cmd/internal/gc: separate func-only Node fields

Nodes dominate gc's memory usage, but many fields are only used
for a subset of kinds of nodes. This change pulls out fields
used only for func-like Nodes. This reduces the size of the
Node struct on a 64-bit machine from 504 bytes to 416 bytes (-17%).

Compiling the runtime, 1.5% of nodes have a non-nil Func.
In html/template, 2.7% of nodes have a non-nil Func.

This change introduces an extra alloc and associated GC overhead
when Func is non-nil. However, when Func is nil, as it almost
always is, it spares the garbage collector scanning some Node fields.
Empirically, this change appears to be roughly neutral with regard to GC.

To keep the diff readable, this CL uses an embedded Func field.
A subsequent CL will unembed the field.

Passes toolstash -cmp.

Change-Id: Ide86aa954b097fb8e6154f0811d3691497477004
Reviewed-on: https://go-review.googlesource.com/7360
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/gc/closure.go

@@ -191,7 +191,7 @@ func makeclosure(func_ *Node) *Node {
 	// create the function
 	xfunc := Nod(ODCLFUNC, nil, nil)
 
-	xfunc.Nname = newname(closurename(func_))
+	xfunc.Nname = newfuncname(closurename(func_))
 	xfunc.Nname.Sym.Flags |= SymExported // disable export
 	xfunc.Nname.Ntype = xtype
 	xfunc.Nname.Defn = xfunc
@@ -581,7 +581,7 @@ func makepartialcall(fn *Node, t0 *Type, meth *Node) *Node {
 	xtype.Rlist = l
 
 	xfunc.Dupok = true
-	xfunc.Nname = newname(sym)
+	xfunc.Nname = newfuncname(sym)
 	xfunc.Nname.Sym.Flags |= SymExported // disable export
 	xfunc.Nname.Ntype = xtype
 	xfunc.Nname.Defn = xfunc

src/cmd/internal/gc/dcl.go

@@ -373,6 +373,14 @@ func newname(s *Sym) *Node {
 	return n
 }
 
+// newfuncname generates a new name node for a function or method.
+// TODO(rsc): Use an ODCLFUNC node instead. See comment in CL 7360.
+func newfuncname(s *Sym) *Node {
+	n := newname(s)
+	n.Func = new(Func)
+	return n
+}
+
 /*
  * this generates a new name node for a name
  * being declared.
@@ -542,6 +550,7 @@ func ifacedcl(n *Node) {
 		Yyerror("methods must have a unique non-blank name")
 	}
 
+	n.Func = new(Func)
 	dclcontext = PPARAM
 	markdcl()
 	Funcdepth++
@@ -1312,7 +1321,7 @@ func methodname1(n *Node, t *Node) *Node {
 	}
 
 	if t.Sym == nil || isblank(n) {
-		return newname(n.Sym)
+		return newfuncname(n.Sym)
 	}
 
 	var p string
@@ -1323,9 +1332,9 @@ func methodname1(n *Node, t *Node) *Node {
 	}
 
 	if exportname(t.Sym.Name) {
-		n = newname(Lookup(p))
+		n = newfuncname(Lookup(p))
 	} else {
-		n = newname(Pkglookup(p, t.Sym.Pkg))
+		n = newfuncname(Pkglookup(p, t.Sym.Pkg))
 	}
 
 	return n
@@ -1476,7 +1485,7 @@ func funcsym(s *Sym) *Sym {
 
 	s1 := Pkglookup(s.Name+"·f", s.Pkg)
 	if s1.Def == nil {
-		s1.Def = newname(s1)
+		s1.Def = newfuncname(s1)
 		s1.Def.Shortname = newname(s)
 		funcsyms = list(funcsyms, s1.Def)
 	}

src/cmd/internal/gc/export.go

@@ -239,7 +239,7 @@ func dumpexportvar(s *Sym) {
 	dumpexporttype(t)
 
 	if t.Etype == TFUNC && n.Class == PFUNC {
-		if n.Inl != nil {
+		if n.Func != nil && n.Inl != nil {
 			// when lazily typechecking inlined bodies, some re-exported ones may not have been typechecked yet.
 			// currently that can leave unresolved ONONAMEs in import-dot-ed packages in the wrong package
 			if Debug['l'] < 2 {

