feat(avm): Dynamic gas costs for arithmetic, calldatacopy, and set (#…

…5473)

Computes dynamic gas cost for 3-operand arithmetic instructions,
calldatacopy, and set. Base constants are arbitrary.

yarn-project/simulator/src/avm/avm_gas_cost.test.ts

@@ -0,0 +1,34 @@
+import { TypeTag } from './avm_memory_types.js';
+import { AvmSimulator } from './avm_simulator.js';
+import { initContext } from './fixtures/index.js';
+import { Add, CalldataCopy, Div, Mul, Set as SetInstruction, Sub } from './opcodes/index.js';
+import { encodeToBytecode } from './serialization/bytecode_serialization.js';
+
+describe('AVM simulator: dynamic gas costs per instruction', () => {
+  it.each([
+    [new SetInstruction(/*indirect=*/ 0, /*inTag=*/ TypeTag.UINT8, /*value=*/ 1, /*dstOffset=*/ 0), [100, 0, 0]],
+    [new SetInstruction(/*indirect=*/ 0, /*inTag=*/ TypeTag.UINT32, /*value=*/ 1, /*dstOffset=*/ 0), [400, 0, 0]],
+    [new CalldataCopy(/*indirect=*/ 0, /*cdOffset=*/ TypeTag.UINT8, /*copySize=*/ 1, /*dstOffset=*/ 0), [10, 0, 0]],
+    [new CalldataCopy(/*indirect=*/ 0, /*cdOffset=*/ TypeTag.UINT8, /*copySize=*/ 5, /*dstOffset=*/ 0), [50, 0, 0]],
+    [new Add(/*indirect=*/ 0, /*inTag=*/ TypeTag.UINT8, /*aOffset=*/ 1, /*bOffset=*/ 2, /*dstOffset=*/ 3), [10, 0, 0]],
+    [new Add(/*indirect=*/ 0, /*inTag=*/ TypeTag.UINT32, /*aOffset=*/ 1, /*bOffset=*/ 2, /*dstOffset=*/ 3), [40, 0, 0]],
+    [new Add(/*indirect=*/ 3, /*inTag=*/ TypeTag.UINT8, /*aOffset=*/ 1, /*bOffset=*/ 2, /*dstOffset=*/ 3), [20, 0, 0]],
+    [new Sub(/*indirect=*/ 3, /*inTag=*/ TypeTag.UINT8, /*aOffset=*/ 1, /*bOffset=*/ 2, /*dstOffset=*/ 3), [20, 0, 0]],
+    [new Mul(/*indirect=*/ 3, /*inTag=*/ TypeTag.UINT8, /*aOffset=*/ 1, /*bOffset=*/ 2, /*dstOffset=*/ 3), [20, 0, 0]],
+    [new Div(/*indirect=*/ 3, /*inTag=*/ TypeTag.UINT8, /*aOffset=*/ 1, /*bOffset=*/ 2, /*dstOffset=*/ 3), [20, 0, 0]],
+  ] as const)('computes gas cost for %s', async (instruction, [l2GasCost, l1GasCost, daGasCost]) => {
+    const bytecode = encodeToBytecode([instruction]);
+    const context = initContext();
+    const {
+      l2GasLeft: initialL2GasLeft,
+      daGasLeft: initialDaGasLeft,
+      l1GasLeft: initialL1GasLeft,
+    } = context.machineState;
+
+    await new AvmSimulator(context).executeBytecode(bytecode);
+
+    expect(initialL2GasLeft - context.machineState.l2GasLeft).toEqual(l2GasCost);
+    expect(initialL1GasLeft - context.machineState.l1GasLeft).toEqual(l1GasCost);
+    expect(initialDaGasLeft - context.machineState.daGasLeft).toEqual(daGasCost);
+  });
+});

yarn-project/simulator/src/avm/avm_gas_cost.ts

@@ -1,3 +1,4 @@
+import { TypeTag } from './avm_memory_types.js';
 import { Opcode } from './serialization/instruction_serialization.js';
 
 /** Gas cost in L1, L2, and DA for a given instruction. */
@@ -7,25 +8,33 @@ export type GasCost = {
   daGas: number;
 };
 
+/** Creates a new instance with all values set to zero except the ones set. */
+export function makeGasCost(gasCost: Partial<GasCost>) {
+  return { ...EmptyGasCost, ...gasCost };
+}
+
 /** Gas cost of zero across all gas dimensions. */
 export const EmptyGasCost = {
   l1Gas: 0,
   l2Gas: 0,
   daGas: 0,
 };
 
