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esc.go
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esc.go
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// Copyright 2011 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"
"fmt"
"strconv"
"strings"
)
// Run analysis on minimal sets of mutually recursive functions
// or single non-recursive functions, bottom up.
//
// Finding these sets is finding strongly connected components
// by reverse topological order in the static call graph.
// The algorithm (known as Tarjan's algorithm) for doing that is taken from
// Sedgewick, Algorithms, Second Edition, p. 482, with two adaptations.
//
// First, a hidden closure function (n.Func.IsHiddenClosure()) cannot be the
// root of a connected component. Refusing to use it as a root
// forces it into the component of the function in which it appears.
// This is more convenient for escape analysis.
//
// Second, each function becomes two virtual nodes in the graph,
// with numbers n and n+1. We record the function's node number as n
// but search from node n+1. If the search tells us that the component
// number (min) is n+1, we know that this is a trivial component: one function
// plus its closures. If the search tells us that the component number is
// n, then there was a path from node n+1 back to node n, meaning that
// the function set is mutually recursive. The escape analysis can be
// more precise when analyzing a single non-recursive function than
// when analyzing a set of mutually recursive functions.
type bottomUpVisitor struct {
analyze func([]*Node, bool)
visitgen uint32
nodeID map[*Node]uint32
stack []*Node
}
// visitBottomUp invokes analyze on the ODCLFUNC nodes listed in list.
// It calls analyze with successive groups of functions, working from
// the bottom of the call graph upward. Each time analyze is called with
// a list of functions, every function on that list only calls other functions
// on the list or functions that have been passed in previous invocations of
// analyze. Closures appear in the same list as their outer functions.
// The lists are as short as possible while preserving those requirements.
// (In a typical program, many invocations of analyze will be passed just
// a single function.) The boolean argument 'recursive' passed to analyze
// specifies whether the functions on the list are mutually recursive.
// If recursive is false, the list consists of only a single function and its closures.
// If recursive is true, the list may still contain only a single function,
// if that function is itself recursive.
func visitBottomUp(list []*Node, analyze func(list []*Node, recursive bool)) {
var v bottomUpVisitor
v.analyze = analyze
v.nodeID = make(map[*Node]uint32)
for _, n := range list {
if n.Op == ODCLFUNC && !n.Func.IsHiddenClosure() {
v.visit(n)
}
}
}
func (v *bottomUpVisitor) visit(n *Node) uint32 {
if id := v.nodeID[n]; id > 0 {
// already visited
return id
}
v.visitgen++
id := v.visitgen
v.nodeID[n] = id
v.visitgen++
min := v.visitgen
v.stack = append(v.stack, n)
min = v.visitcodelist(n.Nbody, min)
if (min == id || min == id+1) && !n.Func.IsHiddenClosure() {
// This node is the root of a strongly connected component.
// The original min passed to visitcodelist was v.nodeID[n]+1.
// If visitcodelist found its way back to v.nodeID[n], then this
// block is a set of mutually recursive functions.
// Otherwise it's just a lone function that does not recurse.
recursive := min == id
// Remove connected component from stack.
// Mark walkgen so that future visits return a large number
// so as not to affect the caller's min.
var i int
for i = len(v.stack) - 1; i >= 0; i-- {
x := v.stack[i]
if x == n {
break
}
v.nodeID[x] = ^uint32(0)
}
v.nodeID[n] = ^uint32(0)
block := v.stack[i:]
// Run escape analysis on this set of functions.
v.stack = v.stack[:i]
v.analyze(block, recursive)
}
return min
}
func (v *bottomUpVisitor) visitcodelist(l Nodes, min uint32) uint32 {
for _, n := range l.Slice() {
min = v.visitcode(n, min)
}
return min
}
func (v *bottomUpVisitor) visitcode(n *Node, min uint32) uint32 {
if n == nil {
return min
}
min = v.visitcodelist(n.Ninit, min)
min = v.visitcode(n.Left, min)
min = v.visitcode(n.Right, min)
min = v.visitcodelist(n.List, min)
min = v.visitcodelist(n.Nbody, min)
min = v.visitcodelist(n.Rlist, min)
switch n.Op {
case OCALLFUNC, OCALLMETH:
fn := asNode(n.Left.Type.Nname())
if fn != nil && fn.Op == ONAME && fn.Class() == PFUNC && fn.Name.Defn != nil {
m := v.visit(fn.Name.Defn)
if m < min {
min = m
}
}
case OCLOSURE:
m := v.visit(n.Func.Closure)
if m < min {
min = m
}
}
return min
}
// Escape analysis.
