cmd/compile/internal/gc: recursive-descent parser

This is a translation of the yacc-based parser with adjustements
to make the grammar work for a recursive-descent parser followed
by cleanups and simplifications.

The yacc actions were mostly literally copied for correctness
with better temporary names.

A few of the syntax tests were adjusted for slightly different
error messages (it is very difficult to match the yacc-based
error messages in all cases, and sometimes the new parser could
produce better errors).

The new parser is enabled by default.
To switch back to the yacc-based parser, set -oldparser.
To hardwire the switch back, uncomment "oldparser = 1" in lex.go.

- passes all.bash
- ~18% reduced parse time per file on average for make.bash
- ~3% reduced compile time for building cmd/compile

Change-Id: Icb5651bb9d8b9f66261762d2c94a03793050d4ce
Reviewed-on: https://go-review.googlesource.com/16665
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

6 files changed, 9 insertions, 10 deletions

diff --git a/test/syntax/chan.go b/test/syntax/chan.go
index 3b68bda35f..b016790fe7 100644
--- a/test/syntax/chan.go
+++ b/test/syntax/chan.go
@@ -8,10 +8,10 @@ package main
 
 type xyz struct {
     ch chan
-} // ERROR "unexpected .*}.* in channel type"
+} // ERROR "unexpected .*}.* in channel type|missing channel element type"
 
-func Foo(y chan) { // ERROR "unexpected .*\).* in channel type"
+func Foo(y chan) { // ERROR "unexpected .*\).* in channel type|missing channel element type"
 }
 
-func Bar(x chan, y int) { // ERROR "unexpected comma in channel type"
+func Bar(x chan, y int) { // ERROR "unexpected comma in channel type|missing channel element type"
 }
diff --git a/test/syntax/forvar.go b/test/syntax/forvar.go
index dc592d2b64..043c299040 100644
--- a/test/syntax/forvar.go
+++ b/test/syntax/forvar.go
@@ -7,4 +7,5 @@
 package main
 
 func main() {
+	var x int // avoid undefined: x error below with recursive-descent parser
 	for var x = 0; x < 10; x++ {	// ERROR "var declaration not allowed in for initializer"
diff --git a/test/syntax/semi4.go b/test/syntax/semi4.go
index 99c2d22561..1f4e679cf8 100644
--- a/test/syntax/semi4.go
+++ b/test/syntax/semi4.go
@@ -8,7 +8,7 @@ package main
 
 func main() {
 	for x		// GCCGO_ERROR "undefined"
-	{		// ERROR "missing .*{.* after for clause"
+	{		// ERROR "missing .*{.* after for clause|missing operand"
 		z	// GCCGO_ERROR "undefined"
 
 
diff --git a/test/syntax/semi6.go b/test/syntax/semi6.go
index c1e1cc363a..1b51d8ba7e 100644
--- a/test/syntax/semi6.go
+++ b/test/syntax/semi6.go
@@ -7,7 +7,5 @@
 package main
 
 type T	// ERROR "unexpected semicolon or newline in type declaration"
-{
-
-
-
+// line below uncommented to avoid follow-up error
+// {
\ No newline at end of file
diff --git a/test/syntax/semi7.go b/test/syntax/semi7.go
index 6c9ade8bc2..357352dea9 100644
--- a/test/syntax/semi7.go
+++ b/test/syntax/semi7.go
@@ -8,7 +8,7 @@ package main
 
 func main() {
 	if x { }	// GCCGO_ERROR "undefined"
-	else { }	// ERROR "unexpected semicolon or newline before .?else.?"
+	else { }	// ERROR "unexpected semicolon or newline before .?else.?|unexpected else"
 }
 
 
diff --git a/test/syntax/vareq1.go b/test/syntax/vareq1.go
index e900eabebe..d4952fedd7 100644
--- a/test/syntax/vareq1.go
+++ b/test/syntax/vareq1.go
@@ -6,5 +6,5 @@
 
 package main
 
-var x map[string]string{"a":"b"}		// ERROR "unexpected { at end of statement|expected ';' or newline after top level declaration"
+var x map[string]string{"a":"b"}		// ERROR "unexpected { at end of statement|unexpected { after top level declaration|expected ';' or newline after top level declaration"