Auto merge of #109097 - matthiaskrgr:rollup-6ydc4ri, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #108419 (Stabilize `atomic_as_ptr`)
 - #108507 (use `as_ptr` to determine the address of atomics)
 - #108607 (Don't use fd-lock on Solaris in bootstrap)
 - #108830 (Treat projections with infer as placeholder during fast reject in new solver)
 - #109055 (create `config::tests::detect_src_and_out` test for bootstrap)
 - #109058 (Document BinOp::is_checkable)
 - #109081 (simd-wide-sum test: adapt for LLVM 17 codegen change)
 - #109083 (Update books)
 - #109088 (Gracefully handle `#[target_feature]` on statics)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

18 files changed, 209 insertions, 101 deletions

diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
index 8b6bf886b0d..f9bb8359208 100644
--- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
+++ b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -61,25 +61,29 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
 
     let supported_target_features = tcx.supported_target_features(LOCAL_CRATE);
 
-    // In some cases, attribute are only valid on functions, but it's the `check_attr`
-    // pass that check that they aren't used anywhere else, rather this module.
-    // In these cases, we bail from performing further checks that are only meaningful for
-    // functions (such as calling `fn_sig`, which ICEs if given a non-function). We also
-    // report a delayed bug, just in case `check_attr` isn't doing its job.
-    let validate_fn_only_attr = |attr_sp| -> bool {
-        let def_kind = tcx.def_kind(did);
-        if let DefKind::Fn | DefKind::AssocFn | DefKind::Variant | DefKind::Ctor(..) = def_kind {
-            true
-        } else {
-            tcx.sess.delay_span_bug(attr_sp, "this attribute can only be applied to functions");
-            false
-        }
-    };
-
     let mut inline_span = None;
     let mut link_ordinal_span = None;
     let mut no_sanitize_span = None;
+
     for attr in attrs.iter() {
+        // In some cases, attribute are only valid on functions, but it's the `check_attr`
+        // pass that check that they aren't used anywhere else, rather this module.
+        // In these cases, we bail from performing further checks that are only meaningful for
+        // functions (such as calling `fn_sig`, which ICEs if given a non-function). We also
+        // report a delayed bug, just in case `check_attr` isn't doing its job.
+        let fn_sig = || {
+            use DefKind::*;
+
+            let def_kind = tcx.def_kind(did);
+            if let Fn | AssocFn | Variant | Ctor(..) = def_kind {
+                Some(tcx.fn_sig(did))
+            } else {
+                tcx.sess
+                    .delay_span_bug(attr.span, "this attribute can only be applied to functions");
+                None
+            }
+        };
+
         if attr.has_name(sym::cold) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
         } else if attr.has_name(sym::rustc_allocator) {
@@ -169,8 +173,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
                 }
             }
         } else if attr.has_name(sym::cmse_nonsecure_entry) {
-            if validate_fn_only_attr(attr.span)
-                && !matches!(tcx.fn_sig(did).skip_binder().abi(), abi::Abi::C { .. })
+            if let Some(fn_sig) = fn_sig()
+                && !matches!(fn_sig.skip_binder().abi(), abi::Abi::C { .. })
             {
                 struct_span_err!(
                     tcx.sess,
@@ -189,8 +193,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL;
         } else if attr.has_name(sym::track_caller) {
             if !tcx.is_closure(did.to_def_id())
-                && validate_fn_only_attr(attr.span)
-                && tcx.fn_sig(did).skip_binder().abi() != abi::Abi::Rust
+                && let Some(fn_sig) = fn_sig()
+                && fn_sig.skip_binder().abi() != abi::Abi::Rust
             {
                 struct_span_err!(tcx.sess, attr.span, E0737, "`#[track_caller]` requires Rust ABI")
                     .emit();
@@ -222,7 +226,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
             }
         } else if attr.has_name(sym::target_feature) {
             if !tcx.is_closure(did.to_def_id())
-                && tcx.fn_sig(did).skip_binder().unsafety() == hir::Unsafety::Normal
+                && let Some(fn_sig) = fn_sig()
+                && fn_sig.skip_binder().unsafety() == hir::Unsafety::Normal
             {
                 if tcx.sess.target.is_like_wasm || tcx.sess.opts.actually_rustdoc {
                     // The `#[target_feature]` attribute is allowed on
diff --git a/compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs b/compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs
index 02f3eeee0e7..07a33bcbb50 100644
--- a/compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs
@@ -11,7 +11,7 @@ use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
-use rustc_middle::ty::fast_reject::{simplify_type, SimplifiedType, TreatParams};
+use rustc_middle::ty::fast_reject::{simplify_type, SimplifiedType, TreatParams, TreatProjections};
 use rustc_middle::ty::{self, CrateInherentImpls, Ty, TyCtxt};
 use rustc_span::symbol::sym;
 
