Fix redo keyword

[dearblue]

The main purpose is to fix #6439, but includes additional testing and a fix to allow redo from nested loopinfo.

The additional test code should be correct as it was also confirmed by “ruby 3.4.0preview2 (2024-10-07 master 32c733f57b) +PRISM [amd64-freebsd14]”.

[dearblue]

I'll leave here a patch to include the OP_REDO instruction based on this PR.
This patch also tests successfully.

Details

diff --git a/include/mruby/ops.h b/include/mruby/ops.h
index cda796f08..56e430a33 100644
--- a/include/mruby/ops.h
+++ b/include/mruby/ops.h
@@ -54,6 +54,7 @@ OPCODE(JMPIF,      BS)       /* if R[a] pc+=b */
 OPCODE(JMPNOT,     BS)       /* if !R[a] pc+=b */
 OPCODE(JMPNIL,     BS)       /* if R[a]==nil pc+=b */
 OPCODE(JMPUW,      S)        /* unwind_and_jump_to(a) */
+OPCODE(REDO,       S)        /* pc+=b (with ensure handler) */
 OPCODE(EXCEPT,     B)        /* R[a] = exc */
 OPCODE(RESCUE,     BB)       /* R[b] = R[a].isa?(R[b]) */
 OPCODE(RAISEIF,    B)        /* raise(R[a]) if R[a] */
diff --git a/mrbgems/mruby-compiler/core/codegen.c b/mrbgems/mruby-compiler/core/codegen.c
index 364ce2048..05e1c9260 100644
--- a/mrbgems/mruby-compiler/core/codegen.c
+++ b/mrbgems/mruby-compiler/core/codegen.c
@@ -1323,7 +1323,6 @@ for_body(codegen_scope *s, node *tree)
   /* construct loop */
   lp = loop_push(s, LOOP_FOR);
   lp->pc1 = new_label(s);
-  genop_0(s, OP_NOP); /* for redo */
 
   /* loop body */
   codegen(s, tree->cdr->cdr->car, VAL);
@@ -2590,7 +2589,6 @@ codegen(codegen_scope *s, node *tree, int val)
         pos = genjmp2_0(s, OP_JMPIF, cursp(), NOVAL);
       }
       lp->pc1 = new_label(s);
-      genop_0(s, OP_NOP); /* for redo */
       codegen(s, tree->cdr, NOVAL);
       genjmp(s, OP_JMP, lp->pc0);
       dispatch(s, pos);
@@ -3190,7 +3188,7 @@ codegen(codegen_scope *s, node *tree, int val)
         raise_error(s, "unexpected redo");
       }
       if (lp->type != LOOP_BEGIN && lp->type != LOOP_RESCUE) {
-        genjmp(s, OP_JMPUW, lp->pc1);
+        genjmp(s, OP_REDO, lp->pc1);
         break;
       }
     }
diff --git a/src/codedump.c b/src/codedump.c
index 556e4f62d..f9e6b08c4 100644
--- a/src/codedump.c
+++ b/src/codedump.c
@@ -308,6 +308,10 @@ codedump(mrb_state *mrb, const mrb_irep *irep, FILE *out)
       i = pc - irep->iseq;
       fprintf(out, "JMPUW\t\t%03d\n", (int)i+(int16_t)a);
       break;
+    CASE(OP_REDO, S):
+      i = pc - irep->iseq;
+      fprintf(out, "REDO\t\t%03d\n", (int)i+(int16_t)a);
+      break;
     CASE(OP_JMPIF, BS):
       i = pc - irep->iseq;
       fprintf(out, "JMPIF\t\tR%d\t%03d\t", a, (int)i+(int16_t)b);
diff --git a/src/vm.c b/src/vm.c
index 4d78035ad..54db0c8e8 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1124,7 +1124,8 @@ mrb_yield_cont(mrb_state *mrb, mrb_value b, mrb_value self, mrb_int argc, const
 #define RBREAK_TAG_FOREACH(f) \
   f(RBREAK_TAG_BREAK, 0) \
   f(RBREAK_TAG_JUMP, 1) \
-  f(RBREAK_TAG_STOP, 2)
+  f(RBREAK_TAG_REDO, 2) \
+  f(RBREAK_TAG_STOP, 3)
 
 #define RBREAK_TAG_DEFINE(tag, i) tag = i,
 enum {
@@ -1733,6 +1734,29 @@ RETRY_TRY_BLOCK:
       JUMP;
     }
 
+    // TODO: OP_JMPUW との共通処理が出来るかもしれない
+    CASE(OP_REDO, S) {
+      a = (uint32_t)((ci->pc - irep->iseq) + (int16_t)a);
+      CHECKPOINT_RESTORE(RBREAK_TAG_REDO) {
+        struct RBreak *brk = (struct RBreak*)mrb->exc;
+        mrb_value target = mrb_break_value_get(brk);
+        mrb_assert(mrb_integer_p(target));
+        a = (uint32_t)mrb_integer(target);
+        mrb_assert(a >= 0 && a < irep->ilen);
+      }
+      CHECKPOINT_MAIN(RBREAK_TAG_REDO) {
+        if (irep->clen > 0 &&
+            (ch = catch_handler_find(irep, ci->pc, MRB_CATCH_FILTER_ENSURE))) {
+          THROW_TAGGED_BREAK(mrb, RBREAK_TAG_REDO, mrb->c->ci, mrb_fixnum_value(a));
+        }
+      }
+      CHECKPOINT_END(RBREAK_TAG_REDO);
+
+      mrb->exc = NULL; /* clear break object */
+      ci->pc = irep->iseq + a;
+      JUMP;
+    }
+
     CASE(OP_EXCEPT, B) {
       mrb_value exc;