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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 implements the Function and BasicBlock types.
import (
"bytes"
"fmt"
"go/ast"
"go/token"
"go/types"
"io"
"os"
"strings"
)
// addEdge adds a control-flow graph edge from from to to.
func addEdge(from, to *BasicBlock) {
from.Succs = append(from.Succs, to)
to.Preds = append(to.Preds, from)
}
// Parent returns the function that contains block b.
func (b *BasicBlock) Parent() *Function { return b.parent }
// String returns a human-readable label of this block.
// It is not guaranteed unique within the function.
//
func (b *BasicBlock) String() string {
return fmt.Sprintf("%d", b.Index)
}
// emit appends an instruction to the current basic block.
// If the instruction defines a Value, it is returned.
//
func (b *BasicBlock) emit(i Instruction) Value {
i.setBlock(b)
b.Instrs = append(b.Instrs, i)
v, _ := i.(Value)
return v
}
// predIndex returns the i such that b.Preds[i] == c or panics if
// there is none.
func (b *BasicBlock) predIndex(c *BasicBlock) int {
for i, pred := range b.Preds {
if pred == c {
return i
}
}
panic(fmt.Sprintf("no edge %s -> %s", c, b))
}
// hasPhi returns true if b.Instrs contains φ-nodes.
func (b *BasicBlock) hasPhi() bool {
_, ok := b.Instrs[0].(*Phi)
return ok
}
// phis returns the prefix of b.Instrs containing all the block's φ-nodes.
func (b *BasicBlock) phis() []Instruction {
for i, instr := range b.Instrs {
if _, ok := instr.(*Phi); !ok {
return b.Instrs[:i]
}
}
return nil // unreachable in well-formed blocks
}
// replacePred replaces all occurrences of p in b's predecessor list with q.
// Ordinarily there should be at most one.
//
func (b *BasicBlock) replacePred(p, q *BasicBlock) {
for i, pred := range b.Preds {
if pred == p {
b.Preds[i] = q
}
}
}
// replaceSucc replaces all occurrences of p in b's successor list with q.
// Ordinarily there should be at most one.
//
func (b *BasicBlock) replaceSucc(p, q *BasicBlock) {
for i, succ := range b.Succs {
if succ == p {
b.Succs[i] = q
}
}
}
// removePred removes all occurrences of p in b's
// predecessor list and φ-nodes.
// Ordinarily there should be at most one.
//
func (b *BasicBlock) removePred(p *BasicBlock) {
phis := b.phis()
// We must preserve edge order for φ-nodes.
j := 0
for i, pred := range b.Preds {
if pred != p {
b.Preds[j] = b.Preds[i]
// Strike out φ-edge too.
for _, instr := range phis {
phi := instr.(*Phi)
phi.Edges[j] = phi.Edges[i]
}
j++
}
}
// Nil out b.Preds[j:] and φ-edges[j:] to aid GC.
for i := j; i < len(b.Preds); i++ {
b.Preds[i] = nil
for _, instr := range phis {
instr.(*Phi).Edges[i] = nil
}
}
b.Preds = b.Preds[:j]
for _, instr := range phis {
phi := instr.(*Phi)
phi.Edges = phi.Edges[:j]
}
}
// Destinations associated with unlabelled for/switch/select stmts.
// We push/pop one of these as we enter/leave each construct and for
// each BranchStmt we scan for the innermost target of the right type.
//
type targets struct {
tail *targets // rest of stack
_break *BasicBlock
_continue *BasicBlock
_fallthrough *BasicBlock
}
// Destinations associated with a labelled block.
// We populate these as labels are encountered in forward gotos or
// labelled statements.
//
type lblock struct {
_goto *BasicBlock
_break *BasicBlock
_continue *BasicBlock
}
// labelledBlock returns the branch target associated with the
// specified label, creating it if needed.
//
func (f *Function) labelledBlock(label *ast.Ident) *lblock {
lb := f.lblocks[label.Obj]
if lb == nil {
lb = &lblock{_goto: f.newBasicBlock(label.Name)}
if f.lblocks == nil {
f.lblocks = make(map[*ast.Object]*lblock)
}
f.lblocks[label.Obj] = lb
}
return lb
}
// addParam adds a (non-escaping) parameter to f.Params of the
// specified name, type and source position.
