[PGO] internal option cleanups

1. Added comments for options
2. Added missing option cl::desc field
3. Uniified function filter option for graph viewing.
   Now PGO count/raw-counts share the same
   filter option: -view-bfi-func-name=.

llvm-svn: 293938
diff --git a/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp b/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp
index 856aadc..c496e32 100644
--- a/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp
+++ b/llvm/lib/CodeGen/MachineBlockFrequencyInfo.cpp
@@ -59,7 +59,11 @@
                           "display a graph using the real "
                           "profile count if available.")));
 
+// Command line option to specify the name of the function for CFG dump
+// Defined in Analysis/BlockFrequencyInfo.cpp:  -view-bfi-func-name=
 extern cl::opt<std::string> ViewBlockFreqFuncName;
+// Command line option to specify hot frequency threshold.
+// Defined in Analysis/BlockFrequencyInfo.cpp:  -view-hot-freq-perc=
 extern cl::opt<unsigned> ViewHotFreqPercent;
 
 static GVDAGType getGVDT() {