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

[Chris B via cfe-commits]

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@@ -2752,7 +2787,17 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     llvm::Value *Zero = llvm::Constant::getNullValue(CGF.SizeTy);
     return Builder.CreateExtractElement(Vec, Zero, "cast.vtrunc");
   }
+  case CK_HLSLAggregateCast: {
+    RValue RV = CGF.EmitAnyExpr(E);
+    SourceLocation Loc = CE->getExprLoc();
+    QualType SrcTy = E->getType();
 
+    if (RV.isAggregate()) { // RHS is an aggregate
+      Address SrcVal = RV.getAggregateAddress();
+      return EmitHLSLAggregateFlatCast(CGF, SrcVal, SrcTy, DestTy, Loc);
+    }
+    llvm_unreachable("Not a valid HLSL Flat Cast.");
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llvm-beanz wrote:

I'd also make this an assert rather than an unreachable.

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