cost_model: implement [compute_min_k]

halo2_frontend/src/dev/cost_model.rs

@@ -5,6 +5,7 @@ use std::collections::HashSet;
 use std::panic::AssertUnwindSafe;
 use std::{iter, num::ParseIntError, panic, str::FromStr};
 
+use crate::circuit::compile_circuit;
 use crate::plonk::Circuit;
 use halo2_middleware::ff::{Field, FromUniformBytes};
 use serde::Deserialize;
@@ -280,18 +281,16 @@ pub fn from_circuit_to_model_circuit<
     options.into_model_circuit::<COMM, SCALAR>(comm_scheme)
 }
 
-fn run_mock_prover_with_fallback<F: Ord + Field + FromUniformBytes<64>, C: Circuit<F>>(
-    circuit: &C,
-    instances: Vec<Vec<F>>,
-) -> MockProver<F> {
-    (5..25)
+pub fn compute_min_k<F: Ord + Field + FromUniformBytes<64>, C: Circuit<F>>(circuit: &C) -> u32 {
+    // TODO: We could optimize the order here.
+    let (_, _, cs) = (5..25)
         .find_map(|k| {
-            panic::catch_unwind(AssertUnwindSafe(|| {
-                MockProver::run(k, circuit, instances.clone()).unwrap()
-            }))
-            .ok()
+            panic::catch_unwind(AssertUnwindSafe(|| compile_circuit(k, circuit, false))).ok()
         })
         .expect("A circuit which can be implemented with at most 2^24 rows.")
+        .ok()
+        .unwrap();
+    cs.degree() as u32
 }
 
 /// Given a circuit, this function returns [CostOptions]. If no upper bound for `k` is
@@ -303,11 +302,8 @@ pub fn from_circuit_to_cost_model_options<F: Ord + Field + FromUniformBytes<64>,
 ) -> CostOptions {
     let instance_len = instances.iter().map(Vec::len).max().unwrap_or(0);
 
-    let prover = if let Some(k) = k_upper_bound {
-        MockProver::run(k, circuit, instances).unwrap()
-    } else {
-        run_mock_prover_with_fallback(circuit, instances.clone())
-    };
+    let k = k_upper_bound.unwrap_or_else(|| compute_min_k(circuit));
+    let prover = MockProver::run(k, circuit, instances).unwrap();
 
     let cs = prover.cs;