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use par_for_each_in in par_body_owners and collect_crate_mono_items #99457

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Jul 19, 2022
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use par_for_each_in in par_body_owners and collect_crate_mono_items #99457

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2 changes: 1 addition & 1 deletion compiler/rustc_data_structures/src/sync.rs
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Expand Up @@ -146,7 +146,7 @@ cfg_if! {
t.into_iter()
}

pub fn par_for_each_in<T: IntoIterator>(t: T, for_each: impl Fn(T::Item) + Sync + Send) {
pub fn par_for_each_in<T: IntoIterator>(t: T, mut for_each: impl FnMut(T::Item) + Sync + Send) {
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Wouldn't this break the parallel compiler? The requirement is relaxed and then if we switch to parallel rustc it would fail to compile.

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@SparrowLii SparrowLii Jul 19, 2022 •
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It doesn't break the compiler from actual testing.

This function signature change is only required in non-parallel mode, and the one in parallel mode does not need to be changed. I think this is because the internal implementation of IntoParallelIterator does some kind of encapsulation of this(not sure).
#[Edit] See the new explanation below

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If we want to maintain consistency in both modes, we should change Fn in the signature in parallel mode to FnMut. I'm not sure if this is necessary.

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I don't think we can do that, if we run it in parallel then the function would be called from multiple threads thus requiring it to be called without having exclusive access.

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That makes sense. So I think we can keep the Fn in the signature in parallel mode, as it doesn't cause compilation errors

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@SparrowLii SparrowLii Jul 19, 2022 •
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I revisited the implementation of both patterns. The place to call this interface is in collect.rs. Because the MTRef type is not a &mut reference in parallel mode, the Fn type can be used without causing a compilation error.

// We catch panics here ensuring that all the loop iterations execute.
// This makes behavior consistent with the parallel compiler.
let mut panic = None;
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4 changes: 1 addition & 3 deletions compiler/rustc_middle/src/hir/map/mod.rs
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Expand Up @@ -491,9 +491,7 @@ impl<'hir> Map<'hir> {
}

pub fn par_body_owners<F: Fn(LocalDefId) + Sync + Send>(self, f: F) {
use rustc_data_structures::sync::{par_iter, ParallelIterator};

par_iter(&self.tcx.hir_crate_items(()).body_owners[..]).for_each(|&def_id| f(def_id));
par_for_each_in(&self.tcx.hir_crate_items(()).body_owners[..], |&def_id| f(def_id));
}

pub fn ty_param_owner(self, def_id: LocalDefId) -> LocalDefId {
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4 changes: 2 additions & 2 deletions compiler/rustc_monomorphize/src/collector.rs
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Expand Up @@ -180,7 +180,7 @@
//! regardless of whether it is actually needed or not.

use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::sync::{par_iter, MTLock, MTRef, ParallelIterator};
use rustc_data_structures::sync::{par_for_each_in, MTLock, MTRef};
use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId};
Expand Down Expand Up @@ -346,7 +346,7 @@ pub fn collect_crate_mono_items(
let inlining_map: MTRef<'_, _> = &mut inlining_map;

tcx.sess.time("monomorphization_collector_graph_walk", || {
par_iter(roots).for_each(|root| {
par_for_each_in(roots, |root| {
let mut recursion_depths = DefIdMap::default();
collect_items_rec(
tcx,
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8 changes: 7 additions & 1 deletion src/test/ui/privacy/privacy2.stderr
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Expand Up @@ -23,7 +23,13 @@ LL | pub fn foo() {}

error: requires `sized` lang_item

error: aborting due to 3 previous errors
error: requires `sized` lang_item

error: requires `sized` lang_item

error: requires `sized` lang_item

error: aborting due to 6 previous errors

Some errors have detailed explanations: E0432, E0603.
For more information about an error, try `rustc --explain E0432`.
8 changes: 7 additions & 1 deletion src/test/ui/privacy/privacy3.stderr
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Expand Up @@ -6,6 +6,12 @@ LL | use bar::gpriv;

error: requires `sized` lang_item

error: aborting due to 2 previous errors
error: requires `sized` lang_item

error: requires `sized` lang_item

error: requires `sized` lang_item

error: aborting due to 5 previous errors

For more information about this error, try `rustc --explain E0432`.
11 changes: 10 additions & 1 deletion src/test/ui/type_length_limit.stderr
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Expand Up @@ -7,5 +7,14 @@ LL | pub fn drop<T>(_x: T) {}
= note: the full type name has been written to '$TEST_BUILD_DIR/type_length_limit/type_length_limit.long-type.txt'
= help: consider adding a `#![type_length_limit="8"]` attribute to your crate

error: aborting due to previous error
error: reached the type-length limit while instantiating `<[closure@std::rt::lang_start<()...e<()>>::call_once - shim(vtable)`
--> $SRC_DIR/core/src/ops/function.rs:LL:COL
|
LL | extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: the full type name has been written to '$TEST_BUILD_DIR/type_length_limit/type_length_limit.long-type.txt'
= help: consider adding a `#![type_length_limit="8"]` attribute to your crate

error: aborting due to 2 previous errors