src/cmd/compile/internal/escape/escape.go - toolchain/go - Git at Google

 // 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 (
 	"fmt"

 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/logopt"
 	"cmd/compile/internal/typecheck"
 	"cmd/compile/internal/types"
 	"cmd/internal/src"
 )

 // Escape analysis.
 //
 // Here we analyze functions to determine which Go variables
 // (including implicit allocations such as calls to "new" or "make",
 // composite literals, etc.) can be allocated on the stack. The two
 // key invariants we have to ensure are: (1) pointers to stack objects
 // cannot be stored in the heap, and (2) pointers to a stack object
 // cannot outlive that object (e.g., because the declaring function
 // returned and destroyed the object's stack frame, or its space is
 // reused across loop iterations for logically distinct variables).
 //
 // We implement this with a static data-flow analysis of the AST.
 // First, we construct a directed weighted graph where vertices
 // (termed "locations") represent variables allocated by statements
 // and expressions, and edges represent assignments between variables
 // (with weights representing addressing/dereference counts).
 //
 // Next we walk the graph looking for assignment paths that might
 // violate the invariants stated above. If a variable v's address is
 // stored in the heap or elsewhere that may outlive it, then v is
 // marked as requiring heap allocation.
 //
 // To support interprocedural analysis, we also record data-flow from
 // each function's parameters to the heap and to its result
 // parameters. This information is summarized as "parameter tags",
 // which are used at static call sites to improve escape analysis of
 // function arguments.

 // Constructing the location graph.
 //
 // Every allocating statement (e.g., variable declaration) or
 // expression (e.g., "new" or "make") is first mapped to a unique
 // "location."
 //
 // We also model every Go assignment as a directed edges between
 // locations. The number of dereference operations minus the number of
 // addressing operations is recorded as the edge's weight (termed
 // "derefs"). For example:
 //
 //     p = &q    // -1
 //     p = q     //  0
 //     p = *q    //  1
 //     p = **q   //  2
 //
 //     p = **&**&q  // 2
 //
 // Note that the & operator can only be applied to addressable
 // expressions, and the expression &x itself is not addressable, so
 // derefs cannot go below -1.
 //
 // Every Go language construct is lowered into this representation,
 // generally without sensitivity to flow, path, or context; and
 // without distinguishing elements within a compound variable. For
 // example:
 //
 //     var x struct { f, g *int }
 //     var u []*int
 //
 //     x.f = u[0]
 //
 // is modeled simply as
 //
 //     x = *u
 //
 // That is, we don't distinguish x.f from x.g, or u[0] from u[1],
 // u[2], etc. However, we do record the implicit dereference involved
 // in indexing a slice.

 // A batch holds escape analysis state that's shared across an entire
 // batch of functions being analyzed at once.
 type batch struct {
 	allLocs  []*location
 	closures []closure

 	heapLoc    location
 	mutatorLoc location
 	calleeLoc  location
 	blankLoc   location
 }

 // A closure holds a closure expression and its spill hole (i.e.,
 // where the hole representing storing into its closure record).
 type closure struct {
 	k   hole
 	clo *ir.ClosureExpr
 }

 // An escape holds state specific to a single function being analyzed
 // within a batch.
 type escape struct {
 	*batch

 	curfn *ir.Func // function being analyzed

 	labels map[*types.Sym]labelState // known labels

 	// loopDepth counts the current loop nesting depth within
 	// curfn. It increments within each "for" loop and at each
 	// label with a corresponding backwards "goto" (i.e.,
 	// unstructured loop).
 	loopDepth int
 }

 func Funcs(all []*ir.Func) {
 	ir.VisitFuncsBottomUp(all, Batch)
 }

 // Batch performs escape analysis on a minimal batch of
 // functions.
 func Batch(fns []*ir.Func, recursive bool) {
 	var b batch
 	b.heapLoc.attrs = attrEscapes | attrPersists | attrMutates | attrCalls
 	b.mutatorLoc.attrs = attrMutates
 	b.calleeLoc.attrs = attrCalls

