[llvm] r361590 - Clarify how musttail can be used to create forwarding thunks

[Reid Kleckner via llvm-commits]

Author: rnk
Date: Thu May 23 18:45:47 2019
New Revision: 361590

URL: http://llvm.org/viewvc/llvm-project?rev=361590&view=rev
Log:
Clarify how musttail can be used to create forwarding thunks

Modified:
    llvm/trunk/docs/LangRef.rst

Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=361590&r1=361589&r2=361590&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Thu May 23 18:45:47 2019
@@ -10006,12 +10006,16 @@ This instruction requires several argume
       recursive cycle in the call graph.
    #. Arguments with the :ref:`inalloca <attr_inalloca>` attribute are
       forwarded in place.
+   #. If the musttail call appears in a function with the ``"thunk"`` attribute
+      and the caller and callee both have varargs, than any unprototyped
+      arguments in register or memory are forwarded to the callee. Similarly,
+      the return value of the callee is returned the 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, while ``musttail`` implies that varargs from the
-   caller are passed to the callee. Calls marked ``musttail`` must obey the
-   following additional  rules:
+   varargs from the caller. Calls marked ``musttail`` must obey the following
+   additional  rules:
 
    - The call must immediately precede a :ref:`ret <i_ret>` instruction,
      or a pointer bitcast followed by a ret instruction.