508 lines
11 KiB
Go
508 lines
11 KiB
Go
|
// Copyright 2016 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 cfg
|
||
|
|
|
||
|
|
// This file implements the CFG construction pass.
|
||
|
|
|
||
|
|
import (
|
||
|
|
"fmt"
|
||
|
|
"go/ast"
|
||
|
|
"go/token"
|
||
|
|
)
|
||
|
|
|
||
|
|
type builder struct {
|
||
|
|
cfg *CFG
|
||
|
|
mayReturn func(*ast.CallExpr) bool
|
||
|
|
current *Block
|
||
|
|
lblocks map[*ast.Object]*lblock // labeled blocks
|
||
|
|
targets *targets // linked stack of branch targets
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) stmt(_s ast.Stmt) {
|
||
|
|
// The label of the current statement. If non-nil, its _goto
|
||
|
|
// target is always set; its _break and _continue are set only
|
||
|
|
// within the body of switch/typeswitch/select/for/range.
|
||
|
|
// It is effectively an additional default-nil parameter of stmt().
|
||
|
|
var label *lblock
|
||
|
|
start:
|
||
|
|
switch s := _s.(type) {
|
||
|
|
case *ast.BadStmt,
|
||
|
|
*ast.SendStmt,
|
||
|
|
*ast.IncDecStmt,
|
||
|
|
*ast.GoStmt,
|
||
|
|
*ast.DeferStmt,
|
||
|
|
*ast.EmptyStmt,
|
||
|
|
*ast.AssignStmt:
|
||
|
|
// No effect on control flow.
|
||
|
|
b.add(s)
|
||
|
|
|
||
|
|
case *ast.ExprStmt:
|
||
|
|
b.add(s)
|
||
|
|
if call, ok := s.X.(*ast.CallExpr); ok && !b.mayReturn(call) {
|
||
|
|
// Calls to panic, os.Exit, etc, never return.
|
||
|
|
b.current = b.newBlock("unreachable.call")
|
||
|
|
}
|
||
|
|
|
||
|
|
case *ast.DeclStmt:
|
||
|
|
// Treat each var ValueSpec as a separate statement.
|
||
|
|
d := s.Decl.(*ast.GenDecl)
|
||
|
|
if d.Tok == token.VAR {
|
||
|
|
for _, spec := range d.Specs {
|
||
|
|
if spec, ok := spec.(*ast.ValueSpec); ok {
|
||
|
|
b.add(spec)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
case *ast.LabeledStmt:
|
||
|
|
label = b.labeledBlock(s.Label)
|
||
|
|
b.jump(label._goto)
|
||
|
|
b.current = label._goto
|
||
|
|
_s = s.Stmt
|
||
|
|
goto start // effectively: tailcall stmt(g, s.Stmt, label)
|
||
|
|
|
||
|
|
case *ast.ReturnStmt:
|
||
|
|
b.add(s)
|
||
|
|
b.current = b.newBlock("unreachable.return")
|
||
|
|
|
||
|
|
case *ast.BranchStmt:
|
||
|
|
b.branchStmt(s)
|
||
|
|
|
||
|
|
case *ast.BlockStmt:
|
||
|
|
b.stmtList(s.List)
|
||
|
|
|
||
|
|
case *ast.IfStmt:
|
||
|
|
if s.Init != nil {
|
||
|
|
b.stmt(s.Init)
|
||
|
|
}
|
||
|
|
then := b.newBlock("if.then")
|
||
|
|
done := b.newBlock("if.done")
|
||
|
|
_else := done
|
||
|
|
if s.Else != nil {
|
||
|
|
_else = b.newBlock("if.else")
|
||
|
|
}
|
||
|
|
b.add(s.Cond)
|
||
|
|
b.ifelse(then, _else)
|
||
|
|
b.current = then
|
||
|
|
b.stmt(s.Body)
|
||
|
|
b.jump(done)
|
||
|
|
|
||
|
|
if s.Else != nil {
|
||
|
|
b.current = _else
|
||
|
|
b.stmt(s.Else)
|
||
|
|
b.jump(done)
|
||
|
|
}
|
||
|
|
|
||
|
|
b.current = done
|
||
|
|
|
||
|
|
case *ast.SwitchStmt:
|
||
|
|
b.switchStmt(s, label)
|
||
|
|
|
||
|
|
case *ast.TypeSwitchStmt:
