#2050: Add assertion to check that no transform uses StObj.TargetSlot incorrectly.

Author: dgrunwald

ICSharpCode.Decompiler/IL/Instructions.cs

@@ -4117,6 +4117,7 @@ internal override void CheckInvariant(ILPhase phase)
 			base.CheckInvariant(phase);
 			Debug.Assert(target.ResultType == StackType.Ref || target.ResultType == StackType.I);
 			Debug.Assert(value.ResultType == type.GetStackType());
+			CheckTargetSlot();
 		}
 	}
 }

ICSharpCode.Decompiler/IL/Instructions.tt

@@ -253,7 +253,8 @@
 		new OpCode("stobj", "Indirect store (store to ref/pointer)." + Environment.NewLine
 				+ "Evaluates to the value that was stored (when using type byte/short: evaluates to the truncated value, sign/zero extended back to I4 based on type.GetSign())",
 			CustomClassName("StObj"), CustomArguments(("target", new[] { "Ref", "I" }), ("value", new[] { "type.GetStackType()" })), HasTypeOperand, MemoryAccess, CustomWriteToButKeepOriginal,
-			SupportsVolatilePrefix, SupportsUnalignedPrefix, MayThrow, ResultType("type.GetStackType()")),
+			SupportsVolatilePrefix, SupportsUnalignedPrefix, MayThrow, ResultType("type.GetStackType()"),
+			CustomInvariant("CheckTargetSlot();")),
 
 		new OpCode("box", "Boxes a value.",
 			Unary, HasTypeOperand, MemoryAccess, MayThrow, ResultType("O")),

ICSharpCode.Decompiler/IL/Instructions/LdFlda.cs

@@ -68,5 +68,20 @@ public bool CanInlineIntoTargetSlot(ILInstruction inst)
 					return true;
 			}
 		}
+
+		/// <summary>
+		/// called as part of CheckInvariant()
+		/// </summary>
+		void CheckTargetSlot()
+		{
+			switch (this.Target.OpCode) {
+				case OpCode.LdElema:
+				case OpCode.LdFlda:
+					if (this.Target.HasDirectFlag(InstructionFlags.MayThrow)) {
+						Debug.Assert(SemanticHelper.IsPure(this.Value.Flags));
+					}
+					break;
+			}
+		}
 	}
 }