From: Ken Thompson <ken@golang.org>
Date: Thu, 24 Jul 2008 22:57:30 +0000 (-0700)
Subject: select
X-Git-Tag: weekly.2009-11-06~3434
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=cb9b1038db77198c2b0961634cf161258af2374d;p=gostls13.git

select

R=r
APPROVED=r
DELTA=638  (433 added, 21 deleted, 184 changed)
OCL=13426
CL=13438
---

diff --git a/src/cmd/6g/gen.c b/src/cmd/6g/gen.c
index 3bab7425f7..dfc343d158 100644
--- a/src/cmd/6g/gen.c
+++ b/src/cmd/6g/gen.c
@@ -255,6 +255,17 @@ loop:
 		breakpc = sbreak;
 		break;
 
+	case OSELECT:
+		gen(n->ninit);
+		sbreak = breakpc;
+		p1 = gbranch(AJMP, T);			// 		goto test
+		breakpc = gbranch(AJMP, T);		// break:	goto done
+		patch(p1, pc);				// test:
+		gen(n->nbody);				//		select() body
+		patch(breakpc, pc);			// done:
+		breakpc = sbreak;
+		break;
+
 	case OASOP:
 		cgen_asop(n);
 		break;
diff --git a/src/cmd/6g/gg.h b/src/cmd/6g/gg.h
index c6ee3ab4b3..9b35228528 100644
--- a/src/cmd/6g/gg.h
+++ b/src/cmd/6g/gg.h
@@ -107,6 +107,7 @@ void	compile(Node*);
 void	proglist(void);
 void	gen(Node*);
 void	swgen(Node*);
+void	selgen(Node*);
 Node*	lookdot(Node*, Node*, int);
 void	inarggen(void);
 void	agen_inter(Node*, Node*);
diff --git a/src/cmd/gc/go.h b/src/cmd/gc/go.h
index 9a49f6f12c..9e37c79465 100644
--- a/src/cmd/gc/go.h
+++ b/src/cmd/gc/go.h
@@ -219,8 +219,8 @@ enum
 	OLIST, OCMP,
 	OPTR, OARRAY,
 	ORETURN, OFOR, OIF, OSWITCH, OI2S, OS2I, OI2I,
-	OAS, OASOP, OCASE, OXCASE, OFALL, OXFALL, OSELECT,
-	OGOTO, OPROC, ONEW, OPANIC, OPRINT, OEMPTY,
+	OAS, OASOP, OCASE, OXCASE, OSCASE, OFALL, OXFALL,
+	OGOTO, OPROC, ONEW, OPANIC, OPRINT, OEMPTY, OSELECT,
 
 	OOROR,
 	OANDAND,
@@ -575,6 +575,7 @@ void	walktype(Node*, int);
 void	walkbool(Node*);
 Type*	walkswitch(Node*, Type*(*)(Node*, Type*));
 int	casebody(Node*);
+void	walkselect(Node*);
 int	whatis(Node*);
 void	walkdot(Node*, int);
 Node*	ascompatee(int, Node**, Node**);
@@ -585,7 +586,9 @@ Node*	prcompat(Node*);
 Node*	nodpanic(long);
 Node*	newcompat(Node*);
 Node*	stringop(Node*, int);
+Type*	fixmap(Type*);
 Node*	mapop(Node*, int);
+Type*	fixchan(Type*);
 Node*	chanop(Node*, int);
 Node*	convas(Node*);
 void	arrayconv(Type*, Node*);
diff --git a/src/cmd/gc/go.y b/src/cmd/gc/go.y
index 13c08baf02..769c95333f 100644
--- a/src/cmd/gc/go.y
+++ b/src/cmd/gc/go.y
@@ -338,8 +338,6 @@ complex_stmt:
 |	LSWITCH if_stmt
 	{
 		popdcl();
-		if(!casebody($2->nbody))
-			yyerror("switch statement must have case labels");
 		$$ = $2;
 		$$->op = OSWITCH;
 		//if($$->ninit != N && $$->ntest == N)
diff --git a/src/cmd/gc/mksys.bash b/src/cmd/gc/mksys.bash
index 7d6a8ecdc4..c920cde61a 100755
--- a/src/cmd/gc/mksys.bash
+++ b/src/cmd/gc/mksys.bash
@@ -7,6 +7,7 @@
 6g sys.go
 echo '1,/((/d
 /))/+1,$d
+g/init_.*_function/d
 1,$s/foop/sys/g
 1,$s/^[ 	]*/	"/g
 1,$s/$/\\n"/g
diff --git a/src/cmd/gc/subr.c b/src/cmd/gc/subr.c
index b9c0da5407..8609f39dfc 100644
--- a/src/cmd/gc/subr.c
+++ b/src/cmd/gc/subr.c
@@ -603,6 +603,7 @@ opnames[] =
 	[OCALLINTER]	= "CALLINTER",
 	[OCASE]		= "CASE",
 	[OXCASE]	= "XCASE",
+	[OSCASE]	= "SCASE",
 	[OCMP]		= "CMP",
 	[OFALL]		= "FALL",
 	[OCONV]		= "CONV",
diff --git a/src/cmd/gc/sys.go b/src/cmd/gc/sys.go
index 06848c1f32..502d44914b 100644
--- a/src/cmd/gc/sys.go
+++ b/src/cmd/gc/sys.go
@@ -51,6 +51,11 @@ func	chanrecv3(hchan *chan any) (elem any, pres bool);
 func	chansend1(hchan *chan any, elem any);
 func	chansend2(hchan *chan any, elem any) (pres bool);
 
+func	newselect(size uint32) (sel *byte);
+func	selectsend(sel *byte, hchan *chan any, elem any) (selected bool);
+func	selectrecv(sel *byte, hchan *chan any, elem *any) (selected bool);
+func	selectgo(sel *byte);
+
 func	gosched();
 func	goexit();
 
