diff --git a/llvm/include/llvm/ADT/SmallVector.h b/llvm/include/llvm/ADT/SmallVector.h
index 9347f01a4191f..466acb83d4668 100644
--- a/llvm/include/llvm/ADT/SmallVector.h
+++ b/llvm/include/llvm/ADT/SmallVector.h
@@ -13,7 +13,6 @@
 #ifndef LLVM_ADT_SMALLVECTOR_H
 #define LLVM_ADT_SMALLVECTOR_H
 
-#include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/type_traits.h"
 #include <algorithm>
@@ -32,6 +31,8 @@
 
 namespace llvm {
 
+template <typename IteratorT> class iterator_range;
+
 /// This is all the stuff common to all SmallVectors.
 ///
 /// The template parameter specifies the type which should be used to hold the
diff --git a/llvm/include/llvm/Support/ARMTargetParser.h b/llvm/include/llvm/Support/ARMTargetParser.h
index b40704c24e87c..1ada6daaad3ba 100644
--- a/llvm/include/llvm/Support/ARMTargetParser.h
+++ b/llvm/include/llvm/Support/ARMTargetParser.h
@@ -14,7 +14,6 @@
 #ifndef LLVM_SUPPORT_ARMTARGETPARSER_H
 #define LLVM_SUPPORT_ARMTARGETPARSER_H
 
-#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/ARMBuildAttributes.h"
 #include <vector>
diff --git a/llvm/include/llvm/Support/ConvertUTF.h b/llvm/include/llvm/Support/ConvertUTF.h
index 1add185330fa0..374cdb907fdc2 100644
--- a/llvm/include/llvm/Support/ConvertUTF.h
+++ b/llvm/include/llvm/Support/ConvertUTF.h
@@ -91,7 +91,10 @@
 
 #include <cstddef>
 #include <string>
+
+#if defined(_WIN32)
 #include <system_error>
+#endif
 
 // Wrap everything in namespace llvm so that programs can link with llvm and
 // their own version of the unicode libraries.
diff --git a/llvm/include/llvm/Support/TargetParser.h b/llvm/include/llvm/Support/TargetParser.h
index 1d7594ebedc22..a6f8ebe1381a6 100644
--- a/llvm/include/llvm/Support/TargetParser.h
+++ b/llvm/include/llvm/Support/TargetParser.h
@@ -16,12 +16,14 @@
 
 // FIXME: vector is used because that's what clang uses for subtarget feature
 // lists, but SmallVector would probably be better
-#include "llvm/ADT/Triple.h"
 #include "llvm/Support/RISCVISAInfo.h"
 #include <vector>
 
 namespace llvm {
+
 class StringRef;
+template <typename T> class SmallVectorImpl;
+class Triple;
 
 // Target specific information in their own namespaces.
 // (ARM/AArch64/X86 are declared in ARM/AArch64/X86TargetParser.h)
diff --git a/llvm/include/llvm/Support/ThreadPool.h b/llvm/include/llvm/Support/ThreadPool.h
index aecff122d3cbe..868dd2819f836 100644
--- a/llvm/include/llvm/Support/ThreadPool.h
+++ b/llvm/include/llvm/Support/ThreadPool.h
@@ -19,7 +19,6 @@
 
 #include <future>
 
-#include <atomic>
 #include <condition_variable>
 #include <functional>
 #include <memory>
diff --git a/llvm/include/llvm/Support/X86TargetParser.h b/llvm/include/llvm/Support/X86TargetParser.h
index bfa3e23dbd9db..6f5db64714e03 100644
--- a/llvm/include/llvm/Support/X86TargetParser.h
+++ b/llvm/include/llvm/Support/X86TargetParser.h
@@ -14,10 +14,10 @@
 #define LLVM_SUPPORT_X86TARGETPARSER_H
 
 #include "llvm/ADT/ArrayRef.h"
-#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 
 namespace llvm {
+template <typename T> class SmallVectorImpl;;
 class StringRef;
 
 namespace X86 {
diff --git a/llvm/include/llvm/Support/YAMLTraits.h b/llvm/include/llvm/Support/YAMLTraits.h
index 66529075e2e71..b7e41f662810e 100644
--- a/llvm/include/llvm/Support/YAMLTraits.h
+++ b/llvm/include/llvm/Support/YAMLTraits.h
@@ -20,7 +20,6 @@
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/SMLoc.h"
 #include "llvm/Support/SourceMgr.h"
-#include "llvm/Support/VersionTuple.h"
 #include "llvm/Support/YAMLParser.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
@@ -34,6 +33,9 @@
 #include <vector>
 
 namespace llvm {
+
+class VersionTuple;
+
 namespace yaml {
 
 enum class NodeKind : uint8_t {
diff --git a/llvm/lib/Support/BinaryStreamError.cpp b/llvm/lib/Support/BinaryStreamError.cpp
index f22523f09ac80..9b8f6862b65c2 100644
--- a/llvm/lib/Support/BinaryStreamError.cpp
+++ b/llvm/lib/Support/BinaryStreamError.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/BinaryStreamError.h"
-#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
 
diff --git a/llvm/lib/Support/CrashRecoveryContext.cpp b/llvm/lib/Support/CrashRecoveryContext.cpp
index b6aaf373a5221..2ee3074b840e4 100644
--- a/llvm/lib/Support/CrashRecoveryContext.cpp
+++ b/llvm/lib/Support/CrashRecoveryContext.cpp
@@ -9,7 +9,6 @@
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/ExitCodes.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/ThreadLocal.h"
@@ -17,6 +16,10 @@
 #include <mutex>
 #include <setjmp.h>
 
+#if !defined(_MSC_VER) && !defined(_WIN32)
+#include "llvm/Support/ExitCodes.h"
+#endif
+
 using namespace llvm;
 
 namespace {
diff --git a/llvm/lib/Support/FileUtilities.cpp b/llvm/lib/Support/FileUtilities.cpp
index 1a14ed2673606..489b8d119e6f3 100644
--- a/llvm/lib/Support/FileUtilities.cpp
+++ b/llvm/lib/Support/FileUtilities.cpp
@@ -18,7 +18,6 @@
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
-#include <cmath>
 #include <cstdint>
 #include <cstdlib>
 #include <cstring>
diff --git a/llvm/lib/Support/MemoryBuffer.cpp b/llvm/lib/Support/MemoryBuffer.cpp
index 7192fb1321cb6..bf34a242c4c3f 100644
--- a/llvm/lib/Support/MemoryBuffer.cpp
+++ b/llvm/lib/Support/MemoryBuffer.cpp
@@ -18,7 +18,6 @@
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MathExtras.h"
-#include "llvm/Support/Path.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/SmallVectorMemoryBuffer.h"
diff --git a/llvm/lib/Support/TargetParser.cpp b/llvm/lib/Support/TargetParser.cpp
index c14ddbeea5c39..0105cd2e81532 100644
--- a/llvm/lib/Support/TargetParser.cpp
+++ b/llvm/lib/Support/TargetParser.cpp
@@ -14,7 +14,7 @@
 #include "llvm/Support/TargetParser.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringSwitch.h"
-#include "llvm/Support/ARMBuildAttributes.h"
+#include "llvm/ADT/Triple.h"
 
 using namespace llvm;
 using namespace AMDGPU;
diff --git a/llvm/lib/Support/ThreadPool.cpp b/llvm/lib/Support/ThreadPool.cpp
index 6eec368e626ff..bf2584950c4ac 100644
--- a/llvm/lib/Support/ThreadPool.cpp
+++ b/llvm/lib/Support/ThreadPool.cpp
@@ -14,7 +14,6 @@
 
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/Threading.h"
-#include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
 
diff --git a/llvm/lib/Support/YAMLTraits.cpp b/llvm/lib/Support/YAMLTraits.cpp
index b79d520900d2c..939427d3fc818 100644
--- a/llvm/lib/Support/YAMLTraits.cpp
+++ b/llvm/lib/Support/YAMLTraits.cpp
@@ -18,6 +18,7 @@
 #include "llvm/Support/Format.h"
 #include "llvm/Support/LineIterator.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/VersionTuple.h"
 #include "llvm/Support/YAMLParser.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>