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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 ssa
// This file defines utilities for working with source positions
// or source-level named entities ("objects").
// TODO(adonovan): test that {Value,Instruction}.Pos() positions match
// the originating syntax, as specified.
import (
"go/ast"
"go/token"
"go/types"
)
// EnclosingFunction returns the function that contains the syntax
// node denoted by path.
//
// Syntax associated with package-level variable specifications is
// enclosed by the package's init() function.
//
// Returns nil if not found; reasons might include:
// - the node is not enclosed by any function.
// - the node is within an anonymous function (FuncLit) and
// its SSA function has not been created yet
// (pkg.Build() has not yet been called).
//
func EnclosingFunction(pkg *Package, path []ast.Node) *Function {
// Start with package-level function...
fn := findEnclosingPackageLevelFunction(pkg, path)
if fn == nil {
return nil // not in any function
}
// ...then walk down the nested anonymous functions.
n := len(path)
outer:
for i := range path {
if lit, ok := path[n-1-i].(*ast.FuncLit); ok {
for _, anon := range fn.AnonFuncs {
if anon.Pos() == lit.Type.Func {
fn = anon
continue outer
}
}
// SSA function not found:
// - package not yet built, or maybe
// - builder skipped FuncLit in dead block
// (in principle; but currently the Builder
// generates even dead FuncLits).
return nil
}
}
return fn
}
// HasEnclosingFunction returns true if the AST node denoted by path
// is contained within the declaration of some function or
// package-level variable.
//
// Unlike EnclosingFunction, the behaviour of this function does not
// depend on whether SSA code for pkg has been built, so it can be
// used to quickly reject check inputs that will cause
// EnclosingFunction to fail, prior to SSA building.
//
func HasEnclosingFunction(pkg *Package, path []ast.Node) bool {
return findEnclosingPackageLevelFunction(pkg, path) != nil
}
// findEnclosingPackageLevelFunction returns the Function
// corresponding to the package-level function enclosing path.
//
func findEnclosingPackageLevelFunction(pkg *Package, path []ast.Node) *Function {
if n := len(path); n >= 2 { // [... {Gen,Func}Decl File]
switch decl := path[n-2].(type) {
case *ast.GenDecl:
if decl.Tok == token.VAR && n >= 3 {
// Package-level 'var' initializer.
return pkg.init
}
case *ast.FuncDecl:
if decl.Recv == nil && decl.Name.Name == "init" {
// Explicit init() function.
for _, b := range pkg.init.Blocks {
for _, instr := range b.Instrs {
if instr, ok := instr.(*Call); ok {
if callee, ok := instr.Call.Value.(*Function); ok && callee.Pkg == pkg && callee.Pos() == decl.Name.NamePos {
return callee
}
}
}
}
// Hack: return non-nil when SSA is not yet
// built so that HasEnclosingFunction works.
return pkg.init
}
// Declared function/method.
return findNamedFunc(pkg, decl.Name.NamePos)
}
}
return nil // not in any function
}
// findNamedFunc returns the named function whose FuncDecl.Ident is at
// position pos.
//
func findNamedFunc(pkg *Package, pos token.Pos) *Function {
// Look at all package members and method sets of named types.
// Not very efficient.
for _, mem := range pkg.Members {
switch mem := mem.(type) {
case *Function:
if mem.Pos() == pos {
return mem
}
case *Type:
mset := pkg.Prog.MethodSets.MethodSet(types.NewPointer(mem.Type()))
for i, n := 0, mset.Len(); i < n; i++ {
// Don't call Program.Method: avoid creating wrappers.
obj := mset.At(i).Obj().(*types.Func)
if obj.Pos() == pos {
return pkg.values[obj].(*Function)
}
}
}
}
return nil
}
// ValueForExpr returns the SSA Value that corresponds to non-constant
// expression e.
//
// It returns nil if no value was found, e.g.
// - the expression is not lexically contained within f;
// - f was not built with debug information; or
// - e is a constant expression. (For efficiency, no debug
// information is stored for constants. Use
// go/types.Info.Types[e].Value instead.)
// - e is a reference to nil or a built-in function.
// - the value was optimised away.
//
// If e is an addressable expression used in an lvalue context,
// value is the address denoted by e, and isAddr is true.
//
// The types of e (or &e, if isAddr) and the result are equal
// (modulo "untyped" bools resulting from comparisons).
