[fix] skip value is zero in end_tx (privacy-scaling-explorations#1600)

Author: lightsing

bus-mapping/src/circuit_input_builder/input_state_ref.rs

@@ -611,6 +611,43 @@ impl<'a> CircuitInputStateRef<'a> {
         )
     }
 
+    /// Transfer to an address irreversibly.
+    pub fn transfer_to_irreversible(
+        &mut self,
+        step: &mut ExecStep,
+        receiver: Address,
+        receiver_exists: bool,
+        must_create: bool,
+        value: Word,
+    ) -> Result<(), Error> {
+        // If receiver doesn't exist, create it
+        if (!receiver_exists && !value.is_zero()) || must_create {
+            self.account_write(
+                step,
+                receiver,
+                AccountField::CodeHash,
+                CodeDB::empty_code_hash().to_word(),
+                Word::zero(),
+            )?;
+        }
+        if value.is_zero() {
+            // Skip transfer if value == 0
+            return Ok(());
+        }
+        let (_found, receiver_account) = self.sdb.get_account(&receiver);
+        let receiver_balance_prev = receiver_account.balance;
+        let receiver_balance = receiver_account.balance + value;
+        self.account_write(
+            step,
+            receiver,
+            AccountField::Balance,
+            receiver_balance,
+            receiver_balance_prev,
+        )?;
+
+        Ok(())
+    }
+
     /// Fetch and return code for the given code hash from the code DB.
     pub fn code(&self, code_hash: H256) -> Result<Vec<u8>, Error> {
         self.code_db

bus-mapping/src/evm/opcodes/begin_end_tx.rs

@@ -277,10 +277,8 @@ fn gen_end_tx_steps(state: &mut CircuitInputStateRef) -> Result<ExecStep, Error>
     if !found {
         return Err(Error::AccountNotFound(state.block.coinbase));
     }
-    let coinbase_account = coinbase_account.clone();
-    let coinbase_balance_prev = coinbase_account.balance;
+    let coinbase_exist = !coinbase_account.is_empty();
     let coinbase_transfer_value = effective_tip * (state.tx.gas() - exec_step.gas_left);
-    let coinbase_balance = coinbase_balance_prev + coinbase_transfer_value;
     state.account_read(
         &mut exec_step,
         state.block.coinbase,
@@ -291,21 +289,12 @@ fn gen_end_tx_steps(state: &mut CircuitInputStateRef) -> Result<ExecStep, Error>
             coinbase_account.code_hash.to_word()
         },
     );
-    if coinbase_account.is_empty() {
-        state.account_write(
-            &mut exec_step,
-            state.block.coinbase,
-            AccountField::CodeHash,
-            CodeDB::empty_code_hash().to_word(),
-            Word::zero(),
-        )?;
-    }
-    state.account_write(
+    state.transfer_to_irreversible(
         &mut exec_step,
         state.block.coinbase,
-        AccountField::Balance,
-        coinbase_balance,
-        coinbase_balance_prev,
+        coinbase_exist,
+        false,
+        coinbase_transfer_value,
     )?;
 
     // handle tx receipt tag