[LV] Iterate over recipes in VPlan to fix PHI (NFC).

[fhahn]

Summary

As we gradually move more elements of LV to VPlan, we are trying to
reduce the number of places that still has to check IR of the original
loop.

This patch adjusts the code to fix cross iteration phis to get the PHIs
to fix directly from the VPlan that is executed. We still need the
original PHI to check for first-order recurrences, but we can get rid of
that once we model that explicitly in VPlan as well.

[fhahn]

rebase & ping

[fhahn]

rebase

[fhahn]

ping :)

[fhahn]

Rebase after cb96d802d4d7

[fhahn]

Updated to use phis() from D100101.

[Ayal]

Looks good to me, adding a minor nit; worth adding "NFC" to title.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

4035

iterate over Header->phis()?

[fhahn]

Rebased. This depends on the patch adding phis() (D100101)

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

4035

This should be updated now I think.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

protected:
   void fixCrossIterationPHIs(VPTransformState &State);
 
   /// Fix a first-order recurrence. This is the second phase of vectorizing
   /// this phi node.
   void fixFirstOrderRecurrence(PHINode *Phi, VPTransformState &State);
 
   /// Fix a reduction cross-iteration phi. This is the second phase of
   /// vectorizing this phi node.
-  void fixReduction(PHINode *Phi, VPTransformState &State);
+  void fixReduction(VPWidenPHIRecipe *Phi, VPTransformState &State);
 
   /// Clear NSW/NUW flags from reduction instructions if necessary.
   void clearReductionWrapFlags(RecurrenceDescriptor &RdxDesc,
                                VPTransformState &State);
 
   /// Fixup the LCSSA phi nodes in the unique exit block.  This simply
   /// means we need to add the appropriate incoming value from the middle
   /// block as exiting edges from the scalar epilogue loop (if present) are

 
 void InnerLoopVectorizer::fixCrossIterationPHIs(VPTransformState &State) {
   // In order to support recurrences we need to be able to vectorize Phi nodes.
   // Phi nodes have cycles, so we need to vectorize them in two stages. This is
   // stage #2: We now need to fix the recurrences by adding incoming edges to
   // the currently empty PHI nodes. At this point every instruction in the
   // original loop is widened to a vector form so we can use them to construct
   // the incoming edges.
-  for (PHINode &Phi : OrigLoop->getHeader()->phis()) {
-    // Handle first-order recurrences and reductions that need to be fixed.
-    if (Legal->isFirstOrderRecurrence(&Phi))
-      fixFirstOrderRecurrence(&Phi, State);
-    else if (Legal->isReductionVariable(&Phi))
-      fixReduction(&Phi, State);
+  VPBasicBlock *Header = State.Plan->getEntry()->getEntryBasicBlock();
+  for (VPRecipeBase &R : *Header) {
+    if (isa<VPWidenIntOrFpInductionRecipe>(&R))
+      continue;
+    VPWidenPHIRecipe *PhiR = dyn_cast<VPWidenPHIRecipe>(&R);
+    if (!PhiR)
+      break;
+
+    auto *OrigPhi = cast<PHINode>(PhiR->getUnderlyingValue());
+    if (PhiR->getRecurrenceDescriptor()) {
+      fixReduction(PhiR, State);
+    } else if (Legal->isFirstOrderRecurrence(OrigPhi))
+      fixFirstOrderRecurrence(OrigPhi, State);
   }
 }
 
 void InnerLoopVectorizer::fixFirstOrderRecurrence(PHINode *Phi,
                                                   VPTransformState &State) {
   // This is the second phase of vectorizing first-order recurrences. An
   // overview of the transformation is described below. Suppose we have the
   // following loop.
void InnerLoopVectorizer::fixFirstOrderRecurrence(PHINode *Phi,
   // scalar epilogue); in that case, the exiting path through middle will be
   // dynamically dead and the value picked for the phi doesn't matter.
   for (PHINode &LCSSAPhi : LoopExitBlock->phis())
     if (any_of(LCSSAPhi.incoming_values(),
                [Phi](Value *V) { return V == Phi; }))
       LCSSAPhi.addIncoming(ExtractForPhiUsedOutsideLoop, LoopMiddleBlock);
 }
 
-void InnerLoopVectorizer::fixReduction(PHINode *Phi, VPTransformState &State) {
+void InnerLoopVectorizer::fixReduction(VPWidenPHIRecipe *PhiR,
+                                       VPTransformState &State) {
+  PHINode *OrigPhi = cast<PHINode>(PhiR->getUnderlyingValue());
   // Get it's reduction variable descriptor.
-  assert(Legal->isReductionVariable(Phi) &&
+  assert(Legal->isReductionVariable(OrigPhi) &&
          "Unable to find the reduction variable");
-  RecurrenceDescriptor RdxDesc = Legal->getReductionVars()[Phi];
+  RecurrenceDescriptor RdxDesc = *PhiR->getRecurrenceDescriptor();
 
   RecurKind RK = RdxDesc.getRecurrenceKind();
   TrackingVH<Value> ReductionStartValue = RdxDesc.getRecurrenceStartValue();
   Instruction *LoopExitInst = RdxDesc.getLoopExitInstr();
   setDebugLocFromInst(Builder, ReductionStartValue);
-  bool IsInLoopReductionPhi = Cost->isInLoopReduction(Phi);
+  bool IsInLoopReductionPhi = Cost->isInLoopReduction(OrigPhi);
 
   VPValue *LoopExitInstDef = State.Plan->getVPValue(LoopExitInst);
   // This is the vector-clone of the value that leaves the loop.
   Type *VecTy = State.get(LoopExitInstDef, 0)->getType();
 
   // Wrap flags are in general invalid after vectorization, clear them.
   clearReductionWrapFlags(RdxDesc, State);
 
   // Fix the vector-loop phi.
 