 	// Construct data-flow graph from syntax trees.
 	for _, fn := range fns {
 		if base.Flag.W > 1 {
 			s := fmt.Sprintf("\nbefore escape %v", fn)
 			ir.Dump(s, fn)
 		}
 		b.initFunc(fn)
 	}
 	for _, fn := range fns {
 		if !fn.IsHiddenClosure() {
 			b.walkFunc(fn)
 		}
 	}

 	// We've walked the function bodies, so we've seen everywhere a
 	// variable might be reassigned or have it's address taken. Now we
 	// can decide whether closures should capture their free variables
 	// by value or reference.
 	for _, closure := range b.closures {
 		b.flowClosure(closure.k, closure.clo)
 	}
 	b.closures = nil

 	for _, loc := range b.allLocs {
 		if why := HeapAllocReason(loc.n); why != "" {
 			b.flow(b.heapHole().addr(loc.n, why), loc)
 		}
 	}

 	b.walkAll()
 	b.finish(fns)
 }

 func (b *batch) with(fn *ir.Func) *escape {
 	return &escape{
 		batch:     b,
 		curfn:     fn,
 		loopDepth: 1,
 	}
 }

 func (b *batch) initFunc(fn *ir.Func) {
 	e := b.with(fn)
 	if fn.Esc() != escFuncUnknown {
 		base.Fatalf("unexpected node: %v", fn)
 	}
 	fn.SetEsc(escFuncPlanned)
 	if base.Flag.LowerM > 3 {
 		ir.Dump("escAnalyze", fn)
 	}

 	// Allocate locations for local variables.
 	for _, n := range fn.Dcl {
 		e.newLoc(n, true)
 	}

 	// Also for hidden parameters (e.g., the ".this" parameter to a
 	// method value wrapper).
 	if fn.OClosure == nil {
 		for _, n := range fn.ClosureVars {
 			e.newLoc(n.Canonical(), true)
 		}
 	}

 	// Initialize resultIndex for result parameters.
 	for i, f := range fn.Type().Results() {
 		e.oldLoc(f.Nname.(*ir.Name)).resultIndex = 1 + i
 	}
 }

 func (b *batch) walkFunc(fn *ir.Func) {
 	e := b.with(fn)
 	fn.SetEsc(escFuncStarted)

 	// Identify labels that mark the head of an unstructured loop.
 	ir.Visit(fn, func(n ir.Node) {
 		switch n.Op() {
 		case ir.OLABEL:
 			n := n.(*ir.LabelStmt)
 			if n.Label.IsBlank() {
 				break
 			}
 			if e.labels == nil {
 				e.labels = make(map[*types.Sym]labelState)
 			}
 			e.labels[n.Label] = nonlooping

 		case ir.OGOTO:
 			// If we visited the label before the goto,
 			// then this is a looping label.
 			n := n.(*ir.BranchStmt)
 			if e.labels[n.Label] == nonlooping {
 				e.labels[n.Label] = looping
 			}
 		}
 	})

 	e.block(fn.Body)

 	if len(e.labels) != 0 {
 		base.FatalfAt(fn.Pos(), "leftover labels after walkFunc")
 	}
 }

 func (b *batch) flowClosure(k hole, clo *ir.ClosureExpr) {
 	for _, cv := range clo.Func.ClosureVars {
 		n := cv.Canonical()
 		loc := b.oldLoc(cv)
 		if !loc.captured {
 			base.FatalfAt(cv.Pos(), "closure variable never captured: %v", cv)
 		}

 		// Capture by value for variables <= 128 bytes that are never reassigned.
 		n.SetByval(!loc.addrtaken && !loc.reassigned && n.Type().Size() <= 128)
 		if !n.Byval() {
 			n.SetAddrtaken(true)
 			if n.Sym().Name == typecheck.LocalDictName {
 				base.FatalfAt(n.Pos(), "dictionary variable not captured by value")
 			}
 		}

 		if base.Flag.LowerM > 1 {
 			how := "ref"
 			if n.Byval() {
 				how = "value"
 			}
 			base.WarnfAt(n.Pos(), "%v capturing by %s: %v (addr=%v assign=%v width=%d)", n.Curfn, how, n, loc.addrtaken, loc.reassigned, n.Type().Size())
 		}

