compile.c: comments for r52517 [ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52538 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

compile.c

@@ -2001,11 +2001,19 @@ iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcal
     }
 
     if (iobj->insn_id == BIN(pop)) {
+	/*
+	 *  putself / putnil / putobject obj / putstring "..."
+	 *  pop
+	 * =>
+	 *  # do nothing
+	 */
 	LINK_ELEMENT *prev = iobj->link.prev;
 	if (prev->type == ISEQ_ELEMENT_INSN) {
 	    enum ruby_vminsn_type previ = ((INSN *)prev)->insn_id;
 	    if (previ == BIN(putobject) || previ == BIN(putnil) ||
 		previ == BIN(putself) || previ == BIN(putstring)) {
+		/* just push operand or static value and pop soon, no
+		 * side effects */
 		REMOVE_ELEM(prev);
 		REMOVE_ELEM(&iobj->link);
 	    }