Make sure expected __isa_enabled bit was set before disabling it in feature-dependent tests

tests/std/include/test_vector_algorithms_support.hpp

@@ -7,6 +7,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <cstdio>
+#include <cstdlib>
 #include <functional>
 #include <isa_availability.h>
 #include <random>
@@ -41,7 +42,32 @@ inline void initialize_randomness(std::mt19937_64& gen) {
 extern "C" long __isa_enabled;
 
 inline void disable_instructions(ISA_AVAILABILITY isa) {
-    __isa_enabled &= ~(1UL << static_cast<unsigned long>(isa));
+    const unsigned long as_ulong = static_cast<unsigned long>(isa);
+
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+#else // ^^^ defined(__clang__) / !defined(__clang__) vvv
+#pragma warning(push)
+#pragma warning(disable : 4996)
+#endif // ^^^ !defined(__clang__) ^^^
+    const char* const env_val = std::getenv("STL_TEST_DOWNLEVEL_HOST");
+#ifdef __clang__
+#pragma clang diagnostic pop
+#else // ^^^ defined(__clang__) / !defined(__clang__) vvv
+#pragma warning(pop)
+#endif // ^^^ !defined(__clang__) ^^^
+
+    if (env_val == nullptr || std::atoi(env_val) == 0) {
+        if ((__isa_enabled & (1UL << as_ulong)) == 0) {
+            std::printf("The feature %lu is not available, the test does not have full coverage!\n", as_ulong);
+            std::printf("You can set environment variable STL_TEST_DOWNLEVEL_HOST to 1,\n"
+                        "if you intentionally test on a host with not all features available.");
+            abort();
+        }
+    }
+
+    __isa_enabled &= ~(1UL << as_ulong);
 }
 #endif // (defined(_M_IX86) || defined(_M_X64)) && !defined(_M_CEE_PURE)
 

tests/std/tests/GH_002431_byte_range_find_with_unreachable_sentinel/test.cpp

@@ -12,6 +12,8 @@
 #include <Windows.h>
 #pragma warning(pop)
 
+#include "test_vector_algorithms_support.hpp"
+
 using namespace std;
 
 template <class T>
@@ -31,14 +33,6 @@ void test_impl(void* sv, void* ev) {
     }
 }
 
-#if defined(_M_IX86) || defined(_M_X64)
-extern "C" long __isa_enabled;
-
-void disable_instructions(ISA_AVAILABILITY isa) {
-    __isa_enabled &= ~(1UL << static_cast<unsigned long>(isa));
-}
-#endif // defined(_M_IX86) || defined(_M_X64)
-
 void test_all_element_sizes(void* p, size_t page) {
     test_impl<char>(p, reinterpret_cast<char*>(p) + page);
     test_impl<short>(p, reinterpret_cast<char*>(p) + page);

tests/std/tests/GH_003617_vectorized_meow_element/test.cpp

@@ -10,15 +10,10 @@
 #include <vector>
 
 #include "test_min_max_element_support.hpp"
+#include "test_vector_algorithms_support.hpp"
 
 using namespace std;
 
-extern "C" long __isa_enabled;
-
-void disable_instructions(ISA_AVAILABILITY isa) {
-    __isa_enabled &= ~(1UL << static_cast<unsigned long>(isa));
-}
-
 void test_gh_3617() {
     // Test GH-3617 "<algorithm>: Silent bad codegen for vectorized meow_element() above 4 GB".
     constexpr size_t n = 0x4000'0010;