Use env var to disable/enable avx512 dispatch

Author: Raghuveer Devulapalli

lib/x86simdsort.cpp

@@ -7,20 +7,22 @@
 
 static int check_cpu_feature_support(std::string_view cpufeature)
 {
-    if (cpufeature == "avx512_spr")
+    const char* disable_avx512 = std::getenv("XSS_DISABLE_AVX512");
+
+    if ((cpufeature == "avx512_spr") && (!disable_avx512))
 #ifdef __FLT16_MAX__
         return __builtin_cpu_supports("avx512f")
                 && __builtin_cpu_supports("avx512fp16")
                 && __builtin_cpu_supports("avx512vbmi2");
 #else
         return 0;
 #endif
-    else if (cpufeature == "avx512_icl")
+    else if ((cpufeature == "avx512_icl") && (!disable_avx512))
         return __builtin_cpu_supports("avx512f")
                 && __builtin_cpu_supports("avx512vbmi2")
                 && __builtin_cpu_supports("avx512bw")
                 && __builtin_cpu_supports("avx512vl");
-    else if (cpufeature == "avx512_skx")
+    else if ((cpufeature == "avx512_skx") && (!disable_avx512))
         return __builtin_cpu_supports("avx512f")
                 && __builtin_cpu_supports("avx512dq")
                 && __builtin_cpu_supports("avx512vl");