Use BaseColumnPool in CommitmentSchemeProver::commit to avoid allocation during polynomial evaluation.

Add BaseColumnPool for Col<B, BaseField> buffers, add evaluate_into to PolyOps trait
(CPU and SIMD backends), and thread the pool through commit → CommitmentTreeProver::new
→ evaluate_polynomials. Buffers are pre-taken before parallel iteration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ilyalesokhin-starkware

crates/stwo/benches/pcs.rs

@@ -9,6 +9,7 @@ use stwo::core::poly::circle::CanonicCoset;
 use stwo::core::vcs_lifted::blake2_merkle::Blake2sMerkleChannel;
 use stwo::prover::backend::simd::SimdBackend;
 use stwo::prover::backend::{BackendForChannel, CpuBackend};
+use stwo::prover::mempool::BaseColumnPool;
 use stwo::prover::poly::circle::CircleEvaluation;
 use stwo::prover::poly::twiddles::TwiddleTree;
 use stwo::prover::poly::BitReversedOrder;
@@ -35,6 +36,7 @@ fn benched_fn<B: BackendForChannel<Blake2sMerkleChannel>>(
         twiddles,
         false,
         None,
+        &mut BaseColumnPool::new(),
     );
 }
 

crates/stwo/src/core/utils.rs

@@ -1,9 +1,38 @@
 use core::iter::Peekable;
+use core::ops::{Deref, DerefMut};
 
 use std_shims::Vec;
 
 use super::fields::Field;
 
+/// An enum that either borrows mutably or owns a value.
+/// Useful when a struct can optionally receive an external `&mut T` but also needs a fallback owned
+/// instance.
+pub enum MaybeOwned<'a, T> {
+    Borrowed(&'a mut T),
+    Owned(T),
+}
+
+impl<T> Deref for MaybeOwned<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        match self {
+            MaybeOwned::Borrowed(r) => r,
+            MaybeOwned::Owned(ref v) => v,
+        }
+    }
+}
+
+impl<T> DerefMut for MaybeOwned<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        match self {
+            MaybeOwned::Borrowed(r) => r,
+            MaybeOwned::Owned(ref mut v) => v,
+        }
+    }
+}
+
 pub trait IteratorMutExt<'a, T: 'a>: Iterator<Item = &'a mut T> {
     fn assign(self, other: impl IntoIterator<Item = T>)
     where

crates/stwo/src/prover/backend/cpu/circle.rs

@@ -191,40 +191,62 @@ impl PolyOps for CpuBackend {
         poly: &CircleCoefficients<Self>,
         domain: CircleDomain,
         twiddles: &TwiddleTree<Self>,
+    ) -> CircleEvaluation<Self, BaseField, BitReversedOrder> {
+        let buffer = vec![BaseField::zero(); domain.size()];
+        Self::evaluate_into(poly, domain, twiddles, buffer)
+    }
+
+    fn evaluate_into(
+        poly: &CircleCoefficients<Self>,
+        domain: CircleDomain,
+        twiddles: &TwiddleTree<Self>,
+        mut buffer: Col<Self, BaseField>,
     ) -> CircleEvaluation<Self, BaseField, BitReversedOrder> {
         assert!(domain.half_coset.is_doubling_of(twiddles.root_coset));
+        assert_eq!(buffer.len(), domain.size());
 
-        let mut values = poly.extend(domain.log_size()).coeffs;
+        // Copy extended coefficients into the buffer.
+        let poly_len = poly.coeffs.len();
+        buffer[..poly_len].copy_from_slice(&poly.coeffs);
+        for v in &mut buffer[poly_len..] {
+            *v = BaseField::zero();
+        }
 
         if domain.log_size() == 1 {
-            let (mut v0, mut v1) = (values[0], values[1]);
+            let (mut v0, mut v1) = (buffer[0], buffer[1]);
             butterfly(&mut v0, &mut v1, domain.half_coset.initial.y);
-            return CircleEvaluation::new(domain, vec![v0, v1]);
+            buffer[0] = v0;
+            buffer[1] = v1;
+            return CircleEvaluation::new(domain, buffer);
         }
 