@@ -99,7 +99,12 @@ impl<'tcx> InherentCollect<'tcx> {
                 }
             }
 
-            if let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsInfer) {
+            if let Some(simp) = simplify_type(
+                self.tcx,
+                self_ty,
+                TreatParams::AsCandidateKey,
+                TreatProjections::AsCandidateKey,
+            ) {
                 self.impls_map.incoherent_impls.entry(simp).or_default().push(impl_def_id);
             } else {
                 bug!("unexpected self type: {:?}", self_ty);
@@ -159,7 +164,12 @@ impl<'tcx> InherentCollect<'tcx> {
             }
         }
 
-        if let Some(simp) = simplify_type(self.tcx, ty, TreatParams::AsInfer) {
+        if let Some(simp) = simplify_type(
+            self.tcx,
+            ty,
+            TreatParams::AsCandidateKey,
+            TreatProjections::AsCandidateKey,
+        ) {
             self.impls_map.incoherent_impls.entry(simp).or_default().push(impl_def_id);
         } else {
             bug!("unexpected primitive type: {:?}", ty);
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 57805f7c800..562dd2caae3 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -15,6 +15,7 @@ use rustc_infer::infer::canonical::OriginalQueryValues;
 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
 use rustc_middle::middle::stability;
+use rustc_middle::ty::fast_reject::TreatProjections;
 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
 use rustc_middle::ty::AssocItem;
 use rustc_middle::ty::GenericParamDefKind;
@@ -699,7 +700,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     }
 
