Remove legacy::FunctionPassManager usage in Codegen_PTX_Dev (halide#6722

)

LLVM devs indicate that none of the passes in this usage actually do anything and it can be safely removed.

src/CodeGen_PTX_Dev.cpp

@@ -720,11 +720,8 @@ vector<char> CodeGen_PTX_Dev::compile_to_src() {
  // https://lists.llvm.org/pipermail/llvm-dev/2021-April/150100.html
  // https://releases.llvm.org/13.0.0/docs/ReleaseNotes.html#changes-to-the-llvm-ir
  // https://groups.google.com/g/llvm-dev/c/HoS07gXx0p8
- legacy::FunctionPassManager function_pass_manager(module.get());
  legacy::PassManager module_pass_manager;
-
  module_pass_manager.add(createTargetTransformInfoWrapperPass(target_machine->getTargetIRAnalysis()));
- function_pass_manager.add(createTargetTransformInfoWrapperPass(target_machine->getTargetIRAnalysis()));
 
  // Override default to generate verbose assembly.
  target_machine->Options.MCOptions.AsmVerbose = true;
@@ -735,19 +732,10 @@ vector<char> CodeGen_PTX_Dev::compile_to_src() {
  bool fail = target_machine->addPassesToEmitFile(module_pass_manager, ostream, nullptr,
  ::llvm::CGFT_AssemblyFile,
  true);
- if (fail) {
- internal_error << "Failed to set up passes to emit PTX source\n";
- }
-
- function_pass_manager.doInitialization();
- for (auto &function : *module) {
- function_pass_manager.run(function);
- }
- function_pass_manager.doFinalization();
+ internal_assert(!fail) << "Failed to set up passes to emit PTX source\n";
  module_pass_manager.run(*module);
 
  // Codegen pipeline completed.
-
  if (debug::debug_level() >= 2) {
  dump();
  }