LLVM ERROR compiling Clap on 1.17.0 Nightly

[leonardo-m]

As reported here:
https://users.rust-lang.org/t/mandel-rust-v0-4/7481/3

Compiling this little project:
https://github.com/willi-kappler/mandel-rust

On x86_64-pc-windows-gnu, rustc 1.17.0-nightly, 691eba1 2017-03-01:

Instruction does not dominate all uses!
%27 = load i32, i32* %26, !range !2
%71 = icmp eq i32 %27, 60
LLVM ERROR: Broken function found, compilation aborted!
error: Could not compile clap.

Further notes:

I can confirm this on MacOS and Linux. Stable and beta ran fine, but nightly has problems on both platforms

[TimNN]

Only happens with --release for me on macOS.

[nagisa]

First bad: 1572bf104 2017-02-25
Last good: 08230775a 2017-02-24

Changes

[TimNN]

Note that while the error does not occur when everything is compiled in debug mode, it does occur when clap itself is compiled with -Copt-level=0 but all the dependencies are -Copt-level=3.

[nagisa]

It also sounds a lot like an LLVM bug, since the issue happens during LLVM passes – should check if LLVM 4.0 works or not. Us giving LLVM more information is most likely the trigger.

My bad! It is us who are generating bad IR!

[TimNN]

@nagisa: This also fails with LLVM 4.0

[nagisa]

Minimal-ish reproducer:

pub fn name(c: char) -> char {
    while let Some(c) = Some('[') {
        break;
    }
    c
}

Another interesting case is

    while let Some(c) = Some('[') {
    }
    c

Which ICEs:

error: internal compiler error: /checkout/src/librustc_trans/mir/operand.rs:189: use of _8 before def

This points pretty squarely on the normalize breaks PR.

[nagisa]

cc @cramertj

[nikomatsakis]

cc me

[cramertj]

Is this a dup of #40235? (Fixed in #40242)