     fn assemble_inherent_candidates_for_incoherent_ty(&mut self, self_ty: Ty<'tcx>) {
-        let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsInfer) else {
+        let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsCandidateKey, TreatProjections::AsCandidateKey) else {
             bug!("unexpected incoherent type: {:?}", self_ty)
         };
         for &impl_def_id in self.tcx.incoherent_impls(simp) {
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 4b15e48bd27..7055d9257ec 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -25,6 +25,7 @@ use rustc_infer::infer::{
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::traits::util::supertraits;
 use rustc_middle::ty::fast_reject::DeepRejectCtxt;
+use rustc_middle::ty::fast_reject::TreatProjections;
 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
 use rustc_middle::ty::print::{with_crate_prefix, with_forced_trimmed_paths};
 use rustc_middle::ty::{self, GenericArgKind, Ty, TyCtxt, TypeVisitableExt};
@@ -1257,7 +1258,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let target_ty = self
                 .autoderef(sugg_span, rcvr_ty)
                 .find(|(rcvr_ty, _)| {
-                    DeepRejectCtxt { treat_obligation_params: TreatParams::AsInfer }
+                    DeepRejectCtxt { treat_obligation_params: TreatParams::AsCandidateKey }
                         .types_may_unify(*rcvr_ty, impl_ty)
                 })
                 .map_or(impl_ty, |(ty, _)| ty)
@@ -1516,7 +1517,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .into_iter()
             .any(|info| self.associated_value(info.def_id, item_name).is_some());
         let found_assoc = |ty: Ty<'tcx>| {
-            simplify_type(tcx, ty, TreatParams::AsInfer)
+            simplify_type(tcx, ty, TreatParams::AsCandidateKey, TreatProjections::AsCandidateKey)
                 .and_then(|simp| {
                     tcx.incoherent_impls(simp)
                         .iter()
@@ -2645,9 +2646,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // FIXME: Even though negative bounds are not implemented, we could maybe handle
                 // cases where a positive bound implies a negative impl.
                 (candidates, Vec::new())
-            } else if let Some(simp_rcvr_ty) =
-                simplify_type(self.tcx, rcvr_ty, TreatParams::AsPlaceholder)
-            {
+            } else if let Some(simp_rcvr_ty) = simplify_type(
+                self.tcx,
+                rcvr_ty,
+                TreatParams::ForLookup,
+                TreatProjections::ForLookup,
+            ) {
                 let mut potential_candidates = Vec::new();
                 let mut explicitly_negative = Vec::new();
                 for candidate in candidates {
@@ -2660,8 +2664,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         })
                         .any(|imp_did| {
                             let imp = self.tcx.impl_trait_ref(imp_did).unwrap().subst_identity();
-                            let imp_simp =
-                                simplify_type(self.tcx, imp.self_ty(), TreatParams::AsPlaceholder);
+                            let imp_simp = simplify_type(
+                                self.tcx,
+                                imp.self_ty(),
+                                TreatParams::ForLookup,
+                                TreatProjections::ForLookup,
+                            );
                             imp_simp.map_or(false, |s| s == simp_rcvr_ty)
                         })
                     {
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 16306bef42e..bbab8a62a2b 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -26,7 +26,7 @@ use rustc_middle::middle::exported_symbols::{
 use rustc_middle::mir::interpret;
 use rustc_middle::traits::specialization_graph;
 use rustc_middle::ty::codec::TyEncoder;
-use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
+use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams, TreatProjections};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, SymbolName, Ty, TyCtxt};
 use rustc_middle::util::common::to_readable_str;
@@ -1858,7 +1858,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     let simplified_self_ty = fast_reject::simplify_type(
                         self.tcx,
                         trait_ref.self_ty(),
-                        TreatParams::AsInfer,
+                        TreatParams::AsCandidateKey,
+                        TreatProjections::AsCandidateKey,
                     );
 
                     fx_hash_map
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 5215e3db798..b34651c3ea7 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -1999,6 +1999,9 @@ impl BorrowKind {
 }
 
 impl BinOp {
+    /// The checkable operators are those whose overflow checking behavior is controlled by
+    /// -Coverflow-checks option. The remaining operators have either no overflow conditions (e.g.,
+    /// BitAnd, BitOr, BitXor) or are always checked for overflow (e.g., Div, Rem).
     pub fn is_checkable(self) -> bool {
         use self::BinOp::*;
         matches!(self, Add | Sub | Mul | Shl | Shr)
diff --git a/compiler/rustc_middle/src/ty/fast_reject.rs b/compiler/rustc_middle/src/ty/fast_reject.rs
index 59deade0a07..ee505742be9 100644
--- a/compiler/rustc_middle/src/ty/fast_reject.rs
+++ b/compiler/rustc_middle/src/ty/fast_reject.rs
@@ -51,15 +51,35 @@ pub enum SimplifiedType {
 /// generic parameters as if they were inference variables in that case.
 #[derive(PartialEq, Eq, Debug, Clone, Copy)]
 pub enum TreatParams {
-    /// Treat parameters as placeholders in the given environment.
+    /// Treat parameters as infer vars. This is the correct mode for caching
+    /// an impl's type for lookup.
+    AsCandidateKey,
+    /// Treat parameters as placeholders in the given environment. This is the
+    /// correct mode for *lookup*, as during candidate selection.
+    ForLookup,
+}
+
+/// During fast-rejection, we have the choice of treating projection types
+/// as either simplifyable or not, depending on whether we expect the projection
+/// to be normalized/rigid.
+#[derive(PartialEq, Eq, Debug, Clone, Copy)]
+pub enum TreatProjections {
+    /// In candidates, we may be able to normalize the projection
+    /// after instantiating the candidate and equating it with a goal.
     ///
-    /// Note that this also causes us to treat projections as if they were
-    /// placeholders. This is only correct if the given projection cannot
-    /// be normalized in the current context. Even if normalization fails,
-    /// it may still succeed later if the projection contains any inference
-    /// variables.
-    AsPlaceholder,
-    AsInfer,
+    /// We must assume that the `impl<T> Trait<T> for <T as Id>::This`
+    /// can apply to all self types so we don't return a simplified type
+    /// for `<T as Id>::This`.
+    AsCandidateKey,
+    /// In the old solver we don't try to normalize projections
+    /// when looking up impls and only access them by using the
+    /// current self type. This means that if the self type is
+    /// a projection which could later be normalized, we must not
+    /// treat it as rigid.
+    ForLookup,
+    /// We can treat projections in the self type as opaque as
+    /// we separately look up impls for the normalized self type.
+    NextSolverLookup,
 }
 
