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refactor(tvix/eval): add name-based index over compiler's locals

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Instead of finding locals by doing 2x O(n) walks over the compiler's
locals list, use a secondary name-based index for resolving locals by
name.

Previously, almost 60% (!!) of eval time on some expressions over
nixpkgs was spent in `Local::has_name`. This function doesn't even
exist anymore now, and eval speed about doubles as a result.

Note that this doesn't exactly make the locals code easier to read,
but I'm also not sure what we can simplify in there in general.

This fixes b/227.

Change-Id: I29ce5eb9452b02d3b358c673e1f5cf8082e2fef9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7560
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI
This commit is contained in:
Vincent Ambo 2022-12-12 03:00:12 +03:00 • committed by tazjin
parent 922bf7aca9
commit 87995ed355
2 changed files with 106 additions and 32 deletions
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13
tvix/eval/src/compiler/mod.rs
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@ -1120,16 +1120,17 @@ impl Compiler<'_> {
self.scope_mut().poison(global_ident, depth);
}
for other in self.scope().locals.iter().rev() {
if other.has_name(&name) && other.depth == depth {
self.emit_error(node, ErrorKind::VariableAlreadyDefined(other.span));
let span = self.span_for(node);
let (idx, shadowed) = self.scope_mut().declare_local(name, span);
break;
if let Some(shadow_idx) = shadowed {
let other = &self.scope()[shadow_idx];
if other.depth == depth {
self.emit_error(node, ErrorKind::VariableAlreadyDefined(other.span));
}
}
let span = self.span_for(node);
self.scope_mut().declare_local(name, span)
idx
}
/// Determine whether the current lambda context has any ancestors