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, 9 deletions

diff --git a/iseq.c b/iseq.c
index e03f1f2a98..e5210ca750 100644
--- a/iseq.c
+++ b/iseq.c
@@ -118,15 +118,7 @@ rb_iseq_free(const rb_iseq_t *iseq)
 static VALUE
 rb_vm_insn_addr2insn2(const void *addr)
 {
-    VALUE insn;
-    const void * const *table = rb_vm_get_insns_address_table();
-
-    for (insn = 0; insn < VM_INSTRUCTION_SIZE; insn++) {
-	if (table[insn] == addr) {
-	    return insn;
-	}
-    }
-    rb_bug("rb_vm_insn_addr2insn: invalid insn address: %p", addr);
+    return (VALUE)rb_vm_insn_addr2insn(addr);
 }
 #endif