[Bug target/115921] Missed optimization: and->ashift might be cheaper than ashift->and on typical RISC targets

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115921

--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jeff Law <law@gcc.gnu.org>:

https://gcc.gnu.org/g:a9ebf249063d2e8f6e8813fc954276766ad3a2fe

commit r15-6877-ga9ebf249063d2e8f6e8813fc954276766ad3a2fe
Author: Xi Ruoyao <xry111@xry111.site>
Date:   Mon Jan 13 13:11:38 2025 -0700

    RISC-V: Remove zba check in bitwise and ashift reassociation [PR 115921]

    The test case

        long
        test (long x, long y)
        {
          return ((x | 0x1ff) << 3) + y;
        }

    is now compiled (-O2 -march=rv64g_zba) to

        li      a4,4096
        slliw   a5,a0,3
        addi    a4,a4,-8
        or      a5,a5,a4
        addw    a0,a5,a1
        ret

    Despite this check was originally intended to use zba better, now
    removing it actually enables the use of zba for this test case (thanks
    to late combine):

        ori    a5,a0,511
        sh3add  a0,a5,a1
        ret

    Obviously, bitmanip.md does not cover
    (any_or (ashift (reg) (imm123)) imm) at all, and even for and it just
    seems more natural splitting to (ashift (and (reg) (imm')) (imm123))
    first, then let late combine to combine the outer ashift and the plus.

    I've not found any test case regressed by the removal.
    And "make check-gcc RUNTESTFLAGS=riscv.exp='zba-*.c'" also reports no
    failure.

    gcc/ChangeLog:

            PR target/115921
            * config/riscv/riscv.md (<optab>_shift_reverse): Remove
            check for TARGET_ZBA.

    gcc/testsuite/ChangeLog:

            PR target/115921
            * gcc.target/riscv/zba-shNadd-08.c: New test.