@@ -112,6 +117,12 @@ export
 	chansend1
 	chansend2
 
+	// select
+	newselect
+	selectsend
+	selectrecv
+	selectgo
+
 	// go routines
 	gosched
 	goexit
diff --git a/src/cmd/gc/sysimport.c b/src/cmd/gc/sysimport.c
index b5964087e3..571c7e83ec 100644
--- a/src/cmd/gc/sysimport.c
+++ b/src/cmd/gc/sysimport.c
@@ -3,10 +3,10 @@ char*	sysimport =
 	"type sys._esys_002 {}\n"
 	"type sys.any 24\n"
 	"type sys._esys_003 *sys.any\n"
-	"type sys._osys_332 {_esys_330 sys._esys_003}\n"
+	"type sys._osys_361 {_esys_359 sys._esys_003}\n"
 	"type sys.uint32 6\n"
-	"type sys._isys_334 {_esys_331 sys.uint32}\n"
-	"type sys._esys_001 (sys._esys_002 sys._osys_332 sys._isys_334)\n"
+	"type sys._isys_363 {_esys_360 sys.uint32}\n"
+	"type sys._esys_001 (sys._esys_002 sys._osys_361 sys._isys_363)\n"
 	"var !sys.mal sys._esys_001\n"
 	"type sys._esys_005 {}\n"
 	"type sys._esys_006 {}\n"
@@ -16,249 +16,282 @@ char*	sysimport =
 	"type sys._esys_009 {}\n"
 	"type sys._esys_010 {}\n"
 	"type sys.int32 5\n"
-	"type sys._isys_340 {_esys_339 sys.int32}\n"
-	"type sys._esys_008 (sys._esys_009 sys._esys_010 sys._isys_340)\n"
+	"type sys._isys_369 {_esys_368 sys.int32}\n"
+	"type sys._esys_008 (sys._esys_009 sys._esys_010 sys._isys_369)\n"
 	"var !sys.panicl sys._esys_008\n"
 	"type sys._esys_012 {}\n"
 	"type sys._esys_013 {}\n"
 	"type sys.bool 12\n"
-	"type sys._isys_345 {_esys_344 sys.bool}\n"
-	"type sys._esys_011 (sys._esys_012 sys._esys_013 sys._isys_345)\n"
+	"type sys._isys_374 {_esys_373 sys.bool}\n"
+	"type sys._esys_011 (sys._esys_012 sys._esys_013 sys._isys_374)\n"
 	"var !sys.printbool sys._esys_011\n"
 	"type sys._esys_015 {}\n"
 	"type sys._esys_016 {}\n"
 	"type sys.float64 10\n"
-	"type sys._isys_350 {_esys_349 sys.float64}\n"
-	"type sys._esys_014 (sys._esys_015 sys._esys_016 sys._isys_350)\n"
+	"type sys._isys_379 {_esys_378 sys.float64}\n"
+	"type sys._esys_014 (sys._esys_015 sys._esys_016 sys._isys_379)\n"
 	"var !sys.printfloat sys._esys_014\n"
 	"type sys._esys_018 {}\n"
 	"type sys._esys_019 {}\n"
 	"type sys.int64 7\n"
-	"type sys._isys_355 {_esys_354 sys.int64}\n"
-	"type sys._esys_017 (sys._esys_018 sys._esys_019 sys._isys_355)\n"
+	"type sys._isys_384 {_esys_383 sys.int64}\n"
+	"type sys._esys_017 (sys._esys_018 sys._esys_019 sys._isys_384)\n"
 	"var !sys.printint sys._esys_017\n"
 	"type sys._esys_021 {}\n"
 	"type sys._esys_022 {}\n"
 	"type sys._esys_023 25\n"
 	"type sys.string *sys._esys_023\n"
-	"type sys._isys_360 {_esys_359 sys.string}\n"
-	"type sys._esys_020 (sys._esys_021 sys._esys_022 sys._isys_360)\n"
+	"type sys._isys_389 {_esys_388 sys.string}\n"
+	"type sys._esys_020 (sys._esys_021 sys._esys_022 sys._isys_389)\n"
 	"var !sys.printstring sys._esys_020\n"
 	"type sys._esys_025 {}\n"
 	"type sys._esys_026 {}\n"
 	"type sys._esys_027 *sys.any\n"
-	"type sys._isys_365 {_esys_364 sys._esys_027}\n"
-	"type sys._esys_024 (sys._esys_025 sys._esys_026 sys._isys_365)\n"
+	"type sys._isys_394 {_esys_393 sys._esys_027}\n"
+	"type sys._esys_024 (sys._esys_025 sys._esys_026 sys._isys_394)\n"
 	"var !sys.printpointer sys._esys_024\n"
 	"type sys._esys_029 {}\n"
-	"type sys._osys_372 {_esys_369 sys.string}\n"
-	"type sys._isys_374 {_esys_370 sys.string _esys_371 sys.string}\n"
-	"type sys._esys_028 (sys._esys_029 sys._osys_372 sys._isys_374)\n"
+	"type sys._osys_401 {_esys_398 sys.string}\n"
+	"type sys._isys_403 {_esys_399 sys.string _esys_400 sys.string}\n"
+	"type sys._esys_028 (sys._esys_029 sys._osys_401 sys._isys_403)\n"
 	"var !sys.catstring sys._esys_028\n"
 	"type sys._esys_031 {}\n"
-	"type sys._osys_382 {_esys_379 sys.int32}\n"
-	"type sys._isys_384 {_esys_380 sys.string _esys_381 sys.string}\n"
-	"type sys._esys_030 (sys._esys_031 sys._osys_382 sys._isys_384)\n"
+	"type sys._osys_411 {_esys_408 sys.int32}\n"
+	"type sys._isys_413 {_esys_409 sys.string _esys_410 sys.string}\n"
+	"type sys._esys_030 (sys._esys_031 sys._osys_411 sys._isys_413)\n"
 	"var !sys.cmpstring sys._esys_030\n"
 	"type sys._esys_033 {}\n"
-	"type sys._osys_393 {_esys_389 sys.string}\n"
-	"type sys._isys_395 {_esys_390 sys.string _esys_391 sys.int32 _esys_392 sys.int32}\n"
-	"type sys._esys_032 (sys._esys_033 sys._osys_393 sys._isys_395)\n"
+	"type sys._osys_422 {_esys_418 sys.string}\n"
+	"type sys._isys_424 {_esys_419 sys.string _esys_420 sys.int32 _esys_421 sys.int32}\n"
+	"type sys._esys_032 (sys._esys_033 sys._osys_422 sys._isys_424)\n"
 	"var !sys.slicestring sys._esys_032\n"
 	"type sys._esys_035 {}\n"
 	"type sys.uint8 2\n"
-	"type sys._osys_404 {_esys_401 sys.uint8}\n"
-	"type sys._isys_406 {_esys_402 sys.string _esys_403 sys.int32}\n"
-	"type sys._esys_034 (sys._esys_035 sys._osys_404 sys._isys_406)\n"
+	"type sys._osys_433 {_esys_430 sys.uint8}\n"
+	"type sys._isys_435 {_esys_431 sys.string _esys_432 sys.int32}\n"
+	"type sys._esys_034 (sys._esys_035 sys._osys_433 sys._isys_435)\n"
 	"var !sys.indexstring sys._esys_034\n"
 	"type sys._esys_037 {}\n"
-	"type sys._osys_413 {_esys_411 sys.string}\n"
-	"type sys._isys_415 {_esys_412 sys.int64}\n"
-	"type sys._esys_036 (sys._esys_037 sys._osys_413 sys._isys_415)\n"
+	"type sys._osys_442 {_esys_440 sys.string}\n"
+	"type sys._isys_444 {_esys_441 sys.int64}\n"
+	"type sys._esys_036 (sys._esys_037 sys._osys_442 sys._isys_444)\n"
 	"var !sys.intstring sys._esys_036\n"
 	"type sys._esys_039 {}\n"
-	"type sys._osys_422 {_esys_419 sys.string}\n"
+	"type sys._osys_451 {_esys_448 sys.string}\n"
 	"type sys._esys_040 *sys.uint8\n"
-	"type sys._isys_424 {_esys_420 sys._esys_040 _esys_421 sys.int32}\n"
-	"type sys._esys_038 (sys._esys_039 sys._osys_422 sys._isys_424)\n"
+	"type sys._isys_453 {_esys_449 sys._esys_040 _esys_450 sys.int32}\n"
+	"type sys._esys_038 (sys._esys_039 sys._osys_451 sys._isys_453)\n"
 	"var !sys.byteastring sys._esys_038\n"
 	"type sys._esys_042 {}\n"
 	"type sys._esys_043 <>\n"
-	"type sys._osys_433 {_esys_429 sys._esys_043}\n"
+	"type sys._osys_462 {_esys_458 sys._esys_043}\n"
 	"type sys._esys_044 *sys.uint8\n"
 	"type sys._esys_045 *sys.uint8\n"
-	"type sys._ssys_440 {}\n"
-	"type sys._esys_046 *sys._ssys_440\n"
-	"type sys._isys_435 {_esys_430 sys._esys_044 _esys_431 sys._esys_045 _esys_432 sys._esys_046}\n"
-	"type sys._esys_041 (sys._esys_042 sys._osys_433 sys._isys_435)\n"
+	"type sys._ssys_469 {}\n"
+	"type sys._esys_046 *sys._ssys_469\n"
+	"type sys._isys_464 {_esys_459 sys._esys_044 _esys_460 sys._esys_045 _esys_461 sys._esys_046}\n"
+	"type sys._esys_041 (sys._esys_042 sys._osys_462 sys._isys_464)\n"
 	"var !sys.mkiface sys._esys_041\n"
 	"type sys._esys_048 {}\n"
-	"type sys._osys_444 {_esys_443 sys.int32}\n"
+	"type sys._osys_473 {_esys_472 sys.int32}\n"
 	"type sys._esys_049 {}\n"
-	"type sys._esys_047 (sys._esys_048 sys._osys_444 sys._esys_049)\n"
+	"type sys._esys_047 (sys._esys_048 sys._osys_473 sys._esys_049)\n"
 	"var !sys.argc sys._esys_047\n"
 	"type sys._esys_051 {}\n"
-	"type sys._osys_448 {_esys_447 sys.int32}\n"
+	"type sys._osys_477 {_esys_476 sys.int32}\n"
 	"type sys._esys_052 {}\n"
-	"type sys._esys_050 (sys._esys_051 sys._osys_448 sys._esys_052)\n"
+	"type sys._esys_050 (sys._esys_051 sys._osys_477 sys._esys_052)\n"