|
||
|
|
b.typeSwitchStmt(s, label)
|
||
|
|
|
||
|
|
case *ast.SelectStmt:
|
||
|
|
b.selectStmt(s, label)
|
||
|
|
|
||
|
|
case *ast.ForStmt:
|
||
|
|
b.forStmt(s, label)
|
||
|
|
|
||
|
|
case *ast.RangeStmt:
|
||
|
|
b.rangeStmt(s, label)
|
||
|
|
|
||
|
|
default:
|
||
|
|
panic(fmt.Sprintf("unexpected statement kind: %T", s))
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) stmtList(list []ast.Stmt) {
|
||
|
|
for _, s := range list {
|
||
|
|
b.stmt(s)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) branchStmt(s *ast.BranchStmt) {
|
||
|
|
var block *Block
|
||
|
|
switch s.Tok {
|
||
|
|
case token.BREAK:
|
||
|
|
if s.Label != nil {
|
||
|
|
if lb := b.labeledBlock(s.Label); lb != nil {
|
||
|
|
block = lb._break
|
||
|
|
}
|
||
|
|
} else {
|
||
|
|
for t := b.targets; t != nil && block == nil; t = t.tail {
|
||
|
|
block = t._break
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
case token.CONTINUE:
|
||
|
|
if s.Label != nil {
|
||
|
|
if lb := b.labeledBlock(s.Label); lb != nil {
|
||
|
|
block = lb._continue
|
||
|
|
}
|
||
|
|
} else {
|
||
|
|
for t := b.targets; t != nil && block == nil; t = t.tail {
|
||
|
|
block = t._continue
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
case token.FALLTHROUGH:
|
||
|
|
for t := b.targets; t != nil && block == nil; t = t.tail {
|
||
|
|
block = t._fallthrough
|
||
|
|
}
|
||
|
|
|
||
|
|
case token.GOTO:
|
||
|
|
if s.Label != nil {
|
||
|
|
block = b.labeledBlock(s.Label)._goto
|
||
|
|
}
|
||
|
|
}
|
||
|
|
if block == nil {
|
||
|
|
block = b.newBlock("undefined.branch")
|
||
|
|
}
|
||
|
|
b.jump(block)
|
||
|
|
b.current = b.newBlock("unreachable.branch")
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) switchStmt(s *ast.SwitchStmt, label *lblock) {
|
||
|
|
if s.Init != nil {
|
||
|
|
b.stmt(s.Init)
|
||
|
|
}
|
||
|
|
if s.Tag != nil {
|
||
|
|
b.add(s.Tag)
|
||
|
|
}
|
||
|
|
done := b.newBlock("switch.done")
|
||
|
|
if label != nil {
|
||
|
|
label._break = done
|
||
|
|
}
|
||
|
|
// We pull the default case (if present) down to the end.
|
||
|
|
// But each fallthrough label must point to the next
|
||
|
|
// body block in source order, so we preallocate a
|
||
|
|
// body block (fallthru) for the next case.
|
||
|
|
// Unfortunately this makes for a confusing block order.
|
||
|
|
var defaultBody *[]ast.Stmt
|
||
|
|
var defaultFallthrough *Block
|
||
|
|
var fallthru, defaultBlock *Block
|
||
|
|
ncases := len(s.Body.List)
|
||
|
|
for i, clause := range s.Body.List {
|
||
|
|
body := fallthru
|
||
|
|
if body == nil {
|
||
|
|
body = b.newBlock("switch.body") // first case only
|
||
|
|
}
|
||
|
|
|
||
|
|
// Preallocate body block for the next case.
|
||
|
|
fallthru = done
|
||
|
|
if i+1 < ncases {
|
||
|
|
fallthru = b.newBlock("switch.body")
|
||
|
|
}
|
||
|
|
|
||
|
|
cc := clause.(*ast.CaseClause)
|
||
|
|
if cc.List == nil {
|
||
|
|
// Default case.
