LLVM checked arithmetic for 128-bit ints is broken

[StefanKarpinski]

This is largely an upstream bug tracking issue.

[StefanKarpinski]

Oh, also 8-bit checked multiplies are also broken. Tracking that upstream bug here too.

[ViralBShah]

It would be nice to have the upstream bug url here, if one has been filed.

[StefanKarpinski]

I have not filed one. @loladiro has generally been our go-to guy for that interaction with the LLVM community.

[Keno]

I'll verify against trunk and file a bug report, no problem.

[StefanKarpinski]

Thanks, Keno!

[JeffBezanson]

Also broken for 64-bit ints on a 32-bit platform.
update: only 64-bit checked multiply is broken on 32-bit.

[Keno]

Fixed upstream by llvm-mirror/llvm@0bedfa4

[pao]

Mentioning Int128 explicitly to make this easier to find.

[simonbyrne]

What's the status of this? Are the other cases (Int128, Int64 on 32 bit) also fixed on new llvm?

[eschnett]

Just checked on Ubuntu 14.04, 32-bit, with LLVM 3.7: Int64 and Int128 remain broken; the respective run-time functions (e.g. mulodi4, muloti4) are not found. With 64 bits, only Int128 is broken.

[Keno]

The codegen bug is fixed for all cases, but as mentioned there may still be missing run-time functions.

[simonbyrne]

This has been monkey-patched by #14362. Should we close this or wait for the run-time functions?

[eschnett]

#14362 didn't change anything for Julia users -- the work-around were already there before.

[vtjnash]

compiler-rt support will be fixed by #17344 allowing fixing of the underlying issue here

[StefanKarpinski]

Fixed:

julia> a = rand(Int128)
168787286807142666394438386944935173819

julia> b = rand(Int128)
20332519185114748867952745427073576754

julia> a + b
-151162560928681048200983475059759460883

julia> Base.Checked.checked_add(a, b)
ERROR: OverflowError: 168787286807142666394438386944935173819 + 20332519185114748867952745427073576754 overflowed for type Int128
Stacktrace:
 [1] throw_overflowerr_binaryop(::Symbol, ::Int128, ::Int128) at ./checked.jl:154
 [2] checked_add(::Int128, ::Int128) at ./checked.jl:166
 [3] top-level scope at REPL[13]:1

I also checked UInt128 to be sure.

[oscardssmith]

@StefanKarpinski since this is fixed, can

julia/base/checked.jl

Line 43 in 8e3e970

# LLVM has several code generation bugs for checked integer arithmetic (see e.g.

be cleaned up?

[StefanKarpinski]

I dunno, I guess see if you can revert and it still works.