src/cmd/internal/gc/go.y

@@ -1358,7 +1358,7 @@ fndcl:
 		t.Rlist = $5;
 
 		$$ = Nod(ODCLFUNC, nil, nil);
-		$$.Nname = newname($1);
+		$$.Nname = newfuncname($1);
 		$$.Nname.Defn = $$;
 		$$.Nname.Ntype = t;		// TODO: check if nname already has an ntype
 		declare($$.Nname, PFUNC);
@@ -1392,7 +1392,7 @@ fndcl:
 		t.Rlist = $8;
 
 		$$ = Nod(ODCLFUNC, nil, nil);
-		$$.Shortname = newname($4);
+		$$.Shortname = newfuncname($4);
 		$$.Nname = methodname1($$.Shortname, rcvr.Right);
 		$$.Nname.Defn = $$;
 		$$.Nname.Ntype = t;
@@ -1422,7 +1422,7 @@ hidden_fndcl:
 			Yyerror("inconsistent definition for func %v during import\n\t%v\n\t%v", Sconv(s, 0), Tconv(s.Def.Type, 0), Tconv(t, 0));
 		}
 
-		$$ = newname(s);
+		$$ = newfuncname(s);
 		$$.Type = t;
 		declare($$, PFUNC);
 

src/cmd/internal/gc/inl.go

@@ -169,7 +169,7 @@ func ishairy(n *Node, budget *int) bool {
 	switch n.Op {
 	// Call is okay if inlinable and we have the budget for the body.
 	case OCALLFUNC:
-		if n.Left.Inl != nil {
+		if n.Left.Func != nil && n.Left.Inl != nil {
 			*budget -= int(n.Left.InlCost)
 			break
 		}
@@ -247,7 +247,9 @@ func inlcopy(n *Node) *Node {
 
 	m := Nod(OXXX, nil, nil)
 	*m = *n
+	if m.Func != nil {
 		m.Inl = nil
+	}
 	m.Left = inlcopy(n.Left)
 	m.Right = inlcopy(n.Right)
 	m.List = inlcopylist(n.List)
@@ -457,7 +459,7 @@ func inlnode(np **Node) {
 		if Debug['m'] > 3 {
 			fmt.Printf("%v:call to func %v\n", n.Line(), Nconv(n.Left, obj.FmtSign))
 		}
-		if n.Left.Inl != nil { // normal case
+		if n.Left.Func != nil && n.Left.Inl != nil { // normal case
 			mkinlcall(np, n.Left, n.Isddd)
 		} else if n.Left.Op == ONAME && n.Left.Left != nil && n.Left.Left.Op == OTYPE && n.Left.Right != nil && n.Left.Right.Op == ONAME { // methods called as functions
 			if n.Left.Sym.Def != nil {

src/cmd/internal/gc/subr.go

@@ -394,6 +394,10 @@ func Nod(op int, nleft *Node, nright *Node) *Node {
 	n.Xoffset = BADWIDTH
 	n.Orig = n
 	n.Curfn = Curfn
+	switch op {
+	case OCLOSURE, ODCLFUNC:
+		n.Func = new(Func)
+	}
 	return n
 }
 

src/cmd/internal/gc/syntax.go

@@ -34,9 +34,7 @@ type Node struct {
 	Embedded    uint8 // ODCLFIELD embedded type
 	Colas       uint8 // OAS resulting from :=
 	Diag        uint8 // already printed error about this
-	Noescape       bool  // func arguments do not escape
-	Nosplit        bool  // func should not execute on separate stack
-	Nowritebarrier bool  // emit compiler error instead of write barrier
+	Noescape    bool  // func arguments do not escape; TODO(rsc): move Noescape to Func struct (see CL 7360)
 	Walkdef     uint8
 	Typecheck   uint8
 	Local       bool
@@ -50,31 +48,20 @@ type Node struct {
 	Assigned    bool  // is the variable ever assigned to
 	Captured    bool  // is the variable captured by a closure
 	Byval       bool  // is the variable captured by value or by reference
-	Dupok          bool  // duplicate definitions ok (for func)
-	Wrapper        bool  // is method wrapper (for func)
 	Reslice     bool  // this is a reslice x = x[0:y] or x = append(x, ...)
 	Likely      int8  // likeliness of if statement
 	Hasbreak    bool  // has break statement
 	Needzero    bool  // if it contains pointers, needs to be zeroed on function entry
-	Needctxt       bool  // function uses context register (has closure variables)
 	Esc         uint8 // EscXXX
 	Funcdepth   int32
 
