[libcxx-commits] [PATCH] D70343: Add a `_LIBCPP_HARDEN` define

[Jan Wilken Dörrie via Phabricator via libcxx-commits]

jdoerrie added a comment.

In D70343#1748522 <https://reviews.llvm.org/D70343#1748522>, @EricWF wrote:

> What's the difference between `_LIBCPP_HARDEN` and simply defining `_LIBCPP_DEBUG=0`? That should turn on `_LIBCPP_ASSERT` in the same cases.


I believe the intent of `_LIBCPP_HARDEN` is to turn asserts into program terminations. Ideally this happens as quickly as possible with as little overhead as possible. Thus we directly call `__builtin_trap()` instead of going through `_VSTD::__libcpp_debug_function`. Furthermore, I believe we were under the impression that defining `_LIBCPP_DEBUG=0` turns on other checks as well, that we are not necessarily interested in. Please correct me if I'm wrong.



================
Comment at: libcxx/include/string_view:282
+    const_reference operator[](size_type __pos) const _NOEXCEPT {
+      return _LIBCPP_ASSERT(size() == 0 || __pos < size(), "string_view[] index out of bounds"), __data[__pos];
+    }
----------------
Checking that `size() == 0` seems like a mistake, as otherwise you would allow arbitrary indices for an empty string_view. This should just be `_LIBCPP_ASSERT(__pos < size(), "...");` unless I'm missing something obvious.

Given that string_view implies C++17 or newer, you should also be able to use multiple expressions in a constexpr function. IMO the following is easier to read:

```
    _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
    const_reference operator[](size_type __pos) const _NOEXCEPT {
      _LIBCPP_ASSERT(__pos < size(), "string_view[] index out of bounds");
      return __data[__pos];
    }
```



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  https://reviews.llvm.org/D70343/new/

https://reviews.llvm.org/D70343