[clang] [HLSL][Matrix] Add support for single subscript accessor (PR #170779)

[Farzon Lotfi via cfe-commits]

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@@ -2440,6 +2443,35 @@ RValue CodeGenFunction::EmitLoadOfLValue(LValue LV, SourceLocation Loc) {
         Builder.CreateLoad(LV.getMatrixAddress(), LV.isVolatileQualified());
     return RValue::get(Builder.CreateExtractElement(Load, Idx, "matrixext"));
   }
+  if (LV.isMatrixRow()) {
+    QualType MatTy = LV.getType();
+    const ConstantMatrixType *MT = MatTy->castAs<ConstantMatrixType>();
+
+    unsigned NumRows = MT->getNumRows();
+    unsigned NumCols = MT->getNumColumns();
+
+    llvm::Value *MatrixVec = EmitLoadOfScalar(LV, Loc);
+
+    llvm::Value *Row = LV.getMatrixRowIdx();
+    llvm::Value *Result =
+        llvm::PoisonValue::get(ConvertType(LV.getType())); // <NumCols x T>
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farzonl wrote:

That said I don't know how the size of the vector is getting set. It seems to just work, but maybe it would be better for me to be more explicit.

https://github.com/llvm/llvm-project/pull/170779