[Transforms] Drop unnecessary const from return types (NFC)

Identified with readability-const-return-type.

Author: kazutakahirata

llvm/lib/Transforms/Scalar/SROA.cpp

@@ -122,7 +122,7 @@ namespace {
 class IRBuilderPrefixedInserter final : public IRBuilderDefaultInserter {
   std::string Prefix;
 
-  const Twine getNameWithPrefix(const Twine &Name) const {
+  Twine getNameWithPrefix(const Twine &Name) const {
     return Name.isTriviallyEmpty() ? Name : Prefix + Name;
   }
 

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -933,12 +933,12 @@ void VPlan::updateDominatorTree(DominatorTree *DT, BasicBlock *LoopPreHeaderBB,
 }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-const Twine VPlanPrinter::getUID(const VPBlockBase *Block) {
+Twine VPlanPrinter::getUID(const VPBlockBase *Block) {
   return (isa<VPRegionBlock>(Block) ? "cluster_N" : "N") +
          Twine(getOrCreateBID(Block));
 }
 
-const Twine VPlanPrinter::getOrCreateName(const VPBlockBase *Block) {
+Twine VPlanPrinter::getOrCreateName(const VPBlockBase *Block) {
   const std::string &Name = Block->getName();
   if (!Name.empty())
     return Name;

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -2250,9 +2250,9 @@ class VPlanPrinter {
     return BlockID.count(Block) ? BlockID[Block] : BlockID[Block] = BID++;
   }
 
-  const Twine getOrCreateName(const VPBlockBase *Block);
+  Twine getOrCreateName(const VPBlockBase *Block);
 
-  const Twine getUID(const VPBlockBase *Block);
+  Twine getUID(const VPBlockBase *Block);
 
   /// Print the information related to a CFG edge between two VPBlockBases.
   void drawEdge(const VPBlockBase *From, const VPBlockBase *To, bool Hidden,