Once the front end of DMD becomes fully D, I read that the backend will also become D, but then what will happen to GDC and LDC whose backends are C++ IIUC?

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Shriramana Sharma ஶ்ரீரமணஶர்மா श्रीरमणशर्मा

On Wednesday, 22 July 2015 at 11:42:24 UTC, Shriramana Sharma wrote:
> Once the front end of DMD becomes fully D, I read that the backend will also become D, but then what will happen to GDC and LDC whose backends are C++ IIUC?

I don't see an issue there. A compiler is a program that implements a standard, as long as it generates good asm it could be written in brainfuck there would be no reason to care.

A D compiler written in D is a symbol, and D was written so that D-programmers could stop writting so much C++ so the idea of a DMD written in D is appealing, but that doesn't mean that all D compilers have to be written in D.

The only question is "Do they copy DMD correctly?". There is no doubt that it is doable in C++.

On Wednesday, 22 July 2015 at 11:42:24 UTC, Shriramana Sharma wrote:
> Once the front end of DMD becomes fully D, I read that the backend will also become D, but then what will happen to GDC and LDC whose backends are C++ IIUC?

The Rust compiler is written in Rust but uses LLVM as a backend, like LDC. I don't know the complexities of linking a D frontend with a C++ backend, but if the Rust team can do it, I'm sure that means GDC and LDC will continue to live on.

On Wed, 22 Jul 2015 17:12:14 +0530
Shriramana Sharma via Digitalmars-d <digitalmars-d@puremagic.com> wrote:

> Once the front end of DMD becomes fully D, I read that the backend will also become D, but then what will happen to GDC and LDC whose backends are C++ IIUC?
> 

They will use same dmd frontend written in D.

On Wednesday, 22 July 2015 at 12:02:50 UTC, Xinok wrote:
> On Wednesday, 22 July 2015 at 11:42:24 UTC, Shriramana Sharma wrote:
>> Once the front end of DMD becomes fully D, I read that the backend will also become D, but then what will happen to GDC and LDC whose backends are C++ IIUC?
>
> The Rust compiler is written in Rust but uses LLVM as a backend, like LDC. I don't know the complexities of linking a D frontend with a C++ backend, but if the Rust team can do it, I'm sure that means GDC and LDC will continue to live on.

Both gcc and llvm expose a C api afaik

On Wednesday, 22 July 2015 at 11:42:24 UTC, Shriramana Sharma wrote:
> Once the front end of DMD becomes fully D, I read that the backend will also become D, but then what will happen to GDC and LDC whose backends are C++ IIUC?

Hi Shriramana!

My current *plan A* for LDC is:

Prerequisite: Enable LLVM Cpp backend
For release: Compile DDMD frontend to C++ and distribute D and C++ version of DDMD.
Bootstrap process:
- Create stage1 ldc compiler from C++ version of frontend.
- Use stage1 ldc to compile stage2 ldc compiler from D version of frontend.
- For verification it could be useful to create a stage3 ldc compiler using the stage2 compiler.

Advantage is that you only need a C/C++ compiler for bootstrap. Drawback is compile time.

I have not yet tested this approach. Therefore *plan B*:

Use a previous version of LDC to compile the current version. This will work as long as the used language in the frontend is stable.

The non-frontend parts of LDC might slowly migrate from C++ to D. The pain point here is that LDC makes use of the LLVM C++ API which is really superior to the C API.

Regards,
Kai

On Wednesday, 22 July 2015 at 15:11:58 UTC, Kai Nacke wrote:
> Use a previous version of LDC to compile the current version. This will work as long as the used language in the frontend is stable.

I have a feeling this is going to end up being an issue.
Whatever D version ddmd is shipped with is going to need to be a LTS version.