chore(avm-simulator): revive field comparison (#4957)

Partially roll back #4516. Field comparison is needed in Brillig to assert bit sizes.

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

@@ -177,6 +177,13 @@ describe('Field', () => {
     expect(field1.equals(field3)).toBe(false);
   });
 
+  it(`Should check if one Field is less than another correctly`, () => {
+    const field1 = new Field(5);
+    const field2 = new Field(10);
+    expect(field1.lt(field2)).toBe(true);
+    expect(field2.lt(field1)).toBe(false);
+  });
+
   it(`Should convert Field to BigInt correctly`, () => {
     const field = new Field(5);
     expect(field.toBigInt()).toStrictEqual(5n);

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

@@ -13,6 +13,7 @@ export abstract class MemoryValue {
   public abstract div(rhs: MemoryValue): MemoryValue;
 
   public abstract equals(rhs: MemoryValue): boolean;
+  public abstract lt(rhs: MemoryValue): boolean;
 
   // We need this to be able to build an instance of the subclasses.
   public abstract build(n: bigint): MemoryValue;
@@ -37,8 +38,6 @@ export abstract class IntegralValue extends MemoryValue {
   public abstract or(rhs: IntegralValue): IntegralValue;
   public abstract xor(rhs: IntegralValue): IntegralValue;
   public abstract not(): IntegralValue;
-
-  public abstract lt(rhs: IntegralValue): boolean;
 }
 
 /**
@@ -164,6 +163,10 @@ export class Field extends MemoryValue {
     return this.rep.equals(rhs.rep);
   }
 
+  public lt(rhs: Field): boolean {
+    return this.rep.lt(rhs.rep);
+  }
+
   public toBigInt(): bigint {
     return this.rep.toBigInt();
   }

yarn-project/simulator/src/avm/opcodes/comparators.test.ts

@@ -110,11 +110,19 @@ describe('Comparators', () => {
       expect(actual).toEqual([new Uint32(0), new Uint32(1), new Uint32(0)]);
     });
 
-    it('Does not work on field elements', async () => {
-      await expect(() =>
-        new Lt(/*indirect=*/ 0, TypeTag.FIELD, /*aOffset=*/ 0, /*bOffset=*/ 1, /*dstOffset=*/ 10).execute(context),
-      ).rejects.toThrow(TagCheckError);
+    it('Works on field elements', async () => {
+      context.machineState.memory.setSlice(0, [new Field(1), new Field(2), new Field(0)]);
+
+      [
+        new Lt(/*indirect=*/ 0, TypeTag.FIELD, /*aOffset=*/ 0, /*bOffset=*/ 0, /*dstOffset=*/ 10),
+        new Lt(/*indirect=*/ 0, TypeTag.FIELD, /*aOffset=*/ 0, /*bOffset=*/ 1, /*dstOffset=*/ 11),
+        new Lt(/*indirect=*/ 0, TypeTag.FIELD, /*aOffset=*/ 0, /*bOffset=*/ 2, /*dstOffset=*/ 12),
+      ].forEach(i => i.execute(context));
+
+      const actual = context.machineState.memory.getSlice(/*offset=*/ 10, /*size=*/ 4);
+      expect(actual).toEqual([new Field(0), new Field(1), new Field(0)]);
     });
+
     it('InTag is checked', async () => {
       context.machineState.memory.setSlice(0, [new Field(1), new Uint32(2), new Uint16(3)]);
 
@@ -166,10 +174,17 @@ describe('Comparators', () => {
       expect(actual).toEqual([new Uint32(1), new Uint32(1), new Uint32(0)]);
     });
 
-    it('Does not work on field elements', async () => {
-      await expect(() =>
-        new Lte(/*indirect=*/ 0, TypeTag.FIELD, /*aOffset=*/ 0, /*bOffset=*/ 1, /*dstOffset=*/ 10).execute(context),
-      ).rejects.toThrow(TagCheckError);
+    it('Works on field elements', async () => {
+      context.machineState.memory.setSlice(0, [new Field(1), new Field(2), new Field(0)]);
+
+      [
+        new Lte(/*indirect=*/ 0, TypeTag.FIELD, /*aOffset=*/ 0, /*bOffset=*/ 0, /*dstOffset=*/ 10),
+        new Lte(/*indirect=*/ 0, TypeTag.FIELD, /*aOffset=*/ 0, /*bOffset=*/ 1, /*dstOffset=*/ 11),
+        new Lte(/*indirect=*/ 0, TypeTag.FIELD, /*aOffset=*/ 0, /*bOffset=*/ 2, /*dstOffset=*/ 12),
+      ].forEach(i => i.execute(context));
+
+      const actual = context.machineState.memory.getSlice(/*offset=*/ 10, /*size=*/ 4);
+      expect(actual).toEqual([new Field(1), new Field(1), new Field(0)]);
     });
 
     it('InTag is checked', async () => {

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

@@ -1,5 +1,4 @@
 import type { AvmContext } from '../avm_context.js';
-import { IntegralValue, TaggedMemory } from '../avm_memory_types.js';
 import { Opcode } from '../serialization/instruction_serialization.js';
 import { ThreeOperandInstruction } from './instruction_impl.js';
 
