diff --git a/llvm/include/llvm/Analysis/BasicAliasAnalysis.h b/llvm/include/llvm/Analysis/BasicAliasAnalysis.h
index ed9d1ba4c5a75..528f56eb65c8c 100644
--- a/llvm/include/llvm/Analysis/BasicAliasAnalysis.h
+++ b/llvm/include/llvm/Analysis/BasicAliasAnalysis.h
@@ -25,7 +25,6 @@
 
 namespace llvm {
 
-struct AAMDNodes;
 class AssumptionCache;
 class BasicBlock;
 class DataLayout;
diff --git a/llvm/include/llvm/Analysis/MemoryBuiltins.h b/llvm/include/llvm/Analysis/MemoryBuiltins.h
index bc9613a5eb4a8..28104c5ed420a 100644
--- a/llvm/include/llvm/Analysis/MemoryBuiltins.h
+++ b/llvm/include/llvm/Analysis/MemoryBuiltins.h
@@ -44,7 +44,6 @@ class IntToPtrInst;
 class LLVMContext;
 class LoadInst;
 class PHINode;
-class PointerType;
 class SelectInst;
 class Type;
 class UndefValue;
diff --git a/llvm/include/llvm/CodeGen/MIRFormatter.h b/llvm/include/llvm/CodeGen/MIRFormatter.h
index 12c90600f6df9..3f145ff224ad0 100644
--- a/llvm/include/llvm/CodeGen/MIRFormatter.h
+++ b/llvm/include/llvm/CodeGen/MIRFormatter.h
@@ -23,7 +23,6 @@ namespace llvm {
 class MachineFunction;
 class MachineInstr;
 struct PerFunctionMIParsingState;
-struct SlotMapping;
 
 /// MIRFormater - Interface to format MIR operand based on target
 class MIRFormatter {
diff --git a/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugInfoEntry.h b/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugInfoEntry.h
index c4370cb541139..6bdd23900182e 100644
--- a/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugInfoEntry.h
+++ b/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugInfoEntry.h
@@ -16,7 +16,6 @@
 
 namespace llvm {
 
-class DataExtractor;
 class DWARFUnit;
 
 /// DWARFDebugInfoEntry - A DIE with only the minimum required data.
diff --git a/llvm/include/llvm/DebugInfo/GSYM/LookupResult.h b/llvm/include/llvm/DebugInfo/GSYM/LookupResult.h
index 211a352595fde..3dabbce32bb2d 100644
--- a/llvm/include/llvm/DebugInfo/GSYM/LookupResult.h
+++ b/llvm/include/llvm/DebugInfo/GSYM/LookupResult.h
@@ -17,7 +17,6 @@
 namespace llvm {
 class raw_ostream;
 namespace gsym {
-struct FileEntry;
 
 struct SourceLocation {
   StringRef Name;      ///< Function or symbol name.
diff --git a/llvm/include/llvm/DebugInfo/GSYM/ObjectFileTransformer.h b/llvm/include/llvm/DebugInfo/GSYM/ObjectFileTransformer.h
index bcde92e94fc52..dcbda39a76962 100644
--- a/llvm/include/llvm/DebugInfo/GSYM/ObjectFileTransformer.h
+++ b/llvm/include/llvm/DebugInfo/GSYM/ObjectFileTransformer.h
@@ -21,7 +21,6 @@ class ObjectFile;
 
 namespace gsym {
 
-struct CUInfo;
 class GsymCreator;
 
 class ObjectFileTransformer {
diff --git a/llvm/include/llvm/DebugInfo/MSF/MSFBuilder.h b/llvm/include/llvm/DebugInfo/MSF/MSFBuilder.h
index 282870f5b3f1b..1a03d42ded922 100644
--- a/llvm/include/llvm/DebugInfo/MSF/MSFBuilder.h
+++ b/llvm/include/llvm/DebugInfo/MSF/MSFBuilder.h
@@ -20,7 +20,6 @@
 
 namespace llvm {
 class FileBufferByteStream;
-class WritableBinaryStream;
 namespace msf {
 
