perf(stark): deduplicate LdeTwiddles by domain size in multi_prove

Tables sharing the same lde_size now reuse a single Arc<LdeTwiddles>
instead of each allocating their own copy. This avoids redundant twiddle
computation and allocation when multiple tables happen to have the same
trace length (e.g., all 2^19-row tables after the cap change).

Author: diegokingston

crypto/stark/src/prover.rs

@@ -635,7 +635,7 @@ pub trait IsStarkProver<
         air_trace_pairs: &[AirTracePair<'_, Field, FieldExtension, PI>],
         metadatas: &[Round1Metadata<Field, FieldExtension>],
         domains: &[Domain<Field>],
-        twiddle_caches: &[LdeTwiddles<Field>],
+        twiddle_caches: &[Arc<LdeTwiddles<Field>>],
         main_pool: &mut [Vec<FieldElement<Field>>],
         aux_pool: &mut [Vec<FieldElement<FieldExtension>>],
     ) where
@@ -651,7 +651,13 @@ pub trait IsStarkProver<
             .zip(domains.iter().zip(twiddle_caches.iter()))
         {
             let result = Self::reconstruct_round1(
-                *air, *trace, domain, metadata, twiddles, main_pool, aux_pool,
+                *air,
+                *trace,
+                domain,
+                metadata,
+                &**twiddles,
+                main_pool,
+                aux_pool,
             )
             .expect("reconstruct_round1 failed in debug-checks");
             temp_results.push(result);
@@ -1512,24 +1518,42 @@ pub trait IsStarkProver<
         let phase_start = Instant::now();
 
         let mut domains = Vec::with_capacity(num_airs);
-        let mut twiddle_caches: Vec<LdeTwiddles<Field>> = Vec::with_capacity(num_airs);
+        let mut twiddle_caches: Vec<Arc<LdeTwiddles<Field>>> = Vec::with_capacity(num_airs);
         let mut max_main_cols = 0usize;
         let mut max_aux_cols = 0usize;
         let mut max_lde_size = 0usize;
 
+        // Deduplicate twiddle caches: tables with identical domain parameters share one Arc.
+        // Key on (interpolation_domain_size, blowup_factor, coset_offset_bytes) because each
+        // affects the twiddle values: interpolation_domain_size sizes `inv` and `coset_weights`,
+        // blowup_factor sizes `fwd`, and coset_offset sets `coset_weights` values.
+        // coset_offset is serialized via AsBytes since FieldElement<F> does not impl Hash without
+        // a BaseType: Hash bound.
+        let mut twiddle_by_domain: std::collections::HashMap<
+            (usize, usize, Vec<u8>),
+            Arc<LdeTwiddles<Field>>,
+        > = std::collections::HashMap::new();
+
         for (air, trace, _pub_inputs) in &*air_trace_pairs {
             let trace_length = trace.num_rows();
             let domain = new_domain(*air, trace_length);
 
             let lde_size = domain.interpolation_domain_size * domain.blowup_factor;
-            let twiddles = LdeTwiddles::new(&domain);
+            let key = (
+                domain.interpolation_domain_size,
+                domain.blowup_factor,
+                domain.coset_offset.as_bytes(),
+            );
+            let twiddles = twiddle_by_domain
+                .entry(key)
+                .or_insert_with(|| Arc::new(LdeTwiddles::new(&domain)));
 
             max_main_cols = max_main_cols.max(trace.num_main_columns);
             max_aux_cols = max_aux_cols.max(air.num_auxiliary_rap_columns());
             max_lde_size = max_lde_size.max(lde_size);
 
             domains.push(domain);
-            twiddle_caches.push(twiddles);
+            twiddle_caches.push(Arc::clone(twiddles));
         }
 
         // Allocate K independent LDE column buffer pool sets for parallel table processing.
@@ -1573,7 +1597,7 @@ pub trait IsStarkProver<
                     let idx = chunk_start + j;
                     let (air, trace, _) = &air_trace_pairs[idx];
                     let domain = &domains[idx];
-                    let twiddles = &twiddle_caches[idx];
+                    let twiddles = &*twiddle_caches[idx];
 
                     if air.is_preprocessed() {
                         Self::commit_preprocessed_trace(
@@ -1693,7 +1717,7 @@ pub trait IsStarkProver<
                     let idx = chunk_start + j;
                     let (air, trace, _) = &air_trace_pairs[idx];
                     let domain = &domains[idx];
-                    let twiddles = &twiddle_caches[idx];
+                    let twiddles = &*twiddle_caches[idx];
 
                     if air.has_aux_trace() {
                         let num_aux_cols = trace.num_aux_columns;
@@ -1809,7 +1833,7 @@ pub trait IsStarkProver<
                     let (air, trace, pub_inputs) = &air_trace_pairs[idx];
                     let metadata = &metadatas[idx];
                     let domain = &domains[idx];
-                    let twiddles = &twiddle_caches[idx];
+                    let twiddles = &*twiddle_caches[idx];
 
                     #[cfg(feature = "instruments")]
                     let table_start = Instant::now();