Use trampoline technique for `instance_exec`; ref #3359

A new function `mrb_yield_cont()` is provided. You have to call it
at the end of a C defined method, e.g. `return mrb_yield_cont()`.

include/mruby.h

@@ -1121,6 +1121,11 @@ MRB_API mrb_value mrb_yield(mrb_state *mrb, mrb_value b, mrb_value arg);
 MRB_API mrb_value mrb_yield_argv(mrb_state *mrb, mrb_value b, mrb_int argc, const mrb_value *argv);
 MRB_API mrb_value mrb_yield_with_class(mrb_state *mrb, mrb_value b, mrb_int argc, const mrb_value *argv, mrb_value self, struct RClass *c);
 
+/* continue execution to the proc */
+/* this function should always be called as the last function of a method */
+/* e.g. return mrb_yield_cont(mrb, proc, self, argc, argv); */
+mrb_value mrb_yield_cont(mrb_state *mrb, mrb_value b, mrb_value self, mrb_int argc, const mrb_value *argv);
+
 /* mrb_gc_protect() leaves the object in the arena */
 MRB_API void mrb_gc_protect(mrb_state *mrb, mrb_value obj);
 /* mrb_gc_register() keeps the object from GC. */

mrbgems/mruby-object-ext/src/object.c

 #include <mruby.h>
 #include <mruby/array.h>
 #include <mruby/class.h>
+#include <mruby/proc.h>
 
 /*
  *  call-seq:
@@ -86,7 +87,8 @@ mrb_obj_instance_exec(mrb_state *mrb, mrb_value self)
   }
   args = mrb_ary_new_from_values(mrb, argc, argv);
   argv = RARRAY_PTR(args);
-  return mrb_yield_with_class(mrb, blk, argc, argv, self, c);
+  mrb->c->ci->target_class = c;
+  return mrb_yield_cont(mrb, blk, self, argc, argv);
 }
 
 void

src/vm.c

@@ -467,6 +467,7 @@ mrb_exec_irep(mrb_state *mrb, mrb_value self, struct RProc *p)
 {
   mrb_callinfo *ci = mrb->c->ci;
 
+  mrb->c->stack[0] = self;
   ci->proc = p;
   ci->target_class = p->target_class;
   if (MRB_PROC_CFUNC_P(p)) {
@@ -562,7 +563,8 @@ eval_under(mrb_state *mrb, mrb_value self, mrb_value blk, struct RClass *c)
   }
   ci = mrb->c->ci;
   if (ci->acc == CI_ACC_DIRECT) {
-    return mrb_yield_with_class(mrb, blk, 1, &self, self, c);
+    ci->target_class = c;
+    return mrb_yield_cont(mrb, blk, self, 1, &self);
   }
   ci->target_class = c;
   p = mrb_proc_ptr(blk);
@@ -726,6 +728,29 @@ mrb_yield(mrb_state *mrb, mrb_value b, mrb_value arg)
   return mrb_yield_with_class(mrb, b, 1, &arg, p->env->stack[0], p->target_class);
 }
 
+mrb_value
+mrb_yield_cont(mrb_state *mrb, mrb_value b, mrb_value self, mrb_int argc, const mrb_value *argv)
+{
+  struct RProc *p;
+  mrb_callinfo *ci;
+
+  if (mrb_nil_p(b)) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "no block given");
+  }
+  if (mrb_type(b) != MRB_TT_PROC) {
+    mrb_raise(mrb, E_TYPE_ERROR, "not a block");
+  }
+
+  p = mrb_proc_ptr(b);
+  ci = mrb->c->ci;
+
+  stack_extend(mrb, 3);
+  mrb->c->stack[1] = mrb_ary_new_from_values(mrb, argc, argv);
+  mrb->c->stack[2] = mrb_nil_value();
+  ci->argc = -1;
+  return mrb_exec_irep(mrb, self, p);
+}
+
 typedef enum {
   LOCALJUMP_ERROR_RETURN = 0,
   LOCALJUMP_ERROR_BREAK = 1,