Index: lib/Transforms/Instrumentation/GCOVProfiling.cpp
===================================================================
--- lib/Transforms/Instrumentation/GCOVProfiling.cpp
+++ lib/Transforms/Instrumentation/GCOVProfiling.cpp
@@ -109,6 +109,8 @@
   insertCounterWriteout(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
   Function *insertFlush(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
 
+  void AddFlushBeforeFork();
+
   enum class GCovFileType { GCNO, GCDA };
   std::string mangleName(const DICompileUnit *CU, GCovFileType FileType);
 
@@ -468,6 +470,8 @@
   this->TLI = &TLI;
   Ctx = &M.getContext();
 
+  AddFlushBeforeFork();
+
   if (Options.EmitNotes) emitProfileNotes();
   if (Options.EmitData) return emitProfileArcs();
   return false;
@@ -524,6 +528,35 @@
 	return false;
 }
 
+void GCOVProfiler::AddFlushBeforeFork() {
+  SmallVector<Instruction *, 2> Forks;
+  for (auto &F : M->functions()) {
+    for (auto &BB : F) {
+      for (auto &I : BB) {
+        if (CallInst *CI = dyn_cast<CallInst>(&I)) {
+          if (Function *Callee = CI->getCalledFunction()) {
+            if (Callee->getName() == "fork") {
+              FunctionType *FT = Callee->getFunctionType();
+              if (FT->getReturnType()->isIntegerTy(32) &&
+                  FT->getNumParams() == 0) {
+                Forks.push_back(&I);
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+
+  for (auto I : Forks) {
+    IRBuilder<> Builder(I);
+    FunctionType *FTy = FunctionType::get(Builder.getVoidTy(), {}, false);
+    Constant *GCOVFlush = M->getOrInsertFunction("__gcov_flush", FTy);
+    Builder.CreateCall(GCOVFlush);
+    I->getParent()->splitBasicBlock(I);
+  }
+}
+
 void GCOVProfiler::emitProfileNotes() {
   NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu");
   if (!CU_Nodes) return;