Silence compiler warning

benchmark.cpp

@@ -89,6 +89,7 @@ int main(int argc, char* argv[])
  std::cout << "Array size: " << std::fixed << std::setprecision(2) << bytes / (1024.0 * 1024.0) << " MB" << std::endl;
 
 #if defined(X86_OR_X64)
+
  #if defined(HAVE_CPUID)
  int cpuid = get_cpuid();
  if ((cpuid & bit_AVX512) && bytes >= 1024)
@@ -97,7 +98,21 @@ int main(int argc, char* argv[])
  algo = "AVX2";
  else if (cpuid & bit_POPCNT)
  algo = "POPCNT";
+ #else
+ #if defined(HAVE_AVX512) && (defined(__AVX512__) || defined(__AVX512BW__))
+ if (algo.empty() && bytes >= 1024)
+ algo = "AVX512";
+ #endif
+ #if defined(HAVE_AVX2) && defined(__AVX2__)
+ if (algo.empty() && bytes >= 512)
+ algo = "AVX2";
+ #endif
+ #if defined(HAVE_POPCNT) && defined(__POPCNT__)
+ if (algo.empty())
+ algo = "POPCNT";
+ #endif
  #endif
+
 #elif defined(__ARM_NEON) || \
  defined(__aarch64__)
  algo = "NEON";

libpopcnt.h

@@ -69,14 +69,6 @@
  #define X86_OR_X64
 #endif
 
-#if defined(X86_OR_X64) && \
- (defined(__cplusplus) || \
- defined(_MSC_VER) || \
- (GNUC_PREREQ(4, 2) || \
- __has_builtin(__sync_val_compare_and_swap)))
- #define HAVE_CPUID
-#endif
-
 #if GNUC_PREREQ(4, 2) || \
  __has_builtin(__builtin_popcount)
  #define HAVE_BUILTIN_POPCOUNT
@@ -87,51 +79,66 @@
  #define HAVE_ASM_POPCNT
 #endif
 
-#if defined(HAVE_CPUID) && \
+#if defined(X86_OR_X64) && \
  (defined(HAVE_ASM_POPCNT) || \
  defined(_MSC_VER))
  #define HAVE_POPCNT
 #endif
 
-#if defined(HAVE_CPUID) && \
+#if defined(X86_OR_X64) && \
  GNUC_PREREQ(4, 9)
  #define HAVE_AVX2
 #endif
 
-#if defined(HAVE_CPUID) && \
+#if defined(X86_OR_X64) && \
  GNUC_PREREQ(5, 0)
  #define HAVE_AVX512
 #endif
 
-/* MSVC compatible compilers (Windows) */
-#if defined(_MSC_VER) && \
- defined(HAVE_CPUID)
- /* clang-cl (LLVM 10 from 2020) requires /arch:AVX2 or
- * /arch:AVX512 to enable vector instructions */
- #if defined(__clang__)
- #if defined(__AVX2__)
- #define HAVE_AVX2
- #endif
- #if defined(__AVX512__)
+#if defined(X86_OR_X64)
+ /* MSVC compatible compilers (Windows) */
+ #if defined(_MSC_VER)
+ /* clang-cl (LLVM 10 from 2020) requires /arch:AVX2 or
+ * /arch:AVX512 to enable vector instructions */
+ #if defined(__clang__)
+ #if defined(__AVX2__)
+ #define HAVE_AVX2
+ #endif
+ #if defined(__AVX512__)
+ #define HAVE_AVX2
+ #define HAVE_AVX512
+ #endif
+ /* MSVC 2017 or later does not require
+ * /arch:AVX2 or /arch:AVX512 */
+ #elif _MSC_VER >= 1910
  #define HAVE_AVX2
  #define HAVE_AVX512
  #endif
- /* MSVC 2017 or later does not require
- * /arch:AVX2 or /arch:AVX512 */
- #elif _MSC_VER >= 1910
- #define HAVE_AVX2
- #define HAVE_AVX512
- #endif
-#else /* Clang (Unix-like OSes) */
- #if defined(HAVE_CPUID) && \
- CLANG_PREREQ(3, 8) && \
- __has_attribute(target) && \
- (!defined(__apple_build_version__) || __apple_build_version__ >= 8000000)
+ /* Clang (Unix-like OSes) */
+ #elif CLANG_PREREQ(3, 8) && \
+ __has_attribute(target) && \
+ (!defined(__apple_build_version__) || __apple_build_version__ >= 8000000)
  #define HAVE_AVX2
  #define HAVE_AVX512
  #endif
 #endif
 
+/*
+ * Only enable CPUID runtime checks if this is really
+ * needed. E.g. do not enable if user has compiled
+ * using -march=native on a CPU that supports AVX512.
+ */
+#if defined(X86_OR_X64) && \
+ (defined(__cplusplus) || \
+ defined(_MSC_VER) || \
+ (GNUC_PREREQ(4, 2) || \
+ __has_builtin(__sync_val_compare_and_swap))) && \
+ !(defined(HAVE_AVX512) && (defined(__AVX512__) || defined(__AVX512BW__)) && \
+ defined(HAVE_AVX2) && defined(__AVX2__) && \
+ defined(HAVE_POPCNT) && defined(__POPCNT__))
+ #define HAVE_CPUID
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -555,6 +562,11 @@ static inline uint64_t popcnt(const void* data, uint64_t size)
  uint64_t cnt = 0;
  const uint8_t* ptr = (const uint8_t*) data;
 
+/*
+ * CPUID runtime checks are only enabled if this is needed.
+ * E.g. CPUID is disabled when a user compiles his
+ * code using -march=native on a CPU with AVX512.
+ */
 #if defined(HAVE_CPUID)
  #if defined(__cplusplus)
  /* C++11 thread-safe singleton */