Describe where pref is used, rewrap to 80

Author: tgross35

llvm/docs/LangRef.rst

@@ -3240,23 +3240,24 @@ as follows:
     as :ref:`Non-Integral Pointer Type <nointptrtype>` s.  The ``0``
     address space cannot be specified as non-integral.
 
-``<abi>`` is a lower bound on what is required for a type to be
-considered aligned. This is used in various places, such as:
+``<abi>`` is a lower bound on what is required for a type to be considered
+aligned. This is used in various places, such as:
 
 - The alignment for loads and stores if none is explicitly given.
 - The alignment used to compute struct layout.
-- The alignment used to compute allocation sizes and thus
-  ``getelementptr`` offsets.
+- The alignment used to compute allocation sizes and thus ``getelementptr``
+  offsets.
 - The alignment below which accesses are considered underaligned.
 
-``<pref>`` allows providing a more optimal alignment that should be used
-when possible. ``<pref>`` is an optional value that must be greater than
-or equal to ``<abi>``. If omitted, the preceding ``:`` should also be
-omitted and ``<pref>`` will be equal to ``<abi>``.
+``<pref>`` allows providing a more optimal alignment that should be used when
+possible, primarily for ``alloca`` and the alignment of global variables. It is
+an optional value that must be greater than or equal to ``<abi>``. If omitted,
+the preceding ``:`` should also be omitted and ``<pref>`` will be equal to
+``<abi>``.
 
-Unless explicitly stated otherwise, every alignment specification is
-provided in bits and must be in the range [1,2^16). The value must be a
-power of times the width of a byte (i.e. ``align = 8 * 2^N``).
+Unless explicitly stated otherwise, every alignment specification is provided in
+bits and must be in the range [1,2^16). The value must be a power of two times
+the width of a byte (i.e. ``align = 8 * 2^N``).
 
 When constructing the data layout for a given target, LLVM starts with a
 default set of specifications which are then (possibly) overridden by