 	"var !sys.envc sys._esys_050\n"
 	"type sys._esys_054 {}\n"
-	"type sys._osys_453 {_esys_451 sys.string}\n"
-	"type sys._isys_455 {_esys_452 sys.int32}\n"
-	"type sys._esys_053 (sys._esys_054 sys._osys_453 sys._isys_455)\n"
+	"type sys._osys_482 {_esys_480 sys.string}\n"
+	"type sys._isys_484 {_esys_481 sys.int32}\n"
+	"type sys._esys_053 (sys._esys_054 sys._osys_482 sys._isys_484)\n"
 	"var !sys.argv sys._esys_053\n"
 	"type sys._esys_056 {}\n"
-	"type sys._osys_461 {_esys_459 sys.string}\n"
-	"type sys._isys_463 {_esys_460 sys.int32}\n"
-	"type sys._esys_055 (sys._esys_056 sys._osys_461 sys._isys_463)\n"
+	"type sys._osys_490 {_esys_488 sys.string}\n"
+	"type sys._isys_492 {_esys_489 sys.int32}\n"
+	"type sys._esys_055 (sys._esys_056 sys._osys_490 sys._isys_492)\n"
 	"var !sys.envv sys._esys_055\n"
 	"type sys._esys_058 {}\n"
-	"type sys._osys_470 {_esys_467 sys.float64 _esys_468 sys.int32}\n"
-	"type sys._isys_472 {_esys_469 sys.float64}\n"
-	"type sys._esys_057 (sys._esys_058 sys._osys_470 sys._isys_472)\n"
+	"type sys._osys_499 {_esys_496 sys.float64 _esys_497 sys.int32}\n"
+	"type sys._isys_501 {_esys_498 sys.float64}\n"
+	"type sys._esys_057 (sys._esys_058 sys._osys_499 sys._isys_501)\n"
 	"var !sys.frexp sys._esys_057\n"
 	"type sys._esys_060 {}\n"
-	"type sys._osys_479 {_esys_476 sys.float64}\n"
-	"type sys._isys_481 {_esys_477 sys.float64 _esys_478 sys.int32}\n"
-	"type sys._esys_059 (sys._esys_060 sys._osys_479 sys._isys_481)\n"
+	"type sys._osys_508 {_esys_505 sys.float64}\n"
+	"type sys._isys_510 {_esys_506 sys.float64 _esys_507 sys.int32}\n"
+	"type sys._esys_059 (sys._esys_060 sys._osys_508 sys._isys_510)\n"
 	"var !sys.ldexp sys._esys_059\n"
 	"type sys._esys_062 {}\n"
-	"type sys._osys_489 {_esys_486 sys.float64 _esys_487 sys.float64}\n"
-	"type sys._isys_491 {_esys_488 sys.float64}\n"
-	"type sys._esys_061 (sys._esys_062 sys._osys_489 sys._isys_491)\n"
+	"type sys._osys_518 {_esys_515 sys.float64 _esys_516 sys.float64}\n"
+	"type sys._isys_520 {_esys_517 sys.float64}\n"
+	"type sys._esys_061 (sys._esys_062 sys._osys_518 sys._isys_520)\n"
 	"var !sys.modf sys._esys_061\n"
 	"type sys._esys_064 {}\n"
-	"type sys._osys_498 {_esys_495 sys.bool}\n"
-	"type sys._isys_500 {_esys_496 sys.float64 _esys_497 sys.int32}\n"
-	"type sys._esys_063 (sys._esys_064 sys._osys_498 sys._isys_500)\n"
+	"type sys._osys_527 {_esys_524 sys.bool}\n"
+	"type sys._isys_529 {_esys_525 sys.float64 _esys_526 sys.int32}\n"
+	"type sys._esys_063 (sys._esys_064 sys._osys_527 sys._isys_529)\n"
 	"var !sys.isInf sys._esys_063\n"
 	"type sys._esys_066 {}\n"
-	"type sys._osys_507 {_esys_505 sys.bool}\n"
-	"type sys._isys_509 {_esys_506 sys.float64}\n"
-	"type sys._esys_065 (sys._esys_066 sys._osys_507 sys._isys_509)\n"
+	"type sys._osys_536 {_esys_534 sys.bool}\n"
+	"type sys._isys_538 {_esys_535 sys.float64}\n"
+	"type sys._esys_065 (sys._esys_066 sys._osys_536 sys._isys_538)\n"
 	"var !sys.isNaN sys._esys_065\n"
 	"type sys._esys_068 {}\n"
-	"type sys._osys_515 {_esys_513 sys.float64}\n"
-	"type sys._isys_517 {_esys_514 sys.int32}\n"
-	"type sys._esys_067 (sys._esys_068 sys._osys_515 sys._isys_517)\n"
+	"type sys._osys_544 {_esys_542 sys.float64}\n"
+	"type sys._isys_546 {_esys_543 sys.int32}\n"
+	"type sys._esys_067 (sys._esys_068 sys._osys_544 sys._isys_546)\n"
 	"var !sys.Inf sys._esys_067\n"
 	"type sys._esys_070 {}\n"
-	"type sys._osys_522 {_esys_521 sys.float64}\n"
+	"type sys._osys_551 {_esys_550 sys.float64}\n"
 	"type sys._esys_071 {}\n"
-	"type sys._esys_069 (sys._esys_070 sys._osys_522 sys._esys_071)\n"
+	"type sys._esys_069 (sys._esys_070 sys._osys_551 sys._esys_071)\n"
 	"var !sys.NaN sys._esys_069\n"
 	"type sys._esys_073 {}\n"
 	"type sys._esys_075 [sys.any] sys.any\n"
 	"type sys._esys_074 *sys._esys_075\n"
-	"type sys._osys_525 {hmap sys._esys_074}\n"
-	"type sys._isys_527 {keysize sys.uint32 valsize sys.uint32 keyalg sys.uint32 valalg sys.uint32 hint sys.uint32}\n"
-	"type sys._esys_072 (sys._esys_073 sys._osys_525 sys._isys_527)\n"
+	"type sys._osys_554 {hmap sys._esys_074}\n"
+	"type sys._isys_556 {keysize sys.uint32 valsize sys.uint32 keyalg sys.uint32 valalg sys.uint32 hint sys.uint32}\n"
+	"type sys._esys_072 (sys._esys_073 sys._osys_554 sys._isys_556)\n"
 	"var !sys.newmap sys._esys_072\n"
 	"type sys._esys_077 {}\n"
-	"type sys._osys_536 {val sys.any}\n"
+	"type sys._osys_565 {val sys.any}\n"
 	"type sys._esys_079 [sys.any] sys.any\n"
 	"type sys._esys_078 *sys._esys_079\n"
-	"type sys._isys_538 {hmap sys._esys_078 key sys.any}\n"
-	"type sys._esys_076 (sys._esys_077 sys._osys_536 sys._isys_538)\n"
+	"type sys._isys_567 {hmap sys._esys_078 key sys.any}\n"
+	"type sys._esys_076 (sys._esys_077 sys._osys_565 sys._isys_567)\n"
 	"var !sys.mapaccess1 sys._esys_076\n"
 	"type sys._esys_081 {}\n"
-	"type sys._osys_544 {val sys.any pres sys.bool}\n"
+	"type sys._osys_573 {val sys.any pres sys.bool}\n"
 	"type sys._esys_083 [sys.any] sys.any\n"
 	"type sys._esys_082 *sys._esys_083\n"
-	"type sys._isys_546 {hmap sys._esys_082 key sys.any}\n"
-	"type sys._esys_080 (sys._esys_081 sys._osys_544 sys._isys_546)\n"
+	"type sys._isys_575 {hmap sys._esys_082 key sys.any}\n"
+	"type sys._esys_080 (sys._esys_081 sys._osys_573 sys._isys_575)\n"
 	"var !sys.mapaccess2 sys._esys_080\n"
 	"type sys._esys_085 {}\n"
 	"type sys._esys_086 {}\n"
 	"type sys._esys_088 [sys.any] sys.any\n"
 	"type sys._esys_087 *sys._esys_088\n"
-	"type sys._isys_553 {hmap sys._esys_087 key sys.any val sys.any}\n"
-	"type sys._esys_084 (sys._esys_085 sys._esys_086 sys._isys_553)\n"
+	"type sys._isys_582 {hmap sys._esys_087 key sys.any val sys.any}\n"
+	"type sys._esys_084 (sys._esys_085 sys._esys_086 sys._isys_582)\n"
 	"var !sys.mapassign1 sys._esys_084\n"
 	"type sys._esys_090 {}\n"
 	"type sys._esys_091 {}\n"
 	"type sys._esys_093 [sys.any] sys.any\n"
 	"type sys._esys_092 *sys._esys_093\n"
-	"type sys._isys_559 {hmap sys._esys_092 key sys.any val sys.any pres sys.bool}\n"
-	"type sys._esys_089 (sys._esys_090 sys._esys_091 sys._isys_559)\n"
+	"type sys._isys_588 {hmap sys._esys_092 key sys.any val sys.any pres sys.bool}\n"
+	"type sys._esys_089 (sys._esys_090 sys._esys_091 sys._isys_588)\n"
 	"var !sys.mapassign2 sys._esys_089\n"
 	"type sys._esys_095 {}\n"
 	"type sys._esys_097 1 sys.any\n"
 	"type sys._esys_096 *sys._esys_097\n"
-	"type sys._osys_566 {hchan sys._esys_096}\n"
-	"type sys._isys_568 {elemsize sys.uint32 elemalg sys.uint32 hint sys.uint32}\n"
-	"type sys._esys_094 (sys._esys_095 sys._osys_566 sys._isys_568)\n"
+	"type sys._osys_595 {hchan sys._esys_096}\n"
+	"type sys._isys_597 {elemsize sys.uint32 elemalg sys.uint32 hint sys.uint32}\n"
+	"type sys._esys_094 (sys._esys_095 sys._osys_595 sys._isys_597)\n"
 	"var !sys.newchan sys._esys_094\n"
 	"type sys._esys_099 {}\n"
-	"type sys._osys_575 {elem sys.any}\n"
+	"type sys._osys_604 {elem sys.any}\n"
 	"type sys._esys_101 1 sys.any\n"
 	"type sys._esys_100 *sys._esys_101\n"
-	"type sys._isys_577 {hchan sys._esys_100}\n"
-	"type sys._esys_098 (sys._esys_099 sys._osys_575 sys._isys_577)\n"
+	"type sys._isys_606 {hchan sys._esys_100}\n"
