[llvm] [IR] Split vector.splice into vector.splice.down and vector.splice.up (PR #170796)

[Nikita Popov via llvm-commits]

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@@ -20738,21 +20738,70 @@ This is an overloaded intrinsic.
 
 ::
 
-      declare <2 x double> @llvm.vector.splice.v2f64(<2 x double> %vec1, <2 x double> %vec2, i32 %imm)
-      declare <vscale x 4 x i32> @llvm.vector.splice.nxv4i32(<vscale x 4 x i32> %vec1, <vscale x 4 x i32> %vec2, i32 %imm)
+      declare <2 x double> @llvm.vector.splice.down.v2f64(<2 x double> %vec1, <2 x double> %vec2, i32 %imm)
+      declare <vscale x 4 x i32> @llvm.vector.splice.down.nxv4i32(<vscale x 4 x i32> %vec1, <vscale x 4 x i32> %vec2, i32 %imm)
 
 Overview:
 """""""""
 
-The '``llvm.vector.splice.*``' intrinsics construct a vector by
-concatenating elements from the first input vector with elements of the second
-input vector, returning a vector of the same type as the input vectors. The
-signed immediate, modulo the number of elements in the vector, is the index
-into the first vector from which to extract the result value. This means
-conceptually that for a positive immediate, a vector is extracted from
-``concat(%vec1, %vec2)`` starting at index ``imm``, whereas for a negative
-immediate, it extracts ``-imm`` trailing elements from the first vector, and
-the remaining elements from ``%vec2``.
+The '``llvm.vector.splice.down.*``' intrinsics construct a vector by
+concatenating two vectors together, shifting the elements down by ``imm``, and
+extracting the lower half.
+
+This is equivalent to :ref:`llvm.fshr.* <int_fshr>`, but operating on elements
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nikic wrote:

Hm, isn't this one fshl?

https://github.com/llvm/llvm-project/pull/170796