go_agent/src/code.google.com/p/go.tools/ssa/sanity.go
// 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
// An optional pass for sanity-checking invariants of the SSA representation.
// Currently it checks CFG invariants but little at the instruction level.
import (
"fmt"
"io"
"os"
"strings"
"code.google.com/p/go.tools/go/types"
)
type sanity struct {
reporter io.Writer
fn *Function
block *BasicBlock
insane bool
}
// sanityCheck performs integrity checking of the SSA representation
// of the function fn and returns true if it was valid. Diagnostics
// are written to reporter if non-nil, os.Stderr otherwise. Some
// diagnostics are only warnings and do not imply a negative result.
//
// Sanity-checking is intended to facilitate the debugging of code
// transformation passes.
//
func sanityCheck(fn *Function, reporter io.Writer) bool {
if reporter == nil {
reporter = os.Stderr
}
return (&sanity{reporter: reporter}).checkFunction(fn)
}
// mustSanityCheck is like sanityCheck but panics instead of returning
// a negative result.
//
func mustSanityCheck(fn *Function, reporter io.Writer) {
if !sanityCheck(fn, reporter) {
fn.DumpTo(os.Stderr)
panic("SanityCheck failed")
}
}
func (s *sanity) diagnostic(prefix, format string, args ...interface{}) {
fmt.Fprintf(s.reporter, "%s: function %s", prefix, s.fn)
if s.block != nil {
fmt.Fprintf(s.reporter, ", block %s", s.block)
}
io.WriteString(s.reporter, ": ")
fmt.Fprintf(s.reporter, format, args...)
io.WriteString(s.reporter, "\n")
}
func (s *sanity) errorf(format string, args ...interface{}) {
s.insane = true
s.diagnostic("Error", format, args...)
}
func (s *sanity) warnf(format string, args ...interface{}) {
s.diagnostic("Warning", format, args...)
}
// findDuplicate returns an arbitrary basic block that appeared more
// than once in blocks, or nil if all were unique.
func findDuplicate(blocks []*BasicBlock) *BasicBlock {
if len(blocks) < 2 {
return nil
}
if blocks[0] == blocks[1] {
return blocks[0]
}
// Slow path:
m := make(map[*BasicBlock]bool)
for _, b := range blocks {
if m[b] {
return b
}
m[b] = true
}
return nil
}
func (s *sanity) checkInstr(idx int, instr Instruction) {
switch instr := instr.(type) {
case *If, *Jump, *Return, *Panic:
s.errorf("control flow instruction not at end of block")
case *Phi:
if idx == 0 {
// It suffices to apply this check to just the first phi node.
if dup := findDuplicate(s.block.Preds); dup != nil {
s.errorf("phi node in block with duplicate predecessor %s", dup)
}
} else {
prev := s.block.Instrs[idx-1]
if _, ok := prev.(*Phi); !ok {
s.errorf("Phi instruction follows a non-Phi: %T", prev)
}
}
if ne, np := len(instr.Edges), len(s.block.Preds); ne != np {
s.errorf("phi node has %d edges but %d predecessors", ne, np)
} else {
for i, e := range instr.Edges {
if e == nil {
s.errorf("phi node '%s' has no value for edge #%d from %s", instr.Comment, i, s.block.Preds[i])
}
}
}
case *Alloc:
if !instr.Heap {
found := false
for _, l := range s.fn.Locals {
if l == instr {
found = true
break
}
}
if !found {
s.errorf("local alloc %s = %s does not appear in Function.Locals", instr.Name(), instr)
}
}
case *BinOp:
case *Call:
case *ChangeInterface:
case *ChangeType:
case *Convert:
if _, ok := instr.X.Type().Underlying().(*types.Basic); !ok {
if _, ok := instr.Type().Underlying().(*types.Basic); !ok {
s.errorf("convert %s -> %s: at least one type must be basic", instr.X.Type(), instr.Type())
}
}
case *Defer:
case *Extract:
case *Field:
case *FieldAddr:
case *Go:
case *Index:
case *IndexAddr:
case *Lookup:
case *MakeChan:
case *MakeClosure:
numFree := len(instr.Fn.(*Function).FreeVars)
numBind := len(instr.Bindings)
if numFree != numBind {
s.errorf("MakeClosure has %d Bindings for function %s with %d free vars",
numBind, instr.Fn, numFree)
}
if recv := instr.Type().(*types.Signature).Recv(); recv != nil {
s.errorf("MakeClosure's type includes receiver %s", recv.Type())
}
case *MakeInterface:
case *MakeMap:
case *MakeSlice:
case *MapUpdate:
case *Next:
case *Range:
case *RunDefers:
case *Select:
case *Send:
case *Slice:
case *Store:
case *TypeAssert:
case *UnOp:
case *DebugRef:
// TODO(adonovan): implement checks.
