[VPlan] Compute interleave count for VPlan.

Move selectInterleaveCount to LoopVectorizationPlanner and retrieve some
information directly from VPlan. Register pressure was already computed
for a VPlan, and with this patch we now also check for reductions
directly on VPlan, as well as checking how many load and store
operations remain in the loop.

This should be mostly NFC, but we may compute slightly different
interleave counts, except for some edge cases, e.g. where dead loads have
been removed. This shouldn't happen in practice, and the patch doesn't
cause changes across a large test corpus on AArch64.

Computing the interleave count based on VPlan allows for making better
decisions in presence of VPlan optimizations, for example when
operations on interleave groups are narrowed.

Note that there are a few test changes for tests that were still
checking the legacy cost-model output when it was computed in
selectInterleaveCount.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h

@@ -487,6 +487,9 @@ class LoopVectorizationPlanner {
   /// all profitable VFs in ProfitableVFs.
   VectorizationFactor computeBestVF();
 
+  unsigned selectInterleaveCount(VPlan &Plan, ElementCount VF,
+                                 InstructionCost LoopCost);
+
   /// Generate the IR code for the vectorized loop captured in VPlan \p BestPlan
   /// according to the best selected \p VF and  \p UF.
   ///

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -955,13 +955,6 @@ class LoopVectorizationCostModel {
   /// 64 bit loop indices.
   std::pair<unsigned, unsigned> getSmallestAndWidestTypes();
 
-  /// \return The desired interleave count.
-  /// If interleave count has been specified by metadata it will be returned.
-  /// Otherwise, the interleave count is computed and returned. VF and LoopCost
-  /// are the selected vectorization factor and the cost of the selected VF.
-  unsigned selectInterleaveCount(VPlan &Plan, ElementCount VF,
-                                 InstructionCost LoopCost);
-
   /// Memory access instruction may be vectorized in more than one way.
   /// Form of instruction after vectorization depends on cost.
   /// This function takes cost-based decisions for Load/Store instructions
@@ -4606,8 +4599,8 @@ void LoopVectorizationCostModel::collectElementTypesForWidening() {
 }
 
 unsigned
-LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
-                                                  InstructionCost LoopCost) {
+LoopVectorizationPlanner::selectInterleaveCount(VPlan &Plan, ElementCount VF,
+                                                InstructionCost LoopCost) {
   // -- The interleave heuristics --
   // We interleave the loop in order to expose ILP and reduce the loop overhead.
   // There are many micro-architectural considerations that we can't predict
@@ -4622,32 +4615,36 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
   // 3. We don't interleave if we think that we will spill registers to memory
   // due to the increased register pressure.
 
-  if (!isScalarEpilogueAllowed())
+  if (!CM.isScalarEpilogueAllowed())
     return 1;
 
-  // Do not interleave if EVL is preferred and no User IC is specified.
-  if (foldTailWithEVL()) {
+  if (any_of(Plan.getVectorLoopRegion()->getEntryBasicBlock()->phis(),
+             IsaPred<VPEVLBasedIVPHIRecipe>)) {
     LLVM_DEBUG(dbgs() << "LV: Preference for VP intrinsics indicated. "
                          "Unroll factor forced to be 1.\n");
     return 1;
   }
-
   // We used the distance for the interleave count.
   if (!Legal->isSafeForAnyVectorWidth())
     return 1;
 
   // We don't attempt to perform interleaving for loops with uncountable early
   // exits because the VPInstruction::AnyOf code cannot currently handle
   // multiple parts.
-  if (Legal->hasUncountableEarlyExit())
+  if (Plan.hasEarlyExit())
     return 1;
 
-  const bool HasReductions = !Legal->getReductionVars().empty();
+  const bool HasReductions =
+      any_of(Plan.getVectorLoopRegion()->getEntryBasicBlock()->phis(),
+             IsaPred<VPReductionPHIRecipe>);
 
   // If we did not calculate the cost for VF (because the user selected the VF)
   // then we calculate the cost of VF here.
   if (LoopCost == 0) {
-    LoopCost = expectedCost(VF);
+    if (VF.isScalar())
+      LoopCost = CM.expectedCost(VF);
+    else
+      LoopCost = cost(Plan, VF);
     assert(LoopCost.isValid() && "Expected to have chosen a VF with valid cost");
 
     // Loop body is free and there is no need for interleaving.
@@ -4656,7 +4653,7 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
   }
 
   VPRegisterUsage R =
-      calculateRegisterUsageForPlan(Plan, {VF}, TTI, ValuesToIgnore)[0];
+      calculateRegisterUsageForPlan(Plan, {VF}, TTI, CM.ValuesToIgnore)[0];
   // We divide by these constants so assume that we have at least one
   // instruction that uses at least one register.
   for (auto &Pair : R.MaxLocalUsers) {
@@ -4717,21 +4714,21 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
       MaxInterleaveCount = ForceTargetMaxVectorInterleaveFactor;
   }
 
