Using -C codegen_units=N while bootstrapping rust generates an LLVM assertion

[japaric]

STR

$ git clone https://github.com/rust-lang/rust
$ cd rust
$ mkdir build
$ cd build
$ ../configure
$ RUSTFLAGS=-Ccodegen_units=2 make
rustc: x86_64-unknown-linux-gnu/stage0/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc
rustc: x86_64-unknown-linux-gnu/stage0/lib/rustlib/x86_64-unknown-linux-gnu/lib/librand
rustc: x86_64-unknown-linux-gnu/stage0/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunicode
rustc: x86_64-unknown-linux-gnu/stage0/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc
rustc: /home/rustbuild/src/rust-buildbot/slave/snap3-linux/build/src/llvm/lib/IR/Constants.cpp:1609: static llvm::Constant* llvm::ConstantExpr::getPointerCast(llvm::Constant*, llvm::Type*): Assertion `S->getType()->isPtrOrPtrVectorTy() && "Invalid cast"' failed.
Aborted (core dumped)

Version

444fa1b

---

Sadly, I couldn't generate a minimal script that reproduces the problem. But these seem to be the required ingredients:

• Cross crate. The linked crate must use unboxed closures.
• There must be some #[inline]d function in the root crate.
• And, of course, the -C codegen_units flag.

cc @nikomatsakis @nick29581

[bkoropoff]

I can reproduce this. Backtrace:

#0  0x00007f7760346877 in raise () from /lib64/libc.so.6
#1  0x00007f7760347f68 in abort () from /lib64/libc.so.6
#2  0x00007f776033f7d6 in __assert_fail_base () from /lib64/libc.so.6
#3  0x00007f776033f882 in __assert_fail () from /lib64/libc.so.6
#4  0x00007f7762a4d40b in llvm::ConstantExpr::getPointerCast(llvm::Constant*, llvm::Type*) ()
#5  0x00007f77629e97f5 in LLVMBuildPointerCast ()
#6  0x00007f7761b489f5 in trans::callee::trans_arg_datum::h03f85d308ba46cd1Oxh ()
#7  0x00007f7761b42988 in trans::callee::trans_args::h87945a0a00d776c99oh ()
#8  0x00007f7761b0aa5d in trans::callee::trans_call_inner::h3407dfe88b63d12913g ()
#9  0x00007f7761b4b8ef in trans::expr::trans_rvalue_dps_unadjusted::h9838b52bc02d24d9cgj ()
#10 0x00007f7761b020f8 in trans::expr::trans_into::h3e5c3cd16b2b4e12WMh ()
#11 0x00007f7761b02df4 in trans::controlflow::trans_block::hf81d152713271e77FYd ()
#12 0x00007f7761bb442f in trans::base::trans_closure::hd73aafc90fa3ac9cVfu ()
#13 0x00007f7761af54ce in trans::base::trans_fn::h8314c0146f176259cru ()
#14 0x00007f7761af7447 in trans::monomorphize::monomorphic_fn::ha2624864fe6af428Yqd ()
#15 0x00007f7761b2d402 in trans::callee::trans_fn_ref_with_substs::h15cf4988c4a3d900dIg ()
#16 0x00007f7761b0df29 in trans::meth::trans_method_callee::h2987066aa8871c6bwGz ()
#17 0x00007f7761b3a14e in trans::callee::trans_method_call::closure.38397 ()
#18 0x00007f7761b0957f in trans::callee::trans_call_inner::h3407dfe88b63d12913g ()
#19 0x00007f7761b4b8ef in trans::expr::trans_rvalue_dps_unadjusted::h9838b52bc02d24d9cgj ()
#20 0x00007f7761b020f8 in trans::expr::trans_into::h3e5c3cd16b2b4e12WMh ()
#21 0x00007f7761b02df4 in trans::controlflow::trans_block::hf81d152713271e77FYd ()
#22 0x00007f7761bb442f in trans::base::trans_closure::hd73aafc90fa3ac9cVfu ()
#23 0x00007f7761af54ce in trans::base::trans_fn::h8314c0146f176259cru ()
#24 0x00007f7761af1007 in trans::base::trans_item::hdac7426481f8746aeMu ()
#25 0x00007f7761bb5c49 in trans::base::trans_mod::h03145c37fc751d9cJRu ()
#26 0x00007f7761af0e7f in trans::base::trans_item::hdac7426481f8746aeMu ()
#27 0x00007f7761bb5c49 in trans::base::trans_mod::h03145c37fc751d9cJRu ()
#28 0x00007f7761bbad07 in trans::base::trans_crate::hff0a239bca25518eoIv ()
#29 0x00007f77615dd75d in driver::phase_4_translate_to_llvm::h1d8e5fa121da5744BCa ()
#30 0x00007f77615c4b98 in driver::compile_input::h99875561ae679834pba ()
#31 0x00007f776165fd38 in run_compiler::h68c8d9fcc09b1d69kYb ()
#32 0x00007f776165e62c in run::closure.21400 ()
#33 0x00007f776166ff3b in task::TaskBuilder::try_future::closure.22849 ()
#34 0x00007f776321d8f3 in task::TaskBuilder::spawn_internal::closure.30601 ()
#35 0x00007f7763238732 in task::Task::spawn::closure.5727 ()
#36 0x00007f776323ae9c in rust_try_inner ()
#37 0x00007f776323ae86 in rust_try ()
#38 0x00007f77632387d3 in unwind::try::h67138f1a9143bb4fTyc ()
#39 0x00007f77632385dc in task::Task::run::hd7a7ebf54ed491e4fKb ()
#40 0x00007f7763238228 in task::Task::spawn::closure.5703 ()
#41 0x00007f7763239655 in thread::thread_start::h69086febf2f5cecdw1b ()
#42 0x00007f7760fffee5 in start_thread () from /lib64/libpthread.so.0
#43 0x00007f7760405b8d in clone () from /lib64/libc.so.6

[nrc]

We're hitting this on builds of rustc now, that makes me very, very sad.

@nikomatsakis is this the same bug you were hitting earlier? Did you get much of a handle on it?

@epdtry If you have any spare cycles over the Christmas break, we would appreciate a fix :-)

[japaric]

Managed to get a reduced test case (~100 lines). Check this gist for details.

[tomjakubowski]

Here's an updated gist that ICEs on rustc 1.0.0-dev (ea6f65c5f 2015-01-06 19:47:08 +0000):

https://gist.github.com/tomjakubowski/9c49af9cd2582c37d0e8/a056ead1b0ba5bd29fae8b709fc031ebdc49e4fd

[Aatch]

To people from the future, I'm going to add notes of my investigation here.

It looks like we're getting some oddness with types appearing to be different when using multiple codegen units. Specifically, Rust is trying to cast an unboxed closure to an identical-looking unboxed closure.

[ghost]

Don't know how related, but the same error comes with this, too (on linux and with no flags to rustc):

fn main() {
    let a: [u8; 2] = [97, 98];
    //if &a[0..2] == b"ab" {    // works
    if a[0..2] == *b"ab" {    // ICE
        println!("test");
    }
}

(rustc 1.0.0-nightly (f4f10db 2015-01-17 20:31:08 +0000))

[tamird]

Triage:

@lgvz's code no longer produces an error.

@tomjakubowski/@japaric's gist no longer compiles.