[llvm] IRSymtab: Use StringSet instead of DenseMap for preserved symbols (PR #149836)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/149836

Microbenchmarking shows this is faster

>From c33cfb83d30830b5082b07f3c01fdc7ff0076537 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Tue, 22 Jul 2025 00:05:44 +0900
Subject: [PATCH] IRSymtab: Use StringSet instead of DenseMap for preserved
 symbols

Microbenchmarking shows this is faster
---
 llvm/lib/Object/IRSymtab.cpp | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Object/IRSymtab.cpp b/llvm/lib/Object/IRSymtab.cpp
index 2579fa37935f0..0f194953787e6 100644
--- a/llvm/lib/Object/IRSymtab.cpp
+++ b/llvm/lib/Object/IRSymtab.cpp
@@ -8,11 +8,11 @@
 
 #include "llvm/Object/IRSymtab.h"
 #include "llvm/ADT/ArrayRef.h"
-#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/Bitcode/BitcodeReader.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/IR/Comdat.h"
@@ -213,9 +213,10 @@ Expected<int> Builder::getComdatIndex(const Comdat *C, const Module *M) {
   return P.first->second;
 }
 
-static DenseSet<StringRef> buildPreservedSymbolsSet(const Triple &TT) {
-  DenseSet<StringRef> PreservedSymbolSet(std::begin(PreservedSymbols),
-                                         std::end(PreservedSymbols));
+static StringSet<> buildPreservedSymbolsSet(const Triple &TT) {
+  StringSet<> PreservedSymbolSet;
+  PreservedSymbolSet.insert(std::begin(PreservedSymbols),
+                            std::end(PreservedSymbols));
   // FIXME: Do we need to pass in ABI fields from TargetOptions?
   RTLIB::RuntimeLibcallsInfo Libcalls(TT);
   for (RTLIB::LibcallImpl Impl : Libcalls.getLibcallImpls()) {
@@ -280,7 +281,7 @@ Error Builder::addSymbol(const ModuleSymbolTable &Msymtab,
 
   setStr(Sym.IRName, GV->getName());
 
-  static const DenseSet<StringRef> PreservedSymbolsSet =
+  static const StringSet<> PreservedSymbolsSet =
       buildPreservedSymbolsSet(GV->getParent()->getTargetTriple());
   bool IsPreservedSymbol = PreservedSymbolsSet.contains(GV->getName());