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Use unused_generic_params from crate metadata #109109

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Mar 15, 2023
Merged

Use unused_generic_params from crate metadata #109109

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10 changes: 9 additions & 1 deletion compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -226,7 +226,15 @@ provide! { tcx, def_id, other, cdata,
lookup_default_body_stability => { table }
lookup_deprecation_entry => { table }
params_in_repr => { table }
unused_generic_params => { table }
// FIXME: Could be defaulted, but `LazyValue<UnusedGenericParams>` is not `FixedSizeEncoding`..
unused_generic_params => {
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You had a FIXME in the other PR, could you add this here as well? Would be nice to just default

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Oh also, is there a reason why the type doesn't implement that trait? Could you just add the impl? Or is there something to it

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@compiler-errors compiler-errors Mar 14, 2023 •
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For us to have a defaulted table, the value must implement FixedSizeEncoding and IsDefault. Lazy<T> can be FixedSizeEncoding, but can't be checked for defaultness because they're just a file offset.

I could instead encode the table value as Option<LazyValue<UnusedGenericParams>>, but then ProcessQueryValue<T> for Option<T> panics if the value decoded is None -- we could use specializtion to do:

impl ProcessQueryValue<'_, UnusedGenericParams> for Option<UnusedGenericParams> {
    #[inline(always)]
    fn process_decoded(self, _tcx: TyCtxt<'_>, _err: impl Fn() -> !) -> UnusedGenericParams {
        self.unwrap_or_else(|| UnusedGenericParams::new_all_used())
    }
}

but I don't feel like using specialization here is compelling enough to save a few lines in the decoder rather than providing an explicit body here.

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haha, yeah, it's fine

cdata
.root
.tables
.unused_generic_params
.get(cdata, def_id.index)
.map_or_else(|| ty::UnusedGenericParams::new_all_used(), |lazy| lazy.decode((cdata, tcx)))
}
opt_def_kind => { table_direct }
impl_parent => { table }
impl_polarity => { table_direct }
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4 changes: 2 additions & 2 deletions compiler/rustc_middle/src/query/keys.rs
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Expand Up @@ -63,7 +63,7 @@ impl<'tcx> Key for ty::InstanceDef<'tcx> {

#[inline(always)]
fn query_crate_is_local(&self) -> bool {
true
self.def_id().is_local()
}

fn default_span(&self, tcx: TyCtxt<'_>) -> Span {
Expand All @@ -76,7 +76,7 @@ impl<'tcx> Key for ty::Instance<'tcx> {

#[inline(always)]
fn query_crate_is_local(&self) -> bool {
true
self.def_id().is_local()
}

fn default_span(&self, tcx: TyCtxt<'_>) -> Span {
Expand Down
9 changes: 2 additions & 7 deletions compiler/rustc_monomorphize/src/polymorphize.rs
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Expand Up @@ -36,6 +36,8 @@ fn unused_generic_params<'tcx>(
tcx: TyCtxt<'tcx>,
instance: ty::InstanceDef<'tcx>,
) -> UnusedGenericParams {
assert!(instance.def_id().is_local());

if !tcx.sess.opts.unstable_opts.polymorphize {
// If polymorphization disabled, then all parameters are used.
return UnusedGenericParams::new_all_used();
Expand Down Expand Up @@ -100,13 +102,6 @@ fn should_polymorphize<'tcx>(
return false;
}

// Polymorphization results are stored in cross-crate metadata only when there are unused
// parameters, so assume that non-local items must have only used parameters (else this query
// would not be invoked, and the cross-crate metadata used instead).
if !def_id.is_local() {
return false;
}

// Foreign items have no bodies to analyze.
if tcx.is_foreign_item(def_id) {
return false;
Expand Down
4 changes: 4 additions & 0 deletions tests/codegen-units/polymorphization/auxiliary/poly-dep.rs
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@@ -0,0 +1,4 @@
// compile-flags: -Zpolymorphize=on

#[inline(never)]
pub fn foo<T>() {}
11 changes: 11 additions & 0 deletions tests/codegen-units/polymorphization/poly-foreign.rs
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@@ -0,0 +1,11 @@
// aux-build:poly-dep.rs
// compile-flags: --crate-type=lib -Zprint-mono-items=eager -Zpolymorphize=on

extern crate poly_dep;

pub static FN1: fn() = poly_dep::foo::<i32>;
pub static FN2: fn() = poly_dep::foo::<u32>;

//~ MONO_ITEM static FN1
//~ MONO_ITEM static FN2
//~ MONO_ITEM fn poly_dep::foo::<T>