[GCOV] Remove function names from gcno when using option -coverage-no-function-names-in-data

[calixte]

Summary

This option allows to remove function names from gcda but in this case they're pretty useless in gcno too.
So this patch just puts an empty string for function names when the option is enabled.
In a software like Firefox, we win ~140M in removing them from gcnos.

[marco-c]

We might have to introduce a separate option here.
-coverage-no-function-names-in-data could be useful when you want smaller GCDA files, but still want to be able to parse the function names.

lib/Transforms/Instrumentation/GCOVProfiling.cpp

namespace {
   };
 
   // A function has a unique identifier, a checksum (we leave as zero) and a
   // set of blocks and a map of edges between blocks. This is the only GCOV
   // object users can construct, the blocks and lines will be rooted here.
   class GCOVFunction : public GCOVRecord {
    public:
      GCOVFunction(const DISubprogram *SP, Function *F, raw_ostream *os,
-                  uint32_t Ident, bool UseCfgChecksum, bool ExitBlockBeforeBody)
+                  uint32_t Ident, bool UseCfgChecksum, bool ExitBlockBeforeBody,
+                  bool FunctionNamesInData)
          : SP(SP), Ident(Ident), UseCfgChecksum(UseCfgChecksum), CfgChecksum(0),
-           ReturnBlock(1, os) {
+           FunctionNamesInData(FunctionNamesInData), ReturnBlock(1, os) {
       this->os = os;
 
       LLVM_DEBUG(dbgs() << "Function: " << getFunctionName(SP) << "\n");
 
       uint32_t i = 0;
       for (auto &BB : *F) {
         // Skip index 1 if it's assigned to the ReturnBlock.
         if (i == 1 && ExitBlockBeforeBody)
void writeOut() {
                           1 + lengthOfGCOVString(SP->getFilename()) + 1;
       if (UseCfgChecksum)
         ++BlockLen;
       write(BlockLen);
       write(Ident);
       write(FuncChecksum);
       if (UseCfgChecksum)
         write(CfgChecksum);
-      writeGCOVString(getFunctionName(SP));
+      writeGCOVString(FunctionNamesInData ? getFunctionName(SP) : "");
       writeGCOVString(SP->getFilename());
       write(SP->getLine());
 
       // Emit count of blocks.
       writeBytes(BlockTag, 4);
       write(Blocks.size() + 1);
       for (int i = 0, e = Blocks.size() + 1; i != e; ++i) {
         write(0);  // No flags on our blocks.
public:
     }
 
    private:
      const DISubprogram *SP;
     uint32_t Ident;
     uint32_t FuncChecksum;
     bool UseCfgChecksum;
     uint32_t CfgChecksum;
+    bool FunctionNamesInData;
     DenseMap<BasicBlock *, GCOVBlock> Blocks;
     GCOVBlock ReturnBlock;
   };
 }
 
 std::string GCOVProfiler::mangleName(const DICompileUnit *CU,
                                      GCovFileType OutputType) {
   bool Notes = OutputType == GCovFileType::GCNO;
for (auto &F : M->functions()) {
       BasicBlock &EntryBlock = F.getEntryBlock();
       BasicBlock::iterator It = EntryBlock.begin();
       while (shouldKeepInEntry(It))
         ++It;
       EntryBlock.splitBasicBlock(It);
 
       Funcs.push_back(make_unique<GCOVFunction>(SP, &F, &out, FunctionIdent++,
                                                 Options.UseCfgChecksum,
-                                                Options.ExitBlockBeforeBody));
+                                                Options.ExitBlockBeforeBody,
+                                                Options.FunctionNamesInData));
       GCOVFunction &Func = *Funcs.back();
 
       for (auto &BB : F) {
         GCOVBlock &Block = Func.getBlock(&BB);
         TerminatorInst *TI = BB.getTerminator();
         if (int successors = TI->getNumSuccessors()) {
           for (int i = 0; i != successors; ++i) {
             Block.addEdge(Func.getBlock(TI->getSuccessor(i)));