[mips] Add initial release notes for MIPS32.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_38@260095 91177308-0d34-0410-b5e6-96231b3b80d8

Author: dsandersllvm

docs/ReleaseNotes.rst

@@ -107,8 +107,63 @@ Changes to the ARM Backend
 Changes to the MIPS Target
 --------------------------
 
- During this release ...
-
+During this release the MIPS target has:
+
+* Significantly extended support for the Integrated Assembler. See below for
+  more information
+* Added support for the ``P5600`` processor.
+* Added support for the ``interrupt`` attribute for MIPS32R2 and later. This
+  attribute will generate a function which can be used as a interrupt handler
+  on bare metal MIPS targets using the static relocation model.
+* Added support for the ``ERETNC`` instruction found in MIPS32R5 and later.
+* Added support for OpenCL. See http://portablecl.org/.
+
+  * Address spaces 1 to 255 are now reserved for software use and conversions
+    between them are no-op casts.
+
+* Removed the ``mips16`` value for the -mcpu option since it is an :abbr:`ASE
+  (Application Specific Extension)` and not a processor. If you were using this,
+  please specify another CPU and use ``-mips16`` to enable MIPS16.
+* Removed ``copy_u.w`` from 32-bit MSA and ``copy_u.d`` from 64-bit MSA since
+  they have been removed from the MSA specification due to forward compatibility
+  issues.  For example, 32-bit MSA code containing ``copy_u.w`` would behave
+  differently on a 64-bit processor supporting MSA. The corresponding intrinsics
+  are still available and may expand to ``copy_s.[wd]`` where this is
+  appropriate for forward compatibility purposes.
+* Relaxed the ``-mnan`` option to allow ``-mnan=2008`` on MIPS32R2/MIPS64R2 for
+  compatibility with GCC.
+* Made MIPS64R6 the default CPU for 64-bit Android triples.
+
+The MIPS target has also fixed various bugs including the following notable
+fixes:
+
+* Fixed reversed operands on ``mthi``/``mtlo`` in the DSP :abbr:`ASE
+  (Application Specific Extension)`.
+* The code generator no longer uses ``jal`` for calls to absolute immediate
+  addresses.
+* Disabled fast instruction selection on MIPS32R6 and MIPS64R6 since this is not
+  yet supported.
+* Corrected addend for ``R_MIPS_HI16`` and ``R_MIPS_PCHI16`` in MCJIT
+* The code generator no longer crashes when handling subregisters of an 64-bit
+  FPU register with undefined value.
+* The code generator no longer attempts to use ``$zero`` for operands that do
+  not permit ``$zero``.
+* Corrected the opcode used for ``ll``/``sc`` when using MIPS32R6/MIPS64R6 and
+  the Integrated Assembler.
+* Added support for atomic load and atomic store.
+* Corrected debug info when dynamically re-aligning the stack.
+ 
+Integrated Assembler
+^^^^^^^^^^^^^^^^^^^^
+We have made a large number of improvements to the integrated assembler for
+MIPS. In this release, the integrated assembler isn't quite production-ready
+since there are a few known issues related to bare-metal support, checking
+immediates on instructions, and the N32/N64 ABI's. However, the current support
+should be sufficient for many users of the O32 ABI, particularly those targeting
+MIPS32 on Linux or bare-metal MIPS32.
+
+If you would like to try the integrated assembler, please use
+``-fintegrated-as``.
 
 Changes to the PowerPC Target
 -----------------------------