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Commitdb03ec6

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Rollup merge ofrust-lang#126242 - yaahc:simplify-provider, r=jhpratt
Simplify provider api to improve llvm irThis PR seeks to resolve the last concern inrust-lang#99301 (comment)We resolve the issue by moving the type_id to be stored in the `Request` itself rather than being accessed through the `Erased` trait, letting the compiler infer that the value of the type id will not change between lookups.### LLVM Codegen**Before**```; <provider_test::MyError as core::error::Error>::provide; Function Attrs: nonlazybind uwtabledefine void `@"_ZN61_$LT$provider_test..MyError$u20$as$u20$core..error..Error$GT$7provide17hd9c9de412063aa73E"(ptr` noalias nocapture noundef nonnull readonly align 1 %self, ptr noundef nonnull align 1 %request.0, ptr noalias nocapture noundef readonly align 8 dereferenceable(32) %request.1) unnamed_addr #0 personality ptr `@rust_eh_personality` {start: %0 = getelementptr inbounds i8, ptr %request.1, i64 24 %self.1.val.i = load ptr, ptr %0, align 8 %1 = tail call { i64, i64 } %self.1.val.i(ptr noundef nonnull align 1 %request.0), !noalias !15 %2 = extractvalue { i64, i64 } %1, 0 %3 = extractvalue { i64, i64 } %1, 1 %_18.i.i = icmp ne i64 %2, 1101338453689927725 %_2.i.i = icmp ne i64 %3, 472224167662714873 %or.cond.i.not.i = select i1 %_18.i.i, i1 true, i1 %_2.i.i br i1 %or.cond.i.not.i, label %_ZN4core5error7Request7provide17h8f8125d2543333e0E.exit, label %bb2.i```**After**```; <provider_test::MyError as provider_test::Error>::provide; Function Attrs: mustprogress nofree norecurse nosync nounwind nonlazybind willreturn memory(argmem: readwrite) uwtabledefine void `@"_ZN63_$LT$provider_test..MyError$u20$as$u20$provider_test..Error$GT$7provide17h5bbf091795a6d359E"(ptr` noalias nocapture noundef nonnull readonly align 1 %self, ptr nocapture noundef nonnull align 8 %request.0, ptr noalias nocapture noundef readonly align 8 dereferenceable(24) %request.1) unnamed_addr#2 personality ptr `@rust_eh_personality` {start: %_19.i = load i64, ptr %request.0, align 8, !noalias !3, !noundef !3 switch i64 %_19.i, label %_ZN13provider_test7Request7provide17heb3ee140962e3b2fE.exit [ i64 7665305208997882008, label %bb12.i i64 7050211241160863540, label %bb12.i3 i64 9112786072622981063, label %bb12.i11 ]```
2 parents956efde +8b6f468 commitdb03ec6

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‎core/src/error.rs‎

Lines changed: 23 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -404,9 +404,9 @@ fn request_by_type_tag<'a, I>(err: &'a (impl Error + ?Sized)) -> Option<I::Reifi
404404
where
405405
I: tags::Type<'a>,
406406
{
407-
letmut tagged =TaggedOption::<'a,I>(None);
407+
letmut tagged =Tagged{tag_id:TypeId::of::<I>(),value:TaggedOption::<'a,I>(None)};
408408
err.provide(tagged.as_request());
409-
tagged.0
409+
tagged.value.0
410410
}
411411

412412
///////////////////////////////////////////////////////////////////////////////
@@ -507,16 +507,9 @@ where
507507
///
508508
#[unstable(feature ="error_generic_member_access", issue ="99301")]
509509
#[cfg_attr(not(doc), repr(transparent))]// work around https://github.com/rust-lang/rust/issues/90435
510-
pubstructRequest<'a>(dynErased<'a> +'a);
510+
pubstructRequest<'a>(Tagged<dynErased<'a> +'a>);
511511

