[clang] b7c8c4d - [Clang] Introduce `--offload-link` option to perform offload device linking

[Joseph Huber via cfe-commits]

Author: Joseph Huber
Date: 2022-05-25T16:30:53-04:00
New Revision: b7c8c4d8cf07d2e9e8cd157bccc8bd9e7c76415a

URL: https://github.com/llvm/llvm-project/commit/b7c8c4d8cf07d2e9e8cd157bccc8bd9e7c76415a
DIFF: https://github.com/llvm/llvm-project/commit/b7c8c4d8cf07d2e9e8cd157bccc8bd9e7c76415a.diff

LOG: [Clang] Introduce `--offload-link` option to perform offload device linking

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 `--offload-link` 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 --offload-link -lcudart
```

I was considering if this could be merged into the `-fuse-ld` option,
but because 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 and we would use this option to
enable the device linking feature. Let me know what you think for this.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D126398

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
index 5926decc85fc..73dccf6a9a04 100644
--- a/clang/docs/ClangCommandLineReference.rst
+++ b/clang/docs/ClangCommandLineReference.rst
@@ -4209,6 +4209,10 @@ Set starting address of TEXT to <addr>
 
 Pass the comma separated arguments in <arg> to the linker
 
+.. option:: --offload-link
+
+Use the linker supporting offloading device linking.
+
 .. option:: -X
 
 .. option:: -Xlinker <arg>, --for-linker <arg>, --for-linker=<arg>

diff  --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index d34cec766a2e..e19baac5860a 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -820,6 +820,8 @@ def Xopenmp_target_EQ : JoinedAndSeparate<["-"], "Xopenmp-target=">, Group<Compi
 def z : Separate<["-"], "z">, Flags<[LinkerInput, RenderAsInput]>,
   HelpText<"Pass -z <arg> to the linker">, MetaVarName<"<arg>">,
   Group<Link_Group>;
+def offload_link : Flag<["--"], "offload-link">, Group<Link_Group>,
+  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>;

diff  --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 3edbaed9ae7f..94925568aec2 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -4158,7 +4158,8 @@ void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
     // 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_offload_link)) {
       LA = C.MakeAction<LinkerWrapperJobAction>(LinkerInputs, types::TY_Image);
       LA->propagateHostOffloadInfo(C.getActiveOffloadKinds(),
                                    /*BoundArch=*/nullptr);

diff  --git a/clang/test/Driver/cuda-openmp-driver.cu b/clang/test/Driver/cuda-openmp-driver.cu
index dec0288db263..b27195da2fb1 100644
--- a/clang/test/Driver/cuda-openmp-driver.cu
+++ b/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 --offload-link %s 2>&1 \
+// RUN: | FileCheck -check-prefix DEVICE-LINK %s
+
+// DEVICE-LINK: "x86_64-unknown-linux-gnu" - "Offload::Linker", inputs: ["[[INPUT:.+]]"], output: "a.out"