Can't get `Reverse` to work

[marcpabst]

This example, taken directly from the docs, either always returns 0 for the derivative (debug) or does not even compile (release):

#![feature(autodiff)]

#[autodiff(df, Reverse, Active, Active, Active)]
 fn f(x: f32, y: f32) -> f32 {
     x * x + 3.0 * y
 }

 fn main() {
     let (x, y) = (5.0, 7.0);
     let (z, bx, by) = df(x, y, 1.0);
     assert_eq!(46.0, z);
     assert_eq!(10.0, bx);
     assert_eq!(3.0, by);
 }

Error in debug mode:

thread 'main' panicked at src/main.rs:12:6:
assertion `left == right` failed
  left: 10.0
 right: 0.0

Stack trace in release mode:

thread 'coordinator' panicked at compiler/rustc_codegen_llvm/src/back/write.rs:761:17:
assertion failed: llvm::LLVMRustGetTypeKind(outer_arg_ty) == llvm::TypeKind::Integer
stack backtrace:
   0:        0x101fcc848 - std::backtrace::Backtrace::create::h274c998bd3e77e61
   1:        0x1066b2624 - <alloc[9eedf9a5b017d5f0]::boxed::Box<rustc_driver_impl[4092d44f8fc6cf45]::install_ice_hook::{closure#0}> as core[4bc86d92358c3fc9]::ops::function::Fn<(&dyn for<'a, 'b> core[4bc86d92358c3fc9]::ops::function::Fn<(&'a core[4bc86d92358c3fc9]::panic::panic_info::PanicInfo<'b>,), Output = ()> + core[4bc86d92358c3fc9]::marker::Send + core[4bc86d92358c3fc9]::marker::Sync, &core[4bc86d92358c3fc9]::panic::panic_info::PanicInfo)>>::call
   2:        0x101ff7a64 - std::panicking::rust_panic_with_hook::h7b497338c9ec8662
   3:        0x101fd1628 - std::panicking::begin_panic_handler::{{closure}}::h880ad4dd90e1a8f8
   4:        0x101fd12a4 - std::sys_common::backtrace::__rust_end_short_backtrace::h10f05ee841af1dbc
   5:        0x101ff76c4 - _rust_begin_unwind
   6:        0x10204f588 - core::panicking::panic_fmt::heb8a25d7321e04b5
   7:        0x10204f610 - core::panicking::panic::h1b598ba5ca68e7a2
   8:        0x10699d8f0 - rustc_codegen_llvm[aebffebb323e7405]::back::write::enzyme_ad
   9:        0x10699ed9c - rustc_codegen_llvm[aebffebb323e7405]::back::write::differentiate
  10:        0x1069cded4 - <rustc_codegen_llvm[aebffebb323e7405]::LlvmCodegenBackend as rustc_codegen_ssa[1b61eafb5d4c07bc]::traits::write::WriteBackendMethods>::autodiff
  11:        0x106987214 - <rustc_codegen_ssa[1b61eafb5d4c07bc]::back::lto::LtoModuleCodegen<rustc_codegen_llvm[aebffebb323e7405]::LlvmCodegenBackend>>::autodiff
  12:        0x1068e45f4 - std[94fe895d40b1402d]::sys_common::backtrace::__rust_begin_short_backtrace::<<rustc_codegen_llvm[aebffebb323e7405]::LlvmCodegenBackend as rustc_codegen_ssa[1b61eafb5d4c07bc]::traits::backend::ExtraBackendMethods>::spawn_named_thread<rustc_codegen_ssa[1b61eafb5d4c07bc]::back::write::start_executing_work<rustc_codegen_llvm[aebffebb323e7405]::LlvmCodegenBackend>::{closure#5}, core[4bc86d92358c3fc9]::result::Result<rustc_codegen_ssa[1b61eafb5d4c07bc]::back::write::CompiledModules, ()>>::{closure#0}, core[4bc86d92358c3fc9]::result::Result<rustc_codegen_ssa[1b61eafb5d4c07bc]::back::write::CompiledModules, ()>>
  13:        0x1068e99b8 - <<std[94fe895d40b1402d]::thread::Builder>::spawn_unchecked_<<rustc_codegen_llvm[aebffebb323e7405]::LlvmCodegenBackend as rustc_codegen_ssa[1b61eafb5d4c07bc]::traits::backend::ExtraBackendMethods>::spawn_named_thread<rustc_codegen_ssa[1b61eafb5d4c07bc]::back::write::start_executing_work<rustc_codegen_llvm[aebffebb323e7405]::LlvmCodegenBackend>::{closure#5}, core[4bc86d92358c3fc9]::result::Result<rustc_codegen_ssa[1b61eafb5d4c07bc]::back::write::CompiledModules, ()>>::{closure#0}, core[4bc86d92358c3fc9]::result::Result<rustc_codegen_ssa[1b61eafb5d4c07bc]::back::write::CompiledModules, ()>>::{closure#1} as core[4bc86d92358c3fc9]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  14:        0x101ffe8c4 - std::sys::unix::thread::Thread::new::thread_start::h530c9e8206466847
  15:        0x1805a6034 - __pthread_joiner_wake


