[SimplifyCFG] markAliveBlocks(): catchswitch: preserve PostDomTree

When removing catchpad's from catchswitch, if that removes a successor,
we need to record that in DomTreeUpdater.

This fixes PostDomTree preservation failure in an existing test.
This appears to be the single issue that i see in my current test coverage.

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 6e526cc..1f94c61 100644 (file)
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -2286,6 +2286,7 @@ static bool markAliveBlocks(Function &F,
         }
       };
 
+      SmallMapVector<BasicBlock *, int, 8> NumPerSuccessorCases;
       // Set of unique CatchPads.
       SmallDenseMap<CatchPadInst *, detail::DenseSetEmpty, 4,
                     CatchPadDenseMapInfo, detail::DenseSetPair<CatchPadInst *>>
@@ -2295,14 +2296,22 @@ static bool markAliveBlocks(Function &F,
                                              E = CatchSwitch->handler_end();
            I != E; ++I) {
         BasicBlock *HandlerBB = *I;
+        ++NumPerSuccessorCases[HandlerBB];
         auto *CatchPad = cast<CatchPadInst>(HandlerBB->getFirstNonPHI());
         if (!HandlerSet.insert({CatchPad, Empty}).second) {
+          --NumPerSuccessorCases[HandlerBB];
           CatchSwitch->removeHandler(I);
           --I;
           --E;
           Changed = true;
         }
       }
+      std::vector<DominatorTree::UpdateType> Updates;
+      for (const std::pair<BasicBlock *, int> &I : NumPerSuccessorCases)
+        if (I.second == 0)
+          Updates.push_back({DominatorTree::Delete, BB, I.first});
+      if (DTU)
+        DTU->applyUpdates(Updates);
     }
 
     Changed |= ConstantFoldTerminator(BB, true, nullptr, DTU);