cmd/internal/gc: rearrange Node fields

Rearrange Node fields to enable better struct packing.
This reduces readability in favor of shrinking
the size of Nodes.

This reduces the size of Node from 328 to 312.
This reduces the memory usage to compile the
rotate tests by about 4.4%.

No functional changes. Passes toolstash -cmp.

Updates #9933.

Change-Id: I2764c5847fb1635ddc898e2ee385d007d67f03c5
Reviewed-on: https://go-review.googlesource.com/10141Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/internal/gc/syntax.go

@@ -23,32 +23,6 @@ type Node struct {
 	List  *NodeList
 	Rlist *NodeList
 
-	Op          uint8
-	Nointerface bool
-	Ullman      uint8 // sethi/ullman number
-	Addable     bool  // addressable
-	Etype       uint8 // op for OASOP, etype for OTYPE, exclam for export, 6g saved reg
-	Bounded     bool  // bounds check unnecessary
-	Class       uint8 // PPARAM, PAUTO, PEXTERN, etc
-	Embedded    uint8 // ODCLFIELD embedded type
-	Colas       bool  // OAS resulting from :=
-	Diag        uint8 // already printed error about this
-	Noescape    bool  // func arguments do not escape; TODO(rsc): move Noescape to Func struct (see CL 7360)
-	Walkdef     uint8
-	Typecheck   uint8
-	Local       bool
-	Dodata      uint8
-	Initorder   uint8
-	Used        bool
-	Isddd       bool // is the argument variadic
-	Implicit    bool
-	Addrtaken   bool   // address taken, even if not moved to heap
-	Assigned    bool   // is the variable ever assigned to
-	Likely      int8   // likeliness of if statement
-	Hasbreak    bool   // has break statement
-	Esc         uint16 // EscXXX
-	Funcdepth   int32
-
 	// most nodes
 	Type  *Type
 	Orig  *Node // original form, for printing, and tracking copies of ONAMEs
@@ -57,12 +31,6 @@ type Node struct {
 	// func
 	Func *Func
 
-	// OLITERAL
-	Val Val
-
-	// OREGISTER, OINDREG
-	Reg int16
-
 	// ONAME
 	Name     *Name
 	Defn     *Node // ONAME: initializing assignment; OLABEL: labeled statement
@@ -81,17 +49,57 @@ type Node struct {
 	// Escape analysis.
 	Escflowsrc *NodeList // flow(this, src)
 	Escretval  *NodeList // on OCALLxxx, list of dummy return values
-	Escloopdepth int32     // -1: global, 0: return variables, 1:function top level, increased inside function for every loop or label to mark scopes
 
 	Sym *Sym // various
-	Vargen   int32 // unique name for OTYPE/ONAME within a function.  Function outputs are numbered starting at one.
-	Lineno   int32
+
+	Opt interface{} // for optimization passes
+
+	// OLITERAL
+	Val Val
+
 	Xoffset  int64
 	Stkdelta int64 // offset added by stack frame compaction phase.
+
+	// Escape analysis.
+	Escloopdepth int32 // -1: global, 0: return variables, 1:function top level, increased inside function for every loop or label to mark scopes
+
+	Vargen  int32 // unique name for OTYPE/ONAME within a function.  Function outputs are numbered starting at one.
+	Lineno  int32
 	Iota    int32
 	Walkgen uint32
+
+	Funcdepth int32
+
+	// OREGISTER, OINDREG
+	Reg int16
+
+	// most nodes - smaller fields
 	Esclevel Level
-	Opt      interface{} // for optimization passes
+	Esc      uint16 // EscXXX
+
+	Op          uint8
+	Nointerface bool
+	Ullman      uint8 // sethi/ullman number
+	Addable     bool  // addressable
+	Etype       uint8 // op for OASOP, etype for OTYPE, exclam for export, 6g saved reg
+	Bounded     bool  // bounds check unnecessary
+	Class       uint8 // PPARAM, PAUTO, PEXTERN, etc
+	Embedded    uint8 // ODCLFIELD embedded type
+	Colas       bool  // OAS resulting from :=
+	Diag        uint8 // already printed error about this
+	Noescape    bool  // func arguments do not escape; TODO(rsc): move Noescape to Func struct (see CL 7360)
+	Walkdef     uint8
+	Typecheck   uint8
+	Local       bool
+	Dodata      uint8
+	Initorder   uint8
+	Used        bool
+	Isddd       bool // is the argument variadic
+	Implicit    bool
+	Addrtaken   bool // address taken, even if not moved to heap
+	Assigned    bool // is the variable ever assigned to
+	Likely      int8 // likeliness of if statement
+	Hasbreak    bool // has break statement
 }
 
 // Name holds Node fields used only by ONAME nodes.