[llvm] [VPlan] Factor out logic to common compute costs to helper (NFCI). (PR #153361)

[Florian Hahn via llvm-commits]

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@@ -940,28 +940,88 @@ Value *VPInstruction::generate(VPTransformState &State) {
   }
 }
 
+std::optional<InstructionCost>
+VPRecipeWithIRFlags::getCommonCost(unsigned Opcode, ElementCount VF,
+                                   VPCostContext &Ctx, bool IsVector) const {
+  Type *ScalarTy = Ctx.Types.inferScalarType(this);
+  Type *ResultTy = IsVector ? toVectorTy(ScalarTy, VF) : ScalarTy;
+  switch (Opcode) {
+  case Instruction::FNeg:
+    return Ctx.TTI.getArithmeticInstrCost(
+        Opcode, ResultTy, Ctx.CostKind,
+        {TargetTransformInfo::OK_AnyValue, TargetTransformInfo::OP_None},
+        {TargetTransformInfo::OK_AnyValue, TargetTransformInfo::OP_None});
+  case Instruction::UDiv:
+  case Instruction::SDiv:
+  case Instruction::SRem:
+  case Instruction::URem:
+  case Instruction::Add:
+  case Instruction::FAdd:
+  case Instruction::Sub:
+  case Instruction::FSub:
+  case Instruction::Mul:
+  case Instruction::FMul:
+  case Instruction::FDiv:
+  case Instruction::FRem:
+  case Instruction::Shl:
+  case Instruction::LShr:
+  case Instruction::AShr:
+  case Instruction::And:
+  case Instruction::Or:
+  case Instruction::Xor: {
+    VPValue *RHS = getOperand(1);
+    // Certain instructions can be cheaper to vectorize if they have a constant
+    // second vector operand. One example of this are shifts on x86.
+    TargetTransformInfo::OperandValueInfo RHSInfo = Ctx.getOperandInfo(RHS);
+
+    if (RHSInfo.Kind == TargetTransformInfo::OK_AnyValue &&
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fhahn wrote:

`OK_UniformValue` is only relevant for vector versions, so the we currently compute exactly the same costs. But it is not necessary to preform the check for scalar VFs, so I made it conditional.

https://github.com/llvm/llvm-project/pull/153361