Fix il corruption (#2966)

This prevents invalid IL in situations where removing the last
instruction of a method would result in the last instruction
being a conditional branch. There needs to be some IL in the
not-taken branch for the IL to be valid, so this fixes the issue
by injecting "ldnull; throw" at the end.

Co-authored-by: vitek-karas <10670590+vitek-karas@users.noreply.github.com>
Co-authored-by: Adam Sitnik <adam.sitnik@gmail.com>

1 files changed, 32 insertions, 1 deletions

diff --git a/test/Mono.Linker.Tests.Cases/UnreachableBlock/ReplacedJumpTarget.cs b/test/Mono.Linker.Tests.Cases/UnreachableBlock/ReplacedJumpTarget.cs
index 5c7ee375f..90d9a3e7e 100644
--- a/test/Mono.Linker.Tests.Cases/UnreachableBlock/ReplacedJumpTarget.cs
+++ b/test/Mono.Linker.Tests.Cases/UnreachableBlock/ReplacedJumpTarget.cs
@@ -1,5 +1,4 @@
 using System;
-using System.Reflection.Emit;
 using Mono.Linker.Tests.Cases.Expectations.Assertions;
 using Mono.Linker.Tests.Cases.Expectations.Metadata;
 
@@ -12,6 +11,7 @@ namespace Mono.Linker.Tests.Cases.UnreachableBlock
 		public static void Main ()
 		{
 			Test_1 (int.Parse ("91"));
+			TestRemovedLastBranch (int.Parse ("92"));
 		}
 
 		[Kept]
@@ -73,5 +73,36 @@ namespace Mono.Linker.Tests.Cases.UnreachableBlock
 		}
 
 		static int Value => 2;
+
+		[Kept]
+		[ExpectedInstructionSequence (new[] {
+			"br.s il_3",
+			"ret",
+			"ldc.i4.1",
+			"brtrue.s il_2",
+			"ldnull",
+			"throw"
+			})]
+		static void TestRemovedLastBranch (int param)
+		{
+			goto DoWork;
+
+		ReturnFromMethod:
+			return;
+
+		DoWork:
+			if (AlwaysTrue) {
+				goto ReturnFromMethod;
+			} else { // This branch will be removed
+				DoSomething ();
+				goto ReturnFromMethod;
+			}
+		}
+
+		static void DoSomething ()
+		{
+		}
+
+		static bool AlwaysTrue => true;
 	}
 }
\ No newline at end of file