cmd/compile: adjust PGO inlining default parameters

[gostls13.git] / src / cmd / compile / internal / inline / inl.go

// 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.
//
// The inlining facility makes 2 passes: first CanInline determines which
// functions are suitable for inlining, and for those that are it
// saves a copy of the body. Then InlineCalls walks each function body to
// expand calls to inlinable functions.
//
// The Debug.l flag controls the aggressiveness. Note that main() swaps level 0 and 1,
// making 1 the default and -l disable. Additional levels (beyond -l) may be buggy and
// are not supported.
//      0: disabled
//      1: 80-nodes leaf functions, oneliners, panic, lazy typechecking (default)
//      2: (unassigned)
//      3: (unassigned)
//      4: allow non-leaf functions
//
// At some point this may get another default and become switch-offable with -N.
//
// The -d typcheckinl flag enables early typechecking of all imported bodies,
// which is useful to flush out bugs.
//
// The Debug.m flag enables diagnostic output.  a single -m is useful for verifying
// which calls get inlined or not, more is for debugging, and may go away at any point.

package inline

import (
        "fmt"
        "go/constant"
        "sort"
        "strconv"
        "strings"

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

// Inlining budget parameters, gathered in one place
const (
        inlineMaxBudget       = 80
        inlineExtraAppendCost = 0
        // default is to inline if there's at most one call. -l=4 overrides this by using 1 instead.
        inlineExtraCallCost  = 57              // 57 was benchmarked to provided most benefit with no bad surprises; see https://github.com/golang/go/issues/19348#issuecomment-439370742
        inlineExtraPanicCost = 1               // do not penalize inlining panics.
        inlineExtraThrowCost = inlineMaxBudget // with current (2018-05/1.11) code, inlining runtime.throw does not help.

        inlineBigFunctionNodes   = 5000 // Functions with this many nodes are considered "big".
        inlineBigFunctionMaxCost = 20   // Max cost of inlinee when inlining into a "big" function.
)

var (
        // List of all hot callee nodes.
        // TODO(prattmic): Make this non-global.
        candHotCalleeMap = make(map[*pgo.IRNode]struct{})

        // List of all hot call sites. CallSiteInfo.Callee is always nil.
        // TODO(prattmic): Make this non-global.
        candHotEdgeMap = make(map[pgo.CallSiteInfo]struct{})

        // List of inlined call sites. CallSiteInfo.Callee is always nil.
        // TODO(prattmic): Make this non-global.
        inlinedCallSites = make(map[pgo.CallSiteInfo]struct{})

        // Threshold in percentage for hot callsite inlining.
        inlineHotCallSiteThresholdPercent float64

        // Threshold in CDF percentage for hot callsite inlining,
        // that is, for a threshold of X the hottest callsites that
        // make up the top X% of total edge weight will be
        // considered hot for inlining candidates.
        inlineCDFHotCallSiteThresholdPercent = float64(99)

        // Budget increased due to hotness.
        inlineHotMaxBudget int32 = 2000
)

// pgoInlinePrologue records the hot callsites from ir-graph.
func pgoInlinePrologue(p *pgo.Profile, decls []ir.Node) {
        if s, err := strconv.ParseFloat(base.Debug.PGOInlineCDFThreshold, 64); err == nil {
                inlineCDFHotCallSiteThresholdPercent = s
        }
        var hotCallsites []pgo.NodeMapKey
        inlineHotCallSiteThresholdPercent, hotCallsites = computeThresholdFromCDF(p)
        if base.Debug.PGOInline > 0 {
                fmt.Printf("hot-callsite-thres-from-CDF=%v\n", inlineHotCallSiteThresholdPercent)
        }

        if x := base.Debug.PGOInlineBudget; x != 0 {
                inlineHotMaxBudget = int32(x)
        }

        // mark inlineable callees from hot edges
        for _, n := range hotCallsites {
                if fn := p.WeightedCG.IRNodes[n.CalleeName]; fn != nil {
                        candHotCalleeMap[fn] = struct{}{}
                }
        }
        // mark hot call sites
        ir.VisitFuncsBottomUp(decls, func(list []*ir.Func, recursive bool) {
                for _, f := range list {
                        name := ir.PkgFuncName(f)
                        if n, ok := p.WeightedCG.IRNodes[name]; ok {
                                for _, e := range p.WeightedCG.OutEdges[n] {
                                        if e.Weight != 0 {
                                                edgeweightpercent := pgo.WeightInPercentage(e.Weight, p.TotalEdgeWeight)
                                                if edgeweightpercent > inlineHotCallSiteThresholdPercent {
                                                        csi := pgo.CallSiteInfo{LineOffset: e.CallSiteOffset, Caller: n.AST}
                                                        if _, ok := candHotEdgeMap[csi]; !ok {
                                                                candHotEdgeMap[csi] = struct{}{}
                                                        }
                                                }
                                        }
                                }
                        }
                }
        })
        if base.Debug.PGOInline >= 2 {
                fmt.Printf("hot-cg before inline in dot format:")
                p.PrintWeightedCallGraphDOT(inlineHotCallSiteThresholdPercent)
        }
}

// computeThresholdFromCDF computes an edge weight threshold based on the
// CDF of edge weights from the profile. Returns the threshold, and the
// list of edges that make up the given percentage of the CDF.
func computeThresholdFromCDF(p *pgo.Profile) (float64, []pgo.NodeMapKey) {
        nodes := make([]pgo.NodeMapKey, len(p.NodeMap))
        i := 0
        for n := range p.NodeMap {
                nodes[i] = n
                i++
        }
        sort.Slice(nodes, func(i, j int) bool {
                ni, nj := nodes[i], nodes[j]
                if wi, wj := p.NodeMap[ni].EWeight, p.NodeMap[nj].EWeight; wi != wj {
                        return wi > wj // want larger weight first
                }
                // same weight, order by name/line number
                if ni.CallerName != nj.CallerName {
                        return ni.CallerName < nj.CallerName
                }
                if ni.CalleeName != nj.CalleeName {
                        return ni.CalleeName < nj.CalleeName
                }
                return ni.CallSiteOffset < nj.CallSiteOffset
        })
        cum := int64(0)
        for i, n := range nodes {
                w := p.NodeMap[n].EWeight
                cum += w
                if pgo.WeightInPercentage(cum, p.TotalEdgeWeight) > inlineCDFHotCallSiteThresholdPercent {
                        return pgo.WeightInPercentage(w, p.TotalEdgeWeight), nodes[:i]
                }
        }
        return 100, nil
}

// pgoInlineEpilogue updates IRGraph after inlining.
func pgoInlineEpilogue(p *pgo.Profile, decls []ir.Node) {
        if base.Debug.PGOInline >= 2 {
                ir.VisitFuncsBottomUp(decls, func(list []*ir.Func, recursive bool) {
                        for _, f := range list {
                                name := ir.PkgFuncName(f)
                                if n, ok := p.WeightedCG.IRNodes[name]; ok {
                                        p.RedirectEdges(n, inlinedCallSites)
                                }
                        }
                })
                // Print the call-graph after inlining. This is a debugging feature.
                fmt.Printf("hot-cg after inline in dot:")
                p.PrintWeightedCallGraphDOT(inlineHotCallSiteThresholdPercent)
        }
}

// InlinePackage finds functions that can be inlined and clones them before walk expands them.
func InlinePackage(p *pgo.Profile) {
        InlineDecls(p, typecheck.Target.Decls, true)
}

