From e5b981b08c2b345f00426acafe47b76d5262254d Mon Sep 17 00:00:00 2001
From: guipublic <47281315+guipublic@users.noreply.github.com>
Date: Fri, 1 Dec 2023 19:00:31 +0100
Subject: [PATCH] fix: do not simply divisions (#3664)

# Description

## Problem\*

Resolves #3607

## Summary\*
Identical divisions happening in both 'else' and 'then' should not be
simplified, because the non-taken branch will output (0,0) instead of
the division result.


## Additional Context



## Documentation\*

Check one:
- [X] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[Exceptional Case]** 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        | 6 +++++-
 .../execution_success/regression_3607/Nargo.toml          | 6 ++++++
 .../execution_success/regression_3607/Prover.toml         | 1 +
 .../execution_success/regression_3607/src/main.nr         | 8 ++++++++
 4 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 test_programs/execution_success/regression_3607/Nargo.toml
 create mode 100644 test_programs/execution_success/regression_3607/Prover.toml
 create mode 100644 test_programs/execution_success/regression_3607/src/main.nr

diff --git a/compiler/noirc_evaluator/src/ssa/ir/instruction.rs b/compiler/noirc_evaluator/src/ssa/ir/instruction.rs
index 63b32766f62..e940b719cb6 100644
--- a/compiler/noirc_evaluator/src/ssa/ir/instruction.rs
+++ b/compiler/noirc_evaluator/src/ssa/ir/instruction.rs
@@ -232,7 +232,11 @@ impl Instruction {
         use Instruction::*;
 
         match self {
-            Binary(_) | Cast(_, _) | Not(_) | ArrayGet { .. } | ArraySet { .. } => true,
+            Binary(bin) => {
+                // In ACIR, a division with a false predicate outputs (0,0), so it cannot replace another instruction unless they have the same predicate
+                bin.operator != BinaryOp::Div
+            }
+            Cast(_, _) | Not(_) | ArrayGet { .. } | ArraySet { .. } => true,
 
             // Unclear why this instruction causes problems.
             Truncate { .. } => false,
diff --git a/test_programs/execution_success/regression_3607/Nargo.toml b/test_programs/execution_success/regression_3607/Nargo.toml
new file mode 100644
index 00000000000..8757f88b90e
--- /dev/null
+++ b/test_programs/execution_success/regression_3607/Nargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "regression_3607"
+type = "bin"
+authors = [""]
+
+[dependencies]
diff --git a/test_programs/execution_success/regression_3607/Prover.toml b/test_programs/execution_success/regression_3607/Prover.toml
new file mode 100644
index 00000000000..4dd6b405159
--- /dev/null
+++ b/test_programs/execution_success/regression_3607/Prover.toml
@@ -0,0 +1 @@
+x = "1"
diff --git a/test_programs/execution_success/regression_3607/src/main.nr b/test_programs/execution_success/regression_3607/src/main.nr
new file mode 100644
index 00000000000..c09211c2810
--- /dev/null
+++ b/test_programs/execution_success/regression_3607/src/main.nr
@@ -0,0 +1,8 @@
+fn main(mut x: u32) {
+    if x == 0 {
+        x = (x+1) / x;
+    } else {
+        x = (x+1) / x;
+    }
+    assert(x != 0);
+}
\ No newline at end of file