[LV] Move IV bypass value creation out of ILV (NFC)

createInductionAdditionalBypassValues is only used for epilogue
vectorization now. Move it out of ILV, which means we do not have to
thread through ExpandedSCEVs and also don't have to track the bypass
values in ILV. Instead, directly create them if needed after executing
the epilogue plan. This moves more the epilogue specific logic out of
the generic executePlan.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h

@@ -442,17 +442,15 @@ class LoopVectorizationPlanner {
   /// TODO: \p VectorizingEpilogue indicates if the executed VPlan is for the
   /// epilogue vector loop. It should be removed once the re-use issue has been
   /// fixed.
-  /// \p ExpandedSCEVs is passed during execution of the plan for epilogue loop
-  /// to re-use expansion results generated during main plan execution.
   ///
   /// Returns a mapping of SCEVs to their expanded IR values.
   /// Note that this is a temporary workaround needed due to the current
   /// epilogue handling.
-  DenseMap<const SCEV *, Value *>
-  executePlan(ElementCount VF, unsigned UF, VPlan &BestPlan,
-              InnerLoopVectorizer &LB, DominatorTree *DT,
-              bool VectorizingEpilogue,
-              const DenseMap<const SCEV *, Value *> *ExpandedSCEVs = nullptr);
+  DenseMap<const SCEV *, Value *> executePlan(ElementCount VF, unsigned UF,
+                                              VPlan &BestPlan,
+                                              InnerLoopVectorizer &LB,
+                                              DominatorTree *DT,
+                                              bool VectorizingEpilogue);
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
   void printPlans(raw_ostream &O);

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -494,11 +494,8 @@ class InnerLoopVectorizer {
   /// is generated around the vectorized (and scalar epilogue) loops consisting
   /// of various checks and bypasses. Return the pre-header block of the new
   /// loop. In the case of epilogue vectorization, this function is overriden to
-  /// handle the more complex control flow around the loops. \p ExpandedSCEVs is
-  /// used to look up SCEV expansions for expressions needed during skeleton
-  /// creation.
-  virtual BasicBlock *
-  createVectorizedLoopSkeleton(const SCEV2ValueTy &ExpandedSCEVs);
+  /// handle the more complex control flow around the loops.
+  virtual BasicBlock *createVectorizedLoopSkeleton();
 
   /// Fix the vectorized code, taking care of header phi's, and more.
   void fixVectorizedLoop(VPTransformState &State);
@@ -526,12 +523,6 @@ class InnerLoopVectorizer {
   /// count of the original loop for both main loop and epilogue vectorization.
   void setTripCount(Value *TC) { TripCount = TC; }
 
-  // Retrieve the additional bypass value associated with an original
-  /// induction header phi.
-  Value *getInductionAdditionalBypassValue(PHINode *OrigPhi) const {
-    return Induction2AdditionalBypassValue.at(OrigPhi);
-  }
-
   /// Return the additional bypass block which targets the scalar loop by
   /// skipping the epilogue loop after completing the main loop.
   BasicBlock *getAdditionalBypassBlock() const {
@@ -568,11 +559,6 @@ class InnerLoopVectorizer {
   /// vector loop preheader, middle block and scalar preheader.
   void createVectorLoopSkeleton(StringRef Prefix);
 
-  /// Create and record the values for induction variables to resume coming from
-  /// the additional bypass block.
-  void createInductionAdditionalBypassValues(const SCEV2ValueTy &ExpandedSCEVs,
-                                             Value *MainVectorTripCount);
-
   /// Allow subclasses to override and print debug traces before/after vplan
   /// execution, when trace information is requested.
   virtual void printDebugTracesAtStart() {}
@@ -666,11 +652,6 @@ class InnerLoopVectorizer {
   /// for cleaning the checks, if vectorization turns out unprofitable.
   GeneratedRTChecks &RTChecks;
 
-  /// Mapping of induction phis to their additional bypass values. They
-  /// need to be added as operands to phi nodes in the scalar loop preheader
-  /// after the epilogue skeleton has been created.
-  DenseMap<PHINode *, Value *> Induction2AdditionalBypassValue;
-
   /// The additional bypass block which conditionally skips over the epilogue
   /// loop after executing the main loop. Needed to resume inductions and
   /// reductions during epilogue vectorization.
@@ -733,16 +714,14 @@ class InnerLoopAndEpilogueVectorizer : public InnerLoopVectorizer {
 
   // Override this function to handle the more complex control flow around the
   // three loops.
-  BasicBlock *
-  createVectorizedLoopSkeleton(const SCEV2ValueTy &ExpandedSCEVs) final {
-    return createEpilogueVectorizedLoopSkeleton(ExpandedSCEVs);
+  BasicBlock *createVectorizedLoopSkeleton() final {
+    return createEpilogueVectorizedLoopSkeleton();
   }
 
