[VPlan] Add VFRange::begin() and end() iterators. (NFCI)

[fhahn]

Summary

Add an iterator to iterate over all VFs in VFRange. This simplifies some
existing code and allows using all_of,any_of and none_of on a VFRange.

[Ayal]

Nice cleanup, minor nits.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

8052

nit (Independent of this patch): can iterate over entire Range, rather than excluding its start element.

8898

nit (here and below): are the parentheses needed?

llvm/lib/Transforms/Vectorize/VPlan.h

125

TODO: instead of implicitly bumping End to next power-of-2 here, set it to MaxVFTimesTwo originally instead of MaxVFPlusOne and assert both Start and End are powers-of-two upon construction above?

[fhahn]

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

8052

Excluding the start seems to be a minor optimization. I can remove it, but not sure if it improves things by much?

8898

Remove all these in the committed version, thanks!

llvm/lib/Transforms/Vectorize/VPlan.h

125

This should be done in c7a34d355a61396d438ea095e1e6996cde1ef880, thanks!

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

void EpilogueVectorizerEpilogueLoop::printDebugTracesAtEnd() {
   });
 }
 
 bool LoopVectorizationPlanner::getDecisionAndClampRange(
     const std::function<bool(ElementCount)> &Predicate, VFRange &Range) {
   assert(!Range.isEmpty() && "Trying to test an empty VF range.");
   bool PredicateAtRangeStart = Predicate(Range.Start);
 
-  for (ElementCount TmpVF = Range.Start * 2;
-       ElementCount::isKnownLT(TmpVF, Range.End); TmpVF *= 2)
+  for (ElementCount TmpVF : VFRange(Range.Start * 2, Range.End))
     if (Predicate(TmpVF) != PredicateAtRangeStart) {
       Range.End = TmpVF;
       break;
     }
 
   return PredicateAtRangeStart;
 }
 
VPlanPtr LoopVectorizationPlanner::buildVPlanWithVPRecipes(
   VPBlockUtils::insertBlockAfter(TopRegion, Preheader);
   VPBasicBlock *MiddleVPBB = new VPBasicBlock("middle.block");
   VPBlockUtils::insertBlockAfter(MiddleVPBB, TopRegion);
 
   // Don't use getDecisionAndClampRange here, because we don't know the UF
   // so this function is better to be conservative, rather than to split
   // it up into different VPlans.
   bool IVUpdateMayOverflow = false;
-  for (ElementCount VF = Range.Start;
-       ElementCount::isKnownLT(VF, Range.End); VF *= 2)
+  for (ElementCount VF : Range) {
     IVUpdateMayOverflow |= !isIndvarOverflowCheckKnownFalse(&CM, VF);
+  }
 
   Instruction *DLInst =
       getDebugLocFromInstOrOperands(Legal->getPrimaryInduction());
   addCanonicalIVRecipes(*Plan, Legal->getWidestInductionType(),
                         DLInst ? DLInst->getDebugLoc() : DebugLoc(),
                         CM.getTailFoldingStyle(IVUpdateMayOverflow));
 
   // Scan the body of the loop in a topological order to visit each basic block
for (unsigned i = 0; i < IG->getFactor(); ++i)
           Plan->addVPValue(Member, VPIG->getVPValue(J));
           OriginalV->replaceAllUsesWith(VPIG->getVPValue(J));
           J++;
         }
         RecipeBuilder.getRecipe(Member)->eraseFromParent();
       }
   }
 
-  for (ElementCount VF = Range.Start; ElementCount::isKnownLT(VF, Range.End);
-       VF *= 2)
+  for (ElementCount VF : Range) {
     Plan->addVF(VF);
+  }
   Plan->setName("Initial VPlan");
 
   // From this point onwards, VPlan-to-VPlan transformations may change the plan
   // in ways that accessing values using original IR values is incorrect.
   Plan->disableValue2VPValue();
 
   VPlanTransforms::optimizeInductions(*Plan, *PSE.getSE());
   VPlanTransforms::removeDeadRecipes(*Plan);
VPlanPtr LoopVectorizationPlanner::buildVPlan(VFRange &Range) {
 
   // Create new empty VPlan
   auto Plan = std::make_unique<VPlan>();
 
   // Build hierarchical CFG
   VPlanHCFGBuilder HCFGBuilder(OrigLoop, LI, *Plan);
   HCFGBuilder.buildHierarchicalCFG();
 
-  for (ElementCount VF = Range.Start; ElementCount::isKnownLT(VF, Range.End);
-       VF *= 2)
+  for (ElementCount VF : Range) {
     Plan->addVF(VF);
+  }
 
   SmallPtrSet<Instruction *, 1> DeadInstructions;
   VPlanTransforms::VPInstructionsToVPRecipes(
       Plan,
       [this](PHINode *P) { return Legal->getIntOrFpInductionDescriptor(P); },
       DeadInstructions, *PSE.getSE(), *TLI);
 
   // Remove the existing terminator of the exiting block of the top-most region.

llvm/lib/Transforms/Vectorize/VPlan.h

struct VFRange {
 
   VFRange(const ElementCount &Start, const ElementCount &End)
       : Start(Start), End(End) {
     assert(Start.isScalable() == End.isScalable() &&
            "Both Start and End should have the same scalable flag");
     assert(isPowerOf2_32(Start.getKnownMinValue()) &&
            "Expected Start to be a power of 2");
   }
+
+  /// Iterator to iterate over vectorization factors in a VFRange.
+  class iterator
+      : public iterator_facade_base<iterator, std::forward_iterator_tag,
+                                    ElementCount> {
+    ElementCount VF;
+
+  public:
+    iterator(ElementCount VF) : VF(VF) {}
+
+    bool operator==(const iterator &Other) const { return VF == Other.VF; }
+
+    ElementCount operator*() const { return VF; }
+
+    iterator &operator++() {
+      VF *= 2;
+      return *this;
+    }
+  };
+
+  iterator begin() { return iterator(Start); }
+  iterator end() {
+    ElementCount EndVF = End;
+    // Make sure the end iterator is a power-of-2 so != comparisons with end work as expected.
+    if (!isPowerOf2_64(End.getKnownMinValue()))
+      EndVF = ElementCount::get(NextPowerOf2(End.getKnownMinValue()),
+                                End.isScalable());
+    return iterator(EndVF);
+  }
 };
 
 using VPlanPtr = std::unique_ptr<VPlan>;
 
 /// In what follows, the term "input IR" refers to code that is fed into the
 /// vectorizer whereas the term "output IR" refers to code that is generated by
 /// the vectorizer.