[lld] [llvm] Re-apply "[NFCI][LTO][lld] Optimize away symbol copies within LTO global resolution in ELF" (PR #107792)

[Jan Voung via llvm-commits]

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@@ -1797,18 +1799,18 @@ void BitcodeFile::parse() {
 void BitcodeFile::parseLazy() {
   numSymbols = obj->symbols().size();
   symbols = std::make_unique<Symbol *[]>(numSymbols);
-  for (auto [i, irSym] : llvm::enumerate(obj->symbols()))
+  for (auto [i, irSym] : llvm::enumerate(obj->symbols())) {
+    // Keep copies of per-module undefined symbols for LTO::GlobalResolutions
+    // usage.
+    irSym.Name = unique_saver().save(irSym.getName());
     if (!irSym.isUndefined()) {
       // Symbols can be duplicated in bitcode files because of '#include' and
       // linkonce_odr. Use unique_saver to save symbol names for de-duplication.
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jvoung wrote:

The unique_saver is now moved out, so should this comment be moved up too and merged with the "Keep copies of per-module undefined symbols" in some way?

https://github.com/llvm/llvm-project/pull/107792