Simplify AVX512 code

ChangeLog

@@ -1,6 +1,8 @@
 Changes in primecount-7.14, 2024-06-17
 
 * int128_t.hpp: Rename namespace port to pstd (portable std namespace).
+* Sieve.hpp: Simplify AVX512 code.
+* multiarch_avx512_vpopcnt.cmake: Simplify AVX512 code.
 
 Changes in primecount-7.13, 2024-04-15
 

cmake/multiarch_avx512_vpopcnt.cmake

@@ -11,24 +11,23 @@ set(CMAKE_REQUIRED_INCLUDES "${PROJECT_SOURCE_DIR}/include")
 
 check_cxx_source_compiles("
     // GCC/Clang function multiversioning for AVX512 is not needed if
-    // the user compiles with -mavx512f -mavx512vpopcntdq -mbmi2.
+    // the user compiles with -mavx512f -mavx512vpopcntdq.
     // GCC/Clang function multiversioning generally causes a minor
     // overhead, hence we disable it if it is not needed.
     #if defined(__AVX512F__) && \
-        defined(__AVX512VPOPCNTDQ__) && \
-        defined(__BMI2__)
-      Error: AVX512 BMI2 multiarch not needed!
+        defined(__AVX512VPOPCNTDQ__)
+      Error: AVX512 VPOPCNT multiarch not needed!
     #endif
 
-    #include <cpu_supports_avx512_bmi2.hpp>
+    #include <cpu_supports_avx512_vpopcnt.hpp>
     #include <immintrin.h>
     #include <stdint.h>
 
     class Sieve {
     public:
         uint64_t count_default(uint64_t* array, uint64_t stop_idx);
-        __attribute__ ((target (\"avx512f,avx512vpopcntdq,bmi2\")))
-        uint64_t count_avx512_bmi2(uint64_t* array, uint64_t stop_idx);
+        __attribute__ ((target (\"avx512f,avx512vpopcntdq\")))
+        uint64_t count_avx512_vpopcnt(uint64_t* array, uint64_t stop_idx);
     };
 
     uint64_t Sieve::count_default(uint64_t* array, uint64_t stop_idx)
@@ -39,20 +38,23 @@ check_cxx_source_compiles("
         return res;
     }
 
-    __attribute__ ((target (\"avx512f,avx512vpopcntdq,bmi2\")))
-    uint64_t Sieve::count_avx512_bmi2(uint64_t* array, uint64_t stop_idx)
+    __attribute__ ((target (\"avx512f,avx512vpopcntdq\")))
+    uint64_t Sieve::count_avx512_vpopcnt(uint64_t* array, uint64_t stop_idx)
     {
         uint64_t i = 0;
         __m512i vcnt = _mm512_setzero_si512();
-        do
+
+        for (; i + 8 < stop_idx; i += 8)
         {
-          __mmask8 mask = (i + 8 < stop_idx) ? 0xff : (__mmask8) _bzhi_u64(0xff, stop_idx - i);
-          __m512i vec = _mm512_maskz_loadu_epi64(mask , &array[i]);
-          vec = _mm512_popcnt_epi64(vec);
-          vcnt = _mm512_add_epi64(vcnt, vec);
-          i += 8;
+            __m512i vec = _mm512_loadu_epi64(&array[i]);
+            vec = _mm512_popcnt_epi64(vec);
+            vcnt = _mm512_add_epi64(vcnt, vec);
         }
-        while (i < stop_idx);
+
+        __mmask8 mask = 0xff >> (stop_idx - i);
+        __m512i vec = _mm512_maskz_loadu_epi64(mask , &array[i]);
+        vec = _mm512_popcnt_epi64(vec);
+        vcnt = _mm512_add_epi64(vcnt, vec);
         return _mm512_reduce_add_epi64(vcnt);
     }
 
@@ -62,8 +64,8 @@ check_cxx_source_compiles("
         uint64_t cnt = 0;
         Sieve sieve;
 
-        if (cpu_supports_avx512_bmi2)
-            cnt = sieve.count_avx512_bmi2(&array[0], 10);
+        if (cpu_supports_avx512_vpopcnt)
+            cnt = sieve.count_avx512_vpopcnt(&array[0], 10);
         else
             cnt = sieve.count_default(&array[0], 10);
 