-/** Dimensions of gas usage: L1, L2, and DA */
+/** Dimensions of gas usage: L1, L2, and DA. */
 export const GasDimensions = ['l1Gas', 'l2Gas', 'daGas'] as const;
 
+/** Null object to represent a gas cost that's dynamic instead of fixed for a given instruction. */
+export const DynamicGasCost = Symbol('DynamicGasCost');
+
 /** Temporary default gas cost. We should eventually remove all usage of this variable in favor of actual gas for each opcode. */
 const TemporaryDefaultGasCost = { l1Gas: 0, l2Gas: 10, daGas: 0 };
 
 /** Gas costs for each instruction. */
-export const GasCosts: Record<Opcode, GasCost> = {
-  [Opcode.ADD]: TemporaryDefaultGasCost,
-  [Opcode.SUB]: TemporaryDefaultGasCost,
-  [Opcode.MUL]: TemporaryDefaultGasCost,
-  [Opcode.DIV]: TemporaryDefaultGasCost,
+export const GasCosts = {
+  [Opcode.ADD]: DynamicGasCost,
+  [Opcode.SUB]: DynamicGasCost,
+  [Opcode.MUL]: DynamicGasCost,
+  [Opcode.DIV]: DynamicGasCost,
   [Opcode.FDIV]: TemporaryDefaultGasCost,
   [Opcode.EQ]: TemporaryDefaultGasCost,
   [Opcode.LT]: TemporaryDefaultGasCost,
@@ -55,7 +64,7 @@ export const GasCosts: Record<Opcode, GasCost> = {
   [Opcode.BLOCKL1GASLIMIT]: TemporaryDefaultGasCost,
   [Opcode.BLOCKL2GASLIMIT]: TemporaryDefaultGasCost,
   [Opcode.BLOCKDAGASLIMIT]: TemporaryDefaultGasCost,
-  [Opcode.CALLDATACOPY]: TemporaryDefaultGasCost,
+  [Opcode.CALLDATACOPY]: DynamicGasCost,
   // Gas
   [Opcode.L1GASLEFT]: TemporaryDefaultGasCost,
   [Opcode.L2GASLEFT]: TemporaryDefaultGasCost,
@@ -66,7 +75,7 @@ export const GasCosts: Record<Opcode, GasCost> = {
   [Opcode.INTERNALCALL]: TemporaryDefaultGasCost,
   [Opcode.INTERNALRETURN]: TemporaryDefaultGasCost,
   // Memory
-  [Opcode.SET]: TemporaryDefaultGasCost,
+  [Opcode.SET]: DynamicGasCost,
   [Opcode.MOV]: TemporaryDefaultGasCost,
   [Opcode.CMOV]: TemporaryDefaultGasCost,
   // World state
@@ -91,4 +100,33 @@ export const GasCosts: Record<Opcode, GasCost> = {
   [Opcode.POSEIDON]: TemporaryDefaultGasCost,
   [Opcode.SHA256]: TemporaryDefaultGasCost, // temp - may be removed, but alot of contracts rely on i: TemporaryDefaultGasCost,
   [Opcode.PEDERSEN]: TemporaryDefaultGasCost, // temp - may be removed, but alot of contracts rely on i: TemporaryDefaultGasCost,t
+} as const;
+
+/** Constants used in base cost calculations. */
+export const GasCostConstants = {
+  SET_COST_PER_BYTE: 100,
+  CALLDATACOPY_COST_PER_BYTE: 10,
+  ARITHMETIC_COST_PER_BYTE: 10,
+  ARITHMETIC_COST_PER_INDIRECT_ACCESS: 5,
 };
+
+/** Returns a multiplier based on the size of the type represented by the tag. Throws on uninitialized or invalid. */
+export function getGasCostMultiplierFromTypeTag(tag: TypeTag) {
+  switch (tag) {
+    case TypeTag.UINT8:
+      return 1;
+    case TypeTag.UINT16:
+      return 2;
+    case TypeTag.UINT32:
+      return 4;
+    case TypeTag.UINT64:
+      return 8;
+    case TypeTag.UINT128:
+      return 16;
+    case TypeTag.FIELD:
+      return 32;
+    case TypeTag.INVALID:
+    case TypeTag.UNINITIALIZED:
+      throw new Error(`Invalid tag type for gas cost multiplier: ${TypeTag[tag]}`);
+  }
+}

