[Pallas] Add experimental (private for now) API for manual fusion into Pallas kernels

PiperOrigin-RevId: 733112191

Author: sharadmv

jax/_src/pallas/fuser/BUILD

@@ -0,0 +1,121 @@
+# Copyright 2025 The JAX Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+load(
+    "//jaxlib:jax.bzl",
+    "py_deps",
+    "pytype_strict_library",
+)
+
+package(
+    default_applicable_licenses = [],
+    default_visibility = [
+        "//jax:internal",
+    ],
+)
+
+pytype_strict_library(
+    name = "fuser",
+    srcs = [
+        "__init__.py",
+    ],
+    deps = [
+        ":block_spec",
+        ":fusable",
+        ":fusion",
+        ":jaxpr_fusion",
+    ],
+)
+
+pytype_strict_library(
+    name = "block_spec",
+    srcs = [
+        "block_spec.py",
+    ],
+    deps = [
+        "//jax",
+        "//jax:ad_util",
+        "//jax:api_util",
+        "//jax:core",
+        "//jax:partial_eval",
+        "//jax:tree_util",
+        "//jax:util",
+        "//jax/_src/pallas",
+    ] + py_deps("numpy"),
+)
+
+pytype_strict_library(
+    name = "fusable",
+    srcs = [
+        "fusable.py",
+    ],
+    deps = [
+        ":fusion",
+        "//jax",
+        "//jax:api_util",
+        "//jax:core",
+        "//jax:mlir",
+        "//jax:partial_eval",
+        "//jax:tree_util",
+        "//jax:util",
+    ],
+)
+
+pytype_strict_library(
+    name = "fusion",
+    srcs = [
+        "fusion.py",
+    ],
+    deps = [
+        "//jax",
+        "//jax:util",
+    ],
+)
+
+pytype_strict_library(
+    name = "jaxpr_fusion",
+    srcs = [
+        "jaxpr_fusion.py",
+    ],
+    deps = [
+        ":fusable",
+        ":fusable_dtype",
+        ":fusion",
+        "//jax",
+        "//jax:api_util",
+        "//jax:core",
+        "//jax:partial_eval",
+        "//jax:tree_util",
+    ],
+)
+
+pytype_strict_library(
+    name = "fusable_dtype",
+    srcs = [
+        "fusable_dtype.py",
+    ],
+    deps = [
+        ":block_spec",
+        ":fusable",
+        "//jax",
+        "//jax:api_util",
+        "//jax:core",
+        "//jax:dtypes",
+        "//jax:partial_eval",
+        "//jax:source_info_util",
+        "//jax:tree_util",
+        "//jax:util",
+        "//jax/_src/pallas",
+    ],
+)

jax/_src/pallas/fuser/__init__.py

@@ -0,0 +1,21 @@
+# Copyright 2025 The JAX Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from jax._src.pallas.fuser.block_spec import get_fusion_values as get_fusion_values
+from jax._src.pallas.fuser.block_spec import make_scalar_prefetch_handler as make_scalar_prefetch_handler
+from jax._src.pallas.fuser.block_spec import pull_block_spec as pull_block_spec
+from jax._src.pallas.fuser.block_spec import push_block_spec as push_block_spec
+from jax._src.pallas.fuser.fusable import fusable as fusable
+from jax._src.pallas.fuser.fusion import Fusion as Fusion
+from jax._src.pallas.fuser.jaxpr_fusion import fuse as fuse