[LV] Extend FindLastIV to unsigned case

llvm/include/llvm/Analysis/IVDescriptors.h

@@ -54,9 +54,12 @@ enum class RecurKind {
   FMulAdd,  ///< Sum of float products with llvm.fmuladd(a * b + sum).
   AnyOf,    ///< AnyOf reduction with select(cmp(),x,y) where one of (x,y) is
             ///< loop invariant, and both x and y are integer type.
-  FindLastIV, ///< FindLast reduction with select(cmp(),x,y) where one of
-              ///< (x,y) is increasing loop induction, and both x and y are
-              ///< integer type.
+  FindLastIVSMin, ///< FindLast reduction with select(cmp(),x,y) where one of
+                  ///< (x,y) is increasing loop induction, and both x and y
+                  ///< are integer type, producing a SMin reduction.
+  FindLastIVUMin, ///< FindLast reduction with select(cmp(),x,y) where one of
+                  ///< (x,y) is increasing loop induction, and both x and y
+                  ///< are integer type, producting a UMin reduction.
   // clang-format on
   // TODO: Any_of and FindLast reduction need not be restricted to integer type
   // only.
@@ -260,7 +263,14 @@ class RecurrenceDescriptor {
   /// Returns true if the recurrence kind is of the form
   ///   select(cmp(),x,y) where one of (x,y) is increasing loop induction.
   static bool isFindLastIVRecurrenceKind(RecurKind Kind) {
-    return Kind == RecurKind::FindLastIV;
+    return Kind == RecurKind::FindLastIVSMin ||
+           Kind == RecurKind::FindLastIVUMin;
+  }
+
+  /// Returns true if recurrece kind is a signed redux kind.
+  static bool isSignedRecurrenceKind(RecurKind Kind) {
+    return Kind == RecurKind::SMax || Kind == RecurKind::SMin ||
+           Kind == RecurKind::FindLastIVSMin;
   }
 
   /// Returns the type of the recurrence. This type can be narrower than the
@@ -272,8 +282,10 @@ class RecurrenceDescriptor {
   Value *getSentinelValue() const {
     assert(isFindLastIVRecurrenceKind(Kind) && "Unexpected recurrence kind");
     Type *Ty = StartValue->getType();
-    return ConstantInt::get(Ty,
-                            APInt::getSignedMinValue(Ty->getIntegerBitWidth()));
+    unsigned BW = Ty->getIntegerBitWidth();
+    return ConstantInt::get(Ty, isSignedRecurrenceKind(Kind)
+                                    ? APInt::getSignedMinValue(BW)
+                                    : APInt::getMinValue(BW));
   }
 
   /// Returns a reference to the instructions used for type-promoting the

llvm/lib/Analysis/IVDescriptors.cpp

@@ -50,7 +50,8 @@ bool RecurrenceDescriptor::isIntegerRecurrenceKind(RecurKind Kind) {
   case RecurKind::UMax:
   case RecurKind::UMin:
   case RecurKind::AnyOf:
-  case RecurKind::FindLastIV:
+  case RecurKind::FindLastIVSMin:
+  case RecurKind::FindLastIVUMin:
     return true;
   }
   return false;
@@ -700,47 +701,59 @@ RecurrenceDescriptor::isFindLastIVPattern(Loop *TheLoop, PHINode *OrigPhi,
                                      m_Value(NonRdxPhi)))))
     return InstDesc(false, I);
 
-  auto IsIncreasingLoopInduction = [&](Value *V) {
+  // Returns a non-nullopt boolean indicating the signedness of the recurrence
+  // when a valid FindLastIV pattern is found.
+  auto GetRecurKind = [&](Value *V) -> std::optional<RecurKind> {
     Type *Ty = V->getType();
     if (!SE.isSCEVable(Ty))
-      return false;
+      return std::nullopt;
 
     auto *AR = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(V));
     if (!AR || AR->getLoop() != TheLoop)
-      return false;
+      return std::nullopt;
 
     const SCEV *Step = AR->getStepRecurrence(SE);
     if (!SE.isKnownPositive(Step))
-      return false;
+      return std::nullopt;
 