// InlineDecls applies inlining to the given batch of declarations.
func InlineDecls(p *pgo.Profile, decls []ir.Node, doInline bool) {
        if p != nil {
                pgoInlinePrologue(p, decls)
        }

        ir.VisitFuncsBottomUp(decls, func(list []*ir.Func, recursive bool) {
                numfns := numNonClosures(list)
                for _, n := range list {
                        if !recursive || numfns > 1 {
                                // We allow inlining if there is no
                                // recursion, or the recursion cycle is
                                // across more than one function.
                                CanInline(n, p)
                        } else {
                                if base.Flag.LowerM > 1 {
                                        fmt.Printf("%v: cannot inline %v: recursive\n", ir.Line(n), n.Nname)
                                }
                        }
                        if doInline {
                                InlineCalls(n, p)
                        }
                }
        })

        if p != nil {
                pgoInlineEpilogue(p, decls)
        }
}

// CanInline determines whether fn is inlineable.
// If so, CanInline saves copies of fn.Body and fn.Dcl in fn.Inl.
// fn and fn.Body will already have been typechecked.
func CanInline(fn *ir.Func, profile *pgo.Profile) {
        if fn.Nname == nil {
                base.Fatalf("CanInline no nname %+v", fn)
        }

        var reason string // reason, if any, that the function was not inlined
        if base.Flag.LowerM > 1 || logopt.Enabled() {
                defer func() {
                        if reason != "" {
                                if base.Flag.LowerM > 1 {
                                        fmt.Printf("%v: cannot inline %v: %s\n", ir.Line(fn), fn.Nname, reason)
                                }
                                if logopt.Enabled() {
                                        logopt.LogOpt(fn.Pos(), "cannotInlineFunction", "inline", ir.FuncName(fn), reason)
                                }
                        }
                }()
        }

        // If marked "go:noinline", don't inline
        if fn.Pragma&ir.Noinline != 0 {
                reason = "marked go:noinline"
                return
        }

        // If marked "go:norace" and -race compilation, don't inline.
        if base.Flag.Race && fn.Pragma&ir.Norace != 0 {
                reason = "marked go:norace with -race compilation"
                return
        }

        // If marked "go:nocheckptr" and -d checkptr compilation, don't inline.
        if base.Debug.Checkptr != 0 && fn.Pragma&ir.NoCheckPtr != 0 {
                reason = "marked go:nocheckptr"
                return
        }

        // If marked "go:cgo_unsafe_args", don't inline, since the
        // function makes assumptions about its argument frame layout.
        if fn.Pragma&ir.CgoUnsafeArgs != 0 {
                reason = "marked go:cgo_unsafe_args"
                return
        }

        // If marked as "go:uintptrkeepalive", don't inline, since the
        // keep alive information is lost during inlining.
        //
        // TODO(prattmic): This is handled on calls during escape analysis,
        // which is after inlining. Move prior to inlining so the keep-alive is
        // maintained after inlining.
        if fn.Pragma&ir.UintptrKeepAlive != 0 {
                reason = "marked as having a keep-alive uintptr argument"
                return
        }

        // If marked as "go:uintptrescapes", don't inline, since the
        // escape information is lost during inlining.
        if fn.Pragma&ir.UintptrEscapes != 0 {
                reason = "marked as having an escaping uintptr argument"
                return
        }

        // The nowritebarrierrec checker currently works at function
        // granularity, so inlining yeswritebarrierrec functions can
        // confuse it (#22342). As a workaround, disallow inlining
        // them for now.
        if fn.Pragma&ir.Yeswritebarrierrec != 0 {
                reason = "marked go:yeswritebarrierrec"
                return
        }

        // If fn has no body (is defined outside of Go), cannot inline it.
        if len(fn.Body) == 0 {
                reason = "no function body"
                return
        }

        if fn.Typecheck() == 0 {
                base.Fatalf("CanInline on non-typechecked function %v", fn)
        }

        n := fn.Nname
        if n.Func.InlinabilityChecked() {
                return
        }
        defer n.Func.SetInlinabilityChecked(true)

        cc := int32(inlineExtraCallCost)
        if base.Flag.LowerL == 4 {
                cc = 1 // this appears to yield better performance than 0.
        }

        // Update the budget for profile-guided inlining.
        budget := int32(inlineMaxBudget)
        if profile != nil {
                if n, ok := profile.WeightedCG.IRNodes[ir.PkgFuncName(fn)]; ok {
                        if _, ok := candHotCalleeMap[n]; ok {
                                budget = int32(inlineHotMaxBudget)
                                if base.Debug.PGOInline > 0 {
                                        fmt.Printf("hot-node enabled increased budget=%v for func=%v\n", budget, ir.PkgFuncName(fn))
                                }
                        }
                }
        }

        // At this point in the game the function we're looking at may
        // have "stale" autos, vars that still appear in the Dcl list, but
        // which no longer have any uses in the function body (due to
        // elimination by deadcode). We'd like to exclude these dead vars
        // when creating the "Inline.Dcl" field below; to accomplish this,
        // the hairyVisitor below builds up a map of used/referenced
        // locals, and we use this map to produce a pruned Inline.Dcl
        // list. See issue 25249 for more context.

        visitor := hairyVisitor{
                curFunc:       fn,
                budget:        budget,
                maxBudget:     budget,
                extraCallCost: cc,
                profile:       profile,
        }
        if visitor.tooHairy(fn) {
                reason = visitor.reason
                return
        }

        n.Func.Inl = &ir.Inline{
                Cost: budget - visitor.budget,
                Dcl:  pruneUnusedAutos(n.Defn.(*ir.Func).Dcl, &visitor),
                Body: inlcopylist(fn.Body),

                CanDelayResults: canDelayResults(fn),
        }

        if base.Flag.LowerM > 1 {
                fmt.Printf("%v: can inline %v with cost %d as: %v { %v }\n", ir.Line(fn), n, budget-visitor.budget, fn.Type(), ir.Nodes(n.Func.Inl.Body))
        } else if base.Flag.LowerM != 0 {
                fmt.Printf("%v: can inline %v\n", ir.Line(fn), n)
        }
        if logopt.Enabled() {
                logopt.LogOpt(fn.Pos(), "canInlineFunction", "inline", ir.FuncName(fn), fmt.Sprintf("cost: %d", budget-visitor.budget))
        }
}

// canDelayResults reports whether inlined calls to fn can delay
// declaring the result parameter until the "return" statement.
func canDelayResults(fn *ir.Func) bool {
        // We can delay declaring+initializing result parameters if:
        // (1) there's exactly one "return" statement in the inlined function;
        // (2) it's not an empty return statement (#44355); and
        // (3) the result parameters aren't named.

        nreturns := 0
        ir.VisitList(fn.Body, func(n ir.Node) {
                if n, ok := n.(*ir.ReturnStmt); ok {
                        nreturns++
                        if len(n.Results) == 0 {
                                nreturns++ // empty return statement (case 2)
                        }
                }
        })

        if nreturns != 1 {
                return false // not exactly one return statement (case 1)
        }

        // temporaries for return values.
        for _, param := range fn.Type().Results().FieldSlice() {
                if sym := types.OrigSym(param.Sym); sym != nil && !sym.IsBlank() {
                        return false // found a named result parameter (case 3)
                }
        }

        return true
}

// hairyVisitor visits a function body to determine its inlining
// hairiness and whether or not it can be inlined.
type hairyVisitor struct {
        // This is needed to access the current caller in the doNode function.
        curFunc       *ir.Func
        budget        int32
        maxBudget     int32
        reason        string
        extraCallCost int32
        usedLocals    ir.NameSet
        do            func(ir.Node) bool
        profile       *pgo.Profile
}

func (v *hairyVisitor) tooHairy(fn *ir.Func) bool {
        v.do = v.doNode // cache closure
        if ir.DoChildren(fn, v.do) {
                return true
        }
        if v.budget < 0 {
                v.reason = fmt.Sprintf("function too complex: cost %d exceeds budget %d", v.maxBudget-v.budget, v.maxBudget)
                return true
        }
        return false
}