 /// Tries to simplify a type by only returning the outermost injective¹ layer, if one exists.
@@ -87,6 +107,7 @@ pub fn simplify_type<'tcx>(
     tcx: TyCtxt<'tcx>,
     ty: Ty<'tcx>,
     treat_params: TreatParams,
+    treat_projections: TreatProjections,
 ) -> Option<SimplifiedType> {
     match *ty.kind() {
         ty::Bool => Some(BoolSimplifiedType),
@@ -115,19 +136,13 @@ pub fn simplify_type<'tcx>(
         ty::FnPtr(f) => Some(FunctionSimplifiedType(f.skip_binder().inputs().len())),
         ty::Placeholder(..) => Some(PlaceholderSimplifiedType),
         ty::Param(_) => match treat_params {
-            TreatParams::AsPlaceholder => Some(PlaceholderSimplifiedType),
-            TreatParams::AsInfer => None,
+            TreatParams::ForLookup => Some(PlaceholderSimplifiedType),
+            TreatParams::AsCandidateKey => None,
         },
-        ty::Alias(..) => match treat_params {
-            // When treating `ty::Param` as a placeholder, projections also
-            // don't unify with anything else as long as they are fully normalized.
-            //
-            // We will have to be careful with lazy normalization here.
-            TreatParams::AsPlaceholder if !ty.has_non_region_infer() => {
-                debug!("treating `{}` as a placeholder", ty);
-                Some(PlaceholderSimplifiedType)
-            }
-            TreatParams::AsPlaceholder | TreatParams::AsInfer => None,
+        ty::Alias(..) => match treat_projections {
+            TreatProjections::ForLookup if !ty.needs_infer() => Some(PlaceholderSimplifiedType),
+            TreatProjections::NextSolverLookup => Some(PlaceholderSimplifiedType),
+            TreatProjections::AsCandidateKey | TreatProjections::ForLookup => None,
         },
         ty::Foreign(def_id) => Some(ForeignSimplifiedType(def_id)),
         ty::Bound(..) | ty::Infer(_) | ty::Error(_) => None,
@@ -295,8 +310,8 @@ impl DeepRejectCtxt {
             // Depending on the value of `treat_obligation_params`, we either
             // treat generic parameters like placeholders or like inference variables.
             ty::Param(_) => match self.treat_obligation_params {
-                TreatParams::AsPlaceholder => false,
-                TreatParams::AsInfer => true,
+                TreatParams::ForLookup => false,
+                TreatParams::AsCandidateKey => true,
             },
 
             ty::Infer(_) => true,
@@ -333,8 +348,8 @@ impl DeepRejectCtxt {
         let k = impl_ct.kind();
         match obligation_ct.kind() {
             ty::ConstKind::Param(_) => match self.treat_obligation_params {
-                TreatParams::AsPlaceholder => false,
-                TreatParams::AsInfer => true,
+                TreatParams::ForLookup => false,
+                TreatParams::AsCandidateKey => true,
             },
 
