[Clang] Use metadata to make identifying embedded objects easier

Currently we use the `embedBufferInModule` function to store binary
strings containing device offloading data inside the host object to
create a fatbinary. In the case of LTO, we need to extract this object
from the LLVM-IR. This patch adds a metadata node for the embedded
objects containing the embedded pointers and the sections they were
stored at. This should create a cleaner interface for identifying these
values.

In the future it may be worthwhile to also encode an `ID` in the
metadata corresponding to the object's special section type if relevant.
This would allow us to extract the data from an object file and LLVM-IR
using the same ID.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D129033

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/ModuleUtils.cpp b/llvm/lib/Transforms/Utils/ModuleUtils.cpp
index 5120ade..a3529bf 100644
--- a/llvm/lib/Transforms/Utils/ModuleUtils.cpp
+++ b/llvm/lib/Transforms/Utils/ModuleUtils.cpp
@@ -275,5 +275,12 @@ void llvm::embedBufferInModule(Module &M, MemoryBufferRef Buf,
   GV->setSection(SectionName);
   GV->setAlignment(Alignment);
 
+  LLVMContext &Ctx = M.getContext();
+  NamedMDNode *MD = M.getOrInsertNamedMetadata("llvm.embedded.objects");
+  Metadata *MDVals[] = {ConstantAsMetadata::get(GV),
+                        MDString::get(Ctx, SectionName)};
+
+  MD->addOperand(llvm::MDNode::get(Ctx, MDVals));
+
   appendToCompilerUsed(M, GV);
 }