Revert "[InstCombine] Fix infinite loop due to bitcast <-> phi transforms" (#35)

This reverts commit 8813358, which was
incorrect without dependent changes.

Author: tmandry

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -2234,14 +2234,9 @@ Instruction *InstCombiner::optimizeBitCastFromPhi(CastInst &CI, PHINode *PN) {
       if (auto *C = dyn_cast<Constant>(V)) {
         NewV = ConstantExpr::getBitCast(C, DestTy);
       } else if (auto *LI = dyn_cast<LoadInst>(V)) {
-        // Explicitly perform load combine to make sure no opposing transform
-        // can remove the bitcast in the meantime and trigger an infinite loop.
-        Builder.SetInsertPoint(LI);
-        NewV = combineLoadToNewType(*LI, DestTy);
-        // Remove the old load and its use in the old phi, which itself becomes
-        // dead once the whole transform finishes.
-        replaceInstUsesWith(*LI, UndefValue::get(LI->getType()));
-        eraseInstFromFunction(*LI);
+        Builder.SetInsertPoint(LI->getNextNode());
+        NewV = Builder.CreateBitCast(LI, DestTy);
+        Worklist.Add(LI);
       } else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
         NewV = BCI->getOperand(0);
       } else if (auto *PrevPN = dyn_cast<PHINode>(V)) {