+	"type sys._esys_098 (sys._esys_099 sys._osys_604 sys._isys_606)\n"
 	"var !sys.chanrecv1 sys._esys_098\n"
 	"type sys._esys_103 {}\n"
-	"type sys._osys_582 {elem sys.any pres sys.bool}\n"
+	"type sys._osys_611 {elem sys.any pres sys.bool}\n"
 	"type sys._esys_105 1 sys.any\n"
 	"type sys._esys_104 *sys._esys_105\n"
-	"type sys._isys_584 {hchan sys._esys_104}\n"
-	"type sys._esys_102 (sys._esys_103 sys._osys_582 sys._isys_584)\n"
+	"type sys._isys_613 {hchan sys._esys_104}\n"
+	"type sys._esys_102 (sys._esys_103 sys._osys_611 sys._isys_613)\n"
 	"var !sys.chanrecv2 sys._esys_102\n"
 	"type sys._esys_107 {}\n"
-	"type sys._osys_590 {elem sys.any pres sys.bool}\n"
+	"type sys._osys_619 {elem sys.any pres sys.bool}\n"
 	"type sys._esys_109 1 sys.any\n"
 	"type sys._esys_108 *sys._esys_109\n"
-	"type sys._isys_592 {hchan sys._esys_108}\n"
-	"type sys._esys_106 (sys._esys_107 sys._osys_590 sys._isys_592)\n"
+	"type sys._isys_621 {hchan sys._esys_108}\n"
+	"type sys._esys_106 (sys._esys_107 sys._osys_619 sys._isys_621)\n"
 	"var !sys.chanrecv3 sys._esys_106\n"
 	"type sys._esys_111 {}\n"
 	"type sys._esys_112 {}\n"
 	"type sys._esys_114 1 sys.any\n"
 	"type sys._esys_113 *sys._esys_114\n"
-	"type sys._isys_598 {hchan sys._esys_113 elem sys.any}\n"
-	"type sys._esys_110 (sys._esys_111 sys._esys_112 sys._isys_598)\n"
+	"type sys._isys_627 {hchan sys._esys_113 elem sys.any}\n"
+	"type sys._esys_110 (sys._esys_111 sys._esys_112 sys._isys_627)\n"
 	"var !sys.chansend1 sys._esys_110\n"
 	"type sys._esys_116 {}\n"
-	"type sys._osys_603 {pres sys.bool}\n"
+	"type sys._osys_632 {pres sys.bool}\n"
 	"type sys._esys_118 1 sys.any\n"
 	"type sys._esys_117 *sys._esys_118\n"
-	"type sys._isys_605 {hchan sys._esys_117 elem sys.any}\n"
-	"type sys._esys_115 (sys._esys_116 sys._osys_603 sys._isys_605)\n"
+	"type sys._isys_634 {hchan sys._esys_117 elem sys.any}\n"
+	"type sys._esys_115 (sys._esys_116 sys._osys_632 sys._isys_634)\n"
 	"var !sys.chansend2 sys._esys_115\n"
 	"type sys._esys_120 {}\n"
-	"type sys._esys_121 {}\n"
-	"type sys._esys_122 {}\n"
-	"type sys._esys_119 (sys._esys_120 sys._esys_121 sys._esys_122)\n"
-	"var !sys.gosched sys._esys_119\n"
-	"type sys._esys_124 {}\n"
-	"type sys._esys_125 {}\n"
-	"type sys._esys_126 {}\n"
-	"type sys._esys_123 (sys._esys_124 sys._esys_125 sys._esys_126)\n"
-	"var !sys.goexit sys._esys_123\n"
+	"type sys._esys_121 *sys.uint8\n"
+	"type sys._osys_640 {sel sys._esys_121}\n"
+	"type sys._isys_642 {size sys.uint32}\n"
+	"type sys._esys_119 (sys._esys_120 sys._osys_640 sys._isys_642)\n"
+	"var !sys.newselect sys._esys_119\n"
+	"type sys._esys_123 {}\n"
+	"type sys._osys_647 {selected sys.bool}\n"
+	"type sys._esys_124 *sys.uint8\n"
+	"type sys._esys_126 1 sys.any\n"
+	"type sys._esys_125 *sys._esys_126\n"
+	"type sys._isys_649 {sel sys._esys_124 hchan sys._esys_125 elem sys.any}\n"
+	"type sys._esys_122 (sys._esys_123 sys._osys_647 sys._isys_649)\n"
+	"var !sys.selectsend sys._esys_122\n"
 	"type sys._esys_128 {}\n"
-	"type sys._osys_616 {_esys_613 sys.string _esys_614 sys.bool}\n"
-	"type sys._isys_618 {_esys_615 sys.string}\n"
-	"type sys._esys_127 (sys._esys_128 sys._osys_616 sys._isys_618)\n"
-	"var !sys.readfile sys._esys_127\n"
-	"type sys._esys_130 {}\n"
-	"type sys._osys_625 {_esys_622 sys.bool}\n"
-	"type sys._isys_627 {_esys_623 sys.string _esys_624 sys.string}\n"
-	"type sys._esys_129 (sys._esys_130 sys._osys_625 sys._isys_627)\n"
-	"var !sys.writefile sys._esys_129\n"
-	"type sys._esys_132 {}\n"
-	"type sys._osys_637 {_esys_632 sys.int32 _esys_633 sys.int32}\n"
-	"type sys._esys_133 *sys.uint8\n"
-	"type sys._isys_639 {_esys_634 sys._esys_133 _esys_635 sys.int32 _esys_636 sys.int32}\n"
-	"type sys._esys_131 (sys._esys_132 sys._osys_637 sys._isys_639)\n"
-	"var !sys.bytestorune sys._esys_131\n"
+	"type sys._osys_656 {selected sys.bool}\n"
+	"type sys._esys_129 *sys.uint8\n"
+	"type sys._esys_131 1 sys.any\n"
+	"type sys._esys_130 *sys._esys_131\n"
+	"type sys._esys_132 *sys.any\n"
+	"type sys._isys_658 {sel sys._esys_129 hchan sys._esys_130 elem sys._esys_132}\n"
+	"type sys._esys_127 (sys._esys_128 sys._osys_656 sys._isys_658)\n"
+	"var !sys.selectrecv sys._esys_127\n"
+	"type sys._esys_134 {}\n"
 	"type sys._esys_135 {}\n"
-	"type sys._osys_650 {_esys_645 sys.int32 _esys_646 sys.int32}\n"
-	"type sys._isys_652 {_esys_647 sys.string _esys_648 sys.int32 _esys_649 sys.int32}\n"
-	"type sys._esys_134 (sys._esys_135 sys._osys_650 sys._isys_652)\n"
-	"var !sys.stringtorune sys._esys_134\n"
-	"type sys._esys_137 {}\n"
+	"type sys._esys_136 *sys.uint8\n"
+	"type sys._isys_665 {sel sys._esys_136}\n"
+	"type sys._esys_133 (sys._esys_134 sys._esys_135 sys._isys_665)\n"
+	"var !sys.selectgo sys._esys_133\n"
 	"type sys._esys_138 {}\n"
-	"type sys._isys_659 {_esys_658 sys.int32}\n"
-	"type sys._esys_136 (sys._esys_137 sys._esys_138 sys._isys_659)\n"
-	"var !sys.exit sys._esys_136\n"
+	"type sys._esys_139 {}\n"
+	"type sys._esys_140 {}\n"
+	"type sys._esys_137 (sys._esys_138 sys._esys_139 sys._esys_140)\n"
+	"var !sys.gosched sys._esys_137\n"
+	"type sys._esys_142 {}\n"
+	"type sys._esys_143 {}\n"
+	"type sys._esys_144 {}\n"
+	"type sys._esys_141 (sys._esys_142 sys._esys_143 sys._esys_144)\n"
+	"var !sys.goexit sys._esys_141\n"
+	"type sys._esys_146 {}\n"
+	"type sys._osys_674 {_esys_671 sys.string _esys_672 sys.bool}\n"
+	"type sys._isys_676 {_esys_673 sys.string}\n"
+	"type sys._esys_145 (sys._esys_146 sys._osys_674 sys._isys_676)\n"
+	"var !sys.readfile sys._esys_145\n"
+	"type sys._esys_148 {}\n"
+	"type sys._osys_683 {_esys_680 sys.bool}\n"
+	"type sys._isys_685 {_esys_681 sys.string _esys_682 sys.string}\n"
+	"type sys._esys_147 (sys._esys_148 sys._osys_683 sys._isys_685)\n"
+	"var !sys.writefile sys._esys_147\n"
+	"type sys._esys_150 {}\n"
+	"type sys._osys_695 {_esys_690 sys.int32 _esys_691 sys.int32}\n"
+	"type sys._esys_151 *sys.uint8\n"
+	"type sys._isys_697 {_esys_692 sys._esys_151 _esys_693 sys.int32 _esys_694 sys.int32}\n"
+	"type sys._esys_149 (sys._esys_150 sys._osys_695 sys._isys_697)\n"
+	"var !sys.bytestorune sys._esys_149\n"
+	"type sys._esys_153 {}\n"
+	"type sys._osys_708 {_esys_703 sys.int32 _esys_704 sys.int32}\n"
+	"type sys._isys_710 {_esys_705 sys.string _esys_706 sys.int32 _esys_707 sys.int32}\n"
+	"type sys._esys_152 (sys._esys_153 sys._osys_708 sys._isys_710)\n"
+	"var !sys.stringtorune sys._esys_152\n"
+	"type sys._esys_155 {}\n"
+	"type sys._esys_156 {}\n"
+	"type sys._isys_717 {_esys_716 sys.int32}\n"
+	"type sys._esys_154 (sys._esys_155 sys._esys_156 sys._isys_717)\n"
+	"var !sys.exit sys._esys_154\n"
+	"type sys._esys_158 {}\n"
+	"type sys._esys_159 {}\n"
+	"type sys._esys_160 {}\n"
+	"type sys._esys_157 (sys._esys_158 sys._esys_159 sys._esys_160)\n"
 	"))\n"
 ;
diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 576fe90b02..422b551367 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -70,7 +70,7 @@ loop:
 		if(top != Etop)
 			goto nottop;
 		walktype(n->left, Erv);
-		*n = *nod(OLIST, prcompat(n->left), nodpanic(n->lineno));
+		*n = *list(prcompat(n->left), nodpanic(n->lineno));
 		goto ret;
 
