exp/ssa: (#2 of 5): core utilities

This CL includes the implementation of Literal, all the
Value.String and Instruction.String methods, the sanity
checker, and other misc utilities.

R=gri, iant, iant
CC=golang-dev
https://golang.org/cl/7199052

src/pkg/exp/ssa/literal.go

+package ssa
+
+// This file defines the Literal SSA value type.
+
+import (
+	"fmt"
+	"go/types"
+	"math/big"
+	"strconv"
+)
+
+// newLiteral returns a new literal of the specified value and type.
+// val must be valid according to the specification of Literal.Value.
+//
+func newLiteral(val interface{}, typ types.Type) *Literal {
+	// This constructor exists to provide a single place to
+	// insert logging/assertions during debugging.
+	return &Literal{typ, val}
+}
+
+// intLiteral returns an untyped integer literal that evaluates to i.
+func intLiteral(i int64) *Literal {
+	return newLiteral(i, types.Typ[types.UntypedInt])
+}
+
+// nilLiteral returns a nil literal of the specified (reference) type.
+func nilLiteral(typ types.Type) *Literal {
+	return newLiteral(types.NilType{}, typ)
+}
+
+func (l *Literal) Name() string {
+	var s string
+	switch x := l.Value.(type) {
+	case bool:
+		s = fmt.Sprintf("%v", l.Value)
+	case int64:
+		s = fmt.Sprintf("%d", l.Value)
+	case *big.Int:
+		s = x.String()
+	case *big.Rat:
+		s = x.FloatString(20)
+	case string:
+		if len(x) > 20 {
+			x = x[:17] + "..." // abbreviate
+		}
+		s = strconv.Quote(x)
+	case types.Complex:
+		r := x.Re.FloatString(20)
+		i := x.Im.FloatString(20)
+		s = fmt.Sprintf("%s+%si", r, i)
+	case types.NilType:
+		s = "nil"
+	default:
+		panic(fmt.Sprintf("unexpected literal value: %T", x))
+	}
+	return s + ":" + l.Type_.String()
+}
+
+func (l *Literal) Type() types.Type {
+	return l.Type_
+}
+
+// IsNil returns true if this literal represents a typed or untyped nil value.
+func (l *Literal) IsNil() bool {
+	_, ok := l.Value.(types.NilType)
+	return ok
+}
+
+// Int64 returns the numeric value of this literal truncated to fit
+// a signed 64-bit integer.
+//
+func (l *Literal) Int64() int64 {
+	switch x := l.Value.(type) {
+	case int64:
+		return x
+	case *big.Int:
+		return x.Int64()
+	case *big.Rat:
+		// TODO(adonovan): fix: is this the right rounding mode?
+		var q big.Int
+		return q.Quo(x.Num(), x.Denom()).Int64()
+	}
+	panic(fmt.Sprintf("unexpected literal value: %T", l.Value))
+}
+
+// Uint64 returns the numeric value of this literal truncated to fit
+// an unsigned 64-bit integer.
+//
+func (l *Literal) Uint64() uint64 {
+	switch x := l.Value.(type) {
+	case int64:
+		if x < 0 {
+			return 0
+		}
+		return uint64(x)
+	case *big.Int:
+		return x.Uint64()
+	case *big.Rat:
+		// TODO(adonovan): fix: is this right?
+		var q big.Int
+		return q.Quo(x.Num(), x.Denom()).Uint64()
+	}
+	panic(fmt.Sprintf("unexpected literal value: %T", l.Value))
+}
+
+// Float64 returns the numeric value of this literal truncated to fit
+// a float64.
+//
+func (l *Literal) Float64() float64 {
+	switch x := l.Value.(type) {
+	case int64:
+		return float64(x)
+	case *big.Int:
+		var r big.Rat
+		f, _ := r.SetInt(x).Float64()
+		return f
+	case *big.Rat:
+		f, _ := x.Float64()
+		return f
+	}
+	panic(fmt.Sprintf("unexpected literal value: %T", l.Value))
+}
+
+// Complex128 returns the complex value of this literal truncated to
+// fit a complex128.
+//
+func (l *Literal) Complex128() complex128 {
+	switch x := l.Value.(type) {
+	case int64, *big.Int, *big.Rat:
+		return complex(l.Float64(), 0)
+	case types.Complex:
+		re64, _ := x.Re.Float64()
+		im64, _ := x.Im.Float64()
+		return complex(re64, im64)
+	}
+	panic(fmt.Sprintf("unexpected literal value: %T", l.Value))
+}

src/pkg/exp/ssa/print.go

+package ssa
+
+// This file implements the String() methods for all Value and
+// Instruction types.
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/types"
+)
+
+func (id Id) String() string {
+	if id.Pkg == nil {
+		return id.Name
+	}
+	return fmt.Sprintf("%s/%s", id.Pkg.Path, id.Name)
+}
+
+// relName returns the name of v relative to i.
+// In most cases, this is identical to v.Name(), but for cross-package
+// references to Functions (including methods) and Globals, the
+// package-qualified FullName is used instead.
+//
+func relName(v Value, i Instruction) string {
+	switch v := v.(type) {
+	case *Global:
+		if v.Pkg == i.Block().Func.Pkg {
+			return v.Name()
+		}
+		return v.FullName()
+	case *Function:
+		if v.Pkg == nil || v.Pkg == i.Block().Func.Pkg {
+			return v.Name()
+		}
+		return v.FullName()
+	}
+	return v.Name()
+}
+
+// Value.String()
+//
+// This method is provided only for debugging.
+// It never appears in disassembly, which uses Value.Name().
+
+func (v *Literal) String() string {
+	return fmt.Sprintf("literal %s rep=%T", v.Name(), v.Value)
+}
+
+func (v *Parameter) String() string {
+	return fmt.Sprintf("parameter %s : %s", v.Name(), v.Type())
+}
+
+func (v *Capture) String() string {
+	return fmt.Sprintf("capture %s : %s", v.Name(), v.Type())
+}
+
+func (v *Global) String() string {
+	return fmt.Sprintf("global %s : %s", v.Name(), v.Type())
+}
+
+func (v *Builtin) String() string {
+	return fmt.Sprintf("builtin %s : %s", v.Name(), v.Type())
+}
+
+func (r *Function) String() string {
+	return fmt.Sprintf("function %s : %s", r.Name(), r.Type())
+}
+
+// FullName returns the name of this function qualified by the
+// package name, unless it is anonymous or synthetic.
+//
+// TODO(adonovan): move to func.go when it's submitted.
+//
+func (f *Function) FullName() string {
+	if f.Enclosing != nil || f.Pkg == nil {
+		return f.Name_ // anonymous or synthetic
+	}
+	return fmt.Sprintf("%s.%s", f.Pkg.ImportPath, f.Name_)
+}
+
+// FullName returns g's package-qualified name.
+func (g *Global) FullName() string {
+	return fmt.Sprintf("%s.%s", g.Pkg.ImportPath, g.Name_)
+}
+
+// Instruction.String()
+
+func (v *Alloc) String() string {
+	op := "local"
+	if v.Heap {
+		op = "new"
+	}
+	return fmt.Sprintf("%s %s", op, indirectType(v.Type()))
+}
+
+func (v *Phi) String() string {
+	var b bytes.Buffer
+	b.WriteString("phi [")
+	for i, edge := range v.Edges {
+		if i > 0 {
+			b.WriteString(", ")
+		}
+		// Be robust against malformed CFG.
+		blockname := "?"
+		if v.Block_ != nil && i < len(v.Block_.Preds) {
+			blockname = v.Block_.Preds[i].Name
+		}
+		b.WriteString(blockname)
+		b.WriteString(": ")
+		b.WriteString(relName(edge, v))
+	}
+	b.WriteString("]")
+	return b.String()
+}
+
+func printCall(v *CallCommon, prefix string, instr Instruction) string {
+	var b bytes.Buffer
+	b.WriteString(prefix)
+	if v.Func != nil {
+		b.WriteString(relName(v.Func, instr))
+	} else {
+		name := underlyingType(v.Recv.Type()).(*types.Interface).Methods[v.Method].Name
+		fmt.Fprintf(&b, "invoke %s.%s [#%d]", relName(v.Recv, instr), name, v.Method)
+	}
+	b.WriteString("(")
+	for i, arg := range v.Args {
+		if i > 0 {
+			b.WriteString(", ")
+		}
+		b.WriteString(relName(arg, instr))
+	}
+	if v.HasEllipsis {
+		b.WriteString("...")
+	}
+	b.WriteString(")")
+	return b.String()
+}
+
+func (v *Call) String() string {
+	return printCall(&v.CallCommon, "", v)
+}
+
+func (v *BinOp) String() string {
+	return fmt.Sprintf("%s %s %s", relName(v.X, v), v.Op.String(), relName(v.Y, v))
+}
+
+func (v *UnOp) String() string {
+	return fmt.Sprintf("%s%s%s", v.Op, relName(v.X, v), commaOk(v.CommaOk))
+}
+
+func (v *Conv) String() string {
+	return fmt.Sprintf("convert %s <- %s (%s)", v.Type(), v.X.Type(), relName(v.X, v))
+}
+
+func (v *ChangeInterface) String() string {
+	return fmt.Sprintf("change interface %s <- %s (%s)", v.Type(), v.X.Type(), relName(v.X, v))
+}
+
+func (v *MakeInterface) String() string {
+	return fmt.Sprintf("make interface %s <- %s (%s)", v.Type(), v.X.Type(), relName(v.X, v))
+}
+
+func (v *MakeClosure) String() string {
+	var b bytes.Buffer
+	fmt.Fprintf(&b, "make closure %s", relName(v.Fn, v))
+	if v.Bindings != nil {
+		b.WriteString(" [")
+		for i, c := range v.Bindings {
+			if i > 0 {
+				b.WriteString(", ")
+			}
+			b.WriteString(relName(c, v))
+		}
+		b.WriteString("]")
+	}
+	return b.String()
+}
+
+func (v *MakeSlice) String() string {
+	var b bytes.Buffer
+	b.WriteString("make slice ")
+	b.WriteString(v.Type().String())
+	b.WriteString(" ")
+	b.WriteString(relName(v.Len, v))
+	b.WriteString(" ")
+	b.WriteString(relName(v.Cap, v))
+	return b.String()
+}
+
+func (v *Slice) String() string {
+	var b bytes.Buffer
+	b.WriteString("slice ")
+	b.WriteString(relName(v.X, v))
+	b.WriteString("[")
+	if v.Low != nil {
+		b.WriteString(relName(v.Low, v))
+	}
+	b.WriteString(":")
+	if v.High != nil {
+		b.WriteString(relName(v.High, v))
+	}
+	b.WriteString("]")
+	return b.String()
+}
+
+func (v *MakeMap) String() string {
+	res := ""
+	if v.Reserve != nil {
+		res = relName(v.Reserve, v)
+	}
+	return fmt.Sprintf("make %s %s", v.Type(), res)
+}
+
+func (v *MakeChan) String() string {
+	return fmt.Sprintf("make %s %s", v.Type(), relName(v.Size, v))
+}
+
+func (v *FieldAddr) String() string {
+	fields := underlyingType(indirectType(v.X.Type())).(*types.Struct).Fields
+	// Be robust against a bad index.
+	name := "?"
+	if v.Field >= 0 && v.Field < len(fields) {
+		name = fields[v.Field].Name
+	}
+	return fmt.Sprintf("&%s.%s [#%d]", relName(v.X, v), name, v.Field)
+}
+
+func (v *Field) String() string {
+	fields := underlyingType(v.X.Type()).(*types.Struct).Fields
+	// Be robust against a bad index.
+	name := "?"
+	if v.Field >= 0 && v.Field < len(fields) {
+		name = fields[v.Field].Name
+	}
+	return fmt.Sprintf("%s.%s [#%d]", relName(v.X, v), name, v.Field)
+}
+
+func (v *IndexAddr) String() string {
+	return fmt.Sprintf("&%s[%s]", relName(v.X, v), relName(v.Index, v))
+}
+
+func (v *Index) String() string {
+	return fmt.Sprintf("%s[%s]", relName(v.X, v), relName(v.Index, v))
+}
+
+func (v *Lookup) String() string {
+	return fmt.Sprintf("%s[%s]%s", relName(v.X, v), relName(v.Index, v), commaOk(v.CommaOk))
+}
+
+func (v *Range) String() string {
+	return "range " + relName(v.X, v)
+}
+
+func (v *Next) String() string {
+	return "next " + relName(v.Iter, v)
+}
+
+func (v *TypeAssert) String() string {
+	return fmt.Sprintf("typeassert%s %s.(%s)", commaOk(v.CommaOk), relName(v.X, v), v.AssertedType)
+}
+
+func (v *Extract) String() string {
+	return fmt.Sprintf("extract %s #%d", relName(v.Tuple, v), v.Index)
+}
+
+func (s *Jump) String() string {
+	// Be robust against malformed CFG.
+	blockname := "?"
+	if s.Block_ != nil && len(s.Block_.Succs) == 1 {
+		blockname = s.Block_.Succs[0].Name
+	}
+	return fmt.Sprintf("jump %s", blockname)
+}
+
+func (s *If) String() string {
+	// Be robust against malformed CFG.
+	tblockname, fblockname := "?", "?"
+	if s.Block_ != nil && len(s.Block_.Succs) == 2 {
+		tblockname = s.Block_.Succs[0].Name
+		fblockname = s.Block_.Succs[1].Name
+	}
+	return fmt.Sprintf("if %s goto %s else %s", relName(s.Cond, s), tblockname, fblockname)
+}
+
+func (s *Go) String() string {
+	return printCall(&s.CallCommon, "go ", s)
+}
+
+func (s *Ret) String() string {
+	var b bytes.Buffer
+	b.WriteString("ret")
+	for i, r := range s.Results {
+		if i == 0 {
+			b.WriteString(" ")
+		} else {
+			b.WriteString(", ")
+		}
+		b.WriteString(relName(r, s))
+	}
+	return b.String()
+}
+
+func (s *Send) String() string {
+	return fmt.Sprintf("send %s <- %s", relName(s.Chan, s), relName(s.X, s))
+}
+
+func (s *Defer) String() string {
+	return printCall(&s.CallCommon, "defer ", s)
+}
+
+func (s *Select) String() string {
+	var b bytes.Buffer
+	for i, st := range s.States {
+		if i > 0 {
+			b.WriteString(", ")
+		}
+		if st.Dir == ast.RECV {
+			b.WriteString("<-")
+			b.WriteString(relName(st.Chan, s))
+		} else {
+			b.WriteString(relName(st.Chan, s))
+			b.WriteString("<-")
+			b.WriteString(relName(st.Send, s))
+		}
+	}
+	non := ""
+	if !s.Blocking {
+		non = "non"
+	}
+	return fmt.Sprintf("select %sblocking [%s]", non, b.String())
+}
+
+func (s *Store) String() string {
+	return fmt.Sprintf("*%s = %s", relName(s.Addr, s), relName(s.Val, s))
+}
+
+func (s *MapUpdate) String() string {
+	return fmt.Sprintf("%s[%s] = %s", relName(s.Map, s), relName(s.Key, s), relName(s.Value, s))
+}
+
+func (p *Package) String() string {
+	// TODO(adonovan): prettify output.
+	var b bytes.Buffer
+	fmt.Fprintf(&b, "Package %s at %s:\n", p.ImportPath, p.Prog.Files.File(p.Pos).Name())
+
+	// TODO(adonovan): make order deterministic.
+	maxname := 0
+	for name := range p.Members {
+		if l := len(name); l > maxname {
+			maxname = l
+		}
+	}
+
+	for name, mem := range p.Members {
+		switch mem := mem.(type) {
+		case *Literal:
+			fmt.Fprintf(&b, " const %-*s %s\n", maxname, name, mem.Name())
+
+		case *Function:
+			fmt.Fprintf(&b, " func  %-*s %s\n", maxname, name, mem.Type())
+
+		case *Type:
+			fmt.Fprintf(&b, " type  %-*s %s\n", maxname, name, mem.NamedType.Underlying)
+			// TODO(adonovan): make order deterministic.
+			for name, method := range mem.Methods {
+				fmt.Fprintf(&b, "       method %s %s\n", name, method.Signature)
+			}
+
+		case *Global:
+			fmt.Fprintf(&b, " var   %-*s %s\n", maxname, name, mem.Type())
+
+		}
+	}
+	return b.String()
+}
+
+func commaOk(x bool) string {
+	if x {
+		return ",ok"
+	}
+	return ""
+}

