[clang] [HLSL] Implement HLSL Flat casting (excluding splat cases) (PR #118842)

[Sarah Spall via cfe-commits]

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@@ -1461,6 +1552,7 @@ static bool castPreservesZero(const CastExpr *CE) {
   case CK_NonAtomicToAtomic:
   case CK_AtomicToNonAtomic:
   case CK_HLSLVectorTruncation:
+  case CK_HLSLAggregateCast: // TODO does CK_HLSLAggregateCast preserve zero?
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spall wrote:

@llvm-beanz Does this cast preserve zero?

https://github.com/llvm/llvm-project/pull/118842