 		// Flow captured variables to closure.
 		k := k
 		if !cv.Byval() {
 			k = k.addr(cv, "reference")
 		}
 		b.flow(k.note(cv, "captured by a closure"), loc)
 	}
 }

 func (b *batch) finish(fns []*ir.Func) {
 	// Record parameter tags for package export data.
 	for _, fn := range fns {
 		fn.SetEsc(escFuncTagged)

 		for i, param := range fn.Type().RecvParams() {
 			param.Note = b.paramTag(fn, 1+i, param)
 		}
 	}

 	for _, loc := range b.allLocs {
 		n := loc.n
 		if n == nil {
 			continue
 		}

 		if n.Op() == ir.ONAME {
 			n := n.(*ir.Name)
 			n.Opt = nil
 		}

 		// Update n.Esc based on escape analysis results.

 		// Omit escape diagnostics for go/defer wrappers, at least for now.
 		// Historically, we haven't printed them, and test cases don't expect them.
 		// TODO(mdempsky): Update tests to expect this.
 		goDeferWrapper := n.Op() == ir.OCLOSURE && n.(*ir.ClosureExpr).Func.Wrapper()

 		if loc.hasAttr(attrEscapes) {
 			if n.Op() == ir.ONAME {
 				if base.Flag.CompilingRuntime {
 					base.ErrorfAt(n.Pos(), 0, "%v escapes to heap, not allowed in runtime", n)
 				}
 				if base.Flag.LowerM != 0 {
 					base.WarnfAt(n.Pos(), "moved to heap: %v", n)
 				}
 			} else {
 				if base.Flag.LowerM != 0 && !goDeferWrapper {
 					base.WarnfAt(n.Pos(), "%v escapes to heap", n)
 				}
 				if logopt.Enabled() {
 					var e_curfn *ir.Func // TODO(mdempsky): Fix.
 					logopt.LogOpt(n.Pos(), "escape", "escape", ir.FuncName(e_curfn))
 				}
 			}
 			n.SetEsc(ir.EscHeap)
 		} else {
 			if base.Flag.LowerM != 0 && n.Op() != ir.ONAME && !goDeferWrapper {
 				base.WarnfAt(n.Pos(), "%v does not escape", n)
 			}
 			n.SetEsc(ir.EscNone)
 			if !loc.hasAttr(attrPersists) {
 				switch n.Op() {
 				case ir.OCLOSURE:
 					n := n.(*ir.ClosureExpr)
 					n.SetTransient(true)
 				case ir.OMETHVALUE:
 					n := n.(*ir.SelectorExpr)
 					n.SetTransient(true)
 				case ir.OSLICELIT:
 					n := n.(*ir.CompLitExpr)
 					n.SetTransient(true)
 				}
 			}
 		}

 		// If the result of a string->[]byte conversion is never mutated,
 		// then it can simply reuse the string's memory directly.
 		if base.Debug.ZeroCopy != 0 {
 			if n, ok := n.(*ir.ConvExpr); ok && n.Op() == ir.OSTR2BYTES && !loc.hasAttr(attrMutates) {
 				if base.Flag.LowerM >= 1 {
 					base.WarnfAt(n.Pos(), "zero-copy string->[]byte conversion")
 				}
 				n.SetOp(ir.OSTR2BYTESTMP)
 			}
 		}
 	}
 }

 // inMutualBatch reports whether function fn is in the batch of
 // mutually recursive functions being analyzed. When this is true,
 // fn has not yet been analyzed, so its parameters and results
 // should be incorporated directly into the flow graph instead of
 // relying on its escape analysis tagging.
 func (b *batch) inMutualBatch(fn *ir.Name) bool {
 	if fn.Defn != nil && fn.Defn.Esc() < escFuncTagged {
 		if fn.Defn.Esc() == escFuncUnknown {
 			base.FatalfAt(fn.Pos(), "graph inconsistency: %v", fn)
 		}
 		return true
 	}
 	return false
 }

 const (
 	escFuncUnknown = 0 + iota
 	escFuncPlanned
 	escFuncStarted
 	escFuncTagged
 )

