[llvm] [GISEL] Add IRTranslation for shufflevector on scalable vector types (PR #80378)

[Thorsten Schütt via llvm-commits]

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@@ -639,6 +639,11 @@ Concatenate two vectors and shuffle the elements according to the mask operand.
 The mask operand should be an IR Constant which exactly matches the
 corresponding mask for the IR shufflevector instruction.
 
+G_SPLAT_VECTOR
+^^^^^^^^^^^^^^^^
+
+Create a vector where all elements are the scalar from the source operand.
+
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tschuett wrote:

Limiting G_SPLAT_VECTOR to scalable vectors would be a nice contribution. G_BUILD_VECTOR would be still be the tool for fixed size vectors. 

https://github.com/llvm/llvm-project/pull/80378