rb_vm_insn_addr2insn: use st to perform addr2insn mapping

The current VM_INSTRUCTION_SIZE is 198, so the linear search
painful during a major GC phase.

I noticed rb_vm_insn_addr2insn2 showing up at the top of some
profiles while working on some malloc-related stuff, so I
decided to attack it.

Most notably, the benchmark/bm_vm3_gc.rb improves by over 40%:

  https://80x24.org/spew/20180602220554.GA9991@whir/raw

[ruby-core:87361] [Feature #14814]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63594 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 5 insertions, 0 deletions

diff --git a/vm_core.h b/vm_core.h
index 8e34ff14a5..0a185a6ceb 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -144,6 +144,11 @@ void *rb_register_sigaltstack(void);
 #endif /* OPT_STACK_CACHING */
 #endif /* OPT_CALL_THREADED_CODE */
 
+#if OPT_DIRECT_THREADED_CODE || OPT_CALL_THREADED_CODE
+void rb_addr2insn_init(void);
+#else
+static inline void rb_addr2insn_init(void) { }
+#endif
 typedef unsigned long rb_num_t;
 typedef   signed long rb_snum_t;