[SAoC 2022] Replace druntime Hooks with Templates: Milestone 1, Week 1

[Teodor Dutu]

On Friday, 27 December 2024 at 14:09:09 UTC, rkompass wrote:
> On Sunday, 25 September 2022 at 17:18:14 UTC, Teodor Dutu wrote:
>> Hi,
>>
>> My project wants to replace dmd hooks to druntime functions 
>> such as `_d_arraycatnTX`, `_d_newclass` and `_d_newitemT` with 
>> templates. This will make lowerings to these functions faster 
>> at runtime, as their templated versions will not require all 
>> the `TypeInfo`-related indirection used by the current hooks. 
>> As a result, the maintainability of the compiler will be 
>> improved as lowerings will now take place in the semantic 
>> analysis phase, as opposed to the IR phase (where the hooks 
>> are currently present). In addition, the compiler will also 
>> infer
> ....
>> So far, I have implemented and tested the new `_d_arraycatnTX` 
>> hook. I have also come up with a draft lowering that manages 
>> to compile druntime and phobos. This was not easy, as they 
>> make extensive use of array concatenations, especially for 
>> strings. Now I am working on fixing the lowering and the hook 
>> to make the tests in dmd pass.
>>
>> Thanks,\
>> Teodor
>
> I don't know how this old post came up, but it's in my listing 
> of new posts.
> The project described seems very promising and attractive.
> Two years have passed since.
>
> How did it develop? Can any of the experts give a short summary 
> please?
> (Was it too ambitious? Has it been completed and became 
> obsolete for some reason. Did it simply die of neglection?)

Hi,

The project has progressed since the point of this post. 
Specifically, the following hooks have been templated:

```
_d_arrayctor
_d_arraysetctor
_d_arrayassign
_d_arrayassign_l
_d_arrayassign_r
_d_delstruct
_d_newThrowable
_d_arrayappendT
_d_arrayappendcTX
_d_arraycatT
_d_arraycatnTX
_d_newitemiT
_d_newitemT
_d_newitemU
_d_newclass
_d_newarrayiT
_d_newarrayT
_d_newarrayU
_d_newarraymTX
_d_newarrayOpT
```

And the following are yet to be templated:

```
_d_arrayliteralTX
_d_assocarrayliteralTX (and the entirety of aa.d)
_d_arraysetcapacity
_d_arraysetlengthiT
_d_arraysetlengthT
_d_arrayshrinkfit
_d_interface_cast
_d_isbaseof
_d_isbaseof2
```

Two things have stalled the project:
1. I started my PhD and can't dedicate enough time to it. I'm 
looking to coach a new student to pick up where I left
2. `_d_arrayliteralTX` is more demanding because array literals 
are optimised in many places in the compiler's frontend, for 
example by coalescing concatenated literals. This happens after 
semantic analysis, and inserting the proper hook into the newly 
created literals is difficult. This would be most elegantly 
handled by introducing a new compiler pass just to perform all 
lowerings for the finalised AST. This in turn would require the 
scope hierarchy to be exposed from the semantic pass, which is 
what constitutes the second blocker.

I gave a broader overview of this project in a talk at this 
year's DConf [1]. You can see the slides here [2]. Feel free to 
ask any further questions.

Thanks,
Teo

[1] https://www.youtube.com/live/FKI9M-KRjvA?t=24245
[2] 
https://docs.google.com/presentation/d/1S_qn8lmi0J_PgX0rd5bdNWyeBFN2UmtHd1EY24jLdzE