             // As we don't necessarily eagerly evaluate constants,
diff --git a/compiler/rustc_middle/src/ty/trait_def.rs b/compiler/rustc_middle/src/ty/trait_def.rs
index 649a58c9170..bf2b121f704 100644
--- a/compiler/rustc_middle/src/ty/trait_def.rs
+++ b/compiler/rustc_middle/src/ty/trait_def.rs
@@ -1,5 +1,5 @@
 use crate::traits::specialization_graph;
-use crate::ty::fast_reject::{self, SimplifiedType, TreatParams};
+use crate::ty::fast_reject::{self, SimplifiedType, TreatParams, TreatProjections};
 use crate::ty::visit::TypeVisitableExt;
 use crate::ty::{Ident, Ty, TyCtxt};
 use hir::def_id::LOCAL_CRATE;
@@ -118,16 +118,32 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Iterate over every impl that could possibly match the self type `self_ty`.
     ///
     /// `trait_def_id` MUST BE the `DefId` of a trait.
-    pub fn for_each_relevant_impl<F: FnMut(DefId)>(
+    pub fn for_each_relevant_impl(
         self,
         trait_def_id: DefId,
         self_ty: Ty<'tcx>,
-        mut f: F,
+        f: impl FnMut(DefId),
     ) {
-        let _: Option<()> = self.find_map_relevant_impl(trait_def_id, self_ty, |did| {
-            f(did);
-            None
-        });
+        self.for_each_relevant_impl_treating_projections(
+            trait_def_id,
+            self_ty,
+            TreatProjections::ForLookup,
+            f,
+        )
+    }
+
+    pub fn for_each_relevant_impl_treating_projections(
+        self,
+        trait_def_id: DefId,
+        self_ty: Ty<'tcx>,
+        treat_projections: TreatProjections,
+        mut f: impl FnMut(DefId),
+    ) {
+        let _: Option<()> =
+            self.find_map_relevant_impl(trait_def_id, self_ty, treat_projections, |did| {
+                f(did);
+                None
+            });
     }
 
     /// `trait_def_id` MUST BE the `DefId` of a trait.
@@ -137,7 +153,12 @@ impl<'tcx> TyCtxt<'tcx> {
         self_ty: Ty<'tcx>,
     ) -> impl Iterator<Item = DefId> + 'tcx {
         let impls = self.trait_impls_of(trait_def_id);
-        if let Some(simp) = fast_reject::simplify_type(self, self_ty, TreatParams::AsInfer) {
+        if let Some(simp) = fast_reject::simplify_type(
+            self,
+            self_ty,
+            TreatParams::AsCandidateKey,
+            TreatProjections::AsCandidateKey,
+        ) {
             if let Some(impls) = impls.non_blanket_impls.get(&simp) {
                 return impls.iter().copied();
             }
@@ -150,11 +171,12 @@ impl<'tcx> TyCtxt<'tcx> {
     /// the first non-none value.
     ///
     /// `trait_def_id` MUST BE the `DefId` of a trait.
-    pub fn find_map_relevant_impl<T, F: FnMut(DefId) -> Option<T>>(
+    pub fn find_map_relevant_impl<T>(
         self,
         trait_def_id: DefId,
         self_ty: Ty<'tcx>,
-        mut f: F,
+        treat_projections: TreatProjections,
+        mut f: impl FnMut(DefId) -> Option<T>,
     ) -> Option<T> {
         // FIXME: This depends on the set of all impls for the trait. That is
         // unfortunate wrt. incremental compilation.
@@ -169,14 +191,13 @@ impl<'tcx> TyCtxt<'tcx> {
             }
         }
 
-        // Note that we're using `TreatParams::AsPlaceholder` to query `non_blanket_impls` while using
-        // `TreatParams::AsInfer` while actually adding them.
-        //
         // This way, when searching for some impl for `T: Trait`, we do not look at any impls
         // whose outer level is not a parameter or projection. Especially for things like
         // `T: Clone` this is incredibly useful as we would otherwise look at all the impls
         // of `Clone` for `Option<T>`, `Vec<T>`, `ConcreteType` and so on.
-        if let Some(simp) = fast_reject::simplify_type(self, self_ty, TreatParams::AsPlaceholder) {
+        if let Some(simp) =
+            fast_reject::simplify_type(self, self_ty, TreatParams::ForLookup, treat_projections)
+        {
             if let Some(impls) = impls.non_blanket_impls.get(&simp) {
                 for &impl_def_id in impls {
                     if let result @ Some(_) = f(impl_def_id) {
@@ -237,9 +258,12 @@ pub(super) fn trait_impls_of_provider(tcx: TyCtxt<'_>, trait_id: DefId) -> Trait
             continue;
         }
 
-        if let Some(simplified_self_ty) =
-            fast_reject::simplify_type(tcx, impl_self_ty, TreatParams::AsInfer)
-        {
+        if let Some(simplified_self_ty) = fast_reject::simplify_type(
+            tcx,
+            impl_self_ty,
+            TreatParams::AsCandidateKey,
+            TreatProjections::AsCandidateKey,
+        ) {
             impls.non_blanket_impls.entry(simplified_self_ty).or_default().push(impl_def_id);
         } else {
             impls.blanket_impls.push(impl_def_id);
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index 8b5469743da..b0f6127baa5 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -2,6 +2,7 @@
 
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::mir;
+use crate::ty::fast_reject::TreatProjections;
 use crate::ty::layout::IntegerExt;
 use crate::ty::{
     self, FallibleTypeFolder, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
@@ -363,14 +364,20 @@ impl<'tcx> TyCtxt<'tcx> {
         self.ensure().coherent_trait(drop_trait);
 
         let ty = self.type_of(adt_did).subst_identity();
-        let (did, constness) = self.find_map_relevant_impl(drop_trait, ty, |impl_did| {
-            if let Some(item_id) = self.associated_item_def_ids(impl_did).first() {
-                if validate(self, impl_did).is_ok() {
-                    return Some((*item_id, self.constness(impl_did)));
+        let (did, constness) = self.find_map_relevant_impl(
+            drop_trait,
+            ty,
+            // FIXME: This could also be some other mode, like "unexpected"
+            TreatProjections::ForLookup,
+            |impl_did| {
+                if let Some(item_id) = self.associated_item_def_ids(impl_did).first() {
+                    if validate(self, impl_did).is_ok() {
+                        return Some((*item_id, self.constness(impl_did)));
+                    }
                 }
-            }
-            None
-        })?;
+                None
+            },
+        )?;
 
         Some(ty::Destructor { did, constness })
     }
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 5ef3e13eff8..c8d371dd084 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -2215,7 +2215,7 @@ impl CheckAttrVisitor<'_> {
             // `fn(TokenStream) -> TokenStream` after some substitution of generic arguments.
             //
             // Properly checking this means pulling in additional `rustc` crates, so we don't.
-            let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsInfer };
+            let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsCandidateKey };
 
             if sig.abi != Abi::Rust {
                 tcx.sess.emit_err(errors::ProcMacroInvalidAbi {
diff --git a/compiler/rustc_trait_selection/src/solve/assembly.rs b/compiler/rustc_trait_selection/src/solve/assembly.rs
index 72b1b35e79b..891ea0cdebe 100644
--- a/compiler/rustc_trait_selection/src/solve/assembly.rs
+++ b/compiler/rustc_trait_selection/src/solve/assembly.rs
@@ -8,6 +8,7 @@ use rustc_hir::def_id::DefId;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::util::elaborate_predicates;
 use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, MaybeCause, QueryResult};
+use rustc_middle::ty::fast_reject::TreatProjections;
 use rustc_middle::ty::TypeFoldable;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use std::fmt::Debug;
@@ -299,9 +300,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         candidates: &mut Vec<Candidate<'tcx>>,
     ) {
         let tcx = self.tcx();
-        tcx.for_each_relevant_impl(
+        tcx.for_each_relevant_impl_treating_projections(
             goal.predicate.trait_def_id(tcx),
             goal.predicate.self_ty(),
+            TreatProjections::NextSolverLookup,
             |impl_def_id| match G::consider_impl_candidate(self, goal, impl_def_id) {
                 Ok(result) => candidates
                     .push(Candidate { source: CandidateSource::Impl(impl_def_id), result }),
diff --git a/compiler/rustc_trait_selection/src/solve/project_goals.rs b/compiler/rustc_trait_selection/src/solve/project_goals.rs
index e206658b4b9..dbb8e722c8f 100644
--- a/compiler/rustc_trait_selection/src/solve/project_goals.rs
+++ b/compiler/rustc_trait_selection/src/solve/project_goals.rs
@@ -184,7 +184,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
 
