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Differential D22205

Update the LangRef description of the 'returned' attribute
ClosedPublic

Authored by hfinkel on Jul 10 2016, 2:47 PM.

Details

Reviewers
chandlerc
reames
majnemer
Commits
rG3b66caa290ab: Update the LangRef description of the 'returned' attribute
rL275026: Update the LangRef description of the 'returned' attribute
Summary

The description of the 'returned' attribute says that it is only used when code-generating the caller. I'd like to make the optimizer smarter about looking through functions with returned arguments (generally, but motivated by my llvm.noalias work). As David pointed out in the review of D22202, the LangRef should be updated to make its expanded uses clearer.

Diff Detail

Event Timeline

hfinkel updated this revision to Diff 63437.Jul 10 2016, 2:47 PM
hfinkel retitled this revision from to Update the LangRef description of the 'returned' attribute.
hfinkel updated this object.
hfinkel added reviewers: majnemer, chandlerc, reames.
hfinkel added a subscriber: llvm-commits.
Herald added a subscriber: mcrosier. · View Herald TranscriptJul 10 2016, 2:47 PM
majnemer accepted this revision.Jul 10 2016, 2:52 PM
majnemer edited edge metadata.

LGTM

This revision is now accepted and ready to land.Jul 10 2016, 2:52 PM
Closed by commit rL275026: Update the LangRef description of the 'returned' attribute (authored by hfinkel). · Explain WhyJul 10 2016, 2:59 PM
This revision was automatically updated to reflect the committed changes.

Revision Contents

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docs/
13 lines

Diff 63437

docs/LangRef.rst

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``nest`` ``nest``
This indicates that the pointer parameter can be excised using the This indicates that the pointer parameter can be excised using the
:ref:`trampoline intrinsics <int_trampoline>`. This is not a valid :ref:`trampoline intrinsics <int_trampoline>`. This is not a valid
attribute for return values and can only be applied to one parameter. attribute for return values and can only be applied to one parameter.
``returned`` ``returned``
This indicates that the function always returns the argument as its return This indicates that the function always returns the argument as its return
value. This is an optimization hint to the code generator when generating value. This is a hint to the optimizer and code generator used when
the caller, allowing tail call optimization and omission of register saves generating the caller, allowing value propagation, tail call optimization,
and restores in some cases; it is not checked or enforced when generating and omission of register saves and restores in some cases; it is not
the callee. The parameter and the function return type must be valid checked or enforced when generating the callee. The parameter and the
operands for the :ref:`bitcast instruction <i_bitcast>`. This is not a function return type must be valid operands for the
valid attribute for return values and can only be applied to one parameter. :ref:`bitcast instruction <i_bitcast>`. This is not a valid attribute for
return values and can only be applied to one parameter.
``nonnull`` ``nonnull``
This indicates that the parameter or return pointer is not null. This This indicates that the parameter or return pointer is not null. This
attribute may only be applied to pointer typed parameters. This is not attribute may only be applied to pointer typed parameters. This is not
checked or enforced by LLVM, the caller must ensure that the pointer checked or enforced by LLVM, the caller must ensure that the pointer
passed in is non-null, or the callee must ensure that the returned pointer passed in is non-null, or the callee must ensure that the returned pointer
is non-null. is non-null.
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