From 185e49d2a99c9edd8adca92d45dd5ba02e9892de Mon Sep 17 00:00:00 2001
From: Techjar <tecknojar@gmail.com>
Date: Sun, 26 Jan 2020 22:08:55 -0500
Subject: [PATCH] x64CPUDetect: Add flag for slow PDEP/PEXT on AMD Zen

For some unknown reason PDEP and PEXT are ridiculously slow on AMD Zen
architecture.
---
 Source/Core/Common/CPUDetect.h      | 3 +++
 Source/Core/Common/x64CPUDetect.cpp | 1 +
 2 files changed, 4 insertions(+)

diff --git a/Source/Core/Common/CPUDetect.h b/Source/Core/Common/CPUDetect.h
index 7ecc3e00cd..f789ba41a2 100644
--- a/Source/Core/Common/CPUDetect.h
+++ b/Source/Core/Common/CPUDetect.h
@@ -42,6 +42,9 @@ struct CPUInfo
   bool bAVX2 = false;
   bool bBMI1 = false;
   bool bBMI2 = false;
+  // PDEP and PEXT are ridiculously slow on AMD Zen, so we have this flag to avoid using them there
+  // Zen 2 is also affected by this issue
+  bool bFastBMI2 = false;
   bool bFMA = false;
   bool bFMA4 = false;
   bool bAES = false;
diff --git a/Source/Core/Common/x64CPUDetect.cpp b/Source/Core/Common/x64CPUDetect.cpp
index 0c3decba05..338c74b808 100644
--- a/Source/Core/Common/x64CPUDetect.cpp
+++ b/Source/Core/Common/x64CPUDetect.cpp
@@ -175,6 +175,7 @@ void CPUInfo::Detect()
   }
 
   bFlushToZero = bSSE;
+  bFastBMI2 = bBMI2 && !bZen;
 
   if (max_ex_fn >= 0x80000004)
   {