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?

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

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

Pass the -betterC flag to dmd/ldc2.

On Thursday, 27 May 2021 at 09:11:35 UTC, Dennis wrote:

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

On Thursday, 27 May 2021 at 10:27:42 UTC, Tariq Siddiqui wrote:

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.

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

In addition to other answers, see https://forum.dlang.org/post/myrjutqyzpzlyltrdkwc@forum.dlang.org

On Thursday, 27 May 2021 at 10:48:43 UTC, Basile B. wrote:

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

int example.square(int):
        mov     eax, edi
        imul    eax, edi
        ret

define i32 @_D7example6squareFiZi(i32 %num_arg) local_unnamed_addr #0 !dbg !5 {
  %1 = mul i32 %num_arg, %num_arg, !dbg !7
  ret i32 %1, !dbg !7
}

attributes #0 = { norecurse nounwind readnone uwtable "frame-pointer"="none" "target-cpu"="x86-64" "target-features"="+cx16" }

Sidequestion.
For what purpose is the registration of dso used ?