294 lines
9.2 KiB
Go
294 lines
9.2 KiB
Go
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// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package ssa
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// This file defines utilities for working with source positions
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// or source-level named entities ("objects").
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// TODO(adonovan): test that {Value,Instruction}.Pos() positions match
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// the originating syntax, as specified.
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import (
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"go/ast"
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"go/token"
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"go/types"
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)
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// EnclosingFunction returns the function that contains the syntax
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// node denoted by path.
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//
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// Syntax associated with package-level variable specifications is
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// enclosed by the package's init() function.
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//
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// Returns nil if not found; reasons might include:
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// - the node is not enclosed by any function.
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// - the node is within an anonymous function (FuncLit) and
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// its SSA function has not been created yet
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// (pkg.Build() has not yet been called).
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//
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func EnclosingFunction(pkg *Package, path []ast.Node) *Function {
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// Start with package-level function...
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fn := findEnclosingPackageLevelFunction(pkg, path)
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if fn == nil {
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return nil // not in any function
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}
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// ...then walk down the nested anonymous functions.
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n := len(path)
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outer:
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for i := range path {
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if lit, ok := path[n-1-i].(*ast.FuncLit); ok {
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for _, anon := range fn.AnonFuncs {
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if anon.Pos() == lit.Type.Func {
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fn = anon
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continue outer
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}
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}
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// SSA function not found:
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// - package not yet built, or maybe
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// - builder skipped FuncLit in dead block
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// (in principle; but currently the Builder
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// generates even dead FuncLits).
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return nil
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}
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}
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return fn
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}
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// HasEnclosingFunction returns true if the AST node denoted by path
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// is contained within the declaration of some function or
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// package-level variable.
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//
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// Unlike EnclosingFunction, the behaviour of this function does not
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// depend on whether SSA code for pkg has been built, so it can be
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// used to quickly reject check inputs that will cause
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// EnclosingFunction to fail, prior to SSA building.
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//
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func HasEnclosingFunction(pkg *Package, path []ast.Node) bool {
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return findEnclosingPackageLevelFunction(pkg, path) != nil
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}
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// findEnclosingPackageLevelFunction returns the Function
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// corresponding to the package-level function enclosing path.
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//
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func findEnclosingPackageLevelFunction(pkg *Package, path []ast.Node) *Function {
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if n := len(path); n >= 2 { // [... {Gen,Func}Decl File]
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switch decl := path[n-2].(type) {
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case *ast.GenDecl:
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if decl.Tok == token.VAR && n >= 3 {
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// Package-level 'var' initializer.
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return pkg.init
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}
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case *ast.FuncDecl:
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if decl.Recv == nil && decl.Name.Name == "init" {
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// Explicit init() function.
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for _, b := range pkg.init.Blocks {
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for _, instr := range b.Instrs {
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if instr, ok := instr.(*Call); ok {
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if callee, ok := instr.Call.Value.(*Function); ok && callee.Pkg == pkg && callee.Pos() == decl.Name.NamePos {
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return callee
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}
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}
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}
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}
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// Hack: return non-nil when SSA is not yet
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// built so that HasEnclosingFunction works.
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return pkg.init
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}
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// Declared function/method.
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return findNamedFunc(pkg, decl.Name.NamePos)
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}
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}
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return nil // not in any function
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}
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// findNamedFunc returns the named function whose FuncDecl.Ident is at
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// position pos.
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//
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func findNamedFunc(pkg *Package, pos token.Pos) *Function {
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// Look at all package members and method sets of named types.
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// Not very efficient.
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for _, mem := range pkg.Members {
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switch mem := mem.(type) {
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case *Function:
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if mem.Pos() == pos {
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return mem
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}
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case *Type:
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mset := pkg.Prog.MethodSets.MethodSet(types.NewPointer(mem.Type()))
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for i, n := 0, mset.Len(); i < n; i++ {
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// Don't call Program.Method: avoid creating wrappers.
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obj := mset.At(i).Obj().(*types.Func)
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if obj.Pos() == pos {
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return pkg.values[obj].(*Function)
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}
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}
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}
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}
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return nil
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}
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// ValueForExpr returns the SSA Value that corresponds to non-constant
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// expression e.
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//
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// It returns nil if no value was found, e.g.
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// - the expression is not lexically contained within f;
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// - f was not built with debug information; or
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// - e is a constant expression. (For efficiency, no debug
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// information is stored for constants. Use
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// go/types.Info.Types[e].Value instead.)
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// - e is a reference to nil or a built-in function.
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// - the value was optimised away.
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//
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// If e is an addressable expression used in an lvalue context,
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// value is the address denoted by e, and isAddr is true.
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//
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// The types of e (or &e, if isAddr) and the result are equal
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// (modulo "untyped" bools resulting from comparisons).
