1 files changed, 22 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopDistribute.cpp b/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
index 1584f0fa3eb..67ebd2532b1 100644
--- a/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
@@ -55,6 +55,11 @@ static cl::opt<bool> DistributeNonIfConvertible(
              "if-convertible by the loop vectorizer"),
     cl::init(false));
 
+static cl::opt<unsigned> DistributeSCEVCheckThreshold(
+    "loop-distribute-scev-check-threshold", cl::init(8), cl::Hidden,
+    cl::desc("The maximum number of SCEV checks allowed for Loop "
+             "Distribution"));
+
 STATISTIC(NumLoopsDistributed, "Number of loops distributed");
 
 namespace {
@@ -577,6 +582,7 @@ public:
     LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
     LAA = &getAnalysis<LoopAccessAnalysis>();
     DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+    SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
 
     // Build up a worklist of inner-loops to vectorize. This is necessary as the
     // act of distributing a loop creates new loops and can invalidate iterators
@@ -599,6 +605,7 @@ public:
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<ScalarEvolutionWrapperPass>();
     AU.addRequired<LoopInfoWrapperPass>();
     AU.addPreserved<LoopInfoWrapperPass>();
     AU.addRequired<LoopAccessAnalysis>();
@@ -753,6 +760,13 @@ private:
         return false;
     }
 
+    // Don't distribute the loop if we need too many SCEV run-time checks.
+    const SCEVUnionPredicate &Pred = LAI.Preds;
+    if (Pred.getComplexity() > DistributeSCEVCheckThreshold) {
+      DEBUG(dbgs() << "Too many SCEV run-time checks needed.\n");
+      return false;
+    }
+
     DEBUG(dbgs() << "\nDistributing loop: " << *L << "\n");
     // We're done forming the partitions set up the reverse mapping from
     // instructions to partitions.
@@ -764,17 +778,19 @@ private:
     if (!PH->getSinglePredecessor() || &*PH->begin() != PH->getTerminator())
       SplitBlock(PH, PH->getTerminator(), DT, LI);
 
-    // If we need run-time checks to disambiguate pointers are run-time, version
-    // the loop now.
+    // If we need run-time checks, version the loop now.
     auto PtrToPartition = Partitions.computePartitionSetForPointers(LAI);
     const auto *RtPtrChecking = LAI.getRuntimePointerChecking();
     const auto &AllChecks = RtPtrChecking->getChecks();
     auto Checks = includeOnlyCrossPartitionChecks(AllChecks, PtrToPartition,
                                                   RtPtrChecking);
-    if (!Checks.empty()) {
+
+    if (!Pred.isAlwaysTrue() || !Checks.empty()) {
       DEBUG(dbgs() << "\nPointers:\n");
       DEBUG(LAI.getRuntimePointerChecking()->printChecks(dbgs(), Checks));
-      LoopVersioning LVer(std::move(Checks), LAI, L, LI, DT);
+      LoopVersioning LVer(LAI, L, LI, DT, SE, false);
+      LVer.setAliasChecks(std::move(Checks));
+      LVer.setSCEVChecks(LAI.Preds);
       LVer.versionLoop(DefsUsedOutside);
     }
 
@@ -801,6 +817,7 @@ private:
   LoopInfo *LI;
   LoopAccessAnalysis *LAA;
   DominatorTree *DT;
+  ScalarEvolution *SE;
 };
 } // anonymous namespace
 
@@ -811,6 +828,7 @@ INITIALIZE_PASS_BEGIN(LoopDistribute, LDIST_NAME, ldist_name, false, false)
 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(LoopAccessAnalysis)
 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
 INITIALIZE_PASS_END(LoopDistribute, LDIST_NAME, ldist_name, false, false)
 
 namespace llvm {