Update the current_witness_index after optimisation

acvm-repo/acvm/src/compiler/transformers/mod.rs

@@ -1,5 +1,12 @@
+use std::collections::BTreeSet;
+
 use acir::{
-    circuit::{brillig::BrilligOutputs, Circuit, ExpressionWidth, Opcode},
+    circuit::{
+        self,
+        brillig::{BrilligInputs, BrilligOutputs},
+        opcodes::{BlackBoxFuncCall, FunctionInput, MemOp},
+        Circuit, ExpressionWidth, Opcode,
+    },
     native_types::{Expression, Witness},
     AcirField,
 };
@@ -79,8 +86,6 @@ pub(super) fn transform_internal<F: AcirField>(
                     &mut next_witness_index,
                 );
 
-                // Update next_witness counter
-                next_witness_index += (intermediate_variables.len() - len) as u32;
                 let mut new_opcodes = Vec::new();
                 for (g, (norm, w)) in intermediate_variables.iter().skip(len) {
                     // de-normalize
@@ -160,13 +165,267 @@ pub(super) fn transform_internal<F: AcirField>(
     let mut merge_optimizer = MergeExpressionsOptimizer::new();
     let (opcodes, new_acir_opcode_positions) =
         merge_optimizer.eliminate_intermediate_variable(&acir, new_acir_opcode_positions);
-    // n.b. we do not update current_witness_index after the eliminate_intermediate_variable pass, the real index could be less.
-    let acir = Circuit {
+
+    // n.b. if we do not update current_witness_index after the eliminate_intermediate_variable pass, the real index could be less.
+    let mut acir = Circuit {
         current_witness_index,
         expression_width,
         opcodes,
         // The optimizer does not add new public inputs
         ..acir
     };
+
+    // After the elimination of intermediate variables the `current_witness_index` is potentially higher than it needs to be,
+    // which would cause gaps if we ran the optimization a second time, making it look like new variables were added.
+    // Here we figure out what is the final state of witnesses by visiting each opcode.
+    let witnesses = WitnessCollector::collect_from_circuit(&acir);
+    if let Some(max_witness) = witnesses.last() {
+        acir.current_witness_index = max_witness.0;
+    }
+
     (acir, new_acir_opcode_positions)
 }
+
+/// Collect all witnesses in a circuit.
+#[derive(Default, Clone, Debug)]
+struct WitnessCollector {
+    witnesses: BTreeSet<Witness>,
+}
+
+impl WitnessCollector {
+    /// Collect all witnesses in a circuit.
+    fn collect_from_circuit<F: AcirField>(circuit: &Circuit<F>) -> BTreeSet<Witness> {
+        let mut collector = Self::default();
+        collector.extend_from_circuit(circuit);
+        collector.witnesses
+    }
+
+    fn add(&mut self, witness: Witness) {
+        self.witnesses.insert(witness);
+    }
+
+    fn add_many(&mut self, witnesses: &[Witness]) {
+        self.witnesses.extend(witnesses);
+    }
+
+    /// Add all witnesses from the circuit.
+    fn extend_from_circuit<F: AcirField>(&mut self, circuit: &Circuit<F>) {
+        self.witnesses.extend(&circuit.private_parameters);
+        self.witnesses.extend(&circuit.public_parameters.0);
+        self.witnesses.extend(&circuit.return_values.0);
+        for opcode in &circuit.opcodes {
+            self.extend_from_opcode(opcode)
+        }
+    }
+
+    /// Add witnesses from the opcode.