 	case OLITERAL:
@@ -121,6 +121,9 @@ loop:
 		if(top != Etop)
 			goto nottop;
 
+		if(!casebody(n->nbody))
+			yyerror("switch statement must have case labels");
+
 		if(n->ntest == N)
 			n->ntest = booltrue;
 		walktype(n->ninit, Etop);
@@ -142,6 +145,20 @@ loop:
 		walktype(n->nincr, Erv);
 		goto ret;
 
+	case OSELECT:
+		if(top != Etop)
+			goto nottop;
+
+		walkselect(n);
+		goto ret;
+
+	case OSCASE:
+		if(top != Etop)
+			goto nottop;
+//		walktype(n->left, Erv);	SPECIAL
+		n = n->right;
+		goto loop;
+
 	case OEMPTY:
 		if(top != Etop)
 			goto nottop;
@@ -216,7 +233,7 @@ loop:
 			l = ascompatte(n->op, getinarg(t), &n->right, 0);
 			r = ascompatte(n->op, getthis(t), &n->left->left, 0);
 			if(l != N)
-				r = nod(OLIST, r, l);
+				r = list(r, l);
 			n->left->left = N;
 			ullmancalc(n->left);
 			n->right = reorder1(r);
@@ -255,7 +272,7 @@ loop:
 				walktype(r, Erv);
 				l = ascompatet(n->op, &n->left, &r->type, 0);
 				if(l != N) {
-					*n = *nod(OLIST, r, reorder2(l));
+					*n = *list(r, reorder2(l));
 				}
 				goto ret;
 			}
@@ -591,8 +608,8 @@ loop:
 	case OSEND:
 		if(top == Elv)
 			goto nottop;
-		walktype(n->left, Erv);
-		walktype(n->right, Erv);
+		walktype(n->left, Erv);		// chan
+		walktype(n->right, Erv);	// e
 		*n = *chanop(n, top);
 		goto ret;
 
@@ -805,7 +822,7 @@ sw2(Node *c, Type *place)
 }
 
 /*
- * check that selected type
+ * check that switch type
  * is compat with all the cases
  */
 Type*
@@ -897,6 +914,125 @@ loop:
 	goto loop;
 }
 