-    const ConstantRange IVRange = SE.getSignedRange(AR);
-    unsigned NumBits = Ty->getIntegerBitWidth();
     // Keep the minimum value of the recurrence type as the sentinel value.
     // The maximum acceptable range for the increasing induction variable,
     // called the valid range, will be defined as
     //   [<sentinel value> + 1, <sentinel value>)
-    // where <sentinel value> is SignedMin(<recurrence type>)
+    // where <sentinel value> is [Signed|Unsigned]Min(<recurrence type>)
     // TODO: This range restriction can be lifted by adding an additional
     // virtual OR reduction.
-    const APInt Sentinel = APInt::getSignedMinValue(NumBits);
-    const ConstantRange ValidRange =
-        ConstantRange::getNonEmpty(Sentinel + 1, Sentinel);
-    LLVM_DEBUG(dbgs() << "LV: FindLastIV valid range is " << ValidRange
-                      << ", and the signed range of " << *AR << " is "
-                      << IVRange << "\n");
-    // Ensure the induction variable does not wrap around by verifying that its
-    // range is fully contained within the valid range.
-    return ValidRange.contains(IVRange);
+    auto CheckRange = [&](bool IsSigned) {
+      const ConstantRange IVRange =
+          IsSigned ? SE.getSignedRange(AR) : SE.getUnsignedRange(AR);
+      unsigned NumBits = Ty->getIntegerBitWidth();
+      const APInt Sentinel = IsSigned ? APInt::getSignedMinValue(NumBits)
+                                      : APInt::getMinValue(NumBits);
+      const ConstantRange ValidRange =
+          ConstantRange::getNonEmpty(Sentinel + 1, Sentinel);
+      LLVM_DEBUG(dbgs() << "LV: FindLastIV valid range is " << ValidRange
+                        << ", and the range of " << *AR << " is " << IVRange
+                        << "\n");
+
+      // Ensure the induction variable does not wrap around by verifying that
+      // its range is fully contained within the valid range.
+      return ValidRange.contains(IVRange);
+    };
+    if (CheckRange(true))
+      return RecurKind::FindLastIVSMin;
+    if (CheckRange(false))
+      return RecurKind::FindLastIVUMin;
+    return std::nullopt;
   };
 
   // We are looking for selects of the form:
   //   select(cmp(), phi, increasing_loop_induction) or
   //   select(cmp(), increasing_loop_induction, phi)
   // TODO: Support for monotonically decreasing induction variable
-  if (!IsIncreasingLoopInduction(NonRdxPhi))
-    return InstDesc(false, I);
+  if (auto RK = GetRecurKind(NonRdxPhi))
+    return InstDesc(I, *RK);
 
-  return InstDesc(I, RecurKind::FindLastIV);
+  return InstDesc(false, I);
 }
 
 RecurrenceDescriptor::InstDesc
@@ -985,8 +998,8 @@ bool RecurrenceDescriptor::isReductionPHI(PHINode *Phi, Loop *TheLoop,
                       << "\n");
     return true;
   }
-  if (AddReductionVar(Phi, RecurKind::FindLastIV, TheLoop, FMF, RedDes, DB, AC,
-                      DT, SE)) {
+  if (AddReductionVar(Phi, RecurKind::FindLastIVSMin, TheLoop, FMF, RedDes, DB,
+                      AC, DT, SE)) {
     LLVM_DEBUG(dbgs() << "Found a FindLastIV reduction PHI." << *Phi << "\n");
     return true;
   }
@@ -1137,7 +1150,8 @@ unsigned RecurrenceDescriptor::getOpcode(RecurKind Kind) {
   case RecurKind::Mul:
     return Instruction::Mul;
   case RecurKind::AnyOf:
-  case RecurKind::FindLastIV:
+  case RecurKind::FindLastIVSMin:
+  case RecurKind::FindLastIVUMin:
   case RecurKind::Or:
     return Instruction::Or;
   case RecurKind::And:

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -23105,7 +23105,8 @@ class HorizontalReduction {
         case RecurKind::FMul:
         case RecurKind::FMulAdd:
         case RecurKind::AnyOf:
-        case RecurKind::FindLastIV:
+        case RecurKind::FindLastIVSMin:
+        case RecurKind::FindLastIVUMin:
         case RecurKind::FMaximumNum:
         case RecurKind::FMinimumNum:
         case RecurKind::None:
@@ -23239,7 +23240,8 @@ class HorizontalReduction {
     case RecurKind::FMul:
     case RecurKind::FMulAdd:
     case RecurKind::AnyOf:
-    case RecurKind::FindLastIV:
+    case RecurKind::FindLastIVSMin:
+    case RecurKind::FindLastIVUMin:
     case RecurKind::FMaximumNum:
     case RecurKind::FMinimumNum:
     case RecurKind::None:
@@ -23338,7 +23340,8 @@ class HorizontalReduction {
     case RecurKind::FMul:
     case RecurKind::FMulAdd:
     case RecurKind::AnyOf:
-    case RecurKind::FindLastIV:
+    case RecurKind::FindLastIVSMin:
+    case RecurKind::FindLastIVUMin:
     case RecurKind::FMaximumNum:
     case RecurKind::FMinimumNum:
     case RecurKind::None:

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -634,8 +634,11 @@ Value *VPInstruction::generate(VPTransformState &State) {
     // each part of the reduction.
     unsigned UF = getNumOperands() - 2;
     Value *ReducedPartRdx = State.get(getOperand(2));
+    auto MinMaxOp = RecurrenceDescriptor::isSignedRecurrenceKind(RK)
+                        ? RecurKind::SMax
+                        : RecurKind::UMax;
     for (unsigned Part = 1; Part < UF; ++Part) {
-      ReducedPartRdx = createMinMaxOp(Builder, RecurKind::SMax, ReducedPartRdx,
+      ReducedPartRdx = createMinMaxOp(Builder, MinMaxOp, ReducedPartRdx,
                                       State.get(getOperand(2 + Part)));
     }