Revert "Reland "[BasicBlockUtils] Handle funclets when detaching EH pad blocks" (llvm#158435)"

This reverts commit 41cef78.

Author: spaits

llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -58,94 +58,37 @@ static cl::opt<unsigned> MaxDeoptOrUnreachableSuccessorCheckDepth(
              "is followed by a block that either has a terminating "
              "deoptimizing call or is terminated with an unreachable"));
 
-/// Zap all the instructions in the block and replace them with an unreachable
-/// instruction and notify the basic block's successors that one of their
-/// predecessors is going away.
-static void
-emptyAndDetachBlock(BasicBlock *BB,
-                    SmallVectorImpl<DominatorTree::UpdateType> *Updates,
-                    bool KeepOneInputPHIs) {
-  // Loop through all of our successors and make sure they know that one
-  // of their predecessors is going away.
-  SmallPtrSet<BasicBlock *, 4> UniqueSuccessors;
-  for (BasicBlock *Succ : successors(BB)) {
-    Succ->removePredecessor(BB, KeepOneInputPHIs);
-    if (Updates && UniqueSuccessors.insert(Succ).second)
-      Updates->push_back({DominatorTree::Delete, BB, Succ});
-  }
-
-  // Zap all the instructions in the block.
-  while (!BB->empty()) {
-    Instruction &I = BB->back();
-    // 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
-    // eventually be removed (they are themselves dead).
-    if (!I.use_empty())
-      I.replaceAllUsesWith(PoisonValue::get(I.getType()));
-    BB->back().eraseFromParent();
-  }
-  new UnreachableInst(BB->getContext(), BB);
-  assert(BB->size() == 1 && isa<UnreachableInst>(BB->getTerminator()) &&
-         "The successor list of BB isn't empty before "
-         "applying corresponding DTU updates.");
-}
-
-void llvm::detachDeadBlocks(ArrayRef<BasicBlock *> BBs,
-                            SmallVectorImpl<DominatorTree::UpdateType> *Updates,
-                            bool KeepOneInputPHIs) {
+void llvm::detachDeadBlocks(
+    ArrayRef<BasicBlock *> BBs,
+    SmallVectorImpl<DominatorTree::UpdateType> *Updates,
+    bool KeepOneInputPHIs) {
   for (auto *BB : BBs) {
-    auto NonFirstPhiIt = BB->getFirstNonPHIIt();
-    if (NonFirstPhiIt != BB->end()) {
-      Instruction &I = *NonFirstPhiIt;
-      // 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)) {
-        for (User *User : make_early_inc_range(I.users())) {
-          Instruction *ReturnInstr = dyn_cast<Instruction>(User);
-          // If we have a cleanupret or catchret block, replace it with just an
-          // unreachable. The other alternative, that may use a catchpad is a
-          // catchswitch. That does not need special handling for now.
-          if (isa<CatchReturnInst>(ReturnInstr) ||
-              isa<CleanupReturnInst>(ReturnInstr)) {
-            BasicBlock *ReturnInstrBB = ReturnInstr->getParent();
-            // This catchret or catchpad basic block is detached now. Let the
-            // successors know it.
-            // This basic block also may have some predecessors too. For
-            // example the following LLVM-IR is valid:
-            //
-            //   [cleanuppad_block]
-            //            |
-            //    [regular_block]
-            //            |
-            //   [cleanupret_block]
-            //
-            // The IR after the cleanup will look like this:
-            //
-            //   [cleanuppad_block]
-            //            |
-            //    [regular_block]
-            //            |
-            //     [unreachable]
-            //
-            // So regular_block will lead to an unreachable block, which is also
-            // valid. There is no need to replace regular_block with unreachable
-            // in this context now.
-            // On the other hand, the cleanupret/catchret block's successors
-            // need to know about the deletion of their predecessors.
-            emptyAndDetachBlock(ReturnInstrBB, Updates, KeepOneInputPHIs);
-          }
-        }
-      }
+    // Loop through all of our successors and make sure they know that one
+    // of their predecessors is going away.
+    SmallPtrSet<BasicBlock *, 4> UniqueSuccessors;
+    for (BasicBlock *Succ : successors(BB)) {
+      Succ->removePredecessor(BB, KeepOneInputPHIs);
+      if (Updates && UniqueSuccessors.insert(Succ).second)
+        Updates->push_back({DominatorTree::Delete, BB, Succ});
     }
 
-    // Detaching and emptying the current basic block.
-    emptyAndDetachBlock(BB, Updates, KeepOneInputPHIs);
+    // Zap all the instructions in the block.
+    while (!BB->empty()) {
+      Instruction &I = BB->back();
+      // 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
+      // eventually be removed (they are themselves dead).
+      if (!I.use_empty())
+        I.replaceAllUsesWith(PoisonValue::get(I.getType()));
+      BB->back().eraseFromParent();
+    }
+    new UnreachableInst(BB->getContext(), BB);
+    assert(BB->size() == 1 &&
+           isa<UnreachableInst>(BB->getTerminator()) &&
+           "The successor list of BB isn't empty before "
+           "applying corresponding DTU updates.");
   }
 }