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Clarify how musttail can be used to create forwarding thunks

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llvm-svn: 361590
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Reid Kleckner 2019-05-24 01:45:47 +00:00
parent 716ccdb957
commit 77d428497c
1 changed files with 7 additions and 3 deletions
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docs/LangRef.rst
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@ -10006,12 +10006,16 @@ This instruction requires several arguments:
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.