[OpenMP] Create COMDAT group for OpenMP offload registration code to avoid multiple copies

Thanks to Sergey Dmitriev for submitting the patch.

Differential Revision: https://reviews.llvm.org/D33509

llvm-svn: 304056

2 files changed, 18 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CGOpenMPRuntime.cpp b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
index 601d662e55e..0644d1b2834 100644
--- a/clang/lib/CodeGen/CGOpenMPRuntime.cpp
+++ b/clang/lib/CodeGen/CGOpenMPRuntime.cpp
@@ -2903,6 +2903,19 @@ CGOpenMPRuntime::createOffloadingBinaryDescriptorRegistration() {
                              Desc);
         CGM.getCXXABI().registerGlobalDtor(CGF, RegUnregVar, UnRegFn, Desc);
       });
+  if (CGM.supportsCOMDAT()) {
+    // It is sufficient to call registration function only once, so create a
+    // COMDAT group for registration/unregistration functions and associated
+    // data. That would reduce startup time and code size. Registration
+    // function serves as a COMDAT group key.
+    auto ComdatKey = M.getOrInsertComdat(RegFn->getName());
+    RegFn->setLinkage(llvm::GlobalValue::LinkOnceAnyLinkage);
+    RegFn->setVisibility(llvm::GlobalValue::HiddenVisibility);
+    RegFn->setComdat(ComdatKey);
+    UnRegFn->setComdat(ComdatKey);
+    DeviceImages->setComdat(ComdatKey);
+    Desc->setComdat(ComdatKey);
+  }
   return RegFn;
 }
 
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index db8f8d32abb..ffbcbfcc291 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -400,8 +400,11 @@ void CodeGenModule::Release() {
   }
   if (OpenMPRuntime)
     if (llvm::Function *OpenMPRegistrationFunction =
-            OpenMPRuntime->emitRegistrationFunction())
-      AddGlobalCtor(OpenMPRegistrationFunction, 0);
+            OpenMPRuntime->emitRegistrationFunction()) {
+      auto ComdatKey = OpenMPRegistrationFunction->hasComdat() ?
+        OpenMPRegistrationFunction : nullptr;
+      AddGlobalCtor(OpenMPRegistrationFunction, 0, ComdatKey);
+    }
   if (PGOReader) {
     getModule().setProfileSummary(PGOReader->getSummary().getMD(VMContext));
     if (PGOStats.hasDiagnostics())