[GCOV] Function counters are wrong when on one line

[calixte]

Summary

After commit https://reviews.llvm.org/rL344228, the function definitions have a counter but when on one line the counter is wrong (e.g. void foo() { })
I added a test in: https://reviews.llvm.org/D53601

llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp

for (auto &F : M->functions()) {
 
       Funcs.push_back(make_unique<GCOVFunction>(SP, &F, &out, FunctionIdent++,
                                                 Options.UseCfgChecksum,
                                                 Options.ExitBlockBeforeBody));
       GCOVFunction &Func = *Funcs.back();
 
       // Add the function line number to the lines of the entry block
       // to have a counter for the function definition.
-      Func.getBlock(&EntryBlock)
-          .getFile(SP->getFilename())
-          .addLine(SP->getLine());
+      uint32_t Line = SP->getLine();
+      Func.getBlock(&EntryBlock).getFile(SP->getFilename()).addLine(Line);
 
       for (auto &BB : F) {
         GCOVBlock &Block = Func.getBlock(&BB);
         Instruction *TI = BB.getTerminator();
         if (int successors = TI->getNumSuccessors()) {
           for (int i = 0; i != successors; ++i) {
             Block.addEdge(Func.getBlock(TI->getSuccessor(i)));
           }
         } else if (isa<ReturnInst>(TI)) {
           Block.addEdge(Func.getReturnBlock());
         }
 
-        uint32_t Line = 0;
         for (auto &I : BB) {
           // Debug intrinsic locations correspond to the location of the
           // declaration, not necessarily any statements or expressions.
           if (isa<DbgInfoIntrinsic>(&I)) continue;
 
           const DebugLoc &Loc = I.getDebugLoc();
           if (!Loc)
             continue;
 
           // Artificial lines such as calls to the global constructors.
           if (Loc.getLine() == 0 || Loc.isImplicitCode())
             continue;
 
           if (Line == Loc.getLine()) continue;
           Line = Loc.getLine();
           if (SP != getDISubprogram(Loc.getScope()))
             continue;
 
           GCOVLines &Lines = Block.getFile(SP->getFilename());
           Lines.addLine(Loc.getLine());
         }
+        Line = 0;
       }
       EdgeDestinations += Func.getEdgeDestinations();
     }
 
     FileChecksums.push_back(hash_value(EdgeDestinations));
     out.write("oncg", 4);
     out.write(ReversedVersion, 4);
     out.write(reinterpret_cast<char*>(&FileChecksums.back()), 4);