512512
impl<'a>Request<'a>{
513-
/// Create a new `&mut Request` from a `&mut dyn Erased` trait object.
514-
fnnew<'b>(erased:&'bmut(dynErased<'a> +'a)) ->&'bmutRequest<'a>{
515-
// SAFETY: transmuting `&mut (dyn Erased<'a> + 'a)` to `&mut Request<'a>` is safe since
516-
// `Request` is repr(transparent).
517-
unsafe{&mut*(erasedas*mutdynErased<'a>as*mutRequest<'a>)}
518-
}
519-
520513
/// Provide a value or other type with only static lifetimes.
521514
///
522515
/// # Examples
@@ -940,37 +933,38 @@ pub(crate) mod tags {
940933
#[repr(transparent)]
941934
pub(crate)structTaggedOption<'a,I: tags::Type<'a>>(pubOption<I::Reified>);
942935

943-
impl<'a,I: tags::Type<'a>>TaggedOption<'a,I>{
936+
impl<'a,I: tags::Type<'a>>Tagged<TaggedOption<'a,I>>{
944937
pub(crate)fnas_request(&mutself) ->&mutRequest<'a>{
945-
Request::new(selfas&mut(dynErased<'a> +'a))
938+
let erased =selfas&mutTagged<dynErased<'a> +'a>;
939+
// SAFETY: transmuting `&mut Tagged<dyn Erased<'a> + 'a>` to `&mut Request<'a>` is safe since
940+
// `Request` is repr(transparent).
941+
unsafe{&mut*(erasedas*mutTagged<dynErased<'a>>as*mutRequest<'a>)}
946942
}
947943
}
948944

949945
/// Represents a type-erased but identifiable object.
950946
///
951947
/// This trait is exclusively implemented by the `TaggedOption` type.
952-
unsafetraitErased<'a>:'a{
953-
/// The `TypeId` of the erased type.
954-
fntag_id(&self) ->TypeId;
955-
}
948+
unsafetraitErased<'a>:'a{}
956949

957-
unsafeimpl<'a,I: tags::Type<'a>>Erased<'a>forTaggedOption<'a,I>{
958-
fntag_id(&self) ->TypeId{
959-
TypeId::of::<I>()
960-
}
950+
unsafeimpl<'a,I: tags::Type<'a>>Erased<'a>forTaggedOption<'a,I>{}
951+
952+
structTagged<E: ?Sized>{
953+
tag_id:TypeId,
954+
value:E,
961955
}
962956

963-
impl<'a>dynErased<'a> +'a{
957+
impl<'a>Tagged<dynErased<'a> +'a>{
964958
/// Returns some reference to the dynamic value if it is tagged with `I`,
965959
/// or `None` otherwise.
966960
#[inline]
967961
fndowncast<I>(&self) ->Option<&TaggedOption<'a,I>>
968962
where
969963
I: tags::Type<'a>,
970964
{
971-
ifself.tag_id() ==TypeId::of::<I>(){
965+
ifself.tag_id ==TypeId::of::<I>(){
972966
// SAFETY: Just checked whether we're pointing to an I.
973-
Some(unsafe{&*(selfas*constSelf).cast::<TaggedOption<'a,I>>()})
967+
Some(&unsafe{&*(selfas*constSelf).cast::<Tagged<TaggedOption<'a,I>>>()}.value)
974968
}else{
975969
None
976970
}
@@ -983,9 +977,12 @@ impl<'a> dyn Erased<'a> + 'a {
983977
where
984978
I: tags::Type<'a>,
985979
{
986-
ifself.tag_id() ==TypeId::of::<I>(){
987-
// SAFETY: Just checked whether we're pointing to an I.
988-
Some(unsafe{&mut*(selfas*mutSelf).cast::<TaggedOption<'a,I>>()})
980+
ifself.tag_id ==TypeId::of::<I>(){
981+
Some(
982+
// SAFETY: Just checked whether we're pointing to an I.
983+
&mutunsafe{&mut*(selfas*mutSelf).cast::<Tagged<TaggedOption<'a,I>>>()}
984+
.value,
985+
)
989986
}else{
990987
None
991988
}

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