 // Mark labels that have no backjumps to them as not increasing e.loopdepth.
 type labelState int

 const (
 	looping labelState = 1 + iota
 	nonlooping
 )

 func (b *batch) paramTag(fn *ir.Func, narg int, f *types.Field) string {
 	name := func() string {
 		if f.Nname != nil {
 			return f.Nname.Sym().Name
 		}
 		return fmt.Sprintf("arg#%d", narg)
 	}

 	// Only report diagnostics for user code;
 	// not for wrappers generated around them.
 	// TODO(mdempsky): Generalize this.
 	diagnose := base.Flag.LowerM != 0 && !(fn.Wrapper() || fn.Dupok())

 	if len(fn.Body) == 0 {
 		// Assume that uintptr arguments must be held live across the call.
 		// This is most important for syscall.Syscall.
 		// See golang.org/issue/13372.
 		// This really doesn't have much to do with escape analysis per se,
 		// but we are reusing the ability to annotate an individual function
 		// argument and pass those annotations along to importing code.
 		fn.Pragma |= ir.UintptrKeepAlive

 		if f.Type.IsUintptr() {
 			if diagnose {
 				base.WarnfAt(f.Pos, "assuming %v is unsafe uintptr", name())
 			}
 			return ""
 		}

 		if !f.Type.HasPointers() { // don't bother tagging for scalars
 			return ""
 		}

 		var esc leaks

 		// External functions are assumed unsafe, unless
 		// //go:noescape is given before the declaration.
 		if fn.Pragma&ir.Noescape != 0 {
 			if diagnose && f.Sym != nil {
 				base.WarnfAt(f.Pos, "%v does not escape", name())
 			}
 			esc.AddMutator(0)
 			esc.AddCallee(0)
 		} else {
 			if diagnose && f.Sym != nil {
 				base.WarnfAt(f.Pos, "leaking param: %v", name())
 			}
 			esc.AddHeap(0)
 		}

 		return esc.Encode()
 	}

 	if fn.Pragma&ir.UintptrEscapes != 0 {
 		if f.Type.IsUintptr() {
 			if diagnose {
 				base.WarnfAt(f.Pos, "marking %v as escaping uintptr", name())
 			}
 			return ""
 		}
 		if f.IsDDD() && f.Type.Elem().IsUintptr() {
 			// final argument is ...uintptr.
 			if diagnose {
 				base.WarnfAt(f.Pos, "marking %v as escaping ...uintptr", name())
 			}
 			return ""
 		}
 	}

 	if !f.Type.HasPointers() { // don't bother tagging for scalars
 		return ""
 	}

 	// Unnamed parameters are unused and therefore do not escape.
 	if f.Sym == nil || f.Sym.IsBlank() {
 		var esc leaks
 		return esc.Encode()
 	}

 	n := f.Nname.(*ir.Name)
 	loc := b.oldLoc(n)
 	esc := loc.paramEsc
 	esc.Optimize()

 	if diagnose && !loc.hasAttr(attrEscapes) {
 		b.reportLeaks(f.Pos, name(), esc, fn.Type())
 	}

 	return esc.Encode()
 }

 func (b *batch) reportLeaks(pos src.XPos, name string, esc leaks, sig *types.Type) {
 	warned := false
 	if x := esc.Heap(); x >= 0 {
 		if x == 0 {
 			base.WarnfAt(pos, "leaking param: %v", name)
 		} else {
 			// TODO(mdempsky): Mention level=x like below?
 			base.WarnfAt(pos, "leaking param content: %v", name)
 		}
 		warned = true
 	}
 	for i := 0; i < numEscResults; i++ {
 		if x := esc.Result(i); x >= 0 {
 			res := sig.Result(i).Nname.Sym().Name
 			base.WarnfAt(pos, "leaking param: %v to result %v level=%d", name, res, x)
 			warned = true
 		}
 	}

 	if base.Debug.EscapeMutationsCalls <= 0 {
 		if !warned {
 			base.WarnfAt(pos, "%v does not escape", name)
 		}
 		return
 	}

 	if x := esc.Mutator(); x >= 0 {
 		base.WarnfAt(pos, "mutates param: %v derefs=%v", name, x)
 		warned = true
 	}
 	if x := esc.Callee(); x >= 0 {
 		base.WarnfAt(pos, "calls param: %v derefs=%v", name, x)
 		warned = true
 	}

 	if !warned {
 		base.WarnfAt(pos, "%v does not escape, mutate, or call", name)
 	}
 }
	// 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 (
	"fmt"