         if domain.log_size() == 2 {
-            let (mut v0, mut v1, mut v2, mut v3) = (values[0], values[1], values[2], values[3]);
+            let (mut v0, mut v1, mut v2, mut v3) = (buffer[0], buffer[1], buffer[2], buffer[3]);
             let CirclePoint { x, y } = domain.half_coset.initial;
             butterfly(&mut v0, &mut v2, x);
             butterfly(&mut v1, &mut v3, x);
             butterfly(&mut v0, &mut v1, y);
             butterfly(&mut v2, &mut v3, -y);
-            return CircleEvaluation::new(domain, vec![v0, v1, v2, v3]);
+            buffer[0] = v0;
+            buffer[1] = v1;
+            buffer[2] = v2;
+            buffer[3] = v3;
+            return CircleEvaluation::new(domain, buffer);
         }
 
         let line_twiddles = domain_line_twiddles_from_tree(domain, &twiddles.twiddles);
         let circle_twiddles = circle_twiddles_from_line_twiddles(line_twiddles[0]);
 
         for (layer, layer_twiddles) in line_twiddles.iter().enumerate().rev() {
             for (h, &t) in layer_twiddles.iter().enumerate() {
-                fft_layer_loop(&mut values, layer + 1, h, t, butterfly);
+                fft_layer_loop(&mut buffer, layer + 1, h, t, butterfly);
             }
         }
         for (h, t) in circle_twiddles.enumerate() {
-            fft_layer_loop(&mut values, 0, h, t, butterfly);
+            fft_layer_loop(&mut buffer, 0, h, t, butterfly);
         }
 
-        CircleEvaluation::new(domain, values)
+        CircleEvaluation::new(domain, buffer)
     }
 
     fn precompute_twiddles(coset: Coset) -> TwiddleTree<Self> {

crates/stwo/src/prover/backend/simd/circle.rs

@@ -378,6 +378,17 @@ impl PolyOps for SimdBackend {
         poly: &CircleCoefficients<Self>,
         domain: CircleDomain,
         twiddles: &TwiddleTree<Self>,
+    ) -> CircleEvaluation<Self, BaseField, BitReversedOrder> {
+        // SAFETY: evaluate_into writes all values via FFT before they are read.
+        let buffer = unsafe { Col::<Self, BaseField>::uninitialized(domain.size()) };
+        Self::evaluate_into(poly, domain, twiddles, buffer)
+    }
+
+    fn evaluate_into(
+        poly: &CircleCoefficients<Self>,
+        domain: CircleDomain,
+        twiddles: &TwiddleTree<Self>,
+        mut buffer: Col<Self, BaseField>,
     ) -> CircleEvaluation<Self, BaseField, BitReversedOrder> {
         let _span = span!(Level::TRACE, "", class = "rFFT").entered();
         let log_size = domain.log_size();
@@ -386,6 +397,7 @@ impl PolyOps for SimdBackend {
             log_size >= fft_log_size,
             "Can only evaluate on larger domains"
         );
+        assert_eq!(buffer.len(), domain.size());
 
         if fft_log_size < MIN_FFT_LOG_SIZE {
             let cpu_poly: CircleCoefficients<CpuBackend> =
@@ -399,16 +411,9 @@ impl PolyOps for SimdBackend {
 
         let twiddles = domain_line_twiddles_from_tree(domain, &twiddles.twiddles);
 
-        // Evaluate on a big domains by evaluating on several subdomains.
+        // Evaluate on big domains by evaluating on several subdomains.
         let log_subdomains = log_size - fft_log_size;
 
