Clarify behavior of work_group_broadcast (#577)

* Clarify behavior of work_group_broadcast

Fix an unrelated typo.
Related to #169.

Signed-off-by: Marco Antognini <marco.antognini@arm.com>

* Improve specification and update sub_group_broadcast

Signed-off-by: Marco Antognini <marco.antognini@arm.com>

* Address typos

Signed-off-by: Marco Antognini <marco.antognini@arm.com>

Author: mantognini

OpenCL_C.txt

@@ -9948,7 +9948,7 @@ NOTE: The functionality described in this section <<unified-spec, requires>>
 support for OpenCL C 2.0, or OpenCL C 3.0 or newer and the
 {opencl_c_work_group_collective_functions} feature.
 
-This section decribes built-in functions that perform collective options
+This section describes built-in functions that perform collective options
 across a work-group.
 These built-in functions must be encountered by all work-items in a
 work-group executing the kernel.
@@ -9978,8 +9978,11 @@ footnote:[{fn-double-supported}] as the type for the arguments.
     | Broadcast the value of _a_ for work-item identified by _local_id_ to
       all work-items in the work-group.
 
-      _local_id_ must be the same value for all work-items in the
-      work-group.
+      Behavior is undefined when the value of _local_id_ is not equivalent for
+      all work-items in the work-group.
+
+      Behavior is undefined when _local_id_ is greater or equal to the
+      work-group size in the corresponding dimension.
 | gentype *work_group_reduce_<op>*(gentype _x_)
     | Return result of reduction operation specified by *<op>* for all
       values of _x_ specified by work-items in a work-group.
@@ -11032,8 +11035,11 @@ footnote:[{fn-int64-supported}], `ulong`, `half` footnote:[{fn-half-supported}],
   _sub_group_local_id_ (value returned by *get_sub_group_local_id*) to all
   work-items in the subgroup.
 
-  _sub_group_local_id_ must be the same value for all work-items in the
-  subgroup.
+  Behavior is undefined when the value of _sub_group_local_id_ is not
+  equivalent for all work-items in the subgroup.
+
+  Behavior is undefined when _sub_group_local_id_ is greater or equal to the
+  subgroup size.
 
 | gentype *sub_group_reduce_<op>* ( +
   gentype _x_)