[Bugpoint][NewPM] Pin bugpoint to legacy PM

[aeubanks]

Summary

Bugpoint has lots of assumptions and hacks around the legacy PM, put off migrating it to NPM until later.
Fixes tests under BugPoint under NPM.

[arsenm]

llvm/tools/bugpoint/OptimizerDriver.cpp

208

Should add a comment explaining why

[aeubanks]

add comment

llvm/test/BugPoint/unsymbolized.ll

 ; REQUIRES: plugins
 ; RUN: echo "import sys" > %t.py
 ; RUN: echo "print('args = ' + str(sys.argv))" >> %t.py
 ; RUN: echo "exit(1)" >> %t.py
 ; RUN: not bugpoint -load %llvmshlibdir/BugpointPasses%shlibext %s -output-prefix %t -bugpoint-crashcalls -opt-command=%python -opt-args %t.py | FileCheck %s
-; RUN: not --crash opt -load %llvmshlibdir/BugpointPasses%shlibext %s -bugpoint-crashcalls -disable-symbolication 2>&1 | FileCheck --check-prefix=CRASH %s
+; RUN: not --crash opt -enable-new-pm=0 -load %llvmshlibdir/BugpointPasses%shlibext %s -bugpoint-crashcalls -disable-symbolication 2>&1 | FileCheck --check-prefix=CRASH %s
 ; RUN: not bugpoint -load %llvmshlibdir/BugpointPasses%shlibext %s -output-prefix %t -bugpoint-crashcalls -opt-command=%t.non.existent.opt.binary -opt-args %t.py 2>&1 | FileCheck %s --check-prefix=BAD-OPT
 
 ; Test that bugpoint disables symbolication on the opt tool to reduce runtime overhead when opt crashes
 ; CHECK: args = {{.*}}'-disable-symbolication'
 
 ; Test that opt, when it crashes & is passed -disable-symbolication, doesn't symbolicate.
 ; In theory this test should maybe be in test/tools/opt or
 ; test/Transforms, but since there doesn't seem to be another convenient way to

llvm/tools/bugpoint/OptimizerDriver.cpp

if (UseValgrind) {
     Args.push_back("--error-exitcode=1");
     Args.push_back("-q");
     Args.push_back(tool);
   } else
     Args.push_back(tool);
 
   for (unsigned i = 0, e = OptArgs.size(); i != e; ++i)
     Args.push_back(OptArgs[i]);
+  // Pin to legacy PM since bugpoint has lots of infra and hacks revolving
+  // around the legacy PM.
+  Args.push_back("-enable-new-pm=0");
   Args.push_back("-disable-symbolication");
   Args.push_back("-o");
   Args.push_back(OutputFilename);
   std::vector<std::string> pass_args;
   for (unsigned i = 0, e = PluginLoader::getNumPlugins(); i != e; ++i) {
     pass_args.push_back(std::string("-load"));
     pass_args.push_back(PluginLoader::getPlugin(i));
   }