Index: include/llvm/ADT/APFloat.h
===================================================================
--- include/llvm/ADT/APFloat.h
+++ include/llvm/ADT/APFloat.h
@@ -25,6 +25,8 @@
 class APSInt;
 class StringRef;
 
+template <typename T> class SmallVectorImpl;
+
 /// Enum that represents what fraction of the LSB truncated bits of an fp number
 /// represent.
 ///
Index: include/llvm/ADT/APInt.h
===================================================================
--- include/llvm/ADT/APInt.h
+++ include/llvm/ADT/APInt.h
@@ -16,7 +16,6 @@
 #ifndef LLVM_ADT_APINT_H
 #define LLVM_ADT_APINT_H
 
-#include "llvm/ADT/ArrayRef.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MathExtras.h"
 #include <cassert>
@@ -31,6 +30,7 @@
 class raw_ostream;
 
 template <typename T> class SmallVectorImpl;
+template <typename T> class ArrayRef;
 
 // An unsigned host type used as a single part of a multi-part
 // bignum.
Index: include/llvm/ADT/FoldingSet.h
===================================================================
--- include/llvm/ADT/FoldingSet.h
+++ include/llvm/ADT/FoldingSet.h
@@ -17,10 +17,8 @@
 #define LLVM_ADT_FOLDINGSET_H
 
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/iterator.h"
 #include "llvm/Support/Allocator.h"
-#include "llvm/Support/DataTypes.h"
 
 namespace llvm {
 /// This folding set used for two purposes:
@@ -98,6 +96,7 @@
 /// The result indicates whether the node existed in the folding set.
 
 class FoldingSetNodeID;
+class StringRef;
 
 //===----------------------------------------------------------------------===//
 /// FoldingSetImpl - Implements the folding set functionality.  The main
Index: include/llvm/ADT/SmallBitVector.h
===================================================================
--- include/llvm/ADT/SmallBitVector.h
+++ include/llvm/ADT/SmallBitVector.h
@@ -15,7 +15,6 @@
 #define LLVM_ADT_SMALLBITVECTOR_H
 
 #include "llvm/ADT/BitVector.h"
-#include "llvm/Support/Compiler.h"
 #include "llvm/Support/MathExtras.h"
 #include <cassert>
 
Index: include/llvm/ADT/StringMap.h
===================================================================
--- include/llvm/ADT/StringMap.h
+++ include/llvm/ADT/StringMap.h
@@ -15,7 +15,6 @@
 #define LLVM_ADT_STRINGMAP_H
 
 #include "llvm/ADT/StringRef.h"
-#include "llvm/ADT/Twine.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/PointerLikeTypeTraits.h"
 #include <cstring>
Index: include/llvm/IR/Comdat.h
===================================================================
--- include/llvm/IR/Comdat.h
+++ include/llvm/IR/Comdat.h
@@ -16,12 +16,10 @@
 #ifndef LLVM_IR_COMDAT_H
 #define LLVM_IR_COMDAT_H
 
-#include "llvm/ADT/StringRef.h"
-#include "llvm/Support/Compiler.h"
-
 namespace llvm {
 
 class raw_ostream;
+class StringRef;
 template <typename ValueTy> class StringMapEntry;
 
 // This is a Name X SelectionKind pair. The reason for having this be an
Index: include/llvm/IR/DIBuilder.h
===================================================================
--- include/llvm/IR/DIBuilder.h
+++ include/llvm/IR/DIBuilder.h
@@ -15,8 +15,6 @@
 #ifndef LLVM_IR_DIBUILDER_H
 #define LLVM_IR_DIBUILDER_H
 
-#include "llvm/ADT/ArrayRef.h"
-#include "llvm/ADT/StringRef.h"
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/TrackingMDRef.h"
 #include "llvm/IR/ValueHandle.h"
@@ -31,6 +29,7 @@
   class Constant;
   class LLVMContext;
   class StringRef;
+  template <typename T> class ArrayRef;
 
   class DIBuilder {
     Module &M;
Index: include/llvm/IR/DataLayout.h
===================================================================
--- include/llvm/IR/DataLayout.h
+++ include/llvm/IR/DataLayout.h
@@ -20,7 +20,6 @@
 #ifndef LLVM_IR_DATALAYOUT_H
 #define LLVM_IR_DATALAYOUT_H
 
