Union split can cause assertion in debug mode

[Keno]

@noinline bar(x::Core.Const) = Base.inferencebarrier(1)
@noinline bar(x::DataType) = Base.inferencebarrier(2)
foo(x) = bar(Base.inferencebarrier(Core.Const(x)))

With assertions enabled:

julia: /home/keno/julia/src/codegen.cpp:1550: jl_cgval_t::jl_cgval_t(const jl_cgval_t&, jl_value_t*, llvm::Value*): Assertion `isboxed || v.typ == typ || tindex' failed.

[3749451] signal (6.-6): Aborted
in expression starting at REPL[13]:1
gsignal at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
abort at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
unknown function (ip: 0x7f5d34112728)
__assert_fail at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
jl_cgval_t at /home/keno/julia/src/codegen.cpp:1550
convert_julia_type at /home/keno/julia/src/codegen.cpp:2343
emit_expr at /home/keno/julia/src/codegen.cpp:5472

Reported-by: @oscardssmith

[oscardssmith]

Was this in the RR I sent you?

[Keno]

Same test case

[gbaraldi]

Did this regress? Or has it always been broken?

[Keno]

I don't know, we don't usually run with assertions enabled.

[DilumAluthge]

We do have one CI job that runs the Base test suite with Julia assertions and LLVM assertions enabled. It only runs on x86_64-linux-gnu. It does not have debug symbols, i.e. it's just make FORCE_ASSERTIONS=1 LLVM_ASSERTIONS=1.

[vtjnash]

Looks like it should be detecting this is dead code and skipping emission of this statement (the assertion is semi-correct at detecting, but not handling, this). Usually this gets handled by the jl_is_concrete_type check in convert_julia_type, but we skip that for KindType (whereas we should only skip it for kinds that are isboxed, or where otherwise the conversion is even possible between different Kind and Type representations).

julia> code_typed(foo, (Int,))
1-element Vector{Any}:
 CodeInfo(
    @ REPL[3]:1 within `foo`
   ┌ @ boot.jl:430 within `Const`
1 ─│ %1  = %new(Core.Const, x)::Core.Const
│  └
│   %2  = Main.bar::typeof(bar)
│   %3  = (isa)(%1, Core.Const)::Bool
└──       goto #3 if not %3
2 ─ %5  = invoke %2(%1::Core.Const)::Any
└──       goto #6
3 ─ %7  = (isa)(%1, DataType)::Bool
└──       goto #5 if not %7
4 ─ %9  = π (%1, DataType) # failure occurs here, `x::Core.Const`
│   %10 = invoke %2(%9::DataType)::Any
└──       goto #6
5 ─ %12 = Main.bar(%1)::Any
└──       goto #6
6 ┄ %14 = φ (#2 => %5, #4 => %10, #5 => %12)::Any
└──       return %14
) => Any

[gbaraldi]

So this regressed in #44512 but I guess it doesn't really matter?

[gbaraldi]

So we should enter this branch

        if (jl_is_concrete_type(v.typ) && !jl_is_kind(v.typ)) {
            if (jl_is_concrete_type(typ) && !jl_is_kind(typ)) {
                // type mismatch: changing from one leaftype to another
                if (skip)
                    *skip = ConstantInt::get(getInt1Ty(ctx.builder.getContext()), 1);
                else
                    CreateTrap(ctx.builder);
                return jl_cgval_t();
            }
        }

[vtjnash]

Yes, that is the expectation of that code. The tests for jl_is_kind can be deleted, since they are not accurate here.