Replace global jump with catch handler implementation

When a global jump occurs, look at the catch handler table to determine where to jump.
In that case, `pc` already shows the following instruction, but since the table shows `begin_offset ... end_offset`, the comparison is done with `begin_offset < pc && pc <= end_offset`.
If there is a corresponding handler, move `pc` to `handler.target_offset` and continue running the VM.

When a global jump across `ensure` is made by `return`, `break`, `next`, `redo` and `retry`, the extended `RBreak` object saves and restores the C-level execution position.
This extended `RBreak` can have tag information, which makes it a pseudo coroutine (the "tag" mimics CRuby).

The implementation of pseudo coroutines by `RBreak` is summarized by `CHECKPOINT_RESTORE ... CHECKPOINT_MAIN ... CHECKPOINT_END` and `throw_tagged_break` / `unwind_ensure` macros.
The restart of processing is branched by `RBREAK_TAG_FOREACH(DISPATCH_CHECKPOINTS)`.

- Not only `rescue` blocks but also `ensure` blocks are now sandwiched between `OP_EXCEPT` and `OP_RAISEIF`.

- Remove the function `ecall()`.
  It is no longer necessary to re-enter the VM to perform an "ensure block".

  This will resolves #1888.

- Added instruction `OP_JUW` (Jump while UnWind).

  It jumps unconditionally like `OP_JMP`, but searches the catch handler table and executes the ensure block.
  Since it searches the catch handler table, it is much heavier than `OP_JMP`.

1 files changed, 0 insertions, 8 deletions

diff --git a/src/gc.c b/src/gc.c
index ab9779e1b..17f7e81e4 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -640,7 +640,6 @@ mark_context_stack(mrb_state *mrb, struct mrb_context *c)
 static void
 mark_context(mrb_state *mrb, struct mrb_context *c)
 {
-  int i;
   mrb_callinfo *ci;
 
  start:
@@ -657,10 +656,6 @@ mark_context(mrb_state *mrb, struct mrb_context *c)
       mrb_gc_mark(mrb, (struct RBasic*)ci->target_class);
     }
   }
-  /* mark ensure stack */
-  for (i=0; i<c->eidx; i++) {
-    mrb_gc_mark(mrb, (struct RBasic*)c->ensure[i]);
-  }
   /* mark fibers */
   mrb_gc_mark(mrb, (struct RBasic*)c->fib);
   if (c->prev) {
@@ -1014,9 +1009,6 @@ gc_gray_counts(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
       if (c->stbase + i > c->stend) i = c->stend - c->stbase;
       children += i;
 
-      /* mark ensure stack */
-      children += c->eidx;
-
       /* mark closure */
       if (c->cibase) {
         for (i=0, ci = c->cibase; ci <= c->ci; i++, ci++)