	"cmd/compile/internal/base"
	"cmd/compile/internal/ir"
	"cmd/compile/internal/logopt"
	"cmd/compile/internal/typecheck"
	"cmd/compile/internal/types"
	"cmd/internal/src"
	)

	// Escape analysis.
	//
	// Here we analyze functions to determine which Go variables
	// (including implicit allocations such as calls to "new" or "make",
	// composite literals, etc.) can be allocated on the stack. The two
	// key invariants we have to ensure are: (1) pointers to stack objects
	// cannot be stored in the heap, and (2) pointers to a stack object
	// cannot outlive that object (e.g., because the declaring function
	// returned and destroyed the object's stack frame, or its space is
	// reused across loop iterations for logically distinct variables).
	//
	// We implement this with a static data-flow analysis of the AST.
	// First, we construct a directed weighted graph where vertices
	// (termed "locations") represent variables allocated by statements
	// and expressions, and edges represent assignments between variables
	// (with weights representing addressing/dereference counts).
	//
	// Next we walk the graph looking for assignment paths that might
	// violate the invariants stated above. If a variable v's address is
	// stored in the heap or elsewhere that may outlive it, then v is
	// marked as requiring heap allocation.
	//
	// To support interprocedural analysis, we also record data-flow from
	// each function's parameters to the heap and to its result
	// parameters. This information is summarized as "parameter tags",
	// which are used at static call sites to improve escape analysis of
	// function arguments.

	// Constructing the location graph.
	//
	// Every allocating statement (e.g., variable declaration) or
	// expression (e.g., "new" or "make") is first mapped to a unique
	// "location."
	//
	// We also model every Go assignment as a directed edges between
	// locations. The number of dereference operations minus the number of
	// addressing operations is recorded as the edge's weight (termed
	// "derefs"). For example:
	//
	// p = &q // -1
	// p = q // 0
	// p = *q // 1
	// p = **q // 2
	//
	// p = &&q // 2
	//
	// Note that the & operator can only be applied to addressable
	// expressions, and the expression &x itself is not addressable, so
	// derefs cannot go below -1.
	//
	// Every Go language construct is lowered into this representation,
	// generally without sensitivity to flow, path, or context; and
	// without distinguishing elements within a compound variable. For
	// example:
	//
	// var x struct { f, g *int }
	// var u []*int
	//
	// x.f = u[0]
	//
	// is modeled simply as
	//
	// x = *u
	//
	// That is, we don't distinguish x.f from x.g, or u[0] from u[1],
	// u[2], etc. However, we do record the implicit dereference involved
	// in indexing a slice.

	// A batch holds escape analysis state that's shared across an entire
	// batch of functions being analyzed at once.
	type batch struct {
	allLocs []*location
	closures []closure

	heapLoc location
	mutatorLoc location
	calleeLoc location
	blankLoc location
	}

	// A closure holds a closure expression and its spill hole (i.e.,
	// where the hole representing storing into its closure record).
	type closure struct {
	k hole
	clo *ir.ClosureExpr
	}

	// An escape holds state specific to a single function being analyzed
	// within a batch.
	type escape struct {
	*batch

	curfn *ir.Func // function being analyzed

	labels map[*types.Sym]labelState // known labels

	// loopDepth counts the current loop nesting depth within
	// curfn. It increments within each "for" loop and at each
	// label with a corresponding backwards "goto" (i.e.,
	// unstructured loop).
	loopDepth int
	}

	func Funcs(all []*ir.Func) {
	ir.VisitFuncsBottomUp(all, Batch)
	}

	// Batch performs escape analysis on a minimal batch of
	// functions.
	func Batch(fns []*ir.Func, recursive bool) {
	var b batch
	b.heapLoc.attrs = attrEscapes \| attrPersists \| attrMutates \| attrCalls
	b.mutatorLoc.attrs = attrMutates
	b.calleeLoc.attrs = attrCalls

