Fix SIMD primitive zero initialization

[tannergooding]

TryPrimitiveInit created a SIMD zero node when converting a zero block initialization into a primitive local store, but the rationalized store retained its original integer-zero data node. This produced a SIMD store with an integer source, leading to invalid codegen and Tier0 compilation failures.

The missing source replacement was introduced by the assignment rationalization changes in #85585 (53b4cd0912d), where the legacy GT_ASG path updated gtOp2 but the rationalized store path did not update Data().

Before the fix, the Vector256 case encoded C4 E1 FD 6E C0 (vmovq with VEX.L=1). The corrected tree emits a SIMD zero (vxorps) in both FullOpts and Tier0. Regression coverage includes Vector128 and Vector256 in both modes.

Fixes #133085

Note

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Copilot review overview

🟢 Approval recommended

The fix is a minimal, localized correctness change (updating the store operand to match the new SIMD zero node) with targeted regression coverage added.

Review tier: Lite
Findings: None

What changed in this PR

This PR fixes a CoreCLR JIT morphing bug where TryPrimitiveInit could retarget an init-block into a SIMD-typed store but leave the store’s Data() operand pointing at the original integer zero constant, producing an invalid SIMD store source and causing Tier0/FullOpts failures. The change updates the rationalized store node to use the newly created SIMD zero constant and adds a JIT regression test covering Vector128 and Vector256 under both Tier0 and FullOpts behavior.

Changes:

• Fix MorphInitBlockHelper::TryPrimitiveInit to replace the store’s Data() operand when creating a SIMD zero source.
• Mark the newly created SIMD zero node as morphed to match surrounding morph-phase conventions.
• Add a JitBlue regression test project validating Vector128<ulong> and Vector256<ulong> zero-init through Unsafe.As<,>() under tiered compilation.

File	Description
src/​coreclr/​jit/​morphblock.cpp	Updates primitive-init morphing to keep store Data() consistent with a newly created SIMD zero node.
src/​tests/​JIT/​Regression/​JitBlue/​Runtime_133085/​Runtime_133085.csproj	Adds a new isolated JIT regression test project with tiered compilation enabled.
src/​tests/​JIT/​Regression/​JitBlue/​Runtime_133085/​Runtime_133085.cs	Adds regression coverage for SIMD local zero-init via initobj-equivalent patterns for Vector128/256.

[tannergooding]

CC. @EgorBo, @jakobbotsch for review. This will need backport to .NET 11 and 10

Fairly old issue and it likely hasn't been hit before due to the exact pattern required to trigger it being a bit unlikely.