[clang] [llvm] [ARM] Fix musttail calls (PR #109943)

[Oliver Stannard via llvm-commits]

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@@ -12658,10 +12658,10 @@ This instruction requires several arguments:
       the return value of the callee is returned to the caller's caller, even
       if a void return type is in use.
 
-   Both markers imply that the callee does not access allocas from the caller.
-   The ``tail`` marker additionally implies that the callee does not access
-   varargs from the caller. Calls marked ``musttail`` must obey the following
-   additional  rules:
+   Both markers imply that the callee does not access allocas or ``byval``
+   arguments from the caller. The ``tail`` marker additionally implies that the
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ostannard wrote:

That was my intention, but the wording here didn't allow it. I've split the langref change out into #110093, and updated the wording. I'll leave the old patch in here for now to avoid a force-push.

https://github.com/llvm/llvm-project/pull/109943