[clang] [HLSL] Allow truncation to scalar (PR #104844)

[Justin Bogner via cfe-commits]

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@@ -2692,14 +2692,19 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     return CGF.CGM.createOpenCLIntToSamplerConversion(E, CGF);
 
   case CK_HLSLVectorTruncation: {
-    assert(DestTy->isVectorType() && "Expected dest type to be vector type");
+    assert((DestTy->isVectorType() || DestTy->isBuiltinType()) &&
+           "Destination type must be a vector or builtin type.");
     Value *Vec = Visit(const_cast<Expr *>(E));
-    SmallVector<int, 16> Mask;
-    unsigned NumElts = DestTy->castAs<VectorType>()->getNumElements();
-    for (unsigned I = 0; I != NumElts; ++I)
-      Mask.push_back(I);
+    if (auto *VecTy = DestTy->getAs<VectorType>()) {
+      SmallVector<int, 16> Mask;
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bogner wrote:

It was already here, but while I see it: better to use `SmallVector<int>` and let it pick the size here 

https://github.com/llvm/llvm-project/pull/104844