have cuda_library output RDC

This allows a `cuda_library` that was built with `rdc=True` to be
depended upon by another such library. This is convenient as such a
library can be consumed by either another `cuda_library` OR a
`cc_library`.

Note: if we have this, I'm not sure why we need a separate cuda_objects
rule anymore. Perhaps it can be removed in a later PR.

Change-Id: I1014d28a0ab3a9c76b788821211b13c4a9956d2a

cuda/private/rules/cuda_library.bzl

@@ -31,13 +31,17 @@ def _cuda_library_impl(ctx):
     # outputs
     objects = depset(compile(ctx, cuda_toolchain, cc_toolchain, src_files, common, pic = False, rdc = use_rdc))
     pic_objects = depset(compile(ctx, cuda_toolchain, cc_toolchain, src_files, common, pic = True, rdc = use_rdc))
+    rdc_objects = depset([])
+    rdc_pic_objects = depset([])
 
     # if rdc is enabled for this cuda_library, then we need futher do a pass of device link
     if use_rdc:
         transitive_objects = depset(transitive = [dep[CudaInfo].rdc_objects for dep in attr.deps if CudaInfo in dep])
         transitive_pic_objects = depset(transitive = [dep[CudaInfo].rdc_pic_objects for dep in attr.deps if CudaInfo in dep])
         objects = depset(transitive = [objects, transitive_objects])
+        rdc_objects = objects
         pic_objects = depset(transitive = [pic_objects, transitive_pic_objects])
+        rdc_pic_objects = pic_objects
         dlink_object = depset([device_link(ctx, cuda_toolchain, cc_toolchain, objects, common, pic = False, rdc = use_rdc)])
         dlink_pic_object = depset([device_link(ctx, cuda_toolchain, cc_toolchain, pic_objects, common, pic = True, rdc = use_rdc)])
         objects = depset(transitive = [objects, dlink_object])
@@ -87,12 +91,19 @@ def _cuda_library_impl(ctx):
             pic_lib = pic_libs,
             objects = objects,
             pic_objects = pic_objects,
+            rdc_objects = rdc_objects,
         ),
         CcInfo(
             compilation_context = cc_info.compilation_context,
             linking_context = cc_info.linking_context,
         ),
-        cuda_helper.create_cuda_info(defines = depset(common.defines)),
+        cuda_helper.create_cuda_info(
+            defines = depset(common.defines),
+            objects = objects,
+            pic_objects = pic_objects,
+            rdc_objects = rdc_objects,
+            rdc_pic_objects = rdc_pic_objects,
+        ),
     ]
 
 cuda_library = rule(
@@ -104,7 +115,7 @@ cuda_library = rule(
         "hdrs": attr.label_list(allow_files = ALLOW_CUDA_HDRS),
         "deps": attr.label_list(providers = [[CcInfo], [CudaInfo]]),
         "alwayslink": attr.bool(default = False),
-        "rdc": attr.bool(default = False, doc = "whether to perform relocateable device code linking, otherwise, normal device link."),
+        "rdc": attr.bool(default = False, doc = "Whether to produce and consume relocateable device code. Transitive deps that contain device code must all either be cuda_objects or cuda_library that has rdc = True. If False, all device code must be in the same translation unit. May have performance implications. See https://docs.nvidia.com/cuda/cuda-compiler-driver-nvcc/index.html#using-separate-compilation-in-cuda."),
         "includes": attr.string_list(doc = "List of include dirs to be added to the compile line."),
         "host_copts": attr.string_list(doc = "Add these options to the CUDA host compilation command."),
         "host_defines": attr.string_list(doc = "List of defines to add to the compile line."),

examples/rdc/BUILD.bazel

@@ -1,29 +1,52 @@
 load("@rules_cuda//cuda:defs.bzl", "cuda_library", "cuda_objects")
 
 cuda_objects(
-    name = "a",
+    name = "a_objects",
     srcs = ["a.cu"],
     deps = [":b"],
 )
 
 cuda_objects(
-    name = "b",
+    name = "b_objects",
     srcs = ["b.cu"],
     hdrs = ["b.cuh"],
 )
 
 cuda_library(
-    name = "librdc",
-    rdc = 1,
+    name = "lib_from_objects",
+    rdc = True,
     deps = [
-        ":a",
-        ":b",
+        ":a_objects",
+        ":b_objects",
     ],
 )
 
 cc_binary(
-    name = "main",
+    name = "main_from_objects",
     deps = [
-        ":librdc",
+        ":lib_from_objects",
+    ],
+)
+
+# Another way of doing it is to just use cuda_library
+cuda_library(
+    name = "a",
+    srcs = ["a.cu"],
+    rdc = True,
+    deps = [":b"],
+)
+
+cuda_library(
+    name = "b",
+    srcs = ["b.cu"],
+    hdrs = ["b.cuh"],
+    rdc = True,
+)
+
+cc_binary(
+    name = "main_from_library",
+    deps = [
+        ":a",
+        ":b",
     ],
 )