10096: Remove initialization for non-derived polynomials

barretenberg/cpp/src/barretenberg/polynomials/polynomial.cpp

@@ -60,17 +60,11 @@ void Polynomial<Fr>::allocate_backing_memory(size_t size, size_t virtual_size, s
  *
  * @param size The size of the polynomial.
  */
-template <typename Fr>
-Polynomial<Fr>::Polynomial(size_t size, size_t virtual_size, size_t start_index, bool disable_parallelisation)
+template <typename Fr> Polynomial<Fr>::Polynomial(size_t size, size_t virtual_size, size_t start_index)
 {
     PROFILE_THIS_NAME("polynomial allocation with zeroing");
 
     allocate_backing_memory(size, virtual_size, start_index);
-    if (disable_parallelisation) {
-        // In AVM polynomials are small and already constructed in parallel
-        memset(static_cast<void*>(coefficients_.backing_memory_.get()), 0, sizeof(Fr) * size);
-        return;
-    }
 
     size_t num_threads = calculate_num_threads(size);
     size_t range_per_thread = size / num_threads;
@@ -293,6 +287,13 @@ template <typename Fr> Polynomial<Fr>& Polynomial<Fr>::operator*=(const Fr scali
     return *this;
 }
 
+template <typename Fr> Polynomial<Fr> Polynomial<Fr>::create_non_parallel_zero_init(size_t size, size_t virtual_size)
+{
+    Polynomial p(size, virtual_size, Polynomial<Fr>::DontZeroMemory::FLAG);
+    memset(static_cast<void*>(p.coefficients_.backing_memory_.get()), 0, sizeof(Fr) * size);
+    return p;
+}
+
 // TODO(https://github.com/AztecProtocol/barretenberg/issues/1113): Optimizing based on actual sizes would involve using
 // expand, but it is currently unused.
 template <typename Fr>

barretenberg/cpp/src/barretenberg/polynomials/polynomial.hpp

@@ -65,7 +65,7 @@ template <typename Fr> class Polynomial {
     using FF = Fr;
     enum class DontZeroMemory { FLAG };
 
-    Polynomial(size_t size, size_t virtual_size, size_t start_index = 0, bool disable_parallelisation = false);
+    Polynomial(size_t size, size_t virtual_size, size_t start_index = 0);
     // Intended just for plonk, where size == virtual_size always
     Polynomial(size_t size)
         : Polynomial(size, size){};
@@ -284,6 +284,14 @@ template <typename Fr> class Polynomial {
         return p;
     }
 
+    /**
+     * @brief A factory to construct a polynomial where parallel initialization is
+     *        not possible (e.g. AVM code).
+     *
+     * @return a polynomial initialized with zero on the range defined by size
+     */
+    static Polynomial create_non_parallel_zero_init(size_t size, size_t virtual_size);
+
     /**
      * @brief Expands the polynomial with new start_index and end_index
      * The value of the polynomial remains the same, but defined memory region differs.

barretenberg/cpp/src/barretenberg/vm/avm/generated/circuit_builder.cpp

@@ -78,24 +78,17 @@ AvmCircuitBuilder::ProverPolynomials AvmCircuitBuilder::compute_polynomials() co
                        bb::parallel_for(num_unshifted, [&](size_t i) {
                            auto& poly = unshifted[i];
                            const auto col_idx = polys_to_cols_unshifted_idx[i];
-                           size_t col_size = 0;
-
-                           // We fully allocate the inverse polynomials. We leave this potential memory optimization for
-                           // later.
-                           if (derived_labels_set.contains(labels[i])) {
-                               col_size = num_rows;
-                           } else {
-                               col_size = col_nonzero_size[col_idx];
-                           }
+                           const bool is_derived = derived_labels_set.contains(labels[i]);
 
                            if (poly.is_empty()) {
-                               // Not set above
-                               poly = Polynomial{ /*memory size*/
-                                                  col_size,
-                                                  /*largest possible index as virtual size*/ circuit_subgroup_size,
-                                                  /*start_index=*/0,
-                                                  /*/*disable parallel initialisation=*/true
-                               };
+                               // Not set above. Non-derived unshifted polynomials are initialized below. The
+                               // non-derived ones do need to be initialized with zeros and are fully allocated (size ==
+                               // num_rows).
+                               poly = is_derived
+                                          ? Polynomial::create_non_parallel_zero_init(num_rows, circuit_subgroup_size)
+                                          : Polynomial{ col_nonzero_size[col_idx],
+                                                        circuit_subgroup_size,
+                                                        Polynomial::DontZeroMemory::FLAG };
                            }
                        });
                    }));

bb-pilcom/bb-pil-backend/templates/circuit_builder.cpp.hbs

@@ -78,22 +78,14 @@ namespace bb {
             bb::parallel_for(num_unshifted, [&](size_t i) {
                 auto& poly = unshifted[i];
                 const auto col_idx = polys_to_cols_unshifted_idx[i];
-                size_t col_size = 0;
-
-                // We fully allocate the inverse polynomials. We leave this potential memory optimization for later.
-                if (derived_labels_set.contains(labels[i])) {
-                    col_size = num_rows;
-                } else {
-                    col_size = col_nonzero_size[col_idx];
-                }
+                const bool is_derived = derived_labels_set.contains(labels[i]);
 
                 if (poly.is_empty()) {
-                    // Not set above
-                        poly = Polynomial{ /*memory size*/ col_size,
-                                                  /*largest possible index as virtual size*/ circuit_subgroup_size,
-                                                  /*start_index=*/0,
-                                                  /*disable parallel initialization=*/true
-                               };                }
+                    // Not set above. Non-derived unshifted polynomials are initialized below. The non-derived ones
+                    // do need to be initialized with zeros and are fully allocated (size == num_rows).
+                    poly = is_derived ? Polynomial::create_non_parallel_zero_init(num_rows, circuit_subgroup_size)
+                                      : Polynomial{ col_nonzero_size[col_idx], circuit_subgroup_size, Polynomial::DontZeroMemory::FLAG };
+                }
             });
         }));