feat: Simplify offsets and sizing using new block structure (#5404)

Fixes two small areas of brittleness using the newly introduced block
and execution trace sorting work.

1) We no longer need the variable num_ecc_op_gates since this is
equivalent to blocks.ecc_op.size() which is a safer representation of
the number of goblin op gates.
2) We can compute pub_inputs_offset once and for all at the trace
generation stage and avoid recomputing it elsewhere.

barretenberg/cpp/src/barretenberg/circuit_checker/goblin_ultra_circuit_builder.test.cpp

@@ -100,7 +100,7 @@ TEST(GoblinUltraCircuitBuilder, GoblinSimple)
     EXPECT_EQ(accumulator, g1::affine_point_at_infinity);
 
     // Check number of ecc op "gates"/rows = 3 ops * 2 rows per op = 6
-    EXPECT_EQ(builder.num_ecc_op_gates, 6);
+    EXPECT_EQ(builder.blocks.ecc_op.size(), 6);
 
     // Check that the expected op codes have been correctly recorded in the 1st op wire
     EXPECT_EQ(builder.blocks.ecc_op.w_l()[0], EccOpCode::ADD_ACCUM);
@@ -150,7 +150,7 @@ TEST(GoblinUltraCircuitBuilder, GoblinEccOpQueueUltraOps)
     // Check that the ultra ops recorded in the EccOpQueue match the ops recorded in the wires
     auto ultra_ops = builder.op_queue->get_aggregate_transcript();
     for (size_t i = 1; i < 4; ++i) {
-        for (size_t j = 0; j < builder.num_ecc_op_gates; ++j) {
+        for (size_t j = 0; j < builder.blocks.ecc_op.size(); ++j) {
             auto op_wire_val = builder.variables[builder.blocks.ecc_op.wires[i][j]];
             auto ultra_op_val = ultra_ops[i][j];
             ASSERT_EQ(op_wire_val, ultra_op_val);

barretenberg/cpp/src/barretenberg/flavor/goblin_ultra.hpp

@@ -270,8 +270,6 @@ class GoblinUltraFlavor {
         std::vector<uint32_t> memory_write_records;
         std::array<Polynomial, 4> sorted_polynomials;
 
-        size_t num_ecc_op_gates; // needed to determine public input offset
-
         auto get_to_be_shifted()
         {
             return RefArray{ this->table_1, this->table_2, this->table_3,      this->table_4, this->w_l,     this->w_r,

barretenberg/cpp/src/barretenberg/proof_system/arithmetization/arithmetization.hpp

@@ -48,7 +48,8 @@ template <typename FF, size_t NUM_WIRES, size_t NUM_SELECTORS> class ExecutionTr
 
     Wires wires; // vectors of indices into a witness variables array
     Selectors selectors;
-    bool has_ram_rom = false; // does the block contain RAM/ROM gates
+    bool has_ram_rom = false;   // does the block contain RAM/ROM gates
+    bool is_pub_inputs = false; // is this the public inputs block
 
     bool operator==(const ExecutionTraceBlock& other) const = default;
 
@@ -156,7 +157,11 @@ template <typename FF_> class UltraArith {
         UltraTraceBlock aux;
         UltraTraceBlock lookup;
 
-        TraceBlocks() { aux.has_ram_rom = true; }
+        TraceBlocks()
+        {
+            aux.has_ram_rom = true;
+            pub_inputs.is_pub_inputs = true;
+        }
 
         auto get() { return RefArray{ pub_inputs, arithmetic, delta_range, elliptic, aux, lookup }; }
 
@@ -264,7 +269,11 @@ template <typename FF_> class UltraHonkArith {
         UltraHonkTraceBlock poseidon_external;
         UltraHonkTraceBlock poseidon_internal;
 
-        TraceBlocks() { aux.has_ram_rom = true; }
+        TraceBlocks()
+        {
+            aux.has_ram_rom = true;
+            pub_inputs.is_pub_inputs = true;
+        }
 
         auto get()
         {

barretenberg/cpp/src/barretenberg/proof_system/circuit_builder/goblin_ultra_circuit_builder.cpp

