diff --git a/llvm/lib/Target/X86/X86ReturnThunks.cpp b/llvm/lib/Target/X86/X86ReturnThunks.cpp
@@ -43,12 +43,14 @@ using namespace llvm;
 #define PASS_KEY "x86-return-thunks"
 #define DEBUG_TYPE PASS_KEY
 
+namespace {
 struct X86ReturnThunks final : public MachineFunctionPass {
   static char ID;
   X86ReturnThunks() : MachineFunctionPass(ID) {}
   StringRef getPassName() const override { return "X86 Return Thunks"; }
   bool runOnMachineFunction(MachineFunction &MF) override;
 };
+} // namespace
 
 char X86ReturnThunks::ID = 0;
 

diff --git a/llvm/lib/Transforms/Scalar/LoopFlatten.cpp b/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
@@ -100,6 +100,7 @@ static cl::opt<bool>
             cl::desc("Widen the loop induction variables, if possible, so "
                      "overflow checks won't reject flattening"));
 
+namespace {
 // We require all uses of both induction variables to match this pattern:
 //
 //   (OuterPHI * InnerTripCount) + InnerPHI
@@ -288,6 +289,7 @@ struct FlattenInfo {
     return true;
   }
 };
+} // namespace
 
 static bool
 setLoopComponents(Value *&TC, Value *&TripCount, BinaryOperator *&Increment,

diff --git a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -1272,6 +1272,7 @@ bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(StoreInst *SI,
                                     StoreEv, LoadEv, BECount);
 }
 
+namespace {
 class MemmoveVerifier {
 public:
   explicit MemmoveVerifier(const Value &LoadBasePtr, const Value &StoreBasePtr,
@@ -1315,6 +1316,7 @@ class MemmoveVerifier {
 public:
   const bool IsSameObject;
 };
+} // namespace
 
 bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(
     Value *DestPtr, Value *SourcePtr, const SCEV *StoreSizeSCEV,

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -419,8 +419,10 @@ static std::optional<unsigned> getSmallBestKnownTC(ScalarEvolution &SE,
   return std::nullopt;
 }
 
+namespace {
 // Forward declare GeneratedRTChecks.
 class GeneratedRTChecks;
+} // namespace
 
 namespace llvm {
 
@@ -1867,6 +1869,7 @@ class LoopVectorizationCostModel {
 };
 } // end namespace llvm
 
+namespace {
 /// Helper struct to manage generating runtime checks for vectorization.
 ///
 /// The runtime checks are created up-front in temporary blocks to allow better
@@ -2131,6 +2134,7 @@ class GeneratedRTChecks {
     return MemCheckBlock;
   }
 };
+} // namespace
 
 // Return true if \p OuterLp is an outer loop annotated with hints for explicit
 // vectorization. The loop needs to be annotated with #pragma omp simd

diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -947,6 +947,7 @@ static bool isMemModifiedBetween(BasicBlock::iterator Begin,
   });
 }
 
+namespace {
 /// Helper class to indicate whether a vector index can be safely scalarized and
 /// if a freeze needs to be inserted.
 class ScalarizationResult {
@@ -1001,6 +1002,7 @@ class ScalarizationResult {
     ToFreeze = nullptr;
   }
 };
+} // namespace
 
 /// Check if it is legal to scalarize a memory access to \p VecTy at index \p
 /// Idx. \p Idx must access a valid vector element.