second draft: add Bitfields to D

[user1234]

On Friday, 3 May 2024 at 12:52:09 UTC, Patrick Schluter wrote:
> Not true. x86 provides BMI1 instructions which are present in 
> x86 CPUs at least since 2013.
> ARM also provides bit field instructions and quite a number of 
> legacy CPU's also had bitfield instructions (m68k, NEC V30, 
> Itanium, PowerPC, etc.).
> Doesn't change the issues with language bitfields

About BMI/BMI2 it would interesting to see if optimizing 
compilers actually generate instructions of these extensions for 
c++ bitfields. I've tried for styx enum-sets, sure that's a bit a 
special case of bitfields, but so far the only difference visible 
is a BMI2 `shlxl` emitted. But once again very special case.