[SjLj] Replace recursive block marking algorithm with iterative algorithm

[Gerolf]

Summary

Some programs run into a stack overflow issue. This change avoids this
problem by replacing the recursive algorithm with the iterative version.

[MatzeB]

Looks good to me. Possible improvement below.

lib/CodeGen/SjLjEHPrepare.cpp

125–132

Maybe

for (BasicBlock *B : inverse_depth_first_ext(BB, LiveBBs)) {
  /* Empty: We want to produce the visited set. */
}

works as well? So we can leave out the first if and only need a single set.

lib/CodeGen/SjLjEHPrepare.cpp

ConstantInt *CallSiteNoC =
       ConstantInt::get(Type::getInt32Ty(I->getContext()), Number);
   Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
 }
 
 /// MarkBlocksLiveIn - Insert BB and all of its predecessors into LiveBBs until
 /// we reach blocks we've already seen.
 static void MarkBlocksLiveIn(BasicBlock *BB,
                              SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
   if (!LiveBBs.insert(BB).second)
     return; // already been here.
 
-  for (BasicBlock *PredBB : predecessors(BB))
-    MarkBlocksLiveIn(PredBB, LiveBBs);
+  df_iterator_default_set<BasicBlock*> Visited;
+
+  for (BasicBlock *B : inverse_depth_first_ext(BB, Visited))
+    LiveBBs.insert(B);
+
 }
 
 /// substituteLPadValues - Substitute the values returned by the landingpad
 /// instruction with those returned by the personality function.
 void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
                                          Value *SelVal) {
   SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
   while (!UseWorkList.empty()) {