[PATCH] D126398: [Clang] Introduce `-dl` option to perform offload device linking

[Joseph Huber via Phabricator via cfe-commits]

jhuber6 created this revision.
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The new driver uses an augmented linker wrapper to perform the device
linking phase, but to the user looks like a regular linker invocation.
Contrary to the old driver, the new driver contains all the information
necessary to produce a linked device image in the host object itself.
Currently, we infer the usage of the device linker by the user
specifying an offloading toolchain, e.g. (--offload-arch=...) or
(-fopenmp-targets=...), but this shouldn't be strictly necessary.
This patch introduces a new option `-dl` to tell the driver to use the
offloading linker instead. So a compilation flow can now look like this,

  clang foo.cu --offload-new-driver -fgpu-rdc --offload-arch=sm_70 -c
  clang foo.o -dl -lcudart

I was considering if this could be merged into the `-fuse-ld` option,
but becuse the device linker wraps over the users linker it would
conflict with that. In the future it's possible to merge this into `lld`
completely or `gold` via a plugin. Let me know what you think for this.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D126398

Files:
  clang/docs/ClangCommandLineReference.rst
  clang/include/clang/Driver/Options.td
  clang/lib/Driver/Driver.cpp
  clang/test/Driver/cuda-openmp-driver.cu


Index: clang/test/Driver/cuda-openmp-driver.cu
===================================================================
--- clang/test/Driver/cuda-openmp-driver.cu
+++ clang/test/Driver/cuda-openmp-driver.cu
@@ -35,3 +35,8 @@
 
 // RUN: %clang -### -target x86_64-linux-gnu -nocudalib --cuda-feature=+ptx61 --offload-arch=sm_70 %s 2>&1 | FileCheck -check-prefix MANUAL-FEATURE %s
 // MANUAL-FEATURE: -cc1{{.*}}-target-feature{{.*}}+ptx61
+
+// RUN: %clang -### -target x86_64-linux-gnu -nocudalib -ccc-print-bindings -dl %s 2>&1 \
+// RUN: | FileCheck -check-prefix DEVICE-LINK %s
+
+// DEVICE-LINK: "x86_64-unknown-linux-gnu" - "Offload::Linker", inputs: ["[[INPUT:.+]]"], output: "a.out"
Index: clang/lib/Driver/Driver.cpp
===================================================================
--- clang/lib/Driver/Driver.cpp
+++ clang/lib/Driver/Driver.cpp
@@ -4158,7 +4158,8 @@
     // Check if this Linker Job should emit a static library.
     if (ShouldEmitStaticLibrary(Args)) {
       LA = C.MakeAction<StaticLibJobAction>(LinkerInputs, types::TY_Image);
-    } else if (UseNewOffloadingDriver) {
+    } else if (UseNewOffloadingDriver ||
+               Args.hasArg(options::OPT_device_link)) {
       LA = C.MakeAction<LinkerWrapperJobAction>(LinkerInputs, types::TY_Image);
       LA->propagateHostOffloadInfo(C.getActiveOffloadKinds(),
                                    /*BoundArch=*/nullptr);
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -820,6 +820,8 @@
 def z : Separate<["-"], "z">, Flags<[LinkerInput, RenderAsInput]>,
   HelpText<"Pass -z <arg> to the linker">, MetaVarName<"<arg>">,
   Group<Link_Group>;
+def device_link : Flag<["-"], "dl">,
+  HelpText<"Use the new offloading linker to perform the link job.">;
 def Xlinker : Separate<["-"], "Xlinker">, Flags<[LinkerInput, RenderAsInput]>,
   HelpText<"Pass <arg> to the linker">, MetaVarName<"<arg>">,
   Group<Link_Group>;
Index: clang/docs/ClangCommandLineReference.rst
===================================================================
--- clang/docs/ClangCommandLineReference.rst
+++ clang/docs/ClangCommandLineReference.rst
@@ -4209,6 +4209,10 @@
 
 Pass the comma separated arguments in <arg> to the linker
 
+.. option:: -dl
+
+Use the linker supporting offloading device linking.
+
 .. option:: -X
 
 .. option:: -Xlinker <arg>, --for-linker <arg>, --for-linker=<arg>


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