|
||
|
|
defaultBody = &cc.Body
|
||
|
|
defaultFallthrough = fallthru
|
||
|
|
defaultBlock = body
|
||
|
|
continue
|
||
|
|
}
|
||
|
|
|
||
|
|
var nextCond *Block
|
||
|
|
for _, cond := range cc.List {
|
||
|
|
nextCond = b.newBlock("switch.next")
|
||
|
|
b.add(cond) // one half of the tag==cond condition
|
||
|
|
b.ifelse(body, nextCond)
|
||
|
|
b.current = nextCond
|
||
|
|
}
|
||
|
|
b.current = body
|
||
|
|
b.targets = &targets{
|
||
|
|
tail: b.targets,
|
||
|
|
_break: done,
|
||
|
|
_fallthrough: fallthru,
|
||
|
|
}
|
||
|
|
b.stmtList(cc.Body)
|
||
|
|
b.targets = b.targets.tail
|
||
|
|
b.jump(done)
|
||
|
|
b.current = nextCond
|
||
|
|
}
|
||
|
|
if defaultBlock != nil {
|
||
|
|
b.jump(defaultBlock)
|
||
|
|
b.current = defaultBlock
|
||
|
|
b.targets = &targets{
|
||
|
|
tail: b.targets,
|
||
|
|
_break: done,
|
||
|
|
_fallthrough: defaultFallthrough,
|
||
|
|
}
|
||
|
|
b.stmtList(*defaultBody)
|
||
|
|
b.targets = b.targets.tail
|
||
|
|
}
|
||
|
|
b.jump(done)
|
||
|
|
b.current = done
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) typeSwitchStmt(s *ast.TypeSwitchStmt, label *lblock) {
|
||
|
|
if s.Init != nil {
|
||
|
|
b.stmt(s.Init)
|
||
|
|
}
|
||
|
|
if s.Assign != nil {
|
||
|
|
b.add(s.Assign)
|
||
|
|
}
|
||
|
|
|
||
|
|
done := b.newBlock("typeswitch.done")
|
||
|
|
if label != nil {
|
||
|
|
label._break = done
|
||
|
|
}
|
||
|
|
var default_ *ast.CaseClause
|
||
|
|
for _, clause := range s.Body.List {
|
||
|
|
cc := clause.(*ast.CaseClause)
|
||
|
|
if cc.List == nil {
|
||
|
|
default_ = cc
|
||
|
|
continue
|
||
|
|
}
|
||
|
|
body := b.newBlock("typeswitch.body")
|
||
|
|
var next *Block
|
||
|
|
for _, casetype := range cc.List {
|
||
|
|
next = b.newBlock("typeswitch.next")
|
||
|
|
// casetype is a type, so don't call b.add(casetype).
|
||
|
|
// This block logically contains a type assertion,
|
||
|
|
// x.(casetype), but it's unclear how to represent x.
|
||
|
|
_ = casetype
|
||
|
|
b.ifelse(body, next)
|
||
|
|
b.current = next
|
||
|
|
}
|
||
|
|
b.current = body
|
||
|
|
b.typeCaseBody(cc, done)
|
||
|
|
b.current = next
|
||
|
|
}
|
||
|
|
if default_ != nil {
|
||
|
|
b.typeCaseBody(default_, done)
|
||
|
|
} else {
|
||
|
|
b.jump(done)
|
||
|
|
}
|
||
|
|
b.current = done
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) typeCaseBody(cc *ast.CaseClause, done *Block) {
|
||
|
|
b.targets = &targets{
|
||
|
|
tail: b.targets,
|
||
|
|
_break: done,
|
||
|
|
}
|
||
|
|
b.stmtList(cc.Body)
|
||
|
|
b.targets = b.targets.tail
|
||
|
|
b.jump(done)
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) selectStmt(s *ast.SelectStmt, label *lblock) {
|
||
|
|
// First evaluate channel expressions.
|
||
|
|
// TODO(adonovan): fix: evaluate only channel exprs here.
