Revert "[BasicBlockUtils] Handle funclets when detaching EH pad blocks" (#158364)

Reverts #157363

Causes crashes, see
#157363 (comment)

Author: aeubanks

llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -58,19 +58,6 @@ static cl::opt<unsigned> MaxDeoptOrUnreachableSuccessorCheckDepth(
              "is followed by a block that either has a terminating "
              "deoptimizing call or is terminated with an unreachable"));
 
-static void replaceFuncletPadsRetWithUnreachable(Instruction &I) {
-  assert(isa<FuncletPadInst>(I) && "Instruction must be a funclet pad!");
-  for (User *User : make_early_inc_range(I.users())) {
-    Instruction *ReturnInstr = dyn_cast<Instruction>(User);
-    if (isa<CatchReturnInst>(ReturnInstr) ||
-        isa<CleanupReturnInst>(ReturnInstr)) {
-      BasicBlock *ReturnInstrBB = ReturnInstr->getParent();
-      ReturnInstr->eraseFromParent();
-      new UnreachableInst(ReturnInstrBB->getContext(), ReturnInstrBB);
-    }
-  }
-}
-
 void llvm::detachDeadBlocks(
     ArrayRef<BasicBlock *> BBs,
     SmallVectorImpl<DominatorTree::UpdateType> *Updates,
@@ -88,36 +75,7 @@ void llvm::detachDeadBlocks(
     // Zap all the instructions in the block.
     while (!BB->empty()) {
       Instruction &I = BB->back();
-      // Exception handling funclets need to be explicitly addressed.
-      // These funclets must begin with cleanuppad or catchpad and end with
-      // cleanupred or catchret. The return instructions can be in different
-      // basic blocks than the pad instruction. If we would only delete the
-      // first block, the we would have possible cleanupret and catchret
-      // instructions with poison arguments, which wouldn't be valid.
-      if (isa<FuncletPadInst>(I))
-        replaceFuncletPadsRetWithUnreachable(I);
-
-      // Catchswitch instructions have handlers, that must be catchpads and
-      // an unwind label, that is either a catchpad or catchswitch.
-      if (CatchSwitchInst *CSI = dyn_cast<CatchSwitchInst>(&I)) {
-        // Iterating over the handlers and the unwind basic block and processing
-        // catchpads. If the unwind label is a catchswitch, we just replace the
-        // label with poison later on.
-        for (unsigned I = 0; I < CSI->getNumSuccessors(); I++) {
-          BasicBlock *SucBlock = CSI->getSuccessor(I);
-          Instruction &SucFstInst = *(SucBlock->getFirstNonPHIIt());
-          if (isa<FuncletPadInst>(SucFstInst)) {
-            replaceFuncletPadsRetWithUnreachable(SucFstInst);
-            // There may be catchswitch instructions using the catchpad.
-            // Just replace those with poison.
-            if (!SucFstInst.use_empty())
-              SucFstInst.replaceAllUsesWith(
-                  PoisonValue::get(SucFstInst.getType()));
-            SucFstInst.eraseFromParent();
-          }
-        }
-      }
-
+      // If this instruction is used, replace uses with an arbitrary value.
       // Because control flow can't get here, we don't care what we replace the
       // value with.  Note that since this block is unreachable, and all values
       // contained within it must dominate their uses, that all uses will