cmd/gc: shorten more temporary lifetimes

1. In functions with heap-allocated result variables or with
defer statements, the return sequence requires more than
just a single RET instruction. There is an optimization that
arranges for all returns to jump to a single copy of the return
epilogue in this case. Unfortunately, that optimization is
fundamentally incompatible with PC-based liveness information:
it takes PCs at many different points in the function and makes
them all land at one PC, making the combined liveness information
at that target PC a mess. Disable this optimization, so that each
return site gets its own copy of the 'call deferreturn' and the
copying of result variables back from the heap.
This removes quite a few spurious 'ambiguously live' variables.

2. Let orderexpr allocate temporaries that are passed by address
to a function call and then die on return, so that we can arrange
an appropriate VARKILL.

2a. Do this for ... slices.

2b. Do this for closure structs.

2c. Do this for runtime.concatstring, which is the implementation
of large string additions. Change representation of OADDSTR to
an explicit list in typecheck to avoid reconstructing list in both
walk and order.

3. Let orderexpr allocate the temporary variable copies used for
range loops, so that they can be killed when the loop is over.
Similarly, let it allocate the temporary holding the map iterator.

CL 81940043 reduced the number of ambiguously live temps
in the godoc binary from 860 to 711.

This CL reduces the number to 121. Still more to do, but another
good checkpoint.

Update issue 7345

LGTM=khr
R=khr
CC=golang-codereviews
https://codereview.appspot.com/83090046

1 files changed, 26 insertions, 23 deletions

diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index c9cff289b..876d95530 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -1190,9 +1190,10 @@ walkexpr(Node **np, NodeList **init)
 		// s + "badgerbadgerbadger" == "badgerbadgerbadger"
 		if((n->etype == OEQ || n->etype == ONE) &&
 		   isconst(n->right, CTSTR) &&
-		   n->left->op == OADDSTR && isconst(n->left->right, CTSTR) &&
-		   cmpslit(n->right, n->left->right) == 0) {
-			r = nod(n->etype, nod(OLEN, n->left->left, N), nodintconst(0));
+		   n->left->op == OADDSTR && count(n->left->list) == 2 &&
+		   isconst(n->left->list->next->n, CTSTR) &&
+		   cmpslit(n->right, n->left->list->next->n) == 0) {
+			r = nod(n->etype, nod(OLEN, n->left->list->n, N), nodintconst(0));
 			typecheck(&r, Erv);
 			walkexpr(&r, init);
 			r->type = n->type;
@@ -1535,11 +1536,16 @@ ascompatet(int op, NodeList *nl, Type **nr, int fp, NodeList **init)
  * package all the arguments that match a ... T parameter into a []T.
  */
 static NodeList*
-mkdotargslice(NodeList *lr0, NodeList *nn, Type *l, int fp, NodeList **init, int esc)
+mkdotargslice(NodeList *lr0, NodeList *nn, Type *l, int fp, NodeList **init, Node *ddd)
 {
 	Node *a, *n;
 	Type *tslice;
-
+	int esc;
+	
+	esc = EscUnknown;
+	if(ddd != nil)
+		esc = ddd->esc;
+	
 	tslice = typ(TARRAY);
 	tslice->type = l->type->type;
 	tslice->bound = -1;
@@ -1549,6 +1555,8 @@ mkdotargslice(NodeList *lr0, NodeList *nn, Type *l, int fp, NodeList **init, int
 		n->type = tslice;
 	} else {
 		n = nod(OCOMPLIT, N, typenod(tslice));
+		if(ddd != nil)
+			n->left = ddd->left; // temporary to use
 		n->list = lr0;
 		n->esc = esc;
 		typecheck(&n, Erv);
@@ -1620,7 +1628,6 @@ dumpnodetypes(NodeList *l, char *what)
 static NodeList*
 ascompatte(int op, Node *call, int isddd, Type **nl, NodeList *lr, int fp, NodeList **init)
 {
-	int esc;
 	Type *l, *ll;
 	Node *r, *a;
 	NodeList *nn, *lr0, *alist;
@@ -1683,10 +1690,7 @@ loop:
 		// normal case -- make a slice of all
 		// remaining arguments and pass it to
 		// the ddd parameter.
-		esc = EscUnknown;
-		if(call->right)
-			esc = call->right->esc;
-		nn = mkdotargslice(lr, nn, l, fp, init, esc);
+		nn = mkdotargslice(lr, nn, l, fp, init, call->right);
 		goto ret;
 	}
 
@@ -2504,26 +2508,24 @@ static Node*
 addstr(Node *n, NodeList **init)
 {
 	Node *r, *cat, *slice;
-	NodeList *args;
-	int count;
+	NodeList *args, *l;
+	int c;
 	Type *t;
 
-	count = 0;
-	for(r=n; r->op == OADDSTR; r=r->left)
-		count++;	// r->right
-	count++;	// r
-	if(count < 2)
-		yyerror("addstr count %d too small", count);
+	// orderexpr rewrote OADDSTR to have a list of strings.
+	c = count(n->list);
+	if(c < 2)
+		yyerror("addstr count %d too small", c);
 
 	// build list of string arguments
 	args = nil;
-	for(r=n; r->op == OADDSTR; r=r->left)
-		args = concat(list1(conv(r->right, types[TSTRING])), args);
-	args = concat(list1(conv(r, types[TSTRING])), args);
+	for(l=n->list; l != nil; l=l->next)
+		args = list(args, conv(l->n, types[TSTRING]));
 
-	if(count <= 5) {
+	if(c <= 5) {
 		// small numbers of strings use direct runtime helpers.
-		snprint(namebuf, sizeof(namebuf), "concatstring%d", count);
+		// note: orderexpr knows this cutoff too.
+		snprint(namebuf, sizeof(namebuf), "concatstring%d", c);
 	} else {
 		// large numbers of strings are passed to the runtime as a slice.
 		strcpy(namebuf, "concatstrings");
@@ -2531,6 +2533,7 @@ addstr(Node *n, NodeList **init)
 		t->type = types[TSTRING];
 		t->bound = -1;
 		slice = nod(OCOMPLIT, N, typenod(t));
+		slice->left = n->left;
 		slice->list = args;
 		slice->esc = EscNone;
 		args = list1(slice);