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/include/mruby.h b/include/mruby.h
index c9425e8a7..9f1d1aa30 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -149,8 +149,6 @@ typedef struct {
   mrb_sym mid;
   const struct RProc *proc;
   mrb_value *stackent;
-  uint16_t ridx;
-  uint16_t epos;
   struct REnv *env;
   const mrb_code *pc;           /* return address */
   const mrb_code *err;          /* error position */
@@ -177,11 +175,6 @@ struct mrb_context {
   mrb_callinfo *ci;
   mrb_callinfo *cibase, *ciend;
 
-  uint16_t *rescue;                       /* exception handler stack */
-  uint16_t rsize;
-  struct RProc **ensure;                  /* ensure handler stack */
-  uint16_t esize, eidx;
-
   enum mrb_fiber_state status : 4;
   mrb_bool vmexec : 1;
   struct RFiber *fib;
@@ -301,7 +294,6 @@ typedef struct mrb_state {
   mrb_atexit_func *atexit_stack;
 #endif
   uint16_t atexit_stack_len;
-  uint16_t ecall_nest;                    /* prevent infinite recursive ecall() */
 } mrb_state;
 
 /**