Add algorithm-specific detection macros for vectorization #5801
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tests/std/tests/GH_000431_equal_memcmp_is_safe/test.compile.pass.cpp
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tests/std/tests/GH_000431_lex_compare_memcmp_classify/test.compile.pass.cpp
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AlexGuteniev
approved these changes
Oct 24, 2025
_VECTORIZED_FIND_LAST_NOT_OF guarded __std_find_last_not_ch_pos_1 which calls _Finding::_Find_last_pos_impl which calls _Finding::_Find_last_impl _VECTORIZED_FIND_LAST guards __std_find_last_trivial_1 which calls _Finding::_Find_last_impl
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
davidmrdavid
approved these changes
Oct 28, 2025
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No functional change for users; this keeps
_USE_STD_VECTOR_ALGORITHMSas our documented control macro.To prepare for adding ARM64 and eventually ARM64EC vectorized implementations, this begins by adding a layer of architecture-specific detection macros. (This layer isn't strictly necessary, but it makes life easier because it (1) allows the control macro to shut everything down, (2) deals with how ARM64EC defines both
_M_ARM64ECand_M_X64, and (3) centralizes how x64/x86 vectorization is always paired.)Then this introduces algorithm-specific detection macros. This makes connections throughout the codebase easier to understand, because a given vectorized algorithm needs declarations of separately compiled functions (
__std_meow_4), a wrapper template (_Meow_vectorized), callsites, and occasionally helper type traits (_Vector_alg_in_meow_is_safe). This will also make it significantly easier to implement algorithms one at a time for ARM64, since this PR is decomposing what was previously a monolithic mode.The
_VECTORIZED_MEOWmacros are named to avoid confusion with any control macros (we usually use the_HAS_BLAHor_USE_BLAHpatterns for control). They're deliberately the mirror image of the_Meow_vectorizedwrappers, to further avoid confusion.In simple cases, the macros are 1:1 with the wrapper templates. However, there are several "algorithm families" implemented in
vector_algorithms.cpp, like theminmaxandminmax_elementfamilies and the variousfindvariants. I tried to introduce macros that corresponded to these algorithm families, since that's how they'll be implemented (and there would be no benefit to introducing an even finer-grained system).There are a couple of places where I had to slightly adjust
if constexprlogic to handle theminmaxandminmax_elementfamilies potentially being variously active.Finally, while removing the old monolithic macro, I allowed the code to expand to empty
extern "C" { ... }blocks when no vectorization is active, because this is harmless and avoids cluttering up the code with even more verbosity.