rustc version: 1.75.0-nightly (bafd64d28 2024-08-01)
platform: aarch64-apple-darwinthread 'rustc' panicked at compiler/rustc_middle/src/util/bug.rs:36:26:
/Users/marc/rust/compiler/rustc_codegen_ssa/src/back/write.rs:1984:17: panic during codegen/LLVM phase
stack backtrace:
   0:        0x101fcc848 - std::backtrace::Backtrace::create::h274c998bd3e77e61
   1:        0x1066b2624 - <alloc[9eedf9a5b017d5f0]::boxed::Box<rustc_driver_impl[4092d44f8fc6cf45]::install_ice_hook::{closure#0}> as core[4bc86d92358c3fc9]::ops::function::Fn<(&dyn for<'a, 'b> core[4bc86d92358c3fc9]::ops::function::Fn<(&'a core[4bc86d92358c3fc9]::panic::panic_info::PanicInfo<'b>,), Output = ()> + core[4bc86d92358c3fc9]::marker::Send + core[4bc86d92358c3fc9]::marker::Sync, &core[4bc86d92358c3fc9]::panic::panic_info::PanicInfo)>>::call
   2:        0x101ff7a64 - std::panicking::rust_panic_with_hook::h7b497338c9ec8662
   3:        0x1086acc90 - std[94fe895d40b1402d]::panicking::begin_panic::<alloc[9eedf9a5b017d5f0]::string::String>::{closure#0}
   4:        0x1086ac6e8 - std[94fe895d40b1402d]::sys_common::backtrace::__rust_end_short_backtrace::<std[94fe895d40b1402d]::panicking::begin_panic<alloc[9eedf9a5b017d5f0]::string::String>::{closure#0}, !>
   5:        0x108c177f4 - std[94fe895d40b1402d]::panicking::begin_panic::<alloc[9eedf9a5b017d5f0]::string::String>
   6:        0x108640758 - rustc_middle[96f22e03556ee0e5]::util::bug::opt_span_bug_fmt::<rustc_span[3fa53b66ea663371]::span_encoding::Span>::{closure#0}
   7:        0x10863d7b4 - rustc_middle[96f22e03556ee0e5]::ty::context::tls::with_opt::<rustc_middle[96f22e03556ee0e5]::util::bug::opt_span_bug_fmt<rustc_span[3fa53b66ea663371]::span_encoding::Span>::{closure#0}, !>::{closure#0}
   8:        0x10863d780 - rustc_middle[96f22e03556ee0e5]::ty::context::tls::with_context_opt::<rustc_middle[96f22e03556ee0e5]::ty::context::tls::with_opt<rustc_middle[96f22e03556ee0e5]::util::bug::opt_span_bug_fmt<rustc_span[3fa53b66ea663371]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
   9:        0x108c187e8 - rustc_middle[96f22e03556ee0e5]::util::bug::bug_fmt
  10:        0x1069b6b94 - <rustc_session[25050e0163d9f6fb]::session::Session>::time::<rustc_codegen_ssa[1b61eafb5d4c07bc]::back::write::CompiledModules, <rustc_codegen_ssa[1b61eafb5d4c07bc]::back::write::OngoingCodegen<rustc_codegen_llvm[aebffebb323e7405]::LlvmCodegenBackend>>::join::{closure#0}>
  11:        0x1068eadfc - <rustc_codegen_ssa[1b61eafb5d4c07bc]::back::write::OngoingCodegen<rustc_codegen_llvm[aebffebb323e7405]::LlvmCodegenBackend>>::join
  12:        0x1069ce8a4 - <rustc_codegen_llvm[aebffebb323e7405]::LlvmCodegenBackend as rustc_codegen_ssa[1b61eafb5d4c07bc]::traits::backend::CodegenBackend>::join_codegen
  13:        0x10685e458 - <rustc_interface[90b1e0870df88c87]::queries::Linker>::link
  14:        0x1066a47fc - rustc_span[3fa53b66ea663371]::set_source_map::<core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>, rustc_interface[90b1e0870df88c87]::interface::run_compiler<core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>, rustc_driver_impl[4092d44f8fc6cf45]::run_compiler::{closure#0}>::{closure#0}::{closure#0}>
  15:        0x1066e1070 - <scoped_tls[df23976295fd3450]::ScopedKey<rustc_span[3fa53b66ea663371]::SessionGlobals>>::set::<rustc_interface[90b1e0870df88c87]::util::run_in_thread_pool_with_globals<rustc_interface[90b1e0870df88c87]::interface::run_compiler<core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>, rustc_driver_impl[4092d44f8fc6cf45]::run_compiler::{closure#0}>::{closure#0}, core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>>::{closure#0}, core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>>
  16:        0x1066a4bb4 - rustc_span[3fa53b66ea663371]::create_session_globals_then::<core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>, rustc_interface[90b1e0870df88c87]::util::run_in_thread_pool_with_globals<rustc_interface[90b1e0870df88c87]::interface::run_compiler<core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>, rustc_driver_impl[4092d44f8fc6cf45]::run_compiler::{closure#0}>::{closure#0}, core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>>::{closure#0}>
  17:        0x1066d94a0 - std[94fe895d40b1402d]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[90b1e0870df88c87]::util::run_in_thread_with_globals<rustc_interface[90b1e0870df88c87]::util::run_in_thread_pool_with_globals<rustc_interface[90b1e0870df88c87]::interface::run_compiler<core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>, rustc_driver_impl[4092d44f8fc6cf45]::run_compiler::{closure#0}>::{closure#0}, core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>>::{closure#0}, core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>>
  18:        0x1066e8a3c - <<std[94fe895d40b1402d]::thread::Builder>::spawn_unchecked_<rustc_interface[90b1e0870df88c87]::util::run_in_thread_with_globals<rustc_interface[90b1e0870df88c87]::util::run_in_thread_pool_with_globals<rustc_interface[90b1e0870df88c87]::interface::run_compiler<core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>, rustc_driver_impl[4092d44f8fc6cf45]::run_compiler::{closure#0}>::{closure#0}, core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>>::{closure#0}, core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[4bc86d92358c3fc9]::result::Result<(), rustc_span[3fa53b66ea663371]::ErrorGuaranteed>>::{closure#1} as core[4bc86d92358c3fc9]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  19:        0x101ffe8c4 - std::sys::unix::thread::Thread::new::thread_start::h530c9e8206466847
  20:        0x1805a6034 - __pthread_joiner_wake