From 7213df65aa8d4d6fca18b1a6cfe76a77eed6a797 Mon Sep 17 00:00:00 2001
From: Christopher Dykes <cdykes@fb.com>
Date: Thu, 10 Nov 2016 12:46:19 -0800
Subject: [PATCH] Always use inline-asm version on GCC/Clang

Summary:
Because the intrinsic version requires explicitly adding `__target__` attributes, which results in things not being inlined. Although the code generated with the `__target__` attribute is strictly better, ensuring it's applied on all the relevant functions is error-prone, so just use the inline assembly version for GCC/Clang so that it can be inlined elsewhere. MSVC will inline the intrinsic version without any issue.
This also marks the functions as `ALWAYS_INLINE`, as the diff that is getting reverted made that change as well.

Reviewed By: yfeldblum, philippv, ot

Differential Revision: D3963935

fbshipit-source-id: 47175d64e7be351eb455a4d053b91ce9392bf152
---
 folly/experimental/Instructions.h | 30 ++++++++++++++----------------
 folly/experimental/Select64.h     |  9 +++++----
 2 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/folly/experimental/Instructions.h b/folly/experimental/Instructions.h
index ffc4fa1b..f8368942 100644
--- a/folly/experimental/Instructions.h
+++ b/folly/experimental/Instructions.h
@@ -18,17 +18,14 @@
 
 #include <glog/logging.h>
 
+#ifdef _MSC_VER
+#include <immintrin.h>
+#endif
+
 #include <folly/CpuId.h>
 #include <folly/Portability.h>
 #include <folly/portability/Builtins.h>
 
-#if defined(__GNUC__) || defined(__clang__)
-// For compilers supporting AT&T assembly syntax.
-#define FOLLY_INSTRUCTIONS_SUPPORTED 1
-#else
-#define FOLLY_INSTRUCTIONS_SUPPORTED 0
-#endif
-
 namespace folly { namespace compression { namespace instructions {
 
 // NOTE: It's recommended to compile EF coding with -msse4.2, starting
@@ -59,8 +56,6 @@ struct Default {
   }
 };
 
-#if FOLLY_INSTRUCTIONS_SUPPORTED
-
 struct Nehalem : public Default {
   static bool supported(const folly::CpuId& cpuId = {}) {
     return cpuId.popcnt();
@@ -68,9 +63,14 @@ struct Nehalem : public Default {
 
   static FOLLY_ALWAYS_INLINE uint64_t popcount(uint64_t value) {
     // POPCNT is supported starting with Intel Nehalem, AMD K10.
+#if defined(__GNUC__) || defined(__clang__)
+    // GCC and Clang won't inline the intrinsics.
     uint64_t result;
     asm ("popcntq %1, %0" : "=r" (result) : "r" (value));
     return result;
+#else
+    return _mm_popcnt_u64(value);
+#endif
   }
 };
 
@@ -82,17 +82,15 @@ struct Haswell : public Nehalem {
   static FOLLY_ALWAYS_INLINE uint64_t blsr(uint64_t value) {
     // BMI1 is supported starting with Intel Haswell, AMD Piledriver.
     // BLSR combines two instuctions into one and reduces register pressure.
+#if defined(__GNUC__) || defined(__clang__)
+    // GCC and Clang won't inline the intrinsics.
     uint64_t result;
     asm ("blsrq %1, %0" : "=r" (result) : "r" (value));
     return result;
+#else
+    return _blsr_u64(value);
+#endif
   }
 };
 
-#else // FOLLY_INSTRUCTIONS_SUPPORTED
-
-struct Nehalem : public Default {};
-struct Haswell : public Nehalem {};
-
-#endif // FOLLY_INSTRUCTIONS_SUPPORTED
-
 }}} // namespaces
diff --git a/folly/experimental/Select64.h b/folly/experimental/Select64.h
index e79b489c..1a2ed35f 100644
--- a/folly/experimental/Select64.h
+++ b/folly/experimental/Select64.h
@@ -63,11 +63,11 @@ inline uint64_t select64(uint64_t x, uint64_t k) {
   return place + detail::kSelectInByte[((x >> place) & 0xFF) | (byteRank << 8)];
 }
 
-#if FOLLY_INSTRUCTIONS_SUPPORTED
-
 template <>
 FOLLY_ALWAYS_INLINE uint64_t
 select64<compression::instructions::Haswell>(uint64_t x, uint64_t k) {
+#if defined(__GNUC__) || defined(__clang__)
+  // GCC and Clang won't inline the intrinsics.
   uint64_t result = uint64_t(1) << k;
 
   asm("pdep %1, %0, %0\n\t"
@@ -76,8 +76,9 @@ select64<compression::instructions::Haswell>(uint64_t x, uint64_t k) {
       : "r"(x));
 
   return result;
+#else
+  return _tzcnt_u64(_pdep_u64(1ULL << k, x));
+#endif
 }
 
-#endif // FOLLY_INSTRUCTIONS_SUPPORTED
-
 } // namespace folly
-- 
2.34.1