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digitalmars.D.learn - Compiler Explorer Assembly Output for C, C++ and D (dlang)

reply Tariq Siddiqui <m.tariqsiddiqui gmail.com> writes:
When using Compiler Explorer (https://godbolt.org/) to compare 
assembly output of simple programs, why D language assembly 
output is so long compared to C or C++ output. The simple square 
function output is the same for C, C++, and D, but the D output 
has additional lines that are not highlighted when hovering over 
the square function in the source code.

  - What are these additional lines?
  - How can I remove these lines from being generated?
May 27 2021
next sibling parent reply Dennis <dkorpel gmail.com> writes:
On Thursday, 27 May 2021 at 08:47:50 UTC, Tariq Siddiqui wrote:

  - What are these additional lines?


D generates extra symbols per module for things like module 
constructors, unittests and class introspection (I think).


  - How can I remove these lines from being generated?


Pass the `-betterC` flag to dmd/ldc2.
May 27 2021
parent reply Tariq Siddiqui <m.tariqsiddiqui gmail.com> writes:
On Thursday, 27 May 2021 at 09:11:35 UTC, Dennis wrote:

 On Thursday, 27 May 2021 at 08:47:50 UTC, Tariq Siddiqui wrote:

  - What are these additional lines?


 D generates extra symbols per module for things like module 
 constructors, unittests and class introspection (I think).


  - How can I remove these lines from being generated?


 Pass the `-betterC` flag to dmd/ldc2.


Thanks for your answer, -betterC works well with simple code but 
when using templates in code -betterC compilation failed.
May 27 2021
parent Dennis <dkorpel gmail.com> writes:
On Thursday, 27 May 2021 at 10:27:42 UTC, Tariq Siddiqui wrote:

 Thanks for your answer, -betterC works well with simple code 
 but when using templates in code -betterC compilation failed.


Templates are supported in -betterC, what's not supported can be 
found here:
https://dlang.org/spec/betterc.html#consequences

You're probably using or importing something that depends on 
Druntime.
For LDC, you can try adding this instead of using `-betterC`:

```
pragma(LDC_no_moduleinfo);
```

Though once you use non-betterC functions, your assembly will 
easily get messy compared to C's assembly.
May 27 2021
prev sibling parent reply Basile B. <b2.temp gmx.com> writes:
On Thursday, 27 May 2021 at 08:47:50 UTC, Tariq Siddiqui wrote:

 When using Compiler Explorer (https://godbolt.org/) to compare 
 assembly output of simple programs, why D language assembly 
 output is so long compared to C or C++ output. The simple 
 square function output is the same for C, C++, and D, but the D 
 output has additional lines that are not highlighted when 
 hovering over the square function in the source code.

  - What are these additional lines?
  - How can I remove these lines from being generated?


In addition to other answers, see 
https://forum.dlang.org/post/myrjutqyzpzlyltrdkwc forum.dlang.org
May 27 2021
parent reply Gavin Ray <gavinray site.com> writes:
On Thursday, 27 May 2021 at 10:48:43 UTC, Basile B. wrote:

 https://forum.dlang.org/post/myrjutqyzpzlyltrdkwc forum.dlang.org


Thank you for sharing this!

The difference between setting `pragma(LDC_no_moduleinfo);` at 
the top, and `-Os -gline-tables-only` in compiler flags is 
drastic.

- Standard
   - https://d.godbolt.org/z/env355M71
- No module info + flags
   - https://d.godbolt.org/z/4KxxvonY5


You wind up with
```c
int example.square(int):
         mov     eax, edi
         imul    eax, edi
         ret
```

```
define i32  _D7example6squareFiZi(i32 %num_arg) 

   %1 = mul i32 %num_arg, %num_arg, !dbg !7
   ret i32 %1, !dbg !7
}


"frame-pointer"="none" "target-cpu"="x86-64" 
"target-features"="+cx16" }
```
May 27 2021
parent Alain De Vos <devosalain ymail.com> writes:
Sidequestion.
For what purpose is the registration of dso used ?
May 27 2021