	// Construct data-flow graph from syntax trees.
	for _, fn := range fns {
	if base.Flag.W > 1 {
	s := fmt.Sprintf("\nbefore escape %v", fn)
	ir.Dump(s, fn)
	}
	b.initFunc(fn)
	}
	for _, fn := range fns {
	if !fn.IsHiddenClosure() {
	b.walkFunc(fn)
	}
	}

	// We've walked the function bodies, so we've seen everywhere a
	// variable might be reassigned or have it's address taken. Now we
	// can decide whether closures should capture their free variables
	// by value or reference.
	for _, closure := range b.closures {
	b.flowClosure(closure.k, closure.clo)
	}
	b.closures = nil

	for _, loc := range b.allLocs {
	if why := HeapAllocReason(loc.n); why != "" {
	b.flow(b.heapHole().addr(loc.n, why), loc)
	}
	}

	b.walkAll()
	b.finish(fns)
	}

	func (b batch) with(fn ir.Func) *escape {
	return &escape{
	batch: b,
	curfn: fn,
	loopDepth: 1,
	}
	}

	func (b batch) initFunc(fn ir.Func) {
	e := b.with(fn)
	if fn.Esc() != escFuncUnknown {
	base.Fatalf("unexpected node: %v", fn)
	}
	fn.SetEsc(escFuncPlanned)
	if base.Flag.LowerM > 3 {
	ir.Dump("escAnalyze", fn)
	}

	// Allocate locations for local variables.
	for _, n := range fn.Dcl {
	e.newLoc(n, true)
	}

	// Also for hidden parameters (e.g., the ".this" parameter to a
	// method value wrapper).
	if fn.OClosure == nil {
	for _, n := range fn.ClosureVars {
	e.newLoc(n.Canonical(), true)
	}
	}

	// Initialize resultIndex for result parameters.
	for i, f := range fn.Type().Results() {
	e.oldLoc(f.Nname.(*ir.Name)).resultIndex = 1 + i
	}
	}

	func (b batch) walkFunc(fn ir.Func) {
	e := b.with(fn)
	fn.SetEsc(escFuncStarted)

	// Identify labels that mark the head of an unstructured loop.
	ir.Visit(fn, func(n ir.Node) {
	switch n.Op() {
	case ir.OLABEL:
	n := n.(*ir.LabelStmt)
	if n.Label.IsBlank() {
	break
	}
	if e.labels == nil {
	e.labels = make(map[*types.Sym]labelState)
	}
	e.labels[n.Label] = nonlooping

	case ir.OGOTO:
	// If we visited the label before the goto,
	// then this is a looping label.
	n := n.(*ir.BranchStmt)
	if e.labels[n.Label] == nonlooping {
	e.labels[n.Label] = looping
	}
	}
	})

	e.block(fn.Body)

	if len(e.labels) != 0 {
	base.FatalfAt(fn.Pos(), "leftover labels after walkFunc")
	}
	}

	func (b batch) flowClosure(k hole, clo ir.ClosureExpr) {
	for _, cv := range clo.Func.ClosureVars {
	n := cv.Canonical()
	loc := b.oldLoc(cv)
	if !loc.captured {
	base.FatalfAt(cv.Pos(), "closure variable never captured: %v", cv)
	}

	// Capture by value for variables <= 128 bytes that are never reassigned.
	n.SetByval(!loc.addrtaken && !loc.reassigned && n.Type().Size() <= 128)
	if !n.Byval() {
	n.SetAddrtaken(true)
	if n.Sym().Name == typecheck.LocalDictName {
	base.FatalfAt(n.Pos(), "dictionary variable not captured by value")
	}
	}

	if base.Flag.LowerM > 1 {
	how := "ref"
	if n.Byval() {
	how = "value"
	}
	base.WarnfAt(n.Pos(), "%v capturing by %s: %v (addr=%v assign=%v width=%d)", n.Curfn, how, n, loc.addrtaken, loc.reassigned, n.Type().Size())
	}

