sign_ext feature flag (#174)

* sign_ext feature flag

* Derive default to fix clippy warning

src/stack_height/max_height.rs

@@ -4,6 +4,9 @@ use super::{resolve_func_type, Error};
 use log::trace;
 use parity_wasm::elements::{self, BlockType, Type};
 
+#[cfg(feature = "sign_ext")]
+use parity_wasm::elements::SignExtInstruction;
+
 /// Control stack frame.
 #[derive(Debug)]
 struct Frame {
@@ -410,6 +413,16 @@ pub(crate) fn compute(func_idx: u32, module: &elements::Module) -> Result<u32, E
 				stack.pop_values(1)?;
 				stack.push_values(1)?;
 			},
+
+			#[cfg(feature = "sign_ext")]
+			SignExt(SignExtInstruction::I32Extend8S) |
+			SignExt(SignExtInstruction::I32Extend16S) |
+			SignExt(SignExtInstruction::I64Extend8S) |
+			SignExt(SignExtInstruction::I64Extend16S) |
+			SignExt(SignExtInstruction::I64Extend32S) => {
+				stack.pop_values(1)?;
+				stack.push_values(1)?;
+			},
 		}
 		pc += 1;
 	}