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/src"
)

// 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") and
// f.Func.Shortname is the bare method name (e.g., "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 OCALLPART otherwise.
// These are like method expressions, except that for ODOTMETH/ODOTINTER,
// the method name is stored in Sym instead of Right.
// Each OCALLPART ends up being implemented as a new
// function, a bit like a closure, with its own ODCLFUNC.
// The OCALLPART uses n.Func to record the linkage to
// the generated ODCLFUNC, but there is no
// pointer from the Func back to the OCALLPART.
type Func struct {
	miniNode
	Body Nodes
	Iota int64

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

	Shortname *types.Sym

	// 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

	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
	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
}

func NewFunc(pos src.XPos) *Func {
	f := new(Func)
	f.pos = pos
	f.op = ODCLFUNC
	f.Iota = -1
	return f
}

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 (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 Nbody for use during inlining.
	Dcl  []*Name
	Body []Node
}

// 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                   // is method wrapper
	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
	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 instrumentation during SSA construction
	funcOpenCodedDeferDisallowed // can't do open-coded defers
	funcClosureCalled            // closure is only immediately called
)

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) 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) 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) ClosureCalled() bool            { return f.flags&funcClosureCalled != 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) 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) 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) SetClosureCalled(b bool)            { f.flags.set(funcClosureCalled, 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 n.
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 n, with package prepended.
// This differs from the compiler's internal convention where local functions lack a package
// because the ultimate consumer of this is a human looking at an IDE; package is only empty
// if the compilation package is actually the empty string.
func PkgFuncName(f *Func) string {
	if f == nil || f.Nname == nil {
		return "<nil>"
	}
	s := f.Sym()
	pkg := s.Pkg

	p := base.Ctxt.Pkgpath
	if pkg != nil && pkg.Path != "" {
		p = pkg.Path
	}
	if p == "" {
		return s.Name
	}
	return p + "." + s.Name
}

var CurFunc *Func

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

// MarkFunc marks a node as a function.
func MarkFunc(n *Name) {
	if n.Op() != ONAME || n.Class != Pxxx {
		base.Fatalf("expected ONAME/Pxxx node, got %v", n)
	}

	n.Class = PFUNC
	n.Sym().SetFunc(true)
}

// 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 {
		base.ErrorfAt(clo.Pos(), "heap-allocated closure, not allowed in runtime")
	}
}

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