undo CL 105260044 / afd6f214cc81

The go:nosplit change wasn't the problem, reinstating.

««« original CL description
undo CL 93380044 / 7f0999348917

Partial undo, just of go:nosplit annotation.  Somehow it
is breaking the windows builders.

TBR=bradfitz

««« original CL description
runtime: implement string ops in Go

Also implement go:nosplit annotation.  Not really needed
for now, but we'll definitely need it for other conversions.

benchmark                 old ns/op     new ns/op     delta
BenchmarkRuneIterate      534           474           -11.24%
BenchmarkRuneIterate2     535           470           -12.15%

LGTM=bradfitz
R=golang-codereviews, dave, bradfitz, minux
CC=golang-codereviews
https://golang.org/cl/93380044
»»»

TBR=bradfitz
CC=golang-codereviews
https://golang.org/cl/105260044
»»»

TBR=bradfitz
R=bradfitz, golang-codereviews
CC=golang-codereviews
https://golang.org/cl/103490043

src/cmd/gc/fmt.c

@@ -649,7 +649,7 @@ typefmt(Fmt *fp, Type *t)
 
 		if(t->funarg) {
 			fmtstrcpy(fp, "(");
-			if(fmtmode == FTypeId || fmtmode == FErr) {	// no argument names on function signature, and no "noescape" tags
+			if(fmtmode == FTypeId || fmtmode == FErr) {	// no argument names on function signature, and no "noescape"/"nosplit" tags
 				for(t1=t->type; t1!=T; t1=t1->down)
 					if(t1->down)
 						fmtprint(fp, "%hT, ", t1);

src/cmd/gc/go.h

@@ -269,6 +269,7 @@ struct	Node
 	uchar	colas;		// OAS resulting from :=
 	uchar	diag;		// already printed error about this
 	uchar	noescape;	// func arguments do not escape
+	uchar	nosplit;	// func should not execute on separate stack
 	uchar	builtin;	// built-in name, like len or close
 	uchar	walkdef;
 	uchar	typecheck;
@@ -980,6 +981,7 @@ EXTERN	char*	flag_installsuffix;
 EXTERN	int	flag_race;
 EXTERN	int	flag_largemodel;
 EXTERN	int	noescape;
+EXTERN	int	nosplit;
 EXTERN	int	debuglive;
 EXTERN	Link*	ctxt;
 

src/cmd/gc/go.y

@@ -1311,6 +1311,7 @@ xfndcl:
 		$$->nbody = $3;
 		$$->endlineno = lineno;
 		$$->noescape = noescape;
+		$$->nosplit = nosplit;
 		funcbody($$);
 	}
 
@@ -1495,6 +1496,7 @@ xdcl_list:
 			testdclstack();
 		nointerface = 0;
 		noescape = 0;
+		nosplit = 0;
 	}
 
 vardcl_list:

src/cmd/gc/lex.c

@@ -1592,6 +1592,10 @@ go:
 		noescape = 1;
 		goto out;
 	}
+	if(strcmp(lexbuf, "go:nosplit") == 0) {
+		nosplit = 1;
+		goto out;
+	}
 	
 out:
 	return c;

src/cmd/gc/pgen.c

@@ -229,6 +229,8 @@ compile(Node *fn)
 		ptxt->TEXTFLAG |= WRAPPER;
 	if(fn->needctxt)
 		ptxt->TEXTFLAG |= NEEDCTXT;
+	if(fn->nosplit)
+		ptxt->TEXTFLAG |= NOSPLIT;
 
 	// Clumsy but important.
 	// See test/recover.go for test cases and src/pkg/reflect/value.go

src/cmd/gc/y.tab.c

@@ -3828,6 +3828,7 @@ yyreduce:
 		(yyval.node)->nbody = (yyvsp[(3) - (3)].list);
 		(yyval.node)->endlineno = lineno;
 		(yyval.node)->noescape = noescape;
+		(yyval.node)->nosplit = nosplit;
 		funcbody((yyval.node));
 	}
     break;
@@ -4037,6 +4038,7 @@ yyreduce:
 			testdclstack();
 		nointerface = 0;
 		noescape = 0;
+		nosplit = 0;
 	}
     break;