cmd/compile: eliminate prectab

While here, merge LINC and LDEC into LINCOP.

Fixes #13244.

Change-Id: I8ea426f986d60d35c3b1a80c056a7aa49d22d802
Reviewed-on: https://go-review.googlesource.com/19928Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/lex.go

@@ -873,9 +873,22 @@ type lexer struct {
 	tok  int32
 	sym_ *Sym   // valid if tok == LNAME
 	val  Val    // valid if tok == LLITERAL
-	op   Op   // valid if tok == LASOP
+	op   Op     // valid if tok == LASOP or LINCOP, or prec > 0
+	prec OpPrec // operator precedence; 0 if not a binary operator
 }
 
+type OpPrec int
+
+const (
+	// Precedences of binary operators (must be > 0).
+	PCOMM OpPrec = 1 + iota
+	POROR
+	PANDAND
+	PCMP
+	PADD
+	PMUL
+)
+
 const (
 	// The value of single-char tokens is just their character's Unicode value.
 	// They are all below utf8.RuneSelf. Shift other tokens up to avoid conflicts.
@@ -912,12 +925,11 @@ const (
 	LANDAND
 	LANDNOT
 	LCOMM
-	LDEC
 	LEQ
 	LGE
 	LGT
 	LIGNORE
-	LINC
+	LINCOP
 	LLE
 	LLSH
 	LLT
@@ -929,6 +941,7 @@ const (
 func (l *lexer) next() {
 	nlsemi := l.nlsemi
 	l.nlsemi = false
+	l.prec = 0
 
 l0:
 	// skip white space
@@ -963,6 +976,7 @@ l0:
 
 	var c1 rune
 	var op Op
+	var prec OpPrec
 
 	switch c {
 	case EOF:
@@ -1056,10 +1070,9 @@ l0:
 			}
 		}
 
-		if c1 == '=' {
 		op = ODIV
-			goto asop
-		}
+		prec = PMUL
+		goto binop1
 
 	case ':':
 		c1 = l.getr()
@@ -1069,94 +1082,75 @@ l0:
 		}
 
 	case '*':
-		c1 = l.getr()
-		if c1 == '=' {
 		op = OMUL
-			goto asop
-		}
+		prec = PMUL
+		goto binop
 
 	case '%':
-		c1 = l.getr()
-		if c1 == '=' {
 		op = OMOD
-			goto asop
-		}
+		prec = PMUL
+		goto binop
 
 	case '+':
-		c1 = l.getr()
-		if c1 == '+' {
-			l.nlsemi = true
-			c = LINC
-			goto lx
-		}
-
-		if c1 == '=' {
 		op = OADD
-			goto asop
-		}
+		goto incop
 
 	case '-':
-		c1 = l.getr()
-		if c1 == '-' {
-			l.nlsemi = true
-			c = LDEC
-			goto lx
-		}
-
-		if c1 == '=' {
 		op = OSUB
-			goto asop
-		}
+		goto incop
 
 	case '>':
 		c1 = l.getr()
 		if c1 == '>' {
 			c = LRSH
-			c1 = l.getr()
-			if c1 == '=' {
 			op = ORSH
-				goto asop
-			}
-
-			break
+			prec = PMUL
+			goto binop
 		}
 
+		l.prec = PCMP
 		if c1 == '=' {
 			c = LGE
+			l.op = OGE
 			goto lx
 		}
-
 		c = LGT
+		l.op = OGT
 
 	case '<':
 		c1 = l.getr()
 		if c1 == '<' {
 			c = LLSH
-			c1 = l.getr()
-			if c1 == '=' {
 			op = OLSH
-				goto asop
+			prec = PMUL
+			goto binop
 		}
 
-			break
+		if c1 == '-' {
+			c = LCOMM
+			// Not a binary operator, but parsed as one
+			// so we can give a good error message when used
+			// in an expression context.
+			l.prec = PCOMM
+			l.op = OSEND
+			goto lx
 		}
 