-  unsigned EstimatedVF = getEstimatedRuntimeVF(VF, VScaleForTuning);
+  unsigned EstimatedVF = getEstimatedRuntimeVF(VF, CM.getVScaleForTuning());
 
   // Try to get the exact trip count, or an estimate based on profiling data or
   // ConstantMax from PSE, failing that.
-  if (auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop)) {
+  if (auto BestKnownTC = getSmallBestKnownTC(PSE, OrigLoop)) {
     // At least one iteration must be scalar when this constraint holds. So the
     // maximum available iterations for interleaving is one less.
-    unsigned AvailableTC = requiresScalarEpilogue(VF.isVector())
+    unsigned AvailableTC = CM.requiresScalarEpilogue(VF.isVector())
                                ? BestKnownTC->getFixedValue() - 1
                                : BestKnownTC->getFixedValue();
 
     unsigned InterleaveCountLB = bit_floor(std::max(
         1u, std::min(AvailableTC / (EstimatedVF * 2), MaxInterleaveCount)));
 
-    if (getSmallConstantTripCount(PSE.getSE(), TheLoop).isNonZero()) {
+    if (getSmallConstantTripCount(PSE.getSE(), OrigLoop).isNonZero()) {
       // If the best known trip count is exact, we select between two
       // prospective ICs, where
       //
@@ -4792,7 +4789,7 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
   // vectorized the loop we will have done the runtime check and so interleaving
   // won't require further checks.
   bool ScalarInterleavingRequiresPredication =
-      (VF.isScalar() && any_of(TheLoop->blocks(), [this](BasicBlock *BB) {
+      (VF.isScalar() && any_of(OrigLoop->blocks(), [this](BasicBlock *BB) {
          return Legal->blockNeedsPredication(BB);
        }));
   bool ScalarInterleavingRequiresRuntimePointerCheck =
@@ -4815,8 +4812,39 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
 
     // Interleave until store/load ports (estimated by max interleave count) are
     // saturated.
-    unsigned NumStores = Legal->getNumStores();
-    unsigned NumLoads = Legal->getNumLoads();
+    unsigned NumStores = 0;
+    unsigned NumLoads = 0;
+    for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
+             vp_depth_first_deep(Plan.getVectorLoopRegion()->getEntry()))) {
+      for (VPRecipeBase &R : *VPBB) {
+        if (isa<VPWidenLoadRecipe, VPWidenLoadEVLRecipe>(&R)) {
+          NumLoads++;
+          continue;
+        }
+        if (isa<VPWidenStoreRecipe, VPWidenStoreEVLRecipe>(&R)) {
+          NumStores++;
+          continue;
+        }
+
+        if (auto *InterleaveR = dyn_cast<VPInterleaveRecipe>(&R)) {
+          if (unsigned StoreOps = InterleaveR->getNumStoreOperands())
+            NumStores += StoreOps;
+          else
+            NumLoads += InterleaveR->getNumDefinedValues();
+          continue;
+        }
+        if (auto *RepR = dyn_cast<VPReplicateRecipe>(&R)) {
+          NumLoads += isa<LoadInst>(RepR->getUnderlyingInstr());
+          NumStores += isa<StoreInst>(RepR->getUnderlyingInstr());
+          continue;
+        }
+        if (isa<VPHistogramRecipe>(&R)) {
+          NumLoads++;
+          NumStores++;
+          continue;
+        }
+      }
+    }
     unsigned StoresIC = IC / (NumStores ? NumStores : 1);
     unsigned LoadsIC = IC / (NumLoads ? NumLoads : 1);
 
