[release/8.0-staging] Ensure that Sse3.MoveAndDuplicate correctly tracks supporting SIMD scalar loads #100417
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tannergooding
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Tagging subscribers to this area: @dotnet/area-system-runtime-intrinsics |
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CC. @jakobbotsch since you reviewed and signed-off on the original fix. |
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CC. @JulieLeeMSFT, @jakobbotsch This is still pending sign-off for backport so it can goto tactics for approval. |
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Backport of #97783 to release/8.0-staging
/cc @tannergooding
Customer Impact
This was reported by a customer in #100404 and was internally found via #97688, where the containment checks around
Sse3.MoveAndDuplicateweren't sufficient and so we missed an opportunity that another code path (related to the AVX-512 embedded broadcast support) was assuming would be made.Regression
Prior to AVX-512 there was a missed containment opportunity, but this wasn't functionally incorrect, just less efficient. With the introduction of AVX-512 support in .NET 8, a new issue was introduced due to us missing the containment opportunity.
Testing
The fix was verified on the customer provided example in #100404 and a minimal regression test was added that validates the fix. The fix has been in .NET 9 for a couple months now with no additional issues having been found.
Risk
Low: This is a net new scenario in .NET 8 and only impacts customers with AVX-512 capable hardware.