perf(RAM): Clear unusable caches

It is possible that the quotient domain codewords are cached for the
main table, but not for the auxiliary table. To compute the quotients,
either both or neither are needed.[^1] For peak memory consumption, it
is beneficial to clear any unused cache.

Throwing away any cache here incurs a performance penalty later, when
revealing the rows indicated by FRI. This is deemed an acceptable
tradeoff when peak memory usage is a larger issue than compute time.

[^1]: Code using exactly one cache could exist, but oh! the engineering.

triton-vm/src/stark.rs

@@ -160,6 +160,21 @@ impl Stark {
         profiler!(stop "Fiat-Shamir");
         profiler!(stop "aux tables");
 
+        // It is possible that the quotient domain codewords are cached for the main
+        // table, but not for the auxiliary table. To compute the quotients, either both
+        // or neither are needed.[^1] For peak memory consumption, it is beneficial to
+        // clear any unused cache.
+        //
+        // Throwing away any cache here incurs a performance penalty later, when
+        // revealing the rows indicated by FRI. This is deemed an acceptable tradeoff
+        // when peak memory usage is a larger issue than compute time.
+        //
+        // [^1]: Code using exactly one cache _could_ exist, but oh! the engineering.
+        if master_main_table.cache_is_empty() || master_aux_table.cache_is_empty() {
+            master_main_table.clear_cache();
+            master_aux_table.clear_cache();
+        }
+
         let (fri_domain_quotient_segment_codewords, quotient_segment_polynomials) =
             Self::compute_quotient_segments(
                 &master_main_table,

triton-vm/src/table/master_table.rs

@@ -294,8 +294,13 @@ where
         low_degree_extended_columns: Array2<Self::Field>,
     );
 
-    /// Return the cached low-degree-extended table, if any.
-    fn low_degree_extended_table(&self) -> Option<ArrayView2<Self::Field>>;
+    #[doc(hidden)]
+    fn cache_is_empty(&self) -> bool {
+        self.fri_domain_table().is_none()
+    }
+
+    #[doc(hidden)]
+    fn clear_cache(&mut self);
 
     /// Return the FRI domain view of the cached low-degree-extended table, if any.
     ///
@@ -711,9 +716,8 @@ impl MasterTable for MasterMainTable {
         self.low_degree_extended_table = Some(low_degree_extended_columns);
     }
 
-    fn low_degree_extended_table(&self) -> Option<ArrayView2<BFieldElement>> {
-        let low_degree_extended_table = self.low_degree_extended_table.as_ref()?;
-        Some(low_degree_extended_table.view())
+    fn clear_cache(&mut self) {
+        drop(self.low_degree_extended_table.take());
     }
 
     fn fri_domain_table(&self) -> Option<ArrayView2<BFieldElement>> {
@@ -784,9 +788,8 @@ impl MasterTable for MasterAuxTable {
         self.low_degree_extended_table = Some(low_degree_extended_columns);
     }
 
-    fn low_degree_extended_table(&self) -> Option<ArrayView2<XFieldElement>> {
-        let low_degree_extended_table = self.low_degree_extended_table.as_ref()?;
-        Some(low_degree_extended_table.view())
+    fn clear_cache(&mut self) {
+        drop(self.low_degree_extended_table.take());
     }
 
     fn fri_domain_table(&self) -> Option<ArrayView2<XFieldElement>> {