sets use non-optimized countBits32

[data-man]

/cc @krux02

related #10617

[krux02]

I am aware of this. Unfortunately I can't do a lot about it.

Nim/lib/system/sets.nim

Line 15 in f774426

# bitops can't be imported here, therefore the code duplication.

This is the problem:

• The fast countSetBits is implemented in bitops.nim
• Slow but compatible countBits32 and countBits64 is implemented in sets.nim
• system.nim includes sets.nim
• bitops defines a macro, setBits (it is a macro, because we don't have proper varargs forwarding like in c++).
• macros may not be imported from system.nim.

Therefore, sets need to be implemented with the slow countBits32/64. The solution that I see possible is the following: Fix varargs in nim templates with proper varargs forwarding that isn't based on macros (like in c++). Then the macros in bitops can be implemented as pure templates and bitops can be imported from sets.nim (and therefore also from system.nim).

[data-man]

@krux02
I don't know all details, but can be bitops added to implicit imports?
Something like conf.implicitImports.add ....
And call countBits there:
https://github.com/nim-lang/Nim/blob/devel/compiler/ccgexprs.nim#L1855-L1857

[krux02]

No don't use implicitImports at all. It only causes harm. That would be worse than importing bitops in system.nim which I just explained isn't possible because of its macros.

[Clyybber]

@krux02 Isn't it possible to use from bitops import countBits32/64 ?

[Araq]

Move countBit32/64 to system, import it from bitops, problem solved.