Intro hasOneUser(), change getSingleUser(), and reuse it.

Author: Mel-Chen

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -2260,15 +2260,10 @@ InstructionCost VPWidenCastRecipe::computeCost(ElementCount VF,
   TTI::CastContextHint CCH = TTI::CastContextHint::None;
   // For Trunc/FPTrunc, get the context from the only user.
   if (Opcode == Instruction::Trunc || Opcode == Instruction::FPTrunc) {
-    auto GetOnlyUser = [](const VPSingleDefRecipe *R) -> VPRecipeBase * {
-      if (R->getNumUsers() == 0 || R->hasMoreThanOneUniqueUser())
-        return nullptr;
-      return dyn_cast<VPRecipeBase>(*R->user_begin());
-    };
-
-    if (VPRecipeBase *Recipe = GetOnlyUser(this)) {
+    if (auto *Recipe = dyn_cast_or_null<VPRecipeBase>(getSingleUser())) {
       if (match(Recipe, m_VPInstruction<VPInstruction::Reverse>(m_VPValue())))
-        Recipe = GetOnlyUser(cast<VPInstruction>(Recipe));
+        Recipe = dyn_cast_or_null<VPRecipeBase>(
+            cast<VPInstruction>(Recipe)->getSingleUser());
       if (Recipe)
         CCH = ComputeCCH(Recipe);
     }

llvm/lib/Transforms/Vectorize/VPlanValue.h

@@ -150,11 +150,21 @@ class LLVM_ABI_FOR_TEST VPValue {
 
   bool hasOneUse() const { return getNumUsers() == 1; }
 
+  /// Returns true if the value has exactly one unique user, ignoring multiple
+  /// uses by the same user.
+  bool hasOneUser() const {
+    if (getNumUsers() == 0)
+      return false;
+    if (hasOneUse())
+      return true;
+    return std::equal(std::next(user_begin()), user_end(), user_begin());
+  }
+
   /// Return the single user of this value, or nullptr if there is not exactly
   /// one user.
-  VPUser *getSingleUser() { return hasOneUse() ? *user_begin() : nullptr; }
+  VPUser *getSingleUser() { return hasOneUser() ? *user_begin() : nullptr; }
   const VPUser *getSingleUser() const {
-    return hasOneUse() ? *user_begin() : nullptr;
+    return hasOneUser() ? *user_begin() : nullptr;
   }
 
   void replaceAllUsesWith(VPValue *New);