@@ -35,10 +34,9 @@ export class Lt extends ThreeOperandInstruction {
 
   async execute(context: AvmContext): Promise<void> {
     context.machineState.memory.checkTags(this.inTag, this.aOffset, this.bOffset);
-    TaggedMemory.checkIsIntegralTag(this.inTag);
 
-    const a = context.machineState.memory.getAs<IntegralValue>(this.aOffset);
-    const b = context.machineState.memory.getAs<IntegralValue>(this.bOffset);
+    const a = context.machineState.memory.get(this.aOffset);
+    const b = context.machineState.memory.get(this.bOffset);
 
     // Result will be of the same type as 'a'.
     const dest = a.build(a.lt(b) ? 1n : 0n);
@@ -58,10 +56,9 @@ export class Lte extends ThreeOperandInstruction {
 
   async execute(context: AvmContext): Promise<void> {
     context.machineState.memory.checkTags(this.inTag, this.aOffset, this.bOffset);
-    TaggedMemory.checkIsIntegralTag(this.inTag);
 
-    const a = context.machineState.memory.getAs<IntegralValue>(this.aOffset);
-    const b = context.machineState.memory.getAs<IntegralValue>(this.bOffset);
+    const a = context.machineState.memory.get(this.aOffset);
+    const b = context.machineState.memory.get(this.bOffset);
 
     // Result will be of the same type as 'a'.
     const dest = a.build(a.equals(b) || a.lt(b) ? 1n : 0n);

yellow-paper/docs/public-vm/gen/_instruction-set.mdx

@@ -591,7 +591,7 @@ Less-than check (a < b)
 - **Category**: Compute - Comparators
 - **Flags**: 
 	- **indirect**: Toggles whether each memory-offset argument is an indirect offset. Rightmost bit corresponds to 0th offset arg, etc. Indirect offsets result in memory accesses like `M[M[offset]]` instead of the more standard `M[offset]`.
-	- **inTag**: The [tag/size](./memory-model#tags-and-tagged-memory) to check inputs against and tag the destination with. `field` type is NOT supported for this instruction.
+	- **inTag**: The [tag/size](./memory-model#tags-and-tagged-memory) to check inputs against and tag the destination with.
 - **Args**: 
 	- **aOffset**: memory offset of the operation's left input
 	- **bOffset**: memory offset of the operation's right input
@@ -612,7 +612,7 @@ Less-than-or-equals check (a <= b)
 - **Category**: Compute - Comparators
 - **Flags**: 
 	- **indirect**: Toggles whether each memory-offset argument is an indirect offset. Rightmost bit corresponds to 0th offset arg, etc. Indirect offsets result in memory accesses like `M[M[offset]]` instead of the more standard `M[offset]`.
-	- **inTag**: The [tag/size](./memory-model#tags-and-tagged-memory) to check inputs against and tag the destination with. `field` type is NOT supported for this instruction.
+	- **inTag**: The [tag/size](./memory-model#tags-and-tagged-memory) to check inputs against and tag the destination with.
 - **Args**: 
 	- **aOffset**: memory offset of the operation's left input
 	- **bOffset**: memory offset of the operation's right input

yellow-paper/src/preprocess/InstructionSet/InstructionSet.js

@@ -130,7 +130,7 @@ const INSTRUCTION_SET_RAW = [
         "Category": "Compute - Comparators",
         "Flags": [
             {"name": "indirect", "description": INDIRECT_FLAG_DESCRIPTION},
-            {"name": "inTag", "description": IN_TAG_DESCRIPTION_NO_FIELD},
+            {"name": "inTag", "description": IN_TAG_DESCRIPTION},
         ],
         "Args": [
             {"name": "aOffset", "description": "memory offset of the operation's left input"},
@@ -149,7 +149,7 @@ const INSTRUCTION_SET_RAW = [
         "Category": "Compute - Comparators",
         "Flags": [
             {"name": "indirect", "description": INDIRECT_FLAG_DESCRIPTION},
-            {"name": "inTag", "description": IN_TAG_DESCRIPTION_NO_FIELD},
+            {"name": "inTag", "description": IN_TAG_DESCRIPTION},
         ],
         "Args": [
             {"name": "aOffset", "description": "memory offset of the operation's left input"},