[ARM64][CollectLOH] Add some comments to explain how the LOHs

framework works (for the compiler part), since the design
document is not available.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205379 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCLinkerOptimizationHint.cpp

@@ -14,6 +14,14 @@
 
 using namespace llvm;
 
+// Each LOH is composed by, in this order (each field is encoded using ULEB128):
+// - Its kind.
+// - Its number of arguments (let say N).
+// - Its arg1.
+// - ...
+// - Its argN.
+// <arg1> to <argN> are absolute addresses in the object file, i.e.,
+// relative addresses from the beginning of the object file.
 void MCLOHDirective::Emit_impl(raw_ostream &OutStream,
                                const MachObjectWriter &ObjWriter,
                                const MCAsmLayout &Layout) const {