Add some brief LLVM 19 release notes for Pointer Authentication ABI support.

Author: asl

clang/docs/ReleaseNotes.rst

@@ -1191,11 +1191,13 @@ Arm and AArch64 Support
   improvements for most targets. We have not changed the default behavior for
   ARMv6, but may revisit that decision in the future. Users can restore the old
   behavior with -m[no-]unaligned-access.
+
 - An alias identifier (rdma) has been added for targeting the AArch64
   Architecture Extension which uses Rounding Doubling Multiply Accumulate
   instructions (rdm). The identifier is available on the command line as
   a feature modifier for -march and -mcpu as well as via target attributes
   like ``target_version`` or ``target_clones``.
+
 - Support has been added for the following processors (-mcpu identifiers in parenthesis):
     * Arm Cortex-R52+ (cortex-r52plus).
     * Arm Cortex-R82AE (cortex-r82ae).
@@ -1213,6 +1215,12 @@ Arm and AArch64 Support
   objects. It doesn't cause any code generation changes, as the code generated
   by clang is already compatible with GCS.
 
+ - Experimental support has been added for pointer authentication ABI for С/C++.
+
+ - Pointer authentication ABI could be enabled for AArch64 Linux via
+   ``-mabi=pauthtest`` option or via specifying ``pauthtest`` environment part of
+   target triple.
+
 Android Support
 ^^^^^^^^^^^^^^^
 

llvm/docs/ReleaseNotes.rst

@@ -80,6 +80,11 @@ Changes to the LLVM IR
     removed. The next argument has been changed from byte index to bit
     index.
 * Added ``llvm.experimental.vector.compress`` intrinsic.
+* Added special kind of `constant expressions
+  <https://llvm.org/docs/LangRef.html#pointer-authentication-constants>`_ to
+  represent pointers with signature embedded into it.
+* Added `pointer authentication operand bundles
+  <https://llvm.org/docs/LangRef.html#pointer-authentication-operand-bundles>`_. 
 
 Changes to LLVM infrastructure
 ------------------------------
@@ -125,6 +130,15 @@ Changes to the AArch64 Backend
   when specified via ``-march=`` or an ``-mcpu=`` that supports them.  The
   attribute ``"target-features"="+v9a"`` no longer implies ``"+sve"`` and
   ``"+sve2"`` respectively.
+* Added support for ELF pointer authentication relocations as specified in
+  `PAuth ABI Extension to ELF
+  <https://github.com/ARM-software/abi-aa/blob/main/pauthabielf64/pauthabielf64.rst>`_.
+* Added codegeneration, ELF object file and linker support for authenticated
+  call lowering, signed constants and emission of signing scheme details in
+  ``GNU_PROPERTY_AARCH64_FEATURE_PAUTH`` property of ``.note.gnu.property``
+  section.
+* Added codegeneration support for ``llvm.ptrauth.auth`` and
+  ``llvm.ptrauth.resign`` intrinsics.
 
 Changes to the AMDGPU Backend
 -----------------------------