-        // Allocate the destination buffer without initializing.
-        let mut values = Vec::with_capacity(domain.size() >> LOG_N_LANES);
-        #[allow(clippy::uninit_vec)]
-        unsafe {
-            values.set_len(domain.size() >> LOG_N_LANES)
-        };
-
         for i in 0..(1 << log_subdomains) {
             // The subdomain twiddles are a slice of the large domain twiddles.
             let subdomain_twiddles = (0..(fft_log_size - 1))
@@ -418,12 +423,12 @@ impl PolyOps for SimdBackend {
                 })
                 .collect::<Vec<_>>();
 
-            // FFT from the coefficients buffer to the values chunk.
+            // FFT from the coefficients buffer directly into the provided buffer.
             unsafe {
                 rfft::fft(
                     transmute::<*const PackedBaseField, *const u32>(poly.coeffs.data.as_ptr()),
                     transmute::<*mut PackedBaseField, *mut u32>(
-                        values[i << (fft_log_size - LOG_N_LANES)
+                        buffer.data[i << (fft_log_size - LOG_N_LANES)
                             ..(i + 1) << (fft_log_size - LOG_N_LANES)]
                             .as_mut_ptr(),
                     ),
@@ -433,13 +438,7 @@ impl PolyOps for SimdBackend {
             }
         }
 
-        CircleEvaluation::new(
-            domain,
-            BaseColumn {
-                data: values,
-                length: domain.size(),
-            },
-        )
+        CircleEvaluation::new(domain, buffer)
     }
 
     /// Precomputes the (doubled) twiddles for a given coset tower.

crates/stwo/src/prover/mempool.rs

@@ -0,0 +1,79 @@
+//! Pre-allocated memory pools for the proving pipeline.
+//!
+//! The [`BaseColumnPool`] manages reusable [`Col<B, BaseField>`] buffers for polynomial evaluation,
+//! avoiding repeated allocation/deallocation of large column buffers during proving.
+
+use std::collections::HashMap;
+
+use crate::core::fields::m31::BaseField;
+use crate::prover::backend::{Col, Column, ColumnOps};
+
+/// A pool of pre-allocated [`Col<B, BaseField>`] buffers, organized by log_size.
+///
+/// Used to avoid repeated allocation of evaluation buffers during polynomial commitment.
+pub struct BaseColumnPool<B: ColumnOps<BaseField>> {
+    /// Map from log_size -> stack of available buffers.
+    pools: HashMap<u32, Vec<Col<B, BaseField>>>,
+}
+
+impl<B: ColumnOps<BaseField>> BaseColumnPool<B> {
+    /// Creates a new empty base column pool.
+    pub fn new() -> Self {
+        Self {
+            pools: HashMap::new(),
+        }
+    }
+
+    /// Pre-allocates `count` zero-initialized buffers of size `1 << log_size`.
+    pub fn reserve(&mut self, log_size: u32, count: usize) {
+        let pool = self.pools.entry(log_size).or_default();
+        for _ in 0..count {
+            pool.push(Col::<B, BaseField>::zeros(1 << log_size));
+        }
+    }
+
+    /// Takes a buffer from the pool for the given `log_size`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if no buffer of the requested size is available.
+    pub fn take(&mut self, log_size: u32) -> Col<B, BaseField> {
+        self.pools
+            .get_mut(&log_size)
+            .and_then(|pool| pool.pop())
+            .unwrap_or_else(|| {
+                panic!("BaseColumnPool: no buffer available for log_size={log_size}")
+            })
+    }
+
+    /// Takes a buffer from the pool, or allocates a new zero-initialized one if none is available.
+    pub fn take_or_alloc(&mut self, log_size: u32) -> Col<B, BaseField> {
+        self.pools
+            .get_mut(&log_size)
+            .and_then(|pool| pool.pop())
+            .unwrap_or_else(|| unsafe { Col::<B, BaseField>::uninitialized(1 << log_size) })
+    }
+
+    /// Returns a buffer to the pool. The caller is responsible for ensuring the buffer's log_size
+    /// matches.
+    pub fn give_back(&mut self, log_size: u32, buf: Col<B, BaseField>) {
+        debug_assert_eq!(buf.len(), 1 << log_size);
+        self.pools.entry(log_size).or_default().push(buf);
+    }
+
+    /// Returns the number of available buffers for a given log_size.
+    pub fn available(&self, log_size: u32) -> usize {
+        self.pools.get(&log_size).map_or(0, |pool| pool.len())
+    }
+
+    /// Returns the total number of buffers across all sizes.
+    pub fn total_available(&self) -> usize {
+        self.pools.values().map(|pool| pool.len()).sum()
+    }
+}
+
+impl<B: ColumnOps<BaseField>> Default for BaseColumnPool<B> {
+    fn default() -> Self {
+        Self::new()
+    }
+}