-#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Type.h"
@@ -34,8 +33,6 @@
 namespace llvm {
 
 class Value;
-class Type;
-class IntegerType;
 class StructType;
 class StructLayout;
 class Triple;
Index: include/llvm/IR/DebugInfo.h
===================================================================
--- include/llvm/IR/DebugInfo.h
+++ include/llvm/IR/DebugInfo.h
@@ -17,10 +17,8 @@
 #ifndef LLVM_IR_DEBUGINFO_H
 #define LLVM_IR_DEBUGINFO_H
 
-#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/Support/Casting.h"
@@ -32,6 +30,8 @@
 class Module;
 class DbgDeclareInst;
 class DbgValueInst;
+template <typename K, typename V, typename KeyInfoT, typename BucketT>
+class DenseMap;
 
 /// \brief Maps from type identifier to the actual MDNode.
 typedef DenseMap<const MDString *, DIType *> DITypeIdentifierMap;
Index: include/llvm/IR/DebugInfoMetadata.h
===================================================================
--- include/llvm/IR/DebugInfoMetadata.h
+++ include/llvm/IR/DebugInfoMetadata.h
@@ -14,7 +14,6 @@
 #ifndef LLVM_IR_DEBUGINFOMETADATA_H
 #define LLVM_IR_DEBUGINFOMETADATA_H
 
-#include "llvm/ADT/Optional.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/Support/Dwarf.h"
 
@@ -44,6 +43,8 @@
 
 namespace llvm {
 
+template <typename T> class Optional;
+
 /// \brief Pointer union between a subclass of DINode and MDString.
 ///
 /// \a DICompositeType can be referenced via an \a MDString unique identifier.
Index: include/llvm/IR/DiagnosticInfo.h
===================================================================
--- include/llvm/IR/DiagnosticInfo.h
+++ include/llvm/IR/DiagnosticInfo.h
@@ -15,7 +15,6 @@
 #ifndef LLVM_IR_DIAGNOSTICINFO_H
 #define LLVM_IR_DIAGNOSTICINFO_H
 
-#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Module.h"
Index: include/llvm/IR/Dominators.h
===================================================================
--- include/llvm/IR/Dominators.h
+++ include/llvm/IR/Dominators.h
@@ -15,23 +15,19 @@
 #ifndef LLVM_IR_DOMINATORS_H
 #define LLVM_IR_DOMINATORS_H
 
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/GraphTraits.h"
 #include "llvm/ADT/SmallPtrSet.h"
-#include "llvm/ADT/SmallVector.h"
-#include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
-#include "llvm/IR/Function.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/Pass.h"
-#include "llvm/Support/Compiler.h"
 #include "llvm/Support/GenericDomTree.h"
-#include "llvm/Support/raw_ostream.h"
-#include <algorithm>
 
 namespace llvm {
 
+class Function;
+class BasicBlock;
+class raw_ostream;
+
 extern template class DomTreeNodeBase<BasicBlock>;
 extern template class DominatorTreeBase<BasicBlock>;
 
Index: include/llvm/IR/Function.h
===================================================================
--- include/llvm/IR/Function.h
+++ include/llvm/IR/Function.h
@@ -19,7 +19,6 @@
 #define LLVM_IR_FUNCTION_H
 
 #include "llvm/ADT/iterator_range.h"
-#include "llvm/ADT/Optional.h"
 #include "llvm/IR/Argument.h"
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/BasicBlock.h"
@@ -30,6 +29,7 @@
 
 namespace llvm {
 
+template <typename T> class Optional;
 class FunctionType;
 class LLVMContext;
 class DISubprogram;
Index: include/llvm/IR/GlobalAlias.h
===================================================================
--- include/llvm/IR/GlobalAlias.h
+++ include/llvm/IR/GlobalAlias.h
@@ -15,12 +15,12 @@
 #ifndef LLVM_IR_GLOBALALIAS_H
 #define LLVM_IR_GLOBALALIAS_H
 
-#include "llvm/ADT/Twine.h"
 #include "llvm/ADT/ilist_node.h"
 #include "llvm/IR/GlobalIndirectSymbol.h"
 
 namespace llvm {
 
+class Twine;
 class Module;
 template <typename ValueSubClass> class SymbolTableListTraits;
 
Index: include/llvm/IR/GlobalIFunc.h
===================================================================
--- include/llvm/IR/GlobalIFunc.h
+++ include/llvm/IR/GlobalIFunc.h
@@ -18,12 +18,12 @@
 #ifndef LLVM_IR_GLOBALIFUNC_H
 #define LLVM_IR_GLOBALIFUNC_H
 
-#include "llvm/ADT/Twine.h"
 #include "llvm/ADT/ilist_node.h"
 #include "llvm/IR/GlobalIndirectSymbol.h"
 
 namespace llvm {
 
+class Twine;
 class Module;
 
 // Traits class for using GlobalIFunc in symbol table in Module.
Index: include/llvm/IR/GlobalObject.h
===================================================================
--- include/llvm/IR/GlobalObject.h
+++ include/llvm/IR/GlobalObject.h
@@ -15,7 +15,6 @@
 #ifndef LLVM_IR_GLOBALOBJECT_H
 #define LLVM_IR_GLOBALOBJECT_H
 
-#include "llvm/IR/Constant.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/GlobalValue.h"
 
Index: include/llvm/IR/Intrinsics.h
===================================================================
--- include/llvm/IR/Intrinsics.h
+++ include/llvm/IR/Intrinsics.h
@@ -17,6 +17,7 @@
 #define LLVM_IR_INTRINSICS_H
 
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/None.h"
 #include <string>
 
 namespace llvm {
Index: include/llvm/IR/LLVMContext.h
===================================================================
--- include/llvm/IR/LLVMContext.h
+++ include/llvm/IR/LLVMContext.h
@@ -16,7 +16,6 @@
 #define LLVM_IR_LLVMCONTEXT_H
 
 #include "llvm/Support/CBindingWrapping.h"
-#include "llvm/Support/Compiler.h"
 #include "llvm/Support/Options.h"
 
 namespace llvm {
Index: include/llvm/IR/LegacyPassManagers.h
===================================================================
--- include/llvm/IR/LegacyPassManagers.h
+++ include/llvm/IR/LegacyPassManagers.h
@@ -14,7 +14,6 @@
 #ifndef LLVM_IR_LEGACYPASSMANAGERS_H
 #define LLVM_IR_LEGACYPASSMANAGERS_H
 
-#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/SmallPtrSet.h"
@@ -93,12 +92,13 @@
 #include "llvm/Support/PrettyStackTrace.h"
 
 namespace llvm {
-  class Module;
-  class Pass;
-  class StringRef;
-  class Value;
-  class Timer;
-  class PMDataManager;
+template <typename T> class ArrayRef;
+class Module;
+class Pass;
+class StringRef;
+class Value;
+class Timer;
+class PMDataManager;
 
 // enums for debugging strings
 enum PassDebuggingString {
Index: include/llvm/IR/Mangler.h
===================================================================
--- include/llvm/IR/Mangler.h
+++ include/llvm/IR/Mangler.h
@@ -16,13 +16,13 @@
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/IR/GlobalValue.h"
-#include "llvm/Support/raw_ostream.h"
 
 namespace llvm {
 
 class DataLayout;
 template <typename T> class SmallVectorImpl;
 class Twine;
+class raw_ostream;
 
 class Mangler {
   /// We need to give global values the same name every time they are mangled.
Index: include/llvm/IR/Module.h
===================================================================
--- include/llvm/IR/Module.h
+++ include/llvm/IR/Module.h
@@ -15,7 +15,6 @@
 #ifndef LLVM_IR_MODULE_H
 #define LLVM_IR_MODULE_H
 
-#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/IR/Comdat.h"
 #include "llvm/IR/DataLayout.h"
@@ -30,6 +29,7 @@
 #include <system_error>
 
 namespace llvm {
+template <typename T> class Optional;
 class FunctionType;
 class GVMaterializer;
 class LLVMContext;
Index: include/llvm/IR/ModuleSummaryIndex.h
===================================================================
--- include/llvm/IR/ModuleSummaryIndex.h
+++ include/llvm/IR/ModuleSummaryIndex.h
@@ -22,10 +22,7 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringMap.h"
-#include "llvm/IR/Function.h"
 #include "llvm/IR/Module.h"
-#include "llvm/Support/MemoryBuffer.h"
-#include "llvm/Support/raw_ostream.h"
 
 #include <array>
 
Index: include/llvm/IR/PassManager.h
===================================================================
--- include/llvm/IR/PassManager.h
+++ include/llvm/IR/PassManager.h
@@ -44,7 +44,6 @@
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/PassManagerInternal.h"
-#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/TypeName.h"
 #include "llvm/Support/raw_ostream.h"
@@ -55,9 +54,6 @@
 
 namespace llvm {
 
-class Module;
-class Function;
-
 /// \brief An abstract set of preserved analyses following a transformation pass
 /// run.
 ///
Index: include/llvm/IR/TrackingMDRef.h
===================================================================
--- include/llvm/IR/TrackingMDRef.h
+++ include/llvm/IR/TrackingMDRef.h
@@ -15,7 +15,6 @@
 #define LLVM_IR_TRACKINGMDREF_H
 
 #include "llvm/IR/Metadata.h"
-#include "llvm/Support/Casting.h"
 
 namespace llvm {
 
Index: include/llvm/IR/Type.h
===================================================================
--- include/llvm/IR/Type.h
+++ include/llvm/IR/Type.h
@@ -16,6 +16,7 @@
 #define LLVM_IR_TYPE_H
 
 #include "llvm/ADT/APFloat.h"
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Support/CBindingWrapping.h"
 #include "llvm/Support/Casting.h"
Index: include/llvm/IR/Use.h
===================================================================
--- include/llvm/IR/Use.h
+++ include/llvm/IR/Use.h
@@ -27,7 +27,6 @@
 
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/Support/CBindingWrapping.h"
-#include "llvm/Support/Compiler.h"
 #include <cstddef>
 #include <iterator>
 
Index: include/llvm/IR/UseListOrder.h
===================================================================
--- include/llvm/IR/UseListOrder.h
+++ include/llvm/IR/UseListOrder.h
@@ -15,8 +15,6 @@
 #ifndef LLVM_IR_USELISTORDER_H
 #define LLVM_IR_USELISTORDER_H
 
-#include "llvm/ADT/ArrayRef.h"
-#include "llvm/ADT/SmallVector.h"
 #include <vector>
 
 namespace llvm {
Index: include/llvm/IR/User.h
===================================================================
--- include/llvm/IR/User.h
+++ include/llvm/IR/User.h
@@ -19,7 +19,6 @@
 #ifndef LLVM_IR_USER_H
 #define LLVM_IR_USER_H
 
-#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/iterator.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/IR/Value.h"
@@ -28,6 +27,9 @@
 
 namespace llvm {
 
+template <typename T> class ArrayRef;
+template <typename T> class MutableArrayRef;
+
 /// \brief Compile-time customization of User operands.
 ///
 /// Customizes operand-related allocators and accessors.
Index: include/llvm/IR/Value.h
===================================================================
--- include/llvm/IR/Value.h
+++ include/llvm/IR/Value.h
@@ -18,7 +18,6 @@
 #include "llvm/IR/Use.h"
 #include "llvm/Support/CBindingWrapping.h"
 #include "llvm/Support/Casting.h"
-#include "llvm/Support/Compiler.h"
 
 namespace llvm {
 
Index: include/llvm/IR/ValueSymbolTable.h
===================================================================
--- include/llvm/IR/ValueSymbolTable.h
+++ include/llvm/IR/ValueSymbolTable.h
@@ -14,13 +14,13 @@
 #ifndef LLVM_IR_VALUESYMBOLTABLE_H
 #define LLVM_IR_VALUESYMBOLTABLE_H
 
