fix: avx512vl masked load/store

[DiamonDinoia]

xsimd::batch<uint32_t, avx512vl_256>::store(ptr, constexpr_mask, mode) used
to compile to a 6-instruction per-lane scalar extract loop instead of a single
EVEX-encoded masked store, because the call site in xsimd_batch.hpp:766
over-specified template arguments and SFINAE'd away every viable masked-store
overload except the scalar common fallback.

The load side was unaffected — its call site (:743) was already correct.

#include <xsimd/xsimd.hpp>

using A    = xsimd::avx512vl_256;
using Bu32 = xsimd::batch<uint32_t, A>;

// Constant alternating mask: lanes 0,2,4,6 active.
struct alt {
    static constexpr bool get(std::size_t i, std::size_t) { return (i & 1) == 0; }
};

static constexpr auto mask = xsimd::make_batch_bool_constant<uint32_t, alt, A>();

Bu32 load_u32(uint32_t const* p) {
    return Bu32::load(p, mask, xsimd::unaligned_mode{});
}

void store_u32(uint32_t* p, Bu32 v) {
    v.store(p, mask, xsimd::unaligned_mode{});
}

g++ -O3 -S -masm=intel -std=c++14 -march=skylake-avx512 -DXSIMD_DEFAULT_ARCH=xsimd::avx512vl_256

Codegen — before (master, commit 7d30b9cc)

_Z8load_u32PKj:                  # load_u32
    mov         eax, 85
    kmovb       k1, eax
    vmovdqu32   ymm0{k1}{z}, YMMWORD PTR [rdi]
    ret

_Z9store_u32PjN5xsimd5batchIjNS0_12avx512vl_256EEE:   # store_u32
    valignd       ymm1, ymm0, ymm0, 6
    vmovd         DWORD PTR  [rdi], xmm0
    vpextrd       DWORD PTR 8[rdi], xmm0, 2
    vextracti32x4 xmm2, ymm0, 1
    vmovd         DWORD PTR 24[rdi], xmm1
    vmovd         DWORD PTR 16[rdi], xmm2
    ret

Load is fine. Store is the scalar fallback: GCC unrolled the 8-lane loop in
xsimd_common_memory.hpp:377 into four per-lane 32-bit stores, materialising
each active lane no mask instruction involved.

Codegen — after

_Z8load_u32PKj:                  # load_u32 — unchanged
    mov         eax, 85
    kmovb       k1, eax
    vmovdqu32   ymm0{k1}{z}, YMMWORD PTR [rdi]
    ret

_Z9store_u32PjN5xsimd5batchIjNS0_12avx512vl_256EEE:   # store_u32
    mov         eax, 85
    kmovb       k1, eax
    vmovdqu32   YMMWORD PTR [rdi]{k1}, ymm0
    ret

One masked instruction.

Bug fixes

• AVX-512VL masked store collapsed to a 6-insn scalar fallback. An over-specified template arg list at the public batch::store(mask) call site pushed a type into a non-type pack, SFINAE'ing every per-arch overload away. The store now reaches the EVEX vmov*{k} intrinsic.

• CI linux.yml typo silently dropped CXXFLAGS in the VL_128 matrix row ($CXX_FLAGS vs $CXXFLAGS), so the VL_128-default test job was building with stock flags instead of the requested override.

• avx512vl register-traits comment misattributed to AVX512DQ.

• Half-confined masked op fell back to scalar on AVX/AVX2/AVX-512F. The half-fold hardcoded sse4_2/avx2 as the half-width target, but two-phase lookup made the better-arch overload invisible at template-definition time — so the recursive call dispatched to the wrong arch. Fixed by include reorder + make_sized_batch_t<T, half>.

Features added

• Per-type load_masked / store_masked for avx512vl_128 and avx512vl_256 covering i32/u32/i64/u64/f32/f64 in both aligned and unaligned modes; partial ordering picks them over the avx2 bridges these archs
  inherit.
• Compile-time guarantee that default_arch matches XSIMD_DEFAULT_ARCH when the macro is set — a static_assert in test_arch.cpp (plus the CMake plumbing to forward the macro) catches default-arch wiring regressions at compile time instead of at runtime.

Cleanups

• AVX detail::maskstore helpers now take batch<> types, symmetric with detail::maskload.
• Half-store sites and the common select use a typed variable (const batch<T, A> lo = …) instead of const auto lo = batch<T, A>{ … }.
• Aligned/unaligned dispatch in the VL overloads uses XSIMD_IF_CONSTEXPR, so the inactive intrinsic isn't instantiated.
• Half-fold in xsimd_avx.hpp / xsimd_avx2.hpp / xsimd_avx512f.hpp uses make_sized_batch_t<T, half> instead of a hardcoded arch — picks avx_128 / avx2_128 / avx512vl_256 when available, so half-confined stores land on the EVEX or VEX masked intrinsic.
• xsimd_isa.hpp include order: _128 siblings before their wider arch, VL before avx512f.hpp. Required so the recursive store_masked<half_arch> call sees the better-arch overload at template-definition time.

(Changelog by @claude)

[serge-sans-paille]

oopsie. Thanks for fixing this one.

[serge-sans-paille]

I wish we could keep each architecture file unaware from other architectures. I do understand this will disappear once we move to C++17-based architecture, but I'd be happier if you could find another way to apply the constraints.

[serge-sans-paille]

there should not be any arch-specific code in xsimd_common_memory.hpp. Could you find another approach?

[serge-sans-paille]

wgy that change? In my mental model, the masked store take a bool mask, not an integer mask

[serge-sans-paille]

I quite dislike the fact that xsimd_avx2.hpp needs to know stuff about avx512vl

[serge-sans-paille]

same architecture mix reference issue here.

[serge-sans-paille]

nice catch.

[serge-sans-paille]

oopsie

[serge-sans-paille]

??

[serge-sans-paille]

Per https://cmake.org/cmake/help/latest/command/if.html#constant I think

if(XSIMD_DEFAULT_ARCH)

is enough

[serge-sans-paille]

(confirmed by https://godbolt.org/z/b64GcKaxM)

[serge-sans-paille]

yay