[VPlan] Get Addr computation cost with scalar type if it is uniform for gather/scatter.

This patch query `getAddressComputationCost()` with scalar type if the
address is uniform. This can help the cost for gather/scatter more
accurate.

In current LV, non consecutive VPWidenMemoryRecipe (gather/scatter) will
account the cost of address computation. But there are some cases that
the addr is uniform accross lanes, that makes the address can be
calculated with scalar type and broadcast.

I have a follow optimization that try to converts gather/scatter with
uniform memory acces to scalar load/store + broadcast. With this
optimization, we can remove this temporary change.

Author: ElvisWang123

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -6932,6 +6932,12 @@ static bool planContainsAdditionalSimplifications(VPlan &Plan,
   auto Iter = vp_depth_first_deep(Plan.getVectorLoopRegion()->getEntry());
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(Iter)) {
     for (VPRecipeBase &R : *VPBB) {
+      if (auto *MR = dyn_cast<VPWidenMemoryRecipe>(&R)) {
+        // The address computation cost can be query as scalar type if the
+        // address is uniform.
+        if (!MR->isConsecutive() && vputils::isSingleScalar(MR->getAddr()))
+          return true;
+      }
       if (auto *IR = dyn_cast<VPInterleaveRecipe>(&R)) {
         auto *IG = IR->getInterleaveGroup();
         unsigned NumMembers = IG->getNumMembers();

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -3083,9 +3083,18 @@ InstructionCost VPWidenMemoryRecipe::computeCost(ElementCount VF,
     const Value *Ptr = getLoadStorePointerOperand(&Ingredient);
     assert(!Reverse &&
            "Inconsecutive memory access should not have the order.");
-    return Ctx.TTI.getAddressComputationCost(Ty) +
-           Ctx.TTI.getGatherScatterOpCost(Opcode, Ty, Ptr, IsMasked, Alignment,
-                                          Ctx.CostKind, &Ingredient);
+    InstructionCost Cost = 0;
+
+    // If the address value is uniform across all lane, then the address can be
+    // calculated with scalar type and broacast.
+    if (vputils::isSingleScalar(getAddr()))
+      Cost += Ctx.TTI.getAddressComputationCost(Ty->getScalarType());
+    else
+      Cost += Ctx.TTI.getAddressComputationCost(Ty);
+
+    return Cost + Ctx.TTI.getGatherScatterOpCost(Opcode, Ty, Ptr, IsMasked,
+                                                 Alignment, Ctx.CostKind,
+                                                 &Ingredient);
   }
 
   InstructionCost Cost = 0;