[VPlan] Manage Sentinel value for FindLastIV in VPlan.

Similar to modeling the start value as operand, also model the sentinel
value as operand explicitly. This makes all require information for
code-gen available directly in VPlan.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7262,9 +7262,11 @@ static void fixReductionScalarResumeWhenVectorizingEpilog(
     using namespace llvm::PatternMatch;
     Value *Cmp, *OrigResumeV, *CmpOp;
     bool IsExpectedPattern =
-        match(MainResumeValue, m_Select(m_OneUse(m_Value(Cmp)),
-                                        m_Specific(RdxDesc.getSentinelValue()),
-                                        m_Value(OrigResumeV))) &&
+        match(MainResumeValue,
+              m_Select(
+                  m_OneUse(m_Value(Cmp)),
+                  m_Specific(EpiRedResult->getOperand(2)->getLiveInIRValue()),
+                  m_Value(OrigResumeV))) &&
         (match(Cmp, m_SpecificICmp(ICmpInst::ICMP_EQ, m_Specific(OrigResumeV),
                                    m_Value(CmpOp))) &&
          ((CmpOp == StartV && isGuaranteedNotToBeUndefOrPoison(CmpOp))));
@@ -9242,9 +9244,11 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
     if (RecurrenceDescriptor::isFindLastIVRecurrenceKind(
             RdxDesc.getRecurrenceKind())) {
       VPValue *Start = PhiR->getStartValue();
-      FinalReductionResult =
-          Builder.createNaryOp(VPInstruction::ComputeFindLastIVResult,
-                               {PhiR, Start, NewExitingVPV}, ExitDL);
+      FinalReductionResult = Builder.createNaryOp(
+          VPInstruction::ComputeFindLastIVResult,
+          {PhiR, Start, Plan->getOrAddLiveIn(RdxDesc.getSentinelValue()),
+           NewExitingVPV},
+          ExitDL);
     } else if (RecurrenceDescriptor::isAnyOfRecurrenceKind(
                    RdxDesc.getRecurrenceKind())) {
       VPValue *Start = PhiR->getStartValue();
@@ -9832,8 +9836,8 @@ preparePlanForEpilogueVectorLoop(VPlan &Plan, Loop *L,
         BasicBlock *ResumeBB = cast<Instruction>(ResumeV)->getParent();
         IRBuilder<> Builder(ResumeBB, ResumeBB->getFirstNonPHIIt());
         Value *Cmp = Builder.CreateICmpEQ(ResumeV, ToFrozen[StartV]);
-        ResumeV =
-            Builder.CreateSelect(Cmp, RdxDesc.getSentinelValue(), ResumeV);
+        ResumeV = Builder.CreateSelect(
+            Cmp, RdxResult->getOperand(2)->getLiveInIRValue(), ResumeV);
       } else {
         VPValue *StartVal = Plan.getOrAddLiveIn(ResumeV);
         auto *PhiR = dyn_cast<VPReductionPHIRecipe>(&R);

llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h

@@ -318,6 +318,25 @@ m_VPInstruction(const Op0_t &Op0, const Op1_t &Op1, const Op2_t &Op2) {
       {Op0, Op1, Op2});
 }
 
+template <typename Op0_t, typename Op1_t, typename Op2_t, typename Op3_t,
+          unsigned Opcode, bool Commutative, typename... RecipeTys>
+using Recipe4Op_match = Recipe_match<std::tuple<Op0_t, Op1_t, Op2_t, Op3_t>,
+                                     Opcode, Commutative, RecipeTys...>;
+
+template <typename Op0_t, typename Op1_t, typename Op2_t, typename Op3_t,
+          unsigned Opcode>
+using VPInstruction4Op_match =
+    Recipe4Op_match<Op0_t, Op1_t, Op2_t, Op3_t, Opcode, /*Commutative*/ false,
+                    VPInstruction>;
+
+template <unsigned Opcode, typename Op0_t, typename Op1_t, typename Op2_t,
+          typename Op3_t>
+inline VPInstruction4Op_match<Op0_t, Op1_t, Op2_t, Op3_t, Opcode>
+m_VPInstruction(const Op0_t &Op0, const Op1_t &Op1, const Op2_t &Op2,
+                const Op3_t &Op3) {
+  return VPInstruction4Op_match<Op0_t, Op1_t, Op2_t, Op3_t, Opcode>(
+      {Op0, Op1, Op2, Op3});
+}
 template <typename Op0_t>
 inline UnaryVPInstruction_match<Op0_t, Instruction::Freeze>
 m_Freeze(const Op0_t &Op0) {

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -646,16 +646,16 @@ Value *VPInstruction::generate(VPTransformState &State) {
 
     // The recipe's operands are the reduction phi, followed by one operand for
     // each part of the reduction.
-    unsigned UF = getNumOperands() - 2;
-    Value *ReducedPartRdx = State.get(getOperand(2));
+    unsigned UF = getNumOperands() - 3;
+    Value *ReducedPartRdx = State.get(getOperand(3));
     for (unsigned Part = 1; Part < UF; ++Part) {
       ReducedPartRdx = createMinMaxOp(Builder, RecurKind::SMax, ReducedPartRdx,
-                                      State.get(getOperand(2 + Part)));
+                                      State.get(getOperand(3 + Part)));
     }
 
     return createFindLastIVReduction(Builder, ReducedPartRdx,
                                      State.get(getOperand(1), true),
-                                     RdxDesc.getSentinelValue());
+                                     getOperand(2)->getLiveInIRValue());
   }
   case VPInstruction::ComputeReductionResult: {
     // FIXME: The cross-recipe dependency on VPReductionPHIRecipe is temporary

llvm/lib/Transforms/Vectorize/VPlanUnroll.cpp

@@ -347,7 +347,7 @@ void UnrollState::unrollBlock(VPBlockBase *VPB) {
         match(&R, m_VPInstruction<VPInstruction::ComputeReductionResult>(
                       m_VPValue(), m_VPValue(Op1))) ||
         match(&R, m_VPInstruction<VPInstruction::ComputeFindLastIVResult>(
-                      m_VPValue(), m_VPValue(), m_VPValue(Op1)))) {
+                      m_VPValue(), m_VPValue(), m_VPValue(), m_VPValue(Op1)))) {
       addUniformForAllParts(cast<VPInstruction>(&R));
       for (unsigned Part = 1; Part != UF; ++Part)
         R.addOperand(getValueForPart(Op1, Part));

llvm/test/Transforms/LoopVectorize/vplan-printing-reductions.ll

@@ -240,7 +240,7 @@ define i64 @find_last_iv(ptr %a, i64 %n, i64 %start) {
 ; CHECK-NEXT: Successor(s): middle.block
 ; CHECK-EMPTY:
 ; CHECK-NEXT: middle.block:
-; CHECK-NEXT:   EMIT vp<[[RDX_RES:%.+]]> = compute-find-last-iv-result ir<%rdx>, ir<%start>, ir<%cond>
+; CHECK-NEXT:   EMIT vp<[[RDX_RES:%.+]]> = compute-find-last-iv-result ir<%rdx>, ir<%start>, ir<-9223372036854775808>, ir<%cond>
 ; CHECK-NEXT:   EMIT vp<[[EXT:%.+]]> = extract-last-element vp<[[RDX_RES]]>
 ; CHECK-NEXT:   EMIT vp<%cmp.n> = icmp eq ir<%n>, vp<{{.+}}>
 ; CHECK-NEXT:   EMIT branch-on-cond vp<%cmp.n>