which is created by transforming a preprocessed vm.c.

Makefile.in: generate MJIT header for UNIX environments

win32/Makefile.sub: generate MJIT header for Windows environments

tool/transform_mjit_header.rb: New. This script was originally written by
Vladimir N. Makarov <vmakarov@redhat.com>. Then I refactored a little,
fixed some bugs and ported it to work on Windows.

Also, as original minimize_mjit_header.rb takes too long time to run,
this is modified to skip minimization step because having *static*
unused definitions does not waste compilation time on -O2 as compiler
can skip to compile unused static functions.

This header installation does NOT include a header to automatically
export symbols used by MJIT. That's because original MJIT code was
failing to export symbols in the import header. But I would like to have
the functionality for maintainability in the future.

mjit.c is authored by Vladimir Makarov <vmakarov@redhat.com>.
After he invented great method JIT infrastructure for MRI as MJIT,
Lars Kanis <lars@greiz-reinsdorf.de> sent the patch to support MinGW
in MJIT. In addition to merging it, I ported pthread to Windows native
threads. Now this MJIT infrastructure can be compiled on Visual Studio.

This commit simplifies mjit.c to decrease code at initial merge. For
example, this commit does not provide AOT compiler and multiple JIT
threads support. We can resurrect them later if we really want them,
but I wanted to minimize diff to make it easier to review this patch.

mjit.h: New. It has `mjit_exec` interface similar to `vm_exec`, which is
for triggering MJIT. This drops interface for AOT compared to the original
MJIT.

Makefile.in: define macros to let MJIT know the path of MJIT header.
Probably we can refactor this to reduce the number of macros (TODO).
win32/Makefile.sub: ditto.

common.mk: compile mjit.o and mjit_compile.o. Unlike original MJIT, this
commit separates MJIT infrastructure and JIT compiler code as
independent object files. As initial patch is going to have not-ultra-fast
JIT compiler, it's likely to replace JIT compiler, e.g. original MJIT's
compiler or some future JIT impelementations which are not public now.
mjit_compile.c: added empty compiler so that you can reuse this commit
to build your own JIT compiler.

inits.c: define MJIT module. This is added because `MJIT.enabled?` was
necessary for testing.
test/lib/zombie_hunter.rb: skip if `MJIT.enabled?`. Obviously this
wouldn't work with current code when JIT is enabled.
test/ruby/test_io.rb: skip this too. This would make no sense with MJIT.

ruby.c: define MJIT CLI options. As major difference from original MJIT,
"-j:l"/"--jit:llvm" are renamed to "-j:c"/"--jit:cc" because I want to
support not only gcc/clang but also cl.exe (Visual Studio) in the future.
It takes only "-j:c=gcc", "-j:c=clang" for now. Original "-j:c" is
renamed to "-j:n" as it conflicts. Also this initializes MJIT thread and
variables.
eval.c: finalize MJIT worker thread and variables.
test/ruby/test_rubyoptions.rb: fix number of CLI options for -j addition.

thread_pthread.c: change for pthread abstraction in MJIT. Prefix rb_ for
functions which are used by other files.
thread_win32.c: ditto, for Windows.  Those pthread porting is one of
major works that YARV-MJIT created, which is my fork of MJIT. We should
share those improvements.
thread.c: follow rb_ prefix changes

vm.c: trigger MJIT on VM invocation. Also trigger `mjit_mark` to avoid
SEGV by race between JIT and GC of ISeq. The improvement was provided by
wanabe <s.wanabe@gmail.com>.
vm_insnhelper.h: trigger MJIT on method calls during VM execution.

vm_core.h: add fields required for mjit.c. `bp` must be `cfp[6]` because
rb_control_frame_struct is likely to be casted to another struct. The
last position is the safest place to add the new field.
vm_insnhelper.c: save initial value of cfp->ep as cfp->bp. This is an
optimization which are done in both MJIT and YARV-MJIT. So this change
is added in this commit. Calculating bp from ep is a little heavy work,
so bp is kind of cache for it.

iseq.c: notify ISeq GC to MJIT. We should know which iseq in MJIT queue
is GCed to avoid SEGV.

gc.c: add hooks so that MJIT can wait GC, and vice versa. Simultaneous
JIT and GC executions may cause SEGV and so we should synchronize them.

cont.c: save continuation information in MJIT worker. As MJIT shouldn't
unload JIT-ed code which is being used, MJIT wants to know full list of
saved execution contexts for continuation and detect ISeqs in use.

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 strips off some aggressive optimizations even from
YARV-MJIT, and thus it's slower than YARV-MJIT too. But it's still
fairly faster than Ruby 2.5.

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 once `MJIT.compile` feature
(synchronous JIT compilation of ISeq) is accepted.

and compile operands unification insns automatically.

sequence with EXEC_EC_CFP so that it can be easily replaced with vm_exec
in JIT-ed code.

vm_insnhelper.h: followed the change
insns.def: ditto

which are not needed

that don't move PC.

PUSH() was unexpected for the current generator.

for some opt_xxx instructions

for now