code review 81370046: runtime: get rid of most uses of REP for copying/zeroing.

src/cmd/6g/cgen.c

 // Copyright 2009 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.
 
 #include <u.h>
 #include <libc.h>
 #include "gg.h"
 
 /*
  * generate:
@@ skipping 1438 matching lines @@
         } else {
                 // normal direction
                 if(q > 128) {
                         gconreg(movptr, q, D_CX);
                         gins(AREP, N, N);       // repeat
                         gins(AMOVSQ, N, N);     // MOVQ *(SI)+,*(DI)+
                 } else if (q >= 4) {
                         p = gins(ADUFFCOPY, N, N);
                         p->to.type = D_ADDR;
                         p->to.sym = linksym(pkglookup("duffcopy", runtimepkg));
-                        // 14 = magic constant: see ../../pkg/runtime/asm_amd64.s
+                        // 14 and 128 = magic constants: see ../../pkg/runtime/asm_amd64.s
                         p->to.offset = 14*(128-q);
                 } else
                 while(q > 0) {
                         gins(AMOVSQ, N, N);     // MOVQ *(SI)+,*(DI)+
                         q--;
                 }
                 // copy the remaining c bytes
                 if(w < 4 || c <= 1 || (odst < osrc && osrc < odst+w)) {
                         while(c > 0) {
                                 gins(AMOVSB, N, N);     // MOVB *(SI)+,*(DI)+
@@ skipping 251 matching lines @@
                 regfree(&nodl);
         return 0;
 
 yes:
         if(freer)
                 regfree(&nodr);
         if(freel)
                 regfree(&nodl);
         return 1;
 }