code review 6245069: cmd/gc: contiguous loop layout

src/cmd/6g/reg.c

 // Derived from Inferno utils/6c/reg.c
 // http://code.google.com/p/inferno-os/source/browse/utils/6c/reg.c
 //
 //      Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
 //      Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
 //      Portions Copyright © 1997-1999 Vita Nuova Limited
 //      Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
 //      Portions Copyright © 2004,2006 Bruce Ellis
 //      Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
 //      Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
@@ skipping 1726 matching lines @@
 mark(Prog *firstp)
 {
         Prog *p;
 ········
         for(p=firstp; p; p=p->link) {
                 if(p->reg != dead)
                         break;
                 p->reg = alive;
                 if(p->as != ACALL && p->to.type == D_BRANCH && p->to.branch)
                         mark(p->to.branch);
-                if(p->as == AJMP || p->as == ARET || (p->as == ACALL && noreturn(p)))
+                if(p->as == AJMP || p->as == ARET || p->as == AUNDEF)
                         break;
         }
 }
 
 static void
 fixjmp(Prog *firstp)
 {
         int jmploop;
         Prog *p, *last;
 ········
@@ skipping 54 matching lines @@
                 last->link = P;
         }
 ········
         if(debug['R'] && debug['v']) {
                 print("\n");
                 for(p=firstp; p; p=p->link)
                         print("%P\n", p);
                 print("\n");
         }
 }