cmd/gc: run escape analysis always (even in -N mode)

Fixes #8585.
Removes some little-used code paths.

LGTM=josharian
R=golang-codereviews, minux, josharian
CC=golang-codereviews, iant, r
https://golang.org/cl/132970043

src/cmd/gc/gen.c

@@ -54,9 +54,6 @@ addrescapes(Node *n)
 		if(n->class == PAUTO && n->esc == EscNever)
 			break;
 
-		if(debug['N'] && n->esc != EscUnknown)
-			fatal("without escape analysis, only PAUTO's should have esc: %N", n);
-
 		switch(n->class) {
 		case PPARAMREF:
 			addrescapes(n->defn);
@@ -91,8 +88,7 @@ addrescapes(Node *n)
 			snprint(buf, sizeof buf, "&%S", n->sym);
 			n->heapaddr->sym = lookup(buf);
 			n->heapaddr->orig->sym = n->heapaddr->sym;
-			if(!debug['N'])
-				n->esc = EscHeap;
+			n->esc = EscHeap;
 			if(debug['m'])
 				print("%L: moved to heap: %N\n", n->lineno, n);
 			curfn = oldfn;

src/cmd/gc/lex.c

@@ -481,8 +481,12 @@ main(int argc, char *argv[])
 	}
 
 	// Phase 5: Escape analysis.
-	if(!debug['N'])
-		escapes(xtop);
+	// Required for moving heap allocations onto stack,
+	// which in turn is required by the closure implementation,
+	// which stores the addresses of stack variables into the closure.
+	// If the closure does not escape, it needs to be on the stack
+	// or else the stack copier will not update it.
+	escapes(xtop);
 	
 	// Escape analysis moved escaped values off stack.
 	// Move large values off stack too.

src/cmd/gc/typecheck.c

@@ -736,10 +736,6 @@ reswitch:
 		l = n->left;
 		if((t = l->type) == T)
 			goto error;
-		// top&Eindir means this is &x in *&x.  (or the arg to built-in print)
-		// n->etype means code generator flagged it as non-escaping.
-		if(debug['N'] && !(top & Eindir) && !n->etype)
-			addrescapes(n->left);
 		n->type = ptrto(t);
 		goto ret;
 
@@ -2119,8 +2115,6 @@ lookdot(Node *n, Type *t, int dostrcmp)
 		if(!eqtype(rcvr, tt)) {
 			if(rcvr->etype == tptr && eqtype(rcvr->type, tt)) {
 				checklvalue(n->left, "call pointer method on");
-				if(debug['N'])
-					addrescapes(n->left);
 				n->left = nod(OADDR, n->left, N);
 				n->left->implicit = 1;
 				typecheck(&n->left, Etype|Erv);

test/escape2.go

@@ -7,6 +7,8 @@
 // Test, using compiler diagnostic flags, that the escape analysis is working.
 // Compiles but does not run.  Inlining is disabled.
 
+// escape2n.go contains all the same tests but compiles with -N.
+
 package foo
 
 import (