func (v *hairyVisitor) doNode(n ir.Node) bool {
        if n == nil {
                return false
        }
        switch n.Op() {
        // Call is okay if inlinable and we have the budget for the body.
        case ir.OCALLFUNC:
                n := n.(*ir.CallExpr)
                // Functions that call runtime.getcaller{pc,sp} can not be inlined
                // because getcaller{pc,sp} expect a pointer to the caller's first argument.
                //
                // runtime.throw is a "cheap call" like panic in normal code.
                if n.X.Op() == ir.ONAME {
                        name := n.X.(*ir.Name)
                        if name.Class == ir.PFUNC && types.IsRuntimePkg(name.Sym().Pkg) {
                                fn := name.Sym().Name
                                if fn == "getcallerpc" || fn == "getcallersp" {
                                        v.reason = "call to " + fn
                                        return true
                                }
                                if fn == "throw" {
                                        v.budget -= inlineExtraThrowCost
                                        break
                                }
                        }
                        // Special case for coverage counter updates; although
                        // these correspond to real operations, we treat them as
                        // zero cost for the moment. This is due to the existence
                        // of tests that are sensitive to inlining-- if the
                        // insertion of coverage instrumentation happens to tip a
                        // given function over the threshold and move it from
                        // "inlinable" to "not-inlinable", this can cause changes
                        // in allocation behavior, which can then result in test
                        // failures (a good example is the TestAllocations in
                        // crypto/ed25519).
                        if isAtomicCoverageCounterUpdate(n) {
                                return false
                        }
                }
                if n.X.Op() == ir.OMETHEXPR {
                        if meth := ir.MethodExprName(n.X); meth != nil {
                                if fn := meth.Func; fn != nil {
                                        s := fn.Sym()
                                        var cheap bool
                                        if types.IsRuntimePkg(s.Pkg) && s.Name == "heapBits.nextArena" {
                                                // Special case: explicitly allow mid-stack inlining of
                                                // runtime.heapBits.next even though it calls slow-path
                                                // runtime.heapBits.nextArena.
                                                cheap = true
                                        }
                                        // Special case: on architectures that can do unaligned loads,
                                        // explicitly mark encoding/binary methods as cheap,
                                        // because in practice they are, even though our inlining
                                        // budgeting system does not see that. See issue 42958.
                                        if base.Ctxt.Arch.CanMergeLoads && s.Pkg.Path == "encoding/binary" {
                                                switch s.Name {
                                                case "littleEndian.Uint64", "littleEndian.Uint32", "littleEndian.Uint16",
                                                        "bigEndian.Uint64", "bigEndian.Uint32", "bigEndian.Uint16",
                                                        "littleEndian.PutUint64", "littleEndian.PutUint32", "littleEndian.PutUint16",
                                                        "bigEndian.PutUint64", "bigEndian.PutUint32", "bigEndian.PutUint16",
                                                        "littleEndian.AppendUint64", "littleEndian.AppendUint32", "littleEndian.AppendUint16",
                                                        "bigEndian.AppendUint64", "bigEndian.AppendUint32", "bigEndian.AppendUint16":
                                                        cheap = true
                                                }
                                        }
                                        if cheap {
                                                break // treat like any other node, that is, cost of 1
                                        }
                                }
                        }
                }

                // Determine if the callee edge is for an inlinable hot callee or not.
                if v.profile != nil && v.curFunc != nil {
                        if fn := inlCallee(n.X, v.profile); fn != nil && typecheck.HaveInlineBody(fn) {
                                lineOffset := pgo.NodeLineOffset(n, fn)
                                csi := pgo.CallSiteInfo{LineOffset: lineOffset, Caller: v.curFunc}
                                if _, o := candHotEdgeMap[csi]; o {
                                        if base.Debug.PGOInline > 0 {
                                                fmt.Printf("hot-callsite identified at line=%v for func=%v\n", ir.Line(n), ir.PkgFuncName(v.curFunc))
                                        }
                                }
                        }
                }

                if ir.IsIntrinsicCall(n) {
                        // Treat like any other node.
                        break
                }

                if fn := inlCallee(n.X, v.profile); fn != nil && typecheck.HaveInlineBody(fn) {
                        v.budget -= fn.Inl.Cost
                        break
                }

                // Call cost for non-leaf inlining.
                v.budget -= v.extraCallCost

        case ir.OCALLMETH:
                base.FatalfAt(n.Pos(), "OCALLMETH missed by typecheck")

        // Things that are too hairy, irrespective of the budget
        case ir.OCALL, ir.OCALLINTER:
                // Call cost for non-leaf inlining.
                v.budget -= v.extraCallCost

        case ir.OPANIC:
                n := n.(*ir.UnaryExpr)
                if n.X.Op() == ir.OCONVIFACE && n.X.(*ir.ConvExpr).Implicit() {
                        // Hack to keep reflect.flag.mustBe inlinable for TestIntendedInlining.
                        // Before CL 284412, these conversions were introduced later in the
                        // compiler, so they didn't count against inlining budget.
                        v.budget++
                }
                v.budget -= inlineExtraPanicCost

        case ir.ORECOVER:
                // recover matches the argument frame pointer to find
                // the right panic value, so it needs an argument frame.
                v.reason = "call to recover"
                return true

        case ir.OCLOSURE:
                if base.Debug.InlFuncsWithClosures == 0 {
                        v.reason = "not inlining functions with closures"
                        return true
                }

                // TODO(danscales): Maybe make budget proportional to number of closure
                // variables, e.g.:
                //v.budget -= int32(len(n.(*ir.ClosureExpr).Func.ClosureVars) * 3)
                v.budget -= 15
                // Scan body of closure (which DoChildren doesn't automatically
                // do) to check for disallowed ops in the body and include the
                // body in the budget.
                if doList(n.(*ir.ClosureExpr).Func.Body, v.do) {
                        return true
                }

        case ir.OGO,
                ir.ODEFER,
                ir.ODCLTYPE, // can't print yet
                ir.OTAILCALL:
                v.reason = "unhandled op " + n.Op().String()
                return true

        case ir.OAPPEND:
                v.budget -= inlineExtraAppendCost

        case ir.OADDR:
                n := n.(*ir.AddrExpr)
                // Make "&s.f" cost 0 when f's offset is zero.
                if dot, ok := n.X.(*ir.SelectorExpr); ok && (dot.Op() == ir.ODOT || dot.Op() == ir.ODOTPTR) {
                        if _, ok := dot.X.(*ir.Name); ok && dot.Selection.Offset == 0 {
                                v.budget += 2 // undo ir.OADDR+ir.ODOT/ir.ODOTPTR
                        }
                }

        case ir.ODEREF:
                // *(*X)(unsafe.Pointer(&x)) is low-cost
                n := n.(*ir.StarExpr)

                ptr := n.X
                for ptr.Op() == ir.OCONVNOP {
                        ptr = ptr.(*ir.ConvExpr).X
                }
                if ptr.Op() == ir.OADDR {
                        v.budget += 1 // undo half of default cost of ir.ODEREF+ir.OADDR
                }

        case ir.OCONVNOP:
                // This doesn't produce code, but the children might.
                v.budget++ // undo default cost

        case ir.ODCLCONST, ir.OFALL:
                // These nodes don't produce code; omit from inlining budget.
                return false

        case ir.OIF:
                n := n.(*ir.IfStmt)
                if ir.IsConst(n.Cond, constant.Bool) {
                        // This if and the condition cost nothing.
                        if doList(n.Init(), v.do) {
                                return true
                        }
                        if ir.BoolVal(n.Cond) {
                                return doList(n.Body, v.do)
                        } else {
                                return doList(n.Else, v.do)
                        }
                }

        case ir.ONAME:
                n := n.(*ir.Name)
                if n.Class == ir.PAUTO {
                        v.usedLocals.Add(n)
                }

        case ir.OBLOCK:
                // The only OBLOCK we should see at this point is an empty one.
                // In any event, let the visitList(n.List()) below take care of the statements,
                // and don't charge for the OBLOCK itself. The ++ undoes the -- below.
                v.budget++

        case ir.OMETHVALUE, ir.OSLICELIT:
                v.budget-- // Hack for toolstash -cmp.

        case ir.OMETHEXPR:
                v.budget++ // Hack for toolstash -cmp.

        case ir.OAS2:
                n := n.(*ir.AssignListStmt)

