Dropper was not dropped in how_to_ontop example

[apatrushev]

I tried how_to_ontop example and found that dropper is not dropped - no message presented in log:

x86_64 macOS
rustc 1.32.0 (9fda7c223 2019-01-16)

$ cargo clean; cargo run --example how_to_ontop
   Compiling cc v1.0.29
   Compiling libc v0.2.49
   Compiling context v2.1.0 (<...>/context-rs)
    Finished dev [unoptimized + debuginfo] target(s) in 4.05s
     Running `target/debug/examples/how_to_ontop`
Entering context_function...
Everything's set up!
Resuming => Yielding 0 => Got 0
Resuming => Yielding 1 => Got 1
Resuming => Yielding 2 => Got 2
Resuming => Yielding 3 => Got 3
Resuming => Yielding 4 => Got 4
Resuming => Yielding 5 => Got 5
Resuming => Yielding 6 => Got 6
Resuming => Yielding 7 => Got 7
Resuming => Yielding 8 => Got 8
Resuming => Yielding 9 => Got 9
Resuming context with unwind_stack() ontop!
Unwinding stack by panicking!
Recovered from a panic!
Defer stack deallocation by returning to main()!
Deleting stack!
Stack has been deleted!
Finished!

I tried to switch toolchain to an older one, but did not find working till 1.24.0.

[zonyitoo]

Well, it seems to be the same problem as #37 .

[apatrushev]

On stable rust example working until the end without crash, but Dropper is not dropped. I was not sure and decided to create the separate issue.

[zonyitoo]

In this example, I uses panic::resume_unwind to trigger a stack unwinding process, which should call all the Drop::drop() as I was expected.

In the other issue, the program crashes when calling to panic::resume_unwind, so there must be something changes in the latest rustc and LLVM's implementation.

[apatrushev]

Have you an idea about versions of LLVM/rustc which is definitely working?

[zonyitoo]

I think those rustc versions in 2017 works.

[apatrushev]

Nope. There is nothing about dropping Dropper in log.

[zonyitoo]

Yes, my fault.
Confirmed not working in:
Linux VM-65-106-debian 4.18.0-1-amd64 #1 SMP Debian 4.18.8-1 (2018-09-18) x86_64 GNU/Linux
rustc 1.24.1 (d3ae9a9e0 2018-02-27)

[apatrushev]

Probably that means that it is not frontend/rustc problem, but llvm one?

[zonyitoo]

I think so.

[zonyitoo]

Maybe we have missed some registers that panic::catch_unwind and panic::resume_unwind are relying on.

[apatrushev]

I suppose that at the beginning this example works as expected, so the good idea is to find environment to reproduce working instance and find the difference in generated code.

[zonyitoo]

No, sorry. It is not working. I have compiled a wrong piece of code.

[zonyitoo]

Older version of cargo is not working with the latest crates-io. Cannot test those versions that are any older than 1.20.0.