On Wed, Sep 23, 2026 at 10:59:58AM +0200, Richard Biener wrote:
> On Wed, Sep 23, 2026 at 12:37 AM David Guillen Fandos <[email protected]>
> wrote:
> > These patches aim to expand and improve the byte swapping pass to recognize
> > some more patterns including bit reverse patterns. The first three patches
> > build on bswap to track bits instead of bytes and recognize some new bswap
> > patterns (ie. with somewhat arbitrary rotation and masking). The last three
> > add bitreverse recognition including 8 and 16 bit variants.
>
> Thanks for improving the symbolic number tracking. One thing that's on my
> wish list for this is tracking of vector lane permutations and vector
> per-element
> shifts/masks with the idea to detect permutes. That would require tracking
> larger symbolic numbers (for AVX512 it's 512 bits), but bit tracking is
> overkill
> there. So I wonder how ugly it gets to make bits vs. bytes configurable?
> As you've transitioned bytes to bits you can probably answer this quickly.
Also, if we change the tracking representation, we should also start
supporting __int128, so don't limit to 64 bits, but 128. Even when no
target actually supports bswapti2 or bitreverseti2, those can be implemented
using 2 bswapdi2 or bitreversedi2.
Except for vectors, we don't need to support more than 128 bits I think,
large/huge _BitInt should be lowered by the time this pass runs.
Jakub
