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/10141
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/internal/gc/syntax.go

@@ -23,6 +23,60 @@ type Node struct {
 	List  *NodeList
 	Rlist *NodeList
 
+	// most nodes
+	Type  *Type
+	Orig  *Node // original form, for printing, and tracking copies of ONAMEs
+	Nname *Node
+
+	// func
+	Func *Func
+
+	// ONAME
+	Name     *Name
+	Defn     *Node // ONAME: initializing assignment; OLABEL: labeled statement
+	Pack     *Node // real package for import . names
+	Curfn    *Node // function for local variables
+	Paramfld *Type // TFIELD for this PPARAM; also for ODOT, curfn
+	Alloc    *Node // allocation call
+	*Param
+
+	// OPACK
+	Pkg *Pkg
+
+	// OARRAYLIT, OMAPLIT, OSTRUCTLIT.
+	Initplan *InitPlan
+
+	// Escape analysis.
+	Escflowsrc *NodeList // flow(this, src)
+	Escretval  *NodeList // on OCALLxxx, list of dummy return values
+
+	Sym *Sym // various
+
+	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
+	Esc      uint16 // EscXXX
+
 	Op          uint8
 	Nointerface bool
 	Ullman      uint8 // sethi/ullman number
@@ -42,56 +96,10 @@ type Node struct {
 	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
-	Nname *Node
-
-	// func
-	Func *Func
-
-	// OLITERAL
-	Val Val
-
-	// OREGISTER, OINDREG
-	Reg int16
-
-	// ONAME
-	Name     *Name
-	Defn     *Node // ONAME: initializing assignment; OLABEL: labeled statement
-	Pack     *Node // real package for import . names
-	Curfn    *Node // function for local variables
-	Paramfld *Type // TFIELD for this PPARAM; also for ODOT, curfn
-	Alloc    *Node // allocation call
-	*Param
-
-	// OPACK
-	Pkg *Pkg
-
-	// OARRAYLIT, OMAPLIT, OSTRUCTLIT.
-	Initplan *InitPlan
-
-	// 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
-	Xoffset  int64
-	Stkdelta int64 // offset added by stack frame compaction phase.
-	Iota     int32
-	Walkgen  uint32
-	Esclevel Level
-	Opt      interface{} // for optimization passes
+	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.