[lld] [lld-macho] Category Merger: add support for addrsig references (PR #90903)

[Kyungwoo Lee via llvm-commits]

================
@@ -1183,26 +1193,66 @@ void ObjcCategoryMerger::eraseMergedCategories() {
   // the references to the ones we merged.
   generateCatListForNonErasedCategories(catListToErasedOffsets);
 
+  // We use erasedIsecs below to track erased sections so we can later remove
+  // references to it.
+  std::unordered_set<InputSection *> erasedIsecs;
+  erasedIsecs.reserve(categoryMap.size());
+
   // Erase the old method lists & names of the categories that were merged
   for (auto &mapEntry : categoryMap) {
     for (InfoInputCategory &catInfo : mapEntry.second) {
       if (!catInfo.wasMerged)
         continue;
 
+      erasedIsecs.insert(catInfo.catBodyIsec);
+      erasedIsecs.insert(catInfo.catListIsec);
----------------
kyulee-com wrote:

The confusion (between `eraseISec` and `eraseISecs`) is exactly what I'm asking. I saw you call `eraseISec` below once for the body while inserting both body and list.  However, I'm also seeing you do these operations in sync in `tryEraseDefinedAtIsecOffset`. 
```
    eraseISec(cisec);
    erased.insert(cisec);
```

This looks confusing and error-prone. I wonder if we can have a single call to handle these together somehow.

https://github.com/llvm/llvm-project/pull/90903