[clang] [Serialization] Use llvm::map_range (NFC) (PR #135990)

[Jakub Kuderski via cfe-commits]

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@@ -103,11 +103,9 @@ template<typename Info> class MultiOnDiskHashTable {
 
   /// The current set of on-disk tables.
   table_range tables() {
-    auto Begin = Tables.begin(), End = Tables.end();
-    if (getMergedTable())
-      ++Begin;
-    return llvm::make_range(llvm::map_iterator(Begin, AsOnDiskTable()),
-                            llvm::map_iterator(End, AsOnDiskTable()));
+    bool DropBegin = getMergedTable();
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kuhar wrote:

Should we make this an integer that denotes how many elements to drop?

https://github.com/llvm/llvm-project/pull/135990