+Node*
+selcase(Node *c, Node *var)
+{
+	Node *a, *r, *on;
+	Type *t;
+
+	walktype(c->left, Erv);		// chan
+	walktype(c->right, Erv);	// elem
+	t = fixchan(c->left->type);
+	if(t == T)
+		return;
+
+	convlit(c->right, t->type);
+	if(!ascompat(t->type, c->right->type)) {
+		badtype(c->op, t->type, c->right->type);
+		return;
+	}
+
+	// selectsend(sel *byte, hchan *chan any, elem any) (selected bool);
+	on = syslook("selectsend", 1);
+	argtype(on, t->type);
+	argtype(on, t->type);
+
+	a = c->right;		// elem
+	r = a;
+	a = c->left;		// chan
+	r = list(a, r);
+	a = var;		// sel-var
+	r = list(a, r);
+
+	a = nod(OCALL, on, r);
+	r = nod(OIF, N, N);
+	r->ntest = a;
+
+	return r;
+
+}
+
+void
+walkselect(Node *sel)
+{
+	Iter iter;
+	Node *n, *oc, *on, *r;
+	Node *var, *bod, *res;
+	int count;
+	long lno;
+
+	lno = setlineno(sel);
+
+	// generate sel-struct
+	var = nod(OXXX, N, N);
+	tempname(var, ptrto(types[TUINT8]));
+
+	n = listfirst(&iter, &sel->left);
+	if(n == N || n->op != OXCASE)
+		yyerror("first select statement must be a case");
+
+	count = 0;	// number of cases
+	res = N;	// entire select body
+	bod = N;	// body of each case
+	oc = N;		// last case
+
+	for(count=0; n!=N; n=listnext(&iter)) {
+		setlineno(n);
+
+		switch(n->op) {
+		default:
+			bod = list(bod, n);
+			break;
+
+		case OXCASE:
+			switch(n->left->op) {
+			default:
+				yyerror("select cases must be send or recv");
+				break;
+
+			case OSEND:
+				if(oc != N) {
+					bod = list(bod, nod(OBREAK, N, N));
+					oc->nbody = rev(bod);
+				}
+				oc = selcase(n->left, var);
+				res = list(res, oc);
+				break;
+			}
+			bod = N;
+			count++;
+			break;
+		}
+	}
+	if(oc != N) {
+		bod = list(bod, nod(OBREAK, N, N));
+		oc->nbody = rev(bod);
+	}
+	setlineno(sel);
+
+	// selectgo(sel *byte);
+	on = syslook("selectgo", 0);
+	r = nod(OCALL, on, var);		// sel-var
+	res = list(res, r);
+
+	// newselect(size uint32) (sel *byte);
+	on = syslook("newselect", 0);
+
+	r = nod(OXXX, N, N);
+	nodconst(r, types[TINT32], count);	// count
+	r = nod(OCALL, on, r);
+	r = nod(OAS, var, r);
+
+	sel->ninit = r;
+	sel->nbody = rev(res);
+	sel->left = N;
+
+	walktype(sel->ninit, Etop);
+	walktype(sel->nbody, Etop);
+
+	lineno = lno;
+}
+
 /*
  * allowable type combinations for
  * normal binary operations.
@@ -1053,7 +1189,7 @@ loop:
 	if(nn == N)
 		nn = a;
 	else
-		nn = nod(OLIST, a, nn);
+		nn = list(a, nn);
 
 	l = listnext(&savel);
 	r = listnext(&saver);
@@ -1093,7 +1229,7 @@ loop:
 	if(nn == N)
 		nn = a;
 	else
-		nn = nod(OLIST, a, nn);
+		nn = list(a, nn);
 
 	l = listnext(&savel);
 	r = structnext(&saver);
@@ -1134,7 +1270,7 @@ loop:
 	if(nn == N)
 		nn = a;
 	else
-		nn = nod(OLIST, a, nn);
+		nn = list(a, nn);
 
 	l = structnext(&savel);
 	r = listnext(&saver);
@@ -1230,7 +1366,7 @@ loop:
 	if(r == N)
 		r = nod(OCALL, on, l);
 	else
-		r = nod(OLIST, r, nod(OCALL, on, l));
+		r = list(r, nod(OCALL, on, l));
 
 	l = listnext(&save);
 	goto loop;
@@ -1305,7 +1441,7 @@ stringop(Node *n, int top)
 	case OLT:
 		// sys_cmpstring(s1, s2) :: 0
 		on = syslook("cmpstring", 0);
-		r = nod(OLIST, n->left, n->right);
+		r = list(n->left, n->right);
 		r = nod(OCALL, on, r);
 		c = nodintconst(0);
 		r = nod(n->op, r, c);
@@ -1314,7 +1450,7 @@ stringop(Node *n, int top)
 	case OADD:
 		// sys_catstring(s1, s2)
 		on = syslook("catstring", 0);
-		r = nod(OLIST, n->left, n->right);
+		r = list(n->left, n->right);
 		r = nod(OCALL, on, r);
 		break;
 
@@ -1328,7 +1464,7 @@ stringop(Node *n, int top)
 			// s1 = sys_catstring(s1, s2)
 			if(n->etype != OADD)
 				fatal("stringop: not cat");
-			r = nod(OLIST, n->left, n->right);
+			r = list(n->left, n->right);
 			on = syslook("catstring", 0);
 			r = nod(OCALL, on, r);
 			r = nod(OAS, n->left, r);
@@ -1344,8 +1480,8 @@ stringop(Node *n, int top)
 		c = nod(OCONV, n->right->right, N);
 		c->type = types[TINT32];
 
-		r = nod(OLIST, r, c);
-		r = nod(OLIST, n->left, r);
+		r = list(r, c);
+		r = list(n->left, r);
 		on = syslook("slicestring", 0);
 		r = nod(OCALL, on, r);
 		break;
@@ -1360,7 +1496,7 @@ stringop(Node *n, int top)
 		}
 		r = nod(OCONV, n->right, N);
 		r->type = types[TINT32];
-		r = nod(OLIST, c, r);
+		r = list(c, r);
 		on = syslook("indexstring", 0);
 		r = nod(OCALL, on, r);
 		break;
@@ -1382,7 +1518,7 @@ stringop(Node *n, int top)
 		l = isbytearray(n->left->type);
 		c = nodintconst(l-1);
 
-		r = nod(OLIST, r, c);
+		r = list(r, c);
 		on = syslook("byteastring", 0);
 		r = nod(OCALL, on, r);
 		break;
@@ -1499,13 +1635,13 @@ mapop(Node *n, int top)
 			a = nodintconst(0);
 		r = a;
 		a = nodintconst(algtype(t->type));	// val algorithm
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 		a = nodintconst(algtype(t->down));	// key algorithm
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 		a = nodintconst(t->type->width);	// val width
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 		a = nodintconst(t->down->width);	// key width
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 
 		on = syslook("newmap", 1);
 
@@ -1541,7 +1677,7 @@ mapop(Node *n, int top)
 
 		r = a;
 		a = n->left;				// map
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 
 		on = syslook("mapaccess1", 1);
 
@@ -1579,9 +1715,9 @@ mapop(Node *n, int top)
 		a = n->right;				// val
 		r = a;
 		a = n->left->right;			// key
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 		a = n->left->left;			// map
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 
 		on = syslook("mapassign1", 1);
 
@@ -1608,11 +1744,11 @@ mapop(Node *n, int top)
 		a = n->right->right;			// pres
 		r = a;
 		a = n->right->left;			// val
-		r =nod(OLIST, a, r);
+		r =list(a, r);
 		a = n->left->right;			// key
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 		a = n->left->left;			// map
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 
 		on = syslook("mapassign2", 1);
 
@@ -1639,7 +1775,7 @@ mapop(Node *n, int top)
 		a = n->right->right;			// key
 		r = a;
 		a = n->right->left;			// map
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 
 		on = syslook("mapaccess2", 1);
 