@@ -190,8 +190,8 @@ ecc_op_tuple GoblinUltraCircuitBuilder_<FF>::decompose_ecc_operands(uint32_t op_
  *
  * @param in Variables array indices corresponding to operation inputs
  * @note We dont explicitly set values for the selectors here since their values are fully determined by
- * num_ecc_op_gates. E.g. in the composer we can reconstruct q_ecc_op as the indicator on the first num_ecc_op_gates
- * indices. All other selectors are simply 0 on this domain.
+ * the number of ecc op gates. E.g. in the composer we can reconstruct q_ecc_op as the indicator over the range of ecc
+ * op gates. All other selectors are simply 0 on this domain.
  */
 template <typename FF> void GoblinUltraCircuitBuilder_<FF>::populate_ecc_op_wires(const ecc_op_tuple& in)
 {
@@ -204,8 +204,6 @@ template <typename FF> void GoblinUltraCircuitBuilder_<FF>::populate_ecc_op_wire
     for (auto& selector : this->blocks.ecc_op.selectors) {
         selector.emplace_back(0);
     }
-
-    num_ecc_op_gates += 2;
 };
 
 template <typename FF> void GoblinUltraCircuitBuilder_<FF>::set_goblin_ecc_op_code_constant_variables()

barretenberg/cpp/src/barretenberg/proof_system/circuit_builder/goblin_ultra_circuit_builder.hpp

@@ -17,8 +17,6 @@ template <typename FF> class GoblinUltraCircuitBuilder_ : public UltraCircuitBui
     static constexpr size_t DEFAULT_NON_NATIVE_FIELD_LIMB_BITS =
         UltraCircuitBuilder_<UltraHonkArith<FF>>::DEFAULT_NON_NATIVE_FIELD_LIMB_BITS;
 
-    size_t num_ecc_op_gates = 0; // number of ecc op "gates" (rows); these are placed at the start of the circuit
-
     // Stores record of ecc operations and performs corresponding native operations internally
     std::shared_ptr<ECCOpQueue> op_queue;
 
@@ -100,7 +98,8 @@ template <typename FF> class GoblinUltraCircuitBuilder_ : public UltraCircuitBui
     size_t get_num_gates() const override
     {
         auto num_ultra_gates = UltraCircuitBuilder_<UltraHonkArith<FF>>::get_num_gates();
-        return num_ultra_gates + num_ecc_op_gates;
+        auto num_goblin_ecc_op_gates = this->blocks.ecc_op.size();
+        return num_ultra_gates + num_goblin_ecc_op_gates;
     }
 
     /**x
@@ -116,11 +115,12 @@ template <typename FF> class GoblinUltraCircuitBuilder_ : public UltraCircuitBui
         size_t nnfcount = 0;
         UltraCircuitBuilder_<UltraHonkArith<FF>>::get_num_gates_split_into_components(
             count, rangecount, romcount, ramcount, nnfcount);
+        auto num_goblin_ecc_op_gates = this->blocks.ecc_op.size();
 
-        size_t total = count + romcount + ramcount + rangecount + num_ecc_op_gates;
+        size_t total = count + romcount + ramcount + rangecount + num_goblin_ecc_op_gates;
         std::cout << "gates = " << total << " (arith " << count << ", rom " << romcount << ", ram " << ramcount
                   << ", range " << rangecount << ", non native field gates " << nnfcount << ", goblin ecc op gates "
-                  << num_ecc_op_gates << "), pubinp = " << this->public_inputs.size() << std::endl;
+                  << num_goblin_ecc_op_gates << "), pubinp = " << this->public_inputs.size() << std::endl;
     }
 
     /**

barretenberg/cpp/src/barretenberg/proof_system/composer/permutation_lib.hpp

@@ -147,20 +147,16 @@ PermutationMapping<Flavor::NUM_WIRES, generalized> compute_permutation_mapping(
         cycle_index++;
     }
 
-    // Add information about public inputs to the computation
+    // Add information about public inputs so that the cycles can be altered later; See the construction of the
+    // permutation polynomials for details.
     const auto num_public_inputs = static_cast<uint32_t>(circuit_constructor.public_inputs.size());
 
-    // TODO(https://github.com/AztecProtocol/barretenberg/issues/862): this is brittle. depends on when PI are placed.
-    // how can we make this more robust?
-    // The public inputs are placed at the top of the execution trace, potentially offset by a zero row.
-    const size_t num_zero_rows = Flavor::has_zero_row ? 1 : 0;
-    size_t pub_input_offset = num_zero_rows;
-    // If Goblin, PI are further offset by number of ecc op gates
-    if constexpr (IsGoblinFlavor<Flavor>) {
-        pub_input_offset += circuit_constructor.num_ecc_op_gates;
+    size_t pub_inputs_offset = 0;
+    if constexpr (IsHonkFlavor<Flavor>) {
+        pub_inputs_offset = proving_key->pub_inputs_offset;
     }
     for (size_t i = 0; i < num_public_inputs; ++i) {
-        size_t idx = i + pub_input_offset;
+        size_t idx = i + pub_inputs_offset;
         mapping.sigmas[0][idx].row_index = static_cast<uint32_t>(idx);
         mapping.sigmas[0][idx].column_index = 0;
         mapping.sigmas[0][idx].is_public_input = true;

barretenberg/cpp/src/barretenberg/proof_system/execution_trace/execution_trace.cpp

