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[release/11.0] Fix SIMD MinMax constant special cases - #133256
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tannergooding wants to merge 1 commit into
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[release/11.0] Fix SIMD MinMax constant special cases#133256tannergooding wants to merge 1 commit into
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SIMD Min/Max constant handling used whole-vector checks for NaN and signed zero when deciding whether native xarch Min/Max needed compensation. Constants containing a mix of ordinary and special lanes could therefore lose the managed NaN or signed-zero semantics. This evaluates the predicates through reusable SIMD mask helpers matching `IsNaN`/`IsNegative` and `AnyWhereAllBitsSet`/`AllWhereAllBitsSet`, then uses any-lane checks for fast-path eligibility. Fixesdotnet#133022 > [!NOTE] > This pull request was created with GitHub Copilot. --------- Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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Copilot review overview
🔵 Needs a closer look
It changes JIT SIMD min/max import-time semantics and fixup generation in a way that can have broad codegen impact across xarch, warranting final human validation for the backport.
Review tier: Lite
Findings: None
What changed in this PR
Backport that fixes xarch SIMD Min/Max/MinNumber/MaxNumber constant-vector special-case handling for mixed-lane NaN and signed-zero semantics by switching from whole-vector checks to per-lane mask evaluation, and adds regression coverage.
Changes:
- Update JIT SIMD constant evaluation helpers to support per-lane mask/predicate evaluation over the active SIMD size.
- Refine xarch SIMD min/max import-time constant classification, operand ordering, and AVX-512 fixup-table construction to correctly handle mixed NaN / signed-zero lanes.
- Add a focused JIT regression test and expand generic-math test data to cover NaN payload + signed-zero interactions.
| File | Description |
|---|---|
| src/coreclr/jit/simd.h | Adds SIMD-size-aware evaluation helpers and predicates used for per-lane special-case detection. |
| src/coreclr/jit/gentree.h | Extends GenTreeVecCon with helpers to detect NaN / ±0 presence in vector constants. |
| src/coreclr/jit/gentree.cpp | Uses new per-lane predicates to drive operand ordering and fixup-table generation for SIMD min/max. |
| src/libraries/Common/tests/System/GenericMathTestMemberData.cs | Adds NaN-payload test inputs and new cases involving NaN and signed zero for min/max variants. |
| src/tests/JIT/Regression/JitBlue/Runtime_133022/Runtime_133022.cs | Adds regression coverage for mixed-lane NaN and signed-zero behavior across vector widths and variants. |
| src/tests/JIT/Regression/Regression_ro_2.csproj | Includes the new regression test in the merged regression project. |
AndyAyersMS
approved these changes
Sep 4, 2026
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Backport of #133173 to release/11.0
/cc @AndyAyersMS
Customer Impact
SIMD
Min,Max,MinNumber, andMaxNumbercan return incorrect results on xarch when a constant vector contains a mix of ordinary values and NaN or signed-zero lanes. The AVX-512 path can incorrectly return the opaque operand wholesale.Regression
The vector mixed-lane regression was introduced by #116804 during .NET 10 development.
Testing
The focused
Runtime_133022regression fails against the pre-fix JIT and passes with the fix. The original change was verified on checked x64 and x86 with AVX-512 enabled and withDOTNET_EnableAVX512=0; all 13,082System.Runtime.Intrinsicstests also passed under both AVX-512 settings.For this backport, the checked x64 JIT build and
jit-formatpassed. The source patch matches the merged change; the test-project conflict was resolved by adding onlyRuntime_133022to the target branch's merged regression project. A fullclr+libsbaseline was attempted but hit unrelated MSVCC1041PDB contention inSystem.Globalization.Native.Risk
Medium. The change is localized to JIT import-time SIMD constant classification and fixup-table construction, but affects shared Min/Max code generation. Mixed NaN and signed-zero cases are covered across
float/double,Vector128/Vector256, operand order, and AVX-512 enabled/disabled configurations.IMPORTANT: If this backport is for a servicing release, please verify that:
release/X.0-staging, notrelease/X.0.release/X.0(no-stagingsuffix).Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.
Note
This pull request description was generated with GitHub Copilot assistance.