Index: clang/lib/CodeGen/BackendUtil.cpp
===================================================================
--- clang/lib/CodeGen/BackendUtil.cpp
+++ clang/lib/CodeGen/BackendUtil.cpp
@@ -917,6 +917,14 @@
   }
 }
 
+FunctionPassManager addSanitizersAtO0() {
+  FunctionPassManager FPM;
+  if (LangOpts.Sanitize.has(SanitizerKind::Memory))
+    FPM.addPass(MemorySanitizerPass());
+
+  return FPM;
+}
+
 /// A clean version of `EmitAssembly` that uses the new pass manager.
 ///
 /// Not all features are currently supported in this system, but where
@@ -1036,7 +1044,7 @@
       if (LangOpts.Sanitize.has(SanitizerKind::Memory))
         PB.registerOptimizerLastEPCallback(
             [](FunctionPassManager &FPM, PassBuilder::OptimizationLevel Level) {
-              FPM.addPass(MemorySanitizerPass({}));
+              FPM.addPass(MemorySanitizerPass());
             });
       if (LangOpts.Sanitize.has(SanitizerKind::Thread))
         PB.registerOptimizerLastEPCallback(
@@ -1063,6 +1071,8 @@
                                                CodeGenOpts.DebugPassManager);
       }
     }
+    if (Level == PassBuilder::O0)
+      MPM.addPass(addSanitizersAtO0());
   }
 
   // FIXME: We still use the legacy pass manager to do code generation. We