feat: Brillig pointer codegen and execution (#5737)

Resolves noir-lang/noir#3907

This PR builds upon
#5709.

These changes do not yet include a Brillig stdlib and removal of the
`Brillig` opcode itself. The generated stdlib Brillig (such as for
quotient) is not created in the same manner as other Brillig calls which
are generated during SSA. I have decided to leave this for another
follow-up where we can actually remove `Brillig`.

---------

Co-authored-by: Tom French <15848336+TomAFrench@users.noreply.github.com>
Co-authored-by: jfecher <jfecher11@gmail.com>

noir/noir-repo/acvm-repo/acir/src/circuit/mod.rs

@@ -266,6 +266,10 @@ impl std::fmt::Display for Program {
             writeln!(f, "func {}", func_index)?;
             writeln!(f, "{}", function)?;
         }
+        for (func_index, function) in self.unconstrained_functions.iter().enumerate() {
+            writeln!(f, "unconstrained func {}", func_index)?;
+            writeln!(f, "{:?}", function.bytecode)?;
+        }
         Ok(())
     }
 }

noir/noir-repo/acvm-repo/acvm/src/pwg/brillig.rs

@@ -1,7 +1,7 @@
 use std::collections::HashMap;
 
 use acir::{
-    brillig::{ForeignCallParam, ForeignCallResult},
+    brillig::{ForeignCallParam, ForeignCallResult, Opcode as BrilligOpcode},
     circuit::{
         brillig::{Brillig, BrilligInputs, BrilligOutputs},
         opcodes::BlockId,
@@ -46,9 +46,9 @@ impl<'b, B: BlackBoxFunctionSolver> BrilligSolver<'b, B> {
     /// Assigns the zero value to all outputs of the given [`Brillig`] bytecode.
     pub(super) fn zero_out_brillig_outputs(
         initial_witness: &mut WitnessMap,
-        brillig: &Brillig,
+        outputs: &[BrilligOutputs],
     ) -> Result<(), OpcodeResolutionError> {
-        for output in &brillig.outputs {
+        for output in outputs {
             match output {
                 BrilligOutputs::Simple(witness) => {
                     insert_value(witness, FieldElement::zero(), initial_witness)?;
@@ -63,6 +63,7 @@ impl<'b, B: BlackBoxFunctionSolver> BrilligSolver<'b, B> {
         Ok(())
     }
 
+    // TODO: Delete this old method once `Brillig` is deleted
     /// Constructs a solver for a Brillig block given the bytecode and initial
     /// witness.
     pub(crate) fn new(
@@ -72,13 +73,45 @@ impl<'b, B: BlackBoxFunctionSolver> BrilligSolver<'b, B> {
         bb_solver: &'b B,
         acir_index: usize,
     ) -> Result<Self, OpcodeResolutionError> {
+        let vm = Self::setup_brillig_vm(
+            initial_witness,
+            memory,
+            &brillig.inputs,
+            &brillig.bytecode,
+            bb_solver,
+        )?;
+        Ok(Self { vm, acir_index })
+    }
+
+    /// Constructs a solver for a Brillig block given the bytecode and initial
+    /// witness.
+    pub(crate) fn new_call(
+        initial_witness: &WitnessMap,
+        memory: &HashMap<BlockId, MemoryOpSolver>,
+        inputs: &'b [BrilligInputs],
+        brillig_bytecode: &'b [BrilligOpcode],
+        bb_solver: &'b B,
+        acir_index: usize,
+    ) -> Result<Self, OpcodeResolutionError> {
+        let vm =
+            Self::setup_brillig_vm(initial_witness, memory, inputs, brillig_bytecode, bb_solver)?;
+        Ok(Self { vm, acir_index })
+    }
+
+    fn setup_brillig_vm(
+        initial_witness: &WitnessMap,
+        memory: &HashMap<BlockId, MemoryOpSolver>,
+        inputs: &[BrilligInputs],
+        brillig_bytecode: &'b [BrilligOpcode],
+        bb_solver: &'b B,
+    ) -> Result<VM<'b, B>, OpcodeResolutionError> {
         // Set input values
         let mut calldata: Vec<FieldElement> = Vec::new();
         // Each input represents an expression or array of expressions to evaluate.
         // Iterate over each input and evaluate the expression(s) associated with it.
         // Push the results into memory.
         // If a certain expression is not solvable, we stall the ACVM and do not proceed with Brillig VM execution.
-        for input in &brillig.inputs {
+        for input in inputs {
             match input {
                 BrilligInputs::Single(expr) => match get_value(expr, initial_witness) {
                     Ok(value) => calldata.push(value),
@@ -118,8 +151,8 @@ impl<'b, B: BlackBoxFunctionSolver> BrilligSolver<'b, B> {
 
         // Instantiate a Brillig VM given the solved calldata
         // along with the Brillig bytecode.
-        let vm = VM::new(calldata, &brillig.bytecode, vec![], bb_solver);
-        Ok(Self { vm, acir_index })
+        let vm = VM::new(calldata, brillig_bytecode, vec![], bb_solver);
+        Ok(vm)
     }
 
     pub fn get_memory(&self) -> &[MemoryValue] {
@@ -204,13 +237,13 @@ impl<'b, B: BlackBoxFunctionSolver> BrilligSolver<'b, B> {
     pub(crate) fn finalize(
         self,
         witness: &mut WitnessMap,
-        brillig: &Brillig,
+        outputs: &[BrilligOutputs],
     ) -> Result<(), OpcodeResolutionError> {
         // Finish the Brillig execution by writing the outputs to the witness map
         let vm_status = self.vm.get_status();
         match vm_status {
             VMStatus::Finished { return_data_offset, return_data_size } => {
-                self.write_brillig_outputs(witness, return_data_offset, return_data_size, brillig)?;
+                self.write_brillig_outputs(witness, return_data_offset, return_data_size, outputs)?;
                 Ok(())
             }
             _ => panic!("Brillig VM has not completed execution"),
@@ -222,12 +255,12 @@ impl<'b, B: BlackBoxFunctionSolver> BrilligSolver<'b, B> {
         witness_map: &mut WitnessMap,
         return_data_offset: usize,
         return_data_size: usize,
-        brillig: &Brillig,
+        outputs: &[BrilligOutputs],
     ) -> Result<(), OpcodeResolutionError> {
         // Write VM execution results into the witness map
         let memory = self.vm.get_memory();
         let mut current_ret_data_idx = return_data_offset;
-        for output in brillig.outputs.iter() {
+        for output in outputs.iter() {
             match output {
                 BrilligOutputs::Simple(witness) => {
                     insert_value(witness, memory[current_ret_data_idx].to_field(), witness_map)?;
@@ -242,6 +275,7 @@ impl<'b, B: BlackBoxFunctionSolver> BrilligSolver<'b, B> {
                 }
             }
         }
+
         assert!(
             current_ret_data_idx == return_data_offset + return_data_size,
             "Brillig VM did not write the expected number of return values"

noir/noir-repo/acvm-repo/acvm/src/pwg/mod.rs

@@ -4,7 +4,7 @@ use std::collections::HashMap;
 
 use acir::{
     brillig::ForeignCallResult,
-    circuit::{opcodes::BlockId, Opcode, OpcodeLocation},
+    circuit::{brillig::BrilligBytecode, opcodes::BlockId, Opcode, OpcodeLocation},
     native_types::{Expression, Witness, WitnessMap},
     BlackBoxFunc, FieldElement,
 };
@@ -165,10 +165,18 @@ pub struct ACVM<'a, B: BlackBoxFunctionSolver> {
     /// Represents the outputs of all ACIR calls during an ACVM process
     /// List is appended onto by the caller upon reaching a [ACVMStatus::RequiresAcirCall]
     acir_call_results: Vec<Vec<FieldElement>>,
+
+    // Each unconstrained function referenced in the program
+    unconstrained_functions: &'a [BrilligBytecode],
 }
 
 impl<'a, B: BlackBoxFunctionSolver> ACVM<'a, B> {
-    pub fn new(backend: &'a B, opcodes: &'a [Opcode], initial_witness: WitnessMap) -> Self {
+    pub fn new(
+        backend: &'a B,
+        opcodes: &'a [Opcode],
+        initial_witness: WitnessMap,
+        unconstrained_functions: &'a [BrilligBytecode],
+    ) -> Self {
         let status = if opcodes.is_empty() { ACVMStatus::Solved } else { ACVMStatus::InProgress };
         ACVM {
             status,
@@ -181,6 +189,7 @@ impl<'a, B: BlackBoxFunctionSolver> ACVM<'a, B> {
             brillig_solver: None,
             acir_call_counter: 0,
             acir_call_results: Vec::default(),
+            unconstrained_functions,
         }
     }
 
