chore: make eval_constants a pure function

compiler/noirc_evaluator/src/ssa/ir/instruction.rs

@@ -646,15 +646,11 @@
         let operand_type = dfg.type_of_value(self.lhs);
 
         if let (Some(lhs), Some(rhs)) = (lhs, rhs) {
-            // If the rhs of a division is zero, attempting to evaluate the divison will cause a compiler panic.
-            // Thus, we do not evaluate this divison as we want to avoid triggering a panic,
-            // and division by zero should be handled by laying down constraints during ACIR generation.
-            if matches!(self.operator, BinaryOp::Div | BinaryOp::Mod) && rhs == FieldElement::zero()
-            {
-                return SimplifyResult::None;
-            }
-            return match self.eval_constants(dfg, lhs, rhs, operand_type) {
-                Some(value) => SimplifyResult::SimplifiedTo(value),
+            return match eval_constant_binary_op(lhs, rhs, self.operator, operand_type) {
+                Some((result, result_type)) => {
+                    let value = dfg.make_constant(result, result_type);
+                    SimplifyResult::SimplifiedTo(value)
+                }
                 None => SimplifyResult::None,
             };
         }
@@ -775,47 +771,51 @@
         }
         SimplifyResult::None
     }
+}
 
-    /// Evaluate the two constants with the operation specified by self.operator.
-    /// Pushes the resulting value to the given DataFlowGraph's constants and returns it.
-    fn eval_constants(
-        &self,
-        dfg: &mut DataFlowGraph,
-        lhs: FieldElement,
-        rhs: FieldElement,
-        mut operand_type: Type,
-    ) -> Option<Id<Value>> {
-        let value = match &operand_type {
-            Type::Numeric(NumericType::NativeField) => {
-                self.operator.get_field_function()?(lhs, rhs)
+/// Evaluate a binary operation with constant arguments.
+fn eval_constant_binary_op(
+    lhs: FieldElement,
+    rhs: FieldElement,
+    operator: BinaryOp,
+    mut operand_type: Type,
+) -> Option<(FieldElement, Type)> {
+    let value = match &operand_type {
+        Type::Numeric(NumericType::NativeField) => {
+            // If the rhs of a division is zero, attempting to evaluate the divison will cause a compiler panic.
+            // Thus, we do not evaluate the division in this method, as we want to avoid triggering a panic,
+            // and the operation should be handled by ACIR generation.
+            if matches!(operator, BinaryOp::Div | BinaryOp::Mod) && rhs == FieldElement::zero() {
+                return None;
             }
-            Type::Numeric(NumericType::Unsigned { bit_size }) => {
-                let function = self.operator.get_u128_function();
-
-                let lhs = truncate(lhs.try_into_u128()?, *bit_size);
-                let rhs = truncate(rhs.try_into_u128()?, *bit_size);
+            operator.get_field_function()?(lhs, rhs)
+        }
+        Type::Numeric(NumericType::Unsigned { bit_size }) => {
+            let function = operator.get_u128_function();
 
-                // The divisor is being truncated into the type of the operand, which can potentially
-                // lead to the rhs being zero.
-                // If the rhs of a division is zero, attempting to evaluate the divison will cause a compiler panic.
-                // Thus, we do not evaluate the division in this method, as we want to avoid triggering a panic,
-                // and the operation should be handled by ACIR generation.
-                if matches!(self.operator, BinaryOp::Div) && rhs == 0 {
-                    return None;
-                }
+            let lhs = truncate(lhs.try_into_u128()?, *bit_size);
+            let rhs = truncate(rhs.try_into_u128()?, *bit_size);
 
-                let result = function(lhs, rhs);
-                truncate(result, *bit_size).into()
+            // The divisor is being truncated into the type of the operand, which can potentially
+            // lead to the rhs being zero.
+            // If the rhs of a division is zero, attempting to evaluate the divison will cause a compiler panic.
+            // Thus, we do not evaluate the division in this method, as we want to avoid triggering a panic,
+            // and the operation should be handled by ACIR generation.
+            if matches!(operator, BinaryOp::Div | BinaryOp::Mod) && rhs == 0 {
+                return None;
             }
-            _ => return None,
-        };
 
-        if matches!(self.operator, BinaryOp::Eq | BinaryOp::Lt) {
-            operand_type = Type::bool();
+            let result = function(lhs, rhs);
+            truncate(result, *bit_size).into()
         }
+        _ => return None,
+    };
 
-        Some(dfg.make_constant(value, operand_type))
+    if matches!(operator, BinaryOp::Eq | BinaryOp::Lt) {
+        operand_type = Type::bool();
     }
+
+    Some((value, operand_type))
 }
 
 fn truncate(int: u128, bit_size: u32) -> u128 {