EIP-3529 Reduction in Refunds (#2020)

* EIP-3529 Implementation:
- Replace SSTORE_CLEARS_SCHEDULE,
- Remove SELFDESTRUCT refund,
- Add new MAX_REFUND_QUOTIENT

* Add newsfragment

Author: kclowes

eth/vm/forks/frontier/state.py

@@ -142,21 +142,28 @@ def build_computation(self,
 
         return computation
 
-    def finalize_computation(self,
-                             transaction: SignedTransactionAPI,
-                             computation: ComputationAPI) -> ComputationAPI:
-        transaction_context = self.vm_state.get_transaction_context(transaction)
-
+    @classmethod
+    def calculate_gas_refund(cls,
+                             computation: ComputationAPI,
+                             gas_used: int) -> int:
         # Self Destruct Refunds
         num_deletions = len(computation.get_accounts_for_deletion())
         if num_deletions:
             computation.refund_gas(REFUND_SELFDESTRUCT * num_deletions)
 
         # Gas Refunds
-        gas_remaining = computation.get_gas_remaining()
         gas_refunded = computation.get_gas_refund()
+
+        return min(gas_refunded, gas_used // 2)
+
+    def finalize_computation(self,
+                             transaction: SignedTransactionAPI,
+                             computation: ComputationAPI) -> ComputationAPI:
+        transaction_context = self.vm_state.get_transaction_context(transaction)
+
+        gas_remaining = computation.get_gas_remaining()
         gas_used = transaction.gas - gas_remaining
-        gas_refund = min(gas_refunded, gas_used // 2)
+        gas_refund = self.calculate_gas_refund(computation, gas_used)
         gas_refund_amount = (gas_refund + gas_remaining) * transaction_context.gas_price
 
         if gas_refund_amount:

eth/vm/forks/london/constants.py

@@ -13,3 +13,4 @@
 ELASTICITY_MULTIPLIER = 2
 
 EIP3541_RESERVED_STARTING_BYTE = b'\xef'
+EIP3529_MAX_REFUND_QUOTIENT = 5

eth/vm/forks/london/opcodes.py

@@ -19,14 +19,23 @@
 from eth.vm.forks.berlin.opcodes import (
     BERLIN_OPCODES,
 )
+from eth.vm.forks.byzantium.opcodes import (
+    ensure_no_static,
+)
 
+from . import storage
 
 UPDATED_OPCODES: Dict[int, Opcode] = {
     opcode_values.BASEFEE: as_opcode(
         gas_cost=constants.GAS_BASE,
         logic_fn=block.basefee,
         mnemonic=mnemonics.BASEFEE,
     ),
+    opcode_values.SSTORE: as_opcode(
+        gas_cost=constants.GAS_NULL,
+        logic_fn=ensure_no_static(storage.sstore_eip3529),
+        mnemonic=mnemonics.SSTORE,
+    ),
 }
 
 

eth/vm/forks/london/state.py

@@ -7,6 +7,7 @@
 
 from eth.abc import (
     AccountDatabaseAPI,
+    ComputationAPI,
     MessageAPI,
     SignedTransactionAPI,
     StateAPI,
@@ -32,6 +33,7 @@
 
 from .computation import LondonComputation
 from .validation import validate_london_normalized_transaction
+from .constants import EIP3529_MAX_REFUND_QUOTIENT
 
 
 class LondonTransactionExecutor(BerlinTransactionExecutor):
@@ -86,6 +88,16 @@ def build_evm_message(self, transaction: SignedTransactionAPI) -> MessageAPI:
         )
         return message
 
+    @classmethod
+    def calculate_gas_refund(cls,
+                             computation: ComputationAPI,
+                             gas_used: int) -> int:
+        # Self destruct refunds were added in Frontier
+        # London removes them in EIP-3529
+        gas_refunded = computation.get_gas_refund()
+
+        return min(gas_refunded, gas_used // EIP3529_MAX_REFUND_QUOTIENT)
+
 
 class LondonState(BerlinState):
     account_db_class: Type[AccountDatabaseAPI] = AccountDB

eth/vm/forks/london/storage.py

@@ -0,0 +1,20 @@
+from eth_utils.toolz import partial
+
+from eth.vm.forks.berlin import constants as berlin_constants
+from eth.vm.forks.berlin.logic import (
+    GAS_SCHEDULE_EIP2929,
+    sstore_eip2929_generic,
+)
+
+
+SSTORE_CLEARS_SCHEDULE_EIP_3529 = (
+    GAS_SCHEDULE_EIP2929.sstore_reset_gas
+    + berlin_constants.ACCESS_LIST_STORAGE_KEY_COST_EIP_2930
+)
+
+
+GAS_SCHEDULE_EIP3529 = GAS_SCHEDULE_EIP2929._replace(
+    sstore_clears_schedule=SSTORE_CLEARS_SCHEDULE_EIP_3529
+)
+
+sstore_eip3529 = partial(sstore_eip2929_generic, GAS_SCHEDULE_EIP3529)

newsfragments/2020.feature.rst

@@ -0,0 +1,4 @@
+Implement EIP-3529:
+- Remove self destruct refunds
+- Change max gas refund from gas_used // 2 -> gas_used // 5
+- Replace sstore_clears_schedule with sstore_reset_gas + access_list_storage_key_cost

tests/core/opcodes/test_opcodes.py

@@ -960,6 +960,130 @@ def test_extcodehash(vm_class, address, expected):
             19200,
             1,
         ),
+        # London reduces refund by changing SSTORE_CLEARS_SCHEDULE
+        # Test cases from: https://eips.ethereum.org/EIPS/eip-3529
+        # Note: test cases assume the storage slot is already warm,
+        # the difference being a one-time cost of 2100 gas.
+        # so gas_used becomes gas_used from EIP-3529 test case + 2100
+        (
+            LondonVM,
+            "0x60006000556000600055",
+            212 + 2100,
+            0,
+            0,
+        ),
+        (
+            LondonVM,
+            "0x60006000556001600055",
+            20112 + 2100,
+            0,
+            0,
+        ),
+        (
+            LondonVM,
+            "0x60016000556000600055",
+            20112 + 2100,
+            19900,
+            0,
+        ),
+        (
+            LondonVM,
+            "0x60016000556002600055",
+            20112 + 2100,
+            0,
+            0,
+        ),
+        (
+            LondonVM,
+            "0x60016000556001600055",
+            20112 + 2100,
+            0,
+            0,
+        ),
+        (
+            LondonVM,
+            "0x60006000556000600055",
+            3012 + 2100,
+            4800,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x60006000556001600055",
+            3012 + 2100,
+            2800,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x60006000556002600055",
+            3012 + 2100,
+            0,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x60026000556000600055",
+            3012 + 2100,
+            4800,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x60026000556003600055",
+            3012 + 2100,
+            0,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x60026000556001600055",
+            3012 + 2100,
+            2800,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x60026000556002600055",
+            3012 + 2100,
+            0,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x60016000556000600055",
+            3012 + 2100,
+            4800,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x60016000556002600055",
+            3012 + 2100,
+            0,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x60016000556001600055",
+            212 + 2100,
+            0,
+            1,
+        ),
+        (
+            LondonVM,
+            "0x600160005560006000556001600055",
+            40118 + 2100,
+            19900,
+            0,
+        ),
+        (
+            LondonVM,
+            "0x600060005560016000556000600055",
+            5918 + 2100,
+            7600,
+            1,
+        ),
     )
 )
 def test_sstore(vm_class, code, gas_used, refund, original):