code review 13334052: cmd/gc: eliminate redundant &x.Field nil checks

src/cmd/gc/pgen.c

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // "Portable" code generation.
 // Compiled separately for 5g, 6g, and 8g, so allowed to use gg.h, opt.h.
 // Must code to the intersection of the three back ends.
 
 #include        <u.h>
 #include        <libc.h>
@@ skipping 163 matching lines @@
                 genlist(curfn->exit);
         gclean();
         if(nerrors != 0)
                 goto ret;
 
         pc->as = ARET;  // overwrite AEND
         pc->lineno = lineno;
 
         if(!debug['N'] || debug['R'] || debug['P']) {
                 regopt(ptxt);
+                nilopt(ptxt);
         }
         expandchecks(ptxt);
 
         oldstksize = stksize;
         allocauto(ptxt);
 
         if(0)
                 print("allocauto: %lld to %lld\n", oldstksize, (vlong)stksize);
 
         setlineno(curfn);
@@ skipping 336 matching lines @@
         }
 }
 
 void
 cgen_checknil(Node *n)
 {
         Node reg;
 
         if(disable_checknil)
                 return;
-        while(n->op == ODOT || (n->op == OINDEX && isfixedarray(n->left->type->type))) // NOTE: not ODOTPTR
-                n = n->left;
+        // Ideally we wouldn't see any TUINTPTR here, but we do.
+        if(n->type == T || (!isptr[n->type->etype] && n->type->etype != TUINTPTR && n->type->etype != TUNSAFEPTR)) {
+                dump("checknil", n);
+                fatal("bad checknil");
+        }
         if((thechar == '5' && n->op != OREGISTER) || !n->addable) {
                 regalloc(&reg, types[tptr], n);
                 cgen(n, &reg);
                 gins(ACHECKNIL, &reg, N);
                 regfree(&reg);
                 return;
         }
         gins(ACHECKNIL, n, N);
 }