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// 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 gc
import (
"cmd/compile/internal/types"
"cmd/internal/sys"
"unicode/utf8"
)
// range
func typecheckrange(n *Node) {
// Typechecking order is important here:
// 0. first typecheck range expression (slice/map/chan),
// it is evaluated only once and so logically it is not part of the loop.
// 1. typecheck produced values,
// this part can declare new vars and so it must be typechecked before body,
// because body can contain a closure that captures the vars.
// 2. decldepth++ to denote loop body.
// 3. typecheck body.
// 4. decldepth--.
typecheckrangeExpr(n)
// second half of dance, the first half being typecheckrangeExpr
n.SetTypecheck(1)
ls := n.List.Slice()
for i1, n1 := range ls {
if n1.Typecheck() == 0 {
ls[i1] = typecheck(ls[i1], ctxExpr|ctxAssign)
}
}
decldepth++
typecheckslice(n.Nbody.Slice(), ctxStmt)
decldepth--
}
func typecheckrangeExpr(n *Node) {
n.Right = typecheck(n.Right, ctxExpr)
t := n.Right.Type
if t == nil {
return
}
// delicate little dance. see typecheckas2
ls := n.List.Slice()
for i1, n1 := range ls {
if n1.Name == nil || n1.Name.Defn != n {
ls[i1] = typecheck(ls[i1], ctxExpr|ctxAssign)
}
}
if t.IsPtr() && t.Elem().IsArray() {
t = t.Elem()
}
n.Type = t
var t1, t2 *types.Type
toomany := false
switch t.Etype {
default:
yyerrorl(n.Pos, "cannot range over %L", n.Right)
return
case TARRAY, TSLICE:
t1 = types.Types[TINT]
t2 = t.Elem()
case TMAP:
t1 = t.Key()
t2 = t.Elem()
case TCHAN:
if !t.ChanDir().CanRecv() {
yyerrorl(n.Pos, "invalid operation: range %v (receive from send-only type %v)", n.Right, n.Right.Type)
return
}
t1 = t.Elem()
t2 = nil
if n.List.Len() == 2 {
toomany = true
}
case TSTRING:
t1 = types.Types[TINT]
t2 = types.Runetype
}
if n.List.Len() > 2 || toomany {
yyerrorl(n.Pos, "too many variables in range")
}
var v1, v2 *Node
if n.List.Len() != 0 {
v1 = n.List.First()
}
if n.List.Len() > 1 {
v2 = n.List.Second()
}
// this is not only an optimization but also a requirement in the spec.
// "if the second iteration variable is the blank identifier, the range
// clause is equivalent to the same clause with only the first variable
// present."
if v2.isBlank() {
if v1 != nil {
n.List.Set1(v1)
}
v2 = nil
}
var why string
if v1 != nil {
if v1.Name != nil && v1.Name.Defn == n {
v1.Type = t1
} else if v1.Type != nil && assignop(t1, v1.Type, &why) == 0 {
yyerrorl(n.Pos, "cannot assign type %v to %L in range%s", t1, v1, why)
}
checkassign(n, v1)
}
if v2 != nil {
if v2.Name != nil && v2.Name.Defn == n {
v2.Type = t2
} else if v2.Type != nil && assignop(t2, v2.Type, &why) == 0 {
yyerrorl(n.Pos, "cannot assign type %v to %L in range%s", t2, v2, why)
}
checkassign(n, v2)
}
}
func cheapComputableIndex(width int64) bool {
switch thearch.LinkArch.Family {
// MIPS does not have R+R addressing
// Arm64 may lack ability to generate this code in our assembler,
// but the architecture supports it.
case sys.PPC64, sys.S390X:
return width == 1
case sys.AMD64, sys.I386, sys.ARM64, sys.ARM:
switch width {
case 1, 2, 4, 8:
return true
}
}
return false
}
// walkrange transforms various forms of ORANGE into
// simpler forms. The result must be assigned back to n.
