[gouarin]

Description

GCC 13 and 15 emit -Warray-bounds at -O2/-O3 on ordinary code using fixed-rank containers, for example assigning 0.5 * (even + odd) to a 1-D xtensor view. The warning comes from a std::copy between two std::array<std::size_t, 1> when the source is a member at a non-zero offset. GCC does not fold the length of the range and warns on the memmove branch that libstdc++ keeps for ranges of more than one element. That branch never runs. Reproducer without xtensor:

struct holder { std::size_t m_size; std::array<std::size_t, 1> m_shape; };
std::array<std::size_t, 1> f(const holder& h)
{
    std::array<std::size_t, 1> s;
    std::copy(h.m_shape.cbegin(), h.m_shape.cend(), s.begin());
    return s;
}

These copies now use std::copy_n(src.begin(), src.size(), dst.begin()). size() is a constant for std::array, so GCC drops the branch. At each site the destination is sized from the same source, so the copied elements do not change. Changed sites: xfunction::broadcast_shape, the xbroadcast constructor, flip (shape and strides), and average with multi-dimensional weights. std::copy(data(), data() + size()) and std::ranges::copy still warn.

No unit test, since this is a compile-time warning and CI does not build with -Wall on GCC. A file using 1-D, 2-D and 3-D views, reductions, broadcasting, flip and xtensor_fixed now compiles without warnings with GCC 13.4 and 15.3 at -O2 and -O3 with -Wall -Wextra, with and without xsimd.

[codspeed]

Merging this PR will not alter performance

1 warning

⚠️ Unable to measure the execution of 1 benchmark

This benchmark measured no execution time, so its result is not comparable and counts as unchanged. This usually happens when the compiler removes the code under test.

Prevent compiler optimizations

See affected benchmarks

✅ 255 untouched benchmarks

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_{Comparing gouarin:fix-array-bounds (5a967e3) with master (57f3d07)}