jhorstmann commented on code in PR #2061:
URL: https://github.com/apache/arrow-rs/pull/2061#discussion_r920876190
##########
arrow/src/util/bit_chunk_iterator.rs:
##########
@@ -333,7 +333,7 @@ impl Iterator for BitChunkIterator<'_> {
// the constructor ensures that bit_offset is in 0..8
// that means we need to read at most one additional byte to fill
in the high bits
let next = unsafe {
- std::ptr::read_unaligned(raw_data.add(index + 1) as *const u8)
as u64
+ std::ptr::read_volatile(raw_data.add(index + 1) as *const u8)
as u64
Review Comment:
Plain `std::ptr::read` should then work just as well for reading a byte. I'm
surprised this makes a difference because the compiler should know that bytes
can't really be unaligned.
The copy inside the implementation of `read_unaligned` is something that the
compiler will optimize away since the size is statically known. My only guess
would be that the slightly larger code before optimizations somehow influences
inlining decisions somewhere else.
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