From c4d8089f001cf6323a1bb8fac08b7f31de33171b Mon Sep 17 00:00:00 2001
From: Dylan MacKenzie <ecstaticmorse@gmail.com>
Date: Tue, 22 Sep 2020 18:30:53 -0700
Subject: [PATCH] Revert "Add an unused field of type `Option<DefId>` to
 `ParamEnv` struct."

This reverts commit ab83d372ed5b1799d418afe83c468e4c5973cc34.
---
 compiler/rustc_infer/src/traits/mod.rs               | 2 +-
 compiler/rustc_middle/src/ty/mod.rs                  | 5 +----
 compiler/rustc_trait_selection/src/traits/fulfill.rs | 2 +-
 3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/compiler/rustc_infer/src/traits/mod.rs b/compiler/rustc_infer/src/traits/mod.rs
index 7e7c8588ffb40..a3c4920fa8af3 100644
--- a/compiler/rustc_infer/src/traits/mod.rs
+++ b/compiler/rustc_infer/src/traits/mod.rs
@@ -57,7 +57,7 @@ pub type TraitObligation<'tcx> = Obligation<'tcx, ty::PolyTraitPredicate<'tcx>>;
 
 // `PredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(target_arch = "x86_64")]
-static_assert_size!(PredicateObligation<'_>, 40);
+static_assert_size!(PredicateObligation<'_>, 32);
 
 pub type Obligations<'tcx, O> = Vec<Obligation<'tcx, O>>;
 pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index d6cf68a900ce0..b7530c077ccd1 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1751,9 +1751,6 @@ pub struct ParamEnv<'tcx> {
     ///
     /// Note: This is packed, use the reveal() method to access it.
     packed: CopyTaggedPtr<&'tcx List<Predicate<'tcx>>, traits::Reveal, true>,
-
-    /// FIXME: This field is not used, but removing it causes a performance degradation. See #76913.
-    unused_field: Option<DefId>,
 }
 
 unsafe impl rustc_data_structures::tagged_ptr::Tag for traits::Reveal {
@@ -1834,7 +1831,7 @@ impl<'tcx> ParamEnv<'tcx> {
     /// Construct a trait environment with the given set of predicates.
     #[inline]
     pub fn new(caller_bounds: &'tcx List<Predicate<'tcx>>, reveal: Reveal) -> Self {
-        ty::ParamEnv { packed: CopyTaggedPtr::new(caller_bounds, reveal), unused_field: None }
+        ty::ParamEnv { packed: CopyTaggedPtr::new(caller_bounds, reveal) }
     }
 
     pub fn with_user_facing(mut self) -> Self {
diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index 7e5be8276f7ff..fdebd88a086c7 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -87,7 +87,7 @@ pub struct PendingPredicateObligation<'tcx> {
 
 // `PendingPredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(target_arch = "x86_64")]
-static_assert_size!(PendingPredicateObligation<'_>, 64);
+static_assert_size!(PendingPredicateObligation<'_>, 56);
 
 impl<'a, 'tcx> FulfillmentContext<'tcx> {
     /// Creates a new fulfillment context.