code review 6733055: cmd/5g, cmd/6g: fix out of registers with array indexing.

src/cmd/6g/gsubr.c

 // Derived from Inferno utils/6c/txt.c
 // http://code.google.com/p/inferno-os/source/browse/utils/6c/txt.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 185 matching lines @@
 
         p = gins(AGLOBL, nam, N);
         p->lineno = nam->lineno;
         p->to.sym = S;
         p->to.type = D_CONST;
         p->to.offset = width;
         if(nam->readonly)
                 p->from.scale = RODATA;
         if(nam->type != T && !haspointers(nam->type))
                 p->from.scale |= NOPTR;
+}
+
+void
+gtrack(Sym *s)
+{
+        Prog *p;
+········
+        p = gins(AUSEFIELD, N, N);
+        p->from.type = D_EXTERN;
+        p->from.index = D_NONE;
+        p->from.sym = s;
 }
 
 void
 ggloblsym(Sym *s, int32 width, int dupok, int rodata)
 {
         Prog *p;
 
         p = gins(AGLOBL, N, N);
         p->from.type = D_EXTERN;
         p->from.index = D_NONE;
@@ skipping 1727 matching lines @@
         case ODOTPTR:
                 cleani += 2;
                 reg = &clean[cleani-1];
                 reg1 = &clean[cleani-2];
                 reg->op = OEMPTY;
                 reg1->op = OEMPTY;
                 goto odot;
 
         case OINDEX:
                 return 0;
+                // disabled: OINDEX case is now covered by agenr
+                // for a more suitable register allocation pattern.
                 if(n->left->type->etype == TSTRING)
                         return 0;
                 goto oindex;
         }
         return 0;
 
 lit:
         switch(as) {
         default:
                 return 0;
@@ skipping 273 matching lines @@
         naddr(&n2, a, 1);
         goto yes;
 
 yes:
         return 1;
 
 no:
         sudoclean();
         return 0;
 }