From b484619f203403fb410d74f165d9a62aa828b1b4 Mon Sep 17 00:00:00 2001
From: Matthew Parkinson <mattpark@microsoft.com>
Date: Mon, 13 May 2019 14:29:02 +0100
Subject: [PATCH] Added branch predictor hint.

---
 src/ds/bits.h   | 4 ++++
 src/mem/alloc.h | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/ds/bits.h b/src/ds/bits.h
index 52b5b18..c07ad92 100644
--- a/src/ds/bits.h
+++ b/src/ds/bits.h
@@ -9,7 +9,11 @@
 #  define ALWAYSINLINE __forceinline
 #  define NOINLINE __declspec(noinline)
 #  define HEADER_GLOBAL __declspec(selectany)
+#  define likely(x)   !!(x)
+#  define unlikely(x) !!(x)
 #else
+#  define likely(x)   __builtin_expect(!!(x), 1)
+#  define unlikely(x) __builtin_expect(!!(x), 0)
 #  include <cpuid.h>
 #  include <emmintrin.h>
 #  define ALWAYSINLINE __attribute__((always_inline))
diff --git a/src/mem/alloc.h b/src/mem/alloc.h
index c00fb5e..e16c2bd 100644
--- a/src/mem/alloc.h
+++ b/src/mem/alloc.h
@@ -872,7 +872,7 @@ namespace snmalloc
     inline void handle_message_queue()
     {
       // Inline the empty check, but not necessarily the full queue handling.
-      if (message_queue().is_empty())
+      if (likely(message_queue().is_empty()))
         return;
 
       handle_message_queue_inner();