[Bug target/113087] [14] RISC-V rv64gcv vector: Runtime mismatch with rv64gc

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113087

--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Pan Li <panli@gcc.gnu.org>:

https://gcc.gnu.org/g:008b80e42eb7cb55c6a2ef55728241b8733dfd17

commit r14-6761-g008b80e42eb7cb55c6a2ef55728241b8733dfd17
Author: Juzhe-Zhong <juzhe.zhong@rivai.ai>
Date:   Wed Dec 20 14:55:26 2023 +0800

    RISC-V: Optimize SELECT_VL codegen when length is known as smaller than VF

    While trying to fix bugs of PR113097, notice this following situation we
    generate redundant vsetvli

    _255 = SELECT_VL (3, POLY_INT_CST [4, 4]);
    COND_LEN (..., _255)

    Before this patch:

    vsetivli a5, 3...
    ...
    vadd.vv (use a5)

    After this patch:

    ...
    vadd.vv (use AVL = 3)

    The reason we can do this is because known_ge (3, [4,4]) is true.
    It's safe to apply such optimization

    Tested on both RV32 and RV64 full coverage testing, no regression.

            PR target/113087

    gcc/ChangeLog:

            * config/riscv/riscv-v.cc (expand_select_vl): Optimize SELECT_VL.

    gcc/testsuite/ChangeLog:

            * gcc.target/riscv/rvv/autovec/pr113087-2.c: New test.