[SLP][NFC]Introduce and use computeCommonAlignment function, NFC.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -3869,6 +3869,15 @@ static bool arePointersCompatible(Value *Ptr1, Value *Ptr2,
               .getOpcode());
 }
 
+/// Calculates minimal alignment as a common alignment.
+template <typename T>
+static Align computeCommonAlignment(ArrayRef<Value *> VL) {
+  Align CommonAlignment = cast<T>(VL.front())->getAlign();
+  for (Value *V : VL.drop_front())
+    CommonAlignment = std::min(CommonAlignment, cast<T>(V)->getAlign());
+  return CommonAlignment;
+}
+
 /// Checks if the given array of loads can be represented as a vectorized,
 /// scatter or just simple gather.
 static LoadsState canVectorizeLoads(ArrayRef<Value *> VL, const Value *VL0,
@@ -3939,10 +3948,7 @@ static LoadsState canVectorizeLoads(ArrayRef<Value *> VL, const Value *VL0,
           return (IsSorted && !GEP && doesNotNeedToBeScheduled(P)) ||
                  (GEP && GEP->getNumOperands() == 2);
         })) {
-      Align CommonAlignment = cast<LoadInst>(VL0)->getAlign();
-      for (Value *V : VL)
-        CommonAlignment =
-            std::min(CommonAlignment, cast<LoadInst>(V)->getAlign());
+      Align CommonAlignment = computeCommonAlignment<LoadInst>(VL);
       auto *VecTy = FixedVectorType::get(ScalarTy, VL.size());
       if (TTI.isLegalMaskedGather(VecTy, CommonAlignment) &&
           !TTI.forceScalarizeMaskedGather(VecTy, CommonAlignment))
@@ -7087,10 +7093,8 @@ class BoUpSLP::ShuffleCostEstimator : public BaseShuffleAnalysis {
         }
         for (std::pair<unsigned, unsigned> P : ScatterVectorized) {
           auto *LI0 = cast<LoadInst>(VL[P.first]);
-          Align CommonAlignment = LI0->getAlign();
-          for (Value *V : VL.slice(P.first + 1, VF - 1))
-            CommonAlignment =
-                std::min(CommonAlignment, cast<LoadInst>(V)->getAlign());
+          Align CommonAlignment =
+              computeCommonAlignment<LoadInst>(VL.slice(P.first + 1, VF - 1));
           GatherCost += TTI.getGatherScatterOpCost(
               Instruction::Load, LoadTy, LI0->getPointerOperand(),
               /*VariableMask=*/false, CommonAlignment, CostKind, LI0);
@@ -8334,10 +8338,8 @@ BoUpSLP::getEntryCost(const TreeEntry *E, ArrayRef<Value *> VectorizedVals,
         assert((E->State == TreeEntry::ScatterVectorize ||
                 E->State == TreeEntry::PossibleStridedVectorize) &&
                "Unknown EntryState");
-        Align CommonAlignment = LI0->getAlign();
-        for (Value *V : UniqueValues)
-          CommonAlignment =
-              std::min(CommonAlignment, cast<LoadInst>(V)->getAlign());
+        Align CommonAlignment =
+            computeCommonAlignment<LoadInst>(UniqueValues.getArrayRef());
         VecLdCost = TTI->getGatherScatterOpCost(
             Instruction::Load, VecTy, LI0->getPointerOperand(),
             /*VariableMask=*/false, CommonAlignment, CostKind);
@@ -11600,10 +11602,7 @@ Value *BoUpSLP::vectorizeTree(TreeEntry *E, bool PostponedPHIs) {
           return E->VectorizedValue;
         }
         // Use the minimum alignment of the gathered loads.
-        Align CommonAlignment = LI->getAlign();
-        for (Value *V : E->Scalars)
-          CommonAlignment =
-              std::min(CommonAlignment, cast<LoadInst>(V)->getAlign());
+        Align CommonAlignment = computeCommonAlignment<LoadInst>(E->Scalars);
         NewLI = Builder.CreateMaskedGather(VecTy, VecPtr, CommonAlignment);
       }
       Value *V = propagateMetadata(NewLI, E->Scalars);