code review 64170043: cmd/gc: correct liveness for fat variables

src/cmd/6g/peep.c

 // Derived from Inferno utils/6c/peep.c
 // http://code.google.com/p/inferno-os/source/browse/utils/6c/peep.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 555 matching lines @@
         }
         for(r=uniqp(r0); r!=nil; r=uniqp(r)) {
                 if(debug['P'] && debug['v'])
                         print("\t? %P\n", r->prog);
                 if(uniqs(r) == nil) {
                         if(debug['P'] && debug['v'])
                                 print("\tno unique successor\n");
                         break;
                 }
                 p = r->prog;
+                if(p->as == AVARDEF)
+                        continue;
                 proginfo(&info, p);
-                if(p->as == AVARDEF)
-                        info.flags = 0;
                 if(info.flags & Call) {
                         if(debug['P'] && debug['v'])
                                 print("\tfound %P; return 0\n", p);
                         return 0;
                 }
 
                 if(info.reguse | info.regset) {
                         if(debug['P'] && debug['v'])
                                 print("\tfound %P; return 0\n", p);
                         return 0;
@@ skipping 194 matching lines @@
                 if(copyau(&p->to, v))
                         return 4;
                 return 3;
 
         case ATEXT:
                 if(REGARG >= 0 && v->type == (uchar)REGARG)
                         return 3;
                 return 0;
         }
 
+        if(p->as == AVARDEF)
+                return 0;
         proginfo(&info, p);
-        if(p->as == AVARDEF)
-                info.flags = 0;
 
         if((info.reguse|info.regset) & RtoB(v->type))
                 return 2;
 ················
         if(info.flags & LeftAddr)
                 if(copyas(&p->from, v))
                         return 2;
 
         if((info.flags & (RightRead|RightWrite)) == (RightRead|RightWrite))
                 if(copyas(&p->to, v))
@@ skipping 170 matching lines @@
                 a->type == D_INDIR + reg->type &&
                 a->index == D_NONE &&
                 0 <= a->offset && a->offset < 4096;
 }
 
 int
 stackaddr(Addr *a)
 {
         return regtyp(a) && a->type == D_SP;
 }