+/// The MachineFrameInfo class represents an abstract stack frame until
+/// prolog/epilog code is inserted. This class is key to allowing stack frame
+/// representation optimizations, such as frame pointer elimination. It also
+/// allows more mundane (but still important) optimizations, such as reordering
+/// of abstract objects on the stack frame.
+///
+/// To support this, the class assigns unique integer identifiers to stack
+/// objects requested clients. These identifiers are negative integers for
+/// fixed stack objects (such as arguments passed on the stack) or nonnegative
+/// for objects that may be reordered. Instructions which refer to stack
+/// objects use a special MO_FrameIndex operand to represent these frame
+/// indexes.
+///
+/// Because this class keeps track of all references to the stack frame, it
+/// knows when a variable sized object is allocated on the stack. This is the
+/// sole condition which prevents frame pointer elimination, which is an
+/// important optimization on register-poor architectures. Because original
+/// variable sized alloca's in the source program are the only source of
+/// variable sized stack objects, it is safe to decide whether there will be
+/// any variable sized objects before all stack objects are known (for
+/// example, register allocator spill code never needs variable sized
+/// objects).
+///
+/// When prolog/epilog code emission is performed, the final stack frame is
+/// built and the machine instructions are modified to refer to the actual
+/// stack offsets of the object, eliminating all MO_FrameIndex operands from
+/// the program.
+///
+/// @brief Abstract Stack Frame Information