--- /dev/null
+// Copyright 2014 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 cha computes the call graph of a Go program using the Class
+// Hierarchy Analysis (CHA) algorithm.
+//
+// CHA was first described in "Optimization of Object-Oriented Programs
+// Using Static Class Hierarchy Analysis", Jeffrey Dean, David Grove,
+// and Craig Chambers, ECOOP'95.
+//
+// CHA is related to RTA (see go/callgraph/rta); the difference is that
+// CHA conservatively computes the entire "implements" relation between
+// interfaces and concrete types ahead of time, whereas RTA uses dynamic
+// programming to construct it on the fly as it encounters new functions
+// reachable from main. CHA may thus include spurious call edges for
+// types that haven't been instantiated yet, or types that are never
+// instantiated.
+//
+// Since CHA conservatively assumes that all functions are address-taken
+// and all concrete types are put into interfaces, it is sound to run on
+// partial programs, such as libraries without a main or test function.
+//
+package cha // import "golang.org/x/tools/go/callgraph/cha"
+
+import (
+ "go/types"
+
+ "golang.org/x/tools/go/callgraph"
+ "golang.org/x/tools/go/ssa"
+ "golang.org/x/tools/go/ssa/ssautil"
+ "golang.org/x/tools/go/types/typeutil"
+)
+
+// CallGraph computes the call graph of the specified program using the
+// Class Hierarchy Analysis algorithm.
+//
+func CallGraph(prog *ssa.Program) *callgraph.Graph {
+ cg := callgraph.New(nil) // TODO(adonovan) eliminate concept of rooted callgraph
+
+ allFuncs := ssautil.AllFunctions(prog)
+
+ // funcsBySig contains all functions, keyed by signature. It is
+ // the effective set of address-taken functions used to resolve
+ // a dynamic call of a particular signature.
+ var funcsBySig typeutil.Map // value is []*ssa.Function
+
+ // methodsByName contains all methods,
+ // grouped by name for efficient lookup.
+ // (methodsById would be better but not every SSA method has a go/types ID.)
+ methodsByName := make(map[string][]*ssa.Function)
+
+ // An imethod represents an interface method I.m.
+ // (There's no go/types object for it;
+ // a *types.Func may be shared by many interfaces due to interface embedding.)
+ type imethod struct {
+ I *types.Interface
+ id string
+ }
+ // methodsMemo records, for every abstract method call I.m on
+ // interface type I, the set of concrete methods C.m of all
+ // types C that satisfy interface I.
+ //
+ // Abstract methods may be shared by several interfaces,
+ // hence we must pass I explicitly, not guess from m.
+ //
+ // methodsMemo is just a cache, so it needn't be a typeutil.Map.
+ methodsMemo := make(map[imethod][]*ssa.Function)
+ lookupMethods := func(I *types.Interface, m *types.Func) []*ssa.Function {
+ id := m.Id()
+ methods, ok := methodsMemo[imethod{I, id}]
+ if !ok {
+ for _, f := range methodsByName[m.Name()] {
+ C := f.Signature.Recv().Type() // named or *named
+ if types.Implements(C, I) {
+ methods = append(methods, f)
+ }
+ }
+ methodsMemo[imethod{I, id}] = methods
+ }
+ return methods
+ }
+
+ for f := range allFuncs {
+ if f.Signature.Recv() == nil {
+ // Package initializers can never be address-taken.
+ if f.Name() == "init" && f.Synthetic == "package initializer" {
+ continue
+ }
+ funcs, _ := funcsBySig.At(f.Signature).([]*ssa.Function)
+ funcs = append(funcs, f)
+ funcsBySig.Set(f.Signature, funcs)
+ } else {
+ methodsByName[f.Name()] = append(methodsByName[f.Name()], f)
+ }
+ }
+
+ addEdge := func(fnode *callgraph.Node, site ssa.CallInstruction, g *ssa.Function) {
+ gnode := cg.CreateNode(g)
+ callgraph.AddEdge(fnode, site, gnode)
+ }
+
+ addEdges := func(fnode *callgraph.Node, site ssa.CallInstruction, callees []*ssa.Function) {
+ // Because every call to a highly polymorphic and
+ // frequently used abstract method such as
+ // (io.Writer).Write is assumed to call every concrete
+ // Write method in the program, the call graph can
+ // contain a lot of duplication.
+ //
+ // TODO(adonovan): opt: consider factoring the callgraph
+ // API so that the Callers component of each edge is a
+ // slice of nodes, not a singleton.
+ for _, g := range callees {
+ addEdge(fnode, site, g)
+ }
+ }
+
+ for f := range allFuncs {
+ fnode := cg.CreateNode(f)
+ for _, b := range f.Blocks {
+ for _, instr := range b.Instrs {
+ if site, ok := instr.(ssa.CallInstruction); ok {
+ call := site.Common()
+ if call.IsInvoke() {
+ tiface := call.Value.Type().Underlying().(*types.Interface)
+ addEdges(fnode, site, lookupMethods(tiface, call.Method))
+ } else if g := call.StaticCallee(); g != nil {
+ addEdge(fnode, site, g)
+ } else if _, ok := call.Value.(*ssa.Builtin); !ok {
+ callees, _ := funcsBySig.At(call.Signature()).([]*ssa.Function)
+ addEdges(fnode, site, callees)
+ }
+ }
+ }
+ }
+ }
+
+ return cg
+}
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