fix: use predicate for curve operations (#5076)

# Description

## Problem\*

Resolves #5045

## Summary\*
use predicate to set is_infinite to true when side_effects are disabled,
to ensure that the curve operation will not fail.


## Additional Context



## Documentation\*

Check one:
- [X] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [X] I have tested the changes locally.
- [X] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

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

@@ -123,7 +123,12 @@ impl Intrinsic {
             | Intrinsic::IsUnconstrained => false,
 
             // Some black box functions have side-effects
-            Intrinsic::BlackBox(func) => matches!(func, BlackBoxFunc::RecursiveAggregation),
+            Intrinsic::BlackBox(func) => matches!(
+                func,
+                BlackBoxFunc::RecursiveAggregation
+                    | BlackBoxFunc::MultiScalarMul
+                    | BlackBoxFunc::EmbeddedCurveAdd
+            ),
         }
     }
 
@@ -340,6 +345,9 @@ impl Instruction {
 
             // Some `Intrinsic`s have side effects so we must check what kind of `Call` this is.
             Call { func, .. } => match dfg[*func] {
+                // Explicitly allows removal of unused ec operations, even if they can fail
+                Value::Intrinsic(Intrinsic::BlackBox(BlackBoxFunc::MultiScalarMul))
+                | Value::Intrinsic(Intrinsic::BlackBox(BlackBoxFunc::EmbeddedCurveAdd)) => true,
                 Value::Intrinsic(intrinsic) => !intrinsic.has_side_effects(),
 
                 // All foreign functions are treated as having side effects.

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

@@ -134,7 +134,7 @@
 use fxhash::FxHashMap as HashMap;
 use std::collections::{BTreeMap, HashSet};
 
-use acvm::{acir::AcirField, FieldElement};
+use acvm::{acir::AcirField, acir::BlackBoxFunc, FieldElement};
 use iter_extended::vecmap;
 
 use crate::ssa::{
@@ -769,7 +769,38 @@ impl<'f> Context<'f> {
 
                         Instruction::Call { func, arguments }
                     }
+                    //Issue #5045: We set curve points to infinity if condition is false
+                    Value::Intrinsic(Intrinsic::BlackBox(BlackBoxFunc::EmbeddedCurveAdd)) => {
+                        arguments[2] = self.var_or_one(arguments[2], condition, call_stack.clone());
+                        arguments[5] = self.var_or_one(arguments[5], condition, call_stack.clone());
 
+                        Instruction::Call { func, arguments }
+                    }
+                    Value::Intrinsic(Intrinsic::BlackBox(BlackBoxFunc::MultiScalarMul)) => {
+                        let mut array_with_predicate = im::Vector::new();
+                        let array_typ;
+                        if let Value::Array { array, typ } =
+                            &self.inserter.function.dfg[arguments[0]]
+                        {
+                            array_typ = typ.clone();
+                            for (i, value) in array.clone().iter().enumerate() {
+                                if i % 3 == 2 {
+                                    array_with_predicate.push_back(self.var_or_one(
+                                        *value,
+                                        condition,
+                                        call_stack.clone(),
+                                    ));
+                                } else {
+                                    array_with_predicate.push_back(*value);
+                                }
+                            }
+                        } else {
+                            unreachable!();
+                        }
+                        arguments[0] =
+                            self.inserter.function.dfg.make_array(array_with_predicate, array_typ);
+                        Instruction::Call { func, arguments }
+                    }
                     _ => Instruction::Call { func, arguments },
                 },
                 other => other,
@@ -779,6 +810,20 @@ impl<'f> Context<'f> {
         }
     }
 
+    // Computes: if condition { var } else { 1 }
+    fn var_or_one(&mut self, var: ValueId, condition: ValueId, call_stack: CallStack) -> ValueId {
+        let field = self.insert_instruction(
+            Instruction::binary(BinaryOp::Mul, var, condition),
+            call_stack.clone(),
+        );
+        let not_condition =
+            self.insert_instruction(Instruction::Not(condition), call_stack.clone());
+        self.insert_instruction(
+            Instruction::binary(BinaryOp::Add, field, not_condition),
+            call_stack,
+        )
+    }
+
     fn undo_stores_in_then_branch(&mut self, store_values: &HashMap<ValueId, Store>) {
         for (address, store) in store_values {
             let address = *address;

test_programs/execution_success/regression_5045/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "regression_5045"
+version = "0.1.0"
+type = "bin"
+authors = [""]
+
+[dependencies]

test_programs/execution_success/regression_5045/Prover.toml

@@ -0,0 +1 @@
+is_active = false

test_programs/execution_success/regression_5045/src/main.nr

@@ -0,0 +1,20 @@
+use dep::std::embedded_curve_ops::EmbeddedCurvePoint;
+use dep::std::embedded_curve_ops::EmbeddedCurveScalar;
+
+fn main(is_active: bool) {
+    let a = EmbeddedCurvePoint {
+        x: 0x1d8eb4378a3bde41e0b6a9a8dcbd21b7ff9c51bdd6ca13ce989abbbf90df3666,
+        y: 0x06075b63354f2504f9cddba0b94ed0cef35fc88615e69ec1f853b51eb79a24a0,
+        is_infinite: false
+    };
+
+    if is_active {
+        let bad = EmbeddedCurvePoint { x: 0, y: 5, is_infinite: false };
+        let d = bad.double();
+        let e = dep::std::embedded_curve_ops::multi_scalar_mul(
+            [a, bad],
+            [EmbeddedCurveScalar { lo: 1, hi: 0 }, EmbeddedCurveScalar { lo: 1, hi: 0 }]
+        );
+        assert(e[0] != d.x);
+    }
+}