tustvold commented on code in PR #5922:
URL: https://github.com/apache/arrow-rs/pull/5922#discussion_r1650031093
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arrow-array/src/array/byte_view_array.rs:
##########
@@ -238,8 +241,18 @@ impl<T: ByteViewType + ?Sized> GenericByteViewArray<T> {
}
/// Returns the element at index `i`
+ ///
+ ///
/// # Safety
/// Caller is responsible for ensuring that the index is within the bounds
of the array
+ //
+ // This function can't be inlined, ow it causes the caller function to run
out of registers and cause register spilling.
+ // Basically you can't just call `l_full_data = left.value_unchecked(...)`,
+ // the compiler tries to inline the `value_unchecked` function, which
introduces many unnecessary variables on stack.
+ // Looking at the assembly, the auto-inlined version run out of the
registers, which causes register spilling, which then causes unnecessary memory
access.
+ //
+ // TLDR: don't change it, unless you have examined the assembly output.
Review Comment:
This feels like an issue with the caller of value_unchecked and not the
nature of inlining this method? In particular I wonder if the issue is compare
/ compare_unchecked is getting inlined. A lot of the comparison kernel
implementations use `inline(never)` for this reason
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