[RemoveDIs] Load into new debug info format by default in llvm-link (#86274)

Directly load all bitcode into the new debug info format in llvm-link.
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/tools/llvm-link/llvm-link.cpp

@@ -136,6 +136,8 @@ static cl::opt<bool> TryUseNewDbgInfoFormat(
 
 extern cl::opt<bool> UseNewDbgInfoFormat;
 
+extern cl::opt<cl::boolOrDefault> LoadBitcodeIntoNewDbgInfoFormat;
+
 static ExitOnError ExitOnErr;
 
 // Read the specified bitcode file in and return it. This routine searches the
@@ -480,6 +482,10 @@ int main(int argc, char **argv) {
   cl::HideUnrelatedOptions({&LinkCategory, &getColorCategory()});
   cl::ParseCommandLineOptions(argc, argv, "llvm 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.
   if (TryUseNewDbgInfoFormat) {