diff --git a/compiler/rustc_ast/src/token.rs b/compiler/rustc_ast/src/token.rs
index 5ccc7d51066d9..c17020ed6632e 100644
--- a/compiler/rustc_ast/src/token.rs
+++ b/compiler/rustc_ast/src/token.rs
@@ -11,6 +11,7 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::Lrc;
 use rustc_macros::HashStable_Generic;
 use rustc_span::symbol::{kw, sym};
+#[allow(clippy::useless_attribute)] // FIXME: following use of `hidden_glob_reexports` incorrectly triggers `useless_attribute` lint.
 #[allow(hidden_glob_reexports)]
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::{edition::Edition, ErrorGuaranteed, Span, DUMMY_SP};
diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index f89c8c9f836bf..f9f7e0d4e3754 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -326,6 +326,7 @@ pub unsafe fn create_module<'ll>(
     //
     // On the wasm targets it will get hooked up to the "producer" sections
     // `processed-by` information.
+    #[allow(clippy::option_env_unwrap)]
     let rustc_producer =
         format!("rustc version {}", option_env!("CFG_VERSION").expect("CFG_VERSION"));
     let name_metadata = llvm::LLVMMDStringInContext(
diff --git a/compiler/rustc_const_eval/src/interpret/intern.rs b/compiler/rustc_const_eval/src/interpret/intern.rs
index 17bb59aae8f17..6775a17987206 100644
--- a/compiler/rustc_const_eval/src/interpret/intern.rs
+++ b/compiler/rustc_const_eval/src/interpret/intern.rs
@@ -291,7 +291,9 @@ pub fn intern_const_alloc_for_constprop<
         return Ok(());
     }
     // Move allocation to `tcx`.
-    for _ in intern_shallow(ecx, alloc_id, Mutability::Not).map_err(|()| err_ub!(DeadLocal))? {
+    if let Some(_) =
+        (intern_shallow(ecx, alloc_id, Mutability::Not).map_err(|()| err_ub!(DeadLocal))?).next()
+    {
         // We are not doing recursive interning, so we don't currently support provenance.
         // (If this assertion ever triggers, we should just implement a
         // proper recursive interning loop -- or just call `intern_const_alloc_recursive`.
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index d8cfceab460a0..9db8bddfae5f9 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -2201,7 +2201,7 @@ impl<D: Decoder> Decodable<D> for EncodedMetadata {
         let mmap = if len > 0 {
             let mut mmap = MmapMut::map_anon(len).unwrap();
             for _ in 0..len {
-                (&mut mmap[..]).write(&[d.read_u8()]).unwrap();
+                (&mut mmap[..]).write_all(&[d.read_u8()]).unwrap();
             }
             mmap.flush().unwrap();
             Some(mmap.make_read_only().unwrap())
diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index 5043bd855ccb9..b56bdb86129bd 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -114,20 +114,16 @@ impl<'hir> Iterator for ParentOwnerIterator<'hir> {
         if self.current_id == CRATE_HIR_ID {
             return None;
         }
-        loop {
-            // There are nodes that do not have entries, so we need to skip them.
-            let parent_id = self.map.def_key(self.current_id.owner.def_id).parent;
 
-            let parent_id = parent_id.map_or(CRATE_OWNER_ID, |local_def_index| {
-                let def_id = LocalDefId { local_def_index };
-                self.map.tcx.local_def_id_to_hir_id(def_id).owner
-            });
-            self.current_id = HirId::make_owner(parent_id.def_id);
+        let parent_id = self.map.def_key(self.current_id.owner.def_id).parent;
+        let parent_id = parent_id.map_or(CRATE_OWNER_ID, |local_def_index| {
+            let def_id = LocalDefId { local_def_index };
+            self.map.tcx.local_def_id_to_hir_id(def_id).owner
+        });
+        self.current_id = HirId::make_owner(parent_id.def_id);
 