@@ -37,6 +37,7 @@ void ExecutionTrace_<Flavor>::add_wires_and_selectors_to_proving_key(
         for (auto [pkey_selector, trace_selector] : zip_view(proving_key->get_selectors(), trace_data.selectors)) {
             pkey_selector = trace_selector.share();
         }
+        proving_key->pub_inputs_offset = trace_data.pub_inputs_offset;
     } else if constexpr (IsPlonkFlavor<Flavor>) {
         for (size_t idx = 0; idx < trace_data.wires.size(); ++idx) {
             std::string wire_tag = "w_" + std::to_string(idx + 1) + "_lagrange";
@@ -106,6 +107,10 @@ typename ExecutionTrace_<Flavor>::TraceData ExecutionTrace_<Flavor>::construct_t
         if (block.has_ram_rom) {
             trace_data.ram_rom_offset = offset;
         }
+        // Store offset of public inputs block for use in the pub input mechanism of the permutation argument
+        if (block.is_pub_inputs) {
+            trace_data.pub_inputs_offset = offset;
+        }
 
         offset += block_size;
     }
@@ -144,14 +149,13 @@ void ExecutionTrace_<Flavor>::add_ecc_op_wires_to_proving_key(
     // Copy the ecc op data from the conventional wires into the op wires over the range of ecc op gates
     const size_t op_wire_offset = Flavor::has_zero_row ? 1 : 0;
     for (auto [ecc_op_wire, wire] : zip_view(op_wire_polynomials, proving_key->get_wires())) {
-        for (size_t i = 0; i < builder.num_ecc_op_gates; ++i) {
+        for (size_t i = 0; i < builder.blocks.ecc_op.size(); ++i) {
             size_t idx = i + op_wire_offset;
             ecc_op_wire[idx] = wire[idx];
             ecc_op_selector[idx] = 1; // construct the selector as the indicator on the ecc op block
         }
     }
 
-    proving_key->num_ecc_op_gates = builder.num_ecc_op_gates;
     proving_key->ecc_op_wire_1 = op_wire_polynomials[0].share();
     proving_key->ecc_op_wire_2 = op_wire_polynomials[1].share();
     proving_key->ecc_op_wire_3 = op_wire_polynomials[2].share();

barretenberg/cpp/src/barretenberg/proof_system/execution_trace/execution_trace.hpp

@@ -21,8 +21,8 @@ template <class Flavor> class ExecutionTrace_ {
         std::array<Polynomial, Builder::Arithmetization::NUM_SELECTORS> selectors;
         // A vector of sets (vectors) of addresses into the wire polynomials whose values are copy constrained
         std::vector<CyclicPermutation> copy_cycles;
-        // The starting index in the trace of the block containing RAM/RAM read/write gates
-        uint32_t ram_rom_offset = 0;
+        uint32_t ram_rom_offset = 0;    // offset of the RAM/ROM block in the execution trace
+        uint32_t pub_inputs_offset = 0; // offset of the public inputs block in the execution trace
 
         TraceData(size_t dyadic_circuit_size, Builder& builder)
         {

barretenberg/cpp/src/barretenberg/sumcheck/instance/prover_instance.cpp

@@ -18,7 +18,7 @@ template <class Flavor> size_t ProverInstance_<Flavor>::compute_dyadic_size(Circ
     // minumum size of execution trace due to everything else
     size_t min_size_of_execution_trace = circuit.public_inputs.size() + circuit.num_gates;
     if constexpr (IsGoblinFlavor<Flavor>) {
-        min_size_of_execution_trace += circuit.num_ecc_op_gates;
+        min_size_of_execution_trace += circuit.blocks.ecc_op.size();
     }
 
     // The number of gates is the maxmimum required by the lookup argument or everything else, plus an optional zero row

barretenberg/cpp/src/barretenberg/sumcheck/instance/prover_instance.hpp

@@ -75,11 +75,6 @@ template <class Flavor> class ProverInstance_ {
 
         std::span<FF> public_wires_source = proving_key->w_r;
 
-        // Determine public input offsets in the circuit relative to the 0th index for Ultra flavors
-        proving_key->pub_inputs_offset = Flavor::has_zero_row ? 1 : 0;
-        if constexpr (IsGoblinFlavor<Flavor>) {
-            proving_key->pub_inputs_offset += proving_key->num_ecc_op_gates;
-        }
         // Construct the public inputs array
         for (size_t i = 0; i < proving_key->num_public_inputs; ++i) {
             size_t idx = i + proving_key->pub_inputs_offset;