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polymorphize: remove predicate logic

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This commit removes all logic which marks parameters as used based on
their presence in predicates - given rust-lang/rust#75675, this will
enable more polymorphization and avoid the symbol clashes that predicate
logic previously sidestepped.

Signed-off-by: David Wood <david@davidtw.co>
This commit is contained in:
David Wood 2020-08-20 11:42:56 +01:00 • committed by David Wood
parent 50433a0bf4
commit da2b69b614
3 changed files with 43 additions and 42 deletions
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41
compiler/rustc_monomorphize/src/polymorphize.rs
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@ -89,9 +89,6 @@ fn unused_generic_params(tcx: TyCtxt<'_>, def_id: DefId) -> FiniteBitSet<u32> {
};
let mut vis = MarkUsedGenericParams { tcx, def_id, unused_parameters: &mut unused_parameters };
vis.visit_body(body);
debug!(?unused_parameters, "(after visitor)");
mark_used_by_predicates(tcx, def_id, &mut unused_parameters);
debug!(?unused_parameters, "(end)");
// Emit errors for debugging and testing if enabled.
@ -161,44 +158,6 @@ fn mark_used_by_default_parameters<'tcx>(
}
}
/// Search the predicates on used generic parameters for any unused generic parameters, and mark
/// those as used.
#[instrument(level = "debug", skip(tcx, def_id))]
fn mark_used_by_predicates<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: DefId,
unused_parameters: &mut FiniteBitSet<u32>,
) {
let def_id = tcx.closure_base_def_id(def_id);
let predicates = tcx.explicit_predicates_of(def_id);
let mut current_unused_parameters = FiniteBitSet::new_empty();
// Run to a fixed point to support `where T: Trait<U>, U: Trait<V>`, starting with an empty
// bit set so that this is skipped if all parameters are already used.
while current_unused_parameters != *unused_parameters {
debug!(?current_unused_parameters, ?unused_parameters);
current_unused_parameters = *unused_parameters;
for (predicate, _) in predicates.predicates {
// Consider all generic params in a predicate as used if any other parameter in the
// predicate is used.
let any_param_used = {
let mut vis = HasUsedGenericParams { tcx, unused_parameters };
predicate.visit_with(&mut vis).is_break()
};
if any_param_used {
let mut vis = MarkUsedGenericParams { tcx, def_id, unused_parameters };
predicate.visit_with(&mut vis);
}
}
}
if let Some(parent) = predicates.parent {
mark_used_by_predicates(tcx, parent, unused_parameters);
}
}
/// Emit errors for the function annotated by `#[rustc_polymorphize_error]`, labelling each generic
/// parameter which was unused.
#[instrument(level = "debug", skip(tcx, generics))]