[Clang][SYCL] Introduce clang-sycl-linker to link SYCL offloading device code (Part 1 of many) (#112245)

This PR is one of the many PRs in the SYCL upstreaming effort focusing
on device code linking during the SYCL offload compilation process. RFC:
https://discourse.llvm.org/t/rfc-offloading-design-for-sycl-offload-kind-and-spir-targets/74088

In this PR, we introduce a new tool that will be used to perform device
code linking for SYCL offload kind. It accepts SYCL device objects in
LLVM IR bitcode format and will generate a fully linked device object
that can then be wrapped and linked into the host object.

A primary use case for this tool is to perform device code linking for
objects with SYCL offload kind inside the clang-linker-wrapper. It can
also be invoked via clang driver as follows:

`clang --target=spirv64 --sycl-link input.bc`

Device code linking for SYCL offloading kind has a number of known
quirks that makes it difficult to use in a unified offloading setting.
Two of the primary issues are:
1. Several finalization steps are required to be run on the fully-linked
LLVM IR bitcode to gaurantee conformance to SYCL standards. This step is
unique to SYCL offloading compilation flow.
2. SPIR-V LLVM Translator tool is an extenal tool and hence SPIR-V IR
code generation cannot be done as part of LTO. This limitation will be
lifted once SPIR-V backend is available as a viable LLVM backend.

Hence, we introduce this new tool to provide a clean wrapper to perform
SYCL device linking.

Co-Author: Michael Toguchi
Thanks

---------

Signed-off-by: Arvind Sudarsanam <arvind.sudarsanam@intel.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 9878a9d..083035d 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -4791,6 +4791,11 @@ Action *Driver::ConstructPhaseAction(
   if (Phase == phases::Assemble && Input->getType() != types::TY_PP_Asm)
     return Input;
 
+  // Use of --sycl-link will only allow for the link phase to occur. This is
+  // for all input files.
+  if (Args.hasArg(options::OPT_sycl_link) && Phase != phases::Link)
+    return Input;
+
   // Build the appropriate action.
   switch (Phase) {
   case phases::Link: