1 files changed, 21 insertions, 2 deletions
diff --git a/contrib/llvm-project/llvm/lib/Transforms/Scalar/SCCP.cpp b/contrib/llvm-project/llvm/lib/Transforms/Scalar/SCCP.cpp
index c34da51e6dc1..fa1cfc84e4fd 100644
--- a/contrib/llvm-project/llvm/lib/Transforms/Scalar/SCCP.cpp
+++ b/contrib/llvm-project/llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -342,7 +342,8 @@ static void findReturnsToZap(Function &F,
 }
 
 static bool removeNonFeasibleEdges(const SCCPSolver &Solver, BasicBlock *BB,
-                                   DomTreeUpdater &DTU) {
+                                   DomTreeUpdater &DTU,
+                                   BasicBlock *&NewUnreachableBB) {
   SmallPtrSet<BasicBlock *, 8> FeasibleSuccessors;
   bool HasNonFeasibleEdges = false;
   for (BasicBlock *Succ : successors(BB)) {
@@ -385,6 +386,23 @@ static bool removeNonFeasibleEdges(const SCCPSolver &Solver, BasicBlock *BB,
   } else if (FeasibleSuccessors.size() > 1) {
     SwitchInstProfUpdateWrapper SI(*cast<SwitchInst>(TI));
     SmallVector<DominatorTree::UpdateType, 8> Updates;
+
+    // If the default destination is unfeasible it will never be taken. Replace
+    // it with a new block with a single Unreachable instruction.
+    BasicBlock *DefaultDest = SI->getDefaultDest();
+    if (!FeasibleSuccessors.contains(DefaultDest)) {
+      if (!NewUnreachableBB) {
+        NewUnreachableBB =
+            BasicBlock::Create(DefaultDest->getContext(), "default.unreachable",
+                               DefaultDest->getParent(), DefaultDest);
+        new UnreachableInst(DefaultDest->getContext(), NewUnreachableBB);
+      }
+
+      SI->setDefaultDest(NewUnreachableBB);
+      Updates.push_back({DominatorTree::Delete, BB, DefaultDest});
+      Updates.push_back({DominatorTree::Insert, BB, NewUnreachableBB});
+    }
+
     for (auto CI = SI->case_begin(); CI != SI->case_end();) {
       if (FeasibleSuccessors.contains(CI->getCaseSuccessor())) {
         ++CI;
@@ -532,8 +550,9 @@ bool llvm::runIPSCCP(
       NumInstRemoved += changeToUnreachable(F.front().getFirstNonPHI(),
                                             /*PreserveLCSSA=*/false, &DTU);
 
+    BasicBlock *NewUnreachableBB = nullptr;
     for (BasicBlock &BB : F)
-      MadeChanges |= removeNonFeasibleEdges(Solver, &BB, DTU);
+      MadeChanges |= removeNonFeasibleEdges(Solver, &BB, DTU, NewUnreachableBB);
 
     for (BasicBlock *DeadBB : BlocksToErase)
       DTU.deleteBB(DeadBB);