Current File : //usr/local/go/src/cmd/compile/internal/walk/convert.go
// Copyright 2009 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 walk
import (
"encoding/binary"
"go/constant"
"cmd/compile/internal/base"
"cmd/compile/internal/ir"
"cmd/compile/internal/reflectdata"
"cmd/compile/internal/ssagen"
"cmd/compile/internal/typecheck"
"cmd/compile/internal/types"
"cmd/internal/sys"
)
// walkConv walks an OCONV or OCONVNOP (but not OCONVIFACE) node.
func walkConv(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
n.X = walkExpr(n.X, init)
if n.Op() == ir.OCONVNOP && n.Type() == n.X.Type() {
return n.X
}
if n.Op() == ir.OCONVNOP && ir.ShouldCheckPtr(ir.CurFunc, 1) {
if n.Type().IsPtr() && n.X.Type().IsUnsafePtr() { // unsafe.Pointer to *T
return walkCheckPtrAlignment(n, init, nil)
}
if n.Type().IsUnsafePtr() && n.X.Type().IsUintptr() { // uintptr to unsafe.Pointer
return walkCheckPtrArithmetic(n, init)
}
}
param, result := rtconvfn(n.X.Type(), n.Type())
if param == types.Txxx {
return n
}
fn := types.BasicTypeNames[param] + "to" + types.BasicTypeNames[result]
return typecheck.Conv(mkcall(fn, types.Types[result], init, typecheck.Conv(n.X, types.Types[param])), n.Type())
}
// walkConvInterface walks an OCONVIFACE node.
func walkConvInterface(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
n.X = walkExpr(n.X, init)
fromType := n.X.Type()
toType := n.Type()
if !fromType.IsInterface() && !ir.IsBlank(ir.CurFunc.Nname) { // skip unnamed functions (func _())
reflectdata.MarkTypeUsedInInterface(fromType, ir.CurFunc.LSym)
}
// typeword generates the type word of the interface value.
typeword := func() ir.Node {
if toType.IsEmptyInterface() {
return reflectdata.TypePtr(fromType)
}
return reflectdata.ITabAddr(fromType, toType)
}
// Optimize convT2E or convT2I as a two-word copy when T is pointer-shaped.
if types.IsDirectIface(fromType) {
l := ir.NewBinaryExpr(base.Pos, ir.OEFACE, typeword(), n.X)
l.SetType(toType)
l.SetTypecheck(n.Typecheck())
return l
}
// Optimize convT2{E,I} for many cases in which T is not pointer-shaped,
// by using an existing addressable value identical to n.Left
// or creating one on the stack.
var value ir.Node
switch {
case fromType.Size() == 0:
// n.Left is zero-sized. Use zerobase.
cheapExpr(n.X, init) // Evaluate n.Left for side-effects. See issue 19246.
value = ir.NewLinksymExpr(base.Pos, ir.Syms.Zerobase, types.Types[types.TUINTPTR])
case fromType.IsBoolean() || (fromType.Size() == 1 && fromType.IsInteger()):
// n.Left is a bool/byte. Use staticuint64s[n.Left * 8] on little-endian
// and staticuint64s[n.Left * 8 + 7] on big-endian.
n.X = cheapExpr(n.X, init)
// byteindex widens n.Left so that the multiplication doesn't overflow.
index := ir.NewBinaryExpr(base.Pos, ir.OLSH, byteindex(n.X), ir.NewInt(3))
if ssagen.Arch.LinkArch.ByteOrder == binary.BigEndian {
index = ir.NewBinaryExpr(base.Pos, ir.OADD, index, ir.NewInt(7))
}
// The actual type is [256]uint64, but we use [256*8]uint8 so we can address
// individual bytes.
staticuint64s := ir.NewLinksymExpr(base.Pos, ir.Syms.Staticuint64s, types.NewArray(types.Types[types.TUINT8], 256*8))
xe := ir.NewIndexExpr(base.Pos, staticuint64s, index)
xe.SetBounded(true)
value = xe
case n.X.Op() == ir.ONAME && n.X.(*ir.Name).Class == ir.PEXTERN && n.X.(*ir.Name).Readonly():
// n.Left is a readonly global; use it directly.
value = n.X
case !fromType.IsInterface() && n.Esc() == ir.EscNone && fromType.Width <= 1024:
// n.Left does not escape. Use a stack temporary initialized to n.Left.
value = typecheck.Temp(fromType)
init.Append(typecheck.Stmt(ir.NewAssignStmt(base.Pos, value, n.X)))
}
if value != nil {
// Value is identical to n.Left.
// Construct the interface directly: {type/itab, &value}.
l := ir.NewBinaryExpr(base.Pos, ir.OEFACE, typeword(), typecheck.Expr(typecheck.NodAddr(value)))
l.SetType(toType)
l.SetTypecheck(n.Typecheck())
return l
}
// Implement interface to empty interface conversion.
// tmp = i.itab
// if tmp != nil {
// tmp = tmp.type
// }
// e = iface{tmp, i.data}
if toType.IsEmptyInterface() && fromType.IsInterface() && !fromType.IsEmptyInterface() {
// Evaluate the input interface.
c := typecheck.Temp(fromType)
init.Append(ir.NewAssignStmt(base.Pos, c, n.X))
// Get the itab out of the interface.
tmp := typecheck.Temp(types.NewPtr(types.Types[types.TUINT8]))
init.Append(ir.NewAssignStmt(base.Pos, tmp, typecheck.Expr(ir.NewUnaryExpr(base.Pos, ir.OITAB, c))))
// Get the type out of the itab.
nif := ir.NewIfStmt(base.Pos, typecheck.Expr(ir.NewBinaryExpr(base.Pos, ir.ONE, tmp, typecheck.NodNil())), nil, nil)
nif.Body = []ir.Node{ir.NewAssignStmt(base.Pos, tmp, itabType(tmp))}
init.Append(nif)
// Build the result.
e := ir.NewBinaryExpr(base.Pos, ir.OEFACE, tmp, ifaceData(n.Pos(), c, types.NewPtr(types.Types[types.TUINT8])))
e.SetType(toType) // assign type manually, typecheck doesn't understand OEFACE.
e.SetTypecheck(1)
return e
}
fnname, argType, needsaddr := convFuncName(fromType, toType)
if !needsaddr && !fromType.IsInterface() {
// Use a specialized conversion routine that only returns a data pointer.
// ptr = convT2X(val)
// e = iface{typ/tab, ptr}
fn := typecheck.LookupRuntime(fnname)
types.CalcSize(fromType)
arg := n.X
switch {
case fromType == argType:
// already in the right type, nothing to do
case fromType.Kind() == argType.Kind(),
fromType.IsPtrShaped() && argType.IsPtrShaped():
// can directly convert (e.g. named type to underlying type, or one pointer to another)
arg = ir.NewConvExpr(n.Pos(), ir.OCONVNOP, argType, arg)
case fromType.IsInteger() && argType.IsInteger():
// can directly convert (e.g. int32 to uint32)
arg = ir.NewConvExpr(n.Pos(), ir.OCONV, argType, arg)
default:
// unsafe cast through memory
arg = copyExpr(arg, arg.Type(), init)
var addr ir.Node = typecheck.NodAddr(arg)
addr = ir.NewConvExpr(n.Pos(), ir.OCONVNOP, argType.PtrTo(), addr)
arg = ir.NewStarExpr(n.Pos(), addr)
arg.SetType(argType)
}
call := ir.NewCallExpr(base.Pos, ir.OCALL, fn, nil)
call.Args = []ir.Node{arg}
e := ir.NewBinaryExpr(base.Pos, ir.OEFACE, typeword(), safeExpr(walkExpr(typecheck.Expr(call), init), init))
e.SetType(toType)
e.SetTypecheck(1)
return e
}
var tab ir.Node
if fromType.IsInterface() {
// convI2I
tab = reflectdata.TypePtr(toType)
} else {
// convT2x
tab = typeword()
}
v := n.X
if needsaddr {
// Types of large or unknown size are passed by reference.
// Orderexpr arranged for n.Left to be a temporary for all
// the conversions it could see. Comparison of an interface
// with a non-interface, especially in a switch on interface value
// with non-interface cases, is not visible to order.stmt, so we
// have to fall back on allocating a temp here.
if !ir.IsAddressable(v) {
v = copyExpr(v, v.Type(), init)
}
v = typecheck.NodAddr(v)
}
types.CalcSize(fromType)
fn := typecheck.LookupRuntime(fnname)
fn = typecheck.SubstArgTypes(fn, fromType, toType)
types.CalcSize(fn.Type())
call := ir.NewCallExpr(base.Pos, ir.OCALL, fn, nil)
call.Args = []ir.Node{tab, v}
return walkExpr(typecheck.Expr(call), init)
}
// walkBytesRunesToString walks an OBYTES2STR or ORUNES2STR node.
func walkBytesRunesToString(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
a := typecheck.NodNil()
if n.Esc() == ir.EscNone {
// Create temporary buffer for string on stack.
a = stackBufAddr(tmpstringbufsize, types.Types[types.TUINT8])
}
if n.Op() == ir.ORUNES2STR {
// slicerunetostring(*[32]byte, []rune) string
return mkcall("slicerunetostring", n.Type(), init, a, n.X)
}
// slicebytetostring(*[32]byte, ptr *byte, n int) string
n.X = cheapExpr(n.X, init)
ptr, len := backingArrayPtrLen(n.X)
return mkcall("slicebytetostring", n.Type(), init, a, ptr, len)
}
// walkBytesToStringTemp walks an OBYTES2STRTMP node.
func walkBytesToStringTemp(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
n.X = walkExpr(n.X, init)
if !base.Flag.Cfg.Instrumenting {
// Let the backend handle OBYTES2STRTMP directly
// to avoid a function call to slicebytetostringtmp.
return n
}
// slicebytetostringtmp(ptr *byte, n int) string
n.X = cheapExpr(n.X, init)
ptr, len := backingArrayPtrLen(n.X)
return mkcall("slicebytetostringtmp", n.Type(), init, ptr, len)
}
// walkRuneToString walks an ORUNESTR node.
func walkRuneToString(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
a := typecheck.NodNil()
if n.Esc() == ir.EscNone {
a = stackBufAddr(4, types.Types[types.TUINT8])
}
// intstring(*[4]byte, rune)
return mkcall("intstring", n.Type(), init, a, typecheck.Conv(n.X, types.Types[types.TINT64]))
}
// walkStringToBytes walks an OSTR2BYTES node.
func walkStringToBytes(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
s := n.X
if ir.IsConst(s, constant.String) {
sc := ir.StringVal(s)
// Allocate a [n]byte of the right size.
t := types.NewArray(types.Types[types.TUINT8], int64(len(sc)))
var a ir.Node
if n.Esc() == ir.EscNone && len(sc) <= int(ir.MaxImplicitStackVarSize) {
a = stackBufAddr(t.NumElem(), t.Elem())
} else {
types.CalcSize(t)
a = ir.NewUnaryExpr(base.Pos, ir.ONEW, nil)
a.SetType(types.NewPtr(t))
a.SetTypecheck(1)
a.MarkNonNil()
}
p := typecheck.Temp(t.PtrTo()) // *[n]byte
init.Append(typecheck.Stmt(ir.NewAssignStmt(base.Pos, p, a)))
// Copy from the static string data to the [n]byte.
if len(sc) > 0 {
as := ir.NewAssignStmt(base.Pos, ir.NewStarExpr(base.Pos, p), ir.NewStarExpr(base.Pos, typecheck.ConvNop(ir.NewUnaryExpr(base.Pos, ir.OSPTR, s), t.PtrTo())))
appendWalkStmt(init, as)
}
// Slice the [n]byte to a []byte.
slice := ir.NewSliceExpr(n.Pos(), ir.OSLICEARR, p, nil, nil, nil)
slice.SetType(n.Type())
slice.SetTypecheck(1)
return walkExpr(slice, init)
}
a := typecheck.NodNil()
if n.Esc() == ir.EscNone {
// Create temporary buffer for slice on stack.
a = stackBufAddr(tmpstringbufsize, types.Types[types.TUINT8])
}
// stringtoslicebyte(*32[byte], string) []byte
return mkcall("stringtoslicebyte", n.Type(), init, a, typecheck.Conv(s, types.Types[types.TSTRING]))
}
// walkStringToBytesTemp walks an OSTR2BYTESTMP node.
func walkStringToBytesTemp(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
// []byte(string) conversion that creates a slice
// referring to the actual string bytes.
// This conversion is handled later by the backend and
// is only for use by internal compiler optimizations
// that know that the slice won't be mutated.
// The only such case today is:
// for i, c := range []byte(string)
n.X = walkExpr(n.X, init)
return n
}
// walkStringToRunes walks an OSTR2RUNES node.
func walkStringToRunes(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
a := typecheck.NodNil()
if n.Esc() == ir.EscNone {
// Create temporary buffer for slice on stack.
a = stackBufAddr(tmpstringbufsize, types.Types[types.TINT32])
}
// stringtoslicerune(*[32]rune, string) []rune
return mkcall("stringtoslicerune", n.Type(), init, a, typecheck.Conv(n.X, types.Types[types.TSTRING]))
}
// convFuncName builds the runtime function name for interface conversion.
// It also returns the argument type that the runtime function takes, and
// whether the function expects the data by address.
// Not all names are possible. For example, we never generate convE2E or convE2I.
func convFuncName(from, to *types.Type) (fnname string, argType *types.Type, needsaddr bool) {
tkind := to.Tie()
switch from.Tie() {
case 'I':
if tkind == 'I' {
return "convI2I", types.Types[types.TINTER], false
}
case 'T':
switch {
case from.Size() == 2 && from.Align == 2:
return "convT16", types.Types[types.TUINT16], false
case from.Size() == 4 && from.Align == 4 && !from.HasPointers():
return "convT32", types.Types[types.TUINT32], false
case from.Size() == 8 && from.Align == types.Types[types.TUINT64].Align && !from.HasPointers():
return "convT64", types.Types[types.TUINT64], false
}
if sc := from.SoleComponent(); sc != nil {
switch {
case sc.IsString():
return "convTstring", types.Types[types.TSTRING], false
case sc.IsSlice():
return "convTslice", types.NewSlice(types.Types[types.TUINT8]), false // the element type doesn't matter
}
}
switch tkind {
case 'E':
if !from.HasPointers() {
return "convT2Enoptr", types.Types[types.TUNSAFEPTR], true
}
return "convT2E", types.Types[types.TUNSAFEPTR], true
case 'I':
if !from.HasPointers() {
return "convT2Inoptr", types.Types[types.TUNSAFEPTR], true
}
return "convT2I", types.Types[types.TUNSAFEPTR], true
}
}
base.Fatalf("unknown conv func %c2%c", from.Tie(), to.Tie())
panic("unreachable")
}
// rtconvfn returns the parameter and result types that will be used by a
// runtime function to convert from type src to type dst. The runtime function
// name can be derived from the names of the returned types.
//
// If no such function is necessary, it returns (Txxx, Txxx).
func rtconvfn(src, dst *types.Type) (param, result types.Kind) {
if ssagen.Arch.SoftFloat {
return types.Txxx, types.Txxx
}
switch ssagen.Arch.LinkArch.Family {
case sys.ARM, sys.MIPS:
if src.IsFloat() {
switch dst.Kind() {
case types.TINT64, types.TUINT64:
return types.TFLOAT64, dst.Kind()
}
}
if dst.IsFloat() {
switch src.Kind() {
case types.TINT64, types.TUINT64:
return src.Kind(), types.TFLOAT64
}
}
case sys.I386:
if src.IsFloat() {
switch dst.Kind() {
case types.TINT64, types.TUINT64:
return types.TFLOAT64, dst.Kind()
case types.TUINT32, types.TUINT, types.TUINTPTR:
return types.TFLOAT64, types.TUINT32
}
}
if dst.IsFloat() {
switch src.Kind() {
case types.TINT64, types.TUINT64:
return src.Kind(), types.TFLOAT64
case types.TUINT32, types.TUINT, types.TUINTPTR:
return types.TUINT32, types.TFLOAT64
}
}
}
return types.Txxx, types.Txxx
}
// byteindex converts n, which is byte-sized, to an int used to index into an array.
// We cannot use conv, because we allow converting bool to int here,
// which is forbidden in user code.
func byteindex(n ir.Node) ir.Node {
// We cannot convert from bool to int directly.
// While converting from int8 to int is possible, it would yield
// the wrong result for negative values.
// Reinterpreting the value as an unsigned byte solves both cases.
if !types.Identical(n.Type(), types.Types[types.TUINT8]) {
n = ir.NewConvExpr(base.Pos, ir.OCONV, nil, n)
n.SetType(types.Types[types.TUINT8])
n.SetTypecheck(1)
}
n = ir.NewConvExpr(base.Pos, ir.OCONV, nil, n)
n.SetType(types.Types[types.TINT])
n.SetTypecheck(1)
return n
}
func walkCheckPtrAlignment(n *ir.ConvExpr, init *ir.Nodes, count ir.Node) ir.Node {
if !n.Type().IsPtr() {
base.Fatalf("expected pointer type: %v", n.Type())
}
elem := n.Type().Elem()
if count != nil {
if !elem.IsArray() {
base.Fatalf("expected array type: %v", elem)
}
elem = elem.Elem()
}
size := elem.Size()
if elem.Alignment() == 1 && (size == 0 || size == 1 && count == nil) {
return n
}
if count == nil {
count = ir.NewInt(1)
}
n.X = cheapExpr(n.X, init)
init.Append(mkcall("checkptrAlignment", nil, init, typecheck.ConvNop(n.X, types.Types[types.TUNSAFEPTR]), reflectdata.TypePtr(elem), typecheck.Conv(count, types.Types[types.TUINTPTR])))
return n
}
func walkCheckPtrArithmetic(n *ir.ConvExpr, init *ir.Nodes) ir.Node {
// Calling cheapExpr(n, init) below leads to a recursive call to
// walkExpr, which leads us back here again. Use n.Checkptr to
// prevent infinite loops.
if n.CheckPtr() {
return n
}
n.SetCheckPtr(true)
defer n.SetCheckPtr(false)
// TODO(mdempsky): Make stricter. We only need to exempt
// reflect.Value.Pointer and reflect.Value.UnsafeAddr.
switch n.X.Op() {
case ir.OCALLFUNC, ir.OCALLMETH, ir.OCALLINTER:
return n
}
if n.X.Op() == ir.ODOTPTR && ir.IsReflectHeaderDataField(n.X) {
return n
}
// Find original unsafe.Pointer operands involved in this
// arithmetic expression.
//
// "It is valid both to add and to subtract offsets from a
// pointer in this way. It is also valid to use &^ to round
// pointers, usually for alignment."
var originals []ir.Node
var walk func(n ir.Node)
walk = func(n ir.Node) {
switch n.Op() {
case ir.OADD:
n := n.(*ir.BinaryExpr)
walk(n.X)
walk(n.Y)
case ir.OSUB, ir.OANDNOT:
n := n.(*ir.BinaryExpr)
walk(n.X)
case ir.OCONVNOP:
n := n.(*ir.ConvExpr)
if n.X.Type().IsUnsafePtr() {
n.X = cheapExpr(n.X, init)
originals = append(originals, typecheck.ConvNop(n.X, types.Types[types.TUNSAFEPTR]))
}
}
}
walk(n.X)
cheap := cheapExpr(n, init)
slice := typecheck.MakeDotArgs(types.NewSlice(types.Types[types.TUNSAFEPTR]), originals)
slice.SetEsc(ir.EscNone)
init.Append(mkcall("checkptrArithmetic", nil, init, typecheck.ConvNop(cheap, types.Types[types.TUNSAFEPTR]), slice))
// TODO(khr): Mark backing store of slice as dead. This will allow us to reuse
// the backing store for multiple calls to checkptrArithmetic.
return cheap
}
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