                // Unified IR unconditionally rewrites:
                //
                //      a, b = f()
                //
                // into:
                //
                //      DCL tmp1
                //      DCL tmp2
                //      tmp1, tmp2 = f()
                //      a, b = tmp1, tmp2
                //
                // so that it can insert implicit conversions as necessary. To
                // minimize impact to the existing inlining heuristics (in
                // particular, to avoid breaking the existing inlinability regress
                // tests), we need to compensate for this here.
                if base.Debug.Unified != 0 {
                        if init := n.Rhs[0].Init(); len(init) == 1 {
                                if _, ok := init[0].(*ir.AssignListStmt); ok {
                                        // 4 for each value, because each temporary variable now
                                        // appears 3 times (DCL, LHS, RHS), plus an extra DCL node.
                                        //
                                        // 1 for the extra "tmp1, tmp2 = f()" assignment statement.
                                        v.budget += 4*int32(len(n.Lhs)) + 1
                                }
                        }
                }

        case ir.OAS:
                // Special case for coverage counter updates and coverage
                // function registrations. Although these correspond to real
                // operations, we treat them as zero cost for the moment. This
                // is primarily due to the existence of tests that are
                // sensitive to inlining-- if the insertion of coverage
                // instrumentation happens to tip a given function over the
                // threshold and move it from "inlinable" to "not-inlinable",
                // this can cause changes in allocation behavior, which can
                // then result in test failures (a good example is the
                // TestAllocations in crypto/ed25519).
                n := n.(*ir.AssignStmt)
                if n.X.Op() == ir.OINDEX && isIndexingCoverageCounter(n.X) {
                        return false
                }
        }

        v.budget--

        // When debugging, don't stop early, to get full cost of inlining this function
        if v.budget < 0 && base.Flag.LowerM < 2 && !logopt.Enabled() {
                v.reason = "too expensive"
                return true
        }

        return ir.DoChildren(n, v.do)
}

func isBigFunc(fn *ir.Func) bool {
        budget := inlineBigFunctionNodes
        return ir.Any(fn, func(n ir.Node) bool {
                budget--
                return budget <= 0
        })
}

// inlcopylist (together with inlcopy) recursively copies a list of nodes, except
// that it keeps the same ONAME, OTYPE, and OLITERAL nodes. It is used for copying
// the body and dcls of an inlineable function.
func inlcopylist(ll []ir.Node) []ir.Node {
        s := make([]ir.Node, len(ll))
        for i, n := range ll {
                s[i] = inlcopy(n)
        }
        return s
}

// inlcopy is like DeepCopy(), but does extra work to copy closures.
func inlcopy(n ir.Node) ir.Node {
        var edit func(ir.Node) ir.Node
        edit = func(x ir.Node) ir.Node {
                switch x.Op() {
                case ir.ONAME, ir.OTYPE, ir.OLITERAL, ir.ONIL:
                        return x
                }
                m := ir.Copy(x)
                ir.EditChildren(m, edit)
                if x.Op() == ir.OCLOSURE {
                        x := x.(*ir.ClosureExpr)
                        // Need to save/duplicate x.Func.Nname,
                        // x.Func.Nname.Ntype, x.Func.Dcl, x.Func.ClosureVars, and
                        // x.Func.Body for iexport and local inlining.
                        oldfn := x.Func
                        newfn := ir.NewFunc(oldfn.Pos())
                        m.(*ir.ClosureExpr).Func = newfn
                        newfn.Nname = ir.NewNameAt(oldfn.Nname.Pos(), oldfn.Nname.Sym())
                        // XXX OK to share fn.Type() ??
                        newfn.Nname.SetType(oldfn.Nname.Type())
                        newfn.Body = inlcopylist(oldfn.Body)
                        // Make shallow copy of the Dcl and ClosureVar slices
                        newfn.Dcl = append([]*ir.Name(nil), oldfn.Dcl...)
                        newfn.ClosureVars = append([]*ir.Name(nil), oldfn.ClosureVars...)
                }
                return m
        }
        return edit(n)
}

// InlineCalls/inlnode walks fn's statements and expressions and substitutes any
// calls made to inlineable functions. This is the external entry point.
func InlineCalls(fn *ir.Func, profile *pgo.Profile) {
        savefn := ir.CurFunc
        ir.CurFunc = fn
        maxCost := int32(inlineMaxBudget)
        if isBigFunc(fn) {
                maxCost = inlineBigFunctionMaxCost
        }
        var inlCalls []*ir.InlinedCallExpr
        var edit func(ir.Node) ir.Node
        edit = func(n ir.Node) ir.Node {
                return inlnode(n, maxCost, &inlCalls, edit, profile)
        }
        ir.EditChildren(fn, edit)

        // If we inlined any calls, we want to recursively visit their
        // bodies for further inlining. However, we need to wait until
        // *after* the original function body has been expanded, or else
        // inlCallee can have false positives (e.g., #54632).
        for len(inlCalls) > 0 {
                call := inlCalls[0]
                inlCalls = inlCalls[1:]
                ir.EditChildren(call, edit)
        }

        ir.CurFunc = savefn
}

// inlnode recurses over the tree to find inlineable calls, which will
// be turned into OINLCALLs by mkinlcall. When the recursion comes
// back up will examine left, right, list, rlist, ninit, ntest, nincr,
// nbody and nelse and use one of the 4 inlconv/glue functions above
// to turn the OINLCALL into an expression, a statement, or patch it
// in to this nodes list or rlist as appropriate.
// NOTE it makes no sense to pass the glue functions down the
// recursion to the level where the OINLCALL gets created because they
// have to edit /this/ n, so you'd have to push that one down as well,
// but then you may as well do it here.  so this is cleaner and
// shorter and less complicated.
// The result of inlnode MUST be assigned back to n, e.g.
//
//      n.Left = inlnode(n.Left)
func inlnode(n ir.Node, maxCost int32, inlCalls *[]*ir.InlinedCallExpr, edit func(ir.Node) ir.Node, profile *pgo.Profile) ir.Node {
        if n == nil {
                return n
        }

        switch n.Op() {
        case ir.ODEFER, ir.OGO:
                n := n.(*ir.GoDeferStmt)
                switch call := n.Call; call.Op() {
                case ir.OCALLMETH:
                        base.FatalfAt(call.Pos(), "OCALLMETH missed by typecheck")
                case ir.OCALLFUNC:
                        call := call.(*ir.CallExpr)
                        call.NoInline = true
                }
        case ir.OTAILCALL:
                n := n.(*ir.TailCallStmt)
                n.Call.NoInline = true // Not inline a tail call for now. Maybe we could inline it just like RETURN fn(arg)?

        // TODO do them here (or earlier),
        // so escape analysis can avoid more heapmoves.
        case ir.OCLOSURE:
                return n
        case ir.OCALLMETH:
                base.FatalfAt(n.Pos(), "OCALLMETH missed by typecheck")
        case ir.OCALLFUNC:
                n := n.(*ir.CallExpr)
                if n.X.Op() == ir.OMETHEXPR {
                        // Prevent inlining some reflect.Value methods when using checkptr,
                        // even when package reflect was compiled without it (#35073).
                        if meth := ir.MethodExprName(n.X); meth != nil {
                                s := meth.Sym()
                                if base.Debug.Checkptr != 0 && types.IsReflectPkg(s.Pkg) && (s.Name == "Value.UnsafeAddr" || s.Name == "Value.Pointer") {
                                        return n
                                }
                        }
                }
        }

        lno := ir.SetPos(n)

        ir.EditChildren(n, edit)

        // with all the branches out of the way, it is now time to
        // transmogrify this node itself unless inhibited by the
        // switch at the top of this function.
        switch n.Op() {
        case ir.OCALLMETH:
                base.FatalfAt(n.Pos(), "OCALLMETH missed by typecheck")

        case ir.OCALLFUNC:
                call := n.(*ir.CallExpr)
                if call.NoInline {
                        break
                }
                if base.Flag.LowerM > 3 {
                        fmt.Printf("%v:call to func %+v\n", ir.Line(n), call.X)
                }
                if ir.IsIntrinsicCall(call) {
                        break
                }
                if fn := inlCallee(call.X, profile); fn != nil && typecheck.HaveInlineBody(fn) {
                        n = mkinlcall(call, fn, maxCost, inlCalls, edit)
                }
        }

        base.Pos = lno

        return n
}

// inlCallee takes a function-typed expression and returns the underlying function ONAME
// that it refers to if statically known. Otherwise, it returns nil.
func inlCallee(fn ir.Node, profile *pgo.Profile) *ir.Func {
        fn = ir.StaticValue(fn)
        switch fn.Op() {
        case ir.OMETHEXPR:
                fn := fn.(*ir.SelectorExpr)
                n := ir.MethodExprName(fn)
                // Check that receiver type matches fn.X.
                // TODO(mdempsky): Handle implicit dereference
                // of pointer receiver argument?
                if n == nil || !types.Identical(n.Type().Recv().Type, fn.X.Type()) {
                        return nil
                }
                return n.Func
        case ir.ONAME:
                fn := fn.(*ir.Name)
                if fn.Class == ir.PFUNC {
                        return fn.Func
                }
        case ir.OCLOSURE:
                fn := fn.(*ir.ClosureExpr)
                c := fn.Func
                CanInline(c, profile)
                return c
        }
        return nil
}

func inlParam(t *types.Field, as ir.InitNode, inlvars map[*ir.Name]*ir.Name) ir.Node {
        if t.Nname == nil {
                return ir.BlankNode
        }
        n := t.Nname.(*ir.Name)
        if ir.IsBlank(n) {
                return ir.BlankNode
        }
        inlvar := inlvars[n]
        if inlvar == nil {
                base.Fatalf("missing inlvar for %v", n)
        }
        as.PtrInit().Append(ir.NewDecl(base.Pos, ir.ODCL, inlvar))
        inlvar.Name().Defn = as
        return inlvar
}

var inlgen int

// SSADumpInline gives the SSA back end a chance to dump the function
// when producing output for debugging the compiler itself.
var SSADumpInline = func(*ir.Func) {}

// InlineCall allows the inliner implementation to be overridden.
// If it returns nil, the function will not be inlined.
var InlineCall = oldInlineCall

// If n is a OCALLFUNC node, and fn is an ONAME node for a
// function with an inlinable body, return an OINLCALL node that can replace n.
// The returned node's Ninit has the parameter assignments, the Nbody is the
// inlined function body, and (List, Rlist) contain the (input, output)
// parameters.
// The result of mkinlcall MUST be assigned back to n, e.g.
//
//      n.Left = mkinlcall(n.Left, fn, isddd)
func mkinlcall(n *ir.CallExpr, fn *ir.Func, maxCost int32, inlCalls *[]*ir.InlinedCallExpr, edit func(ir.Node) ir.Node) ir.Node {
        if fn.Inl == nil {
                if logopt.Enabled() {
                        logopt.LogOpt(n.Pos(), "cannotInlineCall", "inline", ir.FuncName(ir.CurFunc),
                                fmt.Sprintf("%s cannot be inlined", ir.PkgFuncName(fn)))
                }
                return n
        }
        if fn.Inl.Cost > maxCost {
                // If the callsite is hot and it is under the inlineHotMaxBudget budget, then try to inline it, or else bail.
                lineOffset := pgo.NodeLineOffset(n, ir.CurFunc)
                csi := pgo.CallSiteInfo{LineOffset: lineOffset, Caller: ir.CurFunc}
                if _, ok := candHotEdgeMap[csi]; ok {
                        if fn.Inl.Cost > inlineHotMaxBudget {
                                if logopt.Enabled() {
                                        logopt.LogOpt(n.Pos(), "cannotInlineCall", "inline", ir.FuncName(ir.CurFunc),
                                                fmt.Sprintf("cost %d of %s exceeds max large caller cost %d", fn.Inl.Cost, ir.PkgFuncName(fn), inlineHotMaxBudget))
                                }
                                return n
                        }
                        if base.Debug.PGOInline > 0 {
                                fmt.Printf("hot-budget check allows inlining for call %s at %v\n", ir.PkgFuncName(fn), ir.Line(n))
                        }
                } else {
                        // The inlined function body is too big. Typically we use this check to restrict
                        // inlining into very big functions.  See issue 26546 and 17566.
                        if logopt.Enabled() {
                                logopt.LogOpt(n.Pos(), "cannotInlineCall", "inline", ir.FuncName(ir.CurFunc),
                                        fmt.Sprintf("cost %d of %s exceeds max large caller cost %d", fn.Inl.Cost, ir.PkgFuncName(fn), maxCost))
                        }
                        return n
                }
        }

        if fn == ir.CurFunc {
                // Can't recursively inline a function into itself.
                if logopt.Enabled() {
                        logopt.LogOpt(n.Pos(), "cannotInlineCall", "inline", fmt.Sprintf("recursive call to %s", ir.FuncName(ir.CurFunc)))
                }
                return n
        }

        // The non-unified frontend has issues with inlining and shape parameters.
        if base.Debug.Unified == 0 {
                // Don't inline a function fn that has no shape parameters, but is passed at
                // least one shape arg. This means we must be inlining a non-generic function
                // fn that was passed into a generic function, and can be called with a shape
                // arg because it matches an appropriate type parameters. But fn may include
                // an interface conversion (that may be applied to a shape arg) that was not
                // apparent when we first created the instantiation of the generic function.
                // We can't handle this if we actually do the inlining, since we want to know
                // all interface conversions immediately after stenciling. So, we avoid
                // inlining in this case, see issue #49309. (1)
                //
                // See discussion on go.dev/cl/406475 for more background.
                if !fn.Type().Params().HasShape() {
                        for _, arg := range n.Args {
                                if arg.Type().HasShape() {
                                        if logopt.Enabled() {
                                                logopt.LogOpt(n.Pos(), "cannotInlineCall", "inline", ir.FuncName(ir.CurFunc),
                                                        fmt.Sprintf("inlining function %v has no-shape params with shape args", ir.FuncName(fn)))
                                        }
                                        return n
                                }
                        }
                } else {
                        // Don't inline a function fn that has shape parameters, but is passed no shape arg.
                        // See comments (1) above, and issue #51909.
                        inlineable := len(n.Args) == 0 // Function has shape in type, with no arguments can always be inlined.
                        for _, arg := range n.Args {
                                if arg.Type().HasShape() {
                                        inlineable = true
                                        break
                                }
                        }
                        if !inlineable {
                                if logopt.Enabled() {
                                        logopt.LogOpt(n.Pos(), "cannotInlineCall", "inline", ir.FuncName(ir.CurFunc),
                                                fmt.Sprintf("inlining function %v has shape params with no-shape args", ir.FuncName(fn)))
                                }
                                return n
                        }
                }
        }

        if base.Flag.Cfg.Instrumenting && types.IsRuntimePkg(fn.Sym().Pkg) {
                // Runtime package must not be instrumented.
                // Instrument skips runtime package. However, some runtime code can be
                // inlined into other packages and instrumented there. To avoid this,
                // we disable inlining of runtime functions when instrumenting.
                // The example that we observed is inlining of LockOSThread,
                // which lead to false race reports on m contents.
                return n
        }

        parent := base.Ctxt.PosTable.Pos(n.Pos()).Base().InliningIndex()
        sym := fn.Linksym()

        // Check if we've already inlined this function at this particular
        // call site, in order to stop inlining when we reach the beginning
        // of a recursion cycle again. We don't inline immediately recursive
        // functions, but allow inlining if there is a recursion cycle of
        // many functions. Most likely, the inlining will stop before we
        // even hit the beginning of the cycle again, but this catches the
        // unusual case.
        for inlIndex := parent; inlIndex >= 0; inlIndex = base.Ctxt.InlTree.Parent(inlIndex) {
                if base.Ctxt.InlTree.InlinedFunction(inlIndex) == sym {
                        if base.Flag.LowerM > 1 {
                                fmt.Printf("%v: cannot inline %v into %v: repeated recursive cycle\n", ir.Line(n), fn, ir.FuncName(ir.CurFunc))
                        }
                        return n
                }
        }

        typecheck.FixVariadicCall(n)

        inlIndex := base.Ctxt.InlTree.Add(parent, n.Pos(), sym)

        closureInitLSym := func(n *ir.CallExpr, fn *ir.Func) {
                // The linker needs FuncInfo metadata for all inlined
                // functions. This is typically handled by gc.enqueueFunc
                // calling ir.InitLSym for all function declarations in
                // typecheck.Target.Decls (ir.UseClosure adds all closures to
                // Decls).
                //
                // However, non-trivial closures in Decls are ignored, and are
                // insteaded enqueued when walk of the calling function
                // discovers them.
                //
                // This presents a problem for direct calls to closures.
                // Inlining will replace the entire closure definition with its
                // body, which hides the closure from walk and thus suppresses
                // symbol creation.
                //
                // Explicitly create a symbol early in this edge case to ensure
                // we keep this metadata.
                //
                // TODO: Refactor to keep a reference so this can all be done
                // by enqueueFunc.