-            // If this `HirId` doesn't have an entry, skip it and look for its `parent_id`.
-            let node = self.map.tcx.hir_owner_node(self.current_id.owner);
-            return Some((self.current_id.owner, node));
-        }
+        let node = self.map.tcx.hir_owner_node(self.current_id.owner);
+        return Some((self.current_id.owner, node));
     }
 }
 
diff --git a/compiler/rustc_middle/src/mir/interpret/mod.rs b/compiler/rustc_middle/src/mir/interpret/mod.rs
index f9edbb3c5ae21..ad11d3c4d6164 100644
--- a/compiler/rustc_middle/src/mir/interpret/mod.rs
+++ b/compiler/rustc_middle/src/mir/interpret/mod.rs
@@ -671,11 +671,11 @@ pub fn read_target_uint(endianness: Endian, mut source: &[u8]) -> Result<u128, i
     // So we do not read exactly 16 bytes into the u128, just the "payload".
     let uint = match endianness {
         Endian::Little => {
-            source.read(&mut buf)?;
+            source.read_exact(&mut buf)?;
             Ok(u128::from_le_bytes(buf))
         }
         Endian::Big => {
-            source.read(&mut buf[16 - source.len()..])?;
+            source.read_exact(&mut buf[16 - source.len()..])?;
             Ok(u128::from_be_bytes(buf))
         }
     };
diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs
index e7808ff880b57..d2cbbf9be32c3 100644
--- a/compiler/rustc_mir_build/src/build/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/build/matches/mod.rs
@@ -229,7 +229,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         span: Span,
         scrutinee_span: Span,
     ) -> BlockAnd<()> {
-        let scrutinee_span = scrutinee_span;
         let scrutinee_place =
             unpack!(block = self.lower_scrutinee(block, scrutinee_id, scrutinee_span));
 
diff --git a/compiler/stable_mir/src/mir/alloc.rs b/compiler/stable_mir/src/mir/alloc.rs
index c780042ff261c..b2f296387a66b 100644
--- a/compiler/stable_mir/src/mir/alloc.rs
+++ b/compiler/stable_mir/src/mir/alloc.rs
@@ -57,11 +57,11 @@ pub(crate) fn read_target_uint(mut bytes: &[u8]) -> Result<u128, Error> {
     let mut buf = [0u8; std::mem::size_of::<u128>()];
     match MachineInfo::target_endianess() {
         Endian::Little => {
-            bytes.read(&mut buf)?;
+            bytes.read_exact(&mut buf)?;
             Ok(u128::from_le_bytes(buf))
         }
         Endian::Big => {
-            bytes.read(&mut buf[16 - bytes.len()..])?;
+            bytes.read_exact(&mut buf[16 - bytes.len()..])?;
             Ok(u128::from_be_bytes(buf))
         }
     }
@@ -72,11 +72,11 @@ pub(crate) fn read_target_int(mut bytes: &[u8]) -> Result<i128, Error> {
     let mut buf = [0u8; std::mem::size_of::<i128>()];
     match MachineInfo::target_endianess() {
         Endian::Little => {
-            bytes.read(&mut buf)?;
+            bytes.read_exact(&mut buf)?;
             Ok(i128::from_le_bytes(buf))
         }
         Endian::Big => {
-            bytes.read(&mut buf[16 - bytes.len()..])?;
+            bytes.read_exact(&mut buf[16 - bytes.len()..])?;
             Ok(i128::from_be_bytes(buf))
         }
     }
diff --git a/library/std/src/io/buffered/bufreader.rs b/library/std/src/io/buffered/bufreader.rs
index 83db332ee2558..acaa7e9228ecc 100644
--- a/library/std/src/io/buffered/bufreader.rs
+++ b/library/std/src/io/buffered/bufreader.rs
@@ -328,10 +328,9 @@ impl<R: ?Sized + Read> Read for BufReader<R> {
             self.discard_buffer();
             return self.inner.read_vectored(bufs);
         }
-        let nread = {
-            let mut rem = self.fill_buf()?;
-            rem.read_vectored(bufs)?
-        };
+        let mut rem = self.fill_buf()?;
+        let nread = rem.read_vectored(bufs)?;
+
         self.consume(nread);
         Ok(nread)
     }