Hi,

In the process of setting up a new development environment, I noticed that DMD's codegen seems to outperform GDC's or LDC's when building DMD itself.

I wrote a test script to measure the time it takes for DMD (built with different compilers) to build Phobos:

http://dump.thecybershadow.net/9e42ff2858d1419cf41108cc50b0a83a/bench.sh

My results are:

dmd: 11.26
ldc: 15.35
gdc: 14.80

Compiler versions:

LDC - the LLVM D compiler (0.17.0):
  based on DMD v2.068.2 and LLVM 3.7.1
gdc (GCC) 5.3.0

GDC/LDC binaries are the ones packaged in Arch Linux. Host DMD is the one installed and chosen by AUTO_BOOTSTRAP (2.068.2). Target DMD/Phobos is from git master and built with ENABLE_RELEASE=1.

To me this seems surprising, especially considering that on Windows I used to get a significant speed increase when building DMD with MSVC instead of DMC.

On Friday, 11 March 2016 at 13:39:04 UTC, Vladimir Panteleev wrote:
> Hi,
>
> In the process of setting up a new development environment, I noticed that DMD's codegen seems to outperform GDC's or LDC's when building DMD itself.
>
> I wrote a test script to measure the time it takes for DMD (built with different compilers) to build Phobos:
>
> http://dump.thecybershadow.net/9e42ff2858d1419cf41108cc50b0a83a/bench.sh
>
> My results are:
>
> dmd: 11.26
> ldc: 15.35
> gdc: 14.80
>


https://github.com/D-Programming-Language/dmd/blob/master/src/root/rmem.d#L166-L193

How memory is allocated makes a huge difference.

On Friday, 11 March 2016 at 14:32:26 UTC, Iain Buclaw wrote:
> On Friday, 11 March 2016 at 13:39:04 UTC, Vladimir Panteleev wrote:
>> Hi,
>>
>> In the process of setting up a new development environment, I noticed that DMD's codegen seems to outperform GDC's or LDC's when building DMD itself.
>>
>> I wrote a test script to measure the time it takes for DMD (built with different compilers) to build Phobos:
>>
>> http://dump.thecybershadow.net/9e42ff2858d1419cf41108cc50b0a83a/bench.sh
>>
>> My results are:
>>
>> dmd: 11.26
>> ldc: 15.35
>> gdc: 14.80
>>
>
>
> https://github.com/D-Programming-Language/dmd/blob/master/src/root/rmem.d#L166-L193
>
> How memory is allocated makes a huge difference.

Thanks :) After changing that to version(all), LDC is faster now. Doesn't build with GDC though (multiple definitions)...

On Friday, 11 March 2016 at 14:46:59 UTC, Vladimir Panteleev wrote:
> Thanks :) After changing that to version(all), LDC is faster now. Doesn't build with GDC though (multiple definitions)...

How much faster is LDC?

On Friday, 11 March 2016 at 15:04:44 UTC, Edwin van Leeuwen wrote:
> On Friday, 11 March 2016 at 14:46:59 UTC, Vladimir Panteleev wrote:
>> Thanks :) After changing that to version(all), LDC is faster now. Doesn't build with GDC though (multiple definitions)...
>
> How much faster is LDC?

About 10%, but I didn't measure rigorously.

On Friday, 11 March 2016 at 14:46:59 UTC, Vladimir Panteleev wrote:
> On Friday, 11 March 2016 at 14:32:26 UTC, Iain Buclaw wrote:
>>
>> https://github.com/D-Programming-Language/dmd/blob/master/src/root/rmem.d#L166-L193
>>
>> How memory is allocated makes a huge difference.
>
> Thanks :) After changing that to version(all), LDC is faster now. Doesn't build with GDC though (multiple definitions)...

Yes, I know.  And if I were to say which behaviour is desired.  I'd say GDC is doing the right thing.

Marking all functions as 'weak' is a terrible idea on both DMD's and LDC's part.

On Friday, 11 March 2016 at 15:09:26 UTC, Iain Buclaw wrote:
>
> Marking all functions as 'weak' is a terrible idea on both DMD's and LDC's part.

I can't judge what is best here, but LDC does not always mark functions as weak. After the DDMD switch, we have multiple def. problems on Windows when bootstrapping using LDC 0.17: https://github.com/ldc-developers/ldc/issues/1310

On Friday, 11 March 2016 at 15:09:26 UTC, Iain Buclaw wrote:
> Yes, I know.  And if I were to say which behaviour is desired.  I'd say GDC is doing the right thing.
>
> Marking all functions as 'weak' is a terrible idea on both DMD's and LDC's part.

I distinctly remember Daniel and me having to remove those functions from DDMD when we first got it to build with LDC during/after DConf 2015.

LDC definitely does not mark symbols as weak/comdat/etc. by default. However, the linker might not pull in an object file from a static library if the respective symbols have already been resolved using other files.

 — David