JIT: Fix mask AND with zero incorrectly folded

[Copilot]

Description

AND between a mask and constant zero was incorrectly folded to return the mask value instead of zero in the JIT's gtFoldExprHWIntrinsic.

// Expected: <0, 0, 0, ...>  Actual (buggy): <-1, -1, -1, ...>
Vector512.Equals(v, v) & Vector512.LessThan(v.AsUInt32(), Vector512<uint>.Zero).AsInt32();

Changes

• src/coreclr/jit/gentree.cpp: For mask types in GT_AND case, changed resultNode = otherNode to resultNode = gtWrapWithSideEffects(cnsNode, otherNode, GTF_ALL_EFFECT) — matching the non-mask vector case
• src/tests/JIT/Regression/JitBlue/Runtime_123399/: Added regression test (requires AVX-512)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>JIT: Mask AND with zero incorrectly folded</issue_title>
<issue_description>### Description

AND between a mask and a constant zero is incorrectly folded to the mask value in net10.0.

https://github.com/dotnet/runtime/blob/2075e8ffaa8cf598dac9c09f5f690778ef1a6c8e/src/coreclr/jit/gentree.cpp#L32988-L32992

Reproduction Steps

using System.Runtime.CompilerServices;
using System.Runtime.Intrinsics;

Console.WriteLine(AndMaskZero(Vector512<int>.One));

[MethodImpl(MethodImplOptions.NoInlining)]
static Vector512<int> AndMaskZero(Vector512<int> v) =>
	Vector512.Equals(v, v) & Vector512.LessThan(v.AsUInt32(), Vector512<uint>.Zero).AsInt32();

Expected behavior

> dotnet run -c release -f net9.0

<0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>

Actual behavior

> dotnet run -c release -f net10.0

<-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1>

Regression?

Yes, worked in 9.0

Configuration

Requires AVX-512

</issue_description>

<agent_instructions>Fix the bug in jit (see comments in the issue) + add a regression test (JitBlue)</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@JulieLeeMSFT Thanks, @saucecontrol, for the report. @anthonycanino, can your team please take a look? CC @kg.

• Fixes JIT: Mask AND with zero incorrectly folded #123399

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[EgorBo]

PTAL @dotnet/jit-contrib trivial bug-fix for x & 0 -> 0 (SIMD), found & suggested by @saucecontrol

No diffs

[Copilot]

Pull request overview

This PR fixes a JIT optimization bug where AND operations between mask types and zero were incorrectly folded to return the mask value instead of zero. The issue occurred in gtFoldExprHWIntrinsic and has been regression since .NET 9.0. The fix makes mask type handling consistent with vector type handling for the same operation.

Changes:

• Fixed incorrect constant folding for mask AND operations with zero
• Added regression test to prevent future occurrences

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/coreclr/jit/gentree.cpp	Fixed GT_AND case for mask types to use gtWrapWithSideEffects when ANDing with zero, making it consistent with vector type handling
src/tests/JIT/Regression/JitBlue/Runtime_123399/Runtime_123399.cs	Added AVX512-gated regression test that verifies AND between an all-ones mask and a zero mask returns zero
src/tests/JIT/Regression/Regression_ro_1.csproj	Added new test file to the project

[EgorBo]

/ba-g deadletter