[llvm] [IRSymtab] Replace linear time lookup with DenseSet (PR #66376)

[Nikita Popov via llvm-commits]

================
@@ -270,7 +275,9 @@ Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
 
   setStr(Sym.IRName, GV->getName());
 
-  bool IsPreservedSymbol = llvm::is_contained(PreservedSymbols, GV->getName());
+  static const DenseSet<StringRef> PreservedSymbolsSet =
+      buildPreservedSymbolsSet();
+  bool IsPreservedSymbol = PreservedSymbolsSet.count(GV->getName());
----------------
nikic wrote:

```suggestion
  bool IsPreservedSymbol = PreservedSymbolsSet.contains(GV->getName());
```

https://github.com/llvm/llvm-project/pull/66376