This reduces the size of `Builtin` from 88 (!) bytes to 8, and as the
largest variant of `Value`, the size of that type from 96 to 64.
The next largest type is NixList, clocking in at 64 bytes.
This has noticeable performance impact. In an implementation without
disk I/O, evaluating nixpkgs.stdenv looks like this:
Benchmark 1: tvix -E '(import <nixpkgs> {}).stdenv.drvPath'
Time (mean ± σ): 1.151 s ± 0.003 s [User: 1.041 s, System: 0.109 s]
Range (min … max): 1.147 s … 1.155 s 10 runs
After this change, it looks like this:
Benchmark 1: tvix -E '(import <nixpkgs> {}).stdenv.drvPath'
Time (mean ± σ): 1.046 s ± 0.004 s [User: 0.954 s, System: 0.092 s]
Range (min … max): 1.041 s … 1.053 s 10 runs
Change-Id: I5ab7cc02a9a450c0227daf1f1f72966358311ebb
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8027
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
f16b0f24e2