 class MSFBuilder {
diff --git a/llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h b/llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h
index 46daa3885a061..1455dad3d1b2b 100644
--- a/llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h
+++ b/llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h
@@ -283,9 +283,7 @@ struct StructorIdentifierNode;
 struct ThunkSignatureNode;
 struct PointerTypeNode;
 struct ArrayTypeNode;
-struct CustomNode;
 struct TagTypeNode;
-struct IntrinsicTypeNode;
 struct NodeArrayNode;
 struct QualifiedNameNode;
 struct TemplateParameterReferenceNode;
diff --git a/llvm/include/llvm/ExecutionEngine/JITEventListener.h b/llvm/include/llvm/ExecutionEngine/JITEventListener.h
index 4eefd993de2be..effff2ea5cfab 100644
--- a/llvm/include/llvm/ExecutionEngine/JITEventListener.h
+++ b/llvm/include/llvm/ExecutionEngine/JITEventListener.h
@@ -24,7 +24,6 @@
 namespace llvm {
 
 class IntelJITEventsWrapper;
-class MachineFunction;
 class OProfileWrapper;
 
 namespace object {
diff --git a/llvm/include/llvm/ExecutionEngine/Orc/CompileOnDemandLayer.h b/llvm/include/llvm/ExecutionEngine/Orc/CompileOnDemandLayer.h
index 30544e8a17486..30af7a628e913 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/CompileOnDemandLayer.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/CompileOnDemandLayer.h
@@ -51,13 +51,8 @@
 #include <vector>
 
 namespace llvm {
-
-class Value;
-
 namespace orc {
 
-class ExtractingIRMaterializationUnit;
-
 class CompileOnDemandLayer : public IRLayer {
   friend class PartitioningIRMaterializationUnit;
 
diff --git a/llvm/include/llvm/ExecutionEngine/Orc/CompileUtils.h b/llvm/include/llvm/ExecutionEngine/Orc/CompileUtils.h
index c7ba57228ab71..ee53f2383cb07 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/CompileUtils.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/CompileUtils.h
@@ -20,7 +20,6 @@
 
 namespace llvm {
 
-class MCContext;
 class MemoryBuffer;
 class Module;
 class ObjectCache;
diff --git a/llvm/include/llvm/ExecutionEngine/Orc/ExecutionUtils.h b/llvm/include/llvm/ExecutionEngine/Orc/ExecutionUtils.h
index 8e572ea1d0c1d..85fa0bb88688e 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/ExecutionUtils.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/ExecutionUtils.h
@@ -33,7 +33,6 @@ class ConstantArray;
 class GlobalVariable;
 class Function;
 class Module;
-class TargetMachine;
 class Value;
 
 namespace orc {
diff --git a/llvm/include/llvm/ExecutionEngine/Orc/IRTransformLayer.h b/llvm/include/llvm/ExecutionEngine/Orc/IRTransformLayer.h
index f368c92b37021..4f1cde32ff186 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/IRTransformLayer.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/IRTransformLayer.h
@@ -19,7 +19,6 @@
 #include <memory>
 
 namespace llvm {
-class Module;
 namespace orc {
 
 /// A layer that applies a transform to emitted modules.
diff --git a/llvm/include/llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h b/llvm/include/llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h
index e22d7f7de814e..48f6eb4795c79 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h
@@ -38,10 +38,6 @@ class LinkGraph;
 class Symbol;
 } // namespace jitlink
 
-namespace object {
-class ObjectFile;
-} // namespace object
-
 namespace orc {
 
 class ObjectLinkingLayerJITLinkContext;
diff --git a/llvm/include/llvm/Frontend/OpenMP/OMPConstants.h b/llvm/include/llvm/Frontend/OpenMP/OMPConstants.h
index 0479e305fcb50..2178acc90e2c9 100644
--- a/llvm/include/llvm/Frontend/OpenMP/OMPConstants.h
+++ b/llvm/include/llvm/Frontend/OpenMP/OMPConstants.h
@@ -20,13 +20,6 @@
 #include "llvm/Frontend/OpenMP/OMP.h.inc"
 
