Document the CoreCLR GC Strategy

Add notead about the CoreCLR GC Strategy to the 
Garbage Collection document.

llvm-svn: 237869

docs/GarbageCollection.rst

@@ -494,6 +494,7 @@ a ``gcroot`` strategy.
 As there names imply, the binary format produced is intended to model that 
 used by the Erlang and OCaml compilers respectively.  
 
+.. _statepoint_example_gc:
 
 The Statepoint Example GC
 -------------------------
@@ -517,6 +518,28 @@ The stack map format generated by this GC strategy can be found in the
 <statepoint-stackmap-format>`. This format is intended to be the standard 
 format supported by LLVM going forward.
 
+The CoreCLR GC
+-------------------------
+
+.. code-block:: c++
+
+  F.setGC("coreclr");
+
+This GC leverages the ``gc.statepoint`` mechanism to support the 
+`CoreCLR <https://github.com/dotnet/coreclr>`__ runtime.
+
+Support for this GC strategy is a work in progress. This strategy will 
+differ from 
+:ref:`statepoint-example GC<statepoint_example_gc>` strategy in 
+certain aspects like:
+
+* Base-pointers of interior pointers are not explicitly 
+  tracked and reported.
+
+* A different format is used for encoding stack maps.
+
+* Safe-point polls are only needed before loop-back edges
+  and before tail-calls (not needed at function-entry).
 
 Custom GC Strategies
 ====================