cmd/yacc: memory allocation improvements

Places a fixed size initial stack and the lval inside the parser
struct so that they are allocated together. Places $$char inside the
parser struct to avoid allocating the closure used in Lookahead().

Change-Id: I0de664a6d612279fdc3255633e2dff904030bc36
Reviewed-on: https://go-review.googlesource.com/16705
Reviewed-by: Russ Cox <rsc@golang.org>

diff --git a/src/cmd/yacc/yacc.go b/src/cmd/yacc/yacc.go
index 32d2e5e8199569fb7455b710203f22d5fadbdcc3..4f9d13c5453f5c69a6c40122fc3e4d12c953c07c 100644 (file)
--- a/src/cmd/yacc/yacc.go
+++ b/src/cmd/yacc/yacc.go
@@ -172,7 +172,7 @@ func init() {
        flag.BoolVar(&lflag, "l", false, "disable line directives")
 }
 
-var stacksize = 200
+var initialstacksize = 16
 
 // communication variables between various I/O routines
 var infile string  // input file name
@@ -384,7 +384,7 @@ func setup() {
        if flag.NArg() != 1 {
                usage()
        }
-       if stacksize < 1 {
+       if initialstacksize < 1 {
                // never set so cannot happen
                fmt.Fprintf(stderr, "yacc: stack size too small\n")
                usage()
@@ -719,7 +719,7 @@ outer:
        ftable.WriteRune('\n')
        fmt.Fprintf(ftable, "const %sEofCode = 1\n", prefix)
        fmt.Fprintf(ftable, "const %sErrCode = 2\n", prefix)
-       fmt.Fprintf(ftable, "const %sMaxDepth = %v\n", prefix, stacksize)
+       fmt.Fprintf(ftable, "const %sInitialStackSize = %v\n", prefix, initialstacksize)
 
        //
        // copy any postfix code
@@ -3332,18 +3332,17 @@ type $$Parser interface {
 }
 
 type $$ParserImpl struct {
-       lookahead func() int
+       lval  $$SymType
+       stack [$$InitialStackSize]$$SymType
+       char  int
 }
 
 func (p *$$ParserImpl) Lookahead() int {
-       return p.lookahead()
+       return p.char
 }
 
 func $$NewParser() $$Parser {
-       p := &$$ParserImpl{
-               lookahead: func() int { return -1 },
-       }
-       return p
+       return &$$ParserImpl{}
 }
 
 const $$Flag = -1000
@@ -3471,22 +3470,20 @@ func $$Parse($$lex $$Lexer) int {
 
 func ($$rcvr *$$ParserImpl) Parse($$lex $$Lexer) int {
        var $$n int
-       var $$lval $$SymType
        var $$VAL $$SymType
        var $$Dollar []$$SymType
        _ = $$Dollar // silence set and not used
-       $$S := make([]$$SymType, $$MaxDepth)
+       $$S := $$rcvr.stack[:]
 
        Nerrs := 0   /* number of errors */
        Errflag := 0 /* error recovery flag */
        $$state := 0
-       $$char := -1
-       $$token := -1 // $$char translated into internal numbering
-       $$rcvr.lookahead = func() int { return $$char }
+       $$rcvr.char = -1
+       $$token := -1 // $$rcvr.char translated into internal numbering
        defer func() {
                // Make sure we report no lookahead when not parsing.
                $$state = -1
-               $$char = -1
+               $$rcvr.char = -1
                $$token = -1
        }()
        $$p := -1
@@ -3518,8 +3515,8 @@ $$newstate:
        if $$n <= $$Flag {
                goto $$default /* simple state */
        }
-       if $$char < 0 {
-               $$char, $$token = $$lex1($$lex, &$$lval)
+       if $$rcvr.char < 0 {
+               $$rcvr.char, $$token = $$lex1($$lex, &$$rcvr.lval)
        }
        $$n += $$token
        if $$n < 0 || $$n >= $$Last {
@@ -3527,9 +3524,9 @@ $$newstate:
        }
        $$n = $$Act[$$n]
        if $$Chk[$$n] == $$token { /* valid shift */
-               $$char = -1
+               $$rcvr.char = -1
                $$token = -1
-               $$VAL = $$lval
+               $$VAL = $$rcvr.lval
                $$state = $$n
                if Errflag > 0 {
                        Errflag--
@@ -3541,8 +3538,8 @@ $$default:
        /* default state action */
        $$n = $$Def[$$state]
        if $$n == -2 {
-               if $$char < 0 {
-                       $$char, $$token = $$lex1($$lex, &$$lval)
+               if $$rcvr.char < 0 {
+                       $$rcvr.char, $$token = $$lex1($$lex, &$$rcvr.lval)
                }
 
                /* look through exception table */
@@ -3605,7 +3602,7 @@ $$default:
                        if $$token == $$EofCode {
                                goto ret1
                        }
-                       $$char = -1
+                       $$rcvr.char = -1
                        $$token = -1
                        goto $$newstate /* try again in the same state */
                }