// Node n may also be modified in place, and may also be
// the returned node.
func walkrange(n *Node) *Node {
if isMapClear(n) {
m := n.Right
lno := setlineno(m)
n = mapClear(m)
lineno = lno
return n
}
// variable name conventions:
// ohv1, hv1, hv2: hidden (old) val 1, 2
// ha, hit: hidden aggregate, iterator
// hn, hp: hidden len, pointer
// hb: hidden bool
// a, v1, v2: not hidden aggregate, val 1, 2
t := n.Type
a := n.Right
lno := setlineno(a)
n.Right = nil
var v1, v2 *Node
l := n.List.Len()
if l > 0 {
v1 = n.List.First()
}
if l > 1 {
v2 = n.List.Second()
}
if v2.isBlank() {
v2 = nil
}
if v1.isBlank() && v2 == nil {
v1 = nil
}
if v1 == nil && v2 != nil {
Fatalf("walkrange: v2 != nil while v1 == nil")
}
// n.List has no meaning anymore, clear it
// to avoid erroneous processing by racewalk.
n.List.Set(nil)
var ifGuard *Node
translatedLoopOp := OFOR
var body []*Node
var init []*Node
switch t.Etype {
default:
Fatalf("walkrange")
case TARRAY, TSLICE:
if arrayClear(n, v1, v2, a) {
lineno = lno
return n
}
// order.stmt arranged for a copy of the array/slice variable if needed.
ha := a
hv1 := temp(types.Types[TINT])
hn := temp(types.Types[TINT])
init = append(init, nod(OAS, hv1, nil))
init = append(init, nod(OAS, hn, nod(OLEN, ha, nil)))
n.Left = nod(OLT, hv1, hn)
n.Right = nod(OAS, hv1, nod(OADD, hv1, nodintconst(1)))
// for range ha { body }
if v1 == nil {
break
}
// for v1 := range ha { body }
if v2 == nil {
body = []*Node{nod(OAS, v1, hv1)}
break
}
// for v1, v2 := range ha { body }
if cheapComputableIndex(n.Type.Elem().Width) {
// v1, v2 = hv1, ha[hv1]
tmp := nod(OINDEX, ha, hv1)
tmp.SetBounded(true)
// Use OAS2 to correctly handle assignments
// of the form "v1, a[v1] := range".
a := nod(OAS2, nil, nil)
a.List.Set2(v1, v2)
a.Rlist.Set2(hv1, tmp)
body = []*Node{a}
break
}
// TODO(austin): OFORUNTIL is a strange beast, but is
// necessary for expressing the control flow we need
// while also making "break" and "continue" work. It
// would be nice to just lower ORANGE during SSA, but
// racewalk needs to see many of the operations
// involved in ORANGE's implementation. If racewalk
// moves into SSA, consider moving ORANGE into SSA and
// eliminating OFORUNTIL.
// TODO(austin): OFORUNTIL inhibits bounds-check
// elimination on the index variable (see #20711).
// Enhance the prove pass to understand this.
ifGuard = nod(OIF, nil, nil)
ifGuard.Left = nod(OLT, hv1, hn)
translatedLoopOp = OFORUNTIL
hp := temp(types.NewPtr(n.Type.Elem()))
tmp := nod(OINDEX, ha, nodintconst(0))
tmp.SetBounded(true)
init = append(init, nod(OAS, hp, nod(OADDR, tmp, nil)))
// Use OAS2 to correctly handle assignments
// of the form "v1, a[v1] := range".
a := nod(OAS2, nil, nil)
a.List.Set2(v1, v2)
a.Rlist.Set2(hv1, nod(ODEREF, hp, nil))
body = append(body, a)
// Advance pointer as part of the late increment.
//
// This runs *after* the condition check, so we know
// advancing the pointer is safe and won't go past the
// end of the allocation.
a = nod(OAS, hp, addptr(hp, t.Elem().Width))
a = typecheck(a, ctxStmt)
n.List.Set1(a)
case TMAP:
// order.stmt allocated the iterator for us.
// we only use a once, so no copy needed.
ha := a
hit := prealloc[n]
th := hit.Type
n.Left = nil
keysym := th.Field(0).Sym // depends on layout of iterator struct. See reflect.go:hiter
elemsym := th.Field(1).Sym // ditto
fn := syslook("mapiterinit")
fn = substArgTypes(fn, t.Key(), t.Elem(), th)
init = append(init, mkcall1(fn, nil, nil, typename(t), ha, nod(OADDR, hit, nil)))
n.Left = nod(ONE, nodSym(ODOT, hit, keysym), nodnil())
fn = syslook("mapiternext")
fn = substArgTypes(fn, th)
n.Right = mkcall1(fn, nil, nil, nod(OADDR, hit, nil))
key := nodSym(ODOT, hit, keysym)
key = nod(ODEREF, key, nil)
if v1 == nil {
body = nil
} else if v2 == nil {
body = []*Node{nod(OAS, v1, key)}
} else {
elem := nodSym(ODOT, hit, elemsym)
elem = nod(ODEREF, elem, nil)
a := nod(OAS2, nil, nil)
a.List.Set2(v1, v2)
a.Rlist.Set2(key, elem)
body = []*Node{a}
}
case TCHAN:
// order.stmt arranged for a copy of the channel variable.
ha := a
n.Left = nil
hv1 := temp(t.Elem())
hv1.SetTypecheck(1)
if t.Elem().HasPointers() {
init = append(init, nod(OAS, hv1, nil))
}
hb := temp(types.Types[TBOOL])
n.Left = nod(ONE, hb, nodbool(false))
a := nod(OAS2RECV, nil, nil)
a.SetTypecheck(1)
a.List.Set2(hv1, hb)
a.Right = nod(ORECV, ha, nil)
n.Left.Ninit.Set1(a)
if v1 == nil {
body = nil
} else {
body = []*Node{nod(OAS, v1, hv1)}
}
// Zero hv1. This prevents hv1 from being the sole, inaccessible
// reference to an otherwise GC-able value during the next channel receive.
// See issue 15281.
body = append(body, nod(OAS, hv1, nil))
case TSTRING:
// Transform string range statements like "for v1, v2 = range a" into
//
// ha := a
// for hv1 := 0; hv1 < len(ha); {
// hv1t := hv1
// hv2 := rune(ha[hv1])
// if hv2 < utf8.RuneSelf {
// hv1++
// } else {
// hv2, hv1 = decoderune(ha, hv1)
// }
// v1, v2 = hv1t, hv2
// // original body
// }
// order.stmt arranged for a copy of the string variable.
ha := a
hv1 := temp(types.Types[TINT])
hv1t := temp(types.Types[TINT])
hv2 := temp(types.Runetype)
// hv1 := 0
init = append(init, nod(OAS, hv1, nil))
// hv1 < len(ha)
n.Left = nod(OLT, hv1, nod(OLEN, ha, nil))
if v1 != nil {
// hv1t = hv1
body = append(body, nod(OAS, hv1t, hv1))
}
// hv2 := rune(ha[hv1])
nind := nod(OINDEX, ha, hv1)
nind.SetBounded(true)
body = append(body, nod(OAS, hv2, conv(nind, types.Runetype)))
// if hv2 < utf8.RuneSelf
nif := nod(OIF, nil, nil)
nif.Left = nod(OLT, hv2, nodintconst(utf8.RuneSelf))
// hv1++
nif.Nbody.Set1(nod(OAS, hv1, nod(OADD, hv1, nodintconst(1))))
// } else {
eif := nod(OAS2, nil, nil)
nif.Rlist.Set1(eif)
// hv2, hv1 = decoderune(ha, hv1)
eif.List.Set2(hv2, hv1)
fn := syslook("decoderune")
eif.Rlist.Set1(mkcall1(fn, fn.Type.Results(), nil, ha, hv1))
body = append(body, nif)
if v1 != nil {
if v2 != nil {
// v1, v2 = hv1t, hv2
a := nod(OAS2, nil, nil)
a.List.Set2(v1, v2)
a.Rlist.Set2(hv1t, hv2)
body = append(body, a)
} else {
// v1 = hv1t
body = append(body, nod(OAS, v1, hv1t))
}
}
}
n.Op = translatedLoopOp
typecheckslice(init, ctxStmt)
if ifGuard != nil {
ifGuard.Ninit.Append(init...)
ifGuard = typecheck(ifGuard, ctxStmt)
} else {
n.Ninit.Append(init...)
}
typecheckslice(n.Left.Ninit.Slice(), ctxStmt)
n.Left = typecheck(n.Left, ctxExpr)
n.Left = defaultlit(n.Left, nil)
n.Right = typecheck(n.Right, ctxStmt)
typecheckslice(body, ctxStmt)
n.Nbody.Prepend(body...)
if ifGuard != nil {
ifGuard.Nbody.Set1(n)
n = ifGuard
}
n = walkstmt(n)
lineno = lno
return n
}
// isMapClear checks if n is of the form:
//
// for k := range m {
// delete(m, k)
// }
//
// where == for keys of map m is reflexive.
func isMapClear(n *Node) bool {
if Debug['N'] != 0 || instrumenting {
return false
}
if n.Op != ORANGE || n.Type.Etype != TMAP || n.List.Len() != 1 {
return false
}
k := n.List.First()
if k == nil || k.isBlank() {
return false
}
// Require k to be a new variable name.
if k.Name == nil || k.Name.Defn != n {
return false
}
if n.Nbody.Len() != 1 {
return false
}
stmt := n.Nbody.First() // only stmt in body
if stmt == nil || stmt.Op != ODELETE {
return false
}
m := n.Right
if !samesafeexpr(stmt.List.First(), m) || !samesafeexpr(stmt.List.Second(), k) {
return false
}
// Keys where equality is not reflexive can not be deleted from maps.
if !isreflexive(m.Type.Key()) {
return false
}
return true
}
// mapClear constructs a call to runtime.mapclear for the map m.
func mapClear(m *Node) *Node {
t := m.Type
// instantiate mapclear(typ *type, hmap map[any]any)
fn := syslook("mapclear")
fn = substArgTypes(fn, t.Key(), t.Elem())
n := mkcall1(fn, nil, nil, typename(t), m)
n = typecheck(n, ctxStmt)
n = walkstmt(n)
return n
}
// Lower n into runtime·memclr if possible, for
// fast zeroing of slices and arrays (issue 5373).
// Look for instances of
//
// for i := range a {
// a[i] = zero
// }
//
// in which the evaluation of a is side-effect-free.
//
// Parameters are as in walkrange: "for v1, v2 = range a".
func arrayClear(n, v1, v2, a *Node) bool {
if Debug['N'] != 0 || instrumenting {
return false
}
if v1 == nil || v2 != nil {
return false
}
if n.Nbody.Len() != 1 || n.Nbody.First() == nil {
return false
}
stmt := n.Nbody.First() // only stmt in body
if stmt.Op != OAS || stmt.Left.Op != OINDEX {
return false
}
if !samesafeexpr(stmt.Left.Left, a) || !samesafeexpr(stmt.Left.Right, v1) {
return false
}
elemsize := n.Type.Elem().Width
if elemsize <= 0 || !isZero(stmt.Right) {
return false
}
// Convert to
// if len(a) != 0 {
// hp = &a[0]
// hn = len(a)*sizeof(elem(a))
// memclr{NoHeap,Has}Pointers(hp, hn)
// i = len(a) - 1
// }
n.Op = OIF
n.Nbody.Set(nil)
n.Left = nod(ONE, nod(OLEN, a, nil), nodintconst(0))
// hp = &a[0]
hp := temp(types.Types[TUNSAFEPTR])
tmp := nod(OINDEX, a, nodintconst(0))
tmp.SetBounded(true)
tmp = nod(OADDR, tmp, nil)
tmp = convnop(tmp, types.Types[TUNSAFEPTR])
n.Nbody.Append(nod(OAS, hp, tmp))
// hn = len(a) * sizeof(elem(a))
hn := temp(types.Types[TUINTPTR])
tmp = nod(OLEN, a, nil)
tmp = nod(OMUL, tmp, nodintconst(elemsize))
tmp = conv(tmp, types.Types[TUINTPTR])
n.Nbody.Append(nod(OAS, hn, tmp))
var fn *Node
if a.Type.Elem().HasHeapPointer() {
// memclrHasPointers(hp, hn)
Curfn.Func.setWBPos(stmt.Pos)
fn = mkcall("memclrHasPointers", nil, nil, hp, hn)
} else {
// memclrNoHeapPointers(hp, hn)
fn = mkcall("memclrNoHeapPointers", nil, nil, hp, hn)
}
n.Nbody.Append(fn)
// i = len(a) - 1
v1 = nod(OAS, v1, nod(OSUB, nod(OLEN, a, nil), nodintconst(1)))
n.Nbody.Append(v1)
n.Left = typecheck(n.Left, ctxExpr)
n.Left = defaultlit(n.Left, nil)
typecheckslice(n.Nbody.Slice(), ctxStmt)
n = walkstmt(n)
return true
}
// addptr returns (*T)(uintptr(p) + n).
func addptr(p *Node, n int64) *Node {
t := p.Type
p = nod(OCONVNOP, p, nil)
p.Type = types.Types[TUINTPTR]
p = nod(OADD, p, nodintconst(n))
p = nod(OCONVNOP, p, nil)
p.Type = t
return p
}