src/pkg/exp/ssa/sanity.go

+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 (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+)
+
+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) {
+		panic("SanityCheck failed")
+	}
+}
+
+// blockNames returns the names of the specified blocks as a
+// human-readable string.
+//
+func blockNames(blocks []*BasicBlock) string {
+	var buf bytes.Buffer
+	for i, b := range blocks {
+		if i > 0 {
+			io.WriteString(&buf, ", ")
+		}
+		io.WriteString(&buf, b.Name)
+	}
+	return buf.String()
+}
+
+func (s *sanity) diagnostic(prefix, format string, args ...interface{}) {
+	fmt.Fprintf(s.reporter, "%s: function %s", prefix, s.fn.FullName())
+	if s.block != nil {
+		fmt.Fprintf(s.reporter, ", block %s", s.block.Name)
+	}
+	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, *Ret:
+		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.Name)
+			}
+		} 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)
+		}
+
+	case *Alloc:
+	case *Call:
+	case *BinOp:
+	case *UnOp:
+	case *MakeClosure:
+	case *MakeChan:
+	case *MakeMap:
+	case *MakeSlice:
+	case *Slice:
+	case *Field:
+	case *FieldAddr:
+	case *IndexAddr:
+	case *Index:
+	case *Select:
+	case *Range:
+	case *TypeAssert:
+	case *Extract:
+	case *Go:
+	case *Defer:
+	case *Send:
+	case *Store:
+	case *MapUpdate:
+	case *Next:
+	case *Lookup:
+	case *Conv:
+	case *ChangeInterface:
+	case *MakeInterface:
+		// TODO(adonovan): implement checks.
+	default:
+		panic(fmt.Sprintf("Unknown instruction type: %T", instr))
+	}
+}
+
+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].Name)
+			return
+		}
+
+	case *Jump:
+		if nsuccs := len(s.block.Succs); nsuccs != 1 {
+			s.errorf("Jump-terminated block has %d successors; expected 1", nsuccs)
+			return
+		}
+
+	case *Ret:
+		if nsuccs := len(s.block.Succs); nsuccs != 0 {
+			s.errorf("Ret-terminated block has %d successors; expected none", nsuccs)
+			return
+		}
+		// TODO(adonovan): check number and types of results
+
+	default:
+		s.errorf("non-control flow instruction at end of block")
+	}
+}
+
+func (s *sanity) checkBlock(b *BasicBlock, isEntry bool) {
+	s.block = b
+
+	// Check all blocks are reachable.
+	// (The entry block is always implicitly reachable.)
+	if !isEntry && 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 optimisations.
+			return
+		}
+	}
+
+	// Check predecessor and successor relations are dual.
+	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.Name, blockNames(a.Succs))
+		}
+	}
+	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.Name, blockNames(c.Preds))
+		}
+	}
+
+	// Check each instruction is sane.
+	n := len(b.Instrs)
+	if n == 0 {
+		s.errorf("basic block contains no instructions")
+	}
+	for j, instr := range b.Instrs {
+		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.Name, j)
+			continue
+		}
+		if j < n-1 {
+			s.checkInstr(j, instr)
+		} else {
+			s.checkFinalInstr(j, instr)
+		}
+	}
+}
+
+func (s *sanity) checkFunction(fn *Function) bool {
+	// TODO(adonovan): check Function invariants:
+	// - check owning Package (if any) contains this function.
+	// - check params match signature
+	// - check locals are all !Heap
+	// - check transient fields are nil
+	// - check block labels are unique (warning)
+	s.fn = fn
+	if fn.Prog == nil {
+		s.errorf("nil Prog")
+	}
+	for i, b := range fn.Blocks {
+		if b == nil {
+			s.warnf("nil *BasicBlock at f.Blocks[%d]", i)
+			continue
+		}
+		s.checkBlock(b, i == 0)
+	}
+	s.block = nil
+	s.fn = nil
+	return !s.insane
+}

