[llvm] [LTO] Avoid repeated hash lookups (NFC) (PR #112470)

[Teresa Johnson via llvm-commits]

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@@ -635,11 +635,12 @@ void LTO::addModuleToGlobalRes(ArrayRef<InputFile::Symbol> Syms,
     SymbolResolution Res = *ResI++;
 
     StringRef SymbolName = Sym.getName();
+    auto [It, Inserted] = GlobalResolutions->try_emplace(SymbolName);
     // Keep copies of symbols if the client of LTO says so.
-    if (GlobalResolutionSymbolSaver && !GlobalResolutions->contains(SymbolName))
+    if (GlobalResolutionSymbolSaver && Inserted)
       SymbolName = GlobalResolutionSymbolSaver->save(SymbolName);
 
-    auto &GlobalRes = (*GlobalResolutions)[SymbolName];
+    auto &GlobalRes = It->second;
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teresajohnson wrote:

Is this functionally equivalent? Previously if the GlobalResolutions map didn't contain SymbolName then we got a new SymbolName from the symbol saver and created an entry in GlobalResolutions with that. Now we are only indexing GlobalResolutions with the old SymbolName.

https://github.com/llvm/llvm-project/pull/112470