Error : Verify Failed , when using --fast

[gptsarthak]

Came across this error when trying out benchmarks. Error occurs only when compiling with the --fast optimization.

def func() -> i32:
     return 30

def test() -> i32:
    temp: i32 = func()
    return temp

x : i32 
x = test()
print(x)

(lp) sarthak@pop-os:~/lpython$ lpython examples/test.py
30

(lp) sarthak@pop-os:~/lpython$ lpython --fast examples/test.py
ASR verify pass error: ASR verify: Block ~empty_block should resolve in current scope.
Internal Compiler Error: Unhandled exception
Traceback (most recent call last):
  Binary file "/home/sarthak/lpython/src/bin/lpython", in _start()
  File "./csu/../csu/libc-start.c", line 392, in __libc_start_main_impl()
  File "./csu/../sysdeps/nptl/libc_start_call_main.h", line 58, in __libc_start_call_main()
  File "/home/sarthak/lpython/src/bin/lpython.cpp", line 1750, in ??
    err = compile_python_to_object_file(arg_file, tmp_o, runtime_library_dir,
  File "/home/sarthak/lpython/src/bin/lpython.cpp", line 750, in ??
    res = fe.get_llvm3(*asr, pass_manager, diagnostics, infile);
  File "/home/sarthak/lpython/src/lpython/python_evaluator.cpp", line 58, in LCompilers::PythonCompiler::get_llvm3(LCompilers::ASR::TranslationUnit_t&, LCompilers::PassManager&, LCompilers::diag::Diagnostics&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)
    run_fn, infile);
  File "/home/sarthak/lpython/src/libasr/codegen/asr_to_llvm.cpp", line 7027, in LCompilers::asr_to_llvm(LCompilers::ASR::TranslationUnit_t&, LCompilers::diag::Diagnostics&, llvm::LLVMContext&, Allocator&, LCompilers::PassManager&, LCompilers::CompilerOptions&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)
    pass_manager.apply_passes(al, &asr, pass_options, diagnostics);
  File "/home/sarthak/lpython/src/libasr/pass/pass_manager.h", line 214, in LCompilers::PassManager::apply_passes(Allocator&, LCompilers::ASR::TranslationUnit_t*, LCompilers::PassOptions&, LCompilers::diag::Diagnostics&)
    _apply_passes(al, asr, _with_optimization_passes, pass_options,
LCompilersException: Verify failed

[certik]

Thanks for reporting it, I added this to #1600. I think we need to start testing with --fast in our integration_tests to catch this earlier (#1669).