[clang] [CIR] Split RecordType into StructType/UnionType view classes; move union padding to dedicated field (PR #199790)

[Erich Keane via cfe-commits]

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@@ -417,11 +436,11 @@ RecordType::getTypeSizeInBits(const mlir::DataLayout &dataLayout,
 uint64_t
 RecordType::getABIAlignment(const ::mlir::DataLayout &dataLayout,
                             ::mlir::DataLayoutEntryListRef params) const {
-  if (isUnion()) {
-    mlir::Type largest = getLargestMember(dataLayout);
-    if (!largest)
+  if (auto u = mlir::dyn_cast<cir::UnionType>(*this)) {
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erichkeane wrote:

I would expect these to be a different overload, so UnionType::getABIAlignment/StrutType::getABIAlignment.

https://github.com/llvm/llvm-project/pull/199790