Julia: Segfault on compile in ApproxFun

[dlfivefifty]

This is on the branch "bug-crashoncompile" of ApproxFun in Julia v0.7-beta.

I am also on master for FastGaussQuadrature.jl, and FastTransforms.jl (and also BandedMatrices.jl, BlockBandedMatrices.jl but those the tagged versions support Julia v0.7).

               _
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  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
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  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.7.0-beta2.32 (2018-07-17 20:09 UTC)
 _/ |\__'_|_|_|\__'_|  |  Commit b6a60dd660* (2 days old master)
|__/                   |  x86_64-apple-darwin17.6.0

julia> using ApproxFun, Test

julia> x = Fun(0 .. 1); f = sqrt(x); sp = space(f) ∪ ConstantSpace(); cfsin = f.coefficients; A = space(f); B = sp;

julia> precompile(ApproxFun.defaultcoefficients, (typeof(cfsin), typeof(A), typeof(B)))

signal (11): Segmentation fault: 11
in expression starting at no file:0

[JeffBezanson]

I get this stack trace:

emit_unionmove at /home/jeff/src/julia/src/cgutils.cpp:2261
emit_function at /home/jeff/src/julia/src/codegen.cpp:6449
jl_compile_linfo at /home/jeff/src/julia/src/codegen.cpp:1159
emit_invoke at /home/jeff/src/julia/src/codegen.cpp:3083
emit_expr at /home/jeff/src/julia/src/codegen.cpp:3882
emit_ssaval_assign at /home/jeff/src/julia/src/codegen.cpp:3604
emit_stmtpos at /home/jeff/src/julia/src/codegen.cpp:3790 [inlined]
emit_function at /home/jeff/src/julia/src/codegen.cpp:6238
jl_compile_linfo at /home/jeff/src/julia/src/codegen.cpp:1159

[JeffBezanson]

Also, I don't think it's related but these packages hit pathological cases in subtyping that cause very high load times. It's caused by the large StridedArray union type. I believe there is already some awareness of this problem. In the meantime I'll see if I can improve the subtyping code for this case.

[dlfivefifty]

I was at one point hoping to make a PR to deprecate StridedArray, but the second PR in that direction to redesign mul! got bogged down by design discussions so never got merged.

[dlfivefifty]

PS Apart from this Segfault, ApproxFun now passes all tests without errors/warnings 🎉

[dlfivefifty]

This might have been the same issue, but in Julia v0.6: https://github.com/JuliaLang/julia/issues/23792

[JeffBezanson]

What is the severity of this --- does it render the package unusable, or is it a rare case?

[dlfivefifty]

Lots of code funnels through defaultcoefficients so I’d say unusable, though large chunks of ApproxFun still work.

[Keno]

Minimal reduction:

julia> function foo()
           x = (1, 2)
           if rand() < 0.5
               if rand() < 0.5
                   y = nothing
               else
                   y = missing
               end
               x = y
           end
           x
       end
foo (generic function with 1 method)

julia> foo()

signal (11): Segmentation fault
in expression starting at no file:0
getType at /home/keno/julia/usr/include/llvm/IR/Value.h:245
maybe_bitcast at /home/keno/julia/src/cgutils.cpp:460
emit_unionmove at /home/keno/julia/src/cgutils.cpp:2292
emit_function at /home/keno/julia/src/codegen.cpp:6461
jl_compile_linfo at /home/keno/julia/src/codegen.cpp:1160
jl_compile_method_internal at /home/keno/julia/src/gf.c:1777
jl_fptr_trampoline at /home/keno/julia/src/gf.c:1811
jl_apply_generic at /home/keno/julia/src/gf.c:2165
do_call at /home/keno/julia/src/interpreter.c:324
eval_value at /home/keno/julia/src/interpreter.c:428
eval_stmt_value at /home/keno/julia/src/interpreter.c:363
eval_body at /home/keno/julia/src/interpreter.c:683
jl_interpret_toplevel_thunk_callback at /home/keno/julia/src/interpreter.c:800
unknown function (ip: 0xfffffffffffffffe)
unknown function (ip: 0x7f219744b1bf)
unknown function (ip: 0xffffffffffffffff)
jl_interpret_toplevel_thunk at /home/keno/julia/src/interpreter.c:809
jl_toplevel_eval_flex at /home/keno/julia/src/toplevel.c:822
jl_toplevel_eval at /home/keno/julia/src/toplevel.c:831
jl_toplevel_eval_in at /home/keno/julia/src/builtins.c:633
eval at ./boot.jl:319
jl_fptr_args at /home/keno/julia/src/gf.c:1822
jl_apply_generic at /home/keno/julia/src/gf.c:2165
eval_user_input at /home/keno/julia/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:87
macro expansion at /home/keno/julia/usr/share/julia/stdlib/v0.7/REPL/src/REPL.jl:119 [inlined]
#28 at ./task.jl:262
jl_fptr_args at /home/keno/julia/src/gf.c:1822
jl_fptr_trampoline at /home/keno/julia/src/gf.c:1812
jl_apply_generic at /home/keno/julia/src/gf.c:2165
jl_apply at /home/keno/julia/src/julia.h:1538
start_task at /home/keno/julia/src/task.c:268
unknown function (ip: 0xffffffffffffffff)
Allocations: 4833687 (Pool: 4832774; Big: 913); GC: 9
Segmentation fault