 namespace llvm {
-class Type;
-class Module;
-class ArrayType;
-class StructType;
-class PointerType;
-class FunctionType;
-
 namespace omp {
 LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE();
 
diff --git a/llvm/include/llvm/IR/GlobalObject.h b/llvm/include/llvm/IR/GlobalObject.h
index 1f73c8540a4a2..0bb9fd7300596 100644
--- a/llvm/include/llvm/IR/GlobalObject.h
+++ b/llvm/include/llvm/IR/GlobalObject.h
@@ -22,7 +22,6 @@
 namespace llvm {
 
 class Comdat;
-class MDNode;
 class Metadata;
 
 class GlobalObject : public GlobalValue {
diff --git a/llvm/include/llvm/IR/GlobalVariable.h b/llvm/include/llvm/IR/GlobalVariable.h
index 674d49eb9de66..e772964fcc6b5 100644
--- a/llvm/include/llvm/IR/GlobalVariable.h
+++ b/llvm/include/llvm/IR/GlobalVariable.h
@@ -34,7 +34,6 @@ class Constant;
 class Module;
 
 template <typename ValueSubClass> class SymbolTableListTraits;
-class DIGlobalVariable;
 class DIGlobalVariableExpression;
 
 class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> {
diff --git a/llvm/include/llvm/IR/LLVMContext.h b/llvm/include/llvm/IR/LLVMContext.h
index 1c902ebce5add..12d3a45171ce8 100644
--- a/llvm/include/llvm/IR/LLVMContext.h
+++ b/llvm/include/llvm/IR/LLVMContext.h
@@ -32,7 +32,6 @@ class Module;
 class OptPassGate;
 template <typename T> class SmallVectorImpl;
 template <typename T> class StringMapEntry;
-class SMDiagnostic;
 class StringRef;
 class Twine;
 class LLVMRemarkStreamer;
diff --git a/llvm/include/llvm/IR/LegacyPassManagers.h b/llvm/include/llvm/IR/LegacyPassManagers.h
index 0bcb408d49292..e5a29a9c8785b 100644
--- a/llvm/include/llvm/IR/LegacyPassManagers.h
+++ b/llvm/include/llvm/IR/LegacyPassManagers.h
@@ -90,7 +90,6 @@ template <typename T> class ArrayRef;
 class Module;
 class StringRef;
 class Value;
-class Timer;
 class PMDataManager;
 
 // enums for debugging strings
diff --git a/llvm/include/llvm/IR/Module.h b/llvm/include/llvm/IR/Module.h
index 4ddbd6ff14b3c..7b834fbeeebfe 100644
--- a/llvm/include/llvm/IR/Module.h
+++ b/llvm/include/llvm/IR/Module.h
@@ -47,9 +47,7 @@ class GVMaterializer;
 class LLVMContext;
 class MemoryBuffer;
 class ModuleSummaryIndex;
-class Pass;
 class RandomNumberGenerator;
-template <class PtrType> class SmallPtrSetImpl;
 class StructType;
 class VersionTuple;
 
diff --git a/llvm/include/llvm/IR/PseudoProbe.h b/llvm/include/llvm/IR/PseudoProbe.h
index 51ba7e675efe2..7d14213143c08 100644
--- a/llvm/include/llvm/IR/PseudoProbe.h
+++ b/llvm/include/llvm/IR/PseudoProbe.h
@@ -21,7 +21,6 @@
 namespace llvm {
 
 class Instruction;
-class BasicBlock;
 
 constexpr const char *PseudoProbeDescMetadataName = "llvm.pseudo_probe_desc";
 
diff --git a/llvm/include/llvm/IR/SSAContext.h b/llvm/include/llvm/IR/SSAContext.h
index 9d9290a2c1d78..8879512610c2f 100644
--- a/llvm/include/llvm/IR/SSAContext.h
+++ b/llvm/include/llvm/IR/SSAContext.h
@@ -26,7 +26,6 @@ class BasicBlock;
 class Function;
 class Instruction;
 class Value;
-template <typename> class SmallVectorImpl;
 template <typename, bool> class DominatorTreeBase;
 
 template <> class GenericSSAContext<Function> {
diff --git a/llvm/include/llvm/LTO/LTO.h b/llvm/include/llvm/LTO/LTO.h
index d2b0fef1ca47b..0d085a88a193b 100644
--- a/llvm/include/llvm/LTO/LTO.h
+++ b/llvm/include/llvm/LTO/LTO.h
@@ -35,7 +35,6 @@ class LLVMContext;
 class MemoryBufferRef;
 class Module;
 class raw_pwrite_stream;
-class Target;
 class ToolOutputFile;
 