   // Reductions do not have to start at zero. They can start with
   // any loop invariant values.
   BasicBlock *Latch = OrigLoop->getLoopLatch();
-  Value *LoopVal = Phi->getIncomingValueForBlock(Latch);
+  Value *LoopVal = OrigPhi->getIncomingValueForBlock(Latch);
 
   for (unsigned Part = 0; Part < UF; ++Part) {
-    Value *VecRdxPhi = State.get(State.Plan->getVPValue(Phi), Part);
+    Value *VecRdxPhi = State.get(PhiR->getVPValue(), Part);
     Value *Val = State.get(State.Plan->getVPValue(LoopVal), Part);
     cast<PHINode>(VecRdxPhi)
       ->addIncoming(Val, LI->getLoopFor(LoopVectorBody)->getLoopLatch());
   }
 
   // Before each round, move the insertion point right between
   // the PHIs and the values we are going to write.
   // This allows us to write both PHINodes and the extractelement
   // instructions.
   Builder.SetInsertPoint(&*LoopMiddleBlock->getFirstInsertionPt());
 
   setDebugLocFromInst(Builder, LoopExitInst);
 
-  Type *PhiTy = Phi->getType();
+  Type *PhiTy = OrigPhi->getType();
   // If tail is folded by masking, the vector value to leave the loop should be
   // a Select choosing between the vectorized LoopExitInst and vectorized Phi,
   // instead of the former. For an inloop reduction the reduction will already
   // be predicated, and does not need to be handled here.
   if (Cost->foldTailByMasking() && !IsInLoopReductionPhi) {
     for (unsigned Part = 0; Part < UF; ++Part) {
       Value *VecLoopExitInst = State.get(LoopExitInstDef, Part);
       Value *Sel = nullptr;
for (unsigned Part = 0; Part < UF; ++Part) {
       // extra cost in the loop (for example a predicated vadd), it can be
       // cheaper for the select to remain in the loop than be sunk out of it,
       // and so use the select value for the phi instead of the old
       // LoopExitValue.
       if (PreferPredicatedReductionSelect ||
           TTI->preferPredicatedReductionSelect(
               RdxDesc.getOpcode(), PhiTy,
               TargetTransformInfo::ReductionFlags())) {
-        auto *VecRdxPhi =
-            cast<PHINode>(State.get(State.Plan->getVPValue(Phi), Part));
+        auto *VecRdxPhi = cast<PHINode>(State.get(PhiR->getVPValue(), Part));
         VecRdxPhi->setIncomingValueForBlock(
             LI->getLoopFor(LoopVectorBody)->getLoopLatch(), Sel);
       }
     }
   }
 
   // If the vector reduction can be performed in a smaller type, we truncate
   // then extend the loop exit value to enable InstCombine to evaluate the
void InnerLoopVectorizer::fixReduction(VPWidenPHIRecipe *PhiR,
   for (PHINode &LCSSAPhi : LoopExitBlock->phis())
     if (any_of(LCSSAPhi.incoming_values(),
                [LoopExitInst](Value *V) { return V == LoopExitInst; }))
       LCSSAPhi.addIncoming(ReducedPartRdx, LoopMiddleBlock);
 
   // Fix the scalar loop reduction variable with the incoming reduction sum
   // from the vector body and from the backedge value.
   int IncomingEdgeBlockIdx =
-    Phi->getBasicBlockIndex(OrigLoop->getLoopLatch());
+      OrigPhi->getBasicBlockIndex(OrigLoop->getLoopLatch());
   assert(IncomingEdgeBlockIdx >= 0 && "Invalid block index");
   // Pick the other block.
   int SelfEdgeBlockIdx = (IncomingEdgeBlockIdx ? 0 : 1);
-  Phi->setIncomingValue(SelfEdgeBlockIdx, BCBlockPhi);
-  Phi->setIncomingValue(IncomingEdgeBlockIdx, LoopExitInst);
+  OrigPhi->setIncomingValue(SelfEdgeBlockIdx, BCBlockPhi);
+  OrigPhi->setIncomingValue(IncomingEdgeBlockIdx, LoopExitInst);
 }
 
 void InnerLoopVectorizer::clearReductionWrapFlags(RecurrenceDescriptor &RdxDesc,
                                                   VPTransformState &State) {
   RecurKind RK = RdxDesc.getRecurrenceKind();
   if (RK != RecurKind::Add && RK != RecurKind::Mul)
     return;
 

llvm/lib/Transforms/Vectorize/VPlan.h

void addIncoming(VPValue *IncomingV, VPBasicBlock *IncomingBlock) {
     IncomingBlocks.push_back(IncomingBlock);
   }
 
   /// Returns the \p I th incoming VPValue.
   VPValue *getIncomingValue(unsigned I) { return getOperand(I); }
 
   /// Returns the \p I th incoming VPBasicBlock.
   VPBasicBlock *getIncomingBlock(unsigned I) { return IncomingBlocks[I]; }
+
+  RecurrenceDescriptor *getRecurrenceDescriptor() { return RdxDesc; }
 };
 
 /// A recipe for vectorizing a phi-node as a sequence of mask-based select
 /// instructions.
 class VPBlendRecipe : public VPRecipeBase, public VPValue {
   PHINode *Phi;
 
 public: