diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 27b36c23daf46..7dd920c7e39bd 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -189,7 +189,7 @@ pub(super) trait LazyDecoder: BlobDecoder {
         self.read_lazy_offset_then(|pos| LazyArray::from_position_and_num_elems(pos, len))
     }
 
-    fn read_lazy_table<I, T>(&mut self, width: usize, len: usize) -> LazyTable<I, T> {
+    fn read_lazy_table<Ie, Id, T>(&mut self, width: usize, len: usize) -> LazyTable<Ie, Id, T> {
         self.read_lazy_offset_then(|pos| LazyTable::from_position_and_encoded_size(pos, width, len))
     }
 
@@ -667,7 +667,7 @@ impl<D: LazyDecoder, T> Decodable<D> for LazyArray<T> {
     }
 }
 
-impl<I: Idx, D: LazyDecoder, T> Decodable<D> for LazyTable<I, T> {
+impl<Ie: Idx, Id: Idx, D: LazyDecoder, T> Decodable<D> for LazyTable<Ie, Id, T> {
     fn decode(decoder: &mut D) -> Self {
         let width = decoder.read_usize();
         let len = decoder.read_usize();
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index afa5646bea80e..40b61a52d2310 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -133,7 +133,7 @@ impl<'a, 'tcx, T> Encodable<EncodeContext<'a, 'tcx>> for LazyArray<T> {
     }
 }
 
-impl<'a, 'tcx, I, T> Encodable<EncodeContext<'a, 'tcx>> for LazyTable<I, T> {
+impl<'a, 'tcx, Ie, Id, T> Encodable<EncodeContext<'a, 'tcx>> for LazyTable<Ie, Id, T> {
     fn encode(&self, e: &mut EncodeContext<'a, 'tcx>) {
         e.emit_usize(self.width);
         e.emit_usize(self.len);
@@ -547,7 +547,9 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         self.lazy(DefPathHashMapRef::BorrowedFromTcx(self.tcx.def_path_hash_to_def_index_map()))
     }
 
-    fn encode_source_map(&mut self) -> LazyTable<u32, Option<LazyValue<rustc_span::SourceFile>>> {
+    fn encode_source_map(
+        &mut self,
+    ) -> LazyTable<u32, u32, Option<LazyValue<rustc_span::SourceFile>>> {
         let source_map = self.tcx.sess.source_map();
         let all_source_files = source_map.files();
 
@@ -2004,9 +2006,9 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
     }
 
     fn encode_hygiene(&mut self) -> (SyntaxContextTable, ExpnDataTable, ExpnHashTable) {
-        let mut syntax_contexts: TableBuilder<_, _> = Default::default();
-        let mut expn_data_table: TableBuilder<_, _> = Default::default();
-        let mut expn_hash_table: TableBuilder<_, _> = Default::default();
+        let mut syntax_contexts: TableBuilder<_, _, _> = Default::default();
+        let mut expn_data_table: TableBuilder<_, _, _> = Default::default();
+        let mut expn_hash_table: TableBuilder<_, _, _> = Default::default();
 
         HygieneEncodeContext::encode(
             &Rc::clone(&self.hygiene_ctxt),
diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index e3f3257acc137..b70151604f679 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -48,6 +48,7 @@ use rustc_target::spec::{PanicStrategy, TargetTuple};
 use table::TableBuilder;
 
 use crate::eii::EiiMapEncodedKeyValue;
+use crate::rmeta::table::TableBuilderSingleIdx;
 
 mod decoder;
 mod def_path_hash_map;
@@ -143,22 +144,27 @@ impl<T> LazyArray<T> {
 /// Random-access table (i.e. offering constant-time `get`/`set`), similar to
 /// `LazyArray<T>`, but without requiring encoding or decoding all the values
 /// eagerly and in-order.
-struct LazyTable<I, T> {
+///
+/// `IdxEncode` - is a type of index that is used to write to the table,
+/// `IdxDecode` - is a type of index that is used to read from the table.
+struct LazyTable<IdxEncode, IdxDecode, T> {
     position: NonZero<usize>,
     /// The encoded size of the elements of a table is selected at runtime to drop
     /// trailing zeroes. This is the number of bytes used for each table element.
     width: usize,
     /// How many elements are in the table.
     len: usize,
-    _marker: PhantomData<fn(I) -> T>,
+    _marker: PhantomData<fn(IdxEncode, IdxDecode) -> T>,
 }
 
