which has been developed by Takashi Kokubun <takashikkbn@gmail> as
YARV-MJIT. Many of its bugs are fixed by wanabe <s.wanabe@gmail.com>.

This JIT compiler is designed to be a safe migration path to introduce
JIT compiler to MRI. So this commit does not include any bytecode
changes or dynamic instruction modifications, which are done in original
MJIT.

This commit even strips off some aggressive optimizations from
YARV-MJIT, and thus it's slower than YARV-MJIT too. But it's still
fairly faster than Ruby 2.5 in some benchmarks (attached below).

Note that this JIT compiler passes `make test`, `make test-all`, `make
test-spec` without JIT, and even with JIT. Not only it's perfectly safe
with JIT disabled because it does not replace VM instructions unlike
MJIT, but also with JIT enabled it stably runs Ruby applications
including Rails applications.

I'm expecting this version as just "initial" JIT compiler. I have many
optimization ideas which are skipped for initial merging, and you may
easily replace this JIT compiler with a faster one by just replacing
mjit_compile.c. `mjit_compile` interface is designed for the purpose.

common.mk: update dependencies for mjit_compile.c.

internal.h: declare `rb_vm_insn_addr2insn` for MJIT.

vm.c: exclude some definitions if `-DMJIT_HEADER` is provided to
compiler. This avoids to include some functions which take a long time
to compile, e.g. vm_exec_core. Some of the purpose is achieved in
transform_mjit_header.rb (see `IGNORED_FUNCTIONS`) but others are
manually resolved for now. Load mjit_helper.h for MJIT header.
mjit_helper.h: New. This is a file used only by JIT-ed code. I'll
refactor `mjit_call_cfunc` later.
vm_eval.c: add some #ifdef switches to skip compiling some functions
like Init_vm_eval.

win32/mkexports.rb: export thread/ec functions, which are used by MJIT.

include/ruby/defines.h: add MJIT_FUNC_EXPORTED macro alis to clarify
that a function is exported only for MJIT.

array.c: export a function used by MJIT.
bignum.c: ditto.
class.c: ditto.
compile.c: ditto.
error.c: ditto.
gc.c: ditto.
hash.c: ditto.
iseq.c: ditto.
numeric.c: ditto.
object.c: ditto.
proc.c: ditto.
re.c: ditto.
st.c: ditto.
string.c: ditto.
thread.c: ditto.
variable.c: ditto.
vm_backtrace.c: ditto.
vm_insnhelper.c: ditto.
vm_method.c: ditto.

I would like to improve maintainability of function exports, but I
believe this way is acceptable as initial merging if we clarify the
new exports are for MJIT (so that we can use them as TODO list to fix)
and add unit tests to detect unresolved symbols.
I'll add unit tests of JIT compilations in succeeding commits.

Author: Takashi Kokubun <takashikkbn@gmail.com>
Contributor: wanabe <s.wanabe@gmail.com>

Part of [Feature #14235]

---

* Known issues
  * Code generated by gcc is faster than clang. The benchmark may be worse
    in macOS. Following benchmark result is provided by gcc w/ Linux.
  * Performance is decreased when Google Chrome is running
  * JIT can work on MinGW, but it doesn't improve performance at least
    in short running benchmark.
  * Currently it doesn't perform well with Rails. We'll try to fix this
    before release.

---

* Benchmark reslts

Benchmarked with:
Intel 4.0GHz i7-4790K with 16GB memory under x86-64 Ubuntu 8 Cores

- 2.0.0-p0: Ruby 2.0.0-p0
- r62186: Ruby trunk (early 2.6.0), before MJIT changes
- JIT off: On this commit, but without `--jit` option
- JIT on: On this commit, and with `--jit` option

** Optcarrot fps

Benchmark: https://github.com/mame/optcarrot

|         |2.0.0-p0 |r62186   |JIT off  |JIT on   |
|:--------|:--------|:--------|:--------|:--------|
|fps      |37.32    |51.46    |51.31    |58.88    |
|vs 2.0.0 |1.00x    |1.38x    |1.37x    |1.58x    |

** MJIT benchmarks

Benchmark: https://github.com/benchmark-driver/mjit-benchmarks
(Original: https://github.com/vnmakarov/ruby/tree/rtl_mjit_branch/MJIT-benchmarks)

|           |2.0.0-p0 |r62186   |JIT off  |JIT on   |
|:----------|:--------|:--------|:--------|:--------|
|aread      |1.00     |1.09     |1.07     |2.19     |
|aref       |1.00     |1.13     |1.11     |2.22     |
|aset       |1.00     |1.50     |1.45     |2.64     |
|awrite     |1.00     |1.17     |1.13     |2.20     |
|call       |1.00     |1.29     |1.26     |2.02     |
|const2     |1.00     |1.10     |1.10     |2.19     |
|const      |1.00     |1.11     |1.10     |2.19     |
|fannk      |1.00     |1.04     |1.02     |1.00     |
|fib        |1.00     |1.32     |1.31     |1.84     |
|ivread     |1.00     |1.13     |1.12     |2.43     |
|ivwrite    |1.00     |1.23     |1.21     |2.40     |
|mandelbrot |1.00     |1.13     |1.16     |1.28     |
|meteor     |1.00     |2.97     |2.92     |3.17     |
|nbody      |1.00     |1.17     |1.15     |1.49     |
|nest-ntimes|1.00     |1.22     |1.20     |1.39     |
|nest-while |1.00     |1.10     |1.10     |1.37     |
|norm       |1.00     |1.18     |1.16     |1.24     |
|nsvb       |1.00     |1.16     |1.16     |1.17     |
|red-black  |1.00     |1.02     |0.99     |1.12     |
|sieve      |1.00     |1.30     |1.28     |1.62     |
|trees      |1.00     |1.14     |1.13     |1.19     |
|while      |1.00     |1.12     |1.11     |2.41     |

** Discourse's script/bench.rb

Benchmark: https://github.com/discourse/discourse/blob/v1.8.7/script/bench.rb

NOTE: Rails performance was somehow a little degraded with JIT for now.
We should fix this.
(At least I know opt_aref is performing badly in JIT and I have an idea
 to fix it. Please wait for the fix.)

*** JIT off
Your Results: (note for timings- percentile is first, duration is second in millisecs)

categories_admin:
  50: 17
  75: 18
  90: 22
  99: 29
home_admin:
  50: 21
  75: 21
  90: 27
  99: 40
topic_admin:
  50: 17
  75: 18
  90: 22
  99: 32
categories:
  50: 35
  75: 41
  90: 43
  99: 77
home:
  50: 39
  75: 46
  90: 49
  99: 95
topic:
  50: 46
  75: 52
  90: 56
  99: 101

*** JIT on
Your Results: (note for timings- percentile is first, duration is second in millisecs)

categories_admin:
  50: 19
  75: 21
  90: 25
  99: 33
home_admin:
  50: 24
  75: 26
  90: 30
  99: 35
topic_admin:
  50: 19
  75: 20
  90: 25
  99: 30
categories:
  50: 40
  75: 44
  90: 48
  99: 76
home:
  50: 42
  75: 48
  90: 51
  99: 89
topic:
  50: 49
  75: 55
  90: 58
  99: 99

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62197 b2dd03c8-39d4-4d8f-98ff-823fe69b080e