[RemoveDIs] Load into new debug info format by default in llvm-lto and llvm-lto2 (#86271)

Directly load all bitcode into the new debug info format in `llvm-lto`
and `llvm-lto2`. This means that new-mode bitcode no longer round-trips
back to old-mode after parsing, and that old-mode bitcode gets
auto-upgraded to new-mode debug info (which is the current in-memory
default in LLVM).

Author: OCHyams

llvm/lib/LTO/LTO.cpp

@@ -579,7 +579,9 @@ LTO::RegularLTOState::RegularLTOState(unsigned ParallelCodeGenParallelismLevel,
                                       const Config &Conf)
     : ParallelCodeGenParallelismLevel(ParallelCodeGenParallelismLevel),
       Ctx(Conf), CombinedModule(std::make_unique<Module>("ld-temp.o", Ctx)),
-      Mover(std::make_unique<IRMover>(*CombinedModule)) {}
+      Mover(std::make_unique<IRMover>(*CombinedModule)) {
+  CombinedModule->IsNewDbgInfoFormat = UseNewDbgInfoFormat;
+}
 
 LTO::ThinLTOState::ThinLTOState(ThinBackend Backend)
     : Backend(Backend), CombinedIndex(/*HaveGVs*/ false) {

llvm/tools/llvm-lto/llvm-lto.cpp

@@ -270,6 +270,7 @@ static cl::opt<bool> TryUseNewDbgInfoFormat(
     cl::init(false), cl::Hidden);
 
 extern cl::opt<bool> UseNewDbgInfoFormat;
+extern cl::opt<cl::boolOrDefault> LoadBitcodeIntoNewDbgInfoFormat;
 
 namespace {
 
@@ -943,6 +944,9 @@ int main(int argc, char **argv) {
   InitLLVM X(argc, argv);
   cl::HideUnrelatedOptions({&LTOCategory, &getColorCategory()});
   cl::ParseCommandLineOptions(argc, argv, "llvm LTO linker\n");
+  // Load bitcode into the new debug info format by default.
+  if (LoadBitcodeIntoNewDbgInfoFormat == cl::boolOrDefault::BOU_UNSET)
+    LoadBitcodeIntoNewDbgInfoFormat = cl::boolOrDefault::BOU_TRUE;
 
   // RemoveDIs debug-info transition: tests may request that we /try/ to use the
   // new debug-info format.

llvm/tools/llvm-lto2/llvm-lto2.cpp

@@ -193,6 +193,7 @@ static cl::opt<bool> TryUseNewDbgInfoFormat(
     cl::init(false), cl::Hidden);
 
 extern cl::opt<bool> UseNewDbgInfoFormat;
+extern cl::opt<cl::boolOrDefault> LoadBitcodeIntoNewDbgInfoFormat;
 
 static void check(Error E, std::string Msg) {
   if (!E)
@@ -228,6 +229,9 @@ static int usage() {
 
 static int run(int argc, char **argv) {
   cl::ParseCommandLineOptions(argc, argv, "Resolution-based LTO test harness");
+  // Load bitcode into the new debug info format by default.
+  if (LoadBitcodeIntoNewDbgInfoFormat == cl::boolOrDefault::BOU_UNSET)
+    LoadBitcodeIntoNewDbgInfoFormat = cl::boolOrDefault::BOU_TRUE;
 
   // RemoveDIs debug-info transition: tests may request that we /try/ to use the
   // new debug-info format.