//
func (f *Function) addParam(name string, typ types.Type, pos token.Pos) *Parameter {
v := &Parameter{
name: name,
typ: typ,
pos: pos,
parent: f,
}
f.Params = append(f.Params, v)
return v
}
func (f *Function) addParamObj(obj types.Object) *Parameter {
name := obj.Name()
if name == "" {
name = fmt.Sprintf("arg%d", len(f.Params))
}
param := f.addParam(name, obj.Type(), obj.Pos())
param.object = obj
return param
}
// addSpilledParam declares a parameter that is pre-spilled to the
// stack; the function body will load/store the spilled location.
// Subsequent lifting will eliminate spills where possible.
//
func (f *Function) addSpilledParam(obj types.Object) {
param := f.addParamObj(obj)
spill := &Alloc{Comment: obj.Name()}
spill.setType(types.NewPointer(obj.Type()))
spill.setPos(obj.Pos())
f.objects[obj] = spill
f.Locals = append(f.Locals, spill)
f.emit(spill)
f.emit(&Store{Addr: spill, Val: param})
}
// startBody initializes the function prior to generating SSA code for its body.
// Precondition: f.Type() already set.
//
func (f *Function) startBody() {
f.currentBlock = f.newBasicBlock("entry")
f.objects = make(map[types.Object]Value) // needed for some synthetics, e.g. init
}
// createSyntacticParams populates f.Params and generates code (spills
// and named result locals) for all the parameters declared in the
// syntax. In addition it populates the f.objects mapping.
//
// Preconditions:
// f.startBody() was called.
// Postcondition:
// len(f.Params) == len(f.Signature.Params) + (f.Signature.Recv() ? 1 : 0)
//
func (f *Function) createSyntacticParams(recv *ast.FieldList, functype *ast.FuncType) {
// Receiver (at most one inner iteration).
if recv != nil {
for _, field := range recv.List {
for _, n := range field.Names {
f.addSpilledParam(f.Pkg.info.Defs[n])
}
// Anonymous receiver? No need to spill.
if field.Names == nil {
f.addParamObj(f.Signature.Recv())
}
}
}
// Parameters.
if functype.Params != nil {
n := len(f.Params) // 1 if has recv, 0 otherwise
for _, field := range functype.Params.List {
for _, n := range field.Names {
f.addSpilledParam(f.Pkg.info.Defs[n])
}
// Anonymous parameter? No need to spill.
if field.Names == nil {
f.addParamObj(f.Signature.Params().At(len(f.Params) - n))
}
}
}
// Named results.
if functype.Results != nil {
for _, field := range functype.Results.List {
// Implicit "var" decl of locals for named results.
for _, n := range field.Names {
f.namedResults = append(f.namedResults, f.addLocalForIdent(n))
}
}
}
}
// numberRegisters assigns numbers to all SSA registers
// (value-defining Instructions) in f, to aid debugging.
// (Non-Instruction Values are named at construction.)
//
func numberRegisters(f *Function) {
v := 0
for _, b := range f.Blocks {
for _, instr := range b.Instrs {
switch instr.(type) {
case Value:
instr.(interface {
setNum(int)
}).setNum(v)
v++
}
}
}
}
// buildReferrers populates the def/use information in all non-nil
// Value.Referrers slice.
// Precondition: all such slices are initially empty.
func buildReferrers(f *Function) {
var rands []*Value
for _, b := range f.Blocks {
for _, instr := range b.Instrs {
rands = instr.Operands(rands[:0]) // recycle storage
for _, rand := range rands {
if r := *rand; r != nil {
if ref := r.Referrers(); ref != nil {
*ref = append(*ref, instr)
}
}
}
}
}
}
// finishBody() finalizes the function after SSA code generation of its body.
func (f *Function) finishBody() {
f.objects = nil
f.currentBlock = nil
f.lblocks = nil
// Don't pin the AST in memory (except in debug mode).
