Loading a NTuple{N, VecElement{T}} can seqfault

[vchuravy]

Currently SIMD.jl reliably seqfaults on release-0.6 and master. The particular backtrace that I captured in rrstarts at [1] and ends at [2].
After talking to @yuyichao it looks like a load from the heap that is misaligned. Reverting #20975 makes the issue go away.

[1] https://github.com/eschnett/SIMD.jl/blob/a4a12d9ea34e43ba66e14d8cecc71b1019aac65d/test/runtests.jl#L36
[2]

julia/base/strings/io.jl

Line 101 in b7d6be0

for x in xs

[m-j-w]

Regarding alignment issues of NTuple{N, VecElement{T}} see also #20961.
It seems the special treatment of VecElement introduces false alignment assumptions, and in addition LLVM fails at N>32 plus a number of smaller values of N.

[vchuravy]

Yes that is definitely related, but in this case the vector is vec = NTuple{4, VecElement{Float64}} with a size of 32 and an alignment of 32. In my opinion that is correct for AVX.

[vchuravy]

fixed by #21980