Added documentation to getMemsetStores.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190866 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -3811,6 +3811,24 @@ static SDValue getMemmoveLoadsAndStores(SelectionDAG &DAG, SDLoc dl,
                      &OutChains[0], OutChains.size());
 }
 
+/// \brief Lower the call to 'memset' intrinsic function into a series of store
+/// operations.
+///
+/// \param DAG Selection DAG where lowered code is placed.
+/// \param dl Link to corresponding IR location.
+/// \param Chain Control flow dependency.
+/// \param Dst Pointer to destination memory location.
+/// \param Src Value of byte to write into the memory.
+/// \param Size Number of bytes to write.
+/// \param Align Alignment of the destination in bytes.
+/// \param isVol True if destination is volatile.
+/// \param DstPtrInfo IR information on the memory pointer.
+/// \returns New head in the control flow, if lowering was successful, empty
+/// SDValue otherwise.
+///
+/// The function tries to replace 'llvm.memset' intrinsic with several store
+/// operations and value calculation code. This is usually profitable for small
+/// memory size.
 static SDValue getMemsetStores(SelectionDAG &DAG, SDLoc dl,
                                SDValue Chain, SDValue Dst,
                                SDValue Src, uint64_t Size,