[GCOV] Flush counters before to avoid counting the execution before fork twice and for exec** functions we must flush before the call

[calixte]

Summary

This is replacement for patch in https://reviews.llvm.org/D49460.
When we fork, the counters are duplicate as they're and so the values are finally wrong when writing gcda for parent and child.
So just before to fork, we flush the counters and so the parent and the child have new counters set to zero.
For exec** functions, we need to flush before the call to have some data.

[vsk]

Don't you just want to reset the counters in the child process?

lib/Transforms/Instrumentation/GCOVProfiling.cpp

535

See InstIterator.h. The instructions() range helper might be more convenient.

541

Take a look at TargetLibraryInfo.{h, def}. It might be cleaner to define fork() there, then check if you see a LibFunc_fork.

556

Why is this needed?

[calixte]

lib/Transforms/Instrumentation/GCOVProfiling.cpp

556

The line after the fork is executed 2 times: 1 time with the parent and 1 time with the child. So if we don't split the block the counter for this line (and the next ones in the same block as the fork) is only 1. So in putting a new block here and so a new counter in it we can reflect that the lines after the fork are executed two times.

[calixte]

Fix comments from vsk and handle exec** functions too.

[marco-c]

include/llvm/Analysis/TargetLibraryInfo.def

588

There's also execve.

lib/Transforms/Instrumentation/GCOVProfiling.cpp

473

We should do the flushing before fork/exec when we are cross-compiling from Windows to a target that supports fork/exec.
We have two options:

1. Instead of using _WIN32, check that the target of the compilation isn't Windows;
2. Just add the flush always, as it's effect is not important if we are on Windows and the function is defined by a user.

[calixte]

Handle execve, fix issues with execvp and remove _WIN32.

include/llvm/Analysis/TargetLibraryInfo.def

 TLI_DEFINE_ENUM_INTERNAL(coshl)
 TLI_DEFINE_STRING_INTERNAL("coshl")
 /// long double cosl(long double x);
 TLI_DEFINE_ENUM_INTERNAL(cosl)
 TLI_DEFINE_STRING_INTERNAL("cosl")
 /// char *ctermid(char *s);
 TLI_DEFINE_ENUM_INTERNAL(ctermid)
 TLI_DEFINE_STRING_INTERNAL("ctermid")
+/// int execl(const char *path, const char *arg, ...);
+TLI_DEFINE_ENUM_INTERNAL(execl)
+TLI_DEFINE_STRING_INTERNAL("execl")
+/// int execle(const char *file, const char *arg, ..., char * const envp[]);
+TLI_DEFINE_ENUM_INTERNAL(execle)
+TLI_DEFINE_STRING_INTERNAL("execle")
+/// int execlp(const char *file, const char *arg, ...);
+TLI_DEFINE_ENUM_INTERNAL(execlp)
+TLI_DEFINE_STRING_INTERNAL("execlp")
+/// int execv(const char *path, char *const argv[]);
+TLI_DEFINE_ENUM_INTERNAL(execv)
+TLI_DEFINE_STRING_INTERNAL("execv")
+/// int execvP(const char *file, const char *search_path, char *const argv[]);
+TLI_DEFINE_ENUM_INTERNAL(execvP)
+TLI_DEFINE_STRING_INTERNAL("execvP")
+/// int execve(const char *filename, char *const argv[], char *const envp[]);
+TLI_DEFINE_ENUM_INTERNAL(execve)
+TLI_DEFINE_STRING_INTERNAL("execve")
+/// int execvp(const char *file, char *const argv[]);
+TLI_DEFINE_ENUM_INTERNAL(execvp)
+TLI_DEFINE_STRING_INTERNAL("execvp")
+/// int execvpe(const char *file, char *const argv[], char *const envp[]);
+TLI_DEFINE_ENUM_INTERNAL(execvpe)
+TLI_DEFINE_STRING_INTERNAL("execvpe")
 /// double exp(double x);
 TLI_DEFINE_ENUM_INTERNAL(exp)
 TLI_DEFINE_STRING_INTERNAL("exp")
 /// double exp10(double x);
 TLI_DEFINE_ENUM_INTERNAL(exp10)
 TLI_DEFINE_STRING_INTERNAL("exp10")
 /// float exp10f(float x);
 TLI_DEFINE_ENUM_INTERNAL(exp10f)

