Crash (core-dump) in Julia 0.7.0

[mabokhamis]

The following code snippet causes Julia 0.7.0 to crash:

function get_tuple_prefix(tuple::T) where {T <: Tuple}
    prefix::Tuple{T.parameters[1:end-1]...} = tuple[1:length(T.parameters)-1]
    return prefix
end

println(get_tuple_prefix((1, 1, 1)))

Version info:

Julia Version 0.7.0
Commit a4cb80f3ed (2018-08-08 06:46 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, skylake)

The error report is:

Unreachable reached at 0x7f2ba5f00340

signal (4): Illegal instruction
in expression starting at /home/mahmoud/Repositories/raicode/src/QueryEvaluator/playground3.jl:6
get_tuple_prefix at /home/mahmoud/Repositories/raicode/src/QueryEvaluator/playground3.jl:2
unknown function (ip: 0x7f2ba5f003b1)
jl_fptr_trampoline at /buildworker/worker/package_linux64/build/src/gf.c:1829
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2182
do_call at /buildworker/worker/package_linux64/build/src/interpreter.c:324
eval_value at /buildworker/worker/package_linux64/build/src/interpreter.c:428
eval_stmt_value at /buildworker/worker/package_linux64/build/src/interpreter.c:363 [inlined]
eval_body at /buildworker/worker/package_linux64/build/src/interpreter.c:686
jl_interpret_toplevel_thunk_callback at /buildworker/worker/package_linux64/build/src/interpreter.c:799
unknown function (ip: 0xfffffffffffffffe)
unknown function (ip: 0x7f2bb761b1bf)
unknown function (ip: (nil))
jl_interpret_toplevel_thunk at /buildworker/worker/package_linux64/build/src/interpreter.c:808
jl_toplevel_eval_flex at /buildworker/worker/package_linux64/build/src/toplevel.c:831
jl_parse_eval_all at /buildworker/worker/package_linux64/build/src/ast.c:841
jl_load at /buildworker/worker/package_linux64/build/src/toplevel.c:865
include at ./boot.jl:317 [inlined]
include_relative at ./loading.jl:1038
include at ./sysimg.jl:29
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2182
include at ./client.jl:398
jl_fptr_trampoline at /buildworker/worker/package_linux64/build/src/gf.c:1829
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2182
do_call at /buildworker/worker/package_linux64/build/src/interpreter.c:324
eval_value at /buildworker/worker/package_linux64/build/src/interpreter.c:428
eval_stmt_value at /buildworker/worker/package_linux64/build/src/interpreter.c:363 [inlined]
eval_body at /buildworker/worker/package_linux64/build/src/interpreter.c:686
jl_interpret_toplevel_thunk_callback at /buildworker/worker/package_linux64/build/src/interpreter.c:799
unknown function (ip: 0xfffffffffffffffe)
unknown function (ip: 0x7f2bb761864f)
unknown function (ip: 0xffffffffffffffff)
jl_interpret_toplevel_thunk at /buildworker/worker/package_linux64/build/src/interpreter.c:808
jl_toplevel_eval_flex at /buildworker/worker/package_linux64/build/src/toplevel.c:831
jl_toplevel_eval_in at /buildworker/worker/package_linux64/build/src/builtins.c:633
eval at ./boot.jl:319
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2182
eval_user_input at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:85
macro expansion at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:117 [inlined]
#28 at ./task.jl:262
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2182
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1538 [inlined]
start_task at /buildworker/worker/package_linux64/build/src/task.c:268
unknown function (ip: 0xffffffffffffffff)
Allocations: 145764 (Pool: 145684; Big: 80); GC: 0
Illegal instruction (core dumped)

[chethega]

Can reproduce crash 1.0.0, and OOB error on master. Looks like an inference problem? But @code_llvm and @code_native actually produce some code instead of crashing, so it's unclear to me.

