Fix UnreachableBody with only ref to assembly.

src/tools/illink/src/linker/Linker.Steps/MarkStep.cs

@@ -3167,7 +3167,7 @@ void MarkMethodCollection(IList<MethodDefinition> methods, in DependencyInfo rea
             var methodAction = Annotations.GetAction(method);
             if (methodAction is MethodAction.ConvertToStub)
             {
-                // CodeRewriterStep runs after sweeping, and may request the stubbed value for any preserved method
+                // CodeRewriterStep may request the stubbed value for any preserved method
                 // with the action ConvertToStub. Ensure we have precomputed any stub value that may be needed by
                 // CodeRewriterStep. This ensures sweeping doesn't change the stub value (which can be determined by
                 // FeatureGuardAttribute or FeatureSwitchDefinitionAttribute that might have been removed).

src/tools/illink/src/linker/Linker/Driver.cs

@@ -1620,9 +1620,9 @@ static Pipeline GetStandardPipeline()
             p.AppendStep(new ValidateVirtualMethodAnnotationsStep());
             p.AppendStep(new ProcessWarningsStep());
             p.AppendStep(new OutputWarningSuppressions());
+            p.AppendStep(new CodeRewriterStep());
             p.AppendStep(new SweepStep());
             p.AppendStep(new CheckSuppressionsDispatcher());
-            p.AppendStep(new CodeRewriterStep());
             p.AppendStep(new CleanStep());
             p.AppendStep(new RegenerateGuidStep());
             p.AppendStep(new OutputStep());

src/tools/illink/test/ILLink.RoslynAnalyzer.Tests/generated/ILLink.RoslynAnalyzer.Tests.Generator/ILLink.RoslynAnalyzer.Tests.TestCaseGenerator/UnreachableBodyTests.g.cs

@@ -117,6 +117,12 @@ public Task NotWorthConvertingReturnTrue()
             return RunTest(allowMissingWarnings: true);
         }
 
+        [Fact]
+        public Task OnlyReferenceInUnreachableBody()
+        {
+            return RunTest(allowMissingWarnings: true);
+        }
+
         [Fact]
         public Task OverrideOfAbstractAndInterfaceMethodCalledFromLocal()
         {

src/tools/illink/test/Mono.Linker.Tests.Cases/UnreachableBody/Dependencies/OtherAssembly2.cs

@@ -0,0 +1,9 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Mono.Linker.Tests.Cases.UnreachableBody.Dependencies;
+
+public class OtherAssembly2
+{
+    public static int Field;
+}

src/tools/illink/test/Mono.Linker.Tests.Cases/UnreachableBody/OnlyReferenceInUnreachableBody.cs

@@ -0,0 +1,42 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Mono.Linker.Tests.Cases.Expectations.Assertions;
+using Mono.Linker.Tests.Cases.Expectations.Metadata;
+using Mono.Linker.Tests.Cases.UnreachableBody.Dependencies;
+
+namespace Mono.Linker.Tests.Cases.UnreachableBody;
+
+/// <summary>
+/// This test was added to fix an issue with how SweepStep.SweepAssemblyReferences and CodeRewriterStep interact.
+/// CodeRewriterStep must run before SweepStep to ensure that SweepStep.SweepAssemblyReferences doesn't see TypeReferences in method bodies that
+/// are going to be removed by CodeRewriterStep.
+/// </summary>
+[SetupCompileBefore("other.dll", new[] { typeof(OtherAssembly2) })]
+[RemovedAssemblyReference("test", "other")]
+[RemovedAssembly("other.dll")]
+[SetupLinkerArgument("--enable-opt", "unreachablebodies")]
+public class OnlyReferenceInUnreachableBody
+{
+    public static void Main()
+    {
+        UsedToMarkMethod(null);
+    }
+
+    [Kept]
+    static void UsedToMarkMethod(Foo f)
+    {
+        f.Method();
+    }
+
+    [Kept]
+    class Foo
+    {
+        [Kept]
+        [ExpectBodyModified]
+        public void Method()
+        {
+            OtherAssembly2.Field = 1;
+        }
+    }
+}