 TLI_DEFINE_ENUM_INTERNAL(fmodl)
 TLI_DEFINE_STRING_INTERNAL("fmodl")
 /// FILE *fopen(const char *filename, const char *mode);
 TLI_DEFINE_ENUM_INTERNAL(fopen)
 TLI_DEFINE_STRING_INTERNAL("fopen")
 /// FILE *fopen64(const char *filename, const char *opentype)
 TLI_DEFINE_ENUM_INTERNAL(fopen64)
 TLI_DEFINE_STRING_INTERNAL("fopen64")
+/// int fork();
+TLI_DEFINE_ENUM_INTERNAL(fork)
+TLI_DEFINE_STRING_INTERNAL("fork")
 /// int fprintf(FILE *stream, const char *format, ...);
 TLI_DEFINE_ENUM_INTERNAL(fprintf)
 TLI_DEFINE_STRING_INTERNAL("fprintf")
 /// int fputc(int c, FILE *stream);
 TLI_DEFINE_ENUM_INTERNAL(fputc)
 TLI_DEFINE_STRING_INTERNAL("fputc")
 /// int fputc_unlocked(int c, FILE *stream);
 TLI_DEFINE_ENUM_INTERNAL(fputc_unlocked)

lib/Analysis/TargetLibraryInfo.cpp

bool TargetLibraryInfoImpl::isValidProtoForLibFunc(const FunctionType &FTy,
   Type *PCharTy = Type::getInt8PtrTy(Ctx);
   Type *SizeTTy = DL ? DL->getIntPtrType(Ctx, /*AS=*/0) : nullptr;
   auto IsSizeTTy = [SizeTTy](Type *Ty) {
     return SizeTTy ? Ty == SizeTTy : Ty->isIntegerTy();
   };
   unsigned NumParams = FTy.getNumParams();
 
   switch (F) {
+  case LibFunc_execl:
+  case LibFunc_execlp:
+    return (NumParams >= 2 && FTy.getParamType(0)->isPointerTy() &&
+            FTy.getParamType(1)->isPointerTy() &&
+            FTy.getReturnType()->isIntegerTy(32));
+  case LibFunc_execle:
+    return (NumParams >= 3 && FTy.getParamType(0)->isPointerTy() &&
+            FTy.getParamType(1)->isPointerTy() &&
+            FTy.getParamType(NumParams - 1)->isPointerTy() &&
+            FTy.getReturnType()->isIntegerTy(32));
+  case LibFunc_execv:
+  case LibFunc_execvp:
+    return (NumParams == 2 && FTy.getParamType(0)->isPointerTy() &&
+            FTy.getParamType(1)->isPointerTy() &&
+            FTy.getReturnType()->isIntegerTy(32));
+  case LibFunc_execvP:
+  case LibFunc_execvpe:
+  case LibFunc_execve:
+    return (NumParams == 3 && FTy.getParamType(0)->isPointerTy() &&
+            FTy.getParamType(1)->isPointerTy() &&
+            FTy.getParamType(2)->isPointerTy() &&
+            FTy.getReturnType()->isIntegerTy(32));
   case LibFunc_strlen:
     return (NumParams == 1 && FTy.getParamType(0)->isPointerTy() &&
             FTy.getReturnType()->isIntegerTy());
 
   case LibFunc_strchr:
   case LibFunc_strrchr:
     return (NumParams == 2 && FTy.getReturnType()->isPointerTy() &&
             FTy.getParamType(0) == FTy.getReturnType() &&
bool TargetLibraryInfoImpl::isValidProtoForLibFunc(const FunctionType &FTy,
   case LibFunc_mktime:
   case LibFunc_times:
     return (NumParams != 0 && FTy.getParamType(0)->isPointerTy());
 
