From 12d74f702baf58bbb7d80cffb268d2c02e7f8999 Mon Sep 17 00:00:00 2001
From: Adrian Wielgosik <adrian.wielgosik@gmail.com>
Date: Tue, 9 Mar 2021 23:43:38 +0100
Subject: [PATCH 1/2] Mark cheap functions as inline.

---
 src/gc-arena/src/context.rs | 1 +
 src/gc-arena/src/types.rs   | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/src/gc-arena/src/context.rs b/src/gc-arena/src/context.rs
index 3a3d9505..f55380a6 100644
--- a/src/gc-arena/src/context.rs
+++ b/src/gc-arena/src/context.rs
@@ -317,6 +317,7 @@ enum Phase {
     Sleep,
 }
 
+#[inline]
 unsafe fn static_gc_box<'gc>(
     ptr: NonNull<GcBox<dyn Collect + 'gc>>,
 ) -> NonNull<GcBox<dyn Collect>> {
diff --git a/src/gc-arena/src/types.rs b/src/gc-arena/src/types.rs
index 1ccf2906..c8157ff1 100644
--- a/src/gc-arena/src/types.rs
+++ b/src/gc-arena/src/types.rs
@@ -20,10 +20,12 @@ pub(crate) struct GcBox<T: Collect + ?Sized> {
 pub(crate) struct GcFlags(Cell<u8>);
 
 impl GcFlags {
+    #[inline]
     pub(crate) fn new() -> GcFlags {
         GcFlags(Cell::new(0))
     }
 
+    #[inline]
     pub(crate) fn color(&self) -> GcColor {
         match self.0.get() & 0x3 {
             0x0 => GcColor::White,
@@ -33,6 +35,7 @@ impl GcFlags {
         }
     }
 
+    #[inline]
     pub(crate) fn set_color(&self, color: GcColor) {
         self.0.set(
             (self.0.get() & !0x3)
@@ -44,10 +47,12 @@ impl GcFlags {
         )
     }
 
+    #[inline]
     pub(crate) fn needs_trace(&self) -> bool {
         self.0.get() & 0x4 != 0x0
     }
 
+    #[inline]
     pub(crate) fn set_needs_trace(&self, needs_trace: bool) {
         self.0
             .set((self.0.get() & !0x4) | if needs_trace { 0x4 } else { 0x0 });

From e2f9bb086ba8531ead64f0b77bdd0abcb2cd91bc Mon Sep 17 00:00:00 2001
From: Adrian Wielgosik <adrian.wielgosik@gmail.com>
Date: Tue, 9 Mar 2021 23:50:58 +0100
Subject: [PATCH 2/2] Manually initialize GcBox contents post-allocation

---
 src/gc-arena/src/context.rs | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/src/gc-arena/src/context.rs b/src/gc-arena/src/context.rs
index f55380a6..8c8e5af7 100644
--- a/src/gc-arena/src/context.rs
+++ b/src/gc-arena/src/context.rs
@@ -264,13 +264,17 @@ impl Context {
             );
         }
 
-        let gc_box = GcBox {
-            flags: GcFlags::new(),
-            next: Cell::new(self.all.get()),
-            value: UnsafeCell::new(t),
-        };
-        gc_box.flags.set_needs_trace(T::needs_trace());
-        let ptr = NonNull::new_unchecked(Box::into_raw(Box::new(gc_box)));
+        let flags = GcFlags::new();
+        flags.set_needs_trace(T::needs_trace());
+
+        let mut uninitialized = Box::new(mem::MaybeUninit::<GcBox<T>>::uninit());
+
+        std::ptr::write(&mut (*uninitialized.as_mut_ptr()).flags, flags);
+        std::ptr::write(&mut (*uninitialized.as_mut_ptr()).next, Cell::new(self.all.get()));
+        std::ptr::write(&mut (*uninitialized.as_mut_ptr()).value, UnsafeCell::new(t));
+
+        let ptr = NonNull::new_unchecked(Box::into_raw(uninitialized) as *mut GcBox<T>);
+
         self.all.set(Some(static_gc_box(ptr)));
         if self.phase.get() == Phase::Sweep && self.sweep_prev.get().is_none() {
             self.sweep_prev.set(self.all.get());