On Wed, Feb 14, 2024 at 04:13:51PM +0100, Richard Biener wrote:
> The following removes the TBAA violation present in iterative_hash.
> As we eventually LTO that it's important to fix. This also improves
> code generation for the >= 12 bytes loop by using | to compose the
> 4 byte words as at least GCC 7 and up can recognize that pattern
> and perform a 4 byte load while the variant with a + is not
> recognized (not on trunk either), I think we have an enhancement bug
> for this somewhere.
>
> Given we reliably merge and the bogus "optimized" path might be
> only relevant for archs that cannot do misaligned loads efficiently
> I've chosen to keep a specialization for aligned accesses.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, OK for trunk?
>
> Thanks,
> Richard.
>
> libiberty/
> * hashtab.c (iterative_hash): Remove TBAA violating handling
> of aligned little-endian case in favor of just keeping the
> aligned case special-cased. Use | for composing a larger word.
Have you tried using memcpy into a hashval_t temporary?
Just wonder whether you get better or worse code with that compared to
the shifts.
Jakub