@@ -4826,12 +4854,15 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
     // do the final reduction after the loop.
     bool HasSelectCmpReductions =
         HasReductions &&
-        any_of(Legal->getReductionVars(), [&](auto &Reduction) -> bool {
-          const RecurrenceDescriptor &RdxDesc = Reduction.second;
-          RecurKind RK = RdxDesc.getRecurrenceKind();
-          return RecurrenceDescriptor::isAnyOfRecurrenceKind(RK) ||
-                 RecurrenceDescriptor::isFindIVRecurrenceKind(RK);
-        });
+        any_of(Plan.getVectorLoopRegion()->getEntryBasicBlock()->phis(),
+               [](VPRecipeBase &R) {
+                 auto *RedR = dyn_cast<VPReductionPHIRecipe>(&R);
+
+                 return RedR && (RecurrenceDescriptor::isAnyOfRecurrenceKind(
+                                     RedR->getRecurrenceKind()) ||
+                                 RecurrenceDescriptor::isFindIVRecurrenceKind(
+                                     RedR->getRecurrenceKind()));
+               });
     if (HasSelectCmpReductions) {
       LLVM_DEBUG(dbgs() << "LV: Not interleaving select-cmp reductions.\n");
       return 1;
@@ -4842,12 +4873,14 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
     // we're interleaving is inside another loop. For tree-wise reductions
     // set the limit to 2, and for ordered reductions it's best to disable
     // interleaving entirely.
-    if (HasReductions && TheLoop->getLoopDepth() > 1) {
+    if (HasReductions && OrigLoop->getLoopDepth() > 1) {
       bool HasOrderedReductions =
-          any_of(Legal->getReductionVars(), [&](auto &Reduction) -> bool {
-            const RecurrenceDescriptor &RdxDesc = Reduction.second;
-            return RdxDesc.isOrdered();
-          });
+          any_of(Plan.getVectorLoopRegion()->getEntryBasicBlock()->phis(),
+                 [](VPRecipeBase &R) {
+                   auto *RedR = dyn_cast<VPReductionPHIRecipe>(&R);
+
+                   return RedR && RedR->isOrdered();
+                 });
       if (HasOrderedReductions) {
         LLVM_DEBUG(
             dbgs() << "LV: Not interleaving scalar ordered reductions.\n");
@@ -10066,8 +10099,11 @@ bool LoopVectorizePass::processLoop(Loop *L) {
 
   GeneratedRTChecks Checks(PSE, DT, LI, TTI, F->getDataLayout(), CM.CostKind);
   if (LVP.hasPlanWithVF(VF.Width)) {
+    VPCostContext CostCtx(CM.TTI, *CM.TLI, CM.Legal->getWidestInductionType(),
+                          CM, CM.CostKind);
+
     // Select the interleave count.
-    IC = CM.selectInterleaveCount(LVP.getPlanFor(VF.Width), VF.Width, VF.Cost);
+    IC = LVP.selectInterleaveCount(LVP.getPlanFor(VF.Width), VF.Width, VF.Cost);
 
     unsigned SelectedIC = std::max(IC, UserIC);
     //  Optimistically generate runtime checks if they are needed. Drop them if
@@ -10078,8 +10114,6 @@ bool LoopVectorizePass::processLoop(Loop *L) {
     // Check if it is profitable to vectorize with runtime checks.
     bool ForceVectorization =
         Hints.getForce() == LoopVectorizeHints::FK_Enabled;
-    VPCostContext CostCtx(CM.TTI, *CM.TLI, CM.Legal->getWidestInductionType(),
-                          CM, CM.CostKind);
     if (!ForceVectorization &&
         !isOutsideLoopWorkProfitable(Checks, VF, L, PSE, CostCtx,
                                      LVP.getPlanFor(VF.Width), SEL,

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -4215,7 +4215,10 @@ class VPlan {
   /// block with multiple predecessors (one for the exit via the latch and one
   /// via the other early exit).
   bool hasEarlyExit() const {
-    return ExitBlocks.size() > 1 ||
+    return count_if(ExitBlocks,
+                    [](VPIRBasicBlock *EB) {
+                      return EB->getNumPredecessors() != 0;
+                    }) > 1 ||
            (ExitBlocks.size() == 1 && ExitBlocks[0]->getNumPredecessors() > 1);
   }
 