yarn-project/simulator/src/avm/avm_simulator.test.ts

@@ -45,7 +45,7 @@ describe('AVM simulator: injected bytecode', () => {
 
     expect(results.reverted).toBe(false);
     expect(results.output).toEqual([new Fr(3)]);
-    expect(context.machineState.l2GasLeft).toEqual(initialL2GasLeft - 30);
+    expect(context.machineState.l2GasLeft).toEqual(initialL2GasLeft - 350);
   });
 
   it('Should halt if runs out of gas', async () => {

yarn-project/simulator/src/avm/fixtures/index.ts

@@ -89,9 +89,9 @@ export function initGlobalVariables(overrides?: Partial<GlobalVariables>): Globa
  */
 export function initMachineState(overrides?: Partial<AvmMachineState>): AvmMachineState {
   return AvmMachineState.fromState({
-    l1GasLeft: overrides?.l1GasLeft ?? 1e6,
-    l2GasLeft: overrides?.l2GasLeft ?? 1e6,
-    daGasLeft: overrides?.daGasLeft ?? 1e6,
+    l1GasLeft: overrides?.l1GasLeft ?? 100e6,
+    l2GasLeft: overrides?.l2GasLeft ?? 100e6,
+    daGasLeft: overrides?.daGasLeft ?? 100e6,
   });
 }
 

yarn-project/simulator/src/avm/opcodes/addressing_mode.ts

@@ -12,7 +12,7 @@ export enum AddressingMode {
 export class Addressing {
   public constructor(
     /** The addressing mode for each operand. The length of this array is the number of operands of the instruction. */
-    private readonly modePerOperand: AddressingMode[],
+    public readonly modePerOperand: AddressingMode[],
   ) {
     assert(modePerOperand.length <= 8, 'At most 8 operands are supported');
   }

yarn-project/simulator/src/avm/opcodes/arithmetic.ts

@@ -1,84 +1,71 @@
 import type { AvmContext } from '../avm_context.js';
-import { Field, TypeTag } from '../avm_memory_types.js';
+import { GasCost, GasCostConstants, getGasCostMultiplierFromTypeTag, makeGasCost } from '../avm_gas_cost.js';
+import { Field, MemoryValue, TypeTag } from '../avm_memory_types.js';
 import { Opcode, OperandType } from '../serialization/instruction_serialization.js';
+import { Addressing, AddressingMode } from './addressing_mode.js';
 import { Instruction } from './instruction.js';
 import { ThreeOperandInstruction } from './instruction_impl.js';
 
-export class Add extends ThreeOperandInstruction {
-  static readonly type: string = 'ADD';
-  static readonly opcode = Opcode.ADD;
-
-  constructor(indirect: number, inTag: number, aOffset: number, bOffset: number, dstOffset: number) {
-    super(indirect, inTag, aOffset, bOffset, dstOffset);
-  }
-
+export abstract class ThreeOperandArithmeticInstruction extends ThreeOperandInstruction {
   async execute(context: AvmContext): Promise<void> {
     context.machineState.memory.checkTags(this.inTag, this.aOffset, this.bOffset);
 
     const a = context.machineState.memory.get(this.aOffset);
     const b = context.machineState.memory.get(this.bOffset);
 
-    const dest = a.add(b);
+    const dest = this.compute(a, b);
     context.machineState.memory.set(this.dstOffset, dest);
 
     context.machineState.incrementPc();
   }
-}
 
-export class Sub extends ThreeOperandInstruction {
-  static readonly type: string = 'SUB';
-  static readonly opcode = Opcode.SUB;
+  protected gasCost(): GasCost {
+    const indirectCount = Addressing.fromWire(this.indirect).modePerOperand.filter(
+      mode => mode === AddressingMode.INDIRECT,
+    ).length;
 
-  constructor(indirect: number, inTag: number, aOffset: number, bOffset: number, dstOffset: number) {
-    super(indirect, inTag, aOffset, bOffset, dstOffset);
+    const l2Gas =
+      indirectCount * GasCostConstants.ARITHMETIC_COST_PER_INDIRECT_ACCESS +
+      getGasCostMultiplierFromTypeTag(this.inTag) * GasCostConstants.ARITHMETIC_COST_PER_BYTE;
+    return makeGasCost({ l2Gas });
   }
 
-  async execute(context: AvmContext): Promise<void> {
-    const a = context.machineState.memory.get(this.aOffset);
-    const b = context.machineState.memory.get(this.bOffset);
+  protected abstract compute(a: MemoryValue, b: MemoryValue): MemoryValue;
+}
 
-    const dest = a.sub(b);
-    context.machineState.memory.set(this.dstOffset, dest);
+export class Add extends ThreeOperandArithmeticInstruction {
+  static readonly type: string = 'ADD';
+  static readonly opcode = Opcode.ADD;
 
