[clang] Support HLSL matrix initializers (PR #160960)

[Farzon Lotfi via cfe-commits]

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@@ -1877,6 +1887,93 @@ void InitListChecker::CheckReferenceType(const InitializedEntity &Entity,
     AggrDeductionCandidateParamTypes->push_back(DeclType);
 }
 
+void InitListChecker::CheckMatrixType(const InitializedEntity &Entity,
+                                      InitListExpr *IList, QualType DeclType,
+                                      unsigned &Index,
+                                      InitListExpr *StructuredList,
+                                      unsigned &StructuredIndex) {
+  if (!SemaRef.getLangOpts().HLSL)
+    return;
+
+  const ConstantMatrixType *MT = DeclType->castAs<ConstantMatrixType>();
+  QualType ElemTy = MT->getElementType();
+  const unsigned Rows = MT->getNumRows();
+  const unsigned Cols = MT->getNumColumns();
+  const unsigned MaxElts = Rows * Cols;
+
+  unsigned NumEltsInit = 0;
+  InitializedEntity ElemEnt =
+      InitializedEntity::InitializeElement(SemaRef.Context, 0, Entity);
+
+  // A Matrix initalizer should be able to take scalars, vectors, and matrices.
+  auto HandleInit = [&](InitListExpr *List, unsigned &Idx) {
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farzonl wrote:

thats not a bad idea. is there a spec for how clang matrix_type constructors are intended to work that I can compare against what HLSL does? the todos section is pretty light and doesn't indicate what is expected.

https://github.com/llvm/llvm-project/pull/160960