[gostls13.git] / src / cmd / compile / internal / ir / func.go

// Copyright 2020 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 ir

import (
        "cmd/compile/internal/base"
        "cmd/compile/internal/types"
        "cmd/internal/obj"
        "cmd/internal/objabi"
        "cmd/internal/src"
        "fmt"
        "strings"
        "unicode/utf8"
)

// A Func corresponds to a single function in a Go program
// (and vice versa: each function is denoted by exactly one *Func).
//
// There are multiple nodes that represent a Func in the IR.
//
// The ONAME node (Func.Nname) is used for plain references to it.
// The ODCLFUNC node (the Func itself) is used for its declaration code.
// The OCLOSURE node (Func.OClosure) is used for a reference to a
// function literal.
//
// An imported function will have an ONAME node which points to a Func
// with an empty body.
// A declared function or method has an ODCLFUNC (the Func itself) and an ONAME.
// A function literal is represented directly by an OCLOSURE, but it also
// has an ODCLFUNC (and a matching ONAME) representing the compiled
// underlying form of the closure, which accesses the captured variables
// using a special data structure passed in a register.
//
// A method declaration is represented like functions, except f.Sym
// will be the qualified method name (e.g., "T.m").
//
// A method expression (T.M) is represented as an OMETHEXPR node,
// in which n.Left and n.Right point to the type and method, respectively.
// Each distinct mention of a method expression in the source code
// constructs a fresh node.
//
// A method value (t.M) is represented by ODOTMETH/ODOTINTER
// when it is called directly and by OMETHVALUE otherwise.
// These are like method expressions, except that for ODOTMETH/ODOTINTER,
// the method name is stored in Sym instead of Right.
// Each OMETHVALUE ends up being implemented as a new
// function, a bit like a closure, with its own ODCLFUNC.
// The OMETHVALUE uses n.Func to record the linkage to
// the generated ODCLFUNC, but there is no
// pointer from the Func back to the OMETHVALUE.
type Func struct {
        miniNode
        Body Nodes

        Nname    *Name        // ONAME node
        OClosure *ClosureExpr // OCLOSURE node

        // ONAME nodes for all params/locals for this func/closure, does NOT
        // include closurevars until transforming closures during walk.
        // Names must be listed PPARAMs, PPARAMOUTs, then PAUTOs,
        // with PPARAMs and PPARAMOUTs in order corresponding to the function signature.
        // Anonymous and blank params are declared as ~pNN (for PPARAMs) and ~rNN (for PPARAMOUTs).
        Dcl []*Name

        // ClosureVars lists the free variables that are used within a
        // function literal, but formally declared in an enclosing
        // function. The variables in this slice are the closure function's
        // own copy of the variables, which are used within its function
        // body. They will also each have IsClosureVar set, and will have
        // Byval set if they're captured by value.
        ClosureVars []*Name

        // Enclosed functions that need to be compiled.
        // Populated during walk.
        Closures []*Func

        // Parents records the parent scope of each scope within a
        // function. The root scope (0) has no parent, so the i'th
        // scope's parent is stored at Parents[i-1].
        Parents []ScopeID

        // Marks records scope boundary changes.
        Marks []Mark

        FieldTrack map[*obj.LSym]struct{}
        DebugInfo  interface{}
        LSym       *obj.LSym // Linker object in this function's native ABI (Func.ABI)

        Inl *Inline

        // funcLitGen and goDeferGen track how many closures have been
        // created in this function for function literals and go/defer
        // wrappers, respectively. Used by closureName for creating unique
        // function names.
        //
        // Tracking goDeferGen separately avoids wrappers throwing off
        // function literal numbering (e.g., runtime/trace_test.TestTraceSymbolize.func11).
        funcLitGen int32
        goDeferGen int32

        Label int32 // largest auto-generated label in this function

        Endlineno src.XPos
        WBPos     src.XPos // position of first write barrier; see SetWBPos

        Pragma PragmaFlag // go:xxx function annotations

        flags bitset16

        // ABI is a function's "definition" ABI. This is the ABI that
        // this function's generated code is expecting to be called by.
        //
        // For most functions, this will be obj.ABIInternal. It may be
        // a different ABI for functions defined in assembly or ABI wrappers.
        //
        // This is included in the export data and tracked across packages.
        ABI obj.ABI
        // ABIRefs is the set of ABIs by which this function is referenced.
        // For ABIs other than this function's definition ABI, the
        // compiler generates ABI wrapper functions. This is only tracked
        // within a package.
        ABIRefs obj.ABISet

        NumDefers  int32 // number of defer calls in the function
        NumReturns int32 // number of explicit returns in the function

        // nwbrCalls records the LSyms of functions called by this
        // function for go:nowritebarrierrec analysis. Only filled in
        // if nowritebarrierrecCheck != nil.
        NWBRCalls *[]SymAndPos

        // For wrapper functions, WrappedFunc point to the original Func.
        // Currently only used for go/defer wrappers.
        WrappedFunc *Func

        // WasmImport is used by the //go:wasmimport directive to store info about
        // a WebAssembly function import.
        WasmImport *WasmImport
}

// WasmImport stores metadata associated with the //go:wasmimport pragma.
type WasmImport struct {
        Module string
        Name   string
}

// NewFunc returns a new Func with the given name and type.
//
// fpos is the position of the "func" token, and npos is the position
// of the name identifier.
//
// TODO(mdempsky): I suspect there's no need for separate fpos and
// npos.
func NewFunc(fpos, npos src.XPos, sym *types.Sym, typ *types.Type) *Func {
        name := NewNameAt(npos, sym, typ)
        name.Class = PFUNC
        sym.SetFunc(true)

        fn := &Func{Nname: name}
        fn.pos = fpos
        fn.op = ODCLFUNC
        // Most functions are ABIInternal. The importer or symabis
        // pass may override this.
        fn.ABI = obj.ABIInternal
        fn.SetTypecheck(1)

        name.Func = fn

        return fn
}

func (f *Func) isStmt() {}

func (n *Func) copy() Node                                  { panic(n.no("copy")) }
func (n *Func) doChildren(do func(Node) bool) bool          { return doNodes(n.Body, do) }
func (n *Func) editChildren(edit func(Node) Node)           { editNodes(n.Body, edit) }
func (n *Func) editChildrenWithHidden(edit func(Node) Node) { editNodes(n.Body, edit) }

func (f *Func) Type() *types.Type                { return f.Nname.Type() }
func (f *Func) Sym() *types.Sym                  { return f.Nname.Sym() }
func (f *Func) Linksym() *obj.LSym               { return f.Nname.Linksym() }
func (f *Func) LinksymABI(abi obj.ABI) *obj.LSym { return f.Nname.LinksymABI(abi) }

// An Inline holds fields used for function bodies that can be inlined.
type Inline struct {
        Cost int32 // heuristic cost of inlining this function

        // Copy of Func.Dcl for use during inlining. This copy is needed
        // because the function's Dcl may change from later compiler
        // transformations. This field is also populated when a function
        // from another package is imported and inlined.
        Dcl     []*Name
        HaveDcl bool // whether we've loaded Dcl

        // Function properties, encoded as a string (these are used for
        // making inlining decisions). See cmd/compile/internal/inline/inlheur.
        Properties string

        // CanDelayResults reports whether it's safe for the inliner to delay
        // initializing the result parameters until immediately before the
        // "return" statement.
        CanDelayResults bool
}

// A Mark represents a scope boundary.
type Mark struct {
        // Pos is the position of the token that marks the scope
        // change.
        Pos src.XPos

        // Scope identifies the innermost scope to the right of Pos.
        Scope ScopeID
}

// A ScopeID represents a lexical scope within a function.
type ScopeID int32

const (
        funcDupok      = 1 << iota // duplicate definitions ok
        funcWrapper                // hide frame from users (elide in tracebacks, don't count as a frame for recover())
        funcABIWrapper             // is an ABI wrapper (also set flagWrapper)
        funcNeedctxt               // function uses context register (has closure variables)
        // true if closure inside a function; false if a simple function or a
        // closure in a global variable initialization
        funcIsHiddenClosure
        funcIsDeadcodeClosure        // true if closure is deadcode
        funcHasDefer                 // contains a defer statement
        funcNilCheckDisabled         // disable nil checks when compiling this function
        funcInlinabilityChecked      // inliner has already determined whether the function is inlinable
        funcNeverReturns             // function never returns (in most cases calls panic(), os.Exit(), or equivalent)
        funcOpenCodedDeferDisallowed // can't do open-coded defers
        funcClosureResultsLost       // closure is called indirectly and we lost track of its results; used by escape analysis
        funcPackageInit              // compiler emitted .init func for package
)

type SymAndPos struct {
        Sym *obj.LSym // LSym of callee
        Pos src.XPos  // line of call
}

func (f *Func) Dupok() bool                    { return f.flags&funcDupok != 0 }
func (f *Func) Wrapper() bool                  { return f.flags&funcWrapper != 0 }
func (f *Func) ABIWrapper() bool               { return f.flags&funcABIWrapper != 0 }
func (f *Func) Needctxt() bool                 { return f.flags&funcNeedctxt != 0 }
func (f *Func) IsHiddenClosure() bool          { return f.flags&funcIsHiddenClosure != 0 }
func (f *Func) IsDeadcodeClosure() bool        { return f.flags&funcIsDeadcodeClosure != 0 }
func (f *Func) HasDefer() bool                 { return f.flags&funcHasDefer != 0 }
func (f *Func) NilCheckDisabled() bool         { return f.flags&funcNilCheckDisabled != 0 }
func (f *Func) InlinabilityChecked() bool      { return f.flags&funcInlinabilityChecked != 0 }
func (f *Func) NeverReturns() bool             { return f.flags&funcNeverReturns != 0 }
func (f *Func) OpenCodedDeferDisallowed() bool { return f.flags&funcOpenCodedDeferDisallowed != 0 }
func (f *Func) ClosureResultsLost() bool       { return f.flags&funcClosureResultsLost != 0 }
func (f *Func) IsPackageInit() bool            { return f.flags&funcPackageInit != 0 }

func (f *Func) SetDupok(b bool)                    { f.flags.set(funcDupok, b) }
func (f *Func) SetWrapper(b bool)                  { f.flags.set(funcWrapper, b) }
func (f *Func) SetABIWrapper(b bool)               { f.flags.set(funcABIWrapper, b) }
func (f *Func) SetNeedctxt(b bool)                 { f.flags.set(funcNeedctxt, b) }
func (f *Func) SetIsHiddenClosure(b bool)          { f.flags.set(funcIsHiddenClosure, b) }
func (f *Func) SetIsDeadcodeClosure(b bool)        { f.flags.set(funcIsDeadcodeClosure, b) }
func (f *Func) SetHasDefer(b bool)                 { f.flags.set(funcHasDefer, b) }
func (f *Func) SetNilCheckDisabled(b bool)         { f.flags.set(funcNilCheckDisabled, b) }
func (f *Func) SetInlinabilityChecked(b bool)      { f.flags.set(funcInlinabilityChecked, b) }
func (f *Func) SetNeverReturns(b bool)             { f.flags.set(funcNeverReturns, b) }
func (f *Func) SetOpenCodedDeferDisallowed(b bool) { f.flags.set(funcOpenCodedDeferDisallowed, b) }
func (f *Func) SetClosureResultsLost(b bool)       { f.flags.set(funcClosureResultsLost, b) }
func (f *Func) SetIsPackageInit(b bool)            { f.flags.set(funcPackageInit, b) }

func (f *Func) SetWBPos(pos src.XPos) {
        if base.Debug.WB != 0 {
                base.WarnfAt(pos, "write barrier")
        }
        if !f.WBPos.IsKnown() {
                f.WBPos = pos
        }
}

// FuncName returns the name (without the package) of the function f.
func FuncName(f *Func) string {
        if f == nil || f.Nname == nil {
                return "<nil>"
        }
        return f.Sym().Name
}

// PkgFuncName returns the name of the function referenced by f, with package
// prepended.
//
// This differs from the compiler's internal convention where local functions
// lack a package. This is primarily useful when the ultimate consumer of this
// is a human looking at message.
func PkgFuncName(f *Func) string {
        if f == nil || f.Nname == nil {
                return "<nil>"
        }
        s := f.Sym()
        pkg := s.Pkg

        return pkg.Path + "." + s.Name
}

// LinkFuncName returns the name of the function f, as it will appear in the
// symbol table of the final linked binary.
func LinkFuncName(f *Func) string {
        if f == nil || f.Nname == nil {
                return "<nil>"
        }
        s := f.Sym()
        pkg := s.Pkg

        return objabi.PathToPrefix(pkg.Path) + "." + s.Name
}

// ParseLinkFuncName parsers a symbol name (as returned from LinkFuncName) back
// to the package path and local symbol name.
func ParseLinkFuncName(name string) (pkg, sym string, err error) {
        pkg, sym = splitPkg(name)
        if pkg == "" {
                return "", "", fmt.Errorf("no package path in name")
        }

        pkg, err = objabi.PrefixToPath(pkg) // unescape
        if err != nil {
                return "", "", fmt.Errorf("malformed package path: %v", err)
        }

        return pkg, sym, nil
}

// Borrowed from x/mod.
func modPathOK(r rune) bool {
        if r < utf8.RuneSelf {
                return r == '-' || r == '.' || r == '_' || r == '~' ||
                        '0' <= r && r <= '9' ||
                        'A' <= r && r <= 'Z' ||
                        'a' <= r && r <= 'z'
        }
        return false
}

func escapedImportPathOK(r rune) bool {
        return modPathOK(r) || r == '+' || r == '/' || r == '%'
}

// splitPkg splits the full linker symbol name into package and local symbol
// name.
func splitPkg(name string) (pkgpath, sym string) {
        // package-sym split is at first dot after last the / that comes before
        // any characters illegal in a package path.

        lastSlashIdx := 0
        for i, r := range name {
                // Catches cases like:
                // * example.foo[sync/atomic.Uint64].
                // * example%2ecom.foo[sync/atomic.Uint64].
                //
                // Note that name is still escaped; unescape occurs after splitPkg.
                if !escapedImportPathOK(r) {
                        break
                }
                if r == '/' {
                        lastSlashIdx = i
                }
        }
        for i := lastSlashIdx; i < len(name); i++ {
                r := name[i]
                if r == '.' {
                        return name[:i], name[i+1:]
                }
        }

        return "", name
}

var CurFunc *Func

// WithFunc invokes do with CurFunc and base.Pos set to curfn and
// curfn.Pos(), respectively, and then restores their previous values
// before returning.
func WithFunc(curfn *Func, do func()) {
        oldfn, oldpos := CurFunc, base.Pos
        defer func() { CurFunc, base.Pos = oldfn, oldpos }()

        CurFunc, base.Pos = curfn, curfn.Pos()
        do()
}

func FuncSymName(s *types.Sym) string {
        return s.Name + "·f"
}

// ClosureDebugRuntimeCheck applies boilerplate checks for debug flags
// and compiling runtime.
func ClosureDebugRuntimeCheck(clo *ClosureExpr) {
        if base.Debug.Closure > 0 {
                if clo.Esc() == EscHeap {
                        base.WarnfAt(clo.Pos(), "heap closure, captured vars = %v", clo.Func.ClosureVars)
                } else {
                        base.WarnfAt(clo.Pos(), "stack closure, captured vars = %v", clo.Func.ClosureVars)
                }
        }
        if base.Flag.CompilingRuntime && clo.Esc() == EscHeap && !clo.IsGoWrap {
                base.ErrorfAt(clo.Pos(), 0, "heap-allocated closure %s, not allowed in runtime", FuncName(clo.Func))
        }
}

// IsTrivialClosure reports whether closure clo has an
// empty list of captured vars.
func IsTrivialClosure(clo *ClosureExpr) bool {
        return len(clo.Func.ClosureVars) == 0
}

// globClosgen is like Func.Closgen, but for the global scope.
var globClosgen int32

// closureName generates a new unique name for a closure within outerfn at pos.
func closureName(outerfn *Func, pos src.XPos, why Op) *types.Sym {
        pkg := types.LocalPkg
        outer := "glob."
        var prefix string
        switch why {
        default:
                base.FatalfAt(pos, "closureName: bad Op: %v", why)
        case OCLOSURE:
                if outerfn == nil || outerfn.OClosure == nil {
                        prefix = "func"
                }
        case OGO:
                prefix = "gowrap"
        case ODEFER:
                prefix = "deferwrap"
        }
        gen := &globClosgen

        // There may be multiple functions named "_". In those
        // cases, we can't use their individual Closgens as it
        // would lead to name clashes.
        if outerfn != nil && !IsBlank(outerfn.Nname) {
                pkg = outerfn.Sym().Pkg
                outer = FuncName(outerfn)

                if why == OCLOSURE {
                        gen = &outerfn.funcLitGen
                } else {
                        gen = &outerfn.goDeferGen
                }
        }

        // If this closure was created due to inlining, then incorporate any
        // inlined functions' names into the closure's linker symbol name
        // too (#60324).
        if inlIndex := base.Ctxt.InnermostPos(pos).Base().InliningIndex(); inlIndex >= 0 {
                names := []string{outer}
                base.Ctxt.InlTree.AllParents(inlIndex, func(call obj.InlinedCall) {
                        names = append(names, call.Name)
                })
                outer = strings.Join(names, ".")
        }

        *gen++
        return pkg.Lookup(fmt.Sprintf("%s.%s%d", outer, prefix, *gen))
}

// NewClosureFunc creates a new Func to represent a function literal
// with the given type.
//
// fpos the position used for the underlying ODCLFUNC and ONAME,
// whereas cpos is the position used for the OCLOSURE. They're
// separate because in the presence of inlining, the OCLOSURE node
// should have an inline-adjusted position, whereas the ODCLFUNC and
// ONAME must not.
//
// outerfn is the enclosing function, if any. The returned function is
// appending to pkg.Funcs.
//
// why is the reason we're generating this Func. It can be OCLOSURE
// (for a normal function literal) or OGO or ODEFER (for wrapping a
// call expression that has parameters or results).
func NewClosureFunc(fpos, cpos src.XPos, why Op, typ *types.Type, outerfn *Func, pkg *Package) *Func {
        fn := NewFunc(fpos, fpos, closureName(outerfn, cpos, why), typ)
        fn.SetIsHiddenClosure(outerfn != nil)

        clo := &ClosureExpr{Func: fn}
        clo.op = OCLOSURE
        clo.pos = cpos
        clo.SetType(typ)
        clo.SetTypecheck(1)
        fn.OClosure = clo

        fn.Nname.Defn = fn
        pkg.Funcs = append(pkg.Funcs, fn)

        return fn
}

// IsFuncPCIntrinsic returns whether n is a direct call of internal/abi.FuncPCABIxxx functions.
func IsFuncPCIntrinsic(n *CallExpr) bool {
        if n.Op() != OCALLFUNC || n.Fun.Op() != ONAME {
                return false
        }
        fn := n.Fun.(*Name).Sym()
        return (fn.Name == "FuncPCABI0" || fn.Name == "FuncPCABIInternal") &&
                fn.Pkg.Path == "internal/abi"
}

// IsIfaceOfFunc inspects whether n is an interface conversion from a direct
// reference of a func. If so, it returns referenced Func; otherwise nil.
//
// This is only usable before walk.walkConvertInterface, which converts to an
// OMAKEFACE.
func IsIfaceOfFunc(n Node) *Func {
        if n, ok := n.(*ConvExpr); ok && n.Op() == OCONVIFACE {
                if name, ok := n.X.(*Name); ok && name.Op() == ONAME && name.Class == PFUNC {
                        return name.Func
                }
        }
        return nil
}

// FuncPC returns a uintptr-typed expression that evaluates to the PC of a
// function as uintptr, as returned by internal/abi.FuncPC{ABI0,ABIInternal}.
//
// n should be a Node of an interface type, as is passed to
// internal/abi.FuncPC{ABI0,ABIInternal}.
//
// TODO(prattmic): Since n is simply an interface{} there is no assertion that
// it is actually a function at all. Perhaps we should emit a runtime type
// assertion?
func FuncPC(pos src.XPos, n Node, wantABI obj.ABI) Node {
        if !n.Type().IsInterface() {
                base.ErrorfAt(pos, 0, "internal/abi.FuncPC%s expects an interface value, got %v", wantABI, n.Type())
        }

        if fn := IsIfaceOfFunc(n); fn != nil {
                name := fn.Nname
                abi := fn.ABI
                if abi != wantABI {
                        base.ErrorfAt(pos, 0, "internal/abi.FuncPC%s expects an %v function, %s is defined as %v", wantABI, wantABI, name.Sym().Name, abi)
                }
                var e Node = NewLinksymExpr(pos, name.Sym().LinksymABI(abi), types.Types[types.TUINTPTR])
                e = NewAddrExpr(pos, e)
                e.SetType(types.Types[types.TUINTPTR].PtrTo())
                e = NewConvExpr(pos, OCONVNOP, types.Types[types.TUINTPTR], e)
                e.SetTypecheck(1)
                return e
        }
        // fn is not a defined function. It must be ABIInternal.
        // Read the address from func value, i.e. *(*uintptr)(idata(fn)).
        if wantABI != obj.ABIInternal {
                base.ErrorfAt(pos, 0, "internal/abi.FuncPC%s does not accept func expression, which is ABIInternal", wantABI)
        }
        var e Node = NewUnaryExpr(pos, OIDATA, n)
        e.SetType(types.Types[types.TUINTPTR].PtrTo())
        e.SetTypecheck(1)
        e = NewStarExpr(pos, e)
        e.SetType(types.Types[types.TUINTPTR])
        e.SetTypecheck(1)
        return e
}

// DeclareParams creates Names for all of the parameters in fn's
// signature and adds them to fn.Dcl.
//
// If setNname is true, then it also sets types.Field.Nname for each
// parameter.
func (fn *Func) DeclareParams(setNname bool) {
        if fn.Dcl != nil {
                base.FatalfAt(fn.Pos(), "%v already has Dcl", fn)
        }

        declareParams := func(params []*types.Field, ctxt Class, prefix string, offset int) {
                for i, param := range params {
                        sym := param.Sym
                        if sym == nil || sym.IsBlank() {
                                sym = fn.Sym().Pkg.LookupNum(prefix, i)
                        }

                        name := NewNameAt(param.Pos, sym, param.Type)
                        name.Class = ctxt
                        name.Curfn = fn
                        fn.Dcl[offset+i] = name

                        if setNname {
                                param.Nname = name
                        }
                }
        }

        sig := fn.Type()
        params := sig.RecvParams()
        results := sig.Results()

        fn.Dcl = make([]*Name, len(params)+len(results))
        declareParams(params, PPARAM, "~p", 0)
        declareParams(results, PPARAMOUT, "~r", len(params))
}