[llvm] [DWARF] Speedup .gdb_index dumping (PR #151806)

[David Blaikie via llvm-commits]

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@@ -60,6 +61,24 @@ void DWARFGdbIndex::dumpSymbolTable(raw_ostream &OS) const {
                ", filled slots:",
                SymbolTableOffset, (uint64_t)SymbolTable.size())
      << '\n';
+
+  std::unordered_map<uint32_t, decltype(ConstantPoolVectors)::const_iterator>
+      CuVectorMap{};
+  CuVectorMap.reserve(ConstantPoolVectors.size());
+  const auto FindCuVector =
+      [&CuVectorMap, notFound = ConstantPoolVectors.end()](uint32_t vecOffset) {
+        const auto it = CuVectorMap.find(vecOffset);
+        if (it != CuVectorMap.end()) {
+          return it->second;
+        }
+
+        return notFound;
+      };
+  for (auto it = ConstantPoolVectors.begin(); it != ConstantPoolVectors.end();
+       ++it) {
+    CuVectorMap.emplace(it->first, it);
+  }
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dwblaikie wrote:

Could drop the `{}` here.

Could use a range-based for loop, and instead of putting iterators as values in the map, use pointers (then you can get a pointer to the value in the range based for loop where there aren't any visible/name-able iterators)

https://github.com/llvm/llvm-project/pull/151806