[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"
)

// 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

        // Extra entry code for the function. For example, allocate and initialize
        // memory for escaping parameters.
        Enter Nodes
        Exit  Nodes

        // 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.
        // However, as anonymous or blank PPARAMs are not actually declared,
        // they are omitted from Dcl.
        // Anonymous and blank PPARAMOUTs are declared as ~rNN and ~bNN Names, respectively.
        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

        // Closgen tracks how many closures have been generated within
        // this function. Used by closurename for creating unique
        // function names.
        Closgen 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

        // Copies of Func.Dcl and Func.Body for use during inlining. Copies are
        // needed because the function's dcl/body may be changed by later compiler
        // transformations. These fields are also populated when a function from
        // another package is imported.
        Dcl  []*Name
        Body []Node

        // 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)
        funcReflectMethod             // function calls reflect.Type.Method or MethodByName
        // 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
        funcExportInline             // include inline body in export data
        funcInstrumentBody           // add race/msan/asan instrumentation during SSA construction
        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) ReflectMethod() bool            { return f.flags&funcReflectMethod != 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) ExportInline() bool             { return f.flags&funcExportInline != 0 }
func (f *Func) InstrumentBody() bool           { return f.flags&funcInstrumentBody != 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) SetReflectMethod(b bool)            { f.flags.set(funcReflectMethod, 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) SetExportInline(b bool)             { f.flags.set(funcExportInline, b) }
func (f *Func) SetInstrumentBody(b bool)           { f.flags.set(funcInstrumentBody, 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
}

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) *types.Sym {
        pkg := types.LocalPkg
        outer := "glob."
        prefix := "func"
        gen := &globClosgen

        if outerfn != nil {
                if outerfn.OClosure != nil {
                        prefix = ""
                }

                pkg = outerfn.Sym().Pkg
                outer = FuncName(outerfn)

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

        // 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.
func NewClosureFunc(fpos, cpos src.XPos, typ *types.Type, outerfn *Func, pkg *Package) *Func {
        fn := NewFunc(fpos, fpos, closureName(outerfn, cpos), 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
}