[LoopVectorize] Use new getUniqueLatchExitBlock routine

llvm/include/llvm/Support/GenericLoopInfo.h

@@ -294,6 +294,10 @@ template <class BlockT, class LoopT> class LoopBase {
   /// Otherwise return null.
   BlockT *getUniqueExitBlock() const;
 
+  /// Return the unique exit block for the latch, or null if there are multiple
+  /// different exit blocks or the latch is not exiting.
+  BlockT *getUniqueLatchExitBlock() const;
+
   /// Return true if this loop does not have any exit blocks.
   bool hasNoExitBlocks() const;
 

llvm/include/llvm/Support/GenericLoopInfoImpl.h

@@ -159,6 +159,17 @@ BlockT *LoopBase<BlockT, LoopT>::getUniqueExitBlock() const {
   return getExitBlockHelper(this, true).first;
 }
 
+template <class BlockT, class LoopT>
+BlockT *LoopBase<BlockT, LoopT>::getUniqueLatchExitBlock() const {
+  BlockT *Latch = getLoopLatch();
+  assert(Latch && "Latch block must exists");
+  auto IsExitBlock = [this](BlockT *BB, bool AllowRepeats) -> BlockT * {
+    assert(!AllowRepeats && "Unexpected parameter value.");
+    return !contains(BB) ? BB : nullptr;
+  };
+  return find_singleton<BlockT>(children<BlockT *>(Latch), IsExitBlock);
+}
+
 /// getExitEdges - Return all pairs of (_inside_block_,_outside_block_).
 template <class BlockT, class LoopT>
 void LoopBase<BlockT, LoopT>::getExitEdges(

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -634,10 +634,6 @@ class InnerLoopVectorizer {
   /// Middle Block between the vector and the scalar.
   BasicBlock *LoopMiddleBlock;
 
-  /// The unique ExitBlock of the scalar loop if one exists.  Note that
-  /// there can be multiple exiting edges reaching this block.
-  BasicBlock *LoopExitBlock;
-
   /// A list of all bypass blocks. The first block is the entry of the loop.
   SmallVector<BasicBlock *, 4> LoopBypassBlocks;
 
@@ -1365,8 +1361,8 @@ class LoopVectorizationCostModel {
     // If we might exit from anywhere but the latch, must run the exiting
     // iteration in scalar form.
     if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) {
-      LLVM_DEBUG(
-          dbgs() << "LV: Loop requires scalar epilogue: multiple exits\n");
+      LLVM_DEBUG(dbgs() << "LV: Loop requires scalar epilogue: not exiting "
+                           "from latch block\n");
       return true;
     }
     if (IsVectorizing && InterleaveInfo.requiresScalarEpilogue()) {
@@ -2025,8 +2021,7 @@ class GeneratedRTChecks {
   /// adjusts the branches to branch to the vector preheader or \p Bypass,
   /// depending on the generated condition.
   BasicBlock *emitSCEVChecks(BasicBlock *Bypass,
-                             BasicBlock *LoopVectorPreHeader,
-                             BasicBlock *LoopExitBlock) {
+                             BasicBlock *LoopVectorPreHeader) {
     if (!SCEVCheckCond)
       return nullptr;
 
@@ -2522,7 +2517,7 @@ void InnerLoopVectorizer::emitIterationCountCheck(BasicBlock *Bypass) {
 
 BasicBlock *InnerLoopVectorizer::emitSCEVChecks(BasicBlock *Bypass) {
   BasicBlock *const SCEVCheckBlock =
-      RTChecks.emitSCEVChecks(Bypass, LoopVectorPreHeader, LoopExitBlock);
+      RTChecks.emitSCEVChecks(Bypass, LoopVectorPreHeader);
   if (!SCEVCheckBlock)
     return nullptr;
 
@@ -2576,8 +2571,8 @@ BasicBlock *InnerLoopVectorizer::emitMemRuntimeChecks(BasicBlock *Bypass) {
 void InnerLoopVectorizer::createVectorLoopSkeleton(StringRef Prefix) {
   LoopVectorPreHeader = OrigLoop->getLoopPreheader();
   assert(LoopVectorPreHeader && "Invalid loop structure");
-  LoopExitBlock = OrigLoop->getUniqueExitBlock(); // may be nullptr
-  assert((LoopExitBlock || Cost->requiresScalarEpilogue(VF.isVector())) &&
+  assert((OrigLoop->getUniqueExitBlock() ||
+          Cost->requiresScalarEpilogue(VF.isVector())) &&
          "multiple exit loop without required epilogue?");
 
   LoopMiddleBlock =
@@ -7927,7 +7922,7 @@ EpilogueVectorizerEpilogueLoop::createEpilogueVectorizedLoopSkeleton(
     // If there is an epilogue which must run, there's no edge from the
     // middle block to exit blocks  and thus no need to update the immediate
     // dominator of the exit blocks.
-    DT->changeImmediateDominator(LoopExitBlock,
+    DT->changeImmediateDominator(OrigLoop->getUniqueLatchExitBlock(),
                                  EPI.EpilogueIterationCountCheck);
 
   // Keep track of bypass blocks, as they feed start values to the induction and