// An escape analysis pass for a set of functions.
// The analysis assumes that closures and the functions in which they
// appear are analyzed together, so that the aliasing between their
// variables can be modeled more precisely.
//
// First escfunc, esc and escassign recurse over the ast of each
// function to dig out flow(dst,src) edges between any
// pointer-containing nodes and store them in e.nodeEscState(dst).Flowsrc. For
// variables assigned to a variable in an outer scope or used as a
// return value, they store a flow(theSink, src) edge to a fake node
// 'the Sink'. For variables referenced in closures, an edge
// flow(closure, &var) is recorded and the flow of a closure itself to
// an outer scope is tracked the same way as other variables.
//
// Then escflood walks the graph starting at theSink and tags all
// variables of it can reach an & node as escaping and all function
// parameters it can reach as leaking.
//
// If a value's address is taken but the address does not escape,
// then the value can stay on the stack. If the value new(T) does
// not escape, then new(T) can be rewritten into a stack allocation.
// The same is true of slice literals.
func escapes(all []*Node) {
visitBottomUp(all, escAnalyze)
}
const (
EscFuncUnknown = 0 + iota
EscFuncPlanned
EscFuncStarted
EscFuncTagged
)
// There appear to be some loops in the escape graph, causing
// arbitrary recursion into deeper and deeper levels.
// Cut this off safely by making minLevel sticky: once you
// get that deep, you cannot go down any further but you also
// cannot go up any further. This is a conservative fix.
// Making minLevel smaller (more negative) would handle more
// complex chains of indirections followed by address-of operations,
// at the cost of repeating the traversal once for each additional
// allowed level when a loop is encountered. Using -2 suffices to
// pass all the tests we have written so far, which we assume matches
// the level of complexity we want the escape analysis code to handle.
const MinLevel = -2
// A Level encodes the reference state and context applied to
// (stack, heap) allocated memory.
//
// value is the overall sum of *(1) and &(-1) operations encountered
// along a path from a destination (sink, return value) to a source
// (allocation, parameter).
//
// suffixValue is the maximum-copy-started-suffix-level applied to a sink.
// For example:
// sink = x.left.left --> level=2, x is dereferenced twice and does not escape to sink.
// sink = &Node{x} --> level=-1, x is accessible from sink via one "address of"
// sink = &Node{&Node{x}} --> level=-2, x is accessible from sink via two "address of"
// sink = &Node{&Node{x.left}} --> level=-1, but x is NOT accessible from sink because it was indirected and then copied.
// (The copy operations are sometimes implicit in the source code; in this case,
// value of x.left was copied into a field of a newly allocated Node)
//
// There's one of these for each Node, and the integer values
// rarely exceed even what can be stored in 4 bits, never mind 8.
type Level struct {
value, suffixValue int8
}
func (l Level) int() int {
return int(l.value)
}
func levelFrom(i int) Level {
if i <= MinLevel {
return Level{value: MinLevel}
}
return Level{value: int8(i)}
}
func satInc8(x int8) int8 {
if x == 127 {
return 127
}
return x + 1
}
func min8(a, b int8) int8 {
if a < b {
return a
}
return b
}
func max8(a, b int8) int8 {
if a > b {
return a
}
return b
}
// inc returns the level l + 1, representing the effect of an indirect (*) operation.
func (l Level) inc() Level {
if l.value <= MinLevel {
return Level{value: MinLevel}
}
return Level{value: satInc8(l.value), suffixValue: satInc8(l.suffixValue)}
}
// dec returns the level l - 1, representing the effect of an address-of (&) operation.
