fix: array get/set only has side effects with constant indices

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

@@ -285,9 +285,20 @@ impl Instruction {
             | Store { .. }
             | EnableSideEffects { .. }
             | IncrementRc { .. }
-            | RangeCheck { .. }
-            | ArrayGet { .. }
-            | ArraySet { .. } => true,
+            | RangeCheck { .. } => true,
+
+            ArrayGet { array, index } | ArraySet { array, index, .. } => {
+                // This is janky but we only use the side effects flag to check that we're not accessing past the end of the array
+                // unconditionally to provide a compiler error.
+                let array_len = if let Value::Array { array, .. } = &dfg[*array] {
+                    array.len() as u128
+                } else {
+                    return false;
+                };
+                let index_const = dfg.get_numeric_constant(*index);
+
+                index_const.map_or(false, |index| index.to_u128() >= array_len)
+            }
 
             // Some `Intrinsic`s have side effects so we must check what kind of `Call` this is.
             Call { func, .. } => match dfg[*func] {

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

@@ -88,7 +88,7 @@ impl Context {
             // before we insert this new instruction.
             if instruction.has_side_effects(&function.dfg) {
                 if let Some(enable_side_effects_instruction_id) =
-                    last_side_effects_enabled_instruction
+                    last_side_effects_enabled_instruction.take()
                 {
                     new_instructions.push(enable_side_effects_instruction_id);
                 }