Expand cases for generating a witness in prepare inputs (#452)

* preliminary debugging and testing

* more preliminary debugging for prepare_inputs method

* more debugging prints

* add wnew witness for gadget inputs that are set based upon instructions

* working evaluation when inputs to gadget are from aan if statement

* clean up syntax and minor changes from PR review

crates/nargo/tests/test_data/scalar_mul/Prover.toml

@@ -1,3 +1,7 @@
 a = "1"
-pub_x = "0x0000000000000000000000000000000000000000000000000000000000000001"
-pub_y = "0x0000000000000002cf135e7506a45d632d270d45f1181294833fc48d823f272c"
+a_pub_x = "0x0000000000000000000000000000000000000000000000000000000000000001"
+a_pub_y = "0x0000000000000002cf135e7506a45d632d270d45f1181294833fc48d823f272c"
+
+b = "2"
+b_pub_x = "0x06ce1b0827aafa85ddeb49cdaa36306d19a74caa311e13d46d8bc688cdbffffe"
+b_pub_y = "0x1c122f81a3a14964909ede0ba2a6855fc93faf6fa1a788bf467be7e7a43f80ac"

crates/nargo/tests/test_data/scalar_mul/src/main.nr

@@ -1,7 +1,22 @@
 use dep::std;
 
-fn main(a: Field, pub_x: pub Field, pub_y: pub Field) {
-     let res = std::scalar_mul::fixed_base(a);
+fn main(
+     a: Field, 
+     a_pub_x: pub Field, 
+     a_pub_y: pub Field,
+     b: Field,
+     b_pub_x: pub Field,
+     b_pub_y: pub Field
+) {
+     let mut priv_key = a;
+     let mut pub_x: Field = a_pub_x;
+     let mut pub_y: Field = a_pub_y;
+     if a != 1 { // Change `a` in Prover.toml to test input `b`
+          priv_key = b;
+          pub_x = b_pub_x;
+          pub_y = b_pub_y;
+     }
+     let res = std::scalar_mul::fixed_base(priv_key);
      constrain res[0] == pub_x;
      constrain res[1] == pub_y;
 }

crates/noirc_evaluator/src/ssa/acir_gen.rs

@@ -526,11 +526,10 @@ impl Acir {
                 }
                 _ => {
                     if self.arith_cache.contains_key(a) {
-                        if let Some(w) = self.arith_cache[a].clone().witness {
-                            inputs.push(GadgetInput { witness: w, num_bits: l_obj.size_in_bits() });
-                        } else {
-                            todo!();
-                        }
+                        let var = self.arith_cache[a].clone();
+                        let witness =
+                            var.witness.unwrap_or_else(|| generate_witness(&var, evaluator));
+                        inputs.push(GadgetInput { witness, num_bits: l_obj.size_in_bits() });
                     } else {
                         dbg!(&l_obj);
                         unreachable!("invalid input")

crates/noirc_evaluator/src/ssa/node.rs

@@ -736,7 +736,6 @@ impl Binary {
 
         let l_is_zero = lhs.map_or(false, |x| x.is_zero());
         let r_is_zero = rhs.map_or(false, |x| x.is_zero());
-
         match &self.operator {
             BinaryOp::Add | BinaryOp::SafeAdd => {
                 if l_is_zero {