@@ -324,9 +333,10 @@ impl<'a, B: BlackBoxFunctionSolver> ACVM<'a, B> {
                 Ok(Some(foreign_call)) => return self.wait_for_foreign_call(foreign_call),
                 res => res.map(|_| ()),
             },
-            Opcode::BrilligCall { .. } => {
-                todo!("implement brillig pointer handling");
-            }
+            Opcode::BrilligCall { .. } => match self.solve_brillig_call_opcode() {
+                Ok(Some(foreign_call)) => return self.wait_for_foreign_call(foreign_call),
+                res => res.map(|_| ()),
+            },
             Opcode::Call { .. } => match self.solve_call_opcode() {
                 Ok(Some(input_values)) => return self.wait_for_acir_call(input_values),
                 res => res.map(|_| ()),
@@ -381,7 +391,8 @@ impl<'a, B: BlackBoxFunctionSolver> ACVM<'a, B> {
 
         let witness = &mut self.witness_map;
         if is_predicate_false(witness, &brillig.predicate)? {
-            return BrilligSolver::<B>::zero_out_brillig_outputs(witness, brillig).map(|_| None);
+            return BrilligSolver::<B>::zero_out_brillig_outputs(witness, &brillig.outputs)
+                .map(|_| None);
         }
 
         // If we're resuming execution after resolving a foreign call then
@@ -407,7 +418,51 @@ impl<'a, B: BlackBoxFunctionSolver> ACVM<'a, B> {
             }
             BrilligSolverStatus::Finished => {
                 // Write execution outputs
-                solver.finalize(witness, brillig)?;
+                solver.finalize(witness, &brillig.outputs)?;
+                Ok(None)
+            }
+        }
+    }
+
+    fn solve_brillig_call_opcode(
+        &mut self,
+    ) -> Result<Option<ForeignCallWaitInfo>, OpcodeResolutionError> {
+        let Opcode::BrilligCall { id, inputs, outputs, predicate } =
+            &self.opcodes[self.instruction_pointer]
+        else {
+            unreachable!("Not executing a Brillig opcode");
+        };
+
+        let witness = &mut self.witness_map;
+        if is_predicate_false(witness, predicate)? {
+            return BrilligSolver::<B>::zero_out_brillig_outputs(witness, outputs).map(|_| None);
+        }
+
+        // If we're resuming execution after resolving a foreign call then
+        // there will be a cached `BrilligSolver` to avoid recomputation.
+        let mut solver: BrilligSolver<'_, B> = match self.brillig_solver.take() {
+            Some(solver) => solver,
+            None => BrilligSolver::new_call(
+                witness,
+                &self.block_solvers,
+                inputs,
+                &self.unconstrained_functions[*id as usize].bytecode,
+                self.backend,
+                self.instruction_pointer,
+            )?,
+        };
+        match solver.solve()? {
+            BrilligSolverStatus::ForeignCallWait(foreign_call) => {
+                // Cache the current state of the solver
+                self.brillig_solver = Some(solver);
+                Ok(Some(foreign_call))
+            }
+            BrilligSolverStatus::InProgress => {
+                unreachable!("Brillig solver still in progress")
+            }
+            BrilligSolverStatus::Finished => {
+                // Write execution outputs
+                solver.finalize(witness, outputs)?;
                 Ok(None)
             }
         }
@@ -425,7 +480,8 @@ impl<'a, B: BlackBoxFunctionSolver> ACVM<'a, B> {
         };
 
         if should_skip {
-            let resolution = BrilligSolver::<B>::zero_out_brillig_outputs(witness, brillig);
+            let resolution =
+                BrilligSolver::<B>::zero_out_brillig_outputs(witness, &brillig.outputs);
             return StepResult::Status(self.handle_opcode_resolution(resolution));
         }
 

