Change to make bswap(::Vec{<:Any, <:Union{UInt8, Int8}}) a pass-through

[kimikage]

Currently, bswap(::Vec) calls Intrinsics.bswap, but LLVM does not support odd-byte bswap.
https://github.com/llvm/llvm-project/blob/6009708b4367171ccdbf4b5905cb6a803753fe18/llvm/lib/IR/Verifier.cpp#L5790-L5795

Normally, 1-byte (i.e., UInt8 and Int8) bswaps are eliminated somewhere in the code generation path, but they might remain for some reason. (cf. tlnagy/TiffImages.jl#166)

Perhaps this is an issue that should be addressed in LLVM or Julia compiler, but a workaround in SIMD.jl might not be a bad idea.

[maleadt]

TestImages.jl also suffers from this, so I'd say this is something important to fix.

[eschnett]

I have a potential fix but I cannot reproduce the problem. Can you give details? Which Julia/LLVM versions are you using etc.? Which CPU architecture is this? What is the error you see?

[eschnett]

See #137

[maleadt]

I reproduced it on x86_64 (zen3) with:

import TiffImages, Downloads

_wrap(name) = "https://github.com/tlnagy/exampletiffs/blob/master/$name?raw=true"

using Downloads
get_example(x) = Downloads.download(_wrap(x))

filepath = get_example("capitol.tif")
img = TiffImages.load(filepath)

Requires an assertions builds, of course. On latest master:

julia> img = TiffImages.load(filepath)
bswap must be an even number of bytes
  %195 = call <32 x i8> @llvm.bswap.v32i8(<32 x i8> %194), !dbg !206
LLVM ERROR: Broken module found, compilation aborted!

[eschnett]

I did not manage to get an error message, but I did see CI failures when I added a test. #137 is ready for review.

[eschnett]

Fixed in SIMD 3.7.1.