 /// Resolve linkage for prevailing symbols in the \p Index. Linkage changes
diff --git a/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h b/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
index b8daea9441e0d..be1f3154029c0 100644
--- a/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
+++ b/llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
@@ -29,7 +29,6 @@
 
 namespace llvm {
 class StringRef;
-class LLVMContext;
 class TargetMachine;
 
 /// Helper to gather options relevant to the target machine creation
diff --git a/llvm/include/llvm/Linker/Linker.h b/llvm/include/llvm/Linker/Linker.h
index c9b1d42b3903d..ac8041d8df1af 100644
--- a/llvm/include/llvm/Linker/Linker.h
+++ b/llvm/include/llvm/Linker/Linker.h
@@ -14,8 +14,6 @@
 
 namespace llvm {
 class Module;
-class StructType;
-class Type;
 
 /// This class provides the core functionality of linking in LLVM. It keeps a
 /// pointer to the merged module so far. It doesn't take ownership of the
diff --git a/llvm/include/llvm/MC/MCPseudoProbe.h b/llvm/include/llvm/MC/MCPseudoProbe.h
index abc9705f0851a..17b7446baae86 100644
--- a/llvm/include/llvm/MC/MCPseudoProbe.h
+++ b/llvm/include/llvm/MC/MCPseudoProbe.h
@@ -60,7 +60,6 @@
 namespace llvm {
 
 class MCSection;
-class MCStreamer;
 class MCSymbol;
 class MCObjectStreamer;
 class raw_ostream;
diff --git a/llvm/include/llvm/MC/MCStreamer.h b/llvm/include/llvm/MC/MCStreamer.h
index 7bfbdb8800983..e19d03705acdd 100644
--- a/llvm/include/llvm/MC/MCStreamer.h
+++ b/llvm/include/llvm/MC/MCStreamer.h
@@ -40,7 +40,6 @@ namespace llvm {
 
 class AssemblerConstantPools;
 class MCAsmBackend;
-class MCCodeEmitter;
 class MCContext;
 struct MCDwarfFrameInfo;
 class MCExpr;
diff --git a/llvm/include/llvm/Object/Error.h b/llvm/include/llvm/Object/Error.h
index 1fc1f6603a361..af334fc426582 100644
--- a/llvm/include/llvm/Object/Error.h
+++ b/llvm/include/llvm/Object/Error.h
@@ -22,8 +22,6 @@ class Twine;
 
 namespace object {
 
-class Binary;
-
 const std::error_category &object_category();
 
 enum class object_error {
diff --git a/llvm/include/llvm/Object/IRObjectFile.h b/llvm/include/llvm/Object/IRObjectFile.h
index 338b1941eca1b..db47960237a01 100644
--- a/llvm/include/llvm/Object/IRObjectFile.h
+++ b/llvm/include/llvm/Object/IRObjectFile.h
@@ -20,10 +20,7 @@
 
 namespace llvm {
 class BitcodeModule;
-class Mangler;
 class Module;
-class GlobalValue;
-class Triple;
 
 namespace object {
 class ObjectFile;
diff --git a/llvm/include/llvm/Object/MachOUniversal.h b/llvm/include/llvm/Object/MachOUniversal.h
index 9bcacb5101087..e87eb31aad4e5 100644
--- a/llvm/include/llvm/Object/MachOUniversal.h
+++ b/llvm/include/llvm/Object/MachOUniversal.h
@@ -22,7 +22,6 @@
 
 namespace llvm {
 class StringRef;
-class Module;
 class LLVMContext;
 
