Revert "fix: reduce/foreach state variable should not be reset each iteration" (#3349)

This reverts 96e8d893c1. The change
introduced a serious performance regression as reported in #3345.

src/compile.c

@@ -831,7 +831,7 @@ block gen_reduce(block source, block matcher, block init, block body) {
   block loop = BLOCK(gen_op_simple(DUPN),
                      source,
                      bind_alternation_matchers(matcher,
-                                  BLOCK(gen_op_bound(LOADV, res_var),
+                                  BLOCK(gen_op_bound(LOADVN, res_var),
                                         body,
                                         gen_op_bound(STOREV, res_var))),
                      gen_op_simple(BACKTRACK));
@@ -855,7 +855,7 @@ block gen_foreach(block source, block matcher, block init, block update, block e
                // in the body to see
                bind_alternation_matchers(matcher,
                             // load the loop state variable
-                            BLOCK(gen_op_bound(LOADV, state_var),
+                            BLOCK(gen_op_bound(LOADVN, state_var),
                                   // generate updated state
                                   update,
                                   // save the updated state for value extraction