                if n.Op() != ir.OCALLFUNC {
                        // Not a standard call.
                        return
                }
                if n.X.Op() != ir.OCLOSURE {
                        // Not a direct closure call.
                        return
                }

                clo := n.X.(*ir.ClosureExpr)
                if ir.IsTrivialClosure(clo) {
                        // enqueueFunc will handle trivial closures anyways.
                        return
                }

                ir.InitLSym(fn, true)
        }

        closureInitLSym(n, fn)

        if base.Flag.GenDwarfInl > 0 {
                if !sym.WasInlined() {
                        base.Ctxt.DwFixups.SetPrecursorFunc(sym, fn)
                        sym.Set(obj.AttrWasInlined, true)
                }
        }

        if base.Flag.LowerM != 0 {
                fmt.Printf("%v: inlining call to %v\n", ir.Line(n), fn)
        }
        if base.Flag.LowerM > 2 {
                fmt.Printf("%v: Before inlining: %+v\n", ir.Line(n), n)
        }

        if base.Debug.PGOInline > 0 {
                csi := pgo.CallSiteInfo{LineOffset: pgo.NodeLineOffset(n, fn), Caller: ir.CurFunc}
                if _, ok := inlinedCallSites[csi]; !ok {
                        inlinedCallSites[csi] = struct{}{}
                }
        }

        res := InlineCall(n, fn, inlIndex)

        if res == nil {
                base.FatalfAt(n.Pos(), "inlining call to %v failed", fn)
        }

        if base.Flag.LowerM > 2 {
                fmt.Printf("%v: After inlining %+v\n\n", ir.Line(res), res)
        }

        *inlCalls = append(*inlCalls, res)

        return res
}

// CalleeEffects appends any side effects from evaluating callee to init.
func CalleeEffects(init *ir.Nodes, callee ir.Node) {
        for {
                init.Append(ir.TakeInit(callee)...)

                switch callee.Op() {
                case ir.ONAME, ir.OCLOSURE, ir.OMETHEXPR:
                        return // done

                case ir.OCONVNOP:
                        conv := callee.(*ir.ConvExpr)
                        callee = conv.X

                case ir.OINLCALL:
                        ic := callee.(*ir.InlinedCallExpr)
                        init.Append(ic.Body.Take()...)
                        callee = ic.SingleResult()

                default:
                        base.FatalfAt(callee.Pos(), "unexpected callee expression: %v", callee)
                }
        }
}

// oldInlineCall creates an InlinedCallExpr to replace the given call
// expression. fn is the callee function to be inlined. inlIndex is
// the inlining tree position index, for use with src.NewInliningBase
// when rewriting positions.
func oldInlineCall(call *ir.CallExpr, fn *ir.Func, inlIndex int) *ir.InlinedCallExpr {
        if base.Debug.TypecheckInl == 0 {
                typecheck.ImportedBody(fn)
        }

        SSADumpInline(fn)

        ninit := call.Init()

        // For normal function calls, the function callee expression
        // may contain side effects. Make sure to preserve these,
        // if necessary (#42703).
        if call.Op() == ir.OCALLFUNC {
                CalleeEffects(&ninit, call.X)
        }

        // Make temp names to use instead of the originals.
        inlvars := make(map[*ir.Name]*ir.Name)

        // record formals/locals for later post-processing
        var inlfvars []*ir.Name

        for _, ln := range fn.Inl.Dcl {
                if ln.Op() != ir.ONAME {
                        continue
                }
                if ln.Class == ir.PPARAMOUT { // return values handled below.
                        continue
                }
                inlf := typecheck.Expr(inlvar(ln)).(*ir.Name)
                inlvars[ln] = inlf
                if base.Flag.GenDwarfInl > 0 {
                        if ln.Class == ir.PPARAM {
                                inlf.Name().SetInlFormal(true)
                        } else {
                                inlf.Name().SetInlLocal(true)
                        }
                        inlf.SetPos(ln.Pos())
                        inlfvars = append(inlfvars, inlf)
                }
        }

        // We can delay declaring+initializing result parameters if:
        // temporaries for return values.
        var retvars []ir.Node
        for i, t := range fn.Type().Results().Fields().Slice() {
                var m *ir.Name
                if nn := t.Nname; nn != nil && !ir.IsBlank(nn.(*ir.Name)) && !strings.HasPrefix(nn.Sym().Name, "~r") {
                        n := nn.(*ir.Name)
                        m = inlvar(n)
                        m = typecheck.Expr(m).(*ir.Name)
                        inlvars[n] = m
                } else {
                        // anonymous return values, synthesize names for use in assignment that replaces return
                        m = retvar(t, i)
                }

                if base.Flag.GenDwarfInl > 0 {
                        // Don't update the src.Pos on a return variable if it
                        // was manufactured by the inliner (e.g. "~R2"); such vars
                        // were not part of the original callee.
                        if !strings.HasPrefix(m.Sym().Name, "~R") {
                                m.Name().SetInlFormal(true)
                                m.SetPos(t.Pos)
                                inlfvars = append(inlfvars, m)
                        }
                }

                retvars = append(retvars, m)
        }

        // Assign arguments to the parameters' temp names.
        as := ir.NewAssignListStmt(base.Pos, ir.OAS2, nil, nil)
        as.Def = true
        if call.Op() == ir.OCALLMETH {
                base.FatalfAt(call.Pos(), "OCALLMETH missed by typecheck")
        }
        as.Rhs.Append(call.Args...)

        if recv := fn.Type().Recv(); recv != nil {
                as.Lhs.Append(inlParam(recv, as, inlvars))
        }
        for _, param := range fn.Type().Params().Fields().Slice() {
                as.Lhs.Append(inlParam(param, as, inlvars))
        }

        if len(as.Rhs) != 0 {
                ninit.Append(typecheck.Stmt(as))
        }

        if !fn.Inl.CanDelayResults {
                // Zero the return parameters.
                for _, n := range retvars {
                        ninit.Append(ir.NewDecl(base.Pos, ir.ODCL, n.(*ir.Name)))
                        ras := ir.NewAssignStmt(base.Pos, n, nil)
                        ninit.Append(typecheck.Stmt(ras))
                }
        }

        retlabel := typecheck.AutoLabel(".i")

        inlgen++

        // Add an inline mark just before the inlined body.
        // This mark is inline in the code so that it's a reasonable spot
        // to put a breakpoint. Not sure if that's really necessary or not
        // (in which case it could go at the end of the function instead).
        // Note issue 28603.
        ninit.Append(ir.NewInlineMarkStmt(call.Pos().WithIsStmt(), int64(inlIndex)))

        subst := inlsubst{
                retlabel:    retlabel,
                retvars:     retvars,
                inlvars:     inlvars,
                defnMarker:  ir.NilExpr{},
                bases:       make(map[*src.PosBase]*src.PosBase),
                newInlIndex: inlIndex,
                fn:          fn,
        }
        subst.edit = subst.node

        body := subst.list(ir.Nodes(fn.Inl.Body))

        lab := ir.NewLabelStmt(base.Pos, retlabel)
        body = append(body, lab)

        if base.Flag.GenDwarfInl > 0 {
                for _, v := range inlfvars {
                        v.SetPos(subst.updatedPos(v.Pos()))
                }
        }

        //dumplist("ninit post", ninit);

        res := ir.NewInlinedCallExpr(base.Pos, body, retvars)
        res.SetInit(ninit)
        res.SetType(call.Type())
        res.SetTypecheck(1)
        return res
}

