Availability of the immintrin.h should not implicitly disable support of all pre-Haswell CPUs. User needs to explicitly specify AVX2 requirement via SNAPPY_REQUIRE_AVX2 if it was their intention.

Author: gruuk

CMakeLists.txt

@@ -163,11 +163,13 @@ int main() {
   return 0;
 }" SNAPPY_HAVE_SSSE3)
 
-check_cxx_source_compiles("
-#include <immintrin.h>
-int main() {
-  return _bzhi_u32(0, 1);
-}" SNAPPY_HAVE_BMI2)
+if(SNAPPY_REQUIRE_AVX2)
+  check_cxx_source_compiles("
+  #include <immintrin.h>
+  int main() {
+    return _bzhi_u32(0, 1);
+  }" SNAPPY_HAVE_BMI2)
+endif(SNAPPY_REQUIRE_AVX2)
 
 include(CheckSymbolExists)
 check_symbol_exists("mmap" "sys/mman.h" HAVE_FUNC_MMAP)

cmake/config.h.in

@@ -49,8 +49,8 @@
 /* Define to 1 if you target processors with SSSE3+ and have <tmmintrin.h>. */
 #cmakedefine01 SNAPPY_HAVE_SSSE3
 
-/* Define to 1 if you target processors with BMI2+ and have <bmi2intrin.h>. */
-#cmakedefine01 SNAPPY_HAVE_BMI2
+/* Define if you target processors with BMI2+ and have <bmi2intrin.h>. */
+#cmakedefine SNAPPY_HAVE_BMI2
 
 /* Define to 1 if your processor stores words with the most significant byte
    first (like Motorola and SPARC, unlike Intel and VAX). */

snappy.cc

@@ -50,9 +50,7 @@
 // GCC and Clang can build code with AVX2 enabled but BMI2 disabled, in which
 // case issuing BMI2 instructions results in a compiler error.
 #if defined(__BMI2__) || (defined(_MSC_VER) && defined(__AVX2__))
-#define SNAPPY_HAVE_BMI2 1
-#else
-#define SNAPPY_HAVE_BMI2 0
+#define SNAPPY_HAVE_BMI2
 #endif
 #endif  // !defined(SNAPPY_HAVE_BMI2)
 
@@ -62,7 +60,7 @@
 #include <tmmintrin.h>
 #endif
 
-#if SNAPPY_HAVE_BMI2
+#if defined(SNAPPY_HAVE_BMI2)
 // Please do not replace with <x86intrin.h>. or with headers that assume more
 // advanced SSE versions without checking with all the OWNERS.
 #include <immintrin.h>
@@ -749,7 +747,7 @@ static inline void Report(const char *algorithm, size_t compressed_size,
 static inline uint32_t ExtractLowBytes(uint32_t v, int n) {
   assert(n >= 0);
   assert(n <= 4);
-#if SNAPPY_HAVE_BMI2
+#if defined(SNAPPY_HAVE_BMI2)
   return _bzhi_u32(v, 8 * n);
 #else
   // This needs to be wider than uint32_t otherwise `mask << 32` will be