move gen_aten and gen_aten_hip into shared build structure

Pull Request resolved: pytorch#77751

This requires two changes to rule generation:
 * pulling the cpu static dispatch prediction into the rules
 * disabling the Bazel-style generated file aliases

Differential Revision: [D36481918](https://our.internmc.facebook.com/intern/diff/D36481918/)

**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D36481918/)!

Approved by: https://github.com/kit1980, https://github.com/seemethere

build.bzl

@@ -1,3 +1,10 @@
+load(
+    ":ufunc_defs.bzl",
+    "aten_ufunc_generated_cpu_kernel_sources",
+    "aten_ufunc_generated_cpu_sources",
+    "aten_ufunc_generated_cuda_sources",
+)
+
 def define_targets(rules):
     rules.cc_library(
         name = "caffe2_serialize",
@@ -22,6 +29,60 @@ def define_targets(rules):
         ],
     )
 
+    #
+    # ATen generated code
+    # You need to keep this is sync with the files written out
+    # by gen.py (in the cmake build system, we track generated files
+    # via generated_cpp.txt and generated_cpp.txt-cuda
+    #
+    # Sure would be nice to use gen.py to create this list dynamically
+    # instead of hardcoding, no? Well, we can't, as discussed in this
+    # thread:
+    # https://fb.facebook.com/groups/askbuck/permalink/1924258337622772/
+
+    gen_aten_srcs = [
+        "aten/src/ATen/native/native_functions.yaml",
+        "aten/src/ATen/native/tags.yaml",
+    ] + rules.glob(["aten/src/ATen/templates/*"])
+
+    gen_aten_cmd = " ".join([
+        "$(location //torchgen:gen)",
+        "--install_dir=$(RULEDIR)",
+        "--source-path aten/src/ATen",
+    ] + (["--static_dispatch_backend CPU"] if rules.is_cpu_static_dispatch_build() else []))
+
+    gen_aten_outs_cuda = (
+        GENERATED_H_CUDA + GENERATED_CPP_CUDA +
+        aten_ufunc_generated_cuda_sources()
+    )
+
+    gen_aten_outs = (
+        GENERATED_H + GENERATED_H_CORE +
+        GENERATED_CPP + GENERATED_CPP_CORE +
+        aten_ufunc_generated_cpu_sources() +
+        aten_ufunc_generated_cpu_kernel_sources() + [
+            "Declarations.yaml",
+        ] + gen_aten_outs_cuda
+    )
+
+    rules.genrule(
+        name = "gen_aten",
+        srcs = gen_aten_srcs,
+        tools = ["//torchgen:gen"],
+        outs = gen_aten_outs,
+        cmd = gen_aten_cmd,
+    )
+
+    rules.genrule(
+        name = "gen_aten_hip",
+        srcs = gen_aten_srcs,
+        tools = ["//torchgen:gen"],
+        outs = gen_aten_outs_cuda,
+        cmd = gen_aten_cmd + " --rocm",
+        features = ["-create_bazel_outputs"],
+        tags = ["-bazel"],
+    )
+
     rules.genrule(
         name = "generate-code",
         srcs = [

tools/bazel.bzl

@@ -7,6 +7,9 @@ def _genrule(**kwds):
     if _enabled(**kwds):
         native.genrule(**kwds)
 
+def _is_cpu_static_dispatch_build():
+    return False
+
 def _py_library(name, **kwds):
     deps = [dep for dep in kwds.pop("deps", []) if dep != None]
     native.py_library(name = name, deps = deps, **kwds)
@@ -26,6 +29,7 @@ rules = struct(
     genrule = _genrule,
     glob = native.glob,
     if_cuda = if_cuda,
+    is_cpu_static_dispatch_build = _is_cpu_static_dispatch_build,
     py_binary = native.py_binary,
     py_library = _py_library,
     requirement = _requirement,