Undefined behavior with unchecked target_feature calls

[Manishearth]

bitmaps/src/bitmap.rs

Lines 691 to 701 in b449cec

	impl From<Bitmap<128>> for __m128i {
	fn from(data: Bitmap<128>) -> Self {
	unsafe { data.load_m128i() }
	}
	}
	impl From<Bitmap<256>> for __m256i {
	fn from(data: Bitmap<256>) -> Self {
	unsafe { data.load_m256i() }
	}
	}

This is UB: the two load functions are #[target_feature(enable = "avx")], which means they are not unconditionally available on all x86 platforms. This should probably check if cfg_feature_enabled!("avx") or use cfg!(target_feature = "avx2"). In the latter case, the avx calls will only be reached if compiling with AVX enabled (whereas in the former, you can have one binary for all x86 chips and there's a runtime check)