         let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx);
         let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
-        let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
+        let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::ForLookup };
         if iter::zip(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs)
             .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
         {
diff --git a/compiler/rustc_trait_selection/src/solve/trait_goals.rs b/compiler/rustc_trait_selection/src/solve/trait_goals.rs
index 0669975d638..7878539817c 100644
--- a/compiler/rustc_trait_selection/src/solve/trait_goals.rs
+++ b/compiler/rustc_trait_selection/src/solve/trait_goals.rs
@@ -8,7 +8,7 @@ use rustc_hir::LangItem;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::util::supertraits;
 use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, QueryResult};
-use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
+use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams, TreatProjections};
 use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
 use rustc_middle::ty::{TraitPredicate, TypeVisitableExt};
 use rustc_span::DUMMY_SP;
@@ -36,7 +36,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
         let tcx = ecx.tcx();
 
         let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
-        let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
+        let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::ForLookup };
         if iter::zip(goal.predicate.trait_ref.substs, impl_trait_ref.skip_binder().substs)
             .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
         {
@@ -135,9 +135,15 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
         // currently instead lint patterns which can be used to
         // exploit this unsoundness on stable, see #93367 for
         // more details.
+        //
+        // Using `TreatProjections::NextSolverLookup` is fine here because
+        // `instantiate_constituent_tys_for_auto_trait` returns nothing for
+        // projection types anyways. So it doesn't really matter what we do
+        // here, and this is faster.
         if let Some(def_id) = ecx.tcx().find_map_relevant_impl(
             goal.predicate.def_id(),
             goal.predicate.self_ty(),
+            TreatProjections::NextSolverLookup,
             Some,
         ) {
             debug!(?def_id, ?goal, "disqualified auto-trait implementation");
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index 6b688c322c7..96a4b76af55 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -75,7 +75,7 @@ pub fn overlapping_impls(
     // Before doing expensive operations like entering an inference context, do
     // a quick check via fast_reject to tell if the impl headers could possibly
     // unify.
-    let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsInfer };
+    let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsCandidateKey };
     let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
     let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
     let may_overlap = match (impl1_ref, impl2_ref) {
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 704b0d0bd1c..41ffaeeac1c 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -32,6 +32,7 @@ use rustc_infer::infer::{InferOk, TypeTrace};
 use rustc_middle::traits::select::OverflowError;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
+use rustc_middle::ty::fast_reject::TreatProjections;
 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::print::{with_forced_trimmed_paths, FmtPrinter, Print};
 use rustc_middle::ty::{
@@ -1799,12 +1800,17 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     })
                     .and_then(|(trait_assoc_item, id)| {
                         let trait_assoc_ident = trait_assoc_item.ident(self.tcx);
-                        self.tcx.find_map_relevant_impl(id, proj.projection_ty.self_ty(), |did| {
-                            self.tcx
-                                .associated_items(did)
-                                .in_definition_order()
-                                .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
-                        })
+                        self.tcx.find_map_relevant_impl(
+                            id,
+                            proj.projection_ty.self_ty(),
+                            TreatProjections::ForLookup,
+                            |did| {
+                                self.tcx
+                                    .associated_items(did)
+                                    .in_definition_order()
+                                    .find(|assoc| assoc.ident(self.tcx) == trait_assoc_ident)
+                            },
+                        )
                     })
                     .and_then(|item| match self.tcx.hir().get_if_local(item.def_id) {
                         Some(
@@ -2176,7 +2182,12 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         trait_ref: &ty::PolyTraitRef<'tcx>,
     ) -> bool {
         let get_trait_impl = |trait_def_id| {
-            self.tcx.find_map_relevant_impl(trait_def_id, trait_ref.skip_binder().self_ty(), Some)
+            self.tcx.find_map_relevant_impl(
+                trait_def_id,
+                trait_ref.skip_binder().self_ty(),
+                TreatProjections::ForLookup,
+                Some,
+            )
         };
         let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
         let traits_with_same_path: std::collections::BTreeSet<_> = self
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index e91057356a2..3182af989f0 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -9,6 +9,7 @@ use hir::LangItem;
 use rustc_hir as hir;
 use rustc_infer::traits::ObligationCause;
 use rustc_infer::traits::{Obligation, SelectionError, TraitObligation};
+use rustc_middle::ty::fast_reject::TreatProjections;
 use rustc_middle::ty::{self, Ty, TypeVisitableExt};
 use rustc_target::spec::abi::Abi;
 
