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Update the LangRef description of the 'returned' attribute 

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.

Differential Revision: http://reviews.llvm.org/D22205

llvm-svn: 275026
This commit is contained in:
Hal Finkel 2016-07-10 21:52:39 +00:00
parent fedc01ad76
commit 3b66caa290
1 changed files with 7 additions and 6 deletions
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13
llvm/docs/LangRef.rst
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@ -1060,12 +1060,13 @@ Currently, only the following parameter attributes are defined:
``returned``
This indicates that the function always returns the argument as its return
value. This is an optimization hint to the code generator when generating
the caller, allowing tail call optimization and omission of register saves
and restores in some cases; it is not checked or enforced when generating
the callee. The parameter and the function return type must be valid
operands for the :ref:`bitcast instruction <i_bitcast>`. This is not a
valid attribute for return values and can only be applied to one parameter.
value. This is a hint to the optimizer and code generator used when
generating the caller, allowing value propagation, tail call optimization,
and omission of register saves and restores in some cases; it is not
checked or enforced when generating the callee. The parameter and the
function return type must be valid operands for the
:ref:`bitcast instruction <i_bitcast>`. This is not a valid attribute for
return values and can only be applied to one parameter.
``nonnull``
This indicates that the parameter or return pointer is not null. This