+		l.prec = PCMP
 		if c1 == '=' {
 			c = LLE
+			l.op = OLE
 			goto lx
 		}
-
-		if c1 == '-' {
-			c = LCOMM
-			goto lx
-		}
-
 		c = LLT
+		l.op = OLT
 
 	case '=':
 		c1 = l.getr()
 		if c1 == '=' {
 			c = LEQ
+			l.prec = PCMP
+			l.op = OEQ
 			goto lx
 		}
 
@@ -1164,6 +1158,8 @@ l0:
 		c1 = l.getr()
 		if c1 == '=' {
 			c = LNE
+			l.prec = PCMP
+			l.op = ONE
 			goto lx
 		}
 
@@ -1171,43 +1167,39 @@ l0:
 		c1 = l.getr()
 		if c1 == '&' {
 			c = LANDAND
+			l.prec = PANDAND
+			l.op = OANDAND
 			goto lx
 		}
 
 		if c1 == '^' {
 			c = LANDNOT
-			c1 = l.getr()
-			if c1 == '=' {
 			op = OANDNOT
-				goto asop
+			prec = PMUL
+			goto binop
 		}
 
-			break
-		}
-
-		if c1 == '=' {
 		op = OAND
-			goto asop
-		}
+		prec = PMUL
+		goto binop1
 
 	case '|':
 		c1 = l.getr()
 		if c1 == '|' {
 			c = LOROR
+			l.prec = POROR
+			l.op = OOROR
 			goto lx
 		}
 
-		if c1 == '=' {
 		op = OOR
-			goto asop
-		}
+		prec = PADD
+		goto binop1
 
 	case '^':
-		c1 = l.getr()
-		if c1 == '=' {
 		op = OXOR
-			goto asop
-		}
+		prec = PADD
+		goto binop
 
 	case '(', '[', '{', ',', ';':
 		goto lx
@@ -1232,7 +1224,7 @@ l0:
 
 lx:
 	if Debug['x'] != 0 {
-		if c > 0xff {
+		if c >= utf8.RuneSelf {
 			fmt.Printf("%v lex: TOKEN %s\n", Ctxt.Line(int(lineno)), lexname(c))
 		} else {
 			fmt.Printf("%v lex: TOKEN '%c'\n", Ctxt.Line(int(lineno)), c)
@@ -1242,7 +1234,27 @@ lx:
 	l.tok = c
 	return
 
-asop:
+incop:
+	c1 = l.getr()
+	if c1 == c {
+		l.nlsemi = true
+		l.op = op
+		c = LINCOP
+		goto lx
+	}
+	prec = PADD
+	goto binop1
+
+binop:
+	c1 = l.getr()
+binop1:
+	if c1 != '=' {
+		l.ungetr(c1)
+		l.op = op
+		l.prec = prec
+		goto lx
+	}
+
 	l.op = op
 	if Debug['x'] != 0 {
 		fmt.Printf("lex: TOKEN ASOP %s=\n", goopnames[op])
@@ -2319,7 +2331,6 @@ var lexn = map[rune]string{
 	LCONST:     "CONST",
 	LCONTINUE:  "CONTINUE",
 	LDDD:       "...",
-	LDEC:       "DEC",
 	LDEFAULT:   "DEFAULT",
 	LDEFER:     "DEFER",
 	LELSE:      "ELSE",
@@ -2333,7 +2344,7 @@ var lexn = map[rune]string{
 	LGT:        "GT",
 	LIF:        "IF",
 	LIMPORT:    "IMPORT",
-	LINC:       "INC",
+	LINCOP:     "INCOP",
 	LINTERFACE: "INTERFACE",
 	LLE:        "LE",
 	LLITERAL:   "LITERAL",

