AMDGPU: Add some release notes

Author: arsenm

llvm/docs/LangRef.rst

@@ -14732,6 +14732,8 @@ trapping or setting ``errno``.
 When specified with the fast-math-flag 'afn', the result may be approximated
 using a less accurate calculation.
 
+.. _int_ldexp:
+
 '``llvm.ldexp.*``' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

llvm/docs/ReleaseNotes.rst

@@ -149,6 +149,15 @@ Changes to the AMDGPU Backend
   improves the interaction between AMDGPU buffer operations and the LLVM memory
   model, and so the non `.ptr` intrinsics are deprecated.
 
+* SGPR spilling is now performed to virtual VGPRs. This should avoid
+  some assorted register allocation failures.
+
+* Backend now performs range merging of "amdgpu-waves-per-eu" attribute based on
+  known callers.
+
+* Certain :ref:`atomicrmw <i_atomicrmw>` operations are now optimized by
+  performing a wave reduction if the access is uniform by default.
+
 * Removed ``llvm.amdgcn.atomic.inc`` and ``llvm.amdgcn.atomic.dec``
   intrinsics. :ref:`atomicrmw <i_atomicrmw>` should be used instead
   with ``uinc_wrap`` and ``udec_wrap``.
@@ -176,6 +185,9 @@ Changes to the AMDGPU Backend
 * `llvm.sqrt.f64` is now lowered correctly. Use `llvm.amdgcn.sqrt.f64`
   for raw instruction access.
 
+* Deprecate `llvm.amdgcn.ldexp` intrinsic. :ref:`llvm.ldexp <int_ldexp>`
+  should be used instead.
+
 Changes to the ARM Backend
 --------------------------