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//
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// (Tip: to find the ssa.Value given a source position, use
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// astutil.PathEnclosingInterval to locate the ast.Node, then
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// EnclosingFunction to locate the Function, then ValueForExpr to find
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// the ssa.Value.)
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//
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func (f *Function) ValueForExpr(e ast.Expr) (value Value, isAddr bool) {
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if f.debugInfo() { // (opt)
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e = unparen(e)
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for _, b := range f.Blocks {
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for _, instr := range b.Instrs {
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if ref, ok := instr.(*DebugRef); ok {
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if ref.Expr == e {
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return ref.X, ref.IsAddr
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}
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}
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}
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}
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}
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return
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}
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// --- Lookup functions for source-level named entities (types.Objects) ---
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// Package returns the SSA Package corresponding to the specified
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// type-checker package object.
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// It returns nil if no such SSA package has been created.
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//
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func (prog *Program) Package(obj *types.Package) *Package {
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return prog.packages[obj]
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}
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// packageLevelValue returns the package-level value corresponding to
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// the specified named object, which may be a package-level const
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// (*Const), var (*Global) or func (*Function) of some package in
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// prog. It returns nil if the object is not found.
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//
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func (prog *Program) packageLevelValue(obj types.Object) Value {
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if pkg, ok := prog.packages[obj.Pkg()]; ok {
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return pkg.values[obj]
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}
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return nil
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}
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// FuncValue returns the concrete Function denoted by the source-level
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// named function obj, or nil if obj denotes an interface method.
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//
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// TODO(adonovan): check the invariant that obj.Type() matches the
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// result's Signature, both in the params/results and in the receiver.
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//
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func (prog *Program) FuncValue(obj *types.Func) *Function {
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fn, _ := prog.packageLevelValue(obj).(*Function)
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return fn
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}
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// ConstValue returns the SSA Value denoted by the source-level named
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// constant obj.
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//
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func (prog *Program) ConstValue(obj *types.Const) *Const {
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// TODO(adonovan): opt: share (don't reallocate)
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// Consts for const objects and constant ast.Exprs.
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// Universal constant? {true,false,nil}
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if obj.Parent() == types.Universe {
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return NewConst(obj.Val(), obj.Type())
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}
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// Package-level named constant?
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if v := prog.packageLevelValue(obj); v != nil {
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return v.(*Const)
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}
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return NewConst(obj.Val(), obj.Type())
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}
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// VarValue returns the SSA Value that corresponds to a specific
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// identifier denoting the source-level named variable obj.
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//
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// VarValue returns nil if a local variable was not found, perhaps
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// because its package was not built, the debug information was not
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// requested during SSA construction, or the value was optimized away.
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//
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// ref is the path to an ast.Ident (e.g. from PathEnclosingInterval),
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// and that ident must resolve to obj.
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//
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// pkg is the package enclosing the reference. (A reference to a var
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// always occurs within a function, so we need to know where to find it.)
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//
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// If the identifier is a field selector and its base expression is
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// non-addressable, then VarValue returns the value of that field.
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// For example:
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// func f() struct {x int}
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// f().x // VarValue(x) returns a *Field instruction of type int
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//
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// All other identifiers denote addressable locations (variables).
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// For them, VarValue may return either the variable's address or its
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// value, even when the expression is evaluated only for its value; the
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// situation is reported by isAddr, the second component of the result.
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//
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// If !isAddr, the returned value is the one associated with the
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// specific identifier. For example,
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// var x int // VarValue(x) returns Const 0 here
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// x = 1 // VarValue(x) returns Const 1 here
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//
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// It is not specified whether the value or the address is returned in
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// any particular case, as it may depend upon optimizations performed
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// during SSA code generation, such as registerization, constant
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// folding, avoidance of materialization of subexpressions, etc.
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//
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func (prog *Program) VarValue(obj *types.Var, pkg *Package, ref []ast.Node) (value Value, isAddr bool) {
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// All references to a var are local to some function, possibly init.
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fn := EnclosingFunction(pkg, ref)
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if fn == nil {
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return // e.g. def of struct field; SSA not built?
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}
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id := ref[0].(*ast.Ident)
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// Defining ident of a parameter?
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if id.Pos() == obj.Pos() {
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for _, param := range fn.Params {
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if param.Object() == obj {
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return param, false
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}
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}
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}
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// Other ident?
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for _, b := range fn.Blocks {
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for _, instr := range b.Instrs {
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if dr, ok := instr.(*DebugRef); ok {
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if dr.Pos() == id.Pos() {
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return dr.X, dr.IsAddr
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}
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}
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}
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}
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// Defining ident of package-level var?
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if v := prog.packageLevelValue(obj); v != nil {
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return v.(*Global), true
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}
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return // e.g. debug info not requested, or var optimized away
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}
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