-    context.machineState.incrementPc();
+  protected compute(a: MemoryValue, b: MemoryValue): MemoryValue {
+    return a.add(b);
   }
 }
 
-export class Mul extends ThreeOperandInstruction {
-  static type: string = 'MUL';
-  static readonly opcode = Opcode.MUL;
+export class Sub extends ThreeOperandArithmeticInstruction {
+  static readonly type: string = 'SUB';
+  static readonly opcode = Opcode.SUB;
 
-  constructor(indirect: number, inTag: number, aOffset: number, bOffset: number, dstOffset: number) {
-    super(indirect, inTag, aOffset, bOffset, dstOffset);
+  protected compute(a: MemoryValue, b: MemoryValue): MemoryValue {
+    return a.sub(b);
   }
+}
 
-  async execute(context: AvmContext): Promise<void> {
-    const a = context.machineState.memory.get(this.aOffset);
-    const b = context.machineState.memory.get(this.bOffset);
-
-    const dest = a.mul(b);
-    context.machineState.memory.set(this.dstOffset, dest);
+export class Mul extends ThreeOperandArithmeticInstruction {
+  static type: string = 'MUL';
+  static readonly opcode = Opcode.MUL;
 
-    context.machineState.incrementPc();
+  protected compute(a: MemoryValue, b: MemoryValue): MemoryValue {
+    return a.mul(b);
   }
 }
 
-export class Div extends ThreeOperandInstruction {
+export class Div extends ThreeOperandArithmeticInstruction {
   static type: string = 'DIV';
   static readonly opcode = Opcode.DIV;
 
-  constructor(indirect: number, inTag: number, aOffset: number, bOffset: number, dstOffset: number) {
-    super(indirect, inTag, aOffset, bOffset, dstOffset);
-  }
-
-  async execute(context: AvmContext): Promise<void> {
-    const a = context.machineState.memory.get(this.aOffset);
-    const b = context.machineState.memory.get(this.bOffset);
-
-    const dest = a.div(b);
-    context.machineState.memory.set(this.dstOffset, dest);
-
-    context.machineState.incrementPc();
+  protected compute(a: MemoryValue, b: MemoryValue): MemoryValue {
+    return a.div(b);
   }
 }
 

yarn-project/simulator/src/avm/opcodes/instruction.ts

@@ -1,7 +1,7 @@
 import { strict as assert } from 'assert';
 
 import type { AvmContext } from '../avm_context.js';
-import { EmptyGasCost, GasCost, GasCosts } from '../avm_gas_cost.js';
+import { DynamicGasCost, GasCost, GasCosts } from '../avm_gas_cost.js';
 import { BufferCursor } from '../serialization/buffer_cursor.js';
 import { Opcode, OperandType, deserialize, serialize } from '../serialization/instruction_serialization.js';
 
@@ -30,7 +30,11 @@ export abstract class Instruction {
    * Instruction sub-classes can override this if their gas cost is not fixed.
    */
   protected gasCost(): GasCost {
-    return GasCosts[this.opcode] ?? EmptyGasCost;
+    const gasCost = GasCosts[this.opcode];
+    if (gasCost === DynamicGasCost) {
+      throw new Error(`Instruction ${this.type} must define its own gas cost`);
+    }
+    return gasCost;
   }
 
   /**

yarn-project/simulator/src/avm/opcodes/memory.ts

@@ -1,4 +1,5 @@
 import type { AvmContext } from '../avm_context.js';
+import { GasCost, GasCostConstants, getGasCostMultiplierFromTypeTag, makeGasCost } from '../avm_gas_cost.js';
 import { Field, TaggedMemory, TypeTag } from '../avm_memory_types.js';
 import { InstructionExecutionError } from '../errors.js';
 import { BufferCursor } from '../serialization/buffer_cursor.js';
@@ -79,6 +80,10 @@ export class Set extends Instruction {
 
     context.machineState.incrementPc();
   }
+
+  protected gasCost(): GasCost {
+    return makeGasCost({ l2Gas: GasCostConstants.SET_COST_PER_BYTE * getGasCostMultiplierFromTypeTag(this.inTag) });
+  }
 }
 
 export class CMov extends Instruction {
@@ -193,4 +198,8 @@ export class CalldataCopy extends Instruction {
 
     context.machineState.incrementPc();
   }
+
+  protected gasCost(): GasCost {
+    return makeGasCost({ l2Gas: GasCostConstants.CALLDATACOPY_COST_PER_BYTE * this.copySize });
+  }
 }