 	// most nodes
 	Type  *Type
 	Orig  *Node // original form, for printing, and tracking copies of ONAMEs
+	Nname *Node
 
 	// func
-	Nname     *Node
-	Shortname *Node
-	Enter     *NodeList
-	Exit      *NodeList
-	Cvars     *NodeList // closure params
-	Dcl       *NodeList // autodcl for this func/closure
-	Inl       *NodeList // copy of the body for use in inlining
-	Inldcl    *NodeList // copy of dcl for use in inlining
-	Closgen   int
-	Outerfunc *Node
+	*Func
 
 	// OLITERAL/OREGISTER
 	Val Val
@@ -113,19 +100,40 @@ type Node struct {
 	Escloopdepth int       // -1: global, 0: return variables, 1:function top level, increased inside function for every loop or label to mark scopes
 
 	Sym      *Sym  // various
-	InlCost   int32 // unique name for OTYPE/ONAME
-	Vargen    int32
+	Vargen   int32 // unique name for OTYPE/ONAME
 	Lineno   int32
-	Endlineno int32
 	Xoffset  int64
 	Stkdelta int64 // offset added by stack frame compaction phase.
-	Ostk      int32
+	Ostk     int32 // 6g only
 	Iota     int32
 	Walkgen  uint32
 	Esclevel int32
 	Opt      interface{} // for optimization passes
 }
 
+// Func holds Node fields used only with function-like nodes.
+type Func struct {
+	Shortname *Node
+	Enter     *NodeList
+	Exit      *NodeList
+	Cvars     *NodeList // closure params
+	Dcl       *NodeList // autodcl for this func/closure
+	Inldcl    *NodeList // copy of dcl for use in inlining
+	Closgen   int
+	Outerfunc *Node
+
+	Inl     *NodeList // copy of the body for use in inlining
+	InlCost int32
+
+	Endlineno int32
+
+	Nosplit        bool // func should not execute on separate stack
+	Nowritebarrier bool // emit compiler error instead of write barrier
+	Dupok          bool // duplicate definitions ok
+	Wrapper        bool // is method wrapper
+	Needctxt       bool // function uses context register (has closure variables)
+}
+
 // Node ops.
 const (
 	OXXX = iota

src/cmd/internal/gc/y.go

@@ -2523,7 +2523,7 @@ yydefault:
 			t.Rlist = yyDollar[5].list
 
 			yyVAL.node = Nod(ODCLFUNC, nil, nil)
-			yyVAL.node.Nname = newname(yyDollar[1].sym)
+			yyVAL.node.Nname = newfuncname(yyDollar[1].sym)
 			yyVAL.node.Nname.Defn = yyVAL.node
 			yyVAL.node.Nname.Ntype = t // TODO: check if nname already has an ntype
 			declare(yyVAL.node.Nname, PFUNC)
@@ -2559,7 +2559,7 @@ yydefault:
 			t.Rlist = yyDollar[8].list
 
 			yyVAL.node = Nod(ODCLFUNC, nil, nil)
-			yyVAL.node.Shortname = newname(yyDollar[4].sym)
+			yyVAL.node.Shortname = newfuncname(yyDollar[4].sym)
 			yyVAL.node.Nname = methodname1(yyVAL.node.Shortname, rcvr.Right)
 			yyVAL.node.Nname.Defn = yyVAL.node
 			yyVAL.node.Nname.Ntype = t
@@ -2589,7 +2589,7 @@ yydefault:
 				Yyerror("inconsistent definition for func %v during import\n\t%v\n\t%v", Sconv(s, 0), Tconv(s.Def.Type, 0), Tconv(t, 0))
 			}
 
-			yyVAL.node = newname(s)
+			yyVAL.node = newfuncname(s)
 			yyVAL.node.Type = t
 			declare(yyVAL.node, PFUNC)