fix: Divide by zero should fail to satisfy constraints for Field an…

…d ints (#2475)

crates/nargo_cli/tests/compile_failure/div_by_zero_constants/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "divide_by_zero"
+type = "bin"
+authors = [""]
+compiler_version = "0.10.3"
+
+[dependencies]

crates/nargo_cli/tests/compile_failure/div_by_zero_constants/src/main.nr

@@ -0,0 +1,6 @@
+use dep::std;
+
+fn main() {
+    let a: Field = 3 / 0;
+    std::println(a);
+}

crates/nargo_cli/tests/compile_failure/div_by_zero_numerator_witness/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "div_by_zero_numerator_witness"
+type = "bin"
+authors = [""]
+compiler_version = "0.10.3"
+
+[dependencies]

crates/nargo_cli/tests/compile_failure/div_by_zero_numerator_witness/Prover.toml

@@ -0,0 +1 @@
+x = "3"

crates/nargo_cli/tests/compile_failure/div_by_zero_numerator_witness/src/main.nr

@@ -0,0 +1,6 @@
+use dep::std;
+
+fn main(x: Field) {
+    let a: Field = x / 0;
+    std::println(a);
+}

crates/nargo_cli/tests/compile_failure/div_by_zero_witness/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "div_by_zero_witness"
+type = "bin"
+authors = [""]
+compiler_version = "0.10.3"
+
+[dependencies]

crates/nargo_cli/tests/compile_failure/div_by_zero_witness/Prover.toml

@@ -0,0 +1,2 @@
+x = "3"
+y = "0"

crates/nargo_cli/tests/compile_failure/div_by_zero_witness/src/main.nr

@@ -0,0 +1,7 @@
+use dep::std;
+
+// It is expected that `y` must be equal to 0.
+fn main(x : Field, y : pub Field) {
+    let a: Field = x / y;
+    std::println(a);
+}

crates/noirc_evaluator/src/ssa/acir_gen/acir_ir/acir_variable.rs

@@ -284,8 +284,14 @@ impl AcirContext {
         let var_data = &self.vars[&var];
         if let AcirVarData::Const(constant) = var_data {
             // Note that this will return a 0 if the inverse is not available
-            let result_var = self.add_data(AcirVarData::Const(constant.inverse()));
-            return Ok(result_var);
+            let inverted_var = self.add_data(AcirVarData::Const(constant.inverse()));
+
+            // Check that the inverted var is valid.
+            // This check prevents invalid divisons by zero.
+            let should_be_one = self.mul_var(inverted_var, var)?;
+            self.maybe_eq_predicate(should_be_one, predicate)?;
+
+            return Ok(inverted_var);
         }
 
         // Compute the inverse with brillig code
@@ -300,6 +306,8 @@ impl AcirContext {
         )?;
         let inverted_var = Self::expect_one_var(results);
 
+        // Check that the inverted var is valid.
+        // This check prevents invalid divisons by zero.
         let should_be_one = self.mul_var(inverted_var, var)?;
         self.maybe_eq_predicate(should_be_one, predicate)?;
 

crates/noirc_evaluator/src/ssa/acir_gen/acir_ir/generated_acir.rs

@@ -467,6 +467,16 @@ impl GeneratedAcir {
         //
         // If predicate is zero, `q_witness` and `r_witness` will be 0
 
+        // Check that we the rhs is not zero.
+        // Otherwise, when executing the brillig quotient we may attempt to divide by zero, causing a VM panic.
+        //
+        // When the predicate is 0, the equation always passes.
+        // When the predicate is 1, the rhs must not be 0.
+        let rhs_is_zero = self.is_equal(&Expression::zero(), rhs);
+        let rhs_is_not_zero = &self.mul_with_witness(&rhs_is_zero.into(), predicate)
+            - &self.mul_with_witness(&Expression::zero(), predicate);
+        self.push_opcode(AcirOpcode::Arithmetic(rhs_is_not_zero));
+
         // maximum bit size for q and for [r and rhs]
         let mut max_q_bits = max_bit_size;
         let mut max_rhs_bits = max_bit_size;

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

@@ -609,6 +609,12 @@ impl Binary {
         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 a division by zero
+            // should fail to satisfy constraints laid down during ACIR generation.
+            if matches!(self.operator, BinaryOp::Div) && rhs == FieldElement::zero() {
+                return SimplifyResult::None;
+            }
             return match self.eval_constants(dfg, lhs, rhs, operand_type) {
                 Some(value) => SimplifyResult::SimplifiedTo(value),
                 None => SimplifyResult::None,