Avoid generating opt_send with cfunc cc with JIT

only for opt_nil_p and opt_not.

While vm_method_cfunc_is is used for opt_eq too, many fast paths of it
don't call it. So if it's populated, it should generate opt_send,
regardless of cfunc or not. And again, opt_neq isn't relevant due to the
difference in operands.
So opt_nil_p and opt_not are the only variants using vm_method_cfunc_is
like they use.

```
$ benchmark-driver -v --rbenv 'before2 --jit::ruby --jit;before --jit;after --jit' benchmark/mjit_opt_cc_insns.yml --repeat-count=4
before2 --jit: ruby 2.8.0dev (2020-06-22T08:37:37Z master 3238641750) +JIT [x86_64-linux]
before --jit: ruby 2.8.0dev (2020-06-23T01:01:24Z master 9ce2066209) +JIT [x86_64-linux]
after --jit: ruby 2.8.0dev (2020-06-23T06:58:37Z master 17e9df3157) +JIT [x86_64-linux]
last_commit=Avoid generating opt_send with cfunc cc with JIT
Calculating -------------------------------------
                     before2 --jit  before --jit  after --jit
        mjit_nil?(1)       54.204M       75.536M      75.031M i/s -     40.000M times in 0.737947s 0.529548s 0.533110s
         mjit_not(1)       53.822M       70.921M      71.920M i/s -     40.000M times in 0.743195s 0.564007s 0.556171s
     mjit_eq(1, nil)        7.367M        6.496M       7.331M i/s -      8.000M times in 1.085882s 1.231470s 1.091327s

Comparison:
                     mjit_nil?(1)
        before --jit:  75536059.3 i/s
         after --jit:  75031409.4 i/s - 1.01x  slower
       before2 --jit:  54204431.6 i/s - 1.39x  slower

                      mjit_not(1)
         after --jit:  71920324.1 i/s
        before --jit:  70921063.1 i/s - 1.01x  slower
       before2 --jit:  53821697.6 i/s - 1.34x  slower

                  mjit_eq(1, nil)
       before2 --jit:   7367280.0 i/s
         after --jit:   7330527.4 i/s - 1.01x  slower
        before --jit:   6496302.8 i/s - 1.13x  slower
```

mjit_compile.c

@@ -17,6 +17,7 @@
 #include "internal.h"
 #include "internal/compile.h"
 #include "internal/hash.h"
+#include "internal/object.h"
 #include "internal/variable.h"
 #include "mjit.h"
 #include "vm_core.h"
@@ -97,9 +98,16 @@ captured_cc_entries(const struct compile_status *status)
 
 // Returns true if call cache is still not obsoleted and vm_cc_cme(cc)->def->type is available.
 static bool
-has_valid_method_type(CALL_CACHE cc, rb_method_type_t type)
+has_valid_method_type(CALL_CACHE cc)
 {
-    return vm_cc_cme(cc) != NULL && vm_cc_cme(cc)->def->type == type;
+    return vm_cc_cme(cc) != NULL;
+}
+
+// Returns true if MJIT thinks this cc's opt_* insn may fallback to opt_send_without_block.
+static bool
+has_cache_for_send(CALL_CACHE cc, bool cfunc_cached)
+{
+    return has_valid_method_type(cc) && (!cfunc_cached || vm_cc_cme(cc)->def->type != VM_METHOD_TYPE_CFUNC);
 }
 
 // Returns true if iseq can use fastpath for setup, otherwise NULL. This becomes true in the same condition
@@ -439,8 +447,9 @@ precompile_inlinable_iseqs(FILE *f, const rb_iseq_t *iseq, struct compile_status
             const struct rb_callcache *cc = captured_cc_entries(status)[call_data_index(cd, body)]; // use copy to avoid race condition
 
             const rb_iseq_t *child_iseq;
-            if (has_valid_method_type(cc, VM_METHOD_TYPE_ISEQ) &&
+            if (has_valid_method_type(cc) &&
                 !(vm_ci_flag(ci) & VM_CALL_TAILCALL) && // inlining only non-tailcall path
+                vm_cc_cme(cc)->def->type == VM_METHOD_TYPE_ISEQ &&
                 fastpath_applied_iseq_p(ci, cc, child_iseq = def_iseq_ptr(vm_cc_cme(cc)->def)) &&
                 // CC_SET_FASTPATH in vm_callee_setup_arg
                 inlinable_iseq_p(child_iseq->body)) {

tool/ruby_vm/views/_mjit_compile_send.erb

@@ -20,13 +20,13 @@
     const CALL_INFO ci = cd->ci;
     int kw_splat = IS_ARGS_KW_SPLAT(ci) > 0;
     extern bool rb_splat_or_kwargs_p(const struct rb_callinfo *restrict ci);
-    if (!status->compile_info->disable_send_cache && (
+    if (!status->compile_info->disable_send_cache && has_valid_method_type(captured_cc) && (
 %       # `CC_SET_FASTPATH(cd->cc, vm_call_cfunc_with_frame, ...)` in `vm_call_cfunc`
-        (has_valid_method_type(captured_cc, VM_METHOD_TYPE_CFUNC)
+        (vm_cc_cme(captured_cc)->def->type == VM_METHOD_TYPE_CFUNC
          && !rb_splat_or_kwargs_p(ci) && !kw_splat)
 %       # `CC_SET_FASTPATH(cc, vm_call_iseq_setup_func(...), vm_call_iseq_optimizable_p(...))` in `vm_callee_setup_arg`,
 %       # and support only non-VM_CALL_TAILCALL path inside it
-        || (has_valid_method_type(captured_cc, VM_METHOD_TYPE_ISEQ)
+        || (vm_cc_cme(captured_cc)->def->type == VM_METHOD_TYPE_ISEQ
             && fastpath_applied_iseq_p(ci, captured_cc, iseq = def_iseq_ptr(vm_cc_cme(captured_cc)->def))
             && !(vm_ci_flag(ci) & VM_CALL_TAILCALL))
     )) {

tool/ruby_vm/views/mjit_compile.inc.erb

@@ -29,6 +29,12 @@
 %     insn.expr.expr.lines.any? { |l| l.match(/\A\s+CALL_SIMPLE_METHOD\(\);\s+\z/) }
 % end.map(&:name)
 %
+% # These insns cache cfunc in cc under optimized circumstances. They don't generate opt_send when cfunc is cached.
+% cfunc_insns = [
+%   'opt_nil_p',
+%   'opt_not',
+% ]
+%
 % # Available variables and macros in JIT-ed function:
 % #   ec: the first argument of _mjitXXX
 % #   reg_cfp: the second argument of _mjitXXX
@@ -56,7 +62,7 @@ switch (insn) {
 %   when *send_compatible_opt_insns
 %     # To avoid cancel, just emit `opt_send_without_block` instead of `opt_*` insn if call cache is populated.
 %     cd_index = insn.opes.index { |o| o.fetch(:type) == 'CALL_DATA' }
-      if (has_valid_method_type(captured_cc_entries(status)[call_data_index((CALL_DATA)operands[<%= cd_index %>], body)], VM_METHOD_TYPE_ISEQ)) {
+      if (has_cache_for_send(captured_cc_entries(status)[call_data_index((CALL_DATA)operands[<%= cd_index %>], body)], <%= cfunc_insns.include?(insn.name) %>)) {
 <%=       render 'mjit_compile_send', locals: { insn: opt_send_without_block } -%>
 <%=       render 'mjit_compile_insn', locals: { insn: opt_send_without_block } -%>
           break;