fix(ssa): Unused functions removals post folding constant Brillig cal…

…ls (#7265)

compiler/noirc_evaluator/src/ssa.rs

@@ -136,6 +136,9 @@ pub(crate) fn optimize_into_acir(
         print_codegen_timings: options.print_codegen_timings,
     }
     .run_pass(|ssa| ssa.fold_constants_with_brillig(&brillig), "Inlining Brillig Calls Inlining")
+    // It could happen that we inlined all calls to a given brillig function.
+    // In that case it's unused so we can remove it. This is what we check next.
+    .run_pass(Ssa::remove_unreachable_functions, "Removing Unreachable Functions (3rd)")
     .run_pass(Ssa::dead_instruction_elimination, "Dead Instruction Elimination (2nd)")
     .finish();
 

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

@@ -98,49 +98,6 @@ impl Ssa {
             function.constant_fold(false, brillig_info);
         }
 
-        // It could happen that we inlined all calls to a given brillig function.
-        // In that case it's unused so we can remove it. This is what we check next.
-        self.remove_unused_brillig_functions(brillig_functions)
-    }
-
-    fn remove_unused_brillig_functions(
-        mut self,
-        mut brillig_functions: BTreeMap<FunctionId, Function>,
-    ) -> Ssa {
-        // Remove from the above map functions that are called
-        for function in self.functions.values() {
-            for block_id in function.reachable_blocks() {
-                for instruction_id in function.dfg[block_id].instructions() {
-                    let instruction = &function.dfg[*instruction_id];
-                    let Instruction::Call { func: func_id, arguments: _ } = instruction else {
-                        continue;
-                    };
-
-                    let func_value = &function.dfg[*func_id];
-                    let Value::Function(func_id) = func_value else { continue };
-
-                    if function.runtime().is_acir() {
-                        brillig_functions.remove(func_id);
-                    }
-                }
-            }
-        }
-
-        // The ones that remain are never called: let's remove them.
-        for (func_id, func) in &brillig_functions {
-            // We never want to remove the main function (it could be `unconstrained` or it
-            // could have been turned into brillig if `--force-brillig` was given).
-            // We also don't want to remove entry points.
-            let runtime = func.runtime();
-            if self.main_id == *func_id
-                || (runtime.is_entry_point() && matches!(runtime, RuntimeType::Acir(_)))
-            {
-                continue;
-            }
-
-            self.functions.remove(func_id);
-        }
-
         self
     }
 }
@@ -1346,6 +1303,7 @@ mod test {
             }
             ";
         let ssa = ssa.fold_constants_with_brillig(&brillig);
+        let ssa = ssa.remove_unreachable_functions();
         assert_normalized_ssa_equals(ssa, expected);
     }
 
@@ -1374,6 +1332,7 @@ mod test {
             }
             ";
         let ssa = ssa.fold_constants_with_brillig(&brillig);
+        let ssa = ssa.remove_unreachable_functions();
         assert_normalized_ssa_equals(ssa, expected);
     }
 
@@ -1402,6 +1361,7 @@ mod test {
             }
             ";
         let ssa = ssa.fold_constants_with_brillig(&brillig);
+        let ssa = ssa.remove_unreachable_functions();
         assert_normalized_ssa_equals(ssa, expected);
     }
 
@@ -1431,6 +1391,7 @@ mod test {
             }
             ";
         let ssa = ssa.fold_constants_with_brillig(&brillig);
+        let ssa = ssa.remove_unreachable_functions();
         assert_normalized_ssa_equals(ssa, expected);
     }
 
@@ -1460,6 +1421,7 @@ mod test {
             }
             ";
         let ssa = ssa.fold_constants_with_brillig(&brillig);
+        let ssa = ssa.remove_unreachable_functions();
         assert_normalized_ssa_equals(ssa, expected);
     }
 
@@ -1494,6 +1456,7 @@ mod test {
             }
             ";
         let ssa = ssa.fold_constants_with_brillig(&brillig);
+        let ssa = ssa.remove_unreachable_functions();
         assert_normalized_ssa_equals(ssa, expected);
     }
 
@@ -1529,6 +1492,7 @@ mod test {
         ";
 
         let ssa = ssa.fold_constants_with_brillig(&brillig);
+        let ssa = ssa.remove_unreachable_functions();
         assert_normalized_ssa_equals(ssa, expected);
     }
 
@@ -1570,6 +1534,7 @@ mod test {
         ";
 
         let ssa = ssa.fold_constants_with_brillig(&brillig);
+        let ssa = ssa.remove_unreachable_functions();
         assert_normalized_ssa_equals(ssa, expected);
     }