Inconsistent warning code for array parameter passed to annotated location in ILLink/analyzer

[sbomer]

static void Method(Type[] interfaces) {
    foreach (Type i in interfaces)
        i.GetMethods(); // warning here. IL2075 for analyzer, IL2065 for ILLink
}

The ILLink Roslyn analyzer produces IL2075 (unannotated method return value flows to 'this' parameter with requirements), because it sees the return value of Current.get used as the receiver for GetMethods.

ILLink produces IL2065 ('this' parameter cannot be statically determined), because when it sees ldelem.ref of the array method parameter, it turns this into an "unknown" value, which has a different warning code.

Fundamentally this is due to the analyzer seeing a different lowering of the foreach loop than illink. Fixing this seems tricky.

Found while investigating #96462. There's an existing testcase similar to this:

runtime/src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/LocalDataFlow.cs

Lines 443 to 453 in 0451127

	[ExpectedWarning ("IL2063", ProducedBy = Tool.Trimmer)] // The types loaded from the array don't have annotations, so the "return" should warn
	[ExpectedWarning ("IL2073", ProducedBy = Tool.Analyzer)] // Analyzer tracks resultType as the value from IEnumerable.Current.get()
	[return: DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.PublicMethods)]
	public static Type TestBackwardEdgeWithLdElem (Type[] types = null)
	{
	Type resultType = null;
	foreach (var type in types) {
	resultType = type;
	}
	return resultType;

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Issue Details

---

static void Method(Type[] interfaces) {
    foreach (Type i in interfaces)
        i.GetMethods(); // warning here. IL2075 for analyzer, IL2065 for ILLink
}

The ILLink Roslyn analyzer produces IL2075 (unannotated method return value flows to 'this' parameter with requirements), because it sees the return value of Current.get used as the receiver for GetMethods.

ILLink produces IL2065 ('this' parameter cannot be statically determined), because when it sees ldelem.ref of the array method parameter, it turns this into an "unknown" value, which has a different warning code.

Fundamentally this is due to the analyzer seeing a different lowering of the foreach loop than illink. Fixing this seems tricky.

Author:	sbomer
Assignees:	-
Labels:	untriaged, area-Tools-ILLink, needs-area-label
Milestone:	-