Re: suspicious valgrind reports about radixtree/tidstore on arm64

Em qua., 19 de jun. de 2024 às 20:52, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> escreveu:

> I wrote:
> > I hypothesize that the reason we're not seeing equivalent failures
> > on x86_64 is one of
>
> > 1. x86_64 valgrind is stupider than aarch64, and fails to track that
> > the contents of the SIMD registers are only partially defined.
>
> > 2. x86_64 valgrind is smarter than aarch64, and is able to see
> > that the "mask off invalid entries" step removes all the
> > potentially-uninitialized bits.
>
> Hah: it's the second case. If I patch radixtree.h as attached,
> then x86_64 valgrind complains about
>
> ==00:00:00:32.759 247596== Conditional jump or move depends on
> uninitialised value(s)
> ==00:00:00:32.759 247596== at 0x52F668: local_ts_node_16_search_eq
> (radixtree.h:1018)
>
> showing that it knows that the result of vector8_highbit_mask is
> only partly defined.

I wouldn't be surprised if *RT_NODE_16_GET_INSERTPOS*
(src/include/lib/radixtree.h),
does not suffer from the same problem?
Even with Assert trying to protect.

Does the fix not apply here too?

best regards,
Ranier Vilela