	// Flow captured variables to closure.
	k := k
	if !cv.Byval() {
	k = k.addr(cv, "reference")
	}
	b.flow(k.note(cv, "captured by a closure"), loc)
	}
	}

	func (b batch) finish(fns []ir.Func) {
	// Record parameter tags for package export data.
	for _, fn := range fns {
	fn.SetEsc(escFuncTagged)

	for i, param := range fn.Type().RecvParams() {
	param.Note = b.paramTag(fn, 1+i, param)
	}
	}

	for _, loc := range b.allLocs {
	n := loc.n
	if n == nil {
	continue
	}

	if n.Op() == ir.ONAME {
	n := n.(*ir.Name)
	n.Opt = nil
	}

	// Update n.Esc based on escape analysis results.

	// Omit escape diagnostics for go/defer wrappers, at least for now.
	// Historically, we haven't printed them, and test cases don't expect them.
	// TODO(mdempsky): Update tests to expect this.
	goDeferWrapper := n.Op() == ir.OCLOSURE && n.(*ir.ClosureExpr).Func.Wrapper()

	if loc.hasAttr(attrEscapes) {
	if n.Op() == ir.ONAME {
	if base.Flag.CompilingRuntime {
	base.ErrorfAt(n.Pos(), 0, "%v escapes to heap, not allowed in runtime", n)
	}
	if base.Flag.LowerM != 0 {
	base.WarnfAt(n.Pos(), "moved to heap: %v", n)
	}
	} else {
	if base.Flag.LowerM != 0 && !goDeferWrapper {
	base.WarnfAt(n.Pos(), "%v escapes to heap", n)
	}
	if logopt.Enabled() {
	var e_curfn *ir.Func // TODO(mdempsky): Fix.
	logopt.LogOpt(n.Pos(), "escape", "escape", ir.FuncName(e_curfn))
	}
	}
	n.SetEsc(ir.EscHeap)
	} else {
	if base.Flag.LowerM != 0 && n.Op() != ir.ONAME && !goDeferWrapper {
	base.WarnfAt(n.Pos(), "%v does not escape", n)
	}
	n.SetEsc(ir.EscNone)
	if !loc.hasAttr(attrPersists) {
	switch n.Op() {
	case ir.OCLOSURE:
	n := n.(*ir.ClosureExpr)
	n.SetTransient(true)
	case ir.OMETHVALUE:
	n := n.(*ir.SelectorExpr)
	n.SetTransient(true)
	case ir.OSLICELIT:
	n := n.(*ir.CompLitExpr)
	n.SetTransient(true)
	}
	}
	}

	// If the result of a string->[]byte conversion is never mutated,
	// then it can simply reuse the string's memory directly.
	if base.Debug.ZeroCopy != 0 {
	if n, ok := n.(*ir.ConvExpr); ok && n.Op() == ir.OSTR2BYTES && !loc.hasAttr(attrMutates) {
	if base.Flag.LowerM >= 1 {
	base.WarnfAt(n.Pos(), "zero-copy string->[]byte conversion")
	}
	n.SetOp(ir.OSTR2BYTESTMP)
	}
	}
	}
	}

	// inMutualBatch reports whether function fn is in the batch of
	// mutually recursive functions being analyzed. When this is true,
	// fn has not yet been analyzed, so its parameters and results
	// should be incorporated directly into the flow graph instead of
	// relying on its escape analysis tagging.
	func (b batch) inMutualBatch(fn ir.Name) bool {
	if fn.Defn != nil && fn.Defn.Esc() < escFuncTagged {
	if fn.Defn.Esc() == escFuncUnknown {
	base.FatalfAt(fn.Pos(), "graph inconsistency: %v", fn)
	}
	return true
	}
	return false
	}

	const (
	escFuncUnknown = 0 + iota
	escFuncPlanned
	escFuncStarted
	escFuncTagged
	)