noir/noir-repo/acvm-repo/acvm/tests/solver.rs

@@ -104,8 +104,9 @@ fn inversion_brillig_oracle_equivalence() {
         (Witness(2), FieldElement::from(3u128)),
     ])
     .into();
-
-    let mut acvm = ACVM::new(&StubbedBlackBoxSolver, &opcodes, witness_assignments);
+    let unconstrained_functions = vec![];
+    let mut acvm =
+        ACVM::new(&StubbedBlackBoxSolver, &opcodes, witness_assignments, &unconstrained_functions);
     // use the partial witness generation solver with our acir program
     let solver_status = acvm.solve();
 
@@ -241,8 +242,9 @@ fn double_inversion_brillig_oracle() {
         (Witness(9), FieldElement::from(10u128)),
     ])
     .into();
-
-    let mut acvm = ACVM::new(&StubbedBlackBoxSolver, &opcodes, witness_assignments);
+    let unconstrained_functions = vec![];
+    let mut acvm =
+        ACVM::new(&StubbedBlackBoxSolver, &opcodes, witness_assignments, &unconstrained_functions);
 
     // use the partial witness generation solver with our acir program
     let solver_status = acvm.solve();
@@ -370,8 +372,9 @@ fn oracle_dependent_execution() {
 
     let witness_assignments =
         BTreeMap::from([(w_x, FieldElement::from(2u128)), (w_y, FieldElement::from(2u128))]).into();
-
-    let mut acvm = ACVM::new(&StubbedBlackBoxSolver, &opcodes, witness_assignments);
+    let unconstrained_functions = vec![];
+    let mut acvm =
+        ACVM::new(&StubbedBlackBoxSolver, &opcodes, witness_assignments, &unconstrained_functions);
 
     // use the partial witness generation solver with our acir program
     let solver_status = acvm.solve();
@@ -474,8 +477,9 @@ fn brillig_oracle_predicate() {
         (Witness(2), FieldElement::from(3u128)),
     ])
     .into();
-
-    let mut acvm = ACVM::new(&StubbedBlackBoxSolver, &opcodes, witness_assignments);
+    let unconstrained_functions = vec![];
+    let mut acvm =
+        ACVM::new(&StubbedBlackBoxSolver, &opcodes, witness_assignments, &unconstrained_functions);
     let solver_status = acvm.solve();
     assert_eq!(solver_status, ACVMStatus::Solved, "should be fully solved");
 
@@ -509,7 +513,8 @@ fn unsatisfied_opcode_resolved() {
     values.insert(d, FieldElement::from(2_i128));
 
     let opcodes = vec![Opcode::AssertZero(opcode_a)];
-    let mut acvm = ACVM::new(&StubbedBlackBoxSolver, &opcodes, values);
+    let unconstrained_functions = vec![];
+    let mut acvm = ACVM::new(&StubbedBlackBoxSolver, &opcodes, values, &unconstrained_functions);
     let solver_status = acvm.solve();
     assert_eq!(
         solver_status,
@@ -591,8 +596,8 @@ fn unsatisfied_opcode_resolved_brillig() {
     values.insert(w_result, FieldElement::from(0_i128));
 
     let opcodes = vec![brillig_opcode, Opcode::AssertZero(opcode_a)];
-
-    let mut acvm = ACVM::new(&StubbedBlackBoxSolver, &opcodes, values);
+    let unconstrained_functions = vec![];
+    let mut acvm = ACVM::new(&StubbedBlackBoxSolver, &opcodes, values, &unconstrained_functions);
     let solver_status = acvm.solve();
     assert_eq!(
         solver_status,
@@ -635,8 +640,9 @@ fn memory_operations() {
     });
 
     let opcodes = vec![init, read_op, expression];
-
-    let mut acvm = ACVM::new(&StubbedBlackBoxSolver, &opcodes, initial_witness);
+    let unconstrained_functions = vec![];
+    let mut acvm =
+        ACVM::new(&StubbedBlackBoxSolver, &opcodes, initial_witness, &unconstrained_functions);
     let solver_status = acvm.solve();
     assert_eq!(solver_status, ACVMStatus::Solved);
     let witness_map = acvm.finalize();