//
// (Tip: to find the ssa.Value given a source position, use
// importer.PathEnclosingInterval to locate the ast.Node, then
// EnclosingFunction to locate the Function, then ValueForExpr to find
// the ssa.Value.)
//
func (f *Function) ValueForExpr(e ast.Expr) (value Value, isAddr bool) {
if f.debugInfo() { // (opt)
e = unparen(e)
for _, b := range f.Blocks {
for _, instr := range b.Instrs {
if ref, ok := instr.(*DebugRef); ok {
if ref.Expr == e {
return ref.X, ref.IsAddr
}
}
}
}
}
return
}
// --- Lookup functions for source-level named entities (types.Objects) ---
// Package returns the SSA Package corresponding to the specified
// type-checker package object.
// It returns nil if no such SSA package has been created.
//
func (prog *Program) Package(obj *types.Package) *Package {
return prog.packages[obj]
}
// packageLevelValue returns the package-level value corresponding to
// the specified named object, which may be a package-level const
// (*Const), var (*Global) or func (*Function) of some package in
// prog. It returns nil if the object is not found.
//
func (prog *Program) packageLevelValue(obj types.Object) Value {
if pkg, ok := prog.packages[obj.Pkg()]; ok {
return pkg.values[obj]
}
return nil
}
// FuncValue returns the concrete Function denoted by the source-level
// named function obj, or nil if obj denotes an interface method.
//
// TODO(adonovan): check the invariant that obj.Type() matches the
// result's Signature, both in the params/results and in the receiver.
//
func (prog *Program) FuncValue(obj *types.Func) *Function {
fn, _ := prog.packageLevelValue(obj).(*Function)
return fn
}
// ConstValue returns the SSA Value denoted by the source-level named
// constant obj.
//
func (prog *Program) ConstValue(obj *types.Const) *Const {
// TODO(adonovan): opt: share (don't reallocate)
// Consts for const objects and constant ast.Exprs.
// Universal constant? {true,false,nil}
if obj.Parent() == types.Universe {
return NewConst(obj.Val(), obj.Type())
}
// Package-level named constant?
if v := prog.packageLevelValue(obj); v != nil {
return v.(*Const)
}
return NewConst(obj.Val(), obj.Type())
}
// VarValue returns the SSA Value that corresponds to a specific
// identifier denoting the source-level named variable obj.
//
// VarValue returns nil if a local variable was not found, perhaps
// because its package was not built, the debug information was not
// requested during SSA construction, or the value was optimized away.
//
// ref is the path to an ast.Ident (e.g. from PathEnclosingInterval),
// and that ident must resolve to obj.
//
// pkg is the package enclosing the reference. (A reference to a var
// always occurs within a function, so we need to know where to find it.)
//
// If the identifier is a field selector and its base expression is
// non-addressable, then VarValue returns the value of that field.
// For example:
// func f() struct {x int}
// f().x // VarValue(x) returns a *Field instruction of type int
//
// All other identifiers denote addressable locations (variables).
// For them, VarValue may return either the variable's address or its
// value, even when the expression is evaluated only for its value; the
// situation is reported by isAddr, the second component of the result.
//
// If !isAddr, the returned value is the one associated with the
// specific identifier. For example,
// var x int // VarValue(x) returns Const 0 here
// x = 1 // VarValue(x) returns Const 1 here
//
// It is not specified whether the value or the address is returned in
// any particular case, as it may depend upon optimizations performed
// during SSA code generation, such as registerization, constant
// folding, avoidance of materialization of subexpressions, etc.
//
func (prog *Program) VarValue(obj *types.Var, pkg *Package, ref []ast.Node) (value Value, isAddr bool) {
// All references to a var are local to some function, possibly init.
fn := EnclosingFunction(pkg, ref)
if fn == nil {
return // e.g. def of struct field; SSA not built?
}
id := ref[0].(*ast.Ident)
// Defining ident of a parameter?
if id.Pos() == obj.Pos() {
for _, param := range fn.Params {
if param.Object() == obj {
return param, false
}
}
}
// Other ident?
for _, b := range fn.Blocks {
for _, instr := range b.Instrs {
if dr, ok := instr.(*DebugRef); ok {
if dr.Pos() == id.Pos() {
return dr.X, dr.IsAddr
}
}
}
}
// Defining ident of package-level var?
if v := prog.packageLevelValue(obj); v != nil {
return v.(*Global), true
}
return // e.g. debug info not requested, or var optimized away
}