@@ -72,7 +74,7 @@ check_cxx_source_compiles("
 " multiarch_avx512_vpopcnt)
 
 if(multiarch_avx512_vpopcnt)
-    set(ENABLE_MULTIARCH "ENABLE_MULTIARCH_AVX512_BMI2")
+    set(ENABLE_MULTIARCH "ENABLE_MULTIARCH_AVX512_VPOPCNT")
 endif()
 
 cmake_pop_check_state()

include/Sieve.hpp

@@ -49,19 +49,18 @@
   #define ENABLE_ARM_SVE
 
 #elif defined(__AVX512F__) && \
-      defined(__AVX512VPOPCNTDQ__) && \
-      defined(__BMI2__) && \
-     !defined(__i386__) /* misses _bzhi_u64() */ && \
+      defined(__AVX512VPOPCNTDQ__)
       __has_include(<immintrin.h>)
   #include <immintrin.h>
-  #define ENABLE_AVX512_BMI2
+  #define ENABLE_AVX512_VPOPCNT
 
 #elif defined(ENABLE_MULTIARCH_ARM_SVE)
   #include <cpu_supports_arm_sve.hpp>
   #include <arm_sve.h>
   #define ENABLE_DEFAULT
-#elif defined(ENABLE_MULTIARCH_AVX512_BMI2)
-  #include <cpu_supports_avx512_bmi2.hpp>
+
+#elif defined(ENABLE_MULTIARCH_AVX512_VPOPCNT)
+  #include <cpu_supports_avx512_vpopcnt.hpp>
   #include <immintrin.h>
   #define ENABLE_DEFAULT
 #else
@@ -113,12 +112,12 @@ class Sieve
   {
     #if defined(ENABLE_ARM_SVE)
       return count_arm_sve(start, stop);
-    #elif defined(ENABLE_AVX512_BMI2)
-      return count_avx512_bmi2(start, stop);
+    #elif defined(ENABLE_AVX512_VPOPCNT)
+      return count_avx512_vpopcnt(start, stop);
     #elif defined(ENABLE_MULTIARCH_ARM_SVE)
       return cpu_supports_sve ? count_arm_sve(start, stop) : count_default(start, stop);
-    #elif defined(ENABLE_MULTIARCH_AVX512_BMI2)
-      return cpu_supports_avx512_bmi2 ? count_avx512_bmi2(start, stop) : count_default(start, stop);
+    #elif defined(ENABLE_MULTIARCH_AVX512_VPOPCNT)
+      return cpu_supports_avx512_vpopcnt ? count_avx512_vpopcnt(start, stop) : count_default(start, stop);
     #else
       return count_default(start, stop);
     #endif
@@ -174,18 +173,18 @@ class Sieve
 
 #endif
 
-#if defined(ENABLE_AVX512_BMI2) || \
-    defined(ENABLE_MULTIARCH_AVX512_BMI2)
+#if defined(ENABLE_AVX512_VPOPCNT) || \
+    defined(ENABLE_MULTIARCH_AVX512_VPOPCNT)
 
   /// Count 1 bits inside [start, stop].
   /// The distance [start, stop] is small here < sqrt(segment_size),
   /// hence we simply count the number of unsieved elements
   /// by linearly iterating over the sieve array.
   ///
-  #if defined(ENABLE_MULTIARCH_AVX512_BMI2)
-    __attribute__ ((target ("avx512f,avx512vpopcntdq,bmi2")))
+  #if defined(ENABLE_MULTIARCH_AVX512_VPOPCNT)
+    __attribute__ ((target ("avx512f,avx512vpopcntdq")))
   #endif
-  uint64_t count_avx512_bmi2(uint64_t start, uint64_t stop) const
+  uint64_t count_avx512_vpopcnt(uint64_t start, uint64_t stop) const
   {
     if (start > stop)
       return 0;
@@ -216,7 +215,7 @@ class Sieve
         vcnt = _mm512_add_epi64(vcnt, vec);
       }
 
-      __mmask8 mask = (__mmask8) _bzhi_u64(0xff, stop_idx - i);
+      __mmask8 mask = 0xff >> (stop_idx - i);
       __m512i vec = _mm512_maskz_loadu_epi64(mask , &sieve64[i]);
       vec = _mm512_popcnt_epi64(vec);
       vcnt = _mm512_add_epi64(vcnt, vec);

include/cpu_supports_avx512_bmi2.hpp → include/cpu_supports_avx512_vpopcnt.hpp

@@ -1,15 +1,15 @@
 ///
-/// @file  cpu_supports_avx512_bmi2.hpp
-/// @brief Detect if the x86 CPU supports AVX512 and BMI2.
+/// @file  cpu_supports_avx512_vpopcnt.hpp
+/// @brief Detect if the x86 CPU supports AVX512 VPOPCNT.
 ///
 /// Copyright (C) 2024 Kim Walisch, <[email protected]>
 ///
 /// This file is distributed under the BSD License. See the COPYING
 /// file in the top level directory.
 ///
 
-#ifndef CPU_SUPPORTS_AVX512_BMI2_HPP
-#define CPU_SUPPORTS_AVX512_BMI2_HPP
+#ifndef CPU_SUPPORTS_AVX512_VPOPCNT_HPP
+#define CPU_SUPPORTS_AVX512_VPOPCNT_HPP
 
 #include <cpuid.hpp>
 
@@ -18,7 +18,6 @@
 #endif
 
 // %ebx bit flags
-#define bit_BMI2    (1 << 8)
 #define bit_AVX512F (1 << 16)
 
 // %ecx bit flags
@@ -45,7 +44,7 @@ inline int get_xcr0()
   return xcr0;
 }
 
-inline bool run_cpuid_avx512_bmi2()
+inline bool run_cpuid_avx512_vpopcnt()
 {
   int abcd[4];
 
@@ -72,16 +71,13 @@ inline bool run_cpuid_avx512_bmi2()
 
   run_cpuid(7, 0, abcd);
 
-  if ((abcd[1] & bit_BMI2) != bit_BMI2)
-    return false;
-
   // AVX512F, AVX512VPOPCNTDQ
   return ((abcd[1] & bit_AVX512F) == bit_AVX512F &&
           (abcd[2] & bit_AVX512_VPOPCNTDQ) == bit_AVX512_VPOPCNTDQ);
 }
 
 /// Initialized at startup
-bool cpu_supports_avx512_bmi2 = run_cpuid_avx512_bmi2();
+bool cpu_supports_avx512_vpopcnt = run_cpuid_avx512_vpopcnt();
 
 } // namespace
 

scripts/build_clang_multiarch_win_x64.bat

@@ -10,6 +10,6 @@
 :: include all MMX, SSE, POPCNT, BMI, BMI2, AVX, AVX and AVX512 headers.
 
 del /Q ..\src\deleglise-rivat\S2_easy.cpp ..\src\gourdon\AC.cpp
-clang++ -I../include -I../lib/primesieve/include -O3 -mpopcnt -fopenmp -Wall -Wextra -pedantic -DNDEBUG -DENABLE_INT128_OPENMP_PATCH -DENABLE_MULTIARCH_AVX512 -DENABLE_MULTIARCH_AVX512_BMI2 ../lib/primesieve/src/*.cpp ../src/*.cpp ../src/lmo/*.cpp ../src/deleglise-rivat/*.cpp ../src/gourdon/*.cpp ../src/app/*.cpp -o primecount.exe "C:\Program Files\LLVM\lib\clang\18\lib\windows\clang_rt.builtins-x86_64.lib"
+clang++ -I../include -I../lib/primesieve/include -O3 -mpopcnt -fopenmp -Wall -Wextra -pedantic -DNDEBUG -DENABLE_INT128_OPENMP_PATCH -DENABLE_MULTIARCH_AVX512 -DENABLE_MULTIARCH_AVX512_VPOPCNT ../lib/primesieve/src/*.cpp ../src/*.cpp ../src/lmo/*.cpp ../src/deleglise-rivat/*.cpp ../src/gourdon/*.cpp ../src/app/*.cpp -o primecount.exe "C:\Program Files\LLVM\lib\clang\18\lib\windows\clang_rt.builtins-x86_64.lib"
 git checkout ..\src\deleglise-rivat
 git checkout ..\src\gourdon