[dsymutil] Fix spurious warnings for missing symbols with thinLTO

Fix spurious warnings for missing symbols with thinLTO. The latter
appends a unique suffix to avoid collisions for exported private
symbols, resulting in dsymutil complaining it couldn't find the symbol
in the object file.

rdar://75434058

Differential revision: https://reviews.llvm.org/D99125

llvm/test/tools/dsymutil/X86/thinlto.test

@@ -0,0 +1,24 @@
+$ cat foo.cpp
+struct nontrivial {
+  nontrivial() { }
+};
+
+void function2()
+{
+  static const nontrivial magic_static;
+}
+
+$ cat bar.cpp
+void function2();
+
+void function1()
+{
+  function2();
+}
+
+$ xcrun clang++ -g -flto=thin -O2 foo.cpp bar.cpp -c
+$ xcrun clang++ -flto=thin foo.o bar.o -Xlinker -object_path_lto -Xlinker lto -shared -o foobar.dylib
+
+RUN: dsymutil -oso-prepend-path %p/../Inputs %p/../Inputs/private/tmp/thinlto/foobar.dylib -o %t.dSYM 2>&1 | FileCheck %s --allow-empty
+CHECK-NOT: could not find object file symbol for symbol __ZZ9function2vE12magic_static
+CHECK-NOT: could not find object file symbol for symbol __ZGVZ9function2vE12magic_static

llvm/tools/dsymutil/MachODebugMapParser.cpp

@@ -462,6 +462,17 @@ void MachODebugMapParser::handleStabSymbolTableEntry(uint32_t StringIndex,
     }
   }
 
+  // ThinLTO adds a unique suffix to exported private symbols.
+  for (auto Iter = CurrentObjectAddresses.begin();
+       Iter != CurrentObjectAddresses.end(); ++Iter) {
+    llvm::StringRef SymbolName = Iter->getKey();
+    auto Pos = SymbolName.rfind(".llvm.");
+    if (Pos != llvm::StringRef::npos && SymbolName.substr(0, Pos) == Name) {
+      ObjectSymIt = Iter;
+      break;
+    }
+  }
+
   if (ObjectSymIt == CurrentObjectAddresses.end()) {
     Warning("could not find object file symbol for symbol " + Twine(Name));
     return;