Fix enzyme skipping if input ir is optimized by O2Opt (#1024)

**Context:**
Run enzyme pass if checkpoint stage is set to `O2Opt`.

Also rename the functions in the related tests to avoid race condition.

---------

Co-authored-by: Romain Moyard <[email protected]>

Author: Tzung-Han Juang

frontend/test/pytest/test_debug.py

@@ -484,45 +484,49 @@ def f(x: float):
     def test_modify_ir(self, pass_name, target, replacement):
         """Turn a square function in IRs into a cubic one."""
 
-        @qjit(keep_intermediate=True)
         def f(x):
             """Square function."""
             return x**2
 
+        f.__name__ = f.__name__ + pass_name
+
+        jit_f = qjit(f, keep_intermediate=True)
         data = 2.0
-        old_result = f(data)
-        old_ir = get_compilation_stage(f, pass_name)
-        old_workspace = str(f.workspace)
+        old_result = jit_f(data)
+        old_ir = get_compilation_stage(jit_f, pass_name)
+        old_workspace = str(jit_f.workspace)
 
         new_ir = old_ir.replace(target, replacement)
-        replace_ir(f, pass_name, new_ir)
-        new_result = f(data)
+        replace_ir(jit_f, pass_name, new_ir)
+        new_result = jit_f(data)
 
         shutil.rmtree(old_workspace, ignore_errors=True)
-        shutil.rmtree(str(f.workspace), ignore_errors=True)
+        shutil.rmtree(str(jit_f.workspace), ignore_errors=True)
         assert old_result * data == new_result
 
     @pytest.mark.parametrize("pass_name", ["HLOLoweringPass", "O2Opt", "Enzyme"])
     def test_modify_ir_file_generation(self, pass_name):
         """Test if recompilation rerun the same pass."""
 
-        @qjit
         def f(x: float):
             """Square function."""
             return x**2
 
-        grad_f = qjit(value_and_grad(f), keep_intermediate=True)
-        grad_f(3.0)
-        ir = get_compilation_stage(grad_f, pass_name)
-        old_workspace = str(grad_f.workspace)
+        f.__name__ = f.__name__ + pass_name
+
+        jit_f = qjit(f)
+        jit_grad_f = qjit(value_and_grad(jit_f), keep_intermediate=True)
+        jit_grad_f(3.0)
+        ir = get_compilation_stage(jit_grad_f, pass_name)
+        old_workspace = str(jit_grad_f.workspace)
 
-        replace_ir(grad_f, pass_name, ir)
-        grad_f(3.0)
-        file_list = os.listdir(str(grad_f.workspace))
+        replace_ir(jit_grad_f, pass_name, ir)
+        jit_grad_f(3.0)
+        file_list = os.listdir(str(jit_grad_f.workspace))
         res = [i for i in file_list if pass_name in i]
 
         shutil.rmtree(old_workspace, ignore_errors=True)
-        shutil.rmtree(str(grad_f.workspace), ignore_errors=True)
+        shutil.rmtree(str(jit_grad_f.workspace), ignore_errors=True)
         assert len(res) == 0
 
     def test_get_compilation_stage_without_keep_intermediate(self):

mlir/lib/Driver/CompilerDriver.cpp

@@ -648,7 +648,9 @@ LogicalResult QuantumDriverMain(const CompilerOptions &options, CompilerOutput &
     catalyst::utils::LinesCount::ModuleOp(*op);
     output.isCheckpointFound = options.checkpointStage == "mlir";
 
-    bool enzymeRun = false;
+    // Enzyme always happens after O2Opt. If the checkpoint is O2Opt, enzymeRun must be set to
+    // true so that the enzyme pass can be executed.
+    bool enzymeRun = options.checkpointStage == "O2Opt";
     if (op) {
         enzymeRun = containsGradients(*op);
         if (failed(runLowering(options, &ctx, *op, output))) {