Merge pull request #6814 from ethereum/yul-delete-operation

[Sol -> Yul] Implement delete for function pointers

test/libsolidity/semanticTests/viaYul/comparison_functions.sol

@@ -0,0 +1,29 @@
+contract C {
+	function internal1() internal pure returns (bool) {
+		return true;
+	}
+	function internal2() internal pure returns (bool) {
+		return true;
+	}
+
+	function equal() public pure returns (bool same, bool diff, bool inv) {
+		function() internal pure returns (bool) invalid;
+		delete invalid;
+		same = internal1 == internal1;
+		diff = internal1 == internal2;
+		inv  = internal1 == invalid;
+	}
+
+	function unequal() public pure returns (bool same, bool diff, bool inv) {
+		function() internal pure returns (bool) invalid;
+		delete invalid;
+		same = internal1 != internal1;
+		diff = internal1 != internal2;
+		inv  = internal1 != invalid;
+	}
+}
+// ====
+// compileViaYul: true
+// ----
+// equal() -> true, false, false
+// unequal() -> false, true, true

test/libsolidity/semanticTests/viaYul/delete.sol

@@ -0,0 +1,29 @@
+contract C {
+	function internal_func() internal pure returns (int8)
+	{
+		return 1;
+	}
+	function call_internal_func() public pure returns (bool ret)
+	{
+		function() internal pure returns(int8) func = internal_func;
+
+		return func() == internal_func();
+	}
+	function call_deleted_internal_func() public pure returns (bool ret)
+	{
+		function() internal pure returns(int8) func = internal_func;
+
+		delete func;
+
+		return func() == internal_func();
+	}
+	function external_func() external pure returns (int8)
+	{
+		return 1;
+	}
+}
+// ====
+// compileViaYul: true
+// ----
+// call_deleted_internal_func() -> FAILURE
+// call_internal_func() -> true