[GSoC] 'Replace Runtime Hooks with Templates' progress and update thread

[Dan Printzell]

On Tuesday, 28 May 2019 at 10:47:03 UTC, Dan Printzell wrote:
> [...]

I forgot to post the updates after week one due to school and
development, so here is my updates for week one and two.


Week 1
======

This week
~~~~~~~~~

- Turned `_d_arrayappendT` and `_d_arrayappendcTX`, with their 
`*Trace`
   function into templates.
   - `_d_arrayappendcd` and `_d_arrayappendcd` where left alone as 
they
     are wrapper around the `_d_arrayappendT` for when assigning a 
dchar
     to char[], and dchar to wchar[], respectively.
- Started working on the dmd code.
   - Got the lowering code working.
   - Currently battling with the CTFE.
- I started with the templates inside object.d but then moved 
them to
   rt/lifetime.d and did a `public import` inside object.d 
instead. I did
   this because I started getting template recursions problems 
when I use
   `externDFunc`, as it used string concatenations internally. I 
can
   probably later move it back to object.d if needed later when I 
get the
   CTFE code working again.


Next week
~~~~~~~~~

- Continue with the dmd patches and get it be able to compile.
- Submit both the druntime and the dmd PR for review.


Blockers
~~~~~~~~

In the beginning I tried to translate the hook and all of the 
functions
it called to templates. This just got me into a wormhole of needed
changes, and it would have made the PRs harder to review. So I 
restarted
from scratch and instead only translated the entrypoints of each 
hook,
and then internally use `typeid(T)` to pass to the function
underneath. Future work when all hooks are translated, could be to
translate the functions underneath, when applicable.

When I got the hook lowering working I realized how much the 
hooks have
lied about their safety. So I had to add a `@trusted` wrapper 
that fakes
`pure nothrow` for the hook to not break all code. [1]

As mentioned above, I'm currently battling with the CTFE to 
understand
my lowered hooks. I found examples of this is done for 
`__ArrayPostblit`
and `__ArrayDtor` inside dinterpret.d, and I will try and 
understand how
they do it and implement the same for my hooks.


Week 2
======

This week
~~~~~~~~~

- I continued to work on the code to a state were I felt I could 
start
   to get some feedback, even if the code was not in a working 
state.
- I got the CTFE 'intercept' code working so the hooks are now 
using the
   dinterpret.d code instead.
- Submitted work-in-progress PRs
   - druntime: [https://github.com/dlang/druntime/pull/2632]
   - dmd: [https://github.com/dlang/dmd/pull/9982]


Next week
~~~~~~~~~

- I still need to get the PR into a working and mergeable state, 
I will
   try and get this done as soon as possible.
- I need to implement unittests for the dmd patches to verify 
that the
   lowering code works as expected, both for the non-trace and 
trace
   versions.
- When waiting for reviews I will work on the conversion of
   _d_array{setctor,ctor,cat*}, as according to my proposal 
document.

- I will try to get a PR of this submitted earlier than what I 
did the
   previous ones. This should be possible as these functions are 
simpler
   than the last ones and now I know that I should not try and 
translate
   dependencies and instead just add `typeid(T)` whenever 
necessary.


Blockers
~~~~~~~~

I've had compilation problem related to the translation of
_d_arrayappendcTX. I fixed this by instead calling the TypeInfo 
version
of that function.

Due to the exam and school I was not able to finish what I 
allocated
according to my proposal.

Currently I just have small bug where I trigger the postblit one 
too
many times with assigning a single element `arr ~= structVar`. 
This is
because the old backend code assigned the element outside of the
_d_arrayappend call, verses me now doing it internally. I 
probably just
need to need to make sure that it always lowerest the `structVar` 
into a
ref-able form, or make it assign the variable outside the hook 
again.



Footnotes
======
[1]
[https://github.com/Vild/druntime/blob/8f72a8b25f02653445e1b8288583788711b87595/src/rt/lifetime.d#L2871-L2876]