+    fn extend_from_opcode<F: AcirField>(&mut self, opcode: &Opcode<F>) {
+        match opcode {
+            Opcode::AssertZero(expr) => {
+                self.extend_from_expr(expr);
+            }
+            Opcode::BlackBoxFuncCall(call) => self.extend_from_blackbox(call),
+            Opcode::MemoryOp { block_id: _, op, predicate } => {
+                let MemOp { operation, index, value } = op;
+                self.extend_from_expr(operation);
+                self.extend_from_expr(index);
+                self.extend_from_expr(value);
+                if let Some(pred) = predicate {
+                    self.extend_from_expr(pred);
+                }
+            }
+            Opcode::MemoryInit { block_id: _, init, block_type: _ } => {
+                for w in init {
+                    self.add(*w);
+                }
+            }
+            // We keep the display for a BrilligCall and circuit Call separate as they
+            // are distinct in their functionality and we should maintain this separation for debugging.
+            Opcode::BrilligCall { id: _, inputs, outputs, predicate } => {
+                if let Some(pred) = predicate {
+                    self.extend_from_expr(pred);
+                }
+                self.extend_from_brillig_inputs(inputs);
+                self.extend_from_brillig_outputs(outputs);
+            }
+            Opcode::Call { id: _, inputs, outputs, predicate } => {
+                if let Some(pred) = predicate {
+                    self.extend_from_expr(pred);
+                }
+                self.add_many(&inputs);
+                self.add_many(&outputs);
+            }
+        }
+    }
+
+    fn extend_from_expr<F: AcirField>(&mut self, expr: &Expression<F>) {
+        for i in &expr.mul_terms {
+            self.add(i.1);
+            self.add(i.2);
+        }
+        for i in &expr.linear_combinations {
+            self.add(i.1);
+        }
+    }
+
+    fn extend_from_brillig_inputs<F: AcirField>(&mut self, inputs: &[BrilligInputs<F>]) {
+        for input in inputs {
+            match input {
+                BrilligInputs::Single(expr) => {
+                    self.extend_from_expr(expr);
+                }
+                BrilligInputs::Array(exprs) => {
+                    for expr in exprs {
+                        self.extend_from_expr(expr);
+                    }
+                }
+                BrilligInputs::MemoryArray(_) => {}
+            }
+        }
+    }
+
+    fn extend_from_brillig_outputs(&mut self, outputs: &[BrilligOutputs]) {
+        for output in outputs {
+            match output {
+                BrilligOutputs::Simple(w) => {
+                    self.add(*w);
+                }
+                BrilligOutputs::Array(ws) => self.add_many(ws),
+            }
+        }
+    }
+
+    fn extend_from_blackbox<F: AcirField>(&mut self, call: &BlackBoxFuncCall<F>) {
+        match call {
+            BlackBoxFuncCall::AES128Encrypt { inputs, iv, key, outputs } => {
+                self.extend_from_function_inputs(inputs.as_slice());
+                self.extend_from_function_inputs(iv.as_slice());
+                self.extend_from_function_inputs(key.as_slice());
+                self.add_many(outputs);
+            }
+            BlackBoxFuncCall::AND { lhs, rhs, output } => {
+                self.extend_from_function_input(lhs);
+                self.extend_from_function_input(rhs);
+                self.add(*output);
+            }
+            BlackBoxFuncCall::XOR { lhs, rhs, output } => {
+                self.extend_from_function_input(lhs);
+                self.extend_from_function_input(rhs);
+                self.add(*output);
+            }
+            BlackBoxFuncCall::RANGE { input } => {
+                self.extend_from_function_input(input);
+            }
+            BlackBoxFuncCall::Blake2s { inputs, outputs } => {
+                self.extend_from_function_inputs(inputs.as_slice());
+                self.add_many(outputs.as_slice());
+            }
+            BlackBoxFuncCall::Blake3 { inputs, outputs } => {
+                self.extend_from_function_inputs(inputs.as_slice());
+                self.add_many(outputs.as_slice());
+            }
+            BlackBoxFuncCall::SchnorrVerify {
+                public_key_x,
+                public_key_y,
+                signature,
+                message,
+                output,