src/cmd/compile/internal/gc/parser.go

@@ -102,6 +102,8 @@ func (p *parser) syntax_error(msg string) {
 		}
 	case LASOP:
 		tok = goopnames[p.op] + "="
+	case LINCOP:
+		tok = goopnames[p.op] + goopnames[p.op]
 	default:
 		tok = tokstring(p.tok)
 	}
@@ -219,12 +221,11 @@ var tokstrings = map[int32]string{
 	LANDAND:    "&&",
 	LANDNOT:    "&^",
 	LCOMM:      "<-",
-	LDEC:       "--",
 	LEQ:        "==",
 	LGE:        ">=",
 	LGT:        ">",
 	LIGNORE:    "LIGNORE", // we should never see this one
-	LINC:       "++",
+	LINCOP:     "opop",
 	LLE:        "<=",
 	LLSH:       "<<",
 	LLT:        "<",
@@ -562,22 +563,13 @@ func (p *parser) simple_stmt(labelOk, rangeOk bool) *Node {
 			stmt.Etype = EType(op) // rathole to pass opcode
 			return stmt
 
-		case LINC:
-			// expr LINC
+		case LINCOP:
+			// expr LINCOP
 			p.next()
 
 			stmt := Nod(OASOP, lhs, Nodintconst(1))
 			stmt.Implicit = true
-			stmt.Etype = EType(OADD)
-			return stmt
-
-		case LDEC:
-			// expr LDEC
-			p.next()
-
-			stmt := Nod(OASOP, lhs, Nodintconst(1))
-			stmt.Implicit = true
-			stmt.Etype = EType(OSUB)
+			stmt.Etype = EType(p.op)
 			return stmt
 
 		case ':':
@@ -1104,54 +1096,20 @@ func (p *parser) select_stmt() *Node {
 	return hdr
 }
 
-// TODO(gri) should have lexer return this info - no need for separate lookup
-// (issue 13244)
-var prectab = map[int32]struct {
-	prec int // > 0 (0 indicates not found)
-	op   Op
-}{
-	// not an expression anymore, but left in so we can give a good error
-	// message when used in expression context
-	LCOMM: {1, OSEND},
-
-	LOROR: {2, OOROR},
-
-	LANDAND: {3, OANDAND},
-
-	LEQ: {4, OEQ},
-	LNE: {4, ONE},
-	LLE: {4, OLE},
-	LGE: {4, OGE},
-	LLT: {4, OLT},
-	LGT: {4, OGT},
-
-	'+': {5, OADD},
-	'-': {5, OSUB},
-	'|': {5, OOR},
-	'^': {5, OXOR},
-
-	'*':     {6, OMUL},
-	'/':     {6, ODIV},
-	'%':     {6, OMOD},
-	'&':     {6, OAND},
-	LLSH:    {6, OLSH},
-	LRSH:    {6, ORSH},
-	LANDNOT: {6, OANDNOT},
-}
-
 // Expression = UnaryExpr | Expression binary_op Expression .
-func (p *parser) bexpr(prec int) *Node {
+func (p *parser) bexpr(prec OpPrec) *Node {
 	// don't trace bexpr - only leads to overly nested trace output
 
+	// prec is precedence of the prior/enclosing binary operator (if any),
+	// so we only want to parse tokens of greater precedence.
+
 	x := p.uexpr()
-	for {
-		t := prectab[p.tok]
-		if t.prec < prec {
-			return x
-		}
+	for p.prec > prec {
+		op, prec1 := p.op, p.prec
 		p.next()
-		x = Nod(t.op, x, p.bexpr(t.prec+1))
+		x = Nod(op, x, p.bexpr(prec1))
 	}
+	return x
 }
 
 func (p *parser) expr() *Node {
@@ -1159,7 +1117,7 @@ func (p *parser) expr() *Node {
 		defer p.trace("expr")()
 	}
 
-	return p.bexpr(1)
+	return p.bexpr(0)
 }
 
 func unparen(x *Node) *Node {