default:
panic(fmt.Sprintf("Unknown instruction type: %T", instr))
}
// Check that value-defining instructions have valid types.
if v, ok := instr.(Value); ok {
t := v.Type()
if t == nil {
s.errorf("no type: %s = %s", v.Name(), v)
} else if t == tRangeIter {
// not a proper type; ignore.
} else if b, ok := t.Underlying().(*types.Basic); ok && b.Info()&types.IsUntyped != 0 {
s.errorf("instruction has 'untyped' result: %s = %s : %s", v.Name(), v, t)
}
}
// TODO(adonovan): sanity-check Consts used as instruction Operands(),
// e.g. reject Consts with "untyped" types.
//
// All other non-Instruction Values can be found via their
// enclosing Function or Package.
}
func (s *sanity) checkFinalInstr(idx int, instr Instruction) {
switch instr.(type) {
case *If:
if nsuccs := len(s.block.Succs); nsuccs != 2 {
s.errorf("If-terminated block has %d successors; expected 2", nsuccs)
return
}
if s.block.Succs[0] == s.block.Succs[1] {
s.errorf("If-instruction has same True, False target blocks: %s", s.block.Succs[0])
return
}
case *Jump:
if nsuccs := len(s.block.Succs); nsuccs != 1 {
s.errorf("Jump-terminated block has %d successors; expected 1", nsuccs)
return
}
case *Return:
if nsuccs := len(s.block.Succs); nsuccs != 0 {
s.errorf("Return-terminated block has %d successors; expected none", nsuccs)
return
}
// TODO(adonovan): check number and types of results
case *Panic:
if nsuccs := len(s.block.Succs); nsuccs != 0 {
s.errorf("Panic-terminated block has %d successors; expected none", nsuccs)
return
}
default:
s.errorf("non-control flow instruction at end of block")
}
}
func (s *sanity) checkBlock(b *BasicBlock, index int) {
s.block = b
if b.Index != index {
s.errorf("block has incorrect Index %d", b.Index)
}
if b.parent != s.fn {
s.errorf("block has incorrect parent %s", b.parent)
}
// Check all blocks are reachable.
// (The entry block is always implicitly reachable,
// as is the Recover block, if any.)
if (index > 0 && b != b.parent.Recover) && len(b.Preds) == 0 {
s.warnf("unreachable block")
if b.Instrs == nil {
// Since this block is about to be pruned,
// tolerating transient problems in it
// simplifies other optimizations.
return
}
}
// Check predecessor and successor relations are dual,
// and that all blocks in CFG belong to same function.
for _, a := range b.Preds {
found := false
for _, bb := range a.Succs {
if bb == b {
found = true
break
}
}
if !found {
s.errorf("expected successor edge in predecessor %s; found only: %s", a, a.Succs)
}
if a.parent != s.fn {
s.errorf("predecessor %s belongs to different function %s", a, a.parent)
}
}
for _, c := range b.Succs {
found := false
for _, bb := range c.Preds {
if bb == b {
found = true
break
}
}
if !found {
s.errorf("expected predecessor edge in successor %s; found only: %s", c, c.Preds)
}
if c.parent != s.fn {
s.errorf("successor %s belongs to different function %s", c, c.parent)
}
}
// Check each instruction is sane.
n := len(b.Instrs)
if n == 0 {
s.errorf("basic block contains no instructions")
}
var rands [10]*Value // reuse storage
for j, instr := range b.Instrs {
if instr == nil {
s.errorf("nil instruction at index %d", j)
continue
}
if b2 := instr.Block(); b2 == nil {
s.errorf("nil Block() for instruction at index %d", j)
continue
} else if b2 != b {
s.errorf("wrong Block() (%s) for instruction at index %d ", b2, j)
continue
}
if j < n-1 {
s.checkInstr(j, instr)
} else {
s.checkFinalInstr(j, instr)
}
// Check Instruction.Operands.
operands:
for i, op := range instr.Operands(rands[:0]) {
if op == nil {
s.errorf("nil operand pointer %d of %s", i, instr)
continue
}
val := *op
if val == nil {
continue // a nil operand is ok
}
// Check that Operands that are also Instructions belong to same function.