   /// The interface for creating a vectorized skeleton using one of two
   /// different strategies, each corresponding to one execution of the vplan
   /// as described above.
-  virtual BasicBlock *
-  createEpilogueVectorizedLoopSkeleton(const SCEV2ValueTy &ExpandedSCEVs) = 0;
+  virtual BasicBlock *createEpilogueVectorizedLoopSkeleton() = 0;
 
   /// Holds and updates state information required to vectorize the main loop
   /// and its epilogue in two separate passes. This setup helps us avoid
@@ -770,8 +749,7 @@ class EpilogueVectorizerMainLoop : public InnerLoopAndEpilogueVectorizer {
                                        EPI, LVL, CM, BFI, PSI, Check, Plan) {}
   /// Implements the interface for creating a vectorized skeleton using the
   /// *main loop* strategy (ie the first pass of vplan execution).
-  BasicBlock *
-  createEpilogueVectorizedLoopSkeleton(const SCEV2ValueTy &ExpandedSCEVs) final;
+  BasicBlock *createEpilogueVectorizedLoopSkeleton() final;
 
 protected:
   /// Emits an iteration count bypass check once for the main loop (when \p
@@ -801,8 +779,7 @@ class EpilogueVectorizerEpilogueLoop : public InnerLoopAndEpilogueVectorizer {
   }
   /// Implements the interface for creating a vectorized skeleton using the
   /// *epilogue loop* strategy (ie the second pass of vplan execution).
-  BasicBlock *
-  createEpilogueVectorizedLoopSkeleton(const SCEV2ValueTy &ExpandedSCEVs) final;
+  BasicBlock *createEpilogueVectorizedLoopSkeleton() final;
 
 protected:
   /// Emits an iteration count bypass check after the main vector loop has
@@ -2679,44 +2656,7 @@ static void addFullyUnrolledInstructionsToIgnore(
   }
 }
 
-void InnerLoopVectorizer::createInductionAdditionalBypassValues(
-    const SCEV2ValueTy &ExpandedSCEVs, Value *MainVectorTripCount) {
-  assert(MainVectorTripCount && "Must have bypass information");
-
-  Instruction *OldInduction = Legal->getPrimaryInduction();
-  IRBuilder<> BypassBuilder(getAdditionalBypassBlock(),
-                            getAdditionalBypassBlock()->getFirstInsertionPt());
-  for (const auto &InductionEntry : Legal->getInductionVars()) {
-    PHINode *OrigPhi = InductionEntry.first;
-    const InductionDescriptor &II = InductionEntry.second;
-    Value *Step = getExpandedStep(II, ExpandedSCEVs);
-    // For the primary induction the additional bypass end value is known.
-    // Otherwise it is computed.
-    Value *EndValueFromAdditionalBypass = MainVectorTripCount;
-    if (OrigPhi != OldInduction) {
-      auto *BinOp = II.getInductionBinOp();
-      // Fast-math-flags propagate from the original induction instruction.
-      if (isa_and_nonnull<FPMathOperator>(BinOp))
-        BypassBuilder.setFastMathFlags(BinOp->getFastMathFlags());
-
-      // Compute the end value for the additional bypass.
-      EndValueFromAdditionalBypass =
-          emitTransformedIndex(BypassBuilder, MainVectorTripCount,
-                               II.getStartValue(), Step, II.getKind(), BinOp);
-      EndValueFromAdditionalBypass->setName("ind.end");
-    }
-
-    // Store the bypass value here, as it needs to be added as operand to its
-    // scalar preheader phi node after the epilogue skeleton has been created.
-    // TODO: Directly add as extra operand to the VPResumePHI recipe.
-    assert(!Induction2AdditionalBypassValue.contains(OrigPhi) &&
-           "entry for OrigPhi already exits");
-    Induction2AdditionalBypassValue[OrigPhi] = EndValueFromAdditionalBypass;
-  }
-}
-
-BasicBlock *InnerLoopVectorizer::createVectorizedLoopSkeleton(
-    const SCEV2ValueTy &ExpandedSCEVs) {
+BasicBlock *InnerLoopVectorizer::createVectorizedLoopSkeleton() {
   /*
    In this function we generate a new loop. The new loop will contain
    the vectorized instructions while the old loop will continue to run the
@@ -7628,17 +7568,11 @@ static void fixReductionScalarResumeWhenVectorizingEpilog(
 
 DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
     ElementCount BestVF, unsigned BestUF, VPlan &BestVPlan,
-    InnerLoopVectorizer &ILV, DominatorTree *DT, bool VectorizingEpilogue,
-    const DenseMap<const SCEV *, Value *> *ExpandedSCEVs) {
+    InnerLoopVectorizer &ILV, DominatorTree *DT, bool VectorizingEpilogue) {
   assert(BestVPlan.hasVF(BestVF) &&
          "Trying to execute plan with unsupported VF");
   assert(BestVPlan.hasUF(BestUF) &&
          "Trying to execute plan with unsupported UF");
-  assert(
-      ((VectorizingEpilogue && ExpandedSCEVs) ||
-       (!VectorizingEpilogue && !ExpandedSCEVs)) &&
-      "expanded SCEVs to reuse can only be used during epilogue vectorization");
-
   // TODO: Move to VPlan transform stage once the transition to the VPlan-based
   // cost model is complete for better cost estimates.
   VPlanTransforms::unrollByUF(BestVPlan, BestUF,
@@ -7670,8 +7604,8 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   // middle block. The vector loop is created during VPlan execution.
   VPBasicBlock *VectorPH =
       cast<VPBasicBlock>(BestVPlan.getEntry()->getSingleSuccessor());
-  State.CFG.PrevBB = ILV.createVectorizedLoopSkeleton(
-      ExpandedSCEVs ? *ExpandedSCEVs : State.ExpandedSCEVs);
+
+  State.CFG.PrevBB = ILV.createVectorizedLoopSkeleton();
   if (VectorizingEpilogue)
     VPlanTransforms::removeDeadRecipes(BestVPlan);
 
@@ -7712,8 +7646,8 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   BestVPlan.execute(&State);
 
   auto *MiddleVPBB = BestVPlan.getMiddleBlock();
-  // 2.5 When vectorizing the epilogue, fix reduction and induction resume
-  // values from the additional bypass block.
+  // 2.5 When vectorizing the epilogue, fix reduction resume values from the
+  // additional bypass block.
   if (VectorizingEpilogue) {
     assert(!ILV.Legal->hasUncountableEarlyExit() &&
            "Epilogue vectorisation not yet supported with early exits");
@@ -7722,12 +7656,6 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
       fixReductionScalarResumeWhenVectorizingEpilog(
           &R, State, State.CFG.VPBB2IRBB[MiddleVPBB], BypassBlock);
     }
-    BasicBlock *PH = OrigLoop->getLoopPreheader();
-    for (const auto &[IVPhi, _] : Legal->getInductionVars()) {
-      auto *Inc = cast<PHINode>(IVPhi->getIncomingValueForBlock(PH));
-      Value *V = ILV.getInductionAdditionalBypassValue(IVPhi);
-      Inc->setIncomingValueForBlock(BypassBlock, V);
-    }
   }
 
   // 2.6. Maintain Loop Hints
@@ -7789,8 +7717,7 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
 
 /// This function is partially responsible for generating the control flow
 /// depicted in https://llvm.org/docs/Vectorizers.html#epilogue-vectorization.
-BasicBlock *EpilogueVectorizerMainLoop::createEpilogueVectorizedLoopSkeleton(
-    const SCEV2ValueTy &ExpandedSCEVs) {
+BasicBlock *EpilogueVectorizerMainLoop::createEpilogueVectorizedLoopSkeleton() {
   createVectorLoopSkeleton("");
 
   // Generate the code to check the minimum iteration count of the vector
@@ -7900,8 +7827,7 @@ EpilogueVectorizerMainLoop::emitIterationCountCheck(BasicBlock *Bypass,
 /// This function is partially responsible for generating the control flow
 /// depicted in https://llvm.org/docs/Vectorizers.html#epilogue-vectorization.
 BasicBlock *
-EpilogueVectorizerEpilogueLoop::createEpilogueVectorizedLoopSkeleton(
-    const SCEV2ValueTy &ExpandedSCEVs) {
+EpilogueVectorizerEpilogueLoop::createEpilogueVectorizedLoopSkeleton() {
   createVectorLoopSkeleton("vec.epilog.");
 
   // Now, compare the remaining count and if there aren't enough iterations to
@@ -7969,11 +7895,6 @@ EpilogueVectorizerEpilogueLoop::createEpilogueVectorizedLoopSkeleton(
       Phi->removeIncomingValue(EPI.MemSafetyCheck);
   }
 
-  // Generate bypass values from the additional bypass block. Note that when the
-  // vectorized epilogue is skipped due to iteration count check, then the
-  // resume value for the induction variable comes from the trip count of the
-  // main vector loop, passed as the second argument.
-  createInductionAdditionalBypassValues(ExpandedSCEVs, EPI.VectorTripCount);
   return LoopVectorPreHeader;
 }
 
@@ -10314,6 +10235,33 @@ preparePlanForEpilogueVectorLoop(VPlan &Plan, Loop *L,
   }
 }
 