llvm/test/Transforms/LoopVectorize/AArch64/predication_costs.ll

@@ -19,7 +19,7 @@ target triple = "aarch64--linux-gnu"
 ;   (udiv(2) + extractelement(8) + insertelement(4)) / 2 = 7
 ;
 ; CHECK: Scalarizing and predicating: %tmp4 = udiv i32 %tmp2, %tmp3
-; CHECK: Found an estimated cost of 7 for VF 2 For instruction: %tmp4 = udiv i32 %tmp2, %tmp3
+; CHECK: Cost of 7 for VF 2: profitable to scalarize   %tmp4 = udiv i32 %tmp2, %tmp3
 ;
 define i32 @predicated_udiv(ptr %a, ptr %b, i1 %c, i64 %n) {
 entry:
@@ -60,7 +60,7 @@ for.end:
 ;   (store(4) + extractelement(4)) / 2 = 4
 ;
 ; CHECK: Scalarizing and predicating: store i32 %tmp2, ptr %tmp0, align 4
-; CHECK: Found an estimated cost of 4 for VF 2 For instruction: store i32 %tmp2, ptr %tmp0, align 4
+; CHECK: Cost of 4 for VF 2: profitable to scalarize   store i32 %tmp2, ptr %tmp0, align 4
 ;
 define void @predicated_store(ptr %a, i1 %c, i32 %x, i64 %n) {
 entry:
@@ -93,8 +93,8 @@ for.end:
 ; CHECK: Found scalar instruction:   %addr = phi ptr [ %a, %entry ], [ %addr.next, %for.inc ]
 ; CHECK: Found scalar instruction:   %addr.next = getelementptr inbounds i32, ptr %addr, i64 1
 ; CHECK: Scalarizing and predicating: store i32 %tmp2, ptr %addr, align 4
-; CHECK: Found an estimated cost of 0 for VF 2 For instruction:   %addr = phi ptr [ %a, %entry ], [ %addr.next, %for.inc ]
-; CHECK: Found an estimated cost of 4 for VF 2 For instruction: store i32 %tmp2, ptr %addr, align 4
+; CHECK: Cost of 0 for VF 2: induction instruction   %addr = phi ptr [ %a, %entry ], [ %addr.next, %for.inc ]
+; CHECK: Cost of 4 for VF 2: profitable to scalarize   store i32 %tmp2, ptr %addr, align 4
 ;
 define void @predicated_store_phi(ptr %a, i1 %c, i32 %x, i64 %n) {
 entry:
@@ -135,9 +135,10 @@ for.end:
 ;
 ; CHECK: Scalarizing: %tmp3 = add nsw i32 %tmp2, %x
 ; CHECK: Scalarizing and predicating: %tmp4 = udiv i32 %tmp2, %tmp3
-; CHECK: Found an estimated cost of 3 for VF 2 For instruction: %tmp3 = add nsw i32 %tmp2, %x
-; CHECK: Found an estimated cost of 5 for VF 2 For instruction: %tmp4 = udiv i32 %tmp2, %tmp3
+; CHECK: Cost of 3 for VF 2: profitable to scalarize   %tmp3 = add nsw i32 %tmp2, %x
+; CHECK: Cost of 5 for VF 2: profitable to scalarize   %tmp4 = udiv i32 %tmp2, %tmp3
 ;
+
 define i32 @predicated_udiv_scalarized_operand(ptr %a, i1 %c, i32 %x, i64 %n) {
 entry:
   br label %for.body
@@ -180,8 +181,8 @@ for.end:
 ;
 ; CHECK: Scalarizing: %tmp2 = add nsw i32 %tmp1, %x
 ; CHECK: Scalarizing and predicating: store i32 %tmp2, ptr %tmp0, align 4
-; CHECK: Found an estimated cost of 3 for VF 2 For instruction: %tmp2 = add nsw i32 %tmp1, %x
-; CHECK: Found an estimated cost of 2 for VF 2 For instruction: store i32 %tmp2, ptr %tmp0, align 4
+; CHECK: Cost of 3 for VF 2: profitable to scalarize   %tmp2 = add nsw i32 %tmp1, %x
+; CHECK: Cost of 2 for VF 2: profitable to scalarize   store i32 %tmp2, ptr %tmp0, align 4
 ;
 define void @predicated_store_scalarized_operand(ptr %a, i1 %c, i32 %x, i64 %n) {
 entry:
@@ -232,11 +233,11 @@ for.end:
 ; CHECK:     Scalarizing and predicating: %tmp4 = udiv i32 %tmp3, %tmp2
 ; CHECK:     Scalarizing: %tmp5 = sub i32 %tmp4, %x
 ; CHECK:     Scalarizing and predicating: store i32 %tmp5, ptr %tmp0, align 4
-; CHECK:     Found an estimated cost of 1 for VF 2 For instruction: %tmp2 = add i32 %tmp1, %x
-; CHECK:     Found an estimated cost of 7 for VF 2 For instruction: %tmp3 = sdiv i32 %tmp1, %tmp2
-; CHECK:     Found an estimated cost of 7 for VF 2 For instruction: %tmp4 = udiv i32 %tmp3, %tmp2
-; CHECK:     Found an estimated cost of 3 for VF 2 For instruction: %tmp5 = sub i32 %tmp4, %x
-; CHECK:     Found an estimated cost of 2 for VF 2 For instruction: store i32 %tmp5, ptr %tmp0, align 4
+; CHECK: Cost of 7 for VF 2: profitable to scalarize   %tmp4 = udiv i32 %tmp3, %tmp2
+; CHECK: Cost of 7 for VF 2: profitable to scalarize   %tmp3 = sdiv i32 %tmp1, %tmp2
+; CHECK: Cost of 2 for VF 2: profitable to scalarize   store i32 %tmp5, ptr %tmp0, align 4
+; CHECK: Cost of 3 for VF 2: profitable to scalarize   %tmp5 = sub i32 %tmp4, %x
+; CHECK: Cost of 1 for VF 2: WIDEN ir<%tmp2> = add ir<%tmp1>, ir<%x>
 ;
 define void @predication_multi_context(ptr %a, i1 %c, i32 %x, i64 %n) {
 entry: