Add option to compile Eigen with alignment enabled #1196
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@fabiencastan friendly ping :-) I think this PR is good to go. |
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We should also re-evaluate if we cannot switch to C++17 nowadays. |
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@fabiencastan I think just using C++17 is the cleanest solution. While I don't know where exactly AliceVision is used, but full C++17 is already supported in gcc 7.x, which is in e.g. Ubuntu 18.04 LTS already, so more than 4 years old. Similar situation is across other Linux distributions. On Windows it's rather easy to target older versions of Windows, so C++17 support should not be a problem either. |
Eigen is most optimal when using SIMD instructions which require overaligned buffers. In C++14 this is a problem because there's no built-in support for correctly aligned allocations, so this Eigen feature is currently disabled in AliceVision. C++17 solves Eigen alignment issues completely because there now exist additional overloads of operator new() which support correct allocation alignment. We can't upgrade to C++17 yet, but certain compilers added support for this feature earlier, such as -faligned-new in GCC 7.1. Therefore it makes sense to add a configuration option to allow enabling alignment support in Eigen in cases when the compiler is good enough.
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@fabiencastan Just a friendly ping :) I think this PR can be merged. |
fabiencastan
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Eigen is most optimal when using SIMD instructions which require overaligned buffers. In C++14 this is a problem because there's no built-in support for correctly aligned allocations, so this Eigen feature is currently disabled in AliceVision. C++17 solves Eigen alignment issues completely because there now exist additional overloads of operator new() which support correct allocation alignment. We can't upgrade to C++17 yet, but certain compilers added support for this feature earlier, such as
-faligned-newin GCC 7.1.Given the above it makes sense to add a configuration option to allow enabling alignment support in Eigen in cases when the compiler is good enough (we enable
-faligned-newautomatically). This will improve performance for people who can control the set of supported compilers.Clang also supports
-faligned-new, but their documentation is empty and I didn't find which version of clang was the first to support the option, so I didn't add any special cases for clang yet.