-impl<I, T> LazyTable<I, T> {
+type LazyTableSingleIdx<TIdx, TValue> = LazyTable<TIdx, TIdx, TValue>;
+
+impl<Ie, Id, T> LazyTable<Ie, Id, T> {
     fn from_position_and_encoded_size(
         position: NonZero<usize>,
         width: usize,
         len: usize,
-    ) -> LazyTable<I, T> {
+    ) -> LazyTable<Ie, Id, T> {
         LazyTable { position, width, len, _marker: PhantomData }
     }
 }
@@ -177,8 +183,8 @@ impl<T> Clone for LazyArray<T> {
     }
 }
 
-impl<I, T> Copy for LazyTable<I, T> {}
-impl<I, T> Clone for LazyTable<I, T> {
+impl<Ie, Id, T> Copy for LazyTable<Ie, Id, T> {}
+impl<Ie, Id, T> Clone for LazyTable<Ie, Id, T> {
     fn clone(&self) -> Self {
         *self
     }
@@ -199,9 +205,9 @@ enum LazyState {
     Previous(NonZero<usize>),
 }
 
-type SyntaxContextTable = LazyTable<u32, Option<LazyValue<SyntaxContextKey>>>;
-type ExpnDataTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnData>>>;
-type ExpnHashTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnHash>>>;
+type SyntaxContextTable = LazyTableSingleIdx<u32, Option<LazyValue<SyntaxContextKey>>>;
+type ExpnDataTable = LazyTableSingleIdx<ExpnIndex, Option<LazyValue<ExpnData>>>;
+type ExpnHashTable = LazyTableSingleIdx<ExpnIndex, Option<LazyValue<ExpnHash>>>;
 
 #[derive(MetadataEncodable, LazyDecodable)]
 pub(crate) struct ProcMacroData {
@@ -305,7 +311,7 @@ pub(crate) struct CrateRoot {
 
     def_path_hash_map: LazyValue<DefPathHashMapRef<'static>>,
 
-    source_map: LazyTable<u32, Option<LazyValue<rustc_span::SourceFile>>>,
+    source_map: LazyTableSingleIdx<u32, Option<LazyValue<rustc_span::SourceFile>>>,
     target_modifiers: LazyArray<TargetModifier>,
     denied_partial_mitigations: LazyArray<DeniedPartialMitigation>,
 
@@ -389,14 +395,14 @@ macro_rules! define_tables {
     ) => {
         #[derive(MetadataEncodable, LazyDecodable)]
         pub(crate) struct LazyTables {
-            $($name1: LazyTable<$IDX1, $T1>,)+
-            $($name2: LazyTable<$IDX2, Option<$T2>>,)+
+            $($name1: LazyTableSingleIdx<$IDX1, $T1>,)+
+            $($name2: LazyTableSingleIdx<$IDX2, Option<$T2>>,)+
         }
 
         #[derive(Default)]
         struct TableBuilders {
-            $($name1: TableBuilder<$IDX1, $T1>,)+
-            $($name2: TableBuilder<$IDX2, Option<$T2>>,)+
+            $($name1: TableBuilderSingleIdx<$IDX1, $T1>,)+
+            $($name2: TableBuilderSingleIdx<$IDX2, Option<$T2>>,)+
         }
 
         impl TableBuilders {
diff --git a/compiler/rustc_metadata/src/rmeta/table.rs b/compiler/rustc_metadata/src/rmeta/table.rs
index 7b53ebba8adfc..c023b61d73571 100644
--- a/compiler/rustc_metadata/src/rmeta/table.rs
+++ b/compiler/rustc_metadata/src/rmeta/table.rs
@@ -427,34 +427,38 @@ impl<T> FixedSizeEncoding for Option<LazyArray<T>> {
 }
 
