diff --git a/libcxx/include/__assert b/libcxx/include/__assert
--- a/libcxx/include/__assert
+++ b/libcxx/include/__assert
@@ -38,7 +38,10 @@
          ? (void)0                                                                                                     \
          : _LIBCPP_VERBOSE_ABORT(                                                                                      \
                "%s:%d: assertion %s failed: %s\n", __builtin_FILE(), __builtin_LINE(), #expression, message))
-#elif !defined(_LIBCPP_ASSERTIONS_DISABLE_ASSUME) && __has_builtin(__builtin_assume)
+// TODO: __builtin_assume can currently inhibit optimizations. Until this has been fixed and we can add
+//       assumptions without a clear optimization intent, disable that to avoid worsening the code generation.
+//       See https://discourse.llvm.org/t/llvm-assume-blocks-optimization/71609 for a discussion.
+#elif 0 && __has_builtin(__builtin_assume)
 #  define _LIBCPP_ASSERT(expression, message)                                                                          \
     (_LIBCPP_DIAGNOSTIC_PUSH _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wassume")                                              \
          __builtin_assume(static_cast<bool>(expression)) _LIBCPP_DIAGNOSTIC_POP)