[lld] [lld-macho][ObjC] Implement category merging into base class (PR #92448)

[Kyungwoo Lee via llvm-commits]

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@@ -1302,3 +1336,96 @@ void objc::mergeCategories() {
 }
 
 void objc::doCleanup() { ObjcCategoryMerger::doCleanup(); }
+
+void ObjcCategoryMerger::mergeCategoriesIntoBaseClass(
+    const Defined *baseClass, std::vector<InfoInputCategory> &categories) {
+  assert(categories.size() >= 1 && "Expected at least one category to merge");
+
+  // Collect all the info from the categories
+  ClassExtensionInfo extInfo(catLayout);
+  for (auto &catInfo : categories) {
+    parseCatInfoToExtInfo(catInfo, extInfo);
+  }
+
+  // Get metadata for the base class
+  Defined *metaRo = getClassRo(baseClass, /*getMetaRo=*/true);
+  ConcatInputSection *metaIsec = dyn_cast<ConcatInputSection>(metaRo->isec());
+  Defined *classRo = getClassRo(baseClass, /*getMetaRo=*/false);
+  ConcatInputSection *classIsec = dyn_cast<ConcatInputSection>(classRo->isec());
+
+  // Now collect the info from the base class from the various lists in the
+  // class metadata
+  parseProtocolListInfo(classIsec, roClassLayout.baseProtocolsOffset,
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kyulee-com wrote:

Can you also align the order of processing fields consistently? Here is what I'm seeing:
 - reading part: protocol, methods, properties (from meta to class)
 - erasing part: methods, protocol, properties (from meta to class)
 - writing part: methods, protocol, properties (from meta to class)
 
 Does it make sense to handle them in a pair of meta and class, instead of handling all meta followed by class? That way, you might place the use/def chain back-to-back like `protoListSym`,

https://github.com/llvm/llvm-project/pull/92448