Use an explicit allow list for SIMD types in getTypeLayout

[tannergooding]

Follow-up to #131345 (comment).

The intrinsic check in getTypeLayout was a deny form: every [Intrinsic] type in System.Numerics and System.Runtime.Intrinsics was reported to the JIT as an opaque SIMD node, with the decimal floating-point types carved back out via IsDecimalFloatingPointOrHasDecimalFloatingPointFields. That only held while every intrinsic type in those namespaces happened to be SIMD, so each new non-SIMD intrinsic type needs another carve-out.

This names the SIMD types explicitly instead, via a new IsSimdIntrinsicType helper on both the native VM and the managed (crossgen2 / ILCompiler) side, mirroring the set recognized by Compiler::getBaseTypeAndSizeOfSIMDType:

• System.Runtime.Intrinsics: Vector64<T>, Vector128<T>, Vector256<T>, Vector512<T>
• System.Numerics: Vector<T>, Vector2, Vector3, Vector4, Plane, Quaternion

The managed helper reuses the existing VectorFieldLayoutAlgorithm.IsVectorType and VectorOfTFieldLayoutAlgorithm.IsVectorOfTType rather than duplicating those name checks. IsDecimalFloatingPointOrHasDecimalFloatingPointFields is untouched -- it's still used for the by-value marshal restriction in dllimport.cpp, mlinfo.cpp, classlayoutinfo.cpp, and MarshalHelpers.cs.

---

Matrix3x2/Matrix4x4 fall out of the set as well. They're [Intrinsic] and live in System.Numerics, so the old namespace-only test caught them, but getBaseTypeAndSizeOfSIMDType returns TYP_UNDEF for them, so their simdTypeHnd was never usable. Their fields are now enumerated like any other struct:

• TryPromoteValueClassAsPrimitive rejected a Matrix field before (SIMD lookup fails, then numFields == 0 != 1) and rejects it now (simdTypeHnd == null, then numFields == 6 or 16 != 1), so no promotion can be lost.
• TryPromoteStructVar has a 1 + MAX_NumOfFieldsInPromotableStruct * 2 == 9 node budget; a Matrix4x4 field overflows it into Partial -> return false, the same outcome as before.
• ClassLayout::GetNonPadding treats a simdTypeHnd node as entirely non-padding. Matrices have no padding, and SegmentList::Add merges the adjacent per-field segments, so the resulting map is identical.
• For R2R, Matrix types no longer hit the NeedsTypeLayoutCheck -> Failure bail and take the ordinary field-enumeration path. Their fields are primitive floats, which CheckTypeLayout handles; the getClassSize fixup concern applies only to types reported via simdTypeHnd.

---

No JIT-EE GUID bump -- the interface signature and CORINFO_TYPE_LAYOUT_NODE are unchanged.

Deliberately out of scope: MethodTable::ClassifyEightBytes* and SystemVStructClassificator also do intrinsic-type name checks, but against a deliberately smaller set (only Vector64/128/256/512<T> and Vector<T> -- Vector2/3/4, Plane, and Quaternion are passed in registers), so they can't share this helper.

Validation

SuperPMI can't cover this -- it replays recorded getTypeLayout responses, so a VM-side change is invisible to asmdiffs. Validated with a real build instead:

• build.cmd clr -rc checked -- 0 warnings, 0 errors. Both ILCompiler.RyuJit and ILCompiler.ReadyToRun relink, so both #if READYTORUN arms compile.
• A/B JitDump over wrapper structs for all 15 affected types (10 SIMD + Matrix3x2/Matrix4x4 + Decimal32/64/128), before vs. after, address-normalized: 0 differing lines out of 83,382. This confirms empirically that the Matrix delta is inert, including the Matrix3x2 case that fits within the node budget.
• JIT/SIMD: 116/116 passed. JIT/Directed/StructPromote + JIT/Directed/physicalpromotion: 9/9 passed.

Note

This PR description and the accompanying code changes were drafted with GitHub Copilot.

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[Copilot]

Pull request overview

This PR tightens getTypeLayout’s SIMD “primitive” detection by replacing a broad namespace-based intrinsic check with an explicit allow list of SIMD types, ensuring non-SIMD [Intrinsic] types in System.Numerics / System.Runtime.Intrinsics have their fields enumerated and reported to the JIT.

Changes:

• Add a VM-side IsSimdIntrinsicType(MethodTable*) helper and use it to decide when to set simdTypeHnd in CEEInfo::GetTypeLayoutHelper.
• Add a managed (crossgen2/ILCompiler) IsSimdIntrinsicType(MetadataType) helper and use it for the analogous GetTypeLayoutHelper logic.
• Remove the previous “deny-form” namespace-only SIMD detection (and associated decimal carve-out) from both implementations.

Show a summary per file

File	Description
src/coreclr/vm/jitinterface.cpp	Introduces an explicit SIMD allow list helper and uses it to drive simdTypeHnd in getTypeLayout.
src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs	Mirrors the VM behavior for AOT/tooling by introducing the same allow-list concept using existing vector type helpers.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0

[tannergooding]

CC. @MichalStrehovsky, this does the explicit filtering to avoid any potential future issues, only skipping for the types we definitely know are safe (because they map to TYP_SIMD*)