@@ -783,6 +784,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 let relevant_impl = self.tcx().find_map_relevant_impl(
                     self.tcx().require_lang_item(LangItem::Drop, None),
                     obligation.predicate.skip_binder().trait_ref.self_ty(),
+                    TreatProjections::ForLookup,
                     Some,
                 );
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index d7ce0078124..38cdaddc1e7 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2558,7 +2558,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         // We can avoid creating type variables and doing the full
         // substitution if we find that any of the input types, when
         // simplified, do not match.
-        let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
+        let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::ForLookup };
         iter::zip(obligation.predicate.skip_binder().trait_ref.substs, impl_trait_ref.substs)
             .any(|(obl, imp)| !drcx.generic_args_may_unify(obl, imp))
     }
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
index 61ed9ef2ec1..cd665d9471d 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
@@ -3,7 +3,7 @@ use super::OverlapError;
 use crate::traits;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
+use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams, TreatProjections};
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
 
 pub use rustc_middle::traits::specialization_graph::*;
@@ -49,8 +49,12 @@ impl<'tcx> ChildrenExt<'tcx> for Children {
     /// Insert an impl into this set of children without comparing to any existing impls.
     fn insert_blindly(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId) {
         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap().skip_binder();
-        if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer)
-        {
+        if let Some(st) = fast_reject::simplify_type(
+            tcx,
+            trait_ref.self_ty(),
+            TreatParams::AsCandidateKey,
+            TreatProjections::AsCandidateKey,
+        ) {
             debug!("insert_blindly: impl_def_id={:?} st={:?}", impl_def_id, st);
             self.non_blanket_impls.entry(st).or_default().push(impl_def_id)
         } else {
@@ -65,8 +69,12 @@ impl<'tcx> ChildrenExt<'tcx> for Children {
     fn remove_existing(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId) {
         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap().skip_binder();
         let vec: &mut Vec<DefId>;
-        if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer)
-        {
+        if let Some(st) = fast_reject::simplify_type(
+            tcx,
+            trait_ref.self_ty(),
+            TreatParams::AsCandidateKey,
+            TreatProjections::AsCandidateKey,
+        ) {
             debug!("remove_existing: impl_def_id={:?} st={:?}", impl_def_id, st);
             vec = self.non_blanket_impls.get_mut(&st).unwrap();
         } else {
@@ -302,7 +310,12 @@ impl<'tcx> GraphExt<'tcx> for Graph {
 
         let mut parent = trait_def_id;
         let mut last_lint = None;
-        let simplified = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer);
+        let simplified = fast_reject::simplify_type(
+            tcx,
+            trait_ref.self_ty(),
+            TreatParams::AsCandidateKey,
+            TreatProjections::AsCandidateKey,
+        );
 
         // Descend the specialization tree, where `parent` is the current parent node.
         loop {