diff --git a/llvm/include/llvm/CodeGen/DbgEntityHistoryCalculator.h b/llvm/include/llvm/CodeGen/DbgEntityHistoryCalculator.h
index e7425dd3dc04..2ac9d938d281 100644
--- a/llvm/include/llvm/CodeGen/DbgEntityHistoryCalculator.h
+++ b/llvm/include/llvm/CodeGen/DbgEntityHistoryCalculator.h
@@ -17,7 +17,6 @@
 
 namespace llvm {
 
-class DILocalVariable;
 class DILocation;
 class DINode;
 class MachineFunction;
diff --git a/llvm/include/llvm/CodeGen/FaultMaps.h b/llvm/include/llvm/CodeGen/FaultMaps.h
index 12d2872c8c5b..8a8b1d2e6008 100644
--- a/llvm/include/llvm/CodeGen/FaultMaps.h
+++ b/llvm/include/llvm/CodeGen/FaultMaps.h
@@ -18,7 +18,6 @@ namespace llvm {
 
 class AsmPrinter;
 class MCExpr;
-class raw_ostream;
 
 class FaultMaps {
 public:
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/CombinerInfo.h b/llvm/include/llvm/CodeGen/GlobalISel/CombinerInfo.h
index 4a1a4ff2528a..e73f8489497e 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/CombinerInfo.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/CombinerInfo.h
@@ -20,7 +20,6 @@ class GISelChangeObserver;
 class LegalizerInfo;
 class MachineInstr;
 class MachineIRBuilder;
-class MachineRegisterInfo;
 
 // Contains information relevant to enabling/disabling various combines for a
 // pass.
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/GISelWorkList.h b/llvm/include/llvm/CodeGen/GlobalISel/GISelWorkList.h
index c5af64d2bcbe..7d198fada411 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/GISelWorkList.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/GISelWorkList.h
@@ -15,7 +15,6 @@
 namespace llvm {
 
 class MachineInstr;
-class MachineFunction;
 
 // Worklist which mostly works similar to InstCombineWorkList, but on
 // MachineInstrs. The main difference with something like a SetVector is that
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/Legalizer.h b/llvm/include/llvm/CodeGen/GlobalISel/Legalizer.h
index 4871d8d32ebd..c19f1d5330ba 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/Legalizer.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/Legalizer.h
@@ -25,7 +25,6 @@
 
 namespace llvm {
 
-class MachineRegisterInfo;
 class LostDebugLocObserver;
 
 class Legalizer : public MachineFunctionPass {
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h b/llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
index 044f2e22cfdd..3b2f937375eb 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
@@ -30,7 +30,6 @@
 namespace llvm {
 // Forward declarations.
 class LegalizerInfo;
-class Legalizer;
 class MachineRegisterInfo;
 class GISelChangeObserver;
 class LostDebugLocObserver;
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h b/llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
index 0b37539030b1..a02b15639946 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h
@@ -38,7 +38,6 @@ class LegalizerHelper;
 class MachineInstr;
 class MachineRegisterInfo;
 class MCInstrInfo;
-class GISelChangeObserver;
 
 namespace LegalizeActions {
 enum LegalizeAction : std::uint8_t {
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/LoadStoreOpt.h b/llvm/include/llvm/CodeGen/GlobalISel/LoadStoreOpt.h
index 29575f386d7a..0845c001abdb 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/LoadStoreOpt.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/LoadStoreOpt.h
@@ -30,7 +30,6 @@
 namespace llvm {
 // Forward declarations.
 class MachineRegisterInfo;
-class TargetTransformInfo;
 namespace GISelAddressing {
 /// Helper struct to store a base, index and offset that forms an address
 struct BaseIndexOffset {
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/Utils.h b/llvm/include/llvm/CodeGen/GlobalISel/Utils.h
index 8fed79585fe9..a77db3145915 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/Utils.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/Utils.h
@@ -44,7 +44,6 @@ class TargetLowering;
 class TargetPassConfig;
 class TargetRegisterInfo;
 class TargetRegisterClass;
-class ConstantInt;
 class ConstantFP;
 class APFloat;
 class MachineIRBuilder;
diff --git a/llvm/include/llvm/CodeGen/LiveRangeEdit.h b/llvm/include/llvm/CodeGen/LiveRangeEdit.h
index fa4e80179eec..d80522f5bdac 100644
--- a/llvm/include/llvm/CodeGen/LiveRangeEdit.h
+++ b/llvm/include/llvm/CodeGen/LiveRangeEdit.h
@@ -34,9 +34,7 @@ namespace llvm {
 
 class AAResults;
 class LiveIntervals;
-class MachineBlockFrequencyInfo;
 class MachineInstr;
-class MachineLoopInfo;
 class MachineOperand;
 class TargetInstrInfo;
 class TargetRegisterInfo;
diff --git a/llvm/include/llvm/CodeGen/MachineLoopUtils.h b/llvm/include/llvm/CodeGen/MachineLoopUtils.h
index 2352fbca548d..b9bf93b71e25 100644
--- a/llvm/include/llvm/CodeGen/MachineLoopUtils.h
+++ b/llvm/include/llvm/CodeGen/MachineLoopUtils.h
@@ -10,7 +10,6 @@
 #define LLVM_CODEGEN_MACHINELOOPUTILS_H
 
 namespace llvm {
-class MachineLoop;
 class MachineBasicBlock;
 class MachineRegisterInfo;
 class TargetInstrInfo;
diff --git a/llvm/include/llvm/CodeGen/MachineModuleInfo.h b/llvm/include/llvm/CodeGen/MachineModuleInfo.h
index 860a86ee991b..c07606e89374 100644
--- a/llvm/include/llvm/CodeGen/MachineModuleInfo.h
+++ b/llvm/include/llvm/CodeGen/MachineModuleInfo.h
@@ -44,7 +44,6 @@
 namespace llvm {
 
 class BasicBlock;
-class CallInst;
 class Function;
 class LLVMTargetMachine;
 class MMIAddrLabelMap;
diff --git a/llvm/include/llvm/CodeGen/Passes.h b/llvm/include/llvm/CodeGen/Passes.h
index d5ad12fadfa0..f4c6edba61f2 100644
--- a/llvm/include/llvm/CodeGen/Passes.h
+++ b/llvm/include/llvm/CodeGen/Passes.h
@@ -30,7 +30,6 @@ class MemoryBuffer;
 class ModulePass;
 class Pass;
 class TargetMachine;
-class TargetRegisterClass;
 class raw_ostream;
 
 } // End llvm namespace
diff --git a/llvm/include/llvm/CodeGen/TailDuplicator.h b/llvm/include/llvm/CodeGen/TailDuplicator.h
index 6862bb2c3f44..daaa27f72d52 100644
--- a/llvm/include/llvm/CodeGen/TailDuplicator.h
+++ b/llvm/include/llvm/CodeGen/TailDuplicator.h
@@ -26,7 +26,6 @@
 namespace llvm {
 
 class MachineBasicBlock;
-class MachineBlockFrequencyInfo;
 class MachineBranchProbabilityInfo;
 class MachineFunction;
 class MachineInstr;
diff --git a/llvm/include/llvm/CodeGen/TargetLowering.h b/llvm/include/llvm/CodeGen/TargetLowering.h
index b2d82e0cc6e8..aef7973ff20f 100644
--- a/llvm/include/llvm/CodeGen/TargetLowering.h
+++ b/llvm/include/llvm/CodeGen/TargetLowering.h
@@ -63,7 +63,6 @@
 
 namespace llvm {
 
-class BranchProbability;
 class CCState;
 class CCValAssign;
 class Constant;