From a3623e05429952cd8cbfd875409d3cb7c8f8045d Mon Sep 17 00:00:00 2001
From: Tyson Nottingham <tgnottingham@gmail.com>
Date: Sun, 20 Sep 2020 17:40:34 -0700
Subject: [PATCH] rustc_span: avoid hashing ExpnId tag when using cached hash

---
 compiler/rustc_span/src/lib.rs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index d036c07804990..746b516a1b6e0 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -1925,9 +1925,7 @@ impl<CTX: HashStableContext> HashStable<CTX> for ExpnId {
             return;
         }
 
-        TAG_NOT_ROOT.hash_stable(ctx, hasher);
         let index = self.as_u32() as usize;
-
         let res = CACHE.with(|cache| cache.borrow().get(index).copied().flatten());
 
         if let Some(res) = res {
@@ -1936,6 +1934,7 @@ impl<CTX: HashStableContext> HashStable<CTX> for ExpnId {
             let new_len = index + 1;
 
             let mut sub_hasher = StableHasher::new();
+            TAG_NOT_ROOT.hash_stable(ctx, &mut sub_hasher);
             self.expn_data().hash_stable(ctx, &mut sub_hasher);
             let sub_hash: Fingerprint = sub_hasher.finish();