 namespace object {
diff --git a/llvm/include/llvm/Object/ObjectFile.h b/llvm/include/llvm/Object/ObjectFile.h
index 267fe30467381..12704b1fc88e7 100644
--- a/llvm/include/llvm/Object/ObjectFile.h
+++ b/llvm/include/llvm/Object/ObjectFile.h
@@ -31,7 +31,6 @@
 
 namespace llvm {
 
-class ARMAttributeParser;
 class SubtargetFeatures;
 
 namespace object {
diff --git a/llvm/include/llvm/ObjectYAML/DWARFEmitter.h b/llvm/include/llvm/ObjectYAML/DWARFEmitter.h
index eb56d1e293266..30bb16deb8101 100644
--- a/llvm/include/llvm/ObjectYAML/DWARFEmitter.h
+++ b/llvm/include/llvm/ObjectYAML/DWARFEmitter.h
@@ -26,7 +26,6 @@ class raw_ostream;
 namespace DWARFYAML {
 
 struct Data;
-struct PubSection;
 
 Error emitDebugAbbrev(raw_ostream &OS, const Data &DI);
 Error emitDebugStr(raw_ostream &OS, const Data &DI);
diff --git a/llvm/include/llvm/Support/ARMAttributeParser.h b/llvm/include/llvm/Support/ARMAttributeParser.h
index b46a4d9f690f8..1cc30af5eaf03 100644
--- a/llvm/include/llvm/Support/ARMAttributeParser.h
+++ b/llvm/include/llvm/Support/ARMAttributeParser.h
@@ -18,7 +18,6 @@
 #include "llvm/Support/Error.h"
 
 namespace llvm {
-class StringRef;
 
 class ARMAttributeParser : public ELFAttributeParser {
   struct DisplayHandler {
diff --git a/llvm/include/llvm/Support/CodeGenCoverage.h b/llvm/include/llvm/Support/CodeGenCoverage.h
index a5b1796ca4229..2acdd6a36a514 100644
--- a/llvm/include/llvm/Support/CodeGenCoverage.h
+++ b/llvm/include/llvm/Support/CodeGenCoverage.h
@@ -14,7 +14,6 @@
 #include "llvm/ADT/BitVector.h"
 
 namespace llvm {
-class LLVMContext;
 class MemoryBuffer;
 
 class CodeGenCoverage {
diff --git a/llvm/include/llvm/Support/LowLevelTypeImpl.h b/llvm/include/llvm/Support/LowLevelTypeImpl.h
index 2071a08d87117..dd286f5228fe5 100644
--- a/llvm/include/llvm/Support/LowLevelTypeImpl.h
+++ b/llvm/include/llvm/Support/LowLevelTypeImpl.h
@@ -33,7 +33,6 @@
 
 namespace llvm {
 
-class DataLayout;
 class Type;
 class raw_ostream;
 
diff --git a/llvm/include/llvm/TableGen/Record.h b/llvm/include/llvm/TableGen/Record.h
index 5869a5cf0423e..add05bd078d6b 100644
--- a/llvm/include/llvm/TableGen/Record.h
+++ b/llvm/include/llvm/TableGen/Record.h
@@ -44,7 +44,6 @@ struct RecordContext;
 } // namespace detail
 
 class ListRecTy;
-struct MultiClass;
 class Record;
 class RecordKeeper;
 class RecordVal;
diff --git a/llvm/include/llvm/Target/CGPassBuilderOption.h b/llvm/include/llvm/Target/CGPassBuilderOption.h
index 11b904e6e7fe0..f84889392d135 100644
--- a/llvm/include/llvm/Target/CGPassBuilderOption.h
+++ b/llvm/include/llvm/Target/CGPassBuilderOption.h
@@ -19,7 +19,6 @@
 #include "llvm/Target/TargetOptions.h"
 
 namespace llvm {
-class TargetMachine;
 
 enum class RunOutliner { TargetDefault, AlwaysOutline, NeverOutline };
 enum class RegAllocType { Default, Basic, Fast, Greedy, PBQP };
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
index 54b0079dd7ce3..330f3bacca43b 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
@@ -25,9 +25,7 @@ namespace llvm {
 
 class ConstantFP;
 class ConstantInt;
-class DbgVariable;
 class DwarfCompileUnit;
-class MachineOperand;
 class MCDwarfDwoLineTable;
 class MCSymbol;
 
