Add test script for pt2 batch fusion (pytorch#2018)

Summary:

Add test case and torchinductor option for pt2 batch fusion

Reviewed By: ckluk2

Differential Revision: D47609030

torchbenchmark/util/backends/torchdynamo.py

@@ -88,6 +88,11 @@ def parse_torchdynamo_args(dynamo_args: List[str]) -> argparse.Namespace:
         action='store_true',
         help="set to generate unique triton kernel names in Inductor"
     )
+    parser.add_argument(
+        "--torchinductor_post_grad_batch_fusion",
+        type=distutils.util.strtobool,
+        help="Enable BMM Linear Fusion."
+    )
     parser.add_argument(
         "--dynamo_disable_optimizer_step",
         type=distutils.util.strtobool,
@@ -119,6 +124,8 @@ def apply_torchdynamo_args(model: 'torchbenchmark.util.model.BenchmarkModel', ar
     if args.torchdynamo == "inductor":
         import torch._inductor as torchinductor
         torchinductor.config.triton.cudagraphs = bool(args.torchinductor_cudagraph)
+        if bool(args.torchinductor_post_grad_batch_fusion):
+            torchinductor.config.post_grad_fusion_options["batch_fusion"] = {}
         torch._inductor.config.debug = bool(args.dump_triton)
 
         # Setup torchinductor.config.triton.mm