crates/stwo/src/prover/mod.rs

@@ -20,6 +20,7 @@ pub mod channel;
 pub mod fri;
 pub mod line;
 pub mod lookups;
+pub mod mempool;
 pub mod poly;
 pub mod secure_column;
 pub mod vcs;

crates/stwo/src/prover/pcs/mod.rs

@@ -20,6 +20,8 @@ use crate::core::ColumnVec;
 use crate::prover::air::component_prover::{Poly, Trace, WeightsHashMap};
 use crate::prover::backend::{BackendForChannel, Col};
 use crate::prover::fri::{FriDecommitResult, FriProver};
+use crate::core::utils::MaybeOwned;
+use crate::prover::mempool::BaseColumnPool;
 use crate::prover::pcs::quotient_ops::compute_fri_quotients;
 use crate::prover::poly::circle::{CircleCoefficients, CircleEvaluation};
 use crate::prover::poly::twiddles::TwiddleTree;
@@ -34,6 +36,8 @@ pub struct CommitmentSchemeProver<'a, B: BackendForChannel<MC>, MC: MerkleChanne
     pub config: PcsConfig,
     twiddles: &'a TwiddleTree<B>,
     pub store_polynomials_coefficients: bool,
+    /// Pre-allocated base field column pool for polynomial evaluation during commit.
+    pub base_column_pool: MaybeOwned<'a, BaseColumnPool<B>>,
 }
 impl<'a, B: BackendForChannel<MC>, MC: MerkleChannel> CommitmentSchemeProver<'a, B, MC> {
     /// Creates a new empty commitment scheme prover with the given configuration and twiddles. The
@@ -44,6 +48,21 @@ impl<'a, B: BackendForChannel<MC>, MC: MerkleChannel> CommitmentSchemeProver<'a,
             config,
             twiddles,
             store_polynomials_coefficients: false,
+            base_column_pool: MaybeOwned::Owned(BaseColumnPool::new()),
+        }
+    }
+
+    pub fn with_memory_pool(
+        config: PcsConfig,
+        twiddles: &'a TwiddleTree<B>,
+        base_column_pool: &'a mut BaseColumnPool<B>,
+    ) -> Self {
+        CommitmentSchemeProver {
+            trees: TreeVec::default(),
+            config,
+            twiddles,
+            store_polynomials_coefficients: false,
+            base_column_pool: MaybeOwned::Borrowed(base_column_pool),
         }
     }
 
@@ -62,6 +81,7 @@ impl<'a, B: BackendForChannel<MC>, MC: MerkleChannel> CommitmentSchemeProver<'a,
             self.twiddles,
             self.store_polynomials_coefficients,
             self.config.lifting_log_size,
+            &mut self.base_column_pool,
         );
         self.trees.push(tree);
     }
@@ -319,13 +339,15 @@ impl<B: BackendForChannel<MC>, MC: MerkleChannel> CommitmentTreeProver<B, MC> {
         twiddles: &TwiddleTree<B>,
         store_polynomials_coefficients: bool,
         lifting_log_size: Option<u32>,
+        base_column_pool: &mut BaseColumnPool<B>,
     ) -> Self {
         let span = span!(Level::INFO, "Extension").entered();
         let polynomials = B::evaluate_polynomials(
             polynomials,
             log_blowup_factor,
             twiddles,
             store_polynomials_coefficients,
+            base_column_pool,
         );
         span.exit();