diff --git a/llvm/lib/CodeGen/AsmPrinter/PseudoProbePrinter.h b/llvm/lib/CodeGen/AsmPrinter/PseudoProbePrinter.h
index 7d5e51218693f..a92a89084cadb 100644
--- a/llvm/lib/CodeGen/AsmPrinter/PseudoProbePrinter.h
+++ b/llvm/lib/CodeGen/AsmPrinter/PseudoProbePrinter.h
@@ -19,8 +19,6 @@
 namespace llvm {
 
 class AsmPrinter;
-class MCStreamer;
-class Module;
 class DILocation;
 
 class PseudoProbeHandler : public AsmPrinterHandler {
diff --git a/llvm/lib/CodeGen/BranchFolding.h b/llvm/lib/CodeGen/BranchFolding.h
index 2a4ea92a92aa6..95d5dcfbbd0fb 100644
--- a/llvm/lib/CodeGen/BranchFolding.h
+++ b/llvm/lib/CodeGen/BranchFolding.h
@@ -23,7 +23,6 @@ class BasicBlock;
 class MachineBranchProbabilityInfo;
 class MachineFunction;
 class MachineLoopInfo;
-class MachineModuleInfo;
 class MachineRegisterInfo;
 class MBFIWrapper;
 class ProfileSummaryInfo;
diff --git a/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.h b/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.h
index 5ef57e23bd097..1095fa5ce7014 100644
--- a/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.h
+++ b/llvm/lib/ExecutionEngine/JITLink/JITLinkGeneric.h
@@ -19,9 +19,6 @@
 #define DEBUG_TYPE "jitlink"
 
 namespace llvm {
-
-class MemoryBufferRef;
-
 namespace jitlink {
 
 /// Base class for a JIT linker.
diff --git a/llvm/lib/Target/ARM/ARM.h b/llvm/lib/Target/ARM/ARM.h
index 63a7c69ac7e8b..979371bf7cf66 100644
--- a/llvm/lib/Target/ARM/ARM.h
+++ b/llvm/lib/Target/ARM/ARM.h
@@ -25,7 +25,6 @@ class ARMAsmPrinter;
 class ARMBaseTargetMachine;
 class ARMRegisterBankInfo;
 class ARMSubtarget;
-struct BasicBlockInfo;
 class Function;
 class FunctionPass;
 class InstructionSelector;
diff --git a/llvm/lib/Target/X86/X86AsmPrinter.h b/llvm/lib/Target/X86/X86AsmPrinter.h
index b22f25af26cfd..94679e6e3d112 100644
--- a/llvm/lib/Target/X86/X86AsmPrinter.h
+++ b/llvm/lib/Target/X86/X86AsmPrinter.h
@@ -23,7 +23,6 @@ class MCCodeEmitter;
 class MCStreamer;
 class X86Subtarget;
 class TargetMachine;
-struct ASanAccessInfo;
 
 class LLVM_LIBRARY_VISIBILITY X86AsmPrinter : public AsmPrinter {
   const X86Subtarget *Subtarget = nullptr;
diff --git a/llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.h b/llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.h
index 6d0a67c91cfaf..1624cf26094af 100644
--- a/llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.h
+++ b/llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.h
@@ -32,7 +32,6 @@
 namespace llvm {
 
 class AAResults;
-class DataLayout;
 class PHINode;
 class SelectInst;
 class Value;
diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 0027e7db055f7..ceb03eb17f6d1 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -138,8 +138,6 @@ AllowIVWidening("indvars-widen-indvars", cl::Hidden, cl::init(true),
 
 namespace {
 
-struct RewritePhi;
-
 class IndVarSimplify {
   LoopInfo *LI;
   ScalarEvolution *SE;
diff --git a/llvm/lib/Transforms/Vectorize/VPlanValue.h b/llvm/lib/Transforms/Vectorize/VPlanValue.h
index 49bf832a78ece..2df547e960ba9 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanValue.h
+++ b/llvm/lib/Transforms/Vectorize/VPlanValue.h
@@ -405,7 +405,6 @@ class VPDef {
 
 class VPlan;
 class VPBasicBlock;
-class VPRegionBlock;
 
