[docs] Add llvm & clang release notes for LoongArch (#79097)

Author: SixWeining

clang/docs/ReleaseNotes.rst

@@ -1189,8 +1189,14 @@ Windows Support
 
 LoongArch Support
 ^^^^^^^^^^^^^^^^^
-- The ``model`` attribute is now supported for overriding the default code
-  model used to access global variables. The following values are supported:
+- Added builtins support for all LSX (128-bits SIMD) and LASX (256-bits SIMD)
+  instructions.
+- Added builtins support for approximate calculation instructions that were
+  introduced in LoongArch Reference Manual V1.10.
+- Made ``-mcmodel=`` compatible with LoongArch gcc that accepted ``normal``,
+  ``medium`` and ``extreme``.
+- The ``model`` attribute was now supported for overriding the default code
+  model used to access global variables. The following values were supported:
   ``normal``, ``medium`` and ``extreme``.
 
   *Example Code*:
@@ -1199,6 +1205,10 @@ LoongArch Support
 
      int var __attribute((model("extreme")));
 
+- Default to ``-fno-direct-access-external-data`` for non-PIC.
+- An ABI mismatch with gcc/g++ about empty structs/unions passing was fixed.
+- ``_mcount`` was generated instead of ``mcount``.
+
 RISC-V Support
 ^^^^^^^^^^^^^^
 - Unaligned memory accesses can be toggled by ``-m[no-]unaligned-access`` or the

llvm/docs/ReleaseNotes.rst

@@ -132,8 +132,21 @@ Changes to the Hexagon Backend
 
 Changes to the LoongArch Backend
 --------------------------------
-* The code model of global variables can now be overridden by means of
-  the newly added LLVM IR attribute, ``code_model``.
+
+* Added intrinsics support for all LSX (128-bits SIMD) and LASX (256-bits SIMD)
+  instructions.
+* Added definition and intrinsics support for new instructions that were
+  introduced in LoongArch Reference Manual V1.10.
+* Emitted adjacent ``pcaddu18i+jirl`` instrunction sequence with one relocation
+  ``R_LARCH_CALL36`` instead of ``pcalau12i+jirl`` with two relocations
+  ``R_LARCH_PCALA_{HI20,LO12}`` for function call in medium code model.
+* The code model of global variables can now be overridden by means of the newly
+  added LLVM IR attribute, ``code_model``.
+* Added support for the ``llvm.is.fpclass`` intrinsic.
+* ``mulodi4`` and ``muloti4`` libcalls were disabled due to absence in libgcc.
+* Added initial support for auto vectorization.
+* Added initial support for linker relaxation.
+* Assorted codegen improvements.
 
 Changes to the MIPS Backend
 ---------------------------