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Vector algorithms: Add compile time checks for ISA features - #6098

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Stephan T. Lavavej (StephanTLavavej) merged 3 commits into
microsoft:mainfrom
matbech:patch-1
Feb 28, 2026
Merged

Vector algorithms: Add compile time checks for ISA features#6098
Stephan T. Lavavej (StephanTLavavej) merged 3 commits into
microsoft:mainfrom
matbech:patch-1

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@matbech

@matbech Mathias Berchtold (matbech) commented Feb 22, 2026

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When the STL is compiled with /arch:SSE4.2 or /arch:AVX2, the runtime checks for the respective ISA features (SSE42, AVX2) are unnecessary. This change adds a compile time check using __check_arch_support to avoid the runtime cost.
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Vector algorithms: Add compile time checks for ISA features
16eaa21 
When the STL is compiled with /arch:SSE4.2 or /arch:AVX2, the runtime checks for the respective ISA features (SSE42, AVX2) are unnecessary. This change adds a compile time check using __check_arch_support to avoid the runtime cost.
@matbech
Mathias Berchtold (matbech) requested a review from a team as a code owner February 22, 2026 02:23
@github-project-automation github-project-automation Bot moved this to Initial Review in STL Code Reviews Feb 22, 2026
@AlexGuteniev

Alex Guteniev (AlexGuteniev) commented Feb 22, 2026

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But what is the purpose?

For end users, the STL comes precompiled, so /arch flag passed by users, only affects public headers, but not separately compiled code. And when it is compiled for shipping it is always the same /arch option, which is SSE2 for x86, and baseline for x64.
@matbech

Mathias Berchtold (matbech) commented Feb 22, 2026

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For custom built binaries (msvcp140_oss.dll) with modern /arch compiler flags where performance is important.
@StephanTLavavej

Stephan T. Lavavej (StephanTLavavej) commented Feb 22, 2026

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For reference, __check_arch_support:

The __check_arch_support intrinsic can always be evaluated at compile time, so using it in optimized code adds no extra instructions to execute. Support for these intrinsics was added in Visual Studio 2022 version 17.10.
StephanTLavavej
Stephan T. Lavavej (StephanTLavavej) reviewed Feb 25, 2026
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Comment thread stl/src/vector_algorithms.cpp Outdated
@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) moved this from Initial Review to Ready To Merge in STL Code Reviews Feb 25, 2026
@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) moved this from Ready To Merge to Merging in STL Code Reviews Feb 26, 2026
@StephanTLavavej

Stephan T. Lavavej (StephanTLavavej) commented Feb 26, 2026

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I'm mirroring this to the MSVC-internal repo. Please notify me if any further changes are pushed, otherwise no action is required.
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Stephan T. Lavavej (StephanTLavavej) merged commit f25bfb5 into microsoft:main Feb 28, 2026
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@github-project-automation github-project-automation Bot moved this from Merging to Done in STL Code Reviews Feb 28, 2026
@StephanTLavavej

Stephan T. Lavavej (StephanTLavavej) commented Feb 28, 2026

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@matbech @AlexGuteniev @StephanTLavavej