fix: maintain correct type when simplifying x ^ x

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

@@ -1002,7 +1002,7 @@ impl Binary {
                     return SimplifyResult::SimplifiedTo(self.lhs);
                 }
                 if dfg.resolve(self.lhs) == dfg.resolve(self.rhs) {
-                    let zero = dfg.make_constant(FieldElement::zero(), Type::bool());
+                    let zero = dfg.make_constant(FieldElement::zero(), operand_type);
                     return SimplifyResult::SimplifiedTo(zero);
                 }
             }

test_programs/noir_test_success/regression_4080/Nargo.toml

@@ -0,0 +1,5 @@
+[package]
+name = "regression_4080"
+type = "bin"
+authors = [""]
+[dependencies]

test_programs/noir_test_success/regression_4080/Prover.toml

@@ -0,0 +1 @@
+x = "5"

test_programs/noir_test_success/regression_4080/src/main.nr

@@ -0,0 +1,8 @@
+// This test checks that `var^var` is assigned the correct type.
+// https://github.com/noir-lang/noir/issues/4080
+
+#[test(should_fail_with = "attempt to add with overflow")]
+fn main() {
+    let var1: u8 = ((255 + 1) ^ (255 + 1)) - ((255 + 1) - (255 + 1));
+    assert_eq(var1, 0);
+}