A few numbers on allocation in dmd

[kinke]

On Wednesday, 1 July 2020 at 08:15:12 UTC, NilsLankila wrote:
> There's already a micro optim for AliasDeclaration, see 
> https://github.com/dlang/dmd/pull/11354. It should cut the use 
> by 25% (so the number for AliasDecl *only*), minus the problem 
> of allocations blocks, so maybe more 10% to 20% IRL.

For 64-bit, the size of a Declaration instance is 200 bytes 
(2.092 frontend), for AliasDeclaration 232 bytes, and with your 
change, down to 224 bytes, so the correct number is more like 
-3.5%. Thx for doing it anyway.

Another thing to keep in mind is that all new'd allocations are 
padded to a multiple of 16-bytes, see 
https://github.com/dlang/dmd/blob/d97a908d35c8e6c22571688f12138862ef089337/src/dmd/root/rmem.d#L176 (for the GC/-lowmem too, which has a bigger overhead).