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, 1 insertions, 0 deletions

diff --git a/eval.c b/eval.c
index da3bcadb42..aff1b9021b 100644
--- a/eval.c
+++ b/eval.c
@@ -66,6 +66,7 @@ ruby_setup(void)
 #endif
     Init_BareVM();
     Init_heap();
+    rb_addr2insn_init();
     Init_vm_objects();
 
     EC_PUSH_TAG(GET_EC());