5 files changed, 23 insertions, 1 deletions
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index ea81d4465fb..ea5e21901c5 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -2127,4 +2127,9 @@ rustc_queries! {
     ) -> Result<(), ErrorGuaranteed> {
         desc { |tcx| "checking assoc const `{}` has the same type as trait item", tcx.def_path_str(key.0.to_def_id()) }
     }
+
+    query deduced_param_attrs(def_id: DefId) -> &'tcx [ty::DeducedParamAttrs] {
+        desc { |tcx| "deducing parameter attributes for {}", tcx.def_path_str(def_id) }
+        separate_provide_extern
+    }
 }
diff --git a/compiler/rustc_middle/src/ty/codec.rs b/compiler/rustc_middle/src/ty/codec.rs
index 51137c52659..14ec88b7e0d 100644
--- a/compiler/rustc_middle/src/ty/codec.rs
+++ b/compiler/rustc_middle/src/ty/codec.rs
@@ -455,6 +455,7 @@ impl_arena_copy_decoder! {<'tcx>
     rustc_span::def_id::DefId,
     rustc_span::def_id::LocalDefId,
     (rustc_middle::middle::exported_symbols::ExportedSymbol<'tcx>, rustc_middle::middle::exported_symbols::SymbolExportInfo),
+    ty::DeducedParamAttrs,
 }
 
 #[macro_export]
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 03bb7e54fd5..0816a5cb8f1 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -2954,6 +2954,21 @@ impl<'tcx> TyCtxtAt<'tcx> {
     }
 }
 
+/// Parameter attributes that can only be determined by examining the body of a function instead
+/// of just its signature.
+///
+/// These can be useful for optimization purposes when a function is directly called. We compute
+/// them and store them into the crate metadata so that downstream crates can make use of them.
+///
+/// Right now, we only have `read_only`, but `no_capture` and `no_alias` might be useful in the
+/// future.
+#[derive(Clone, Copy, PartialEq, Debug, Default, TyDecodable, TyEncodable, HashStable)]
+pub struct DeducedParamAttrs {
+    /// The parameter is marked immutable in the function and contains no `UnsafeCell` (i.e. its
+    /// type is freeze).
+    pub read_only: bool,
+}
+
 // We are comparing types with different invariant lifetimes, so `ptr::eq`
 // won't work for us.
 fn ptr_eq<T, U>(t: *const T, u: *const U) -> bool {
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index a92bb0f2e55..4400ff12de0 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -78,7 +78,7 @@ pub use self::consts::{
 };
 pub use self::context::{
     tls, CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations,
-    CtxtInterners, DelaySpanBugEmitted, FreeRegionInfo, GeneratorDiagnosticData,
+    CtxtInterners, DeducedParamAttrs, DelaySpanBugEmitted, FreeRegionInfo, GeneratorDiagnosticData,
     GeneratorInteriorTypeCause, GlobalCtxt, Lift, OnDiskCache, TyCtxt, TypeckResults, UserType,
     UserTypeAnnotationIndex,
 };
diff --git a/compiler/rustc_middle/src/ty/parameterized.rs b/compiler/rustc_middle/src/ty/parameterized.rs
index f289f2265a2..e1e705a922f 100644
--- a/compiler/rustc_middle/src/ty/parameterized.rs
+++ b/compiler/rustc_middle/src/ty/parameterized.rs
@@ -61,6 +61,7 @@ trivially_parameterized_over_tcx! {
     crate::middle::resolve_lifetime::ObjectLifetimeDefault,
     crate::mir::ConstQualifs,
     ty::AssocItemContainer,
+    ty::DeducedParamAttrs,
     ty::Generics,
     ty::ImplPolarity,
     ty::ReprOptions,