[llvm] [TableGen] Add a !listflatten operator to TableGen (PR #109346)

[Rahul Joshi via llvm-commits]

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@@ -987,6 +987,29 @@ Init *UnOpInit::Fold(Record *CurRec, bool IsFinal) const {
       }
     }
     break;
+
+  case LISTFLATTEN:
+    if (ListInit *LHSList = dyn_cast<ListInit>(LHS)) {
+      ListRecTy *InnerListTy = dyn_cast<ListRecTy>(LHSList->getElementType());
+      // list of non-lists, !listflatten() is a NOP.
+      if (!InnerListTy)
+        return LHS;
+      std::vector<Init *> Flattened;
+      auto CanFlatten = [LHSList, &Flattened]() {
+        // Concatenate elements of all the inner lists.
+        for (Init *InnerInit : LHSList->getValues()) {
+          ListInit *InnerList = dyn_cast<ListInit>(InnerInit);
+          if (!InnerList)
+            return false;
+          for (Init *InnerElem : InnerList->getValues())
+            Flattened.push_back(InnerElem);
+        };
+        return true;
+      }();
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jurahul wrote:

No, this is defining a lambda and then immediately calling it (with no args).  The lambda will fill up the Flattend array and if failed, return false (which happens when there are still unresolved references from what I can tell. They do get resolved later though).

https://github.com/llvm/llvm-project/pull/109346