Bug in subtyping/method lookup that causes unreacheable reached

[kpamnany]

Testing with Julia 1.10.1 + some patches, we see:

...
Unreachable reached at 0x7fff395e787b
make: *** [Makefile:160: hydra/benchmark.micro.sorting] Illegal instruction (core dumped)
...

@Drvi then ran this test with a debug build of Julia and got:

φ node 207 is not at the beginning of the basic block 53
Internal error: encountered unexpected error in runtime:
MethodError(f=Base.Multimedia.display, args=(Core.Compiler.IRCode(stmts=Core.Compiler.InstructionStream(inst=Array{Any, (272,)}[
  Core.UpsilonNode(val=Core.Argument(n=2)),
  Expr(:enter, 76),
  Expr(:call, Base.getfield, Core.Argument(n=2), :(:cond)),
...

We will share the entire error separately.

[kpamnany]

Attn: @vchuravy and @Keno

[topolarity]

Do you have an MWE?

φ node 207 is not at the beginning of the basic block 53

This indicates that Julia produced invalid IR at some point.

[kpamnany]

I spent some time on this with @gbaraldi and we were able to find the broken IR and also narrow the problem down further. He should also be able to reproduce the error.

Over the last few days, we found that the PackageCompiler step for our system occasionally segfaults with no stack trace. Trying this with a debug build of Julia 1.10.1 with LLVM assertions on reveals many such invalid IR errors:

...
φ node 163 is not at the beginning of the basic block 39
...
φ node 207 is not at the beginning of the basic block 53
...
φ node 320 is not at the beginning of the basic block 105
...
φ node 371 is not at the beginning of the basic block 120
...
φ node 436 is not at the beginning of the basic block 135
...

This has blocked our plan to upgrade to Julia 1.10.1 this week. :(

[kpamnany]

Cc: @KristofferC whom @Drvi had pinged about this, and @Keno, who added this error report.

[topolarity]

I spent some time on this with @gbaraldi and we were able to find the broken IR and also narrow the problem down further. He should also be able to reproduce the error.

Do you have some IR or an MWE? There's still no code attached to this issue...

[kpamnany]

Shared privately.

Edited to add: sorry for the brevity here; there's more discussion on Slack. To summarize, we have not yet been able to reduce the code that triggers this error enough to share it here -- the "MWE" still contains a bunch of proprietary code.

However, @gbaraldi is able to reproduce, and hopefully the problem will be tracked down quickly!

[gbaraldi]

So me and @topolarity reduced this to

function flush!(sc::Threads.Condition)
    @lock sc begin
        try
            if Core.Compiler.inferencebarrier(true)
                return nothing
            end

            return nothing
        finally
        end
    end
end
code_typed(flush!, (Threads.Condition,))

Note that this does not fail if you do a manual macro expansion. It also does not fail on master, so somewhere along the line we fixed this.