 /// This class can be used to assign consecutive numbers to all VPValues in a
 /// VPlan and allows querying the numbering for printing, similar to the
diff --git a/llvm/tools/bugpoint/BugDriver.h b/llvm/tools/bugpoint/BugDriver.h
index fe5201eb2e6c3..b7c9edc5b8121 100644
--- a/llvm/tools/bugpoint/BugDriver.h
+++ b/llvm/tools/bugpoint/BugDriver.h
@@ -25,7 +25,6 @@
 
 namespace llvm {
 
-class Value;
 class PassInfo;
 class Module;
 class GlobalVariable;
@@ -35,8 +34,6 @@ class AbstractInterpreter;
 class Instruction;
 class LLVMContext;
 
-class DebugCrashes;
-
 class CC;
 
 extern bool DisableSimplifyCFG;
diff --git a/llvm/tools/llvm-objdump/COFFDump.h b/llvm/tools/llvm-objdump/COFFDump.h
index f933f79523a09..ffd39671debe4 100644
--- a/llvm/tools/llvm-objdump/COFFDump.h
+++ b/llvm/tools/llvm-objdump/COFFDump.h
@@ -18,7 +18,6 @@ class Error;
 namespace object {
 class COFFObjectFile;
 class COFFImportFile;
-class ObjectFile;
 class RelocationRef;
 } // namespace object
 
diff --git a/llvm/tools/llvm-objdump/llvm-objdump.h b/llvm/tools/llvm-objdump/llvm-objdump.h
index 864a9920efbef..61b6215aa5f55 100644
--- a/llvm/tools/llvm-objdump/llvm-objdump.h
+++ b/llvm/tools/llvm-objdump/llvm-objdump.h
@@ -21,10 +21,6 @@ class StringRef;
 class Twine;
 
 namespace object {
-class ELFObjectFileBase;
-class ELFSectionRef;
-class MachOObjectFile;
-class MachOUniversalBinary;
 class RelocationRef;
 struct VersionEntry;
 } // namespace object
diff --git a/llvm/tools/llvm-pdbutil/DumpOutputStyle.h b/llvm/tools/llvm-pdbutil/DumpOutputStyle.h
index 796cd7a10c362..041fb93a18a52 100644
--- a/llvm/tools/llvm-pdbutil/DumpOutputStyle.h
+++ b/llvm/tools/llvm-pdbutil/DumpOutputStyle.h
@@ -21,12 +21,6 @@
 #include <string>
 
 namespace llvm {
-class BitVector;
-
-namespace codeview {
-class LazyRandomTypeCollection;
-}
-
 namespace object {
 class COFFObjectFile;
 }
diff --git a/llvm/tools/llvm-pdbutil/InputFile.h b/llvm/tools/llvm-pdbutil/InputFile.h
index a5d2897f5600d..633ab34a54d44 100644
--- a/llvm/tools/llvm-pdbutil/InputFile.h
+++ b/llvm/tools/llvm-pdbutil/InputFile.h
@@ -26,7 +26,6 @@ class LazyRandomTypeCollection;
 }
 namespace object {
 class COFFObjectFile;
-class SectionRef;
 } // namespace object
 
 namespace pdb {
diff --git a/llvm/tools/llvm-pdbutil/LinePrinter.h b/llvm/tools/llvm-pdbutil/LinePrinter.h
index aa8159c0e0942..b6bb77280fd5c 100644
--- a/llvm/tools/llvm-pdbutil/LinePrinter.h
+++ b/llvm/tools/llvm-pdbutil/LinePrinter.h
@@ -20,7 +20,6 @@
 #include <list>
 
 namespace llvm {
-class BinaryStreamReader;
 namespace msf {
 class MSFStreamLayout;
 } // namespace msf
diff --git a/llvm/tools/llvm-pdbutil/OutputStyle.h b/llvm/tools/llvm-pdbutil/OutputStyle.h
index 40b0de8bdf726..da93c32053f35 100644
--- a/llvm/tools/llvm-pdbutil/OutputStyle.h
+++ b/llvm/tools/llvm-pdbutil/OutputStyle.h
@@ -13,7 +13,6 @@
 
