chore: pull out SSA changes from sync PR (#7209)

This PR pulls out some more useful changes from the sync PR notably a
bug fix which is blocking @nventuro

noir/noir-repo/compiler/noirc_evaluator/src/ssa/ir/function_inserter.rs

@@ -16,11 +16,12 @@ pub(crate) struct FunctionInserter<'f> {
     pub(crate) function: &'f mut Function,
 
     values: HashMap<ValueId, ValueId>,
+    const_arrays: HashMap<im::Vector<ValueId>, ValueId>,
 }
 
 impl<'f> FunctionInserter<'f> {
     pub(crate) fn new(function: &'f mut Function) -> FunctionInserter<'f> {
-        Self { function, values: HashMap::default() }
+        Self { function, values: HashMap::default(), const_arrays: HashMap::default() }
     }
 
     /// Resolves a ValueId to its new, updated value.
@@ -34,10 +35,17 @@ impl<'f> FunctionInserter<'f> {
                 super::value::Value::Array { array, typ } => {
                     let array = array.clone();
                     let typ = typ.clone();
-                    let new_array = array.iter().map(|id| self.resolve(*id)).collect();
-                    let new_id = self.function.dfg.make_array(new_array, typ);
-                    self.values.insert(value, new_id);
-                    new_id
+                    let new_array: im::Vector<ValueId> =
+                        array.iter().map(|id| self.resolve(*id)).collect();
+                    if self.const_arrays.get(&new_array) == Some(&value) {
+                        value
+                    } else {
+                        let new_array_clone = new_array.clone();
+                        let new_id = self.function.dfg.make_array(new_array, typ);
+                        self.values.insert(value, new_id);
+                        self.const_arrays.insert(new_array_clone, new_id);
+                        new_id
+                    }
                 }
                 _ => value,
             },

noir/noir-repo/compiler/noirc_evaluator/src/ssa/opt/flatten_cfg.rs

@@ -375,7 +375,6 @@ impl<'f> Context<'f> {
         let old_condition = *condition;
         let then_condition = self.inserter.resolve(old_condition);
 
-        let one = FieldElement::one();
         let old_stores = std::mem::take(&mut self.store_values);
         let old_allocations = std::mem::take(&mut self.local_allocations);
         let branch = ConditionalBranch {
@@ -393,15 +392,6 @@ impl<'f> Context<'f> {
         };
         self.condition_stack.push(cond_context);
         self.insert_current_side_effects_enabled();
-        // Optimization: within the then branch we know the condition to be true, so replace
-        // any references of it within this branch with true. Likewise, do the same with false
-        // with the else branch. We must be careful not to replace the condition if it is a
-        // known constant, otherwise we can end up setting 1 = 0 or vice-versa.
-        if self.inserter.function.dfg.get_numeric_constant(old_condition).is_none() {
-            let known_value = self.inserter.function.dfg.make_constant(one, Type::bool());
-
-            self.inserter.map_value(old_condition, known_value);
-        }
         vec![self.branch_ends[if_entry], *else_destination, *then_destination]
     }
 
@@ -414,7 +404,6 @@ impl<'f> Context<'f> {
             self.insert_instruction(Instruction::Not(cond_context.condition), CallStack::new());
         let else_condition = self.link_condition(else_condition);
 
-        let zero = FieldElement::zero();
         // Make sure the else branch sees the previous values of each store
         // rather than any values created in the 'then' branch.
         let old_stores = std::mem::take(&mut cond_context.then_branch.store_values);
@@ -429,21 +418,12 @@ impl<'f> Context<'f> {
             local_allocations: old_allocations,
             last_block: *block,
         };
-        let old_condition = else_branch.old_condition;
         cond_context.then_branch.local_allocations.clear();
         cond_context.else_branch = Some(else_branch);
         self.condition_stack.push(cond_context);
 
         self.insert_current_side_effects_enabled();
-        // Optimization: within the then branch we know the condition to be true, so replace
-        // any references of it within this branch with true. Likewise, do the same with false
-        // with the else branch. We must be careful not to replace the condition if it is a
-        // known constant, otherwise we can end up setting 1 = 0 or vice-versa.
-        if self.inserter.function.dfg.get_numeric_constant(old_condition).is_none() {
-            let known_value = self.inserter.function.dfg.make_constant(zero, Type::bool());
-
-            self.inserter.map_value(old_condition, known_value);
-        }
+
         assert_eq!(self.cfg.successors(*block).len(), 1);
         vec![self.cfg.successors(*block).next().unwrap()]
     }
@@ -471,11 +451,6 @@ impl<'f> Context<'f> {
         // known to be true/false within the then/else branch respectively.
         self.insert_current_side_effects_enabled();
 
-        // We must map back to `then_condition` here. Mapping `old_condition` to itself would
-        // lose any previous mappings.
-        self.inserter
-            .map_value(cond_context.then_branch.old_condition, cond_context.then_branch.condition);
-
         // While there is a condition on the stack we don't compile outside the condition
         // until it is popped. This ensures we inline the full then and else branches
         // before continuing from the end of the conditional here where they can be merged properly.