[Bug tree-optimization/107090] [aarch64] sequence logic should be combined with mul and umulh

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107090

--- Comment #21 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Philipp Tomsich <[email protected]>:

https://gcc.gnu.org/g:6c598e2be7d0adf937d3390bb8f6a16b39603016

commit r17-3438-g6c598e2be7d0adf937d3390bb8f6a16b39603016
Author: Konstantinos Eleftheriou <[email protected]>
Date:   Thu Jun 25 06:01:26 2026 -0700

    forwprop: Add long-multiply carry-low-sum variant

    Extend the long-multiply fold to the variant that collapses the cross
    sum and the low partial product into a single low_sum and tests the
    overflow compare against it:

      xh*yh + (low_sum >> N) + ((hilo > low_sum) << N)
      low_sum = cross_sum + (xl*yl >> N)
      cross_sum = xh*yl + xl*yh

    The outer chain has three summands instead of four; the corresponding
    LOW_PART recovers (xl*yl & mask) | (low_sum << N).

            PR tree-optimization/107090

    gcc/ChangeLog:

            * match.pd: Add mul_low_sum and mul_carry_low_sum atom
            recognizers.
            * tree-ssa-forwprop.cc (gimple_mul_low_sum): Declare.
            (gimple_mul_carry_low_sum): Likewise.
            (create_mul_low_seq): Update the widest-atom note above
            LONG_MUL_MAX_CAPTURES to mul_carry_low_sum (7 captures).
            (enum long_mul_kind): Add LMK_LOW_SUM and LMK_CARRY_LOW_SUM,
            with the long_mul_table HIGH_PART and LOW_PART rows that
            consume them.
            (long_mul_set_summand): Handle the new kinds.
            (long_mul_classify_carry): Try mul_carry_low_sum before
            mul_carry_cross_sum (most-specific first).
            (long_mul_classify_plus_kinds): Try mul_low_sum after
            mul_low_accum (mul_low_sum's first arm is any plus and
            mul_low_accum constrains both arms).

    gcc/testsuite/ChangeLog:

            * gcc.dg/tree-ssa/long-mul-carry.c: Add carry-low-sum
            coverage (mulh_carry_low_sum, full_mul_carry_low_sum,
            mulh_carry_low_sum_comm, mulh_carry_low_sum_lohi,
            mulh_carry_low_sum_128, mulh_carry_low_sum_v2i32) and
            update fold counts.