Add benchmark test for FusionRewriter

tests/tensor/rewriting/test_elemwise.py

@@ -48,7 +48,7 @@ from pytensor.tensor.math import round as at_round
 from pytensor.tensor.math import sin, sinh, sqr, sqrt
 from pytensor.tensor.math import sum as at_sum
 from pytensor.tensor.math import tan, tanh, true_div, xor
-from pytensor.tensor.rewriting.elemwise import local_dimshuffle_lift
+from pytensor.tensor.rewriting.elemwise import FusionOptimizer, local_dimshuffle_lift
 from pytensor.tensor.rewriting.shape import local_useless_dimshuffle_in_reshape
 from pytensor.tensor.shape import reshape
 from pytensor.tensor.type import (
@@ -302,6 +302,29 @@ class TestFusion:
     fwx = fw + fx
     ftanx = tan(fx)
 
+    def large_fuseable_graph(self, n):
+        factors = []
+        sd = dscalar()
+        means = dvector()
+
+        cst_05 = at.constant(0.5)
+        cst_m05 = at.constant(-0.5)
+        cst_2 = at.constant(2)
+        cst_m2 = at.constant(-2)
+        ones = at.constant(np.ones(10))
+
+        for i in range(n):
+            f = cst_m05 * sd**cst_m2 * (ones - means[i]) ** cst_2 + cst_05 * log(
+                cst_05 * (sd**cst_m2) / np.pi
+            )
+            factors.append(at_sum(f))
+
+        logp = add(*factors)
+
+        vars = [sd, means]
+        dlogp = [pytensor.grad(logp, v) for v in vars]
+        return vars, dlogp
+
     @pytest.mark.parametrize(
         "case",
         [
@@ -1059,35 +1082,9 @@ class TestFusion:
 
     @pytest.mark.skipif(not config.cxx, reason="No cxx compiler")
     def test_big_fusion(self):
-        # In the past, pickle of Composite generated in that case
-        # crashed with max recursion limit. So we were not able to
-        # generate C code in that case.
-        factors = []
-        sd = dscalar()
-        means = dvector()
-
-        cst_05 = at.constant(0.5)
-        cst_m05 = at.constant(-0.5)
-        cst_2 = at.constant(2)
-        cst_m2 = at.constant(-2)
-        ones = at.constant(np.ones(10))
-        n = 85
-        if config.mode in ["DebugMode", "DEBUG_MODE"]:
-            n = 10
-
-        for i in range(n):
-            f = cst_m05 * sd**cst_m2 * (ones - means[i]) ** cst_2 + cst_05 * log(
-                cst_05 * (sd**cst_m2) / np.pi
-            )
-            factors.append(at_sum(f))
-
-        logp = add(*factors)
-
-        vars = [sd, means]
-
         # Make sure that C compilation is used
         mode = Mode("cvm", self.rewrites)
-        dlogp = function(vars, [pytensor.grad(logp, v) for v in vars], mode=mode)
+        dlogp = function(*self.large_fuseable_graph(n=85), mode=mode)
 
         # Make sure something was fused
         assert any(
@@ -1362,6 +1359,18 @@ class TestFusion:
         func = pytensor.function([], [logp, grad_logp], mode="FAST_RUN")
         benchmark(func)
 
+    @pytest.mark.skipif(not config.cxx, reason="No cxx compiler")
+    def test_rewrite_benchmark(self, benchmark):
+        inps, outs = self.large_fuseable_graph(n=25)
+        fg = FunctionGraph(inps, outs)
+        opt = FusionOptimizer()
+
+        def rewrite_func():
+            nb_replacement = opt.apply(fg.clone())[2]
+            return nb_replacement
+
+        assert benchmark(rewrite_func) == 103
+
 
 class TimesN(aes.basic.UnaryScalarOp):
     """