@@ -1695,9 +1831,9 @@ chanop(Node *n, int top)
 			a = nodintconst(0);
 		r = a;
 		a = nodintconst(algtype(t->type));	// elem algorithm
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 		a = nodintconst(t->type->width);	// elem width
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 
 		on = syslook("newchan", 1);
 		argtype(on, t->type);	// any-1
@@ -1789,7 +1925,7 @@ fatal("recv2 not yet");
 		a = n->right;			// e
 		r = a;
 		a = n->left;			// chan
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 
 		on = syslook("chansend1", 1);
 		argtype(on, t->type);	// any-1
@@ -1807,7 +1943,7 @@ fatal("recv2 not yet");
 		a = n->right;			// e
 		r = a;
 		a = n->left;			// chan
-		r = nod(OLIST, a, r);
+		r = list(a, r);
 
 		on = syslook("chansend2", 1);
 		argtype(on, t->type);	// any-1
@@ -1981,7 +2117,7 @@ colas(Node *nl, Node *nr)
 		if(n == N)
 			n = a;
 		else
-			n = nod(OLIST, n, a);
+			n = list(n, a);
 
 		l = listnext(&savel);
 		r = listnext(&saver);
@@ -2017,7 +2153,7 @@ multi:
 			if(n == N)
 				n = a;
 			else
-				n = nod(OLIST, n, a);
+				n = list(n, a);
 			l = listnext(&savel);
 			t = structnext(&saver);
 		}
@@ -2039,7 +2175,7 @@ multi:
 		a = old2new(nl->left, t->type);
 		n = a;
 		a = old2new(nl->right, types[TBOOL]);
-		n = nod(OLIST, n, a);
+		n = list(n, a);
 		break;
 
 	case ORECV:
@@ -2052,7 +2188,7 @@ multi:
 		a = old2new(nl->left, t->type->type);
 		n = a;
 		a = old2new(nl->right, types[TBOOL]);
-		n = nod(OLIST, n, a);
+		n = list(n, a);
 	}
 	n = rev(n);
 	return n;
@@ -2107,15 +2243,15 @@ loop2:
 		r = rev(r);
 		g = rev(g);
 		if(g != N)
-			f = nod(OLIST, g, f);
-		r = nod(OLIST, f, r);
+			f = list(g, f);
+		r = list(f, r);
 		return r;
 	}
 	if(l->ullman < UINF) {
 		if(r == N)
 			r = l;
 		else
-			r = nod(OLIST, l, r);
+			r = list(l, r);
 		goto more;
 	}
 	if(f == N) {
@@ -2131,7 +2267,7 @@ loop2:
 	if(g == N)
 		g = a;
 	else
-		g = nod(OLIST, a, g);
+		g = list(a, g);
 
 	// put normal arg assignment on list
 	// with fncall replaced by tempname
@@ -2139,7 +2275,7 @@ loop2:
 	if(r == N)
 		r = l;
 	else
-		r = nod(OLIST, l, r);
+		r = list(l, r);
 
 more:
 	l = listnext(&save);
@@ -2256,7 +2392,7 @@ reorder3(Node *n)
 					if(r == N)
 						r = q;
 					else
-						r = nod(OLIST, r, q);
+						r = list(r, q);
 					break;
 				}
 			}
@@ -2275,7 +2411,7 @@ reorder3(Node *n)
 		if(q == N)
 			q = l1;
 		else
-			q = nod(OLIST, q, l1);
+			q = list(q, l1);
 		l1 = listnext(&save1);
 	}
 
@@ -2285,7 +2421,7 @@ reorder3(Node *n)
 		if(q == N)
 			q = l1;
 		else
-			q = nod(OLIST, q, l1);
+			q = list(q, l1);
 		l1 = listnext(&save1);
 	}
 
diff --git a/src/runtime/chan.c b/src/runtime/chan.c
index 99f9b23857..9f48c5d7ca 100644
--- a/src/runtime/chan.c
+++ b/src/runtime/chan.c
@@ -10,10 +10,13 @@ typedef	struct	Hchan	Hchan;
 typedef	struct	Link	Link;
 typedef	struct	WaitQ	WaitQ;
 typedef	struct	SudoG	SudoG;
+typedef	struct	Select	Select;
+typedef	struct	Scase	Scase;
 
 struct	SudoG
 {
 	G*	g;		// g and selgen constitute
+	byte	elem[8];	// synch data element
 	int64	selgen;		// a weak pointer to g
 	SudoG*	link;
 };
@@ -29,8 +32,8 @@ struct	Hchan
 	uint32	elemsize;
 	uint32	dataqsiz;		// size of the circular q
 	uint32	qcount;			// total data in the q
-	uint32	eo;			// vararg of element
-	uint32	po;			// vararg of present bool
+	uint16	eo;			// vararg of element
+	uint16	po;			// vararg of present bool
 	Alg*	elemalg;		// interface for element type
 	Link*	senddataq;		// pointer for sender
 	Link*	recvdataq;		// pointer for receiver
@@ -41,14 +44,33 @@ struct	Hchan
 
 struct	Link
 {
-	Link*	link;
-	byte	elem[8];
+	Link*	link;			// asynch queue circular linked list
+	byte	elem[8];		// asynch queue data element
 };
 
-static SudoG*	dequeue(WaitQ*, Hchan*);
-static void	enqueue(WaitQ*, SudoG*);
-static SudoG*	allocsg(Hchan*);
-static void	freesg(Hchan*, SudoG*);
+struct	Scase
+{
+	Hchan*	chan;			// chan
+	byte*	pc;			// return pc
+	uint16	send;			// 0-recv 1-send
+	uint16	so;			// vararg of selected bool
+	byte	elem[8];		// element
+};
+
+struct	Select
+{
+	uint16	tcase;			// total count of scase[]
+	uint16	ncase;			// currently filled scase[]
+	Scase	scase[1];		// one per case
+};
+
+static	SudoG*	dequeue(WaitQ*, Hchan*);
+static	void	enqueue(WaitQ*, SudoG*);
+static	SudoG*	allocsg(Hchan*);
+static	void	freesg(Hchan*, SudoG*);
+static	uint32	gcd(uint32, uint32);
+static	uint32	fastrand1(void);
+static	uint32	fastrand2(void);
 
 // newchan(elemsize uint32, elemalg uint32, hint uint32) (hchan *chan any);
 void
@@ -134,16 +156,15 @@ sys·chansend1(Hchan* c, ...)
 
 	sgr = dequeue(&c->recvq, c);
 	if(sgr != nil) {
-		gr = sgr->g;
-		freesg(c, sgr);
+		c->elemalg->copy(c->elemsize, sgr->elem, ae);
 
-		c->elemalg->copy(c->elemsize, gr->elem, ae);
+		gr = sgr->g;
 		gr->status = Grunnable;
 		return;
 	}
 
-	c->elemalg->copy(c->elemsize, g->elem, ae);
 	sgr = allocsg(c);
+	c->elemalg->copy(c->elemsize, sgr->elem, ae);
 	g->status = Gwaiting;
 	enqueue(&c->sendq, sgr);
 	sys·gosched();
@@ -191,9 +212,8 @@ sys·chansend2(Hchan* c, ...)
 	sgr = dequeue(&c->recvq, c);
 	if(sgr != nil) {
 		gr = sgr->g;
-		freesg(c, sgr);
+		c->elemalg->copy(c->elemsize, sgr->elem, ae);
 
-		c->elemalg->copy(c->elemsize, gr->elem, ae);
 		gr->status = Grunnable;
 		*ap = true;
 		return;
@@ -237,18 +257,20 @@ sys·chanrecv1(Hchan* c, ...)
 
 	sgs = dequeue(&c->sendq, c);
 	if(sgs != nil) {
-		gs = sgs->g;
-		freesg(c, sgs);
+		c->elemalg->copy(c->elemsize, ae, sgs->elem);
 
-		c->elemalg->copy(c->elemsize, ae, gs->elem);
+		gs = sgs->g;
 		gs->status = Grunnable;
+
+		freesg(c, sgs);
 		return;
 	}
 	sgs = allocsg(c);
 	g->status = Gwaiting;
 	enqueue(&c->recvq, sgs);
 	sys·gosched();
-	c->elemalg->copy(c->elemsize, ae, g->elem);
+	c->elemalg->copy(c->elemsize, ae, sgs->elem);
+	freesg(c, sgs);
 	return;
 
 asynch:
@@ -291,11 +313,12 @@ sys·chanrecv2(Hchan* c, ...)
 