// TODO(adonovan): also check their block dominates block b.
if val, ok := val.(Instruction); ok {
if val.Parent() != s.fn {
s.errorf("operand %d of %s is an instruction (%s) from function %s", i, instr, val, val.Parent())
}
}
// Check that each function-local operand of
// instr refers back to instr. (NB: quadratic)
switch val := val.(type) {
case *Const, *Global, *Builtin:
continue // not local
case *Function:
if val.Enclosing == nil {
continue // only anon functions are local
}
}
if refs := val.Referrers(); refs != nil {
for _, ref := range *refs {
if ref == instr {
continue operands
}
}
s.errorf("operand %d of %s (%s) does not refer to us", i, instr, val)
} else {
s.errorf("operand %d of %s (%s) has no referrers", i, instr, val)
}
}
}
}
func (s *sanity) checkFunction(fn *Function) bool {
// TODO(adonovan): check Function invariants:
// - check params match signature
// - check transient fields are nil
// - warn if any fn.Locals do not appear among block instructions.
s.fn = fn
if fn.Prog == nil {
s.errorf("nil Prog")
}
fn.String() // must not crash
fn.RelString(fn.pkgobj()) // must not crash
// All functions have a package, except wrappers (which are
// shared across packages, or duplicated as weak symbols in a
// separate-compilation model), and error.Error.
if fn.Pkg == nil {
if strings.Contains(fn.Synthetic, "wrapper") ||
strings.HasSuffix(fn.name, "Error") {
// ok
} else {
s.errorf("nil Pkg")
}
}
if src, syn := fn.Synthetic == "", fn.Syntax() != nil; src != syn {
s.errorf("got fromSource=%t, hasSyntax=%t; want same values", src, syn)
}
for i, l := range fn.Locals {
if l.Parent() != fn {
s.errorf("Local %s at index %d has wrong parent", l.Name(), i)
}
if l.Heap {
s.errorf("Local %s at index %d has Heap flag set", l.Name(), i)
}
}
for i, p := range fn.Params {
if p.Parent() != fn {
s.errorf("Param %s at index %d has wrong parent", p.Name(), i)
}
}
for i, fv := range fn.FreeVars {
if fv.Parent() != fn {
s.errorf("FreeVar %s at index %d has wrong parent", fv.Name(), i)
}
}
if fn.Blocks != nil && len(fn.Blocks) == 0 {
// Function _had_ blocks (so it's not external) but
// they were "optimized" away, even the entry block.
s.errorf("Blocks slice is non-nil but empty")
}
for i, b := range fn.Blocks {
if b == nil {
s.warnf("nil *BasicBlock at f.Blocks[%d]", i)
continue
}
s.checkBlock(b, i)
}
if fn.Recover != nil && fn.Blocks[fn.Recover.Index] != fn.Recover {
s.errorf("Recover block is not in Blocks slice")
}
s.block = nil
for i, anon := range fn.AnonFuncs {
if anon.Enclosing != fn {
s.errorf("AnonFuncs[%d]=%s but %s.Enclosing=%s", i, anon, anon, anon.Enclosing)
}
}
s.fn = nil
return !s.insane
}
// sanityCheckPackage checks invariants of packages upon creation.
// It does not require that the package is built.
// Unlike sanityCheck (for functions), it just panics at the first error.
func sanityCheckPackage(pkg *Package) {
if pkg.Object == nil {
panic(fmt.Sprintf("Package %s has no Object", pkg))
}
pkg.String() // must not crash
for name, mem := range pkg.Members {
if name != mem.Name() {
panic(fmt.Sprintf("%s: %T.Name() = %s, want %s",
pkg.Object.Path(), mem, mem.Name(), name))
}
obj := mem.Object()
if obj == nil {
// This check is sound because fields
// {Global,Function}.object have type
// types.Object. (If they were declared as
// *types.{Var,Func}, we'd have a non-empty
// interface containing a nil pointer.)
continue // not all members have typechecker objects
}
if obj.Name() != name {
panic(fmt.Sprintf("%s: %T.Object().Name() = %s, want %s",
pkg.Object.Path(), mem, obj.Name(), name))
}
if obj.Pos() != mem.Pos() {
panic(fmt.Sprintf("%s Pos=%d obj.Pos=%d", mem, mem.Pos(), obj.Pos()))
}
}
}