 /// Helper for constructing a table's serialization (also see `Table`).
-pub(super) struct TableBuilder<I: Idx, T: FixedSizeEncoding> {
+pub(super) struct TableBuilder<IdxEncode: Idx, IdxDecode: Idx, T: FixedSizeEncoding> {
     width: usize,
-    blocks: IndexVec<I, T::ByteArray>,
-    _marker: PhantomData<T>,
+    blocks: IndexVec<IdxEncode, T::ByteArray>,
+    _marker: PhantomData<(IdxDecode, T)>,
 }
 
-impl<I: Idx, T: FixedSizeEncoding> Default for TableBuilder<I, T> {
+pub(super) type TableBuilderSingleIdx<TIdx, TValue> = TableBuilder<TIdx, TIdx, TValue>;
+
+impl<Ie: Idx, Id: Idx, T: FixedSizeEncoding> Default for TableBuilder<Ie, Id, T> {
     fn default() -> Self {
         TableBuilder { width: 0, blocks: Default::default(), _marker: PhantomData }
     }
 }
 
-impl<I: Idx, const N: usize, T> TableBuilder<I, Option<T>>
+impl<Ie: Idx, Id: Idx, const N: usize, T> TableBuilder<Ie, Id, Option<T>>
 where
     Option<T>: FixedSizeEncoding<ByteArray = [u8; N]>,
 {
-    pub(crate) fn set_some(&mut self, i: I, value: T) {
+    pub(crate) fn set_some(&mut self, i: Ie, value: T) {
         self.set(i, Some(value))
     }
 }
 
-impl<I: Idx, const N: usize, T: FixedSizeEncoding<ByteArray = [u8; N]>> TableBuilder<I, T> {
+impl<Ie: Idx, Id: Idx, const N: usize, T: FixedSizeEncoding<ByteArray = [u8; N]>>
+    TableBuilder<Ie, Id, T>
+{
     /// Sets the table value if it is not default.
     /// ATTENTION: For optimization default values are simply ignored by this function, because
     /// right now metadata tables never need to reset non-default values to default. If such need
     /// arises in the future then a new method (e.g. `clear` or `reset`) will need to be introduced
     /// for doing that explicitly.
-    pub(crate) fn set(&mut self, i: I, value: T) {
+    pub(crate) fn set(&mut self, i: Ie, value: T) {
         #[cfg(debug_assertions)]
         {
             debug_assert!(
@@ -477,7 +481,7 @@ impl<I: Idx, const N: usize, T: FixedSizeEncoding<ByteArray = [u8; N]>> TableBui
         }
     }
 
-    pub(crate) fn encode(&self, buf: &mut FileEncoder<'_>) -> LazyTable<I, T> {
+    pub(crate) fn encode(&self, buf: &mut FileEncoder<'_>) -> LazyTable<Ie, Id, T> {
         let pos = buf.position();
 
         let width = self.width;
@@ -500,13 +504,17 @@ fn trailing_zeros(x: &[u8]) -> usize {
     x.iter().rev().take_while(|b| **b == 0).count()
 }
 
-impl<I: Idx, const N: usize, T: FixedSizeEncoding<ByteArray = [u8; N]> + ParameterizedOverTcx>
-    LazyTable<I, T>
+impl<
+    Ie: Idx,
+    Id: Idx,
+    const N: usize,
+    T: FixedSizeEncoding<ByteArray = [u8; N]> + ParameterizedOverTcx,
+> LazyTable<Ie, Id, T>
 where
     for<'tcx> T::Value<'tcx>: FixedSizeEncoding<ByteArray = [u8; N]>,
 {
     /// Given the metadata, extract out the value at a particular index (if any).
-    pub(super) fn get<'a, 'tcx, M: MetaBlob<'a>>(&self, metadata: M, i: I) -> T::Value<'tcx> {
+    pub(super) fn get<'a, 'tcx, M: MetaBlob<'a>>(&self, metadata: M, i: Id) -> T::Value<'tcx> {
         // Access past the end of the table returns a Default
         if i.index() >= self.len {
             return Default::default();