if n := f.syntax; n != nil && !f.debugInfo() {
f.syntax = extentNode{n.Pos(), n.End()}
}
// Remove from f.Locals any Allocs that escape to the heap.
j := 0
for _, l := range f.Locals {
if !l.Heap {
f.Locals[j] = l
j++
}
}
// Nil out f.Locals[j:] to aid GC.
for i := j; i < len(f.Locals); i++ {
f.Locals[i] = nil
}
f.Locals = f.Locals[:j]
optimizeBlocks(f)
buildReferrers(f)
buildDomTree(f)
if f.Prog.mode&NaiveForm == 0 {
// For debugging pre-state of lifting pass:
// numberRegisters(f)
// f.WriteTo(os.Stderr)
lift(f)
}
f.namedResults = nil // (used by lifting)
numberRegisters(f)
if f.Prog.mode&PrintFunctions != 0 {
printMu.Lock()
f.WriteTo(os.Stdout)
printMu.Unlock()
}
if f.Prog.mode&SanityCheckFunctions != 0 {
mustSanityCheck(f, nil)
}
}
// removeNilBlocks eliminates nils from f.Blocks and updates each
// BasicBlock.Index. Use this after any pass that may delete blocks.
//
func (f *Function) removeNilBlocks() {
j := 0
for _, b := range f.Blocks {
if b != nil {
b.Index = j
f.Blocks[j] = b
j++
}
}
// Nil out f.Blocks[j:] to aid GC.
for i := j; i < len(f.Blocks); i++ {
f.Blocks[i] = nil
}
f.Blocks = f.Blocks[:j]
}
// SetDebugMode sets the debug mode for package pkg. If true, all its
// functions will include full debug info. This greatly increases the
// size of the instruction stream, and causes Functions to depend upon
// the ASTs, potentially keeping them live in memory for longer.
//
func (pkg *Package) SetDebugMode(debug bool) {
// TODO(adonovan): do we want ast.File granularity?
pkg.debug = debug
}
// debugInfo reports whether debug info is wanted for this function.
func (f *Function) debugInfo() bool {
return f.Pkg != nil && f.Pkg.debug
}
// addNamedLocal creates a local variable, adds it to function f and
// returns it. Its name and type are taken from obj. Subsequent
// calls to f.lookup(obj) will return the same local.
//
func (f *Function) addNamedLocal(obj types.Object) *Alloc {
l := f.addLocal(obj.Type(), obj.Pos())
l.Comment = obj.Name()
f.objects[obj] = l
return l
}
func (f *Function) addLocalForIdent(id *ast.Ident) *Alloc {
return f.addNamedLocal(f.Pkg.info.Defs[id])
}
// addLocal creates an anonymous local variable of type typ, adds it
// to function f and returns it. pos is the optional source location.
//
func (f *Function) addLocal(typ types.Type, pos token.Pos) *Alloc {
v := &Alloc{}
v.setType(types.NewPointer(typ))
v.setPos(pos)
f.Locals = append(f.Locals, v)
f.emit(v)
return v
}
// lookup returns the address of the named variable identified by obj
// that is local to function f or one of its enclosing functions.
// If escaping, the reference comes from a potentially escaping pointer
// expression and the referent must be heap-allocated.
//
func (f *Function) lookup(obj types.Object, escaping bool) Value {
if v, ok := f.objects[obj]; ok {
if alloc, ok := v.(*Alloc); ok && escaping {
alloc.Heap = true
}
return v // function-local var (address)
}
// Definition must be in an enclosing function;
// plumb it through intervening closures.
if f.parent == nil {
panic("no ssa.Value for " + obj.String())
}
outer := f.parent.lookup(obj, true) // escaping
v := &FreeVar{
name: obj.Name(),
typ: outer.Type(),
pos: outer.Pos(),
outer: outer,
parent: f,
}
f.objects[obj] = v
f.FreeVars = append(f.FreeVars, v)
return v
}
// emit emits the specified instruction to function f.
func (f *Function) emit(instr Instruction) Value {
return f.currentBlock.emit(instr)
}
// RelString returns the full name of this function, qualified by
// package name, receiver type, etc.
