Linking dylib with "lto = true": assertion failed: !is_full_lto_enabled(sess)

[zachreizner]

Approximate file tree:

├── Cargo.lock
├── Cargo.toml
├── src
│   └── main.rs
└── test_dylib
    ├── Cargo.toml
    └── lib.rs

Top-level Cargo.lock:

[profile.release]
lto = true

[dependencies]
test_dylib = { path = "test_dylib" }

test_dylib/Cargo.toml:

[lib]
path = "lib.rs"
crate-type = ["dylib"]

[profile.release]
lto = true

Snippet of output from RUST_BACKTRACE=1 cargo build --release --verbose:

Running `rustc --crate-name test_package src/main.rs --crate-type bin --emit=dep-info,link -C opt-level=3 -C lto -C metadata=7e778ca5edc7bd6e -C extra-filename=-7e778ca5edc7bd6e --out-dir /src/test_package/target/release/deps -L dependency=/src/test_package/target/release/deps --extern test_dylib=/src/test_package/target/release/deps/libtest_dylib.so -L native=/src/test_package/target/release/build/ring-9d649aa185d933e6/out`
thread 'rustc' panicked at 'assertion failed: !is_full_lto_enabled(sess)', librustc_trans/back/link.rs:1318:9
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at libstd/sys_common/backtrace.rs:59
             at libstd/panicking.rs:380
   3: std::panicking::default_hook
             at libstd/panicking.rs:396
   4: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:576
   5: std::panicking::begin_panic
   6: rustc_trans::back::link::link_args
   7: rustc_trans::back::link::link_natively
   8: <rustc_trans::LlvmTransCrate as rustc_trans_utils::trans_crate::TransCrate>::join_trans_and_link::{{closure}}
   9: <rustc_trans::LlvmTransCrate as rustc_trans_utils::trans_crate::TransCrate>::join_trans_and_link
  10: rustc_driver::driver::compile_input
  11: rustc_driver::run_compiler

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.25.0 (84203cac6 2018-03-25) running on x86_64-unknown-linux-gnu

error: Could not compile `test_package`.

Caused by:
  process didn't exit successfully: `rustc --crate-name test_package src/main.rs --crate-type bin --emit=dep-info,link -C opt-level=3 -C lto -C metadata=7e778ca5edc7bd6e -C extra-filename=-7e778ca5edc7bd6e --out-dir /src/test_package/target/release/deps -L dependency=/src/test_package/target/release/deps --extern test_dylib=/src/test_package/target/release/deps/libtest_dylib.so -L native=/src/test_package/target/release/build/ring-9d649aa185d933e6/out` (exit code: 101)

[michaelwoerister]

Thanks for the bug report, @zachreizner!

cc @alexcrichton

[alexcrichton]

This could either be construed as a bug where it should ignore -C lto when compiling crates with dylib deps, or a bug in rustc as it should just do "as much LTO as it can" which means skipping crates that come in through dylibs. I'd be fine either way!

[matthiaskrgr]

Is this related to #45689 ?

[alexcrichton]

Yes it's probably the same or a very similar assertion

[Michel-Haber]

@alexcrichton any update on this?

[alexcrichton]

No, as far as I know no work has happened on this

[bjorn3]

As of #101403 on nightly -Zdylib-lto can now be passed if you want to LTO a rust dylib.