|
||
|
|
for _, clause := range s.Body.List {
|
||
|
|
if comm := clause.(*ast.CommClause).Comm; comm != nil {
|
||
|
|
b.stmt(comm)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
done := b.newBlock("select.done")
|
||
|
|
if label != nil {
|
||
|
|
label._break = done
|
||
|
|
}
|
||
|
|
|
||
|
|
var defaultBody *[]ast.Stmt
|
||
|
|
for _, cc := range s.Body.List {
|
||
|
|
clause := cc.(*ast.CommClause)
|
||
|
|
if clause.Comm == nil {
|
||
|
|
defaultBody = &clause.Body
|
||
|
|
continue
|
||
|
|
}
|
||
|
|
body := b.newBlock("select.body")
|
||
|
|
next := b.newBlock("select.next")
|
||
|
|
b.ifelse(body, next)
|
||
|
|
b.current = body
|
||
|
|
b.targets = &targets{
|
||
|
|
tail: b.targets,
|
||
|
|
_break: done,
|
||
|
|
}
|
||
|
|
switch comm := clause.Comm.(type) {
|
||
|
|
case *ast.ExprStmt: // <-ch
|
||
|
|
// nop
|
||
|
|
case *ast.AssignStmt: // x := <-states[state].Chan
|
||
|
|
b.add(comm.Lhs[0])
|
||
|
|
}
|
||
|
|
b.stmtList(clause.Body)
|
||
|
|
b.targets = b.targets.tail
|
||
|
|
b.jump(done)
|
||
|
|
b.current = next
|
||
|
|
}
|
||
|
|
if defaultBody != nil {
|
||
|
|
b.targets = &targets{
|
||
|
|
tail: b.targets,
|
||
|
|
_break: done,
|
||
|
|
}
|
||
|
|
b.stmtList(*defaultBody)
|
||
|
|
b.targets = b.targets.tail
|
||
|
|
b.jump(done)
|
||
|
|
}
|
||
|
|
b.current = done
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) forStmt(s *ast.ForStmt, label *lblock) {
|
||
|
|
// ...init...
|
||
|
|
// jump loop
|
||
|
|
// loop:
|
||
|
|
// if cond goto body else done
|
||
|
|
// body:
|
||
|
|
// ...body...
|
||
|
|
// jump post
|
||
|
|
// post: (target of continue)
|
||
|
|
// ...post...
|
||
|
|
// jump loop
|
||
|
|
// done: (target of break)
|
||
|
|
if s.Init != nil {
|
||
|
|
b.stmt(s.Init)
|
||
|
|
}
|
||
|
|
body := b.newBlock("for.body")
|
||
|
|
done := b.newBlock("for.done") // target of 'break'
|
||
|
|
loop := body // target of back-edge
|
||
|
|
if s.Cond != nil {
|
||
|
|
loop = b.newBlock("for.loop")
|
||
|
|
}
|
||
|
|
cont := loop // target of 'continue'
|
||
|
|
if s.Post != nil {
|
||
|
|
cont = b.newBlock("for.post")
|
||
|
|
}
|
||
|
|
if label != nil {
|
||
|
|
label._break = done
|
||
|
|
label._continue = cont
|
||
|
|
}
|
||
|
|
b.jump(loop)
|
||
|
|
b.current = loop
|
||
|
|
if loop != body {
|
||
|
|
b.add(s.Cond)
|
||
|
|
b.ifelse(body, done)
|
||
|
|
b.current = body
|
||
|
|
}
|
||
|
|
b.targets = &targets{
|
||
|
|
tail: b.targets,
|
||
|
|
_break: done,
|
||
|
|
_continue: cont,
|
||
|
|
}
|
||
|
|
b.stmt(s.Body)
|
||
|
|
b.targets = b.targets.tail
|
||
|
|
b.jump(cont)
|
||
|
|
|
||
|
|
if s.Post != nil {
|
||
|
|
b.current = cont
|
||
|
|
b.stmt(s.Post)
|
||
|
|
b.jump(loop) // back-edge
|
||
|
|
}
|
||
|
|
b.current = done
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) rangeStmt(s *ast.RangeStmt, label *lblock) {
|
||
|
|
b.add(s.X)
|
||
|
|
|
||
|
|
if s.Key != nil {
|
||
|
|
b.add(s.Key)
|
||
|
|
}
|
||
|
|
if s.Value != nil {
|
||
|
|
b.add(s.Value)
|
||
|
|
}
|
||
|
|
|
||
|
|
// ...
