[llvm] Add `llvm.vector.partial.reduce.fadd` intrinsic (PR #159776)

[Sander de Smalen via llvm-commits]

================
@@ -20613,6 +20613,48 @@ performance, and an out-of-loop phase to calculate the final scalar result.
 By avoiding the introduction of new ordering constraints, these intrinsics
 enhance the ability to leverage a target's accumulation instructions.
 
+'``llvm.vector.partial.reduce.fadd.*``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+This is an overloaded intrinsic.
+
+::
+
+      declare <4 x f32> @llvm.vector.partial.reduce.fadd.v4f32.v4f32.v8f32(<4 x f32> %a, <8 x f32> %b)
----------------
sdesmalen-arm wrote:

```suggestion
      declare <4 x f32> @llvm.vector.partial.reduce.fadd.v4f32.v8f32(<4 x f32> %a, <8 x f32> %b)
```

https://github.com/llvm/llvm-project/pull/159776