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[PlaceSafepoints] New attributes for patchable statepoints.

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Summary:
This patch teaches the PlaceSafepoints pass about two `CallSite`
function attributes:

 * "statepoint-id": if the string value of this attribute can be parsed
   as an integer, then it is propagated to the ID parameter of the
   statepoint created.

 * "statepoint-num-patch-bytes": if the string value of this attribute
   can be parsed as an integer, then it is propagated to the `num patch
   bytes` parameter of the statepoint created.

This change intentionally does not assert on a malformed value for these
attributes, given that they're not "official" attributes.

Reviewers: reames, pgavlin

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9735

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237286 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjoy Das
2015-05-13 20:11:31 +00:00
parent 7569db4a8c
commit 3f0ca03e94
3 changed files with 99 additions and 12 deletions
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docs/Statepoints.rst
+15
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@@ -677,6 +677,21 @@ of this function is inserted at each poll site desired. While calls or invokes
inside this method are transformed to a ``gc.statepoints``, recursive poll
insertion is not performed.
By default PlaceSafepoints passes in ``0xABCDEF00`` as the statepoint
ID and ``0`` as the number of patchable bytes to the newly constructed
``gc.statepoint``. These values can be configured on a per-callsite
basis using the attributes ``"statepoint-id"`` and
``"statepoint-num-patch-bytes"``. If a call site is marked with a
``"statepoint-id"`` function attribute and its value is a positive
integer (represented as a string), then that value is used as the ID
of the newly constructed ``gc.statepoint``. If a call site is marked
with a ``"statepoint-num-patch-bytes"`` function attribute and its
value is a positive integer, then that value is used as the 'num patch
bytes' parameter of the newly constructed ``gc.statepoint``. The
``"statepoint-id"`` and ``"statepoint-num-patch-bytes"`` attributes
are not propagated to the ``gc.statepoint`` call or invoke if they
could be successfully parsed.
If you are scheduling the RewriteStatepointsForGC pass late in the pass order,
you should probably schedule this pass immediately before it. The exception
would be if you need to preserve abstract frame information (e.g. for