+            } => {
+                self.extend_from_function_input(public_key_x);
+                self.extend_from_function_input(public_key_y);
+                self.extend_from_function_inputs(signature.as_slice());
+                self.extend_from_function_inputs(message.as_slice());
+                self.add(*output);
+            }
+            BlackBoxFuncCall::EcdsaSecp256k1 {
+                public_key_x,
+                public_key_y,
+                signature,
+                hashed_message,
+                output,
+            } => {
+                self.extend_from_function_inputs(public_key_x.as_slice());
+                self.extend_from_function_inputs(public_key_y.as_slice());
+                self.extend_from_function_inputs(signature.as_slice());
+                self.extend_from_function_inputs(hashed_message.as_slice());
+                self.add(*output);
+            }
+            BlackBoxFuncCall::EcdsaSecp256r1 {
+                public_key_x,
+                public_key_y,
+                signature,
+                hashed_message,
+                output,
+            } => {
+                self.extend_from_function_inputs(public_key_x.as_slice());
+                self.extend_from_function_inputs(public_key_y.as_slice());
+                self.extend_from_function_inputs(signature.as_slice());
+                self.extend_from_function_inputs(hashed_message.as_slice());
+                self.add(*output);
+            }
+            BlackBoxFuncCall::MultiScalarMul { points, scalars, outputs } => {
+                self.extend_from_function_inputs(points.as_slice());
+                self.extend_from_function_inputs(scalars.as_slice());
+                let (x, y, i) = outputs;
+                self.add(*x);
+                self.add(*y);
+                self.add(*i);
+            }
+            BlackBoxFuncCall::EmbeddedCurveAdd { input1, input2, outputs } => {
+                self.extend_from_function_inputs(input1.as_slice());
+                self.extend_from_function_inputs(input2.as_slice());
+                let (x, y, i) = outputs;
+                self.add(*x);
+                self.add(*y);
+                self.add(*i);
+            }
+            BlackBoxFuncCall::Keccakf1600 { inputs, outputs } => {
+                self.extend_from_function_inputs(inputs.as_slice());
+                self.add_many(outputs.as_slice());
+            }
+            BlackBoxFuncCall::RecursiveAggregation {
+                verification_key,
+                proof,
+                public_inputs,
+                key_hash,
+                proof_type: _,
+            } => {
+                self.extend_from_function_inputs(verification_key.as_slice());
+                self.extend_from_function_inputs(proof.as_slice());
+                self.extend_from_function_inputs(public_inputs.as_slice());
+                self.extend_from_function_input(key_hash);
+            }
+            BlackBoxFuncCall::BigIntAdd { .. }
+            | BlackBoxFuncCall::BigIntSub { .. }
+            | BlackBoxFuncCall::BigIntMul { .. }
+            | BlackBoxFuncCall::BigIntDiv { .. } => {}
+            BlackBoxFuncCall::BigIntFromLeBytes { inputs, modulus: _, output: _ } => {
+                self.extend_from_function_inputs(inputs.as_slice());
+            }
+            BlackBoxFuncCall::BigIntToLeBytes { input: _, outputs } => {
+                self.add_many(outputs.as_slice());
+            }
+            BlackBoxFuncCall::Poseidon2Permutation { inputs, outputs, len: _ } => {
+                self.extend_from_function_inputs(inputs.as_slice());
+                self.add_many(outputs.as_slice());
+            }
+            BlackBoxFuncCall::Sha256Compression { inputs, hash_values, outputs } => {
+                self.extend_from_function_inputs(inputs.as_slice());
+                self.extend_from_function_inputs(hash_values.as_slice());
+                self.add_many(outputs.as_slice());
+            }
+        }
+    }
+
+    fn extend_from_function_input<F: AcirField>(&mut self, input: &FunctionInput<F>) {
+        if let circuit::opcodes::ConstantOrWitnessEnum::Witness(witness) = input.input() {
+            self.add(witness);
+        }
+    }
+
+    fn extend_from_function_inputs<F: AcirField>(&mut self, inputs: &[FunctionInput<F>]) {
+        for input in inputs {
+            self.extend_from_function_input(input);
+        }
+    }
+}