On Tue, Mar 17, 2026 at 12:54:43PM +0100, Richard Biener wrote:
> This decouples the PRE reference IL from the VN hash tables, following
> the corresponding PR103037 fix for nary expressions in r12-7389 to avoid
> correctness issues regarding to access paths when inserting expressions.
>
> Unfortunately this makes existing workarounds for alignment and alias
> mismatches ineffective so those have to be re-implemented. Instead
> of going back to implement canonexpr() during the ANTIC dataflow the
> following does this at insertion time, hoping all relevant reaching
> expressions will survive. A convenient place to do this is
> sorted_array_from_bitmap_set, the actual magic worker is 'prefer',
> for the moment handling alignment and innermost access size only,
> as those are the cases we have test coverage. In particular the
> access path difference seen in this PR is not covered - it is enough
> to fix the AVAIL_OUT computation in compute_avail for this.
>
> Where the old fixup code massaged the expressions the new code selects
> from existing expressions or as fallback makes sure to not perform
> code insertion when two incompatible expressions met.
Thanks for working on this.
> Bootstrapped and tested on x86_64-unknown-linux-gnu. I've built a
> set of applications looking for ICEs successfully, still I consider
> this moderately risky at this point (but I'd also like to see
> coverage rather than trying to hack the missing alias-set handling
> in place without such coverage). I'll try to come up with a GIMPLE FE
> testcase for this but it's also that the later we're putting this in
> the worse (IMO), defering to stage1 and backporting will also not
> really result in better coverage.
>
> So what's your opinion?
>
> OK for trunk?
I'd put it on the trunk, we still have at least a month to find issues in it
and it will be widely deployed till then to get real-world coverage.
Jakub