 	sgs = dequeue(&c->sendq, c);
 	if(sgs != nil) {
-		gs = sgs->g;
-		freesg(c, sgs);
+		c->elemalg->copy(c->elemsize, ae, sgs->elem);
 
-		c->elemalg->copy(c->elemsize, ae, gs->elem);
+		gs = sgs->g;
 		gs->status = Grunnable;
+
+		freesg(c, sgs);
 		*ap = true;
 		return;
 	}
@@ -320,6 +343,150 @@ asynch:
 	*ap = true;
 }
 
+// newselect(size uint32) (sel *byte);
+void
+sys·newselect(int32 size, Select *sel)
+{
+	int32 n;
+
+	n = 0;
+	if(size > 1)
+		n = size-1;
+	sel = mal(sizeof(*sel) + n*sizeof(sel->scase[0]));
+	sel->tcase = size;
+	sel->ncase = 0;
+	FLUSH(&sel);
+	if(debug) {
+		prints("newselect s=");
+		sys·printpointer(sel);
+		prints("\n");
+	}
+}
+
+// selectsend(sel *byte, hchan *chan any, elem any) (selected bool);
+void
+sys·selectsend(Select *sel, Hchan *c, ...)
+{
+	int32 i, eo;
+	Scase *cas;
+	byte *as, *ae;
+
+	// return val, selected, is preset to false
+	if(c == nil)
+		return;
+
+	i = sel->ncase;
+	if(i >= sel->tcase)
+		throw("selectsend: too many cases");
+	sel->ncase = i+1;
+	cas = &sel->scase[i];
+
+	cas->pc = sys·getcallerpc(&sel);
+	cas->chan = c;
+
+	eo = rnd(sizeof(sel), sizeof(c));
+	eo = rnd(eo+sizeof(c), c->elemsize);
+	cas->so = rnd(eo+c->elemsize, 1);
+	cas->send = 1;
+
+	ae = (byte*)&sel + eo;
+	c->elemalg->copy(c->elemsize, cas->elem, ae);
+
+	as = (byte*)&sel + cas->so;
+	*as = false;
+
+	if(debug) {
+		prints("newselect s=");
+		sys·printpointer(sel);
+		prints(" pc=");
+		sys·printpointer(cas->pc);
+		prints(" chan=");
+		sys·printpointer(cas->chan);
+		prints(" po=");
+		sys·printint(cas->so);
+		prints(" send=");
+		sys·printint(cas->send);
+		prints("\n");
+	}
+}
+
+// selectrecv(sel *byte, hchan *chan any, elem *any) (selected bool);
+void
+sys·selectrecv(Select *sel, Hchan *c, ...)
+{
+	throw("selectrecv");
+}
+
+// selectgo(sel *byte);
+void
+sys·selectgo(Select *sel)
+{
+	uint32 p, o, i;
+	Scase *cas;
+	Hchan *c;
+
+	byte *ae, *as;
+	SudoG *sgr;
+	G *gr;
+
+	if(sel->ncase < 1) {
+		throw("selectgo: no cases");
+	}
+
+	// select a (relative) prime
+	for(i=0;; i++) {
+		p = fastrand1();
+		if(gcd(p, sel->ncase) == 1)
+			break;
+		if(i > 1000) {
+			throw("selectgo: failed to select prime");
+		}
+	}
+	o = fastrand2();
+
+	p %= sel->ncase;
+	o %= sel->ncase;
+
+	// pass 1 - look for something that can go
+	for(i=0; i<sel->ncase; i++) {
+		cas = &sel->scase[o];
+		c = cas->chan;
+		if(cas->send) {
+			if(c->dataqsiz > 0) {
+				throw("selectgo: asynch");
+			}
+			sgr = dequeue(&c->recvq, c);
+			if(sgr == nil)
+				continue;
+
+			c->elemalg->copy(c->elemsize, sgr->elem, cas->elem);
+			gr = sgr->g;
+			gr->status = Grunnable;
+
+			goto retc;
+		}
+
+		o += p;
+		if(o >= sel->ncase)
+			o -= sel->ncase;
+	}
+
+	if(debug) {
+		prints("selectgo s=");
+		sys·printpointer(sel);
+		prints(" p=");
+		sys·printpointer((void*)p);
+		prints("\n");
+	}
+
+	throw("selectgo");
+
+retc:
+	sys·setcallerpc(&sel, cas->pc);
+	as = (byte*)&sel + cas->so;
+	*as = true;
+}
+
 static SudoG*
 dequeue(WaitQ *q, Hchan *c)
 {
@@ -377,3 +544,41 @@ freesg(Hchan *c, SudoG *sg)
 	sg->link = c->free;
 	c->free = sg;
 }
+
+static uint32
+gcd(uint32 u, uint32 v)
+{
+	for(;;) {
+		if(u > v) {
+			if(v == 0)
+				return u;
+			u = u%v;
+			continue;
+		}
+		if(u == 0)
+			return v;
+		v = v%u;
+	}
+}
+
+static uint32
+fastrand1(void)
+{
+	static uint32 x = 0x49f6428aUL;
+
+	x += x;
+	if(x & 0x80000000L)
+		x ^= 0x88888eefUL;
+	return x;
+}
+
+static uint32
+fastrand2(void)
+{
+	static uint32 x = 0x49f6428aUL;
+
+	x += x;
+	if(x & 0x80000000L)
+		x ^= 0xfafd871bUL;
+	return x;
+}
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index df14b76783..fe6ef5457a 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -110,7 +110,6 @@ struct	G
 	int32	status;
 	int32	goid;
 	int64	selgen;		// valid sudog pointer
-	byte	elem[8];	// transfer element for chan
 };
 struct	M
 {
@@ -205,6 +204,7 @@ void	sys·write(int32, void*, int32);
 void	sys·breakpoint(void);
 uint8*	sys·mmap(byte*, uint32, int32, int32, int32, uint32);
 void	sys·memclr(byte*, uint32);
+void	sys·setcallerpc(void*, void*);
 void*	sys·getcallerpc(void*);
 void	sys·sigaction(int64, void*, void*);
 void	sys·rt_sigaction(int64, void*, void*, uint64);
diff --git a/src/runtime/sys_amd64_darwin.s b/src/runtime/sys_amd64_darwin.s
index 26ceaaf6ea..39549cb4b3 100644
--- a/src/runtime/sys_amd64_darwin.s
+++ b/src/runtime/sys_amd64_darwin.s
@@ -110,6 +110,12 @@ TEXT	sys·memclr(SB),1,$-8
 	RET
 
 TEXT	sys·getcallerpc+0(SB),1,$0
-	MOVQ	x+0(FP),AX
-	MOVQ	-8(AX),AX
+	MOVQ	x+0(FP),AX		// addr of first arg
+	MOVQ	-8(AX),AX		// get calling pc
+	RET
+
+TEXT	sys·setcallerpc+0(SB),1,$0
+	MOVQ	x+0(FP),AX		// addr of first arg
+	MOVQ	x+8(FP), BX
+	MOVQ	BX, -8(AX)		// set calling pc
 	RET
diff --git a/src/runtime/sys_amd64_linux.s b/src/runtime/sys_amd64_linux.s
index e98ca52456..106159dc8e 100644
--- a/src/runtime/sys_amd64_linux.s
+++ b/src/runtime/sys_amd64_linux.s
@@ -114,6 +114,12 @@ TEXT	sys·memclr(SB),1,$0-16
 	RET
 
 TEXT	sys·getcallerpc+0(SB),1,$0
-	MOVQ	x+0(FP),AX
-	MOVQ	-8(AX),AX
+	MOVQ	x+0(FP),AX		// addr of first arg
+	MOVQ	-8(AX),AX		// get calling pc
+	RET
+
+TEXT	sys·setcallerpc+0(SB),1,$0
+	MOVQ	x+0(FP),AX		// addr of first arg
+	MOVQ	x+8(FP), BX
+	MOVQ	BX, -8(AX)		// set calling pc
 	RET