Reland [BasicBlockUtils] Handle funclets when detaching EH pad blocks (#159379)

Fixes #148052 .

Last PR did not account for the scenario, when more than one instruction
used the `catchpad` label.
In that case I have deleted uses, which were already "choosen to be
iterated over" by the early increment iterator. This issue was not
visible in normal release build on x86, but luckily later on the address
sanitizer build it has found it on the buildbot.

Here is the diff from the last version of this PR: #158435
```diff
diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 91e245e5e8f5..1dd8cb4ee584 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -106,7 +106,8 @@ void llvm::detachDeadBlocks(ArrayRef<BasicBlock *> BBs,
       // 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())) {
+        SmallPtrSet<BasicBlock *, 4> UniqueEHRetBlocksToDelete;
+        for (User *User : 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
@@ -114,33 +115,12 @@ void llvm::detachDeadBlocks(ArrayRef<BasicBlock *> BBs,
           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);
+            UniqueEHRetBlocksToDelete.insert(ReturnInstrBB);
           }
         }
+        for (BasicBlock *EHRetBB :
+             make_early_inc_range(UniqueEHRetBlocksToDelete))
+          emptyAndDetachBlock(EHRetBB, Updates, KeepOneInputPHIs);
       }
     }
```

0 files changed, 0 insertions, 0 deletions