From 89c3079072e93b1a212304e4eaf691d853b4ef5d Mon Sep 17 00:00:00 2001
From: Leonardo de Moura <leomoura@amazon.com>
Date: Mon, 12 Aug 2024 02:47:08 +0200
Subject: [PATCH] chore: fix typo in hash code for `Expr` equality test (#4990)

We observed a small performance improvement at
https://github.com/leanprover/LNSym/blob/proof_size_expt/Proofs/SHA512/Experiments/Sym30.lean
Before: 2.65s
After: 2.60s
---
 src/kernel/expr_eq_fn.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/kernel/expr_eq_fn.cpp b/src/kernel/expr_eq_fn.cpp
index 7078565217..c0b0d55a7d 100644
--- a/src/kernel/expr_eq_fn.cpp
+++ b/src/kernel/expr_eq_fn.cpp
@@ -23,7 +23,7 @@ template<bool CompareBinderInfo>
 class expr_eq_fn {
     struct key_hasher {
         std::size_t operator()(std::pair<lean_object *, lean_object *> const & p) const {
-            return hash((size_t)p.first >> 3, (size_t)p.first >> 3);
+            return hash((size_t)p.first >> 3, (size_t)p.second >> 3);
         }
     };
     typedef std::unordered_set<std::pair<lean_object *, lean_object *>, key_hasher> cache;