[lld] [llvm] [DTLTO] support distributing bitcode from FatLTO objects (PR #176928)

[Ben Dunbobbin via llvm-commits]

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@@ -134,15 +132,17 @@ lto::DTLTO::addInput(std::unique_ptr<lto::InputFile> InputPtr) {
   StringRef ModuleId = Input->getName();
   StringRef ArchivePath = Input->getArchivePath();
 
-  // Only process archive members.
-  if (ArchivePath.empty())
+  // Only process archive members and FatLTO objects.
+  if (ArchivePath.empty() && !Input->isFatLTOObject())
     return Input;
 
   SmallString<64> NewModuleId;
   BitcodeModule &BM = Input->getPrimaryBitcodeModule();
 
-  // Check if the archive is a thin archive.
-  Expected<bool> IsThin = isThinArchive(ArchivePath);
+  // Check if the archive is a thin archive and the object is not fat.
+  // This means we have a file already that we can point to.
+  Expected<bool> IsThin =
+      Input->isFatLTOObject() ? false : isThinArchive(ArchivePath);
----------------
bd1976bris wrote:

```suggestion
  // For a member of a thin archive that is not a FatLTO object, there is an existing
  // file on disk that can be used, so we can avoid having to materialize.
  Expected<bool> UseThinMember =
      Input->isFatLTOObject() ? false : isThinArchive(ArchivePath);
```

https://github.com/llvm/llvm-project/pull/176928