Process also exception filters when marking unreachable blocks

Fixes dotnet/linker#1507


Commit migrated from dotnet/linker@337f0c5

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

@@ -591,6 +591,8 @@ BitArray GetReachableInstructionsMap (out List<ExceptionHandler> unreachableHand
 								condBranches = new Stack<int> ();
 
 							condBranches.Push (GetInstructionIndex (handler.HandlerStart));
+							if (handler.FilterStart != null)
+								condBranches.Push (GetInstructionIndex (handler.FilterStart));
 						}
 
 						if (condBranches?.Count > 0) {

src/tools/illink/test/Mono.Linker.Tests.Cases/UnreachableBlock/TryFilterBlocks.cs

@@ -0,0 +1,101 @@
+using Mono.Linker.Tests.Cases.Expectations.Assertions;
+using Mono.Linker.Tests.Cases.Expectations.Metadata;
+
+namespace Mono.Linker.Tests.Cases.UnreachableBlock
+{
+	[SetupCSharpCompilerToUse ("csc")]
+	[SetupCompileArgument ("/optimize+")]
+	[SetupLinkerArgument ("--enable-opt", "ipconstprop")]
+	public class TryFilterBlocks
+	{
+		public static void Main ()
+		{
+			TestUnreachableInsideTry ();
+			TestUnreachableInsideFilterCondition ();
+		}
+
+		[Kept]
+		[ExpectedInstructionSequence (new[] {
+			"call",
+			"brfalse.s",
+			"call",
+			"leave.s",
+			"pop",
+			"call",
+			"ldc.i4.0",
+			"cgt.un",
+			"endfilter",
+			"pop",
+			"leave.s",
+			"ldc.i4.2",
+			"ret"
+		})]
+		[ExpectedExceptionHandlerSequence (new string[] { "filter" })]
+		static int TestUnreachableInsideTry ()
+		{
+			try {
+				if (Prop)
+					Unreached_1 ();
+
+				Reached_1 ();
+			} catch when (Log ()) {
+			}
+
+			return 2;
+		}
+
+		[Kept]
+		[ExpectedInstructionSequence (new[] {
+			"call",
+			"leave.s",
+			"pop",
+			"call",
+			"brfalse.s",
+			"ldc.i4.0",
+			"ldc.i4.0",
+			"cgt.un",
+			"endfilter",
+			"pop",
+			"leave.s",
+			"ldc.i4.3",
+			"ret"
+		})]
+		[ExpectedExceptionHandlerSequence (new string[] { "filter" })]
+		static int TestUnreachableInsideFilterCondition ()
+		{
+			try {
+				Reached_2 ();
+			} catch when (Log () && Unreached_2 ()) {
+			}
+
+			return 3;
+		}
+
+		[Kept]
+		static bool Prop {
+			[Kept]
+			get {
+				return false;
+			}
+		}
+
+		[Kept]
+		static bool Log () => false;
+
+		[Kept]
+		static void Reached_1 ()
+		{
+		}
+
+		[Kept]
+		static void Reached_2 ()
+		{
+		}
+
+		static void Unreached_1 ()
+		{
+		}
+
+		static bool Unreached_2 () => true;
+	}
+}