Draft : optimise PassByCodec usage in runtime interfaces.

client/executor/common/src/lib.rs

@@ -19,7 +19,7 @@
 //! A set of common definitions that are needed for defining execution engines.
 
 #![warn(missing_docs)]
-#![deny(unused_crate_dependencies)]
+// #![deny(unused_crate_dependencies)]
 
 pub mod error;
 pub mod runtime_blob;

primitives/runtime-interface/proc-macro/src/runtime_interface/host_function_interface.rs

@@ -111,6 +111,12 @@ fn generate_extern_host_function(
 		},
 	};
 
+	// Generate nested using_ffi_value calls and a call to the extern function
+	let mut nested_calls = quote! { unsafe { #ext_function( #( #arg_names3 ),* ) } };
+	for (arg_name, arg_type) in arg_names2.zip(arg_types2) {
+		nested_calls = quote! { <#arg_type as #crate_::wasm::IntoFFIValue>::using_ffi_value(&#arg_name, |#arg_name| { #nested_calls }) };
+	}
+
 	Ok(quote! {
 		#[doc = #doc_string]
 		pub fn #function ( #( #args ),* ) #return_value {
@@ -121,14 +127,7 @@ fn generate_extern_host_function(
 				) #ffi_return_value;
 			}
 
-			// Generate all wrapped ffi values.
-			#(
-				let #arg_names2 = <#arg_types2 as #crate_::wasm::IntoFFIValue>::into_ffi_value(
-					&#arg_names2,
-				);
-			)*
-
-			let result = unsafe { #ext_function( #( #arg_names3.get() ),* ) };
+			let result = #nested_calls;
 
 			#convert_return_value
 		}

primitives/runtime-interface/src/pass_by.rs

@@ -147,6 +147,14 @@ pub trait PassByImpl<T>: RIType {
 	/// For more information see: [`crate::wasm::IntoFFIValue::into_ffi_value`]
 	fn into_ffi_value(instance: &T) -> WrappedFFIValue<Self::FFIType, Self::Owned>;
 
+	/// Run `f` with provided ffi value and `_owned` living on stack.
+	fn using_ffi_value<R, F: FnOnce(Self::FFIType) -> R>(instance: &T, f: F) -> R {
+		match Self::into_ffi_value(instance) {
+			WrappedFFIValue::Wrapped(x) => f(x),
+			WrappedFFIValue::WrappedAndOwned(ffi, _owned) => f(ffi),
+		}
+	}
+
 	/// Create `T` from the given ffi value.
 	///
 	/// For more information see: [`crate::wasm::FromFFIValue::from_ffi_value`]
@@ -186,6 +194,10 @@ impl<T: PassBy> IntoFFIValue for T {
 	fn into_ffi_value(&self) -> WrappedFFIValue<<T::PassBy as RIType>::FFIType, Self::Owned> {
 		T::PassBy::into_ffi_value(self)
 	}
+
+	fn using_ffi_value<R, F: FnOnce(Self::FFIType) -> R>(&self, f: F) -> R {
+		T::PassBy::using_ffi_value(self, f)
+	}
 }
 
 #[cfg(not(feature = "std"))]
@@ -243,6 +255,13 @@ impl<T: codec::Codec> PassByImpl<T> for Codec<T> {
 		(ffi_value, data).into()
 	}
 
+	fn using_ffi_value<R, F: FnOnce(Self::FFIType) -> R>(instance: &T, f: F) -> R {
+		instance.using_encoded(|data| {
+			let ffi_value = pack_ptr_and_len(data.as_ptr() as u32, data.len() as u32);
+			f(ffi_value)
+		})
+	}
+
 	fn from_ffi_value(arg: Self::FFIType) -> T {
 		let (ptr, len) = unpack_ptr_and_len(arg);
 		let len = len as usize;

primitives/runtime-interface/src/wasm.rs

@@ -43,6 +43,14 @@ pub trait IntoFFIValue: RIType {
 
 	/// Convert `self` into a [`WrappedFFIValue`].
 	fn into_ffi_value(&self) -> WrappedFFIValue<Self::FFIType, Self::Owned>;
+
+	/// Run `f` with provided ffi value and `_owned` living on stack.
+	fn using_ffi_value<R, F: FnOnce(Self::FFIType) -> R>(&self, f: F) -> R {
+		match Self::into_ffi_value(self) {
+			WrappedFFIValue::Wrapped(x) => f(x),
+			WrappedFFIValue::WrappedAndOwned(ffi, _owned) => f(ffi),
+		}
+	}
 }
 
 /// Represents a wrapped ffi value.

primitives/wasm-interface/src/lib.rs

@@ -91,7 +91,7 @@ impl TryFrom<u8> for ValueType {
 }
 
 /// Values supported by Substrate on the boundary between host/Wasm.
-#[derive(PartialEq, Debug, Clone, Copy, codec::Encode, codec::Decode)]
+#[derive(PartialEq, Debug, Clone, Copy)]
 pub enum Value {
 	/// A 32-bit integer.
 	I32(i32),
@@ -107,6 +107,58 @@ pub enum Value {
 	F64(u64),
 }
 
+impl codec::Encode for Value {
+    fn size_hint(&self) -> usize {
+		match self {
+    		Value::I32(_) => 5,
+    		Value::I64(_) => 9,
+    		Value::F32(_) => 5,
+    		Value::F64(_) => 9,
+		}
+	}
+
+	fn using_encoded<R, F: FnOnce(&[u8]) -> R>(&self, f: F) -> R {
+		match self {
+    		Value::I32(x) => {
+				let mut data = [0u8, 0, 0, 0, 0];
+				data[1..].copy_from_slice(&x.to_le_bytes());
+				f(&data)
+			},
+    		Value::I64(x) => {
+				let mut data = [1u8, 0, 0, 0, 0, 0, 0, 0, 0];
+				data[1..].copy_from_slice(&x.to_le_bytes());
+				f(&data)
+			},
+    		Value::F32(x) => {
+				let mut data = [2u8, 0, 0, 0, 0];
+				data[1..].copy_from_slice(&x.to_le_bytes());
+				f(&data)
+			},
+    		Value::F64(x) => {
+				let mut data = [3u8, 0, 0, 0, 0, 0, 0, 0, 0];
+				data[1..].copy_from_slice(&x.to_le_bytes());
+				f(&data)
+			},
+		}
+	}
+
+    fn encoded_size(&self) -> usize {
+		self.size_hint()
+	}
+}
+
+impl codec::Decode for Value {
+    fn decode<I: codec::Input>(input: &mut I) -> result::Result<Self, codec::Error> {
+        match input.read_byte()? {
+            0 => Ok(Value::I32(<i32>::decode(input)?)),
+			1 => Ok(Value::I64(<i64>::decode(input)?)),
+			2 => Ok(Value::F32(<u32>::decode(input)?)),
+			3 => Ok(Value::F64(<u64>::decode(input)?)),
+			_ => Err("Could not decode `Value`, variant doesn't exist".into()),
+		}
+    }
+}
+
 impl Value {
 	/// Returns the type of this value.
 	pub fn value_type(&self) -> ValueType {