	// Mark labels that have no backjumps to them as not increasing e.loopdepth.
	type labelState int

	const (
	looping labelState = 1 + iota
	nonlooping
	)

	func (b batch) paramTag(fn ir.Func, narg int, f *types.Field) string {
	name := func() string {
	if f.Nname != nil {
	return f.Nname.Sym().Name
	}
	return fmt.Sprintf("arg#%d", narg)
	}

	// Only report diagnostics for user code;
	// not for wrappers generated around them.
	// TODO(mdempsky): Generalize this.
	diagnose := base.Flag.LowerM != 0 && !(fn.Wrapper() \|\| fn.Dupok())

	if len(fn.Body) == 0 {
	// Assume that uintptr arguments must be held live across the call.
	// This is most important for syscall.Syscall.
	// See golang.org/issue/13372.
	// This really doesn't have much to do with escape analysis per se,
	// but we are reusing the ability to annotate an individual function
	// argument and pass those annotations along to importing code.
	fn.Pragma \|= ir.UintptrKeepAlive

	if f.Type.IsUintptr() {
	if diagnose {
	base.WarnfAt(f.Pos, "assuming %v is unsafe uintptr", name())
	}
	return ""
	}

	if !f.Type.HasPointers() { // don't bother tagging for scalars
	return ""
	}

	var esc leaks

	// External functions are assumed unsafe, unless
	// //go:noescape is given before the declaration.
	if fn.Pragma&ir.Noescape != 0 {
	if diagnose && f.Sym != nil {
	base.WarnfAt(f.Pos, "%v does not escape", name())
	}
	esc.AddMutator(0)
	esc.AddCallee(0)
	} else {
	if diagnose && f.Sym != nil {
	base.WarnfAt(f.Pos, "leaking param: %v", name())
	}
	esc.AddHeap(0)
	}

	return esc.Encode()
	}

	if fn.Pragma&ir.UintptrEscapes != 0 {
	if f.Type.IsUintptr() {
	if diagnose {
	base.WarnfAt(f.Pos, "marking %v as escaping uintptr", name())
	}
	return ""
	}
	if f.IsDDD() && f.Type.Elem().IsUintptr() {
	// final argument is ...uintptr.
	if diagnose {
	base.WarnfAt(f.Pos, "marking %v as escaping ...uintptr", name())
	}
	return ""
	}
	}

	if !f.Type.HasPointers() { // don't bother tagging for scalars
	return ""
	}

	// Unnamed parameters are unused and therefore do not escape.
	if f.Sym == nil \|\| f.Sym.IsBlank() {
	var esc leaks
	return esc.Encode()
	}

	n := f.Nname.(*ir.Name)
	loc := b.oldLoc(n)
	esc := loc.paramEsc
	esc.Optimize()

	if diagnose && !loc.hasAttr(attrEscapes) {
	b.reportLeaks(f.Pos, name(), esc, fn.Type())
	}

	return esc.Encode()
	}

	func (b batch) reportLeaks(pos src.XPos, name string, esc leaks, sig types.Type) {
	warned := false
	if x := esc.Heap(); x >= 0 {
	if x == 0 {
	base.WarnfAt(pos, "leaking param: %v", name)
	} else {
	// TODO(mdempsky): Mention level=x like below?
	base.WarnfAt(pos, "leaking param content: %v", name)
	}
	warned = true
	}
	for i := 0; i < numEscResults; i++ {
	if x := esc.Result(i); x >= 0 {
	res := sig.Result(i).Nname.Sym().Name
	base.WarnfAt(pos, "leaking param: %v to result %v level=%d", name, res, x)
	warned = true
	}
	}

	if base.Debug.EscapeMutationsCalls <= 0 {
	if !warned {
	base.WarnfAt(pos, "%v does not escape", name)
	}
	return
	}

	if x := esc.Mutator(); x >= 0 {
	base.WarnfAt(pos, "mutates param: %v derefs=%v", name, x)
	warned = true
	}
	if x := esc.Callee(); x >= 0 {
	base.WarnfAt(pos, "calls param: %v derefs=%v", name, x)
	warned = true
	}

	if !warned {
	base.WarnfAt(pos, "%v does not escape, mutate, or call", name)
	}
	}