[clang] aligned attribute doc (PR #195278)

[Vlad Serebrennikov via cfe-commits]

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@@ -10000,3 +9983,61 @@ different languages to coexist on the same call stack while each interpreting
 exceptions according to their own rules.
   }];
 }
+
+def AlignedDocs : Documentation {
+  let Category = DocCatDecl;
+  let Heading = "aligned";
+  let Content = [{
+The ``aligned`` attribute specifies a minimum alignment (in bytes) for a 
+variable, structure field, or type definition. The attribute takes an 
+optional non-negative integral constant expression. If the value is a 
+power of two, the compiler ensures the declaration is aligned to at least 
+that boundary; a value of zero has no effect on the alignment chosen at runtime.
+
+.. code-block:: c++
+
+  struct __attribute__((aligned(8))) S { 
+    short f[3]; 
+  };
+
+If the alignment factor is omitted, the compiler defaults to the largest(the most strict) 
+alignment supported by the target machine for any data type. 
+
+Applying this attribute to a structure or union, or to one of its members, changes the type's layout 
+properties. To ensure that array indexing and pointer arithmetic remain 
+consistent, the compiler automatically increases the structure's total size 
+(via tail padding) to a multiple of the alignment value. For example, a 
+struct with a natural size of 6 bytes marked directly (or indirectly via a member declaration) with ``aligned(8)`` will be 
+padded to 8 bytes.
+
+In C++, alignment requirements are inherited by derived classes. If a base 
+class has an alignment specified, the derived class will honor that 
+requirement to ensure the base subobject remains correctly aligned. 
+
+.. code-block:: c++
+
+  struct alignas(16) Base {
----------------
Endilll wrote:

Why is this example using `alignas(16)`, but `aligned` is nowhere to be found? Is this turning into a documentation for `alignas`?

https://github.com/llvm/llvm-project/pull/195278