-#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/IR/Value.h"
 #include "llvm/Support/DataTypes.h"
 
 namespace llvm {
   template <typename ValueSubClass> class SymbolTableListTraits;
+  template <unsigned InternalLen> class SmallString;
   class BasicBlock;
   class Function;
   class NamedMDNode;
Index: include/llvm/IR/Verifier.h
===================================================================
--- include/llvm/IR/Verifier.h
+++ include/llvm/IR/Verifier.h
@@ -21,9 +21,7 @@
 #ifndef LLVM_IR_VERIFIER_H
 #define LLVM_IR_VERIFIER_H
 
-#include "llvm/ADT/StringRef.h"
 #include "llvm/IR/PassManager.h"
-#include <string>
 
 namespace llvm {
 
Index: include/llvm/MC/MCParser/MCAsmLexer.h
===================================================================
--- include/llvm/MC/MCParser/MCAsmLexer.h
+++ include/llvm/MC/MCParser/MCAsmLexer.h
@@ -11,6 +11,8 @@
 #define LLVM_MC_MCPARSER_MCASMLEXER_H
 
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/DataTypes.h"
Index: lib/CodeGen/MIRParser/MILexer.cpp
===================================================================
--- lib/CodeGen/MIRParser/MILexer.cpp
+++ lib/CodeGen/MIRParser/MILexer.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "MILexer.h"
+#include "llvm/ADT/None.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Twine.h"
Index: lib/CodeGen/RegAllocFast.cpp
===================================================================
--- lib/CodeGen/RegAllocFast.cpp
+++ lib/CodeGen/RegAllocFast.cpp
@@ -12,7 +12,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/CodeGen/Passes.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/IndexedMap.h"
 #include "llvm/ADT/STLExtras.h"
@@ -25,13 +24,11 @@
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/RegAllocRegistry.h"
 #include "llvm/CodeGen/RegisterClassInfo.h"
-#include "llvm/IR/BasicBlock.h"
-#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 #include <algorithm>
Index: lib/Support/APFloat.cpp
===================================================================
--- lib/Support/APFloat.cpp
+++ lib/Support/APFloat.cpp
@@ -14,6 +14,7 @@
 
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APSInt.h"
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/StringExtras.h"
Index: lib/Support/APInt.cpp
===================================================================
--- lib/Support/APInt.cpp
+++ lib/Support/APInt.cpp
@@ -13,6 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/SmallString.h"
Index: lib/Support/APSInt.cpp
===================================================================
--- lib/Support/APSInt.cpp
+++ lib/Support/APSInt.cpp
@@ -14,6 +14,7 @@
 
 #include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/FoldingSet.h"
+#include "llvm/ADT/StringRef.h"
 
 using namespace llvm;
 
Index: lib/Support/ScaledNumber.cpp
===================================================================
--- lib/Support/ScaledNumber.cpp
+++ lib/Support/ScaledNumber.cpp
@@ -13,6 +13,7 @@
 
 #include "llvm/Support/ScaledNumber.h"
 #include "llvm/ADT/APFloat.h"
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
Index: unittests/ADT/APIntTest.cpp
===================================================================
--- unittests/ADT/APIntTest.cpp
+++ unittests/ADT/APIntTest.cpp
@@ -8,10 +8,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallString.h"
 #include "gtest/gtest.h"
 #include <array>
-#include <ostream>
 
 using namespace llvm;
 
Index: unittests/ADT/StringMapTest.cpp
===================================================================
--- unittests/ADT/StringMapTest.cpp
+++ unittests/ADT/StringMapTest.cpp
@@ -7,9 +7,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "gtest/gtest.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/Twine.h"
 #include "llvm/Support/DataTypes.h"
+#include "gtest/gtest.h"
 #include <tuple>
 using namespace llvm;