Revert "[CVP] Check whether the default case is reachable (#79993)" (#81585)

This reverts commit a034e65e972175a2465deacb8c78bc7efc99bd23.

Some protobuf users reported that this patch caused a significant
compile-time regression because `TailDuplicator` works poorly with a
specific pattern.

We will reland it once the codegen issue is fixed.

1 files changed, 0 insertions, 34 deletions

diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index 24e1677..9235850 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -371,7 +371,6 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
   { // Scope for SwitchInstProfUpdateWrapper. It must not live during
     // ConstantFoldTerminator() as the underlying SwitchInst can be changed.
     SwitchInstProfUpdateWrapper SI(*I);
-    unsigned ReachableCaseCount = 0;
 
     for (auto CI = SI->case_begin(), CE = SI->case_end(); CI != CE;) {
       ConstantInt *Case = CI->getCaseValue();
@@ -408,33 +407,6 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
 
       // Increment the case iterator since we didn't delete it.
       ++CI;
-      ++ReachableCaseCount;
-    }
-
-    BasicBlock *DefaultDest = SI->getDefaultDest();
-    if (ReachableCaseCount > 1 &&
-        !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())) {
-      ConstantRange CR = LVI->getConstantRangeAtUse(I->getOperandUse(0),
-                                                    /*UndefAllowed*/ false);
-      // The default dest is unreachable if all cases are covered.
-      if (!CR.isSizeLargerThan(ReachableCaseCount)) {
-        BasicBlock *NewUnreachableBB =
-            BasicBlock::Create(BB->getContext(), "default.unreachable",
-                               BB->getParent(), DefaultDest);
-        new UnreachableInst(BB->getContext(), NewUnreachableBB);
-
-        DefaultDest->removePredecessor(BB);
-        SI->setDefaultDest(NewUnreachableBB);
-
-        if (SuccessorsCount[DefaultDest] == 1)
-          DTU.applyUpdatesPermissive(
-              {{DominatorTree::Delete, BB, DefaultDest}});
-        DTU.applyUpdatesPermissive(
-            {{DominatorTree::Insert, BB, NewUnreachableBB}});
-
-        ++NumDeadCases;
-        Changed = true;
-      }
     }
   }
 
@@ -1255,12 +1227,6 @@ CorrelatedValuePropagationPass::run(Function &F, FunctionAnalysisManager &AM) {
   if (!Changed) {
     PA = PreservedAnalyses::all();
   } else {
-#if defined(EXPENSIVE_CHECKS)
-    assert(DT->verify(DominatorTree::VerificationLevel::Full));
-#else
-    assert(DT->verify(DominatorTree::VerificationLevel::Fast));
-#endif // EXPENSIVE_CHECKS
-
     PA.preserve<DominatorTreeAnalysis>();
     PA.preserve<LazyValueAnalysis>();
   }