Merge environments of nested functions #3718
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This looks like an amazing improvement. Is there something that could be done to get this merged? |
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IIRC, there was some segfault. I can have a look at cherry-picking at least the commits that don't break anything. |
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This pull request has been mentioned on NixOS Discourse. There might be relevant details there: https://discourse.nixos.org/t/tweag-nix-dev-update-5/10560/1 |
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I marked this as stale due to inactivity. → More info |
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Previously an expression like 'x: y: ...' would create two environments with one value. Now it creates one environment with two values. This reduces the number of allocations and the distance in the environment chain that variable lookups need to traverse. On $ nix-instantiate --dry-run '<nixpkgs/nixos/release-combined.nix>' -A nixos.tests.simple.x86_64-linux this gives a ~30% reduction in the number of Env allocations.
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This is not really useful on its own, but it does recover the
'infinite recursion' error message for '{ __functor = x: x; } 1', and
is more efficient in conjunction with NixOS#3718.
Fixes NixOS#5515.
This was referenced Nov 16, 2021
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This is not really useful on its own, but it does recover the
'infinite recursion' error message for '{ __functor = x: x; } 1', and
is more efficient in conjunction with NixOS#3718.
Fixes NixOS#5515.
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I marked this as stale due to inactivity. → More info |
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Functions can now take more than one argument and function applications can apply more than one argument at a time. For non-partially applied functions/primops, this avoids allocation of application thunks. Also, it allows merging of environments (e.g. in a function like
x: y: ..., we only allocate one environment).On
nix-env -qa -f '<nixpkgs>', this gives a ~8.5% speedup, reduces the number of environment allocations by 29.5% and the number of value allocations by 4.8%.