llvm-lto2: Add print-guid subcommand.

This is useful for debugging ThinLTO issues.

Reviewers: teresajohnson

Reviewed By: teresajohnson

Pull Request: #143992

Author: pcc

llvm/test/tools/llvm-lto2/print-guid.test

@@ -0,0 +1,2 @@
+# RUN: llvm-lto2 print-guid foo | FileCheck %s
+# CHECK: 6699318081062747564

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

@@ -247,7 +247,7 @@ template <typename T> static T check(ErrorOr<T> E, std::string Msg) {
 }
 
 static int usage() {
-  errs() << "Available subcommands: dump-symtab run\n";
+  errs() << "Available subcommands: dump-symtab run print-guid\n";
   return 1;
 }
 
@@ -610,5 +610,11 @@ int main(int argc, char **argv) {
     return dumpSymtab(argc - 1, argv + 1);
   if (Subcommand == "run")
     return run(argc - 1, argv + 1);
+  if (Subcommand == "print-guid" && argc > 2) {
+    // Note the name of the function we're calling: this won't return the right
+    // answer for internal linkage symbols.
+    outs() << GlobalValue::getGUIDAssumingExternalLinkage(argv[2]) << '\n';
+    return 0;
+  }
   return usage();
 }