Current File : //usr/local/go119/src/cmd/compile/internal/walk/range.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 (
"unicode/utf8"
"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"
)
func cheapComputableIndex(width int64) bool {
switch ssagen.Arch.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(nrange *ir.RangeStmt) ir.Node {
if isMapClear(nrange) {
m := nrange.X
lno := ir.SetPos(m)
n := mapClear(m)
base.Pos = lno
return n
}
nfor := ir.NewForStmt(nrange.Pos(), nil, nil, nil, nil)
nfor.SetInit(nrange.Init())
nfor.Label = nrange.Label
// 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
a := nrange.X
t := typecheck.RangeExprType(a.Type())
lno := ir.SetPos(a)
v1, v2 := nrange.Key, nrange.Value
if ir.IsBlank(v2) {
v2 = nil
}
if ir.IsBlank(v1) && v2 == nil {
v1 = nil
}
if v1 == nil && v2 != nil {
base.Fatalf("walkRange: v2 != nil while v1 == nil")
}
var ifGuard *ir.IfStmt
var body []ir.Node
var init []ir.Node
switch t.Kind() {
default:
base.Fatalf("walkRange")
case types.TARRAY, types.TSLICE:
if nn := arrayClear(nrange, v1, v2, a); nn != nil {
base.Pos = lno
return nn
}
// order.stmt arranged for a copy of the array/slice variable if needed.
ha := a
hv1 := typecheck.Temp(types.Types[types.TINT])
hn := typecheck.Temp(types.Types[types.TINT])
init = append(init, ir.NewAssignStmt(base.Pos, hv1, nil))
init = append(init, ir.NewAssignStmt(base.Pos, hn, ir.NewUnaryExpr(base.Pos, ir.OLEN, ha)))
nfor.Cond = ir.NewBinaryExpr(base.Pos, ir.OLT, hv1, hn)
nfor.Post = ir.NewAssignStmt(base.Pos, hv1, ir.NewBinaryExpr(base.Pos, ir.OADD, hv1, ir.NewInt(1)))
// for range ha { body }
if v1 == nil {
break
}
// for v1 := range ha { body }
if v2 == nil {
body = []ir.Node{ir.NewAssignStmt(base.Pos, v1, hv1)}
break
}
// for v1, v2 := range ha { body }
if cheapComputableIndex(t.Elem().Size()) {
// v1, v2 = hv1, ha[hv1]
tmp := ir.NewIndexExpr(base.Pos, ha, hv1)
tmp.SetBounded(true)
// Use OAS2 to correctly handle assignments
// of the form "v1, a[v1] := range".
a := ir.NewAssignListStmt(base.Pos, ir.OAS2, []ir.Node{v1, v2}, []ir.Node{hv1, tmp})
body = []ir.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 = ir.NewIfStmt(base.Pos, nil, nil, nil)
ifGuard.Cond = ir.NewBinaryExpr(base.Pos, ir.OLT, hv1, hn)
nfor.SetOp(ir.OFORUNTIL)
hp := typecheck.Temp(types.NewPtr(t.Elem()))
tmp := ir.NewIndexExpr(base.Pos, ha, ir.NewInt(0))
tmp.SetBounded(true)
init = append(init, ir.NewAssignStmt(base.Pos, hp, typecheck.NodAddr(tmp)))
// Use OAS2 to correctly handle assignments
// of the form "v1, a[v1] := range".
a := ir.NewAssignListStmt(base.Pos, ir.OAS2, []ir.Node{v1, v2}, []ir.Node{hv1, ir.NewStarExpr(base.Pos, hp)})
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.
as := ir.NewAssignStmt(base.Pos, hp, addptr(hp, t.Elem().Size()))
nfor.Late = []ir.Node{typecheck.Stmt(as)}
case types.TMAP:
// order.stmt allocated the iterator for us.
// we only use a once, so no copy needed.
ha := a
hit := nrange.Prealloc
th := hit.Type()
// depends on layout of iterator struct.
// See cmd/compile/internal/reflectdata/reflect.go:MapIterType
keysym := th.Field(0).Sym
elemsym := th.Field(1).Sym // ditto
fn := typecheck.LookupRuntime("mapiterinit")
fn = typecheck.SubstArgTypes(fn, t.Key(), t.Elem(), th)
init = append(init, mkcallstmt1(fn, reflectdata.TypePtr(t), ha, typecheck.NodAddr(hit)))
nfor.Cond = ir.NewBinaryExpr(base.Pos, ir.ONE, ir.NewSelectorExpr(base.Pos, ir.ODOT, hit, keysym), typecheck.NodNil())
fn = typecheck.LookupRuntime("mapiternext")
fn = typecheck.SubstArgTypes(fn, th)
nfor.Post = mkcallstmt1(fn, typecheck.NodAddr(hit))
key := ir.NewStarExpr(base.Pos, ir.NewSelectorExpr(base.Pos, ir.ODOT, hit, keysym))
if v1 == nil {
body = nil
} else if v2 == nil {
body = []ir.Node{ir.NewAssignStmt(base.Pos, v1, key)}
} else {
elem := ir.NewStarExpr(base.Pos, ir.NewSelectorExpr(base.Pos, ir.ODOT, hit, elemsym))
a := ir.NewAssignListStmt(base.Pos, ir.OAS2, []ir.Node{v1, v2}, []ir.Node{key, elem})
body = []ir.Node{a}
}
case types.TCHAN:
// order.stmt arranged for a copy of the channel variable.
ha := a
hv1 := typecheck.Temp(t.Elem())
hv1.SetTypecheck(1)
if t.Elem().HasPointers() {
init = append(init, ir.NewAssignStmt(base.Pos, hv1, nil))
}
hb := typecheck.Temp(types.Types[types.TBOOL])
nfor.Cond = ir.NewBinaryExpr(base.Pos, ir.ONE, hb, ir.NewBool(false))
lhs := []ir.Node{hv1, hb}
rhs := []ir.Node{ir.NewUnaryExpr(base.Pos, ir.ORECV, ha)}
a := ir.NewAssignListStmt(base.Pos, ir.OAS2RECV, lhs, rhs)
a.SetTypecheck(1)
nfor.Cond = ir.InitExpr([]ir.Node{a}, nfor.Cond)
if v1 == nil {
body = nil
} else {
body = []ir.Node{ir.NewAssignStmt(base.Pos, 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, ir.NewAssignStmt(base.Pos, hv1, nil))
case types.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 := typecheck.Temp(types.Types[types.TINT])
hv1t := typecheck.Temp(types.Types[types.TINT])
hv2 := typecheck.Temp(types.RuneType)
// hv1 := 0
init = append(init, ir.NewAssignStmt(base.Pos, hv1, nil))
// hv1 < len(ha)
nfor.Cond = ir.NewBinaryExpr(base.Pos, ir.OLT, hv1, ir.NewUnaryExpr(base.Pos, ir.OLEN, ha))
if v1 != nil {
// hv1t = hv1
body = append(body, ir.NewAssignStmt(base.Pos, hv1t, hv1))
}
// hv2 := rune(ha[hv1])
nind := ir.NewIndexExpr(base.Pos, ha, hv1)
nind.SetBounded(true)
body = append(body, ir.NewAssignStmt(base.Pos, hv2, typecheck.Conv(nind, types.RuneType)))
// if hv2 < utf8.RuneSelf
nif := ir.NewIfStmt(base.Pos, nil, nil, nil)
nif.Cond = ir.NewBinaryExpr(base.Pos, ir.OLT, hv2, ir.NewInt(utf8.RuneSelf))
// hv1++
nif.Body = []ir.Node{ir.NewAssignStmt(base.Pos, hv1, ir.NewBinaryExpr(base.Pos, ir.OADD, hv1, ir.NewInt(1)))}
// } else {
// hv2, hv1 = decoderune(ha, hv1)
fn := typecheck.LookupRuntime("decoderune")
call := mkcall1(fn, fn.Type().Results(), &nif.Else, ha, hv1)
a := ir.NewAssignListStmt(base.Pos, ir.OAS2, []ir.Node{hv2, hv1}, []ir.Node{call})
nif.Else.Append(a)
body = append(body, nif)
if v1 != nil {
if v2 != nil {
// v1, v2 = hv1t, hv2
a := ir.NewAssignListStmt(base.Pos, ir.OAS2, []ir.Node{v1, v2}, []ir.Node{hv1t, hv2})
body = append(body, a)
} else {
// v1 = hv1t
body = append(body, ir.NewAssignStmt(base.Pos, v1, hv1t))
}
}
}
typecheck.Stmts(init)
if ifGuard != nil {
ifGuard.PtrInit().Append(init...)
ifGuard = typecheck.Stmt(ifGuard).(*ir.IfStmt)
} else {
nfor.PtrInit().Append(init...)
}
typecheck.Stmts(nfor.Cond.Init())
nfor.Cond = typecheck.Expr(nfor.Cond)
nfor.Cond = typecheck.DefaultLit(nfor.Cond, nil)
nfor.Post = typecheck.Stmt(nfor.Post)
typecheck.Stmts(body)
nfor.Body.Append(body...)
nfor.Body.Append(nrange.Body...)
var n ir.Node = nfor
if ifGuard != nil {
ifGuard.Body = []ir.Node{n}
n = ifGuard
}
n = walkStmt(n)
base.Pos = 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 *ir.RangeStmt) bool {
if base.Flag.N != 0 || base.Flag.Cfg.Instrumenting {
return false
}
t := n.X.Type()
if n.Op() != ir.ORANGE || t.Kind() != types.TMAP || n.Key == nil || n.Value != nil {
return false
}
k := n.Key
// Require k to be a new variable name.
if !ir.DeclaredBy(k, n) {
return false
}
if len(n.Body) != 1 {
return false
}
stmt := n.Body[0] // only stmt in body
if stmt == nil || stmt.Op() != ir.ODELETE {
return false
}
m := n.X
if delete := stmt.(*ir.CallExpr); !ir.SameSafeExpr(delete.Args[0], m) || !ir.SameSafeExpr(delete.Args[1], k) {
return false
}
// Keys where equality is not reflexive can not be deleted from maps.
if !types.IsReflexive(t.Key()) {
return false
}
return true
}
// mapClear constructs a call to runtime.mapclear for the map m.
func mapClear(m ir.Node) ir.Node {
t := m.Type()
// instantiate mapclear(typ *type, hmap map[any]any)
fn := typecheck.LookupRuntime("mapclear")
fn = typecheck.SubstArgTypes(fn, t.Key(), t.Elem())
n := mkcallstmt1(fn, reflectdata.TypePtr(t), m)
return walkStmt(typecheck.Stmt(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(loop *ir.RangeStmt, v1, v2, a ir.Node) ir.Node {
if base.Flag.N != 0 || base.Flag.Cfg.Instrumenting {
return nil
}
if v1 == nil || v2 != nil {
return nil
}
if len(loop.Body) != 1 || loop.Body[0] == nil {
return nil
}
stmt1 := loop.Body[0] // only stmt in body
if stmt1.Op() != ir.OAS {
return nil
}
stmt := stmt1.(*ir.AssignStmt)
if stmt.X.Op() != ir.OINDEX {
return nil
}
lhs := stmt.X.(*ir.IndexExpr)
x := lhs.X
if a.Type().IsPtr() && a.Type().Elem().IsArray() {
if s, ok := x.(*ir.StarExpr); ok && s.Op() == ir.ODEREF {
x = s.X
}
}
if !ir.SameSafeExpr(x, a) || !ir.SameSafeExpr(lhs.Index, v1) {
return nil
}
elemsize := typecheck.RangeExprType(loop.X.Type()).Elem().Size()
if elemsize <= 0 || !ir.IsZero(stmt.Y) {
return nil
}
// 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 := ir.NewIfStmt(base.Pos, nil, nil, nil)
n.Cond = ir.NewBinaryExpr(base.Pos, ir.ONE, ir.NewUnaryExpr(base.Pos, ir.OLEN, a), ir.NewInt(0))
// hp = &a[0]
hp := typecheck.Temp(types.Types[types.TUNSAFEPTR])
ix := ir.NewIndexExpr(base.Pos, a, ir.NewInt(0))
ix.SetBounded(true)
addr := typecheck.ConvNop(typecheck.NodAddr(ix), types.Types[types.TUNSAFEPTR])
n.Body.Append(ir.NewAssignStmt(base.Pos, hp, addr))
// hn = len(a) * sizeof(elem(a))
hn := typecheck.Temp(types.Types[types.TUINTPTR])
mul := typecheck.Conv(ir.NewBinaryExpr(base.Pos, ir.OMUL, ir.NewUnaryExpr(base.Pos, ir.OLEN, a), ir.NewInt(elemsize)), types.Types[types.TUINTPTR])
n.Body.Append(ir.NewAssignStmt(base.Pos, hn, mul))
var fn ir.Node
if a.Type().Elem().HasPointers() {
// memclrHasPointers(hp, hn)
ir.CurFunc.SetWBPos(stmt.Pos())
fn = mkcallstmt("memclrHasPointers", hp, hn)
} else {
// memclrNoHeapPointers(hp, hn)
fn = mkcallstmt("memclrNoHeapPointers", hp, hn)
}
n.Body.Append(fn)
// i = len(a) - 1
v1 = ir.NewAssignStmt(base.Pos, v1, ir.NewBinaryExpr(base.Pos, ir.OSUB, ir.NewUnaryExpr(base.Pos, ir.OLEN, a), ir.NewInt(1)))
n.Body.Append(v1)
n.Cond = typecheck.Expr(n.Cond)
n.Cond = typecheck.DefaultLit(n.Cond, nil)
typecheck.Stmts(n.Body)
return walkStmt(n)
}
// addptr returns (*T)(uintptr(p) + n).
func addptr(p ir.Node, n int64) ir.Node {
t := p.Type()
p = ir.NewConvExpr(base.Pos, ir.OCONVNOP, nil, p)
p.SetType(types.Types[types.TUINTPTR])
p = ir.NewBinaryExpr(base.Pos, ir.OADD, p, ir.NewInt(n))
p = ir.NewConvExpr(base.Pos, ir.OCONVNOP, nil, p)
p.SetType(t)
return p
}
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