ensure ASAN_OPTS takes precedence

Author: davidmrdavid

compiler-rt/lib/asan/asan_flags.cpp

@@ -234,13 +234,10 @@ void InitializeFlags() {
   // __sanitizer_register_weak_function.
   AddRegisterWeakFunctionCallback(
       reinterpret_cast<uptr>(__asan_default_options), []() {
-        FlagParser asan_parser;
-
-        RegisterAsanFlags(&asan_parser, flags());
-        RegisterCommonFlags(&asan_parser);
-        asan_parser.ParseString(__asan_default_options());
-
-        DisplayHelpMessages(&asan_parser);
+        // We call `InitializeDefaultFlags` again, instead of just parsing
+        // `__asan_default_options` directly, to ensure that flags set through
+        // `ASAN_OPTS` take precedence over those set through `__asan_default_options`.
+        InitializeDefaultFlags();
         ProcessFlags();
         ApplyFlags();
       });

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

@@ -5,6 +5,9 @@
 // RUN: %clangxx_asan -O0 %s -o %t -DUSER_FUNCTION
 // RUN: not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-MISMATCH
 
+// It is expected that ASAN_OPTS will override the value set through the user function.
+// RUN: %env_asan_opts=alloc_dealloc_mismatch=0 %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-SUCCESS
+
 #if USER_FUNCTION
 // It's important to test the `alloc_dealloc_mismatch` flag set through the user function because, on Windows,
 // flags configured through the user-defined function `__asan_default_options` are not always be honored.