|
||
|
|
// loop: (target of continue)
|
||
|
|
// if ... goto body else done
|
||
|
|
// body:
|
||
|
|
// ...
|
||
|
|
// jump loop
|
||
|
|
// done: (target of break)
|
||
|
|
|
||
|
|
loop := b.newBlock("range.loop")
|
||
|
|
b.jump(loop)
|
||
|
|
b.current = loop
|
||
|
|
|
||
|
|
body := b.newBlock("range.body")
|
||
|
|
done := b.newBlock("range.done")
|
||
|
|
b.ifelse(body, done)
|
||
|
|
b.current = body
|
||
|
|
|
||
|
|
if label != nil {
|
||
|
|
label._break = done
|
||
|
|
label._continue = loop
|
||
|
|
}
|
||
|
|
b.targets = &targets{
|
||
|
|
tail: b.targets,
|
||
|
|
_break: done,
|
||
|
|
_continue: loop,
|
||
|
|
}
|
||
|
|
b.stmt(s.Body)
|
||
|
|
b.targets = b.targets.tail
|
||
|
|
b.jump(loop) // back-edge
|
||
|
|
b.current = done
|
||
|
|
}
|
||
|
|
|
||
|
|
// -------- helpers --------
|
||
|
|
|
||
|
|
// Destinations associated with unlabeled 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 *Block
|
||
|
|
_continue *Block
|
||
|
|
_fallthrough *Block
|
||
|
|
}
|
||
|
|
|
||
|
|
// Destinations associated with a labeled block.
|
||
|
|
// We populate these as labels are encountered in forward gotos or
|
||
|
|
// labeled statements.
|
||
|
|
type lblock struct {
|
||
|
|
_goto *Block
|
||
|
|
_break *Block
|
||
|
|
_continue *Block
|
||
|
|
}
|
||
|
|
|
||
|
|
// labeledBlock returns the branch target associated with the
|
||
|
|
// specified label, creating it if needed.
|
||
|
|
func (b *builder) labeledBlock(label *ast.Ident) *lblock {
|
||
|
|
lb := b.lblocks[label.Obj]
|
||
|
|
if lb == nil {
|
||
|
|
lb = &lblock{_goto: b.newBlock(label.Name)}
|
||
|
|
if b.lblocks == nil {
|
||
|
|
b.lblocks = make(map[*ast.Object]*lblock)
|
||
|
|
}
|
||
|
|
b.lblocks[label.Obj] = lb
|
||
|
|
}
|
||
|
|
return lb
|
||
|
|
}
|
||
|
|
|
||
|
|
// newBlock appends a new unconnected basic block to b.cfg's block
|
||
|
|
// slice and returns it.
|
||
|
|
// It does not automatically become the current block.
|
||
|
|
// comment is an optional string for more readable debugging output.
|
||
|
|
func (b *builder) newBlock(comment string) *Block {
|
||
|
|
g := b.cfg
|
||
|
|
block := &Block{
|
||
|
|
Index: int32(len(g.Blocks)),
|
||
|
|
comment: comment,
|
||
|
|
}
|
||
|
|
block.Succs = block.succs2[:0]
|
||
|
|
g.Blocks = append(g.Blocks, block)
|
||
|
|
return block
|
||
|
|
}
|
||
|
|
|
||
|
|
func (b *builder) add(n ast.Node) {
|
||
|
|
b.current.Nodes = append(b.current.Nodes, n)
|
||
|
|
}
|
||
|
|
|
||
|
|
// jump adds an edge from the current block to the target block,
|
||
|
|
// and sets b.current to nil.
|
||
|
|
func (b *builder) jump(target *Block) {
|
||
|
|
b.current.Succs = append(b.current.Succs, target)
|
||
|
|
b.current = nil
|
||
|
|
}
|
||
|
|
|
||
|
|
// ifelse emits edges from the current block to the t and f blocks,
|
||
|
|
// and sets b.current to nil.
|
||
|
|
func (b *builder) ifelse(t, f *Block) {
|
||
|
|
b.current.Succs = append(b.current.Succs, t, f)
|
||
|
|
b.current = nil
|
||
|
|
}
|