadows returns the shadows set augmented by the set of names
// locally shadowed at the location of the reference in the callee
// (identified by the stack). The name of the reference itself is
// excluded.
//
// These shadowed names may not be used in a replacement expression
// for the reference.
func addShadows(shadows map[string]bool, info *types.Info, exclude string, stack []ast.Node) map[string]bool {
for _, n := range stack {
if scope := scopeFor(info, n); scope != nil {
for _, name := range scope.Names() {
if name != exclude {
if shadows == nil {
shadows = make(map[string]bool)
}
shadows[name] = true
}
}
}
}
return shadows
}
// deref removes a pointer type constructor from the core type of t.
func deref(t types.Type) types.Type {
if ptr, ok := typeparams.CoreType(t).(*types.Pointer); ok {
return ptr.Elem()
}
return t
}
func isField(obj types.Object) bool {
if v, ok := obj.(*types.Var); ok && v.IsField() {
return true
}
return false
}
func isMethod(obj types.Object) bool {
if f, ok := obj.(*types.Func); ok && f.Type().(*types.Signature).Recv() != nil {
return true
}
return false
}
// -- serialization --
var (
_ gob.GobEncoder = (*Callee)(nil)
_ gob.GobDecoder = (*Callee)(nil)
)
func (callee *Callee) GobEncode() ([]byte, error) {
var out bytes.Buffer
if err := gob.NewEncoder(&out).Encode(callee.impl); err != nil {
return nil, err
}
return out.Bytes(), nil
}
func (callee *Callee) GobDecode(data []byte) error {
return gob.NewDecoder(bytes.NewReader(data)).Decode(&callee.impl)
}