go assign 源码
golang assign 代码
文件路径：/src/cmd/compile/internal/escape/assign.go
// Copyright 2018 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 escape
import (
"cmd/compile/internal/base"
"cmd/compile/internal/ir"
)
// addr evaluates an addressable expression n and returns a hole
// that represents storing into the represented location.
func (e *escape) addr(n ir.Node) hole {
if n == nil || ir.IsBlank(n) {
// Can happen in select case, range, maybe others.
return e.discardHole()
}
k := e.heapHole()
switch n.Op() {
default:
base.Fatalf("unexpected addr: %v", n)
case ir.ONAME:
n := n.(*ir.Name)
if n.Class == ir.PEXTERN {
break
}
k = e.oldLoc(n).asHole()
case ir.OLINKSYMOFFSET:
break
case ir.ODOT:
n := n.(*ir.SelectorExpr)
k = e.addr(n.X)
case ir.OINDEX:
n := n.(*ir.IndexExpr)
e.discard(n.Index)
if n.X.Type().IsArray() {
k = e.addr(n.X)
} else {
e.discard(n.X)
}
case ir.ODEREF, ir.ODOTPTR:
e.discard(n)
case ir.OINDEXMAP:
n := n.(*ir.IndexExpr)
e.discard(n.X)
e.assignHeap(n.Index, "key of map put", n)
}
return k
}
func (e *escape) addrs(l ir.Nodes) []hole {
var ks []hole
for _, n := range l {
ks = append(ks, e.addr(n))
}
return ks
}
func (e *escape) assignHeap(src ir.Node, why string, where ir.Node) {
e.expr(e.heapHole().note(where, why), src)
}
// assignList evaluates the assignment dsts... = srcs....
func (e *escape) assignList(dsts, srcs []ir.Node, why string, where ir.Node) {
ks := e.addrs(dsts)
for i, k := range ks {
var src ir.Node
if i < len(srcs) {
src = srcs[i]
}
if dst := dsts[i]; dst != nil {
// Detect implicit conversion of uintptr to unsafe.Pointer when
// storing into reflect.{Slice,String}Header.
if dst.Op() == ir.ODOTPTR && ir.IsReflectHeaderDataField(dst) {
e.unsafeValue(e.heapHole().note(where, why), src)
continue
}
// Filter out some no-op assignments for escape analysis.
if src != nil && isSelfAssign(dst, src) {
if base.Flag.LowerM != 0 {
base.WarnfAt(where.Pos(), "%v ignoring self-assignment in %v", e.curfn, where)
}
k = e.discardHole()
}
}
e.expr(k.note(where, why), src)
}
e.reassigned(ks, where)
}
// reassigned marks the locations associated with the given holes as
// reassigned, unless the location represents a variable declared and
// assigned exactly once by where.
func (e *escape) reassigned(ks []hole, where ir.Node) {
if as, ok := where.(*ir.AssignStmt); ok && as.Op() == ir.OAS && as.Y == nil {
if dst, ok := as.X.(*ir.Name); ok && dst.Op() == ir.ONAME && dst.Defn == nil {
// Zero-value assignment for variable declared without an
// explicit initial value. Assume this is its initialization
// statement.
return
}
}
for _, k := range ks {
loc := k.dst
// Variables declared by range statements are assigned on every iteration.
if n, ok := loc.n.(*ir.Name); ok && n.Defn == where && where.Op() != ir.ORANGE {
continue
}
loc.reassigned = true
}
}
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