src/pkg/exp/ssa/ssa.go

@@ -222,12 +222,12 @@ type Function struct {
 
 	// The following fields are set transiently during building,
 	// then cleared.
-	currentBlock *BasicBlock            // where to emit code
-	objects      map[types.Object]Value // addresses of local variables
-	results      []*Alloc               // tuple of named results
-	// syntax    *funcSyntax             // abstract syntax trees for Go source functions
-	// targets   *targets                // linked stack of branch targets
-	// lblocks   map[*ast.Object]*lblock // labelled blocks
+	currentBlock *BasicBlock             // where to emit code
+	objects      map[types.Object]Value  // addresses of local variables
+	results      []*Alloc                // tuple of named results
+	syntax       *funcSyntax             // abstract syntax trees for Go source functions
+	targets      *targets                // linked stack of branch targets
+	lblocks      map[*ast.Object]*lblock // labelled blocks
 }
 
 // An SSA basic block.
@@ -984,18 +984,9 @@ func (v *Capture) Name() string     { return v.Outer.Name() }
 
 func (v *Global) Type() types.Type { return v.Type_ }
 func (v *Global) Name() string     { return v.Name_ }
-func (v *Global) String() string   { return v.Name_ } // placeholder
 
 func (v *Function) Name() string     { return v.Name_ }
 func (v *Function) Type() types.Type { return v.Signature }
-func (v *Function) String() string   { return v.Name_ } // placeholder
-
-// FullName returns v's package-qualified name.
-func (v *Global) FullName() string { return fmt.Sprintf("%s.%s", v.Pkg.ImportPath, v.Name_) }
-
-func (v *Literal) Name() string     { return "Literal" } // placeholder
-func (v *Literal) String() string   { return "Literal" } // placeholder
-func (v *Literal) Type() types.Type { return v.Type_ }   // placeholder
 
 func (v *Parameter) Type() types.Type { return v.Type_ }
 func (v *Parameter) Name() string     { return v.Name_ }

src/pkg/exp/ssa/util.go

+package ssa
+
+// This file defines a number of miscellaneous utility functions.
+
+import (
+	"fmt"
+	"go/ast"
+	"go/types"
+)
+
+func unreachable() {
+	panic("unreachable")
+}
+
+//// AST utilities
+
+// noparens returns e with any enclosing parentheses stripped.
+func noparens(e ast.Expr) ast.Expr {
+	for {
+		p, ok := e.(*ast.ParenExpr)
+		if !ok {
+			break
+		}
+		e = p.X
+	}
+	return e
+}
+
+// isBlankIdent returns true iff e is an Ident with name "_".
+// They have no associated types.Object, and thus no type.
+//
+// TODO(gri): consider making typechecker not treat them differently.
+// It's one less thing for clients like us to worry about.
+//
+func isBlankIdent(e ast.Expr) bool {
+	id, ok := e.(*ast.Ident)
+	return ok && id.Name == "_"
+}
+
+//// Type utilities.  Some of these belong in go/types.
+
+// underlyingType returns the underlying type of typ.
+// TODO(gri): this is a copy of go/types.underlying; export that function.
+//
+func underlyingType(typ types.Type) types.Type {
+	if typ, ok := typ.(*types.NamedType); ok {
+		return typ.Underlying // underlying types are never NamedTypes
+	}
+	if typ == nil {
+		panic("underlyingType(nil)")
+	}
+	return typ
+}
+
+// isPointer returns true for types whose underlying type is a pointer.
+func isPointer(typ types.Type) bool {
+	if nt, ok := typ.(*types.NamedType); ok {
+		typ = nt.Underlying
+	}
+	_, ok := typ.(*types.Pointer)
+	return ok
+}
+
+// pointer(typ) returns the type that is a pointer to typ.
+func pointer(typ types.Type) *types.Pointer {
+	return &types.Pointer{Base: typ}
+}
+
+// indirect(typ) assumes that typ is a pointer type,
+// or named alias thereof, and returns its base type.
+// Panic ensures if it is not a pointer.
+//
+func indirectType(ptr types.Type) types.Type {
+	if v, ok := underlyingType(ptr).(*types.Pointer); ok {
+		return v.Base
+	}
+	// When debugging it is convenient to comment out this line
+	// and let it continue to print the (illegal) SSA form.
+	panic("indirect() of non-pointer type: " + ptr.String())
+	return nil
+}
+
+// deref returns a pointer's base type; otherwise it returns typ.
+func deref(typ types.Type) types.Type {
+	if typ, ok := underlyingType(typ).(*types.Pointer); ok {
+		return typ.Base
+	}
+	return typ
+}
+
+// methodIndex returns the method (and its index) named id within the
+// method table methods of named or interface type typ.  If not found,
+// panic ensues.
+//
+func methodIndex(typ types.Type, methods []*types.Method, id Id) (i int, m *types.Method) {
+	for i, m = range methods {
+		if IdFromQualifiedName(m.QualifiedName) == id {
+			return
+		}
+	}
+	panic(fmt.Sprint("method not found: ", id, " in interface ", typ))
+}
+
+// objKind returns the syntactic category of the named entity denoted by obj.
+func objKind(obj types.Object) ast.ObjKind {
+	switch obj.(type) {
+	case *types.Package:
+		return ast.Pkg
+	case *types.TypeName:
+		return ast.Typ
+	case *types.Const:
+		return ast.Con
+	case *types.Var:
+		return ast.Var
+	case *types.Func:
+		return ast.Fun
+	}
+	panic(fmt.Sprintf("unexpected Object type: %T", obj))
+}
+
+// DefaultType returns the default "typed" type for an "untyped" type;
+// it returns the incoming type for all other types. If there is no
+// corresponding untyped type, the result is types.Typ[types.Invalid].
+//
+// Exported to exp/ssa/interp.
+//
+// TODO(gri): this is a copy of go/types.defaultType; export that function.
+//
+func DefaultType(typ types.Type) types.Type {
+	if t, ok := typ.(*types.Basic); ok {
+		k := types.Invalid
+		switch t.Kind {
+		// case UntypedNil:
+		//      There is no default type for nil. For a good error message,
+		//      catch this case before calling this function.
+		case types.UntypedBool:
+			k = types.Bool
+		case types.UntypedInt:
+			k = types.Int
+		case types.UntypedRune:
+			k = types.Rune
+		case types.UntypedFloat:
+			k = types.Float64
+		case types.UntypedComplex:
+			k = types.Complex128
+		case types.UntypedString:
+			k = types.String
+		}
+		typ = types.Typ[k]
+	}
+	return typ
+}
+
+// makeId returns the Id (name, pkg) if the name is exported or
+// (name, nil) otherwise.
+//
+func makeId(name string, pkg *types.Package) (id Id) {
+	id.Name = name
+	if !ast.IsExported(name) {
+		id.Pkg = pkg
+	}
+	return
+}
+
+// IdFromQualifiedName returns the Id (qn.Name, qn.Pkg) if qn is an
+// exported name or (qn.Name, nil) otherwise.
+//
+// Exported to exp/ssa/interp.
+//
+func IdFromQualifiedName(qn types.QualifiedName) Id {
+	return makeId(qn.Name, qn.Pkg)
+}