Accessor aliases

In order to reduce the verbosity of programming with SYCL accessors,
this proposal aims to reduce the number of template parameters
to just 2 from the current 4 (placeholders accessors even have 5).
It achieves this by adding aliases to accessors
based on the access target
and slightly revised rules for access modes.

1. Added aliases to accessors
  * `buffer_accessor`,
  * `constant_buffer_accessor
  * `host_accessor`
2. Deduce access mode based on constness of data type
  * `access::mode::read` for `const dataT`
  * `access::mode::read_write` for `dataT`
3. Allow conversions to new aliases
4. Return aliases from buffer access
  * `get_device_access`
  * `get_device_constant_access`
  * `get_host_access`
5. Allow any accessor to be registered with `handler::require`
6. Overload for `handler::require` that also takes an access mode
  * Hint to the scheduler
7. Type traits to help with deducing access modes
  * `access_mode_from_type`
  * `type_from_access_mode`
8. Default all accessor template parameters
  * Expect the data type
  * Default to an accessor to global buffer with read-write access
  * Assumes any accessor can be a placeholder
9. Discussed some considerations and alternatives
10. Examples of reduced verbosity

Author: ProGTX

README.md

@@ -62,3 +62,4 @@ from this registry in the future.
 | CP019 | [On-chip Memory Allocation](onchip-memory/index.md) | SYCL 1.2.1 vendor extension  | 03 December 2018 | 03 December 2018 | _Available since CE 1.0.3_ |
 | CP020 | [Interop Task](interop_task/interop_task.md) | SYCL 1.2.1 | 16 January 2019 | 16 January 2019 | _Available since CE 1.0.5_ |
 | CP021 | [Default-Constructed Buffers](default-constructed-buffers/default-constructed-buffers.md) | SYCL 1.2.1 | 27 August 2019 | 5 September 2019 | _Draft_ |
+| CP023 | [Accessor aliases](accessor-alias/index.md) | SYCL 1.2.1 vendor extension  | 22 September 2019 | 22 September 2019 | _Work in Progress_ |

accessor-alias/index.md

@@ -0,0 +1,20 @@
+# Accessor aliases
+
+| Proposal ID | CP023  |
+|-------------|--------|
+| Name | Accessor aliases |
+| Date of Creation | 22 September 2019 |
+| Target | SYCL 1.2.1 vendor extension |
+| Current Status | _Work in Progress_ |
+| Reply-to | Peter Žužek <peter@codeplay.com> |
+| Original author | Peter Žužek <peter@codeplay.com> |
+| Contributors |  |
+
+## Overview
+
+This paper proposes the addition of target specific aliases to accessors
+in order to reduce accessor verbosity.
+
+## Versions
+
+[Version 1](sycl-2.2/index.md)