func (l Level) dec() Level {
if l.value <= MinLevel {
return Level{value: MinLevel}
}
return Level{value: l.value - 1, suffixValue: l.suffixValue - 1}
}
// copy returns the level for a copy of a value with level l.
func (l Level) copy() Level {
return Level{value: l.value, suffixValue: max8(l.suffixValue, 0)}
}
func (l1 Level) min(l2 Level) Level {
return Level{
value: min8(l1.value, l2.value),
suffixValue: min8(l1.suffixValue, l2.suffixValue)}
}
// guaranteedDereference returns the number of dereferences
// applied to a pointer before addresses are taken/generated.
// This is the maximum level computed from path suffixes starting
// with copies where paths flow from destination to source.
func (l Level) guaranteedDereference() int {
return int(l.suffixValue)
}
// An EscStep documents one step in the path from memory
// that is heap allocated to the (alleged) reason for the
// heap allocation.
type EscStep struct {
src, dst *Node // the endpoints of this edge in the escape-to-heap chain.
where *Node // sometimes the endpoints don't match source locations; set 'where' to make that right
parent *EscStep // used in flood to record path
why string // explanation for this step in the escape-to-heap chain
busy bool // used in prevent to snip cycles.
}
type NodeEscState struct {
Curfn *Node
Flowsrc []EscStep // flow(this, src)
Retval Nodes // on OCALLxxx, list of dummy return values
Loopdepth int32 // -1: global, 0: return variables, 1:function top level, increased inside function for every loop or label to mark scopes
Level Level
Walkgen uint32
Maxextraloopdepth int32
}
func (e *EscState) nodeEscState(n *Node) *NodeEscState {
if nE, ok := n.Opt().(*NodeEscState); ok {
return nE
}
if n.Opt() != nil {
Fatalf("nodeEscState: opt in use (%T)", n.Opt())
}
nE := &NodeEscState{
Curfn: Curfn,
}
n.SetOpt(nE)
e.opts = append(e.opts, n)
return nE
}
func (e *EscState) track(n *Node) {
if Curfn == nil {
Fatalf("EscState.track: Curfn nil")
}
n.Esc = EscNone // until proven otherwise
nE := e.nodeEscState(n)
nE.Loopdepth = e.loopdepth
e.noesc = append(e.noesc, n)
}
// Escape constants are numbered in order of increasing "escapiness"
// to help make inferences be monotonic. With the exception of
// EscNever which is sticky, eX < eY means that eY is more exposed
// than eX, and hence replaces it in a conservative analysis.
const (
EscUnknown = iota
EscNone // Does not escape to heap, result, or parameters.
EscReturn // Is returned or reachable from returned.
EscHeap // Reachable from the heap
EscNever // By construction will not escape.
EscBits = 3
EscMask = (1 << EscBits) - 1
EscContentEscapes = 1 << EscBits // value obtained by indirect of parameter escapes to heap
EscReturnBits = EscBits + 1
// Node.esc encoding = | escapeReturnEncoding:(width-4) | contentEscapes:1 | escEnum:3
)
// escMax returns the maximum of an existing escape value
// (and its additional parameter flow flags) and a new escape type.
func escMax(e, etype uint16) uint16 {
if e&EscMask >= EscHeap {
// normalize
if e&^EscMask != 0 {
Fatalf("Escape information had unexpected return encoding bits (w/ EscHeap, EscNever), e&EscMask=%v", e&EscMask)
}
}
if e&EscMask > etype {
return e
}
if etype == EscNone || etype == EscReturn {
return (e &^ EscMask) | etype
}
return etype
}
// For each input parameter to a function, the escapeReturnEncoding describes
// how the parameter may leak to the function's outputs. This is currently the
// "level" of the leak where level is 0 or larger (negative level means stored into
// something whose address is returned -- but that implies stored into the heap,
// hence EscHeap, which means that the details are not currently relevant. )
const (
bitsPerOutputInTag = 3 // For each output, the number of bits for a tag
bitsMaskForTag = uint16(1<<bitsPerOutputInTag) - 1 // The bit mask to extract a single tag.
maxEncodedLevel = int(bitsMaskForTag - 1) // The largest level that can be stored in a tag.
)
type EscState struct {
// Fake node that all
// - return values and output variables
// - parameters on imported functions not marked 'safe'
// - assignments to global variables
// flow to.
theSink Node
dsts []*Node // all dst nodes
loopdepth int32 // for detecting nested loop scopes
pdepth int // for debug printing in recursions.
dstcount int // diagnostic
edgecount int // diagnostic
noesc []*Node // list of possible non-escaping nodes, for printing
recursive bool // recursive function or group of mutually recursive functions.
opts []*Node // nodes with .Opt initialized
walkgen uint32
}
func newEscState(recursive bool) *EscState {
e := new(EscState)
e.theSink.Op = ONAME
e.theSink.Orig = &e.theSink
e.theSink.SetClass(PEXTERN)
e.theSink.Sym = lookup(".sink")
e.nodeEscState(&e.theSink).Loopdepth = -1
e.recursive = recursive
return e
}
func (e *EscState) stepWalk(dst, src *Node, why string, parent *EscStep) *EscStep {
// TODO: keep a cache of these, mark entry/exit in escwalk to avoid allocation
// Or perhaps never mind, since it is disabled unless printing is on.
// We may want to revisit this, since the EscStep nodes would make
// an excellent replacement for the poorly-separated graph-build/graph-flood
// stages.
if Debug['m'] == 0 {
return nil
}
return &EscStep{src: src, dst: dst, why: why, parent: parent}
}
func (e *EscState) stepAssign(step *EscStep, dst, src *Node, why string) *EscStep {
if Debug['m'] == 0 {
return nil
}
if step != nil { // Caller may have known better.
if step.why == "" {
step.why = why
}
if step.dst == nil {
step.dst = dst
}
if step.src == nil {
step.src = src
}
return step
}
return &EscStep{src: src, dst: dst, why: why}
}
func (e *EscState) stepAssignWhere(dst, src *Node, why string, where *Node) *EscStep {
if Debug['m'] == 0 {
return nil
}
return &EscStep{src: src, dst: dst, why: why, where: where}
}
// funcSym returns fn.Func.Nname.Sym if no nils are encountered along the way.
func funcSym(fn *Node) *types.Sym {
if fn == nil || fn.Func.Nname == nil {
return nil
}
return fn.Func.Nname.Sym
}
// curfnSym returns n.Curfn.Nname.Sym if no nils are encountered along the way.
func (e *EscState) curfnSym(n *Node) *types.Sym {
nE := e.nodeEscState(n)
return funcSym(nE.Curfn)
}
func escAnalyze(all []*Node, recursive bool) {
e := newEscState(recursive)
for _, n := range all {
if n.Op == ODCLFUNC {
n.Esc = EscFuncPlanned
if Debug['m'] > 3 {
Dump("escAnalyze", n)
}
}
}
// flow-analyze functions
for _, n := range all {
if n.Op == ODCLFUNC {
e.escfunc(n)
}
}
// print("escapes: %d e.dsts, %d edges\n", e.dstcount, e.edgecount);
// visit the upstream of each dst, mark address nodes with
// addrescapes, mark parameters unsafe
escapes := make([]uint16, len(e.dsts))
for i, n := range e.dsts {
escapes[i] = n.Esc
}
for _, n := range e.dsts {
e.escflood(n)
}
for {
done := true
for i, n := range e.dsts {
if n.Esc != escapes[i] {
done = false
if Debug['m'] > 2 {
Warnl(n.Pos, "Reflooding %v %S", e.curfnSym(n), n)
}
escapes[i] = n.Esc
e.escflood(n)
}
}
if done {
break
}
}
// for all top level functions, tag the typenodes corresponding to the param nodes
for _, n := range all {
if n.Op == ODCLFUNC {
e.esctag(n)
}
}
if Debug['m'] != 0 {
for _, n := range e.noesc {
if n.Esc == EscNone {
Warnl(n.Pos, "%v %S does not escape", e.curfnSym(n), n)
}
}
}
for _, x := range e.opts {
x.SetOpt(nil)
}
}
func (e *EscState) escfunc(fn *Node) {
// print("escfunc %N %s\n", fn.Func.Nname, e.recursive?"(recursive)":"");
if fn.Esc != EscFuncPlanned {
Fatalf("repeat escfunc %v", fn.Func.Nname)
}
fn.Esc = EscFuncStarted
saveld := e.loopdepth
e.loopdepth = 1
savefn := Curfn
Curfn = fn
for _, ln := range Curfn.Func.Dcl {
if ln.Op != ONAME {
continue
}
lnE := e.nodeEscState(ln)
switch ln.Class() {
// out params are in a loopdepth between the sink and all local variables
case PPARAMOUT:
lnE.Loopdepth = 0
case PPARAM:
lnE.Loopdepth = 1
if ln.Type != nil && !types.Haspointers(ln.Type) {
break
}
if Curfn.Nbody.Len() == 0 && !Curfn.Noescape() {
ln.Esc = EscHeap
} else {
ln.Esc = EscNone // prime for escflood later
}
e.noesc = append(e.noesc, ln)
}
}
// in a mutually recursive group we lose track of the return values
if e.recursive {
for _, ln := range Curfn.Func.Dcl {
if ln.Op == ONAME && ln.Class() == PPARAMOUT {
e.escflows(&e.theSink, ln, e.stepAssign(nil, ln, ln, "returned from recursive function"))
}
}
}
e.escloopdepthlist(Curfn.Nbody)
e.esclist(Curfn.Nbody, Curfn)
Curfn = savefn
e.loopdepth = saveld
}
// Mark labels that have no backjumps to them as not increasing e.loopdepth.
// Walk hasn't generated (goto|label).Left.Sym.Label yet, so we'll cheat
// and set it to one of the following two. Then in esc we'll clear it again.
var (
looping Node
nonlooping Node
)
func (e *EscState) escloopdepthlist(l Nodes) {
for _, n := range l.Slice() {
e.escloopdepth(n)
}
}
func (e *EscState) escloopdepth(n *Node) {
if n == nil {
return
}
e.escloopdepthlist(n.Ninit)
switch n.Op {
case OLABEL:
if n.Left == nil || n.Left.Sym == nil {
Fatalf("esc:label without label: %+v", n)
}
// Walk will complain about this label being already defined, but that's not until
// after escape analysis. in the future, maybe pull label & goto analysis out of walk and put before esc
// if(n.Left.Sym.Label != nil)
// fatal("escape analysis messed up analyzing label: %+N", n);
n.Left.Sym.Label = asTypesNode(&nonlooping)
case OGOTO:
if n.Left == nil || n.Left.Sym == nil {
Fatalf("esc:goto without label: %+v", n)
}
// If we come past one that's uninitialized, this must be a (harmless) forward jump
// but if it's set to nonlooping the label must have preceded this goto.
if asNode(n.Left.Sym.Label) == &nonlooping {
n.Left.Sym.Label = asTypesNode(&looping)
}
}
e.escloopdepth(n.Left)
e.escloopdepth(n.Right)
e.escloopdepthlist(n.List)
e.escloopdepthlist(n.Nbody)
e.escloopdepthlist(n.Rlist)
}
func (e *EscState) esclist(l Nodes, parent *Node) {
for _, n := range l.Slice() {
e.esc(n, parent)
}
}
func (e *EscState) esc(n *Node, parent *Node) {
if n == nil {
return
}
lno := setlineno(n)
// ninit logically runs at a different loopdepth than the rest of the for loop.
e.esclist(n.Ninit, n)
if n.Op == OFOR || n.Op == OFORUNTIL || n.Op == ORANGE {
e.loopdepth++
}
// type switch variables have no ODCL.
// process type switch as declaration.
// must happen before processing of switch body,
// so before recursion.
if n.Op == OSWITCH && n.Left != nil && n.Left.Op == OTYPESW {
for _, cas := range n.List.Slice() { // cases
// it.N().Rlist is the variable per case
if cas.Rlist.Len() != 0 {
e.nodeEscState(cas.Rlist.First()).Loopdepth = e.loopdepth
}
}
}
// Big stuff escapes unconditionally
// "Big" conditions that were scattered around in walk have been gathered here
if n.Esc != EscHeap && n.Type != nil &&
(n.Type.Width > maxStackVarSize ||
(n.Op == ONEW || n.Op == OPTRLIT) && n.Type.Elem().Width >= 1<<16 ||
n.Op == OMAKESLICE && !isSmallMakeSlice(n)) {
if Debug['m'] > 2 {
Warnl(n.Pos, "%v is too large for stack", n)
}
n.Esc = EscHeap
addrescapes(n)
e.escassignSinkWhy(n, n, "too large for stack") // TODO category: tooLarge
}
e.esc(n.Left, n)
if n.Op == ORANGE {
// ORANGE node's Right is evaluated before the loop
e.loopdepth--
}
e.esc(n.Right, n)
if n.Op == ORANGE {
e.loopdepth++
}
e.esclist(n.Nbody, n)
e.esclist(n.List, n)
e.esclist(n.Rlist, n)
if n.Op == OFOR || n.Op == OFORUNTIL || n.Op == ORANGE {
e.loopdepth--
}
if Debug['m'] > 2 {
fmt.Printf("%v:[%d] %v esc: %v\n", linestr(lineno), e.loopdepth, funcSym(Curfn), n)
}
switch n.Op {
// Record loop depth at declaration.
case ODCL:
if n.Left != nil {
e.nodeEscState(n.Left).Loopdepth = e.loopdepth
}
case OLABEL:
if asNode(n.Left.Sym.Label) == &nonlooping {
if Debug['m'] > 2 {
fmt.Printf("%v:%v non-looping label\n", linestr(lineno), n)
}
} else if asNode(n.Left.Sym.Label) == &looping {
if Debug['m'] > 2 {
fmt.Printf("%v: %v looping label\n", linestr(lineno), n)
}
e.loopdepth++
}
// See case OLABEL in escloopdepth above
// else if(n.Left.Sym.Label == nil)
// fatal("escape analysis missed or messed up a label: %+N", n);
n.Left.Sym.Label = nil
case ORANGE:
if n.List.Len() >= 2 {
// Everything but fixed array is a dereference.
// If fixed array is really the address of fixed array,
// it is also a dereference, because it is implicitly
// dereferenced (see #12588)
if n.Type.IsArray() &&
!(n.Right.Type.IsPtr() && eqtype(n.Right.Type.Elem(), n.Type)) {
e.escassignWhyWhere(n.List.Second(), n.Right, "range", n)
} else {
e.escassignDereference(n.List.Second(), n.Right, e.stepAssignWhere(n.List.Second(), n.Right, "range-deref", n))
}
}
case OSWITCH:
if n.Left != nil && n.Left.Op == OTYPESW {
for _, cas := range n.List.Slice() {
// cases
// n.Left.Right is the argument of the .(type),
// it.N().Rlist is the variable per case
if cas.Rlist.Len() != 0 {
e.escassignWhyWhere(cas.Rlist.First(), n.Left.Right, "switch case", n)
}
}
}
// Filter out the following special case.
//
// func (b *Buffer) Foo() {
// n, m := ...
// b.buf = b.buf[n:m]
// }
//
// This assignment is a no-op for escape analysis,
// it does not store any new pointers into b that were not already there.
