[Bug target/126550] RISC-V: auto-vectorization miscompiles duplicated deinterleave store via vcompress/vrgather (rv64gcv_zvl256b)

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126550

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-16 branch has been updated by Jeff Law <[email protected]>:

https://gcc.gnu.org/g:4e3274800752936bb5cdcafe836b7cd700f8ad6d

commit r16-9524-g4e3274800752936bb5cdcafe836b7cd700f8ad6d
Author: Robin Dapp <[email protected]>
Date:   Tue Aug 4 11:37:33 2026 +0200

    RISC-V: Fix single-step expansion [PR126550].

    In expand_const_vector_single_step_npatterns, we use a second vector
    builder that is derived from the main one, in order to create a
    different alternating pattern for constant synthesis.  We later use the
    second builder's number of patterns for creating an intermediate
    operation.  The second builder can have a different number of patterns
    than the first one, however, for example when its "global" pattern is
    simpler.

    This patch uses npatterns from the original builder.

            PR target/126550

    gcc/ChangeLog:

            * config/riscv/riscv-v.cc
(expand_const_vector_single_step_npatterns):
            User global builder's npatterns.

    gcc/testsuite/ChangeLog:

            * gcc.target/riscv/rvv/autovec/pr126550-2.c: New test.
            * gcc.target/riscv/rvv/autovec/pr126550.c: New test.

    (cherry picked from commit 7cdbbbdecb09e518e28c5116b05e0018b9460b95)