feat(avm): complete SET instruction (AztecProtocol#4378)

This pull request completes the implementation of the SET instruction
and adds handling for invalid tags. It also includes necessary tests for
the new functionality.

SET takes the given u128, casts it to the provided inTag type, and sets
the memory.

Ref: AztecProtocol#4267, AztecProtocol#4271.

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

@@ -6,6 +6,7 @@ import { AvmMachineState } from '../avm_machine_state.js';
 import { Field, TypeTag, Uint8, Uint16, Uint32, Uint64, Uint128 } from '../avm_memory_types.js';
 import { initExecutionEnvironment } from '../fixtures/index.js';
 import { AvmJournal } from '../journal/journal.js';
+import { InstructionExecutionError } from './instruction.js';
 import { CMov, CalldataCopy, Cast, Mov, Set } from './memory.js';
 
 describe('Memory instructions', () => {
@@ -64,6 +65,27 @@ describe('Memory instructions', () => {
       expect(actual).toEqual(new Uint32(1234n));
       expect(tag).toEqual(TypeTag.UINT32);
     });
+
+    it('should correctly set value and tag (truncating)', async () => {
+      await new Set(/*indirect=*/ 0, /*inTag=*/ TypeTag.UINT16, /*value=*/ 0x12345678n, /*offset=*/ 1).execute(
+        machineState,
+        journal,
+      );
+
+      const actual = machineState.memory.get(1);
+      const tag = machineState.memory.getTag(1);
+
+      expect(actual).toEqual(new Uint16(0x5678));
+      expect(tag).toEqual(TypeTag.UINT16);
+    });
+
+    it('should throw if tag is FIELD, UNINITIALIZED, INVALID', async () => {
+      for (const tag of [TypeTag.FIELD, TypeTag.UNINITIALIZED, TypeTag.INVALID]) {
+        await expect(
+          new Set(/*indirect=*/ 0, /*inTag=*/ tag, /*value=*/ 1234n, /*offset=*/ 1).execute(machineState, journal),
+        ).rejects.toThrow(InstructionExecutionError);
+      }
+    });
   });
 
   describe('CAST', () => {

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

@@ -2,7 +2,7 @@ import { AvmMachineState } from '../avm_machine_state.js';
 import { Field, TaggedMemory, TypeTag } from '../avm_memory_types.js';
 import { AvmJournal } from '../journal/index.js';
 import { Opcode, OperandType } from '../serialization/instruction_serialization.js';
-import { Instruction } from './instruction.js';
+import { Instruction, InstructionExecutionError } from './instruction.js';
 import { TwoOperandInstruction } from './instruction_impl.js';
 
 export class Set extends Instruction {
@@ -22,8 +22,12 @@ export class Set extends Instruction {
   }
 
   async execute(machineState: AvmMachineState, _journal: AvmJournal): Promise<void> {
-    const res = TaggedMemory.integralFromTag(this.value, this.inTag);
+    // Per the YP, the tag cannot be a field.
+    if ([TypeTag.FIELD, TypeTag.UNINITIALIZED, TypeTag.INVALID].includes(this.inTag)) {
+      throw new InstructionExecutionError(`Invalid tag ${TypeTag[this.inTag]} for SET.`);
+    }
 
+    const res = TaggedMemory.integralFromTag(this.value, this.inTag);
     machineState.memory.set(this.dstOffset, res);
 
     this.incrementPc(machineState);