//
// The specific formatting rules are not guaranteed and may change.
//
// Examples:
// "math.IsNaN" // a package-level function
// "(*bytes.Buffer).Bytes" // a declared method or a wrapper
// "(*bytes.Buffer).Bytes$thunk" // thunk (func wrapping method; receiver is param 0)
// "(*bytes.Buffer).Bytes$bound" // bound (func wrapping method; receiver supplied by closure)
// "main.main$1" // an anonymous function in main
// "main.init#1" // a declared init function
// "main.init" // the synthesized package initializer
//
// When these functions are referred to from within the same package
// (i.e. from == f.Pkg.Object), they are rendered without the package path.
// For example: "IsNaN", "(*Buffer).Bytes", etc.
//
// All non-synthetic functions have distinct package-qualified names.
// (But two methods may have the same name "(T).f" if one is a synthetic
// wrapper promoting a non-exported method "f" from another package; in
// that case, the strings are equal but the identifiers "f" are distinct.)
//
func (f *Function) RelString(from *types.Package) string {
// Anonymous?
if f.parent != nil {
// An anonymous function's Name() looks like "parentName$1",
// but its String() should include the type/package/etc.
parent := f.parent.RelString(from)
for i, anon := range f.parent.AnonFuncs {
if anon == f {
return fmt.Sprintf("%s$%d", parent, 1+i)
}
}
return f.name // should never happen
}
// Method (declared or wrapper)?
if recv := f.Signature.Recv(); recv != nil {
return f.relMethod(from, recv.Type())
}
// Thunk?
if f.method != nil {
return f.relMethod(from, f.method.Recv())
}
// Bound?
if len(f.FreeVars) == 1 && strings.HasSuffix(f.name, "$bound") {
return f.relMethod(from, f.FreeVars[0].Type())
}
// Package-level function?
// Prefix with package name for cross-package references only.
if p := f.pkg(); p != nil && p != from {
return fmt.Sprintf("%s.%s", p.Path(), f.name)
}
// Unknown.
return f.name
}
func (f *Function) relMethod(from *types.Package, recv types.Type) string {
return fmt.Sprintf("(%s).%s", relType(recv, from), f.name)
}
// writeSignature writes to buf the signature sig in declaration syntax.
func writeSignature(buf *bytes.Buffer, from *types.Package, name string, sig *types.Signature, params []*Parameter) {
buf.WriteString("func ")
if recv := sig.Recv(); recv != nil {
buf.WriteString("(")
if n := params[0].Name(); n != "" {
buf.WriteString(n)
buf.WriteString(" ")
}
types.WriteType(buf, params[0].Type(), types.RelativeTo(from))
buf.WriteString(") ")
}
buf.WriteString(name)
types.WriteSignature(buf, sig, types.RelativeTo(from))
}
func (f *Function) pkg() *types.Package {
if f.Pkg != nil {
return f.Pkg.Pkg
}
return nil
}
var _ io.WriterTo = (*Function)(nil) // *Function implements io.Writer
func (f *Function) WriteTo(w io.Writer) (int64, error) {
var buf bytes.Buffer
WriteFunction(&buf, f)
n, err := w.Write(buf.Bytes())
return int64(n), err
}
// WriteFunction writes to buf a human-readable "disassembly" of f.
func WriteFunction(buf *bytes.Buffer, f *Function) {
fmt.Fprintf(buf, "# Name: %s\n", f.String())
if f.Pkg != nil {
fmt.Fprintf(buf, "# Package: %s\n", f.Pkg.Pkg.Path())
}
if syn := f.Synthetic; syn != "" {
fmt.Fprintln(buf, "# Synthetic:", syn)
}
if pos := f.Pos(); pos.IsValid() {
fmt.Fprintf(buf, "# Location: %s\n", f.Prog.Fset.Position(pos))
}
if f.parent != nil {
fmt.Fprintf(buf, "# Parent: %s\n", f.parent.Name())
}
if f.Recover != nil {
fmt.Fprintf(buf, "# Recover: %s\n", f.Recover)
}
from := f.pkg()
if f.FreeVars != nil {
buf.WriteString("# Free variables:\n")
for i, fv := range f.FreeVars {
fmt.Fprintf(buf, "# % 3d:\t%s %s\n", i, fv.Name(), relType(fv.Type(), from))
}
}
if len(f.Locals) > 0 {
buf.WriteString("# Locals:\n")
for i, l := range f.Locals {
fmt.Fprintf(buf, "# % 3d:\t%s %s\n", i, l.Name(), relType(deref(l.Type()), from))
}
}
writeSignature(buf, from, f.Name(), f.Signature, f.Params)
buf.WriteString(":\n")
if f.Blocks == nil {
buf.WriteString("\t(external)\n")
}
// NB. column calculations are confused by non-ASCII
// characters and assume 8-space tabs.
