Remove dead code from LoopUnswitch

LoopUnswitch's code simplification routine has logic to convert conditional
branches into unconditional branches, after unswitching makes the condition
constant, and then remove any blocks that renders dead. Unfortunately, this
code is dead, currently broken, and furthermore, has never been alive (at least
as far back at 2006).

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194277 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopUnswitch.cpp

@@ -212,8 +212,6 @@ namespace {
                                         Instruction *InsertPt);
 
     void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
-    void RemoveBlockIfDead(BasicBlock *BB,
-                           std::vector<Instruction*> &Worklist, Loop *l);
     void RemoveLoopFromHierarchy(Loop *L);
     bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = 0,
                                     BasicBlock **LoopExit = 0);
@@ -946,114 +944,6 @@ static void ReplaceUsesOfWith(Instruction *I, Value *V,
   ++NumSimplify;
 }
 
-/// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
-/// information, and remove any dead successors it has.
-///
-void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
-                                     std::vector<Instruction*> &Worklist,
-                                     Loop *L) {
-  if (pred_begin(BB) != pred_end(BB)) {
-    // This block isn't dead, since an edge to BB was just removed, see if there
-    // are any easy simplifications we can do now.
-    if (BasicBlock *Pred = BB->getSinglePredecessor()) {
-      // If it has one pred, fold phi nodes in BB.
-      while (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
-        ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
-
-      // If this is the header of a loop and the only pred is the latch, we now
-      // have an unreachable loop.
-      if (Loop *L = LI->getLoopFor(BB))
-        if (loopHeader == BB && L->contains(Pred)) {
-          // Remove the branch from the latch to the header block, this makes
-          // the header dead, which will make the latch dead (because the header
-          // dominates the latch).
-          LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
-          Pred->getTerminator()->eraseFromParent();
-          new UnreachableInst(BB->getContext(), Pred);
-
-          // The loop is now broken, remove it from LI.
-          RemoveLoopFromHierarchy(L);
-
-          // Reprocess the header, which now IS dead.
-          RemoveBlockIfDead(BB, Worklist, L);
-          return;
-        }
-
-      // If pred ends in a uncond branch, add uncond branch to worklist so that
-      // the two blocks will get merged.
-      if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
-        if (BI->isUnconditional())
-          Worklist.push_back(BI);
-    }
-    return;
-  }
-
-  DEBUG(dbgs() << "Nuking dead block: " << *BB);
-
-  // Remove the instructions in the basic block from the worklist.
-  for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
-    RemoveFromWorklist(I, Worklist);
-
-    // Anything that uses the instructions in this basic block should have their
-    // uses replaced with undefs.
-    // If I is not void type then replaceAllUsesWith undef.
-    // This allows ValueHandlers and custom metadata to adjust itself.
-    if (!I->getType()->isVoidTy())
-      I->replaceAllUsesWith(UndefValue::get(I->getType()));
-  }
-
-  // If this is the edge to the header block for a loop, remove the loop and
-  // promote all subloops.
-  if (Loop *BBLoop = LI->getLoopFor(BB)) {
-    if (BBLoop->getLoopLatch() == BB) {
-      RemoveLoopFromHierarchy(BBLoop);
-      if (currentLoop == BBLoop) {
-        currentLoop = 0;
-        redoLoop = false;
-      }
-    }
-  }
-
-  // Remove the block from the loop info, which removes it from any loops it
-  // was in.
-  LI->removeBlock(BB);
-
-  // Remove phi node entries in successors for this block.
-  TerminatorInst *TI = BB->getTerminator();
-  SmallVector<BasicBlock*, 4> Succs;
-  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
-    Succs.push_back(TI->getSuccessor(i));
-    TI->getSuccessor(i)->removePredecessor(BB);
-  }
-
-  // Unique the successors, remove anything with multiple uses.
-  array_pod_sort(Succs.begin(), Succs.end());
-  Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
-
-  // Remove the basic block, including all of the instructions contained in it.
-  LPM->deleteSimpleAnalysisValue(BB, L);
-  BB->eraseFromParent();
-  // Remove successor blocks here that are not dead, so that we know we only
-  // have dead blocks in this list.  Nondead blocks have a way of becoming dead,
-  // then getting removed before we revisit them, which is badness.
-  //
-  for (unsigned i = 0; i != Succs.size(); ++i)
-    if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
-      // One exception is loop headers.  If this block was the preheader for a
-      // loop, then we DO want to visit the loop so the loop gets deleted.
-      // We know that if the successor is a loop header, that this loop had to
-      // be the preheader: the case where this was the latch block was handled
-      // above and headers can only have two predecessors.
-      if (!LI->isLoopHeader(Succs[i])) {
-        Succs.erase(Succs.begin()+i);
-        --i;
-      }
-    }
-
-  for (unsigned i = 0, e = Succs.size(); i != e; ++i)
-    RemoveBlockIfDead(Succs[i], Worklist, L);
-}
-
 /// RemoveLoopFromHierarchy - We have discovered that the specified loop has
 /// become unwrapped, either because the backedge was deleted, or because the
 /// edge into the header was removed.  If the edge into the header from the
@@ -1262,23 +1152,6 @@ void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
         continue;
       }
 
-      if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){
-        // Conditional branch.  Turn it into an unconditional branch, then
-        // remove dead blocks.
-        continue;  // FIXME: Enable.
-
-        DEBUG(dbgs() << "Folded branch: " << *BI);
-        BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue());
-        BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue());
-        DeadSucc->removePredecessor(BI->getParent(), true);
-        Worklist.push_back(BranchInst::Create(LiveSucc, BI));
-        LPM->deleteSimpleAnalysisValue(BI, L);
-        BI->eraseFromParent();
-        RemoveFromWorklist(BI, Worklist);
-        ++NumSimplify;
-
-        RemoveBlockIfDead(DeadSucc, Worklist, L);
-      }
       continue;
     }
   }