Added Arm64 feature detections in STL

[jaykang10]

Added Arm64 feature detections in STL

FEAT_DotProd (PF_ARM_V82_DP_INSTRUCTIONS_AVAILABLE)
FEAT_I8MM (PF_ARM_V82_I8MM_INSTRUCTIONS_AVAILABLE)
FEAT_SHA3 (PF_ARM_SHA3_INSTRUCTIONS_AVAILABLE)
FEAT_SVE (PF_ARM_SVE_INSTRUCTIONS_AVAILABLE)
FEAT_SVE2 (PF_ARM_SVE2_INSTRUCTIONS_AVAILABLE)
FEAT_SVE2p1 (PF_ARM_SVE2_1_INSTRUCTIONS_AVAILABLE)
FEAT_SVE_SHA3 (PF_ARM_SVE_SHA3_INSTRUCTIONS_AVAILABLE)
FEAT_SVE_AES (PF_ARM_SVE_AES_INSTRUCTIONS_AVAILABLE)
FEAT_SVE_BitPerm (PF_ARM_SVE_BITPERM_INSTRUCTIONS_AVAILABLE)

[jaykang10]

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[frederick-vs-ja]

I think we should add them together with certain improvement of vectorization.

[jaykang10]

I think we should add them together with certain improvement of vectorization.

Yep, I agree with it.
@hazzlim I think we don’t need vcruntime support for Arm64 feature detection, and IsProcessorFeaturePresent should be sufficient.
Could you please add explicit feature detection for each case where the algorithms are vectorized for a specific feature?
I think this PR could be used as a reference.

[hazzlim]

I think we should add them together with certain improvement of vectorization.

Yep, I agree with it. @hazzlim I think we don’t need vcruntime support for Arm64 feature detection, and IsProcessorFeaturePresent should be sufficient. Could you please add explicit feature detection for each case where the algorithms are vectorized for a specific feature? I think this PR could be used as a reference.

Seems reasonable, I will take this approach.

From the initial discussion on the STL discord, it sounded like the use of IsProcessorFeaturePresent was considered a suitable temporary workaround until runtime ISA detection was added to vcruntime. @StephanTLavavej are you happy with this being the "final-form"?

[jaykang10]

IsProcessorFeaturePresent

IsProcessorFeaturePresent is supported by the Windows OS. As you know, SVE requires OS support because its stack manipulation differs from NEON, even if the CPU itself supports the feature. From my perspective, using IsProcessorFeaturePresent would be safer.

[AlexGuteniev]

I'm wondering why crypto stuff (FEAT_SHA3, FEAT_SVE_SHA3, FEAT_SVE_AES) would be needed.
The algorithms are general purpose the STL currently doesn't provide any crypto features, as far as I know (it has random and hash, but both are general purpose, not crypto purpose).
Do crypo features include some general purpose instructions?

[hazzlim]

I believe that this list comes from the set of features proposed by my team to add to the vcruntime (not necessarily only for use by the STL). We were advised that there would be quite a high latency between this being added and being available for use, so we were keen to cover a range of features.

I don't think the crypto features are going to be used in the STL.

[StephanTLavavej]

@StephanTLavavej are you happy with this being the "final-form"?

If you're happy with the perf then I think this is perfectly maintainable, thanks.

[AlexGuteniev]

I would like __isa_available from VSRuntime solution more, as it will allow testing with features disabled

[StephanTLavavej]

When creating a new PR, please ensure that your main is up to date, and that your feature branch is properly synced. (Ideally, clean commits rebased on top of main.) Your branch was relative to main as of 2025-10-10 which was pretty old for such a fast-moving file as vector_algorithms.cpp. In this case it made no difference, just something to remember for the future!

[StephanTLavavej]

As mentioned in the discussion, the cryptography stuff is going to be unused by the STL, but I am fine with merging all of this for now, then we can garbage-collect the unused functions when we have the full suite of STL vectorized algorithms for ARM64 completed. These are helpers in an unnamed namespace, so they can be removed without fear of breaking the import lib's compatibility.

[StephanTLavavej]

I would like __isa_available from VSRuntime solution more, as it will allow testing with features disabled

It should be possible to add a "Vulcan nerve pinch" function, present in the import lib only when building the STL's tests, that allows us to simulate the features being disabled. (We had a worse version of this for ConcRT ages ago, that one was bad because it was exposed to users.) This can be retrofitted in the future.

[hazzlim]

Nit: imperative present tense for commit message + slight typo fix:

- Added Arm64 feature detections in STL
+ Add Arm64 feature detection in STL

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo. Please notify me if any further changes are pushed, otherwise no action is required.

[StephanTLavavej]

Thanks for adding this feature detection and congratulations on your first microsoft/STL commit! 🦾 6️⃣ 4️⃣