[llvm] [GISEL] G_SPLAT_VECTOR can take a splat that is smaller than the vector element (PR #86974)

[Michael Maitland via llvm-commits]

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@@ -690,6 +690,10 @@ G_SPLAT_VECTOR
 
 Create a vector where all elements are the scalar from the source operand.
 
+The type of the operand must be equal to or smaller than the vector element
+type. If the operand is smaller than the vector element type, the scalar is
+implicitly truncated to the vector element type.
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michaelmaitland wrote:

I got it all backwards 😆 . The operand should be allowed to be greater than the size of the vector element.

https://github.com/llvm/llvm-project/pull/86974