// Every time we expand a function we generate a new set of tmpnames,
// PAUTO's in the calling functions, and link them off of the
// PPARAM's, PAUTOS and PPARAMOUTs of the called function.
func inlvar(var_ *ir.Name) *ir.Name {
        if base.Flag.LowerM > 3 {
                fmt.Printf("inlvar %+v\n", var_)
        }

        n := typecheck.NewName(var_.Sym())
        n.SetType(var_.Type())
        n.SetTypecheck(1)
        n.Class = ir.PAUTO
        n.SetUsed(true)
        n.SetAutoTemp(var_.AutoTemp())
        n.Curfn = ir.CurFunc // the calling function, not the called one
        n.SetAddrtaken(var_.Addrtaken())

        ir.CurFunc.Dcl = append(ir.CurFunc.Dcl, n)
        return n
}

// Synthesize a variable to store the inlined function's results in.
func retvar(t *types.Field, i int) *ir.Name {
        n := typecheck.NewName(typecheck.LookupNum("~R", i))
        n.SetType(t.Type)
        n.SetTypecheck(1)
        n.Class = ir.PAUTO
        n.SetUsed(true)
        n.Curfn = ir.CurFunc // the calling function, not the called one
        ir.CurFunc.Dcl = append(ir.CurFunc.Dcl, n)
        return n
}

// The inlsubst type implements the actual inlining of a single
// function call.
type inlsubst struct {
        // Target of the goto substituted in place of a return.
        retlabel *types.Sym

        // Temporary result variables.
        retvars []ir.Node

        inlvars map[*ir.Name]*ir.Name
        // defnMarker is used to mark a Node for reassignment.
        // inlsubst.clovar set this during creating new ONAME.
        // inlsubst.node will set the correct Defn for inlvar.
        defnMarker ir.NilExpr

        // bases maps from original PosBase to PosBase with an extra
        // inlined call frame.
        bases map[*src.PosBase]*src.PosBase

        // newInlIndex is the index of the inlined call frame to
        // insert for inlined nodes.
        newInlIndex int

        edit func(ir.Node) ir.Node // cached copy of subst.node method value closure

        // If non-nil, we are inside a closure inside the inlined function, and
        // newclofn is the Func of the new inlined closure.
        newclofn *ir.Func

        fn *ir.Func // For debug -- the func that is being inlined

        // If true, then don't update source positions during substitution
        // (retain old source positions).
        noPosUpdate bool
}

// list inlines a list of nodes.
func (subst *inlsubst) list(ll ir.Nodes) []ir.Node {
        s := make([]ir.Node, 0, len(ll))
        for _, n := range ll {
                s = append(s, subst.node(n))
        }
        return s
}

// fields returns a list of the fields of a struct type representing receiver,
// params, or results, after duplicating the field nodes and substituting the
// Nname nodes inside the field nodes.
func (subst *inlsubst) fields(oldt *types.Type) []*types.Field {
        oldfields := oldt.FieldSlice()
        newfields := make([]*types.Field, len(oldfields))
        for i := range oldfields {
                newfields[i] = oldfields[i].Copy()
                if oldfields[i].Nname != nil {
                        newfields[i].Nname = subst.node(oldfields[i].Nname.(*ir.Name))
                }
        }
        return newfields
}

// clovar creates a new ONAME node for a local variable or param of a closure
// inside a function being inlined.
func (subst *inlsubst) clovar(n *ir.Name) *ir.Name {
        m := ir.NewNameAt(n.Pos(), n.Sym())
        m.Class = n.Class
        m.SetType(n.Type())
        m.SetTypecheck(1)
        if n.IsClosureVar() {
                m.SetIsClosureVar(true)
        }
        if n.Addrtaken() {
                m.SetAddrtaken(true)
        }
        if n.Used() {
                m.SetUsed(true)
        }
        m.Defn = n.Defn

        m.Curfn = subst.newclofn

        switch defn := n.Defn.(type) {
        case nil:
                // ok
        case *ir.Name:
                if !n.IsClosureVar() {
                        base.FatalfAt(n.Pos(), "want closure variable, got: %+v", n)
                }
                if n.Sym().Pkg != types.LocalPkg {
                        // If the closure came from inlining a function from
                        // another package, must change package of captured
                        // variable to localpkg, so that the fields of the closure
                        // struct are local package and can be accessed even if
                        // name is not exported. If you disable this code, you can
                        // reproduce the problem by running 'go test
                        // go/internal/srcimporter'. TODO(mdempsky) - maybe change
                        // how we create closure structs?
                        m.SetSym(types.LocalPkg.Lookup(n.Sym().Name))
                }
                // Make sure any inlvar which is the Defn
                // of an ONAME closure var is rewritten
                // during inlining. Don't substitute
                // if Defn node is outside inlined function.
                if subst.inlvars[n.Defn.(*ir.Name)] != nil {
                        m.Defn = subst.node(n.Defn)
                }
        case *ir.AssignStmt, *ir.AssignListStmt:
                // Mark node for reassignment at the end of inlsubst.node.
                m.Defn = &subst.defnMarker
        case *ir.TypeSwitchGuard:
                // TODO(mdempsky): Set m.Defn properly. See discussion on #45743.
        case *ir.RangeStmt:
                // TODO: Set m.Defn properly if we support inlining range statement in the future.
        default:
                base.FatalfAt(n.Pos(), "unexpected Defn: %+v", defn)
        }

        if n.Outer != nil {
                // Either the outer variable is defined in function being inlined,
                // and we will replace it with the substituted variable, or it is
                // defined outside the function being inlined, and we should just
                // skip the outer variable (the closure variable of the function
                // being inlined).
                s := subst.node(n.Outer).(*ir.Name)
                if s == n.Outer {
                        s = n.Outer.Outer
                }
                m.Outer = s
        }
        return m
}

// closure does the necessary substitions for a ClosureExpr n and returns the new
// closure node.
func (subst *inlsubst) closure(n *ir.ClosureExpr) ir.Node {
        // Prior to the subst edit, set a flag in the inlsubst to indicate
        // that we don't want to update the source positions in the new
        // closure function. If we do this, it will appear that the
        // closure itself has things inlined into it, which is not the
        // case. See issue #46234 for more details. At the same time, we
        // do want to update the position in the new ClosureExpr (which is
        // part of the function we're working on). See #49171 for an
        // example of what happens if we miss that update.
        newClosurePos := subst.updatedPos(n.Pos())
        defer func(prev bool) { subst.noPosUpdate = prev }(subst.noPosUpdate)
        subst.noPosUpdate = true

        //fmt.Printf("Inlining func %v with closure into %v\n", subst.fn, ir.FuncName(ir.CurFunc))

        oldfn := n.Func
        newfn := ir.NewClosureFunc(oldfn.Pos(), true)

        if subst.newclofn != nil {
                //fmt.Printf("Inlining a closure with a nested closure\n")
        }
        prevxfunc := subst.newclofn

        // Mark that we are now substituting within a closure (within the
        // inlined function), and create new nodes for all the local
        // vars/params inside this closure.
        subst.newclofn = newfn
        newfn.Dcl = nil
        newfn.ClosureVars = nil
        for _, oldv := range oldfn.Dcl {
                newv := subst.clovar(oldv)
                subst.inlvars[oldv] = newv
                newfn.Dcl = append(newfn.Dcl, newv)
        }
        for _, oldv := range oldfn.ClosureVars {
                newv := subst.clovar(oldv)
                subst.inlvars[oldv] = newv
                newfn.ClosureVars = append(newfn.ClosureVars, newv)
        }

        // Need to replace ONAME nodes in
        // newfn.Type().FuncType().Receiver/Params/Results.FieldSlice().Nname
        oldt := oldfn.Type()
        newrecvs := subst.fields(oldt.Recvs())
        var newrecv *types.Field
        if len(newrecvs) > 0 {
                newrecv = newrecvs[0]
        }
        newt := types.NewSignature(oldt.Pkg(), newrecv,
                nil, subst.fields(oldt.Params()), subst.fields(oldt.Results()))

        newfn.Nname.SetType(newt)
        newfn.Body = subst.list(oldfn.Body)

        // Remove the nodes for the current closure from subst.inlvars
        for _, oldv := range oldfn.Dcl {
                delete(subst.inlvars, oldv)
        }
        for _, oldv := range oldfn.ClosureVars {
                delete(subst.inlvars, oldv)
        }
        // Go back to previous closure func
        subst.newclofn = prevxfunc

        // Actually create the named function for the closure, now that
        // the closure is inlined in a specific function.
        newclo := newfn.OClosure
        newclo.SetPos(newClosurePos)
        newclo.SetInit(subst.list(n.Init()))
        return typecheck.Expr(newclo)
}

// node recursively copies a node from the saved pristine body of the
// inlined function, substituting references to input/output
// parameters with ones to the tmpnames, and substituting returns with
// assignments to the output.
func (subst *inlsubst) node(n ir.Node) ir.Node {
        if n == nil {
                return nil
        }

        switch n.Op() {
        case ir.ONAME:
                n := n.(*ir.Name)

                // Handle captured variables when inlining closures.
                if n.IsClosureVar() && subst.newclofn == nil {
                        o := n.Outer

                        // Deal with case where sequence of closures are inlined.
                        // TODO(danscales) - write test case to see if we need to
                        // go up multiple levels.
                        if o.Curfn != ir.CurFunc {
                                o = o.Outer
                        }

                        // make sure the outer param matches the inlining location
                        if o == nil || o.Curfn != ir.CurFunc {
                                base.Fatalf("%v: unresolvable capture %v\n", ir.Line(n), n)
                        }

                        if base.Flag.LowerM > 2 {
                                fmt.Printf("substituting captured name %+v  ->  %+v\n", n, o)
                        }
                        return o
                }

                if inlvar := subst.inlvars[n]; inlvar != nil { // These will be set during inlnode
                        if base.Flag.LowerM > 2 {
                                fmt.Printf("substituting name %+v  ->  %+v\n", n, inlvar)
                        }
                        return inlvar
                }

                if base.Flag.LowerM > 2 {
                        fmt.Printf("not substituting name %+v\n", n)
                }
                return n

        case ir.OMETHEXPR:
                n := n.(*ir.SelectorExpr)
                return n

        case ir.OLITERAL, ir.ONIL, ir.OTYPE:
                // If n is a named constant or type, we can continue
                // using it in the inline copy. Otherwise, make a copy
                // so we can update the line number.
                if n.Sym() != nil {
                        return n
                }

        case ir.ORETURN:
                if subst.newclofn != nil {
                        // Don't do special substitutions if inside a closure
                        break
                }
                // Because of the above test for subst.newclofn,
                // this return is guaranteed to belong to the current inlined function.
                n := n.(*ir.ReturnStmt)
                init := subst.list(n.Init())
                if len(subst.retvars) != 0 && len(n.Results) != 0 {
                        as := ir.NewAssignListStmt(base.Pos, ir.OAS2, nil, nil)

                        // Make a shallow copy of retvars.
                        // Otherwise OINLCALL.Rlist will be the same list,
                        // and later walk and typecheck may clobber it.
                        for _, n := range subst.retvars {
                                as.Lhs.Append(n)
                        }
                        as.Rhs = subst.list(n.Results)

                        if subst.fn.Inl.CanDelayResults {
                                for _, n := range as.Lhs {
                                        as.PtrInit().Append(ir.NewDecl(base.Pos, ir.ODCL, n.(*ir.Name)))
                                        n.Name().Defn = as
                                }
                        }

                        init = append(init, typecheck.Stmt(as))
                }
                init = append(init, ir.NewBranchStmt(base.Pos, ir.OGOTO, subst.retlabel))
                typecheck.Stmts(init)
                return ir.NewBlockStmt(base.Pos, init)

        case ir.OGOTO, ir.OBREAK, ir.OCONTINUE:
                if subst.newclofn != nil {
                        // Don't do special substitutions if inside a closure
                        break
                }
                n := n.(*ir.BranchStmt)
                m := ir.Copy(n).(*ir.BranchStmt)
                m.SetPos(subst.updatedPos(m.Pos()))
                m.SetInit(nil)
                m.Label = translateLabel(n.Label)
                return m

        case ir.OLABEL:
                if subst.newclofn != nil {
                        // Don't do special substitutions if inside a closure
                        break
                }
                n := n.(*ir.LabelStmt)
                m := ir.Copy(n).(*ir.LabelStmt)
                m.SetPos(subst.updatedPos(m.Pos()))
                m.SetInit(nil)
                m.Label = translateLabel(n.Label)
                return m

        case ir.OCLOSURE:
                return subst.closure(n.(*ir.ClosureExpr))

        }

        m := ir.Copy(n)
        m.SetPos(subst.updatedPos(m.Pos()))
        ir.EditChildren(m, subst.edit)

        if subst.newclofn == nil {
                // Translate any label on FOR, RANGE loops, SWITCH or SELECT
                switch m.Op() {
                case ir.OFOR:
                        m := m.(*ir.ForStmt)
                        m.Label = translateLabel(m.Label)
                        return m

                case ir.ORANGE:
                        m := m.(*ir.RangeStmt)
                        m.Label = translateLabel(m.Label)
                        return m

                case ir.OSWITCH:
                        m := m.(*ir.SwitchStmt)
                        m.Label = translateLabel(m.Label)
                        return m

                case ir.OSELECT:
                        m := m.(*ir.SelectStmt)
                        m.Label = translateLabel(m.Label)
                        return m
                }
        }

        switch m := m.(type) {
        case *ir.AssignStmt:
                if lhs, ok := m.X.(*ir.Name); ok && lhs.Defn == &subst.defnMarker {
                        lhs.Defn = m
                }
        case *ir.AssignListStmt:
                for _, lhs := range m.Lhs {
                        if lhs, ok := lhs.(*ir.Name); ok && lhs.Defn == &subst.defnMarker {
                                lhs.Defn = m
                        }
                }
        }

        return m
}

// translateLabel makes a label from an inlined function (if non-nil) be unique by
// adding "·inlgen".
func translateLabel(l *types.Sym) *types.Sym {
        if l == nil {
                return nil
        }
        p := fmt.Sprintf("%s·%d", l.Name, inlgen)
        return typecheck.Lookup(p)
}

func (subst *inlsubst) updatedPos(xpos src.XPos) src.XPos {
        if subst.noPosUpdate {
                return xpos
        }
        pos := base.Ctxt.PosTable.Pos(xpos)
        oldbase := pos.Base() // can be nil
        newbase := subst.bases[oldbase]
        if newbase == nil {
                newbase = src.NewInliningBase(oldbase, subst.newInlIndex)
                subst.bases[oldbase] = newbase
        }
        pos.SetBase(newbase)
        return base.Ctxt.PosTable.XPos(pos)
}

func pruneUnusedAutos(ll []*ir.Name, vis *hairyVisitor) []*ir.Name {
        s := make([]*ir.Name, 0, len(ll))
        for _, n := range ll {
                if n.Class == ir.PAUTO {
                        if !vis.usedLocals.Has(n) {
                                continue
                        }
                }
                s = append(s, n)
        }
        return s
}

// numNonClosures returns the number of functions in list which are not closures.
func numNonClosures(list []*ir.Func) int {
        count := 0
        for _, fn := range list {
                if fn.OClosure == nil {
                        count++
                }
        }
        return count
}

func doList(list []ir.Node, do func(ir.Node) bool) bool {
        for _, x := range list {
                if x != nil {
                        if do(x) {
                                return true
                        }
                }
        }
        return false
}

// isIndexingCoverageCounter returns true if the specified node 'n' is indexing
// into a coverage counter array.
func isIndexingCoverageCounter(n ir.Node) bool {
        if n.Op() != ir.OINDEX {
                return false
        }
        ixn := n.(*ir.IndexExpr)
        if ixn.X.Op() != ir.ONAME || !ixn.X.Type().IsArray() {
                return false
        }
        nn := ixn.X.(*ir.Name)
        return nn.CoverageCounter()
}

// isAtomicCoverageCounterUpdate examines the specified node to
// determine whether it represents a call to sync/atomic.AddUint32 to
// increment a coverage counter.
func isAtomicCoverageCounterUpdate(cn *ir.CallExpr) bool {
        if cn.X.Op() != ir.ONAME {
                return false
        }
        name := cn.X.(*ir.Name)
        if name.Class != ir.PFUNC {
                return false
        }
        fn := name.Sym().Name
        if name.Sym().Pkg.Path != "sync/atomic" ||
                (fn != "AddUint32" && fn != "StoreUint32") {
                return false
        }
        if len(cn.Args) != 2 || cn.Args[0].Op() != ir.OADDR {
                return false
        }
        adn := cn.Args[0].(*ir.AddrExpr)
        v := isIndexingCoverageCounter(adn.X)
        return v
}