runtime: faster select

Make selectsend() accept pointer to the element,
it makes it possible to make Scase fixed-size
and allocate/free Select, all Scase's and all SudoG at once.
As a consequence SudoG freelist die out.

benchmark                       old,ns/op  new,ns/op
BenchmarkSelectUncontended	     1080        558
BenchmarkSelectUncontended-2	      675        264
BenchmarkSelectUncontended-4	      459        205
BenchmarkSelectContended	     1086        560
BenchmarkSelectContended-2	     1775       1672
BenchmarkSelectContended-4	     2668       2149
(on Intel Q6600, 4 cores, 2.4GHz)

benchmark                       old ns/op    new ns/op    delta
BenchmarkSelectUncontended         517.00       326.00  -36.94%
BenchmarkSelectUncontended-2       281.00       166.00  -40.93%
BenchmarkSelectUncontended-4       250.00        83.10  -66.76%
BenchmarkSelectUncontended-8       107.00        47.40  -55.70%
BenchmarkSelectUncontended-16       67.80        41.30  -39.09%
BenchmarkSelectContended           513.00       325.00  -36.65%
BenchmarkSelectContended-2         699.00       628.00  -10.16%
BenchmarkSelectContended-4        1085.00      1092.00   +0.65%
BenchmarkSelectContended-8        3253.00      2477.00  -23.85%
BenchmarkSelectContended-16       5313.00      5116.00   -3.71%
(on Intel E5620, 8 HT cores, 2.4 GHz)

R=rsc, ken
CC=golang-dev
https://golang.org/cl/4811041

src/cmd/gc/builtin.c.boot

@@ -76,7 +76,7 @@ char *runtimeimport =
 	"func \"\".selectnbrecv (elem *any, hchan <-chan any) bool\n"
 	"func \"\".selectnbrecv2 (elem *any, received *bool, hchan <-chan any) bool\n"
 	"func \"\".newselect (size int) *uint8\n"
-	"func \"\".selectsend (sel *uint8, hchan chan<- any, elem any) bool\n"
+	"func \"\".selectsend (sel *uint8, hchan chan<- any, elem *any) bool\n"
 	"func \"\".selectrecv (sel *uint8, hchan <-chan any, elem *any) bool\n"
 	"func \"\".selectrecv2 (sel *uint8, hchan <-chan any, elem *any, received *bool) bool\n"
 	"func \"\".selectdefault (sel *uint8) bool\n"

src/cmd/gc/go.h

@@ -1137,6 +1137,7 @@ Sym*	restrictlookup(char *name, Pkg *pkg);
 Node*	safeexpr(Node *n, NodeList **init);
 void	saveerrors(void);
 Node*	cheapexpr(Node *n, NodeList **init);
+Node*	localexpr(Node *n, NodeList **init);
 int32	setlineno(Node *n);
 void	setmaxarg(Type *t);
 Type*	shallow(Type *t);

src/cmd/gc/runtime.go

@@ -103,7 +103,7 @@ func selectnbrecv(elem *any, hchan <-chan any) bool
 func selectnbrecv2(elem *any, received *bool, hchan <-chan any) bool
 
 func newselect(size int) (sel *byte)
-func selectsend(sel *byte, hchan chan<- any, elem any) (selected bool)
+func selectsend(sel *byte, hchan chan<- any, elem *any) (selected bool)
 func selectrecv(sel *byte, hchan <-chan any, elem *any) (selected bool)
 func selectrecv2(sel *byte, hchan <-chan any, elem *any, received *bool) (selected bool)
 func selectdefault(sel *byte) (selected bool)

src/cmd/gc/select.c

@@ -309,7 +309,12 @@ walkselect(Node *sel)
 				fatal("select %O", n->op);
 	
 			case OSEND:
-				// selectsend(sel *byte, hchan *chan any, elem any) (selected bool);
+				// selectsend(sel *byte, hchan *chan any, elem *any) (selected bool);
+				n->left = safeexpr(n->left, &r->ninit);
+				n->right = localexpr(n->right, &r->ninit);
+				n->right = nod(OADDR, n->right, N);
+				n->right->etype = 1;  // pointer does not escape
+				typecheck(&n->right, Erv);
 				r->ntest = mkcall1(chanfn("selectsend", 2, n->left->type), types[TBOOL],
 					&init, var, n->left, n->right);
 				break;

src/cmd/gc/subr.c

@@ -2750,6 +2750,20 @@ safeexpr(Node *n, NodeList **init)
 	return cheapexpr(n, init);
 }
 
+static Node*
+copyexpr(Node *n, NodeList **init)
+{
+	Node *a, *l;
+	
+	l = nod(OXXX, N, N);
+	tempname(l, n->type);
+	a = nod(OAS, l, n);
+	typecheck(&a, Etop);
+	walkexpr(&a, init);
+	*init = list(*init, a);
+	return l;
+}
+
 /*
  * return side-effect free and cheap n, appending side effects to init.
  * result may not be assignable.
@@ -2757,21 +2771,26 @@ safeexpr(Node *n, NodeList **init)
 Node*
 cheapexpr(Node *n, NodeList **init)
 {
-	Node *a, *l;
-
 	switch(n->op) {
 	case ONAME:
 	case OLITERAL:
 		return n;
 	}
 
-	l = nod(OXXX, N, N);
-	tempname(l, n->type);
-	a = nod(OAS, l, n);
-	typecheck(&a, Etop);
-	walkexpr(&a, init);
-	*init = list(*init, a);
-	return l;
+	return copyexpr(n, init);
+}
+
+/*
+ * return n in a local variable if it is not already.
+ */
+Node*
+localexpr(Node *n, NodeList **init)
+{
+	if(n->op == ONAME &&
+		 (n->class == PAUTO || n->class == PPARAM || n->class == PPARAMOUT))
+		return n;
+	
+	return copyexpr(n, init);
 }
 
 void

src/cmd/ld/dwarf.c

@@ -1422,7 +1422,6 @@ synthesizechantypes(DWDie *die)
 		copychildren(dwh, hchan);
 		substitutetype(dwh, "recvq", dww);
 		substitutetype(dwh, "sendq", dww);
-		substitutetype(dwh, "free", defptrto(dws));
 		newattr(dwh, DW_AT_byte_size, DW_CLS_CONSTANT,
 			getattr(hchan, DW_AT_byte_size)->value, nil);