[PATCH] D129135: [doc][ReleaseNotes] Document AArch64 SVE ABI fix from D127209

[Peter Waller via Phabricator via cfe-commits]

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D127209 <https://reviews.llvm.org/D127209> fixed LLVM to bring it in line with the AAPCS. This affects
functions where the first SVE parameter appears in the 9th or later
arguments, and the function does not return an SVE type.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D129135

Files:
  clang/docs/ReleaseNotes.rst


Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -499,6 +499,15 @@
   (e.g. ``int : 0``) no longer prevents the structure from being considered a
   homogeneous floating-point or vector aggregate. The new behavior agrees with
   the AAPCS specification, and matches the similar bug fix in GCC 12.1.
+- Targeting AArch64, LLVM now only preserves the z8-z23 registers across
+  a call if the registers z0-z7 are used to pass data into or out of a
+  subroutine. This new behavior now matches the AAPCS. Previously LLVM
+  preserved z8-z23 across a call if the callee had an SVE type anywhere
+  in its signature. This would cause an incorrect use of the
+  caller-preserved z8-z23 ABI for example if the 9th argument to a
+  function were an SVE type. The analogous issue and fix applies to
+  predicate register arguments (p0-p3 for passing between subroutines,
+  and p4-15 preserved).
 - All copy constructors can now be trivial if they are not user-provided,
   regardless of the type qualifiers of the argument of the defaulted constructor,
   fixing dr2171.


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