[VPlan] Introduce cannotHoistOrSinkRecipe, fix miscompile (#162674)

Factor out common code to determine legality of hoisting and sinking.
The patch has the side-effect of fixing an underlying bug, where a
load/store pair is reordered.

2 files changed, 26 insertions, 27 deletions

diff --git a/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp b/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
index 779ddb8..9a63c80 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
@@ -70,6 +70,7 @@ bool VPRecipeBase::mayWriteToMemory() const {
     return cast<VPWidenIntrinsicRecipe>(this)->mayWriteToMemory();
   case VPCanonicalIVPHISC:
   case VPBranchOnMaskSC:
+  case VPDerivedIVSC:
   case VPFirstOrderRecurrencePHISC:
   case VPReductionPHISC:
   case VPScalarIVStepsSC:
@@ -86,6 +87,7 @@ bool VPRecipeBase::mayWriteToMemory() const {
   case VPWidenLoadEVLSC:
   case VPWidenLoadSC:
   case VPWidenPHISC:
+  case VPWidenPointerInductionSC:
   case VPWidenSC:
   case VPWidenSelectSC: {
     const Instruction *I =
@@ -119,6 +121,7 @@ bool VPRecipeBase::mayReadFromMemory() const {
   case VPWidenIntrinsicSC:
     return cast<VPWidenIntrinsicRecipe>(this)->mayReadFromMemory();
   case VPBranchOnMaskSC:
+  case VPDerivedIVSC:
   case VPFirstOrderRecurrencePHISC:
   case VPPredInstPHISC:
   case VPScalarIVStepsSC:
@@ -134,6 +137,7 @@ bool VPRecipeBase::mayReadFromMemory() const {
   case VPWidenGEPSC:
   case VPWidenIntOrFpInductionSC:
   case VPWidenPHISC:
+  case VPWidenPointerInductionSC:
   case VPWidenSC:
   case VPWidenSelectSC: {
     const Instruction *I =
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 079aa18..acad795 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -131,6 +131,24 @@ bool VPlanTransforms::tryToConvertVPInstructionsToVPRecipes(
   return true;
 }
 
+/// Return true if we do not know how to (mechanically) hoist or sink \p R out
+/// of a loop region.
+static bool cannotHoistOrSinkRecipe(const VPRecipeBase &R) {
+  // Assumes don't alias anything or throw; as long as they're guaranteed to
+  // execute, they're safe to hoist.
+  if (match(&R, m_Intrinsic<Intrinsic::assume>()))
+    return false;
+
+  // TODO: Relax checks in the future, e.g. we could also hoist reads, if their
+  // memory location is not modified in the vector loop.
+  if (R.mayHaveSideEffects() || R.mayReadFromMemory() || R.isPhi())
+    return true;
+
+  // Allocas cannot be hoisted.
+  auto *RepR = dyn_cast<VPReplicateRecipe>(&R);
+  return RepR && RepR->getOpcode() == Instruction::Alloca;
+}
+
 static bool sinkScalarOperands(VPlan &Plan) {
   auto Iter = vp_depth_first_deep(Plan.getEntry());
   bool Changed = false;
@@ -1826,7 +1844,7 @@ sinkRecurrenceUsersAfterPrevious(VPFirstOrderRecurrencePHIRecipe *FOR,
         VPDT.properlyDominates(Previous, SinkCandidate))
       return true;
 
-    if (SinkCandidate->mayHaveSideEffects())
+    if (cannotHoistOrSinkRecipe(*SinkCandidate))
       return false;
 
     WorkList.push_back(SinkCandidate);
@@ -1866,7 +1884,7 @@ sinkRecurrenceUsersAfterPrevious(VPFirstOrderRecurrencePHIRecipe *FOR,
 static bool hoistPreviousBeforeFORUsers(VPFirstOrderRecurrencePHIRecipe *FOR,
                                         VPRecipeBase *Previous,
                                         VPDominatorTree &VPDT) {
-  if (Previous->mayHaveSideEffects() || Previous->mayReadFromMemory())
+  if (cannotHoistOrSinkRecipe(*Previous))
     return false;
 
   // Collect recipes that need hoisting.
@@ -1913,11 +1931,6 @@ static bool hoistPreviousBeforeFORUsers(VPFirstOrderRecurrencePHIRecipe *FOR,
       return nullptr;
     return HoistCandidate;
   };
-  auto CanHoist = [&](VPRecipeBase *HoistCandidate) {
-    // Avoid hoisting candidates with side-effects, as we do not yet analyze
-    // associated dependencies.
-    return !HoistCandidate->mayHaveSideEffects();
-  };
 
   if (!NeedsHoisting(Previous->getVPSingleValue()))
     return true;
@@ -1929,7 +1942,7 @@ static bool hoistPreviousBeforeFORUsers(VPFirstOrderRecurrencePHIRecipe *FOR,
     VPRecipeBase *Current = HoistCandidates[I];
     assert(Current->getNumDefinedValues() == 1 &&
            "only recipes with a single defined value expected");
-    if (!CanHoist(Current))
+    if (cannotHoistOrSinkRecipe(*Current))
       return false;
 
     for (VPValue *Op : Current->operands()) {
@@ -2144,24 +2157,6 @@ void VPlanTransforms::cse(VPlan &Plan) {
 static void licm(VPlan &Plan) {
   VPBasicBlock *Preheader = Plan.getVectorPreheader();
 
-  // Return true if we do not know how to (mechanically) hoist a given recipe
-  // out of a loop region.
-  auto CannotHoistRecipe = [](VPRecipeBase &R) {
-    // Assumes don't alias anything or throw; as long as they're guaranteed to
-    // execute, they're safe to hoist.
-    if (match(&R, m_Intrinsic<Intrinsic::assume>()))
-      return false;
-
-    // TODO: Relax checks in the future, e.g. we could also hoist reads, if
-    // their memory location is not modified in the vector loop.
-    if (R.mayHaveSideEffects() || R.mayReadFromMemory() || R.isPhi())
-      return true;
-
-    // Allocas cannot be hoisted.
-    auto *RepR = dyn_cast<VPReplicateRecipe>(&R);
-    return RepR && RepR->getOpcode() == Instruction::Alloca;
-  };
-
   // Hoist any loop invariant recipes from the vector loop region to the
   // preheader. Preform a shallow traversal of the vector loop region, to
   // exclude recipes in replicate regions. Since the top-level blocks in the
@@ -2173,7 +2168,7 @@ static void licm(VPlan &Plan) {
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
            vp_depth_first_shallow(LoopRegion->getEntry()))) {
     for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
-      if (CannotHoistRecipe(R))
+      if (cannotHoistOrSinkRecipe(R))
         continue;
       if (any_of(R.operands(), [](VPValue *Op) {
             return !Op->isDefinedOutsideLoopRegions();