ILLink Analyzer: Don't assume Tuple operations compile to creation of a ValueTuple

[jtschuster]

The trim analyzer assumed that all ITupleOperations lowered to a creation of a ValueTuple, and deconstruction would be a reference to the ItemN field. This isn't always true. Instead, don't make any assumptions and avoid warning by creating TopValue for elements of an ITupleOperaion.

We track all flow captures that have any ITupleOperations in order to resolve which IFlowCaptureReferenceOperations resolve to a Tuple, then for direct ITupleOperations we construct a (potentially nested) tuple of TopValues.

Fixes #133911

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[Copilot]

Copilot review overview

🟡 Changes recommended

Direct tuple operations currently discard computed element values, causing data-flow regressions and masked warnings.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 1

Open (1)

• Preserve direct tuple element values in dataflow analysis · New

What changed in this PR

Updates ILLink tuple data-flow analysis to avoid assuming tuple expressions lower to ValueTuple operations.

Changes:

• Tracks tuple-producing flow captures.
• Uses conservative values for ambiguous lowering paths.
• Adds and updates deconstruction regression tests.

File	Summary
src/​tools/​illink/​test/​Mono.Linker.Tests.Cases/​DataFlow/​DeconstructFieldTarget.cs	Updates expected warning behavior for deconstruction scenarios.
src/​tools/​illink/​test/​Mono.Linker.Tests.Cases/​DataFlow/​ConstructedTypesDataFlow.cs	Adds tuple and deconstruction data-flow regression coverage.
src/​tools/​illink/​src/​ILLink.RoslynAnalyzer/​DataFlow/​LocalDataFlowVisitor.cs	Adjusts tuple operation and flow-capture modeling.

[agocke]

This doesn't look right. I think we want to break down the lattice state into top/scalar/multi-value (tuple). Something like

  public enum LocalValueKind
    {
        Top,
        Scalar,
        Tuple
    }

    public readonly struct LocalValue<TValue> : IEquatable<LocalValue<TValue>>, IDeepCopyValue<LocalValue<TValue>>
        where TValue : IEquatable<TValue>
    {
        public LocalValueKind Kind { get; }

        public bool HasValue => Kind is not LocalValueKind.Top;

        public bool IsTuple => Kind is LocalValueKind.Tuple;

        public TValue Value { get; }

        public ImmutableArray<LocalValue<TValue>> Elements { get; }

        public LocalValue(TValue value)
        {
            Kind = LocalValueKind.Scalar;
            Value = value;
            Elements = default;
        }

        public LocalValue(ImmutableArray<LocalValue<TValue>> elements)
        {
            Kind = LocalValueKind.Tuple;
            Value = default!;
            Elements = elements;
        }
    }

And then instead of

 public struct LocalState<TValue> : IEquatable<LocalState<TValue>>
        where TValue : IEquatable<TValue>
    {
        public DefaultValueDictionary<LocalKey, TValue> Dictionary;

we swap out TValue with LocalValue<TValue>?

[Copilot]

Copilot review overview

🟡 Changes recommended

Tuple flow captures may lose element-level dataflow and suppress required warnings.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 1

Open (1)

• Preserve element-level DAM information for tuple-producing flows · New

Resolved since last review (1)

• Preserve direct tuple element values in dataflow analysis