[llvm] [BOLT] Use symbol table info in registerFragment (PR #89648)

[Davide Italiano via llvm-commits]

================
@@ -1417,50 +1418,106 @@ void RewriteInstance::registerFragments() {
   if (!BC->HasSplitFunctions)
     return;
 
+  std::vector<std::pair<StringRef, BinaryFunction *>> AmbiguousFragments;
   for (auto &BFI : BC->getBinaryFunctions()) {
     BinaryFunction &Function = BFI.second;
     if (!Function.isFragment())
       continue;
-    unsigned ParentsFound = 0;
-    for (StringRef Name : Function.getNames()) {
+    for (MCSymbol *Symbol : Function.Symbols) {
+      StringRef Name = Symbol->getName();
       StringRef BaseName, Suffix;
       std::tie(BaseName, Suffix) = Name.split('/');
       const size_t ColdSuffixPos = BaseName.find(".cold");
       if (ColdSuffixPos == StringRef::npos)
         continue;
-      // For cold function with local (foo.cold/1) symbol, prefer a parent with
-      // local symbol as well (foo/1) over global symbol (foo).
-      std::string ParentName = BaseName.substr(0, ColdSuffixPos).str();
+      StringRef ParentName = BaseName.substr(0, ColdSuffixPos);
       const BinaryData *BD = BC->getBinaryDataByName(ParentName);
-      if (Suffix != "") {
-        ParentName.append(Twine("/", Suffix).str());
-        const BinaryData *BDLocal = BC->getBinaryDataByName(ParentName);
-        if (BDLocal || !BD)
-          BD = BDLocal;
-      }
-      if (!BD) {
-        if (opts::Verbosity >= 1)
-          BC->outs() << "BOLT-INFO: parent function not found for " << Name
-                     << "\n";
+      uint64_t NumPossibleLocalParents = NR.getNumDuplicates(ParentName);
+      // The most common case: single local parent fragment.
+      if (!BD && NumPossibleLocalParents == 1) {
+        BD = BC->getBinaryDataByName((Twine(ParentName) + "/1").str());
+      } else if (BD && (!NumPossibleLocalParents || Suffix.empty())) {
+        // Global parent and either no local candidates (second most common), or
+        // the fragment is global as well (uncommon).
+      } else {
+        // Any other case: need to disambiguate using FILE symbols.
+        AmbiguousFragments.emplace_back(ParentName, &Function);
         continue;
       }
+      assert(BD);
----------------
dcci wrote:

add a message?

https://github.com/llvm/llvm-project/pull/89648