incorporate PR feedback: merge tests

Author: davidmrdavid

compiler-rt/test/asan/TestCases/Windows/allocator_may_return_null_set_via_user_function.cpp

@@ -1,14 +1,21 @@
 // RUN: %clangxx_asan -O0 %s -o %t
-// RUN: %env_asan_opts=allocator_may_return_null=0 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK1
-// RUN: %env_asan_opts=allocator_may_return_null=1 %run %t 2>&1 | FileCheck %s --check-prefix=CHECK2
+// RUN: %env_asan_opts=allocator_may_return_null=0 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-ABORT
+// RUN: %env_asan_opts=allocator_may_return_null=1 %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-RETURN_NULL
 
-// CHECK1: exceeds maximum supported size
-// CHECK1: ABORT
+// RUN: %clangxx_asan -O0 %s -o %t -DUSER_FUNCTION
+// RUN: %env_asan_opts=allocator_may_return_null=1 %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-RETURN_NULL
 
-// CHECK2: Success
+#if USER_FUNCTION
+// On Windows, flags configured through the user-defined function `__asan_default_options`
+// are suspected to not always be honored according to GitHub bug:
+// https://github.com/llvm/llvm-project/issues/117925
+// This test ensures we do not regress on `allocator_may_return_null` specifically.
+extern "C" __declspec(dllexport) extern const char *__asan_default_options() {
+  return "allocator_may_return_null=1";
+}
+#endif
 
 #include <cstdint>
-#include <cstdio>
 #include <cstdlib>
 #include <limits>
 
@@ -17,7 +24,10 @@ int main() {
   // terminate the program unless `allocator_may_return_null` is set.
   size_t max = std::numeric_limits<size_t>::max();
 
+  // CHECK-ABORT: exceeds maximum supported size
+  // CHECK-ABORT: ABORT
   free(malloc(max));
-  printf("Success");
+
+  printf("Success"); // CHECK-RETURN_NULL: Success
   return 0;
 }