std `Atomic{I,U}{8,16}::fetch_{max,min}` seem to broken on a few platform (LLVM bug)

[taiki-e]

std Atomic{I,U}{8,16}::fetch_{max,min} is currently broken for the following targets

portable-atomic/src/lib.rs

Lines 1458 to 1467 in 55b3d49

	// HACK: the following operations are currently broken (at least on qemu):
	// - aarch64's `AtomicI{8,16}::fetch_{max,min}` (release mode + lse)
	// - armv5te's `Atomic{I,U}{8,16}::fetch_{max,min}`
	// - mips's `AtomicI8::fetch_{max,min}` (release mode)
	// - mipsel's `AtomicI{8,16}::fetch_{max,min}` (debug mode, at least)
	// - mips64's `AtomicI8::fetch_{max,min}` (release mode)
	// - mips64el's `AtomicI{8,16}::fetch_{max,min}` (debug mode, at least)
	// - powerpc's `AtomicI{8,16}::fetch_{max,min}`
	// - powerpc64's `AtomicI{8,16}::fetch_{max,min}` (debug mode, at least)
	// - powerpc64le's `AtomicU{8,16}::fetch_{max,min}` (release mode + fat LTO)

I haven't checked if it's a bug in rustc or in qemu-user, but this crate contains a workaround for this problem.

portable-atomic implements a workaround for this bug, so users aren't affected by this bug. This issue itself is tracking the upstream bug.

[taiki-e]

It seems armv5te's AtomicI{8,16}::compare_exchange is also broken: https://github.com/taiki-e/portable-atomic/runs/7041957669?check_suite_focus=true

[taiki-e]

It seems to be reproducible without qemu: rust-lang/rust#100650

[taiki-e]

I tested MIPS targets because the problem on MIPS was supposedly fixed in LLVM 19, but it seems that only bit-endian's MIPS32R2 is actually fixed, other MIPS targets still have problems.
https://github.com/taiki-e/portable-atomic/actions/runs/11314088026