[clang] [HLSL] Implement HLSL splatting (PR #118992)

[Sarah Spall via cfe-commits]

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@@ -370,6 +370,9 @@ CAST_OPERATION(HLSLArrayRValue)
 // Aggregate by Value cast (HLSL only).
 CAST_OPERATION(HLSLElementwiseCast)
 
+// Splat cast for Aggregates (HLSL only).
+CAST_OPERATION(HLSLSplatCast)
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spall wrote:

This cast technically also splats vectors in 1 very specific case, but I guess vectors are aggregates :) even if not in the clang code.

https://github.com/llvm/llvm-project/pull/118992