Add SimplificationCache

compiler/noirc_evaluator/src/ssa/opt/constant_folding.rs

@@ -160,6 +160,9 @@ impl Function {
     }
 }
 
+/// `ValueId` in an `EnableConstraintsIf` instruction.
+type Predicate = ValueId;
+
 struct Context<'a> {
     use_constraint_info: bool,
     brillig_info: Option<BrilligInfo<'a>>,
@@ -174,7 +177,7 @@ struct Context<'a> {
     /// We partition the maps of constrained values according to the side-effects flag at the point
     /// at which the values are constrained. This prevents constraints which are only sometimes enforced
     /// being used to modify the rest of the program.
-    constraint_simplification_mappings: HashMap<ValueId, HashMap<ValueId, ValueId>>,
+    constraint_simplification_mappings: ConstraitSimplificationCache,
 
     // Cache of instructions without any side-effects along with their outputs.
     cached_instruction_results: InstructionResultCache,
@@ -188,12 +191,39 @@ pub(crate) struct BrilligInfo<'a> {
     brillig_functions: &'a BTreeMap<FunctionId, Function>,
 }
 
+struct SimplificationCache {
+    simplified: ValueId,
+    blocks: HashSet<BasicBlockId>,
+}
+
+impl SimplificationCache {
+    fn new(simplified: ValueId) -> Self {
+        Self { simplified, blocks: Default::default() }
+    }
+    fn merge(&mut self, dfg: &DataFlowGraph, other: ValueId, block: BasicBlockId) {
+        if self.simplified == other {
+            self.blocks.insert(block);
+        } else {
+            match simplify(dfg, self.simplified, other) {
+                Some((complex, simple)) if self.simplified == complex => {
+                    self.simplified = simple;
+                    self.blocks.clear();
+                    self.blocks.insert(block);
+                }
+                _ => {}
+            }
+        }
+    }
+}
+
+type ConstraitSimplificationCache = HashMap<Predicate, HashMap<ValueId, SimplificationCache>>;
+
 /// HashMap from (Instruction, side_effects_enabled_var) to the results of the instruction.
 /// Stored as a two-level map to avoid cloning Instructions during the `.get` call.
 ///
 /// In addition to each result, the original BasicBlockId is stored as well. This allows us
 /// to deduplicate instructions across blocks as long as the new block dominates the original.
-type InstructionResultCache = HashMap<Instruction, HashMap<Option<ValueId>, ResultCache>>;
+type InstructionResultCache = HashMap<Instruction, HashMap<Option<Predicate>, ResultCache>>;
 
 /// Records the results of all duplicate [`Instruction`]s along with the blocks in which they sit.
 ///
@@ -308,7 +338,7 @@ impl<'brillig> Context<'brillig> {
     fn resolve_instruction(
         instruction_id: InstructionId,
         dfg: &DataFlowGraph,
-        constraint_simplification_mapping: &HashMap<ValueId, ValueId>,
+        constraint_simplification_mapping: &HashMap<ValueId, SimplificationCache>,
     ) -> Instruction {
         let instruction = dfg[instruction_id].clone();
 
@@ -319,12 +349,12 @@ impl<'brillig> Context<'brillig> {
         // constraints to the cache.
         fn resolve_cache(
             dfg: &DataFlowGraph,
-            cache: &HashMap<ValueId, ValueId>,
+            cache: &HashMap<ValueId, SimplificationCache>,
             value_id: ValueId,
         ) -> ValueId {
             let resolved_id = dfg.resolve(value_id);
             match cache.get(&resolved_id) {
-                Some(cached_value) => resolve_cache(dfg, cache, *cached_value),
+                Some(cached_value) => resolve_cache(dfg, cache, cached_value.simplified),
                 None => resolved_id,
             }
         }
@@ -378,7 +408,10 @@ impl<'brillig> Context<'brillig> {
             if let Instruction::Constrain(lhs, rhs, _) = instruction {
                 // These `ValueId`s should be fully resolved now.
                 if let Some((complex, simple)) = simplify(dfg, lhs, rhs) {
-                    self.get_constraint_map(side_effects_enabled_var).insert(complex, simple);
+                    self.get_constraint_map(side_effects_enabled_var)
+                        .entry(complex)
+                        .or_insert_with(|| SimplificationCache::new(simple))
+                        .merge(dfg, simple, block);
                 }
             }
         }
@@ -402,7 +435,7 @@ impl<'brillig> Context<'brillig> {
     fn get_constraint_map(
         &mut self,
         side_effects_enabled_var: ValueId,
-    ) -> &mut HashMap<ValueId, ValueId> {
+    ) -> &mut HashMap<ValueId, SimplificationCache> {
         self.constraint_simplification_mappings.entry(side_effects_enabled_var).or_default()
     }