From f459aefdc79abbe159cfd07e0efce620ebeb5d75 Mon Sep 17 00:00:00 2001
From: Ben Kimock <kimockb@gmail.com>
Date: Sat, 15 Feb 2025 12:28:07 -0500
Subject: [PATCH 1/2] Add some rmeta instrumentation

---
 compiler/rustc_metadata/src/rmeta/encoder.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 81fb918c6040a..e6ccf1b8fb161 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -599,6 +599,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         macro_rules! stat {
             ($label:literal, $f:expr) => {{
                 let orig_pos = self.position();
+                $label.encode(&mut self.opaque);
                 let res = $f();
                 stats.push(($label, self.position() - orig_pos));
                 res

From b88d2fd6b70d2a64ef9e4b45f5d39cfbc709f774 Mon Sep 17 00:00:00 2001
From: Ben Kimock <kimockb@gmail.com>
Date: Sat, 15 Feb 2025 15:41:31 -0500
Subject: [PATCH 2/2] instrument harder

---
 compiler/rustc_metadata/src/rmeta/mod.rs | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index 7b34e605c5307..5237d9ea17a05 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -333,12 +333,32 @@ pub(crate) struct CrateDep {
     pub is_private: bool,
 }
 
-#[derive(MetadataEncodable, MetadataDecodable)]
 pub(crate) struct TraitImpls {
     trait_id: (u32, DefIndex),
     impls: LazyArray<(DefIndex, Option<SimplifiedType>)>,
 }
 
+use rustc_serialize::{Encodable, Decodable};
+impl<'tcx, '__a> Encodable<EncodeContext<'__a, 'tcx>> for TraitImpls {
+    #[inline]
+    fn encode(&self, s: &mut EncodeContext<'__a, 'tcx>) {
+        (&b"<<TraitImpls>>"[..]).encode(s);
+        self.trait_id.encode(s);
+        self.impls.encode(s);
+    }
+}
+
+impl<'tcx, '__a> Decodable<DecodeContext<'__a, 'tcx>> for TraitImpls {
+    #[inline]
+    fn decode(d: &mut DecodeContext<'__a, 'tcx>) -> Self {
+        let _header: Vec<u8> = Decodable::decode(d);
+        Self {
+            trait_id: Decodable::decode(d),
+            impls: Decodable::decode(d),
+        }
+    }
+}
+
 #[derive(MetadataEncodable, MetadataDecodable)]
 pub(crate) struct IncoherentImpls {
     self_ty: SimplifiedType,