This implements `Eigen::internal::assume_aligned` to match the API for C++20 standard as best as possible using either `std::assume_aligned` or `__builtin_assume_aligned` if available. If neither is available, the function is a no-op.
The override macro `EIGEN_ASSUME_ALIGNED` was changed to a `EIGEN_DONT_ASSUME_ALIGNED`, which now forces the function to be a no-op.
See merge request libeigen/eigen!2052
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### Description
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Allow user to configure if `free` is allowed at runtime.
Reverts to Eigen 3.4 behavior by default, where `free(...)` is allowed if `EIGEN_RUNTIME_NO_MALLOC` is defined but `set_is_malloc_allowed(true)`. Adds a separate `set_is_free_allowed(...)` to explicitly control use of `std::free`.
### Reference issue
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Fixes#2983.
### Additional information
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Closes#2983
See merge request libeigen/eigen!2047
Fixes#2229.
For dynamic matrices with fixed-sized storage, only copy/swap
elements that have been set. Otherwise, this leads to inefficient
copying, and potential UB for non-initialized elements.
Hex literals are interpreted as unsigned, leading to a comparison between
signed max supported function `abcd[0]` (which was negative) to the unsigned
literal `0x80000006`. Should not change result since signed is
implicitly converted to unsigned for the comparison, but eliminates the
warning.
