[clang] [HLSL] Implement HLSL intialization list support (PR #123141)

[Justin Bogner via cfe-commits]

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@@ -3010,3 +3013,193 @@ void SemaHLSL::processExplicitBindingsOnDecl(VarDecl *VD) {
     }
   }
 }
+
+static bool CastInitializer(Sema &S, ASTContext &Ctx, Expr *E,
+                            llvm::SmallVectorImpl<Expr *> &List,
+                            llvm::SmallVectorImpl<QualType> &DestTypes) {
+  if (List.size() >= DestTypes.size()) {
+    List.push_back(E);
+    // This is odd, but it isn't technically a failure due to conversion, we
+    // handle mismatched counts of arguments differently.
+    return true;
+  }
+  InitializedEntity Entity = InitializedEntity::InitializeParameter(
+      Ctx, DestTypes[List.size()], false);
+  ExprResult Res = S.PerformCopyInitialization(Entity, E->getBeginLoc(), E);
+  if (Res.isInvalid())
+    return false;
+  Expr *Init = Res.get();
+  List.push_back(Init);
+  return true;
+}
+
+static bool BuildInitializerList(Sema &S, ASTContext &Ctx, Expr *E,
+                                 llvm::SmallVectorImpl<Expr *> &List,
+                                 llvm::SmallVectorImpl<QualType> &DestTypes) {
+  // If this is an initialization list, traverse the sub initializers.
+  if (auto *Init = dyn_cast<InitListExpr>(E)) {
+    for (auto *SubInit : Init->inits())
+      if (!BuildInitializerList(S, Ctx, SubInit, List, DestTypes))
+        return false;
+    return true;
+  }
+
+  // If this is a scalar type, just enqueue the expression.
+  QualType Ty = E->getType();
+
+  if (Ty->isScalarType() || (Ty->isRecordType() && !Ty->isAggregateType()))
+    return CastInitializer(S, Ctx, E, List, DestTypes);
+
+  if (auto *ATy = Ty->getAs<VectorType>()) {
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bogner wrote:

I find these abbreviations a bit confusing. `ATy` is a vector type? `VTy` is an array type? Might be best to use longer names here.

https://github.com/llvm/llvm-project/pull/123141