+// Generate bypass values from the additional bypass block. Note that when the
+// vectorized epilogue is skipped due to iteration count check, then the
+// resume value for the induction variable comes from the trip count of the
+// main vector loop, passed as the second argument.
+static Value *createInductionAdditionalBypassValues(
+    PHINode *OrigPhi, const InductionDescriptor &II, IRBuilder<> &BypassBuilder,
+    const SCEV2ValueTy &ExpandedSCEVs, Value *MainVectorTripCount,
+    Instruction *OldInduction) {
+  Value *Step = getExpandedStep(II, ExpandedSCEVs);
+  // For the primary induction the additional bypass end value is known.
+  // Otherwise it is computed.
+  Value *EndValueFromAdditionalBypass = MainVectorTripCount;
+  if (OrigPhi != OldInduction) {
+    auto *BinOp = II.getInductionBinOp();
+    // Fast-math-flags propagate from the original induction instruction.
+    if (isa_and_nonnull<FPMathOperator>(BinOp))
+      BypassBuilder.setFastMathFlags(BinOp->getFastMathFlags());
+
+    // Compute the end value for the additional bypass.
+    EndValueFromAdditionalBypass =
+        emitTransformedIndex(BypassBuilder, MainVectorTripCount,
+                             II.getStartValue(), Step, II.getKind(), BinOp);
+    EndValueFromAdditionalBypass->setName("ind.end");
+  }
+  return EndValueFromAdditionalBypass;
+}
+
 bool LoopVectorizePass::processLoop(Loop *L) {
   assert((EnableVPlanNativePath || L->isInnermost()) &&
          "VPlan-native path is not enabled. Only process inner loops.");
@@ -10699,7 +10647,21 @@ bool LoopVectorizePass::processLoop(Loop *L) {
         preparePlanForEpilogueVectorLoop(BestEpiPlan, L, ExpandedSCEVs, EPI);
 
         LVP.executePlan(EPI.EpilogueVF, EPI.EpilogueUF, BestEpiPlan, EpilogILV,
-                        DT, true, &ExpandedSCEVs);
+                        DT, true);
+
+        // Fix induction resume values from the additional bypass block.
+        BasicBlock *BypassBlock = EpilogILV.getAdditionalBypassBlock();
+        IRBuilder<> BypassBuilder(BypassBlock,
+                                  BypassBlock->getFirstInsertionPt());
+        BasicBlock *PH = L->getLoopPreheader();
+        for (const auto &[IVPhi, II] : LVL.getInductionVars()) {
+          auto *Inc = cast<PHINode>(IVPhi->getIncomingValueForBlock(PH));
+          Value *V = createInductionAdditionalBypassValues(
+              IVPhi, II, BypassBuilder, ExpandedSCEVs, EPI.VectorTripCount,
+              LVL.getPrimaryInduction());
+          // TODO: Directly add as extra operand to the VPResumePHI recipe.
+          Inc->setIncomingValueForBlock(BypassBlock, V);
+        }
         ++LoopsEpilogueVectorized;
 
         if (!MainILV.areSafetyChecksAdded())

llvm/test/Transforms/LoopVectorize/X86/scatter_crash.ll

@@ -183,7 +183,7 @@ define void @_Z3fn1v() #0 {
 ; CHECK-NEXT:    [[DOTSPLAT68:%.*]] = shufflevector <8 x i64> [[DOTSPLATINSERT67]], <8 x i64> poison, <8 x i32> zeroinitializer
 ; CHECK-NEXT:    [[INDUCTION69:%.*]] = add <8 x i64> [[DOTSPLAT68]], <i64 0, i64 2, i64 4, i64 6, i64 8, i64 10, i64 12, i64 14>
 ; CHECK-NEXT:    br label [[VEC_EPILOG_VECTOR_BODY50:%.*]]
-; CHECK:       vec.epilog.vector.body52:
+; CHECK:       vec.epilog.vector.body50:
 ; CHECK-NEXT:    [[INDEX61:%.*]] = phi i64 [ [[VEC_EPILOG_RESUME_VAL51]], [[VEC_EPILOG_PH42]] ], [ [[INDEX_NEXT74:%.*]], [[VEC_EPILOG_VECTOR_BODY50]] ]
 ; CHECK-NEXT:    [[VEC_IND65:%.*]] = phi <8 x i64> [ [[INDUCTION64]], [[VEC_EPILOG_PH42]] ], [ [[VEC_IND_NEXT66:%.*]], [[VEC_EPILOG_VECTOR_BODY50]] ]
 ; CHECK-NEXT:    [[VEC_IND70:%.*]] = phi <8 x i64> [ [[INDUCTION69]], [[VEC_EPILOG_PH42]] ], [ [[VEC_IND_NEXT71:%.*]], [[VEC_EPILOG_VECTOR_BODY50]] ]