On 7/7/2026 3:39 PM, Daniel Barboza wrote:
> Canonicalize right shift non-equality comparisons with constants by
> turn them into a comparison with a left shifted constant. Assuming the
> generic format:
>
> (A >> CST1) CMP CST2
>
> For CMP (<, >=) we'll compare A with CST2 left shifted by CST1:
>
> - (A >> CST1) < CST2 -> A < (CST2 << CST1)
> - (A >> CST1) >= CST2 -> A >= (CST2 << CST1)
>
> And for CMP (<=, >) we need to IOR the lower CST1 bits from the left
> shift:
>
> - (A >> CST1) <= CST2 -> A <= (CST2 << CST1) | mask
> - (A >> CST1) > CST2 -> A > (CST2 << CST1) | mask
>
> Given that the right hand side changes involves just constants, in the
> end we'll replace a rshift + cmp with just a cmp.
>
> Bootstrapped and regression tested in x86, aarch64 and RISC-V.
>
> PR tree-optimization/124808
>
> gcc/ChangeLog:
>
> * match.pd(`(A >> CST1) CMP CST2`): New pattern.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/pr124808-2.c: New test.
> * gcc.dg/tree-ssa/pr124808.c: New test.
> ---
>
> Re-sending this patch since it got stalled since May 16th. Rebased
> and bootstrapped/regtested again with x86_64.
Thanks for re-raising. This clearly got lost.
This is OK for the trunk. And FTR I tested this across the various
embedded targets too with no regressions.
Jeff