julia> @code_lowered get_tuple_prefix((1, 1, 1));
julia> @code_typed get_tuple_prefix((1, 1, 1));
ERROR: BoundsError: attempt to access 0-element Array{Core.Compiler.NewNode,1} at index [6]
Stacktrace:
 [1] typeinf_code(::Method, ::Any, ::Core.SimpleVector, ::Bool, ::Core.Compiler.Params) at ./compiler/typeinfer.jl:515
 [2] #code_typed#18(::Bool, ::Function, ::Any, ::Any) at ./reflection.jl:882
 [3] code_typed(::Any, ::Any) at ./reflection.jl:872
 [4] top-level scope at /build/julia/src/julia/usr/share/julia/stdlib/v1.0/InteractiveUtils/src/macros.jl:110

[JeffBezanson]

Lowering seems to be referencing the wrong ssavalue for computing end inside the declared type:

julia> @code_lowered get_tuple_prefix((1, 1, 1))
CodeInfo(
2 1 ─ %1  = (Base.getproperty)($(Expr(:static_parameter, 1)), :parameters)                     │
  │   %2  = (Main.length)(%1)                                                                  │
  │   %3  = %2 - 1                                                                             │
  │   %4  = 1:%3                                                                               │
  │   %5  = (Base.getindex)(tuple, %4)                                                         │
  │   %6  = (Core.tuple)(Main.Tuple)                                                           │
  │         (Base.getproperty)($(Expr(:static_parameter, 1)), :parameters)                     │
  │   %8  = (Base.lastindex)(%15)                                                              │
  │   %9  = %8 - 1                                                                             │
  │   %10 = 1:%9                                                                               │
  │   %11 = (Base.getindex)(%15, %10)                                                          │
  │   %12 = (Core._apply)(Core.apply_type, %6, %11)                                            │
  │   %13 = (Base.convert)(%12, %5)                                                            │
  │   %14 = (Core.tuple)(Main.Tuple)                                                           │
  │   %15 = (Base.getproperty)($(Expr(:static_parameter, 1)), :parameters)                     │
  │   %16 = (Base.lastindex)(%15)                                                              │
  │   %17 = %16 - 1                                                                            │
  │   %18 = 1:%17                                                                              │
  │   %19 = (Base.getindex)(%15, %18)                                                          │
  │   %20 = (Core._apply)(Core.apply_type, %14, %19)                                           │
  │         prefix = (Core.typeassert)(%13, %20)                                               │
3 └──       return prefix                                                                      │
)

Note the not-dominated use of %15.

[JeffBezanson]

In the meantime if you need an implementation of this, this should be much faster:

get_tuple_prefix(x::Tuple{Any}) = ()
tail(x, rest...) = rest
get_tuple_prefix(x::Tuple{Any,Vararg{Any}}) = (x[1], get_tuple_prefix(tail(x...))...)

[mabokhamis]

In the meantime if you need an implementation of this, this should be much faster:

get_tuple_prefix(x::Tuple{Any}) = ()
tail(x, rest...) = rest
get_tuple_prefix(x::Tuple{Any,Vararg{Any}}) = (x[1], get_tuple_prefix(tail(x...))...)

Interesting that the above code is faster despite the recursion in the last line. If the input tuple x has a large length N, does the above code run in O(N) or O(N^2)? In other words, does the above code result in copying the whole previous tuple get_tuple_prefix(tail(x...)) every time a new x[1] is prepended to the tuple (which would result in O(N^2) time)?

[JeffBezanson]

It will be fully unrolled for small tuples, but yes it will eventually become O(n^2). For long tuples ntuple(i->getfield(t,i), length(t)-1) will work better. Or for a bit more generality you can use a method like this:

@Base.pure function tuple_type_prefix(::Type{T}) where T<:Tuple
    return Tuple{T.parameters[1:end-1]...}
end

function get_tuple_prefix(tuple::T) where {T <: Tuple}
    prefix::tuple_type_prefix(T) = tuple[1:length(tuple)-1]
    return prefix
end