cmd/5g, cmd/6g, cmd/8g: restore occurrences of R replaced by nil in comments.

R=golang-dev, bradfitz, rsc
CC=golang-dev
https://golang.org/cl/12842043

src/cmd/5g/peep.c

@@ -493,15 +493,15 @@ constprop(Adr *c1, Adr *v1, Flow *r)
 /*
  * shortprop eliminates redundant zero/sign extensions.
  *
- *   MOVBS x, nil
- *   <no use nil>
- *   MOVBS nil, nil'
+ *   MOVBS x, R
+ *   <no use R>
+ *   MOVBS R, R'
  *
  * changed to
  *
- *   MOVBS x, nil
+ *   MOVBS x, R
  *   ...
- *   MOVB  nil, nil' (compiled to mov)
+ *   MOVB  R, R' (compiled to mov)
  *
  * MOVBS above can be a MOVBS, MOVBU, MOVHS or MOVHU.
  */

src/cmd/6g/peep.c

@@ -98,9 +98,9 @@ peep(Prog *firstp)
 	elimshortmov(g);
 
 	// constant propagation
-	// find MOV $con,nil followed by
-	// another MOV $con,nil without
-	// setting nil in the interim
+	// find MOV $con,R followed by
+	// another MOV $con,R without
+	// setting R in the interim
 	for(r=g->start; r!=nil; r=r->link) {
 		p = r->prog;
 		switch(p->as) {

src/cmd/8g/peep.c

@@ -97,9 +97,9 @@ peep(Prog *firstp)
 	elimshortmov(g);
 
 	// constant propagation
-	// find MOV $con,nil followed by
-	// another MOV $con,nil without
-	// setting nil in the interim
+	// find MOV $con,R followed by
+	// another MOV $con,R without
+	// setting R in the interim
 	for(r=g->start; r!=nil; r=r->link) {
 		p = r->prog;
 		switch(p->as) {