 namespace llvm {
 namespace pdb {
-class PDBFile;
 
 class OutputStyle {
 public:
diff --git a/llvm/tools/llvm-pdbutil/PdbYaml.h b/llvm/tools/llvm-pdbutil/PdbYaml.h
index 2c2878c16546a..c335eef2f1c5e 100644
--- a/llvm/tools/llvm-pdbutil/PdbYaml.h
+++ b/llvm/tools/llvm-pdbutil/PdbYaml.h
@@ -27,13 +27,9 @@
 #include <vector>
 
 namespace llvm {
-namespace codeview {
-class DebugStringTableSubsection;
-}
 namespace pdb {
 
 namespace yaml {
-struct SerializationContext;
 
 struct MSFHeaders {
   msf::SuperBlock SuperBlock;
diff --git a/llvm/tools/llvm-pdbutil/YAMLOutputStyle.h b/llvm/tools/llvm-pdbutil/YAMLOutputStyle.h
index 7a50af1abe3f5..5d53e0b65d03c 100644
--- a/llvm/tools/llvm-pdbutil/YAMLOutputStyle.h
+++ b/llvm/tools/llvm-pdbutil/YAMLOutputStyle.h
@@ -17,7 +17,6 @@
 
 namespace llvm {
 namespace pdb {
-class ModuleDebugStreamRef;
 
 class YAMLOutputStyle : public OutputStyle {
 public:
diff --git a/llvm/tools/llvm-rc/ResourceScriptParser.h b/llvm/tools/llvm-rc/ResourceScriptParser.h
index fe202073b6bb0..a7d3b595f7943 100644
--- a/llvm/tools/llvm-rc/ResourceScriptParser.h
+++ b/llvm/tools/llvm-rc/ResourceScriptParser.h
@@ -24,9 +24,6 @@
 #include <vector>
 
 namespace llvm {
-namespace opt {
-class InputArgList;
-}
 namespace rc {
 
 class RCParser {
diff --git a/llvm/utils/TableGen/CodeGenIntrinsics.h b/llvm/utils/TableGen/CodeGenIntrinsics.h
index dbfad3bf6b178..b005a5866f80f 100644
--- a/llvm/utils/TableGen/CodeGenIntrinsics.h
+++ b/llvm/utils/TableGen/CodeGenIntrinsics.h
@@ -21,7 +21,6 @@
 namespace llvm {
 class Record;
 class RecordKeeper;
-class CodeGenTarget;
 
 struct CodeGenIntrinsic {
   Record *TheDef;             // The actual record defining this intrinsic.
diff --git a/llvm/utils/TableGen/CodeGenSchedule.h b/llvm/utils/TableGen/CodeGenSchedule.h
index 9020447c940b3..a331a30b51a87 100644
--- a/llvm/utils/TableGen/CodeGenSchedule.h
+++ b/llvm/utils/TableGen/CodeGenSchedule.h
@@ -28,7 +28,6 @@ namespace llvm {
 class CodeGenTarget;
 class CodeGenSchedModels;
 class CodeGenInstruction;
-class CodeGenRegisterClass;
 
 using RecVec = std::vector<Record*>;
 using RecIter = std::vector<Record*>::const_iterator;
diff --git a/llvm/utils/TableGen/GlobalISel/GIMatchDagPredicateDependencyEdge.h b/llvm/utils/TableGen/GlobalISel/GIMatchDagPredicateDependencyEdge.h
index 865455fe4e4d9..9552adc5c6252 100644
--- a/llvm/utils/TableGen/GlobalISel/GIMatchDagPredicateDependencyEdge.h
+++ b/llvm/utils/TableGen/GlobalISel/GIMatchDagPredicateDependencyEdge.h
@@ -14,7 +14,6 @@
 namespace llvm {
 class GIMatchDag;
 class GIMatchDagInstr;
-class GIMatchDagEdge;
 class GIMatchDagPredicate;
 
 /// Represents a dependency that must be met to evaluate a predicate.