   case LibFunc_fopen:
     return (NumParams == 2 && FTy.getReturnType()->isPointerTy() &&
             FTy.getParamType(0)->isPointerTy() &&
             FTy.getParamType(1)->isPointerTy());
+  case LibFunc_fork:
+    return (NumParams == 0 && FTy.getReturnType()->isIntegerTy(32));
   case LibFunc_fdopen:
     return (NumParams == 2 && FTy.getReturnType()->isPointerTy() &&
             FTy.getParamType(1)->isPointerTy());
   case LibFunc_fputc:
   case LibFunc_fputc_unlocked:
   case LibFunc_fstat:
   case LibFunc_frexp:
   case LibFunc_frexpf:

lib/Transforms/Instrumentation/GCOVProfiling.cpp

private:
   Constant *getEndFileFunc();
 
   // Add the function to write out all our counters to the global destructor
   // list.
   Function *
   insertCounterWriteout(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
   Function *insertFlush(ArrayRef<std::pair<GlobalVariable *, MDNode *>>);
 
+  void AddFlushBeforeForkAndExec();
+
   enum class GCovFileType { GCNO, GCDA };
   std::string mangleName(const DICompileUnit *CU, GCovFileType FileType);
 
   GCOVOptions Options;
 
   // Reversed, NUL-terminated copy of Options.Version.
   char ReversedVersion[5];
   // Checksum, produced by hash of EdgeDestinations
std::string GCOVProfiler::mangleName(const DICompileUnit *CU,
   return CurPath.str();
 }
 
 bool GCOVProfiler::runOnModule(Module &M, const TargetLibraryInfo &TLI) {
   this->M = &M;
   this->TLI = &TLI;
   Ctx = &M.getContext();
 
+  AddFlushBeforeForkAndExec();
+
   if (Options.EmitNotes) emitProfileNotes();
   if (Options.EmitData) return emitProfileArcs();
   return false;
 }
 
 PreservedAnalyses GCOVProfilerPass::run(Module &M,
                                         ModuleAnalysisManager &AM) {
 
static bool shouldKeepInEntry(BasicBlock::iterator It) {
   if (isa<DbgInfoIntrinsic>(*It)) return true;
   if (auto *II = dyn_cast<IntrinsicInst>(It)) {
     if (II->getIntrinsicID() == llvm::Intrinsic::localescape) return true;
   }
 
   return false;
 }
 
+void GCOVProfiler::AddFlushBeforeForkAndExec() {
+  SmallVector<Instruction *, 2> ForkAndExecs;
+  for (auto &F : M->functions()) {
+    for (auto &I : instructions(F)) {
+      if (CallInst *CI = dyn_cast<CallInst>(&I)) {
+        if (Function *Callee = CI->getCalledFunction()) {
+          LibFunc LF;
+          if (TLI->getLibFunc(*Callee, LF) &&
+              (LF == LibFunc_fork || LF == LibFunc_execl ||
+               LF == LibFunc_execle || LF == LibFunc_execlp ||
+               LF == LibFunc_execv || LF == LibFunc_execvp ||
+               LF == LibFunc_execve || LF == LibFunc_execvpe ||
+               LF == LibFunc_execvP)) {
+            ForkAndExecs.push_back(&I);
+          }
+        }
+      }
+    }
+  }
+
+  // We need to split the block after the fork/exec call
+  // because else the counters for the lines after will be
+  // the same as before the call.
+  for (auto I : ForkAndExecs) {
+    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;
 
   for (unsigned i = 0, e = CU_Nodes->getNumOperands(); i != e; ++i) {
     // Each compile unit gets its own .gcno file. This means that whether we run
     // this pass over the original .o's as they're produced, or run it after
     // LTO, we'll generate the same .gcno files.