[clang] [HIP] Allow partial linking for `-fgpu-rdc` (PR #81700)

[Artem Belevich via cfe-commits]

================
@@ -36,6 +47,146 @@ static std::string normalizeForBundler(const llvm::Triple &T,
                      : T.normalize();
 }
 
+// Collect undefined __hip_fatbin* and __hip_gpubin_handle* symbols from all
+// input object or archive files.
+class HIPUndefinedFatBinSymbols {
+public:
+  HIPUndefinedFatBinSymbols(const Compilation &C)
+      : C(C), DiagID(C.getDriver().getDiags().getCustomDiagID(
+                  DiagnosticsEngine::Error,
+                  "Error collecting HIP undefined fatbin symbols: %0")),
+        Quiet(C.getArgs().hasArg(options::OPT__HASH_HASH_HASH)),
+        Verbose(C.getArgs().hasArg(options::OPT_v)) {
+    populateSymbols();
+    if (Verbose) {
+      for (auto Name : FatBinSymbols)
+        llvm::errs() << "Found undefined HIP fatbin symbol: " << Name << "\n";
+      for (auto Name : GPUBinHandleSymbols)
+        llvm::errs() << "Found undefined HIP gpubin handle symbol: " << Name
+                     << "\n";
+    }
+  }
+
+  const std::set<std::string> &getFatBinSymbols() const {
+    return FatBinSymbols;
+  }
+
+  const std::set<std::string> &getGPUBinHandleSymbols() const {
+    return GPUBinHandleSymbols;
+  }
+
+private:
+  const Compilation &C;
+  unsigned DiagID;
+  bool Quiet;
+  bool Verbose;
+  std::set<std::string> FatBinSymbols;
+  std::set<std::string> GPUBinHandleSymbols;
+  const std::string FatBinPrefix = "__hip_fatbin";
+  const std::string GPUBinHandlePrefix = "__hip_gpubin_handle";
+
+  void populateSymbols() {
+    std::deque<const Action *> WorkList;
+    std::set<const Action *> Visited;
+
+    for (const auto &Action : C.getActions()) {
+      WorkList.push_back(Action);
+    }
+
+    while (!WorkList.empty()) {
+      const Action *CurrentAction = WorkList.front();
+      WorkList.pop_front();
+
+      if (!CurrentAction || !Visited.insert(CurrentAction).second)
+        continue;
+
+      if (const auto *IA = dyn_cast<InputAction>(CurrentAction)) {
+        std::string ID = IA->getId().str();
+        if (!ID.empty()) {
+          ID = llvm::utohexstr(llvm::MD5Hash(ID), /*LowerCase=*/true);
+          FatBinSymbols.insert(Twine(FatBinPrefix + "_" + ID).str());
+          GPUBinHandleSymbols.insert(
+              Twine(GPUBinHandlePrefix + "_" + ID).str());
+          continue;
+        }
+        const char *Filename = IA->getInputArg().getValue();
+        auto BufferOrErr = llvm::MemoryBuffer::getFile(Filename);
+        // Input action could be options to linker, therefore ignore it
+        // if cannot read it.
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Artem-B wrote:

Comment could use some editing. `therefore, ignore an error if we fail to read the file`.

This makes me ask -- what if the argument *is* an input file, and we do fail to read it. How do we tell apart the linker options from the input file? Relying on a failure to read it does not seem to be a good way to handle it.

https://github.com/llvm/llvm-project/pull/81700