[libcxx-commits] [PATCH] D97802: [libc++] Increase readability of typeinfo comparison of ARM64

[Richard Smith - zygoloid via Phabricator via libcxx-commits]

rsmith added inline comments.


================
Comment at: libcxx/include/typeinfo:265-269
     static bool __lt(__type_name_t __lhs, __type_name_t __rhs) _NOEXCEPT {
-      if (__is_type_name_unique(__lhs, __rhs))
+      if (__is_type_name_unique(__lhs) || __is_type_name_unique(__rhs))
         return __lhs < __rhs;
       return __builtin_strcmp(__type_name_to_string(__lhs), __type_name_to_string(__rhs)) < 0;
     }
----------------
This is not an ordering relation. For example, we could have non-unique C < unique B < non-unique A < non-unique C, where the first and second comparisons are address comparisons, and the third comparison is a string comparison.

I think perhaps something like this would work:

```
bool __lhs_unique = __is_type_name_unique(__lhs);
if (__lhs_unique != __is_type_name_unique(__rhs))
  return __lhs_unique;
if (__lhs_unique)
  return __lhs < __rhs;
return __builtin_strcmp(__type_name_to_string(__lhs), __type_name_to_string(__rhs)) < 0;
```

(That is: order all unique typeinfos before all non-unique ones, then order unique typeinfos by pointer and non-unique ones by string.)


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D97802/new/

https://reviews.llvm.org/D97802