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

tests/std/include/test_vector_algorithms_support.hpp

@@ -4,12 +4,15 @@
 #pragma once
 
 #include <algorithm>
+#include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <cstdio>
+#include <cstdlib>
 #include <functional>
 #include <isa_availability.h>
 #include <random>
+#include <string>
 #include <vector>
 
 inline void initialize_randomness(std::mt19937_64& gen) {
@@ -41,24 +44,53 @@ 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);
+
+    auto has_env_var_escape_hatch = [] {
+        size_t return_value = 0;
+        char buffer[2]{};
+        const errno_t err = ::getenv_s(&return_value, buffer, std::size(buffer), "STL_TEST_DOWNLEVEL_MACHINE");
+        return err == 0 && buffer == std::string{"1"};
+    };
+
+    if (!has_env_var_escape_hatch()) {
+        const bool has_feature = (__isa_enabled & (1UL << as_ulong)) != 0;
+        if (!has_feature) {
+            std::printf("The feature %lu is not available, the test does not have full coverage!\n"
+                        "You can set the environment variable STL_TEST_DOWNLEVEL_MACHINE to 1,\n"
+                        "if you intentionally test on a machine without all features available.\n",
+                as_ulong);
+        }
+        assert(has_feature);
+    }
+
+    __isa_enabled &= ~(1UL << as_ulong);
 }
 #endif // (defined(_M_IX86) || defined(_M_X64)) && !defined(_M_CEE_PURE)
 
 constexpr std::size_t dataCount = 1024;
 
 template <class TestFunc>
-void run_randomized_tests_with_different_isa_levels(TestFunc tests) {
-    std::mt19937_64 gen;
-    initialize_randomness(gen);
+void run_tests_with_different_isa_levels(TestFunc tests) {
+    tests();
 
-    tests(gen);
+#if (defined(_M_IX86) || (defined(_M_X64) && !defined(_M_ARM64EC))) && !defined(_M_CEE_PURE)
+    const auto original_isa = __isa_enabled;
 
-#if (defined(_M_IX86) || defined(_M_X64)) && !defined(_M_CEE_PURE)
     disable_instructions(__ISA_AVAILABLE_AVX2);
-    tests(gen);
+    tests();
 
     disable_instructions(__ISA_AVAILABLE_SSE42);
-    tests(gen);
-#endif // (defined(_M_IX86) || defined(_M_X64)) && !defined(_M_CEE_PURE)
+    tests();
+
+    __isa_enabled = original_isa;
+#endif // (defined(_M_IX86) || (defined(_M_X64) && !defined(_M_ARM64EC))) && !defined(_M_CEE_PURE)
+}
+
+template <class TestFunc>
+void run_randomized_tests_with_different_isa_levels(TestFunc tests) {
+    std::mt19937_64 gen;
+    initialize_randomness(gen);
+
+    run_tests_with_different_isa_levels([&] { tests(gen); });
 }

tests/std/tests/GH_002431_byte_range_find_with_unreachable_sentinel/test.cpp

@@ -4,14 +4,15 @@
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
-#include <isa_availability.h>
 #include <ranges>
 
 #pragma warning(push) // TRANSITION, OS-23694920
 #pragma warning(disable : 4668) // 'MEOW' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'
 #include <Windows.h>
 #pragma warning(pop)
 
+#include "test_vector_algorithms_support.hpp"
+
 using namespace std;
 
 template <class T>
@@ -31,14 +32,6 @@ 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);
@@ -58,13 +51,7 @@ int main() {
     void* p2 = VirtualAlloc(p, page, MEM_COMMIT, PAGE_READWRITE);
     assert(p2 != nullptr);
 
-    test_all_element_sizes(p, page);
-#if defined(_M_IX86) || defined(_M_X64)
-    disable_instructions(__ISA_AVAILABLE_AVX2);
-    test_all_element_sizes(p, page);
-    disable_instructions(__ISA_AVAILABLE_SSE42);
-    test_all_element_sizes(p, page);
-#endif // defined(_M_IX86) || defined(_M_X64)
+    run_tests_with_different_isa_levels([&] { test_all_element_sizes(p, page); });
 
     VirtualFree(p, 0, MEM_RELEASE);
 }

tests/std/tests/GH_003617_vectorized_meow_element/test.cpp

@@ -6,19 +6,13 @@
 #ifdef _M_X64
 
 #include <cstddef>
-#include <isa_availability.h>
 #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;
@@ -31,13 +25,7 @@ void test_gh_3617() {
 }
 
 int main() {
-    test_gh_3617();
-
-    disable_instructions(__ISA_AVAILABLE_AVX2);
-    test_gh_3617();
-
-    disable_instructions(__ISA_AVAILABLE_SSE42);
-    test_gh_3617();
+    run_tests_with_different_isa_levels([] { test_gh_3617(); });
 }
 #else // ^^^ x64 / other architectures vvv
 int main() {}