fix: ensure that purity analysis pass explores all functions

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

@@ -49,10 +49,23 @@ impl Ssa {
             function.dfg.set_function_purities(purities.clone());
         }
 
+        debug_assert!(purity_analysis_post_check(&self));
+
         self
     }
 }
 
+/// Post-check condition for [Function::remove_bit_shifts].
+///
+/// Returns `true` if:
+///   - all functions have a purity status attached to it.
+///
+/// Otherwise returns `false`.
+fn purity_analysis_post_check(ssa: &Ssa) -> bool {
+    // TODO: We have N different copies of the purity hashmap (one per function), ideally this would be deduplicated.
+    ssa.functions.iter().all(|(id, function)| function.dfg.purity_of(*id).is_some())
+}
+
 pub(crate) type FunctionPurities = HashMap<FunctionId, Purity>;
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]

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

@@ -79,6 +79,8 @@ impl Function {
 
             context.replace_value(old_result, new_result);
         });
+
+        debug_assert!(remove_bit_shifts_post_check(self));
     }
 }
 
@@ -343,6 +345,35 @@ impl Context<'_, '_, '_> {
     }
 }
 
+/// Post-check condition for [Function::remove_bit_shifts].
+///
+/// Returns `true` if:
+///   - `func` is not an ACIR function, OR
+///   - `func` does not contain any bitshift instructions.
+///
+/// Otherwise returns `false`.
+fn remove_bit_shifts_post_check(func: &Function) -> bool {
+    // Non-ACIR functions should be unaffected.
+    if !func.runtime().is_acir() {
+        return true;
+    }
+
+    // Otherwise there should be no shift-left or shift-right instructions in any reachable block.
+    for block_id in func.reachable_blocks() {
+        let instruction_ids = func.dfg[block_id].instructions();
+        for instruction_id in instruction_ids {
+            if matches!(
+                func.dfg[*instruction_id],
+                Instruction::Binary(Binary { operator: BinaryOp::Shl | BinaryOp::Shr, .. })
+            ) {
+                return false;
+            }
+        }
+    }
+
+    true
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{assert_ssa_snapshot, ssa::ssa_gen::Ssa};

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

@@ -43,6 +43,7 @@ impl Function {
         } else {
             Context::default().remove_if_else(self);
         }
+        debug_assert!(remove_if_else_post_check(self));
     }
 }
 
@@ -224,6 +225,32 @@ fn slice_capacity_change(
     }
 }
 
+/// Post-check condition for [Function::remove_if_else].
+///
+/// Returns `true` if:
+///   - `func` is a Brillig function, OR
+///   - `func` does not contain any if-else instructions.
+///
+/// Otherwise returns `false`.
+fn remove_if_else_post_check(func: &Function) -> bool {
+    // Brillig functions should be unaffected.
+    if func.runtime().is_brillig() {
+        return true;
+    }
+
+    // Otherwise there should be no shift-left or shift-right instructions in any reachable block.
+    for block_id in func.reachable_blocks() {
+        let instruction_ids = func.dfg[block_id].instructions();
+        for instruction_id in instruction_ids {
+            if matches!(func.dfg[*instruction_id], Instruction::IfElse { .. }) {
+                return false;
+            }
+        }
+    }
+
+    true
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{assert_ssa_snapshot, ssa::ssa_gen::Ssa};