Build: failing Float16 intrinsics on 1.6.6 or 1.7.2 on ubuntu 22.04

[t-bltg]

I'm building julia 1.6.6 on ubuntu 22.04 with gcc 11.2.0 from source archives.

$ cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=22.04
DISTRIB_CODENAME=jammy
DISTRIB_DESCRIPTION="Ubuntu 22.04 LTS"
$ gcc --version
gcc (Ubuntu 11.2.0-19ubuntu1) 11.2.0
[...]
$ ldd --version
ldd (Ubuntu GLIBC 2.35-0ubuntu3) 2.35
[...]

I have two unrelated patches applied, #45419 and #43717 for the build to end without errors.
I'm building all dependencies with USE_BINARYBUILDER := 0 and a prefix set, and standard make -j, make install.

Lots of Float16 intrinsics tests are failing, running $ julia -e 'Base.runtests("intrinsics")':

Test   (Worker) | Time (s) | GC (s) | GC % | Alloc (MB) | RSS (MB)
intrinsics  (1) |        started at 2022-05-24T14:18:57.744
intrinsics  (1) |         failed at 2022-05-24T14:19:02.184
Test Failed at [...]/share/julia/test/intrinsics.jl:128
  Expression: f() === Base.invokelatest(Core.Intrinsics.neg_float, Float16(3.3))
   Evaluated: Float16(-3.3) === Float16(-3.97e-5)
[...]

Here is a simple reproducer:

using InteractiveUtils, Test

main() = begin
  @test Core.Intrinsics.fptrunc(Float16, 4.4) ≈ 4.4
  @test Float16(4.4f0) ≈ 4.4
  @test Float16(4.4) ≈ 4.4
  return
end

main()
versioninfo()

@test Core.Intrinsics.fptrunc(Float16, 4.4) ≈ 4.4
@test Float16(4.4f0) ≈ 4.4
@test Float16(4.4) ≈ 4.4  # KO !!

And the output:

$ julia fail.jl
Julia Version 1.6.6
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: Intel(R) Xeon(R) CPU E5-2670 0 @ 2.60GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-11.0.1 (ORCJIT, sandybridge)
Test Failed at [...]/fail.jl:15
  Expression: Float16(4.4) ≈ 4.4
   Evaluated: Float16(6.1e-6) ≈ 4.4
ERROR: LoadError: There was an error during testing
in expression starting at [...]/fail.jl:15

Same failures observed when building and testing 1.7.2. This used to build fine with tests passing on ubuntu 20.04.

Has anyone seen that before ? Does anyone have any clue on which library or code section might be failing ?

[t-bltg]

The problem seem to originate from handling

julia/src/intrinsics.cpp

Line 1187 in fc52b3f

return generic_cast(ctx, f, Instruction::FPTrunc, argv, false, false);

If I un-comment

julia/src/intrinsics.cpp

Line 1118 in fc52b3f

// return emit_runtime_call(ctx, f, argv, nargs);

, the intrinsics test passes.

[vtjnash]

Duplicate of #44829

[t-bltg]

Thanks @vtjnash for pointing this issue. Will close when we have backported patches (as mentioned in #45249, will continue the discussion there).

EDIT: fixed by #45649.