[libcxx-commits] [libcxx] [libcxx] Align allocation to match `__set_long_cap` and `__get_long_cap` (PR #90292)

[Nikolas Klauser via libcxx-commits]

philnik777 wrote:

I've looked into this a bit more and it turns out that we have two unrelated bugs in `__recommend`. First, we add one if `__guess == __min_cap`, and second our minimum alignment we give to `__align_it` is one, instead of the `__endian_factor`.

I think
```diff
diff --git a/libcxx/include/string b/libcxx/include/string
index 883bc1d7e5dc..13af92fbce3c 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -1959,10 +1959,10 @@ private:
     if (__s < __min_cap) {
       return static_cast<size_type>(__min_cap) - 1;
     }
-    const size_type __boundary = sizeof(value_type) < __alignment ? __alignment / sizeof(value_type) : 1;
+    const size_type __boundary = sizeof(value_type) < __alignment ? __alignment / sizeof(value_type) : __endian_factor;
     size_type __guess          = __align_it<__boundary>(__s + 1) - 1;
     if (__guess == __min_cap)
-      ++__guess;
+      __guess += 2;
     return __guess;
   }
```
should fix the issues you're seeing.

https://github.com/llvm/llvm-project/pull/90292