[JumpThreading] Bail out maybeMergeBasicBlockIntoOnlyPred if SinglePred is in Unreachable.

Merge SinglePred and its successor may delete SinglePred, and causes
garbage pointer in Unreachable. Bail out
maybeMergeBasicBlockIntoOnlyPred if we found this case.

Author: weiguozhi

llvm/lib/Transforms/Scalar/JumpThreading.cpp

@@ -1894,16 +1894,18 @@ bool JumpThreadingPass::maybeMergeBasicBlockIntoOnlyPred(BasicBlock *BB) {
       SinglePred == BB || hasAddressTakenAndUsed(BB))
     return false;
 
+  // MergeBasicBlockIntoOnlyPred may delete SinglePred, we need to avoid
+  // deleting a BB pointer from Unreachable.
+  if (Unreachable.count(SinglePred))
+    return false;
+
   // If SinglePred was a loop header, BB becomes one.
   if (LoopHeaders.erase(SinglePred))
     LoopHeaders.insert(BB);
 
   LVI->eraseBlock(SinglePred);
   MergeBasicBlockIntoOnlyPred(BB, DTU.get());
 
-  if (Unreachable.count(SinglePred) && DTU->isBBPendingDeletion(SinglePred))
-    Unreachable.erase(SinglePred);
-
   // Now that BB is merged into SinglePred (i.e. SinglePred code followed by
   // BB code within one basic block `BB`), we need to invalidate the LVI
   // information associated with BB, because the LVI information need not be

llvm/test/Transforms/JumpThreading/pr62908.ll

@@ -5,7 +5,7 @@
 
 define i32 @test() {
 ; CHECK-LABEL: define i32 @test() {
-; CHECK-NEXT:  end:
+; CHECK:       end:
 ; CHECK-NEXT:    ret i32 0
 ;
 entry: