From 956a84bfe0502e126dcdd173fc84eecc10df5ebc Mon Sep 17 00:00:00 2001
From: Nilstrieb <48135649+Nilstrieb@users.noreply.github.com>
Date: Wed, 8 Jun 2022 18:22:48 +0200
Subject: [PATCH] Optimize `SbTag::eq`

The code before generated really bad code with a branch.
This nudges LLVM towards being smarter and simply comparing
the integers.
---
 src/stacked_borrows.rs | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/stacked_borrows.rs b/src/stacked_borrows.rs
index 0d671ec653b5..fd33eea79026 100644
--- a/src/stacked_borrows.rs
+++ b/src/stacked_borrows.rs
@@ -27,12 +27,27 @@ pub type CallId = NonZeroU64;
 pub type AllocExtra = Stacks;
 
 /// Tracking pointer provenance
-#[derive(Copy, Clone, Hash, PartialEq, Eq)]
+#[derive(Copy, Clone, Hash, Eq)]
 pub enum SbTag {
     Tagged(PtrId),
     Untagged,
 }
 
+impl SbTag {
+    fn as_u64(self) -> u64 {
+        match self {
+            SbTag::Tagged(id) => id.get(),
+            SbTag::Untagged => 0,
+        }
+    }
+}
+
+impl PartialEq for SbTag {
+    fn eq(&self, other: &Self) -> bool {
+        self.as_u64() == other.as_u64()
+    }
+}
+
 impl fmt::Debug for SbTag {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {