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

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.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D147468

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8051,8 +8051,7 @@ bool LoopVectorizationPlanner::getDecisionAndClampRange(
   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;
@@ -8906,8 +8905,7 @@ VPlanPtr LoopVectorizationPlanner::buildVPlanWithVPRecipes(
   // 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 =
@@ -9052,8 +9050,7 @@ VPlanPtr LoopVectorizationPlanner::buildVPlanWithVPRecipes(
       }
   }
 
-  for (ElementCount VF = Range.Start; ElementCount::isKnownLT(VF, Range.End);
-       VF *= 2)
+  for (ElementCount VF : Range)
     Plan->addVF(VF);
   Plan->setName("Initial VPlan");
 
@@ -9088,8 +9085,7 @@ VPlanPtr LoopVectorizationPlanner::buildVPlan(VFRange &Range) {
   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;

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -99,6 +99,36 @@ struct VFRange {
     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>;