// However, without this special case b will escape, because we assign to OIND/ODOTPTR.
case OAS, OASOP:
if (n.Left.Op == OIND || n.Left.Op == ODOTPTR) && n.Left.Left.Op == ONAME && // dst is ONAME dereference
(n.Right.Op == OSLICE || n.Right.Op == OSLICE3 || n.Right.Op == OSLICESTR) && // src is slice operation
(n.Right.Left.Op == OIND || n.Right.Left.Op == ODOTPTR) && n.Right.Left.Left.Op == ONAME && // slice is applied to ONAME dereference
n.Left.Left == n.Right.Left.Left { // dst and src reference the same base ONAME
// Here we also assume that the statement will not contain calls,
// that is, that order will move any calls to init.
// Otherwise base ONAME value could change between the moments
// when we evaluate it for dst and for src.
//
// Note, this optimization does not apply to OSLICEARR,
// because it does introduce a new pointer into b that was not already there
// (pointer to b itself). After such assignment, if b contents escape,
// b escapes as well. If we ignore such OSLICEARR, we will conclude
// that b does not escape when b contents do.
if Debug['m'] != 0 {
Warnl(n.Pos, "%v ignoring self-assignment to %S", e.curfnSym(n), n.Left)
}
break
}
e.escassign(n.Left, n.Right, e.stepAssignWhere(nil, nil, "", n))
case OAS2: // x,y = a,b
if n.List.Len() == n.Rlist.Len() {
rs := n.Rlist.Slice()
for i, n := range n.List.Slice() {
e.escassignWhyWhere(n, rs[i], "assign-pair", n)
}
}
case OAS2RECV: // v, ok = <-ch
e.escassignWhyWhere(n.List.First(), n.Rlist.First(), "assign-pair-receive", n)
case OAS2MAPR: // v, ok = m[k]
e.escassignWhyWhere(n.List.First(), n.Rlist.First(), "assign-pair-mapr", n)
case OAS2DOTTYPE: // v, ok = x.(type)
e.escassignWhyWhere(n.List.First(), n.Rlist.First(), "assign-pair-dot-type", n)
case OSEND: // ch <- x
e.escassignSinkWhy(n, n.Right, "send")
case ODEFER:
if e.loopdepth == 1 { // top level
break
}
// arguments leak out of scope
// TODO: leak to a dummy node instead
// defer f(x) - f and x escape
e.escassignSinkWhy(n, n.Left.Left, "defer func")
e.escassignSinkWhy(n, n.Left.Right, "defer func ...") // ODDDARG for call
for _, arg := range n.Left.List.Slice() {
e.escassignSinkWhy(n, arg, "defer func arg")
}
case OPROC:
// go f(x) - f and x escape
e.escassignSinkWhy(n, n.Left.Left, "go func")
e.escassignSinkWhy(n, n.Left.Right, "go func ...") // ODDDARG for call
for _, arg := range n.Left.List.Slice() {
e.escassignSinkWhy(n, arg, "go func arg")
}
case OCALLMETH, OCALLFUNC, OCALLINTER:
e.esccall(n, parent)
// esccall already done on n.Rlist.First(). tie it's Retval to n.List
case OAS2FUNC: // x,y = f()
rs := e.nodeEscState(n.Rlist.First()).Retval.Slice()
for i, n := range n.List.Slice() {
if i >= len(rs) {
break
}
e.escassignWhyWhere(n, rs[i], "assign-pair-func-call", n)
}
if n.List.Len() != len(rs) {
Fatalf("esc oas2func")
}
case ORETURN:
retList := n.List
if retList.Len() == 1 && Curfn.Type.NumResults() > 1 {
// OAS2FUNC in disguise
// esccall already done on n.List.First()
// tie e.nodeEscState(n.List.First()).Retval to Curfn.Func.Dcl PPARAMOUT's
retList = e.nodeEscState(n.List.First()).Retval
}
i := 0
for _, lrn := range Curfn.Func.Dcl {
if i >= retList.Len() {
break
}
if lrn.Op != ONAME || lrn.Class() != PPARAMOUT {
continue
}
e.escassignWhyWhere(lrn, retList.Index(i), "return", n)
i++
}
if i < retList.Len() {
Fatalf("esc return list")
}
// Argument could leak through recover.
case OPANIC:
e.escassignSinkWhy(n, n.Left, "panic")
case OAPPEND:
if !n.Isddd() {
for _, nn := range n.List.Slice()[1:] {
e.escassignSinkWhy(n, nn, "appended to slice") // lose track of assign to dereference
}
} else {
// append(slice1, slice2...) -- slice2 itself does not escape, but contents do.
slice2 := n.List.Second()
e.escassignDereference(&e.theSink, slice2, e.stepAssignWhere(n, slice2, "appended slice...", n)) // lose track of assign of dereference
if Debug['m'] > 3 {
Warnl(n.Pos, "%v special treatment of append(slice1, slice2...) %S", e.curfnSym(n), n)
}
}
e.escassignDereference(&e.theSink, n.List.First(), e.stepAssignWhere(n, n.List.First(), "appendee slice", n)) // The original elements are now leaked, too
case OCOPY:
e.escassignDereference(&e.theSink, n.Right, e.stepAssignWhere(n, n.Right, "copied slice", n)) // lose track of assign of dereference
case OCONV, OCONVNOP:
e.escassignWhyWhere(n, n.Left, "converted", n)
case OCONVIFACE:
e.track(n)
e.escassignWhyWhere(n, n.Left, "interface-converted", n)
case OARRAYLIT:
// Link values to array
for _, elt := range n.List.Slice() {
if elt.Op == OKEY {
elt = elt.Right
}
e.escassign(n, elt, e.stepAssignWhere(n, elt, "array literal element", n))
}
case OSLICELIT:
// Slice is not leaked until proven otherwise
e.track(n)
// Link values to slice
for _, elt := range n.List.Slice() {
if elt.Op == OKEY {
elt = elt.Right
}
e.escassign(n, elt, e.stepAssignWhere(n, elt, "slice literal element", n))
}
// Link values to struct.
case OSTRUCTLIT:
for _, elt := range n.List.Slice() {
e.escassignWhyWhere(n, elt.Left, "struct literal element", n)
}
case OPTRLIT:
e.track(n)
// Link OSTRUCTLIT to OPTRLIT; if OPTRLIT escapes, OSTRUCTLIT elements do too.
e.escassignWhyWhere(n, n.Left, "pointer literal [assign]", n)
case OCALLPART:
e.track(n)
// Contents make it to memory, lose track.
e.escassignSinkWhy(n, n.Left, "call part")
case OMAPLIT:
e.track(n)
// Keys and values make it to memory, lose track.
for _, elt := range n.List.Slice() {
e.escassignSinkWhy(n, elt.Left, "map literal key")
e.escassignSinkWhy(n, elt.Right, "map literal value")
}
case OCLOSURE:
// Link addresses of captured variables to closure.
for _, v := range n.Func.Cvars.Slice() {
if v.Op == OXXX { // unnamed out argument; see dcl.go:/^funcargs
continue
}
a := v.Name.Defn
if !v.Name.Byval() {
a = nod(OADDR, a, nil)
a.Pos = v.Pos
e.nodeEscState(a).Loopdepth = e.loopdepth
a = typecheck(a, Erv)
}
e.escassignWhyWhere(n, a, "captured by a closure", n)
}
fallthrough
case OMAKECHAN,
OMAKEMAP,
OMAKESLICE,
ONEW,
OARRAYRUNESTR,
OARRAYBYTESTR,
OSTRARRAYRUNE,
OSTRARRAYBYTE,
ORUNESTR:
e.track(n)
case OADDSTR:
e.track(n)
// Arguments of OADDSTR do not escape.
case OADDR:
// current loop depth is an upper bound on actual loop depth
// of addressed value.
e.track(n)
// for &x, use loop depth of x if known.
// it should always be known, but if not, be conservative
// and keep the current loop depth.
if n.Left.Op == ONAME {
switch n.Left.Class() {
case PAUTO:
nE := e.nodeEscState(n)
leftE := e.nodeEscState(n.Left)
if leftE.Loopdepth != 0 {
nE.Loopdepth = leftE.Loopdepth
}
// PPARAM is loop depth 1 always.
// PPARAMOUT is loop depth 0 for writes