[libcxx-commits] [PATCH] D127672: [libc++] Test the size of basic_string

[Hubert Tong via Phabricator via libcxx-commits]

hubert.reinterpretcast added inline comments.


================
Comment at: libcxx/test/libcxx/strings/basic.string/alignof.compile.pass.cpp:99
+static_assert(alignof(test_string<char>) == 4, "");
+static_assert(alignof(small_string<char>) == 2, "");
+
----------------
hubert.reinterpretcast wrote:
> hubert.reinterpretcast wrote:
> > hubert.reinterpretcast wrote:
> > > This used to pass on AIX, but changes to use bitfields (without applying `_LIBCPP_PACKED_BYTE_FOR_AIX`) has broken this.
> > However, using the above also causes other members to be less aligned if padding is not explicitly added.
> Or rather it causes the string type to be less aligned.
```
--- string_20220520     2022-05-20 11:48:54.326820970 -0400
+++ string      2022-06-16 19:30:22.238194020 -0400
@@ -724,3 +724,4 @@

-    struct __long
+_LIBCPP_PACKED_BYTE_FOR_AIX
+    struct __long_impl
     {
@@ -729,2 +730,6 @@
         size_type __size_;
+        char
+            __padding_[sizeof(pointer) *
+                           ((2 * sizeof(size_type) - 1) / sizeof(pointer) + 1) -
+                       2 * sizeof(size_type)];
         pointer   __data_;
@@ -731,2 +736,4 @@
     };
+_LIBCPP_PACKED_BYTE_FOR_AIX_END
+    struct alignas(size_type) alignas(pointer) __long : __long_impl {};

@@ -735,3 +742,4 @@

-    struct __short
+_LIBCPP_PACKED_BYTE_FOR_AIX
+    struct __short_impl
     {
@@ -742,2 +750,4 @@
     };
+_LIBCPP_PACKED_BYTE_FOR_AIX_END
+    struct alignas(value_type) __short : __short_impl {};

```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D127672/new/

https://reviews.llvm.org/D127672