const punchcard = 80 // for old time's sake.
const tabwidth = 8
for _, b := range f.Blocks {
if b == nil {
// Corrupt CFG.
fmt.Fprintf(buf, ".nil:\n")
continue
}
n, _ := fmt.Fprintf(buf, "%d:", b.Index)
bmsg := fmt.Sprintf("%s P:%d S:%d", b.Comment, len(b.Preds), len(b.Succs))
fmt.Fprintf(buf, "%*s%s\n", punchcard-1-n-len(bmsg), "", bmsg)
if false { // CFG debugging
fmt.Fprintf(buf, "\t# CFG: %s --> %s --> %s\n", b.Preds, b, b.Succs)
}
for _, instr := range b.Instrs {
buf.WriteString("\t")
switch v := instr.(type) {
case Value:
l := punchcard - tabwidth
// Left-align the instruction.
if name := v.Name(); name != "" {
n, _ := fmt.Fprintf(buf, "%s = ", name)
l -= n
}
n, _ := buf.WriteString(instr.String())
l -= n
// Right-align the type if there's space.
if t := v.Type(); t != nil {
buf.WriteByte(' ')
ts := relType(t, from)
l -= len(ts) + len(" ") // (spaces before and after type)
if l > 0 {
fmt.Fprintf(buf, "%*s", l, "")
}
buf.WriteString(ts)
}
case nil:
// Be robust against bad transforms.
buf.WriteString("<deleted>")
default:
buf.WriteString(instr.String())
}
buf.WriteString("\n")
}
}
fmt.Fprintf(buf, "\n")
}
// newBasicBlock adds to f a new basic block and returns it. It does
// not automatically become the current block for subsequent calls to emit.
// comment is an optional string for more readable debugging output.
//
func (f *Function) newBasicBlock(comment string) *BasicBlock {
b := &BasicBlock{
Index: len(f.Blocks),
Comment: comment,
parent: f,
}
b.Succs = b.succs2[:0]
f.Blocks = append(f.Blocks, b)
return b
}
// NewFunction returns a new synthetic Function instance belonging to
// prog, with its name and signature fields set as specified.
//
// The caller is responsible for initializing the remaining fields of
// the function object, e.g. Pkg, Params, Blocks.
//
// It is practically impossible for clients to construct well-formed
// SSA functions/packages/programs directly, so we assume this is the
// job of the Builder alone. NewFunction exists to provide clients a
// little flexibility. For example, analysis tools may wish to
// construct fake Functions for the root of the callgraph, a fake
// "reflect" package, etc.
//
// TODO(adonovan): think harder about the API here.
//
func (prog *Program) NewFunction(name string, sig *types.Signature, provenance string) *Function {
return &Function{Prog: prog, name: name, Signature: sig, Synthetic: provenance}
}
type extentNode [2]token.Pos
func (n extentNode) Pos() token.Pos { return n[0] }
func (n extentNode) End() token.Pos { return n[1] }
// Syntax returns an ast.Node whose Pos/End methods provide the
// lexical extent of the function if it was defined by Go source code
// (f.Synthetic==""), or nil otherwise.
//
// If f was built with debug information (see Package.SetDebugRef),
// the result is the *ast.FuncDecl or *ast.FuncLit that declared the
// function. Otherwise, it is an opaque Node providing only position
// information; this avoids pinning the AST in memory.
//
func (f *Function) Syntax() ast.Node { return f.syntax }