Playing around with Godbolt, D seems to generate an embarassing amount of assembly for a simple function (50ish for squaring an int vs 4 for C++ and 7 for Rust). Even Go compiles to less assembly.

Is there something I'm missing?

Godbolt link: https://godbolt.org/g/t5S976

On Saturday, 27 January 2018 at 19:42:01 UTC, Matt wrote:
> Godbolt link: https://godbolt.org/g/t5S976
The actual code is :
 imul edi, edi
 mov eax, edi
 ret


The rest is runtime initialization.
which you can remove using an undocumented -betterC switch.

On Saturday, 27 January 2018 at 19:43:50 UTC, Stefan Koch wrote:
> On Saturday, 27 January 2018 at 19:42:01 UTC, Matt wrote:
>> Godbolt link: https://godbolt.org/g/t5S976
> The actual code is :
>  imul edi, edi
>  mov eax, edi
>  ret
>
>
> The rest is runtime initialization.
> which you can remove using an undocumented -betterC switch.

ah ... -betterC is only for dmd.
try using the gdc compiler instead of ldc.
it does not emit runtime stuff if it's not used.

On Saturday, 27 January 2018 at 19:43:50 UTC, Stefan Koch wrote:
> On Saturday, 27 January 2018 at 19:42:01 UTC, Matt wrote:
>> Godbolt link: https://godbolt.org/g/t5S976
> The actual code is :
>  imul edi, edi
>  mov eax, edi
>  ret

Could you please paste the source code? I mean in say 5 years when there will be no more godbolt.org someone reading this thread will not know what it was about.

On Saturday, 27 January 2018 at 19:45:35 UTC, Stefan Koch wrote:
>
> ah ... -betterC is only for dmd.

`-betterC` works from LDC 1.1.0.

- Johan

On Sat, Jan 27, 2018 at 07:41:21PM +0000, Matt via Digitalmars-d-learn wrote:
> Playing around with Godbolt, D seems to generate an embarassing amount of assembly for a simple function (50ish for squaring an int vs 4 for C++ and 7 for Rust). Even Go compiles to less assembly.
> 
> Is there something I'm missing?

If you're looking for efficiency of generated code, use gdc or ldc. While dmd is the reference compiler with the latest and greatest bleeding-edge features, it's not known to be the best at generating optimized code, even if you run it with -O.  If code size / efficiency is important to you, I highly recommend using gdc or ldc instead.


T

-- 
Век живи - век учись. А дураком помрёшь.

On Saturday, 27 January 2018 at 19:43:50 UTC, Stefan Koch wrote:
> On Saturday, 27 January 2018 at 19:42:01 UTC, Matt wrote:
>> Godbolt link: https://godbolt.org/g/t5S976
> The actual code is :
>  imul edi, edi
>  mov eax, edi
>  ret
>
>
> The rest is runtime initialization.
> which you can remove using an undocumented -betterC switch.

It's not undocumented:

https://dlang.org/spec/betterc.html

On Saturday, 27 January 2018 at 19:43:50 UTC, Stefan Koch wrote:
> On Saturday, 27 January 2018 at 19:42:01 UTC, Matt wrote:
>> Godbolt link: https://godbolt.org/g/t5S976
> The actual code is :
>  imul edi, edi
>  mov eax, edi
>  ret
>
>
> The rest is runtime initialization.
> which you can remove using an undocumented -betterC switch.

BTW as asm.dlang.org is dead, you can use run.dlang.io for these things, e.g.

DMD: https://run.dlang.io/is/lLL1aJ
LDC: https://run.dlang.io/is/sVn5tu

(-output-s / -asm are only added for extra convenience)

Since a couple of days, it even does demangling of the symbols.
Though, of course, if you want to look only at LDC's output, godbolt is still the better choice.

On 01/27/2018 11:42 AM, Matt wrote:
> Godbolt link: https://godbolt.org/g/t5S976

According to that link D and C++ both produce 4 lines of assembly, Rust 7, and Go 38 (for that function).

Ali