git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66866 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67679 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

https://rubyci.org/logs/rubyci.s3.amazonaws.com/centos7/ruby-trunk/log/20190421T040003Z.fail.html.gz

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67678 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Re-committing ruby@7f09b5e

Backport changes from ruby/irb.

```
% ruby -ve 'p (nil..).first'
ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-darwin18]
nil
% ruby -ve 'p (nil..).begin'
ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-darwin18]
nil
```

Wercker seems to randomly fail
https://app.wercker.com/ruby/ruby/runs/mjit-test1/5cc3c1c423fcb70008db9b64?step=5cc3c46a03f4460007da0659

To help debugging, let me isolate the impact from GC.compact in the JIT
testing on Wercker.

r59829 stopped clearing stack_start and enabled the code for
!FIBER_USE_NATIVE, but we need to do the same for register_stack_start
on ia64, otherwise we end up with NULL in cont_save_machine_stack.

Closes: ruby#2155

It refers to `Method#receiver` in the doc, but
there's no class reference in current doc.
Some tools automatically make it a link so it's useful.

Closes: ruby#2156

as it's unstable on the environment
https://ci.appveyor.com/project/ruby/ruby/builds/24138134/job/i7e441u7se11w7ey

* string.c (str_duplicate): share the root shared string if the
  original string is already sharing, so that all shared strings
  refer the root shared string directly.  indirect sharing can
  cause a dangling pointer.

[Bug #15792]

Synced from ruby/irb@5feb361.
This includes a support to colorize named Class instance on IRB inspect.

like https://ci.appveyor.com/project/ruby/ruby/builds/24142523/job/v6aq4srj7c3hgt86

VCS::GITSVN#format_changelog generates previous format, similar to
svn-log, and VCS::GIT#format_changelog stores just git-log as-is
for now.

* Mostly to try the new git repository.

GC is required for pinning / marking objects.  If the compactor runs
without pinning everything, then it will blow up, so just return early
if the GC is disabled.

This prevents the constants from moving.

Aliasing a method preserves its visibility.  These aliases turn
formerly-public methods into private.  Should make them public
again.  [Bug #15847]

I failed to collect any debug info in
https://app.wercker.com/ruby/ruby/runs/mjit-test1/5cda57fcab79a30008f195f6?step=5cda6a4e1090c4000800772e

It seems that it's due to this typo.

This function is used for marking / pinning vm stack values, so it
should have "vm" in the function name to be more clear.

This commit adds an alternative packing strategy for compaction.
Instead of packing towards "most pinned" pages, we can pack towards
"most empty" pages.  The idea is that we can double the heap size, then
pack all objects towards the empty side of the heap.  This will ensure
maximum chaos for testing / verification.

IDs can't move, we need to use them to look up the symbol objects later.

This is my mistake, I thought they were regular objects, but apparently
they are not.  We don't need to pin them.

Revert "Symbols can move so only cache IDs"

This reverts commit 672ee5f.

[Bug #15850]