diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 38181904f871..979c81f6361b 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -390,7 +390,6 @@ def : DiagGroup<"sequence-point", [Unsequenced]>;
 def AmbiguousMacro : DiagGroup<"ambiguous-macro">;
 def KeywordAsMacro : DiagGroup<"keyword-macro">;
 def ReservedIdAsMacro : DiagGroup<"reserved-id-macro">;
-def NonportableIncludePath : DiagGroup<"nonportable-include-path">;
 
 // Just silence warnings about -Wstrict-aliasing for now.
 def : DiagGroup<"strict-aliasing=0">;
diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
index 52116a603d53..dab8cf279ca3 100644
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -274,10 +274,6 @@ def ext_missing_whitespace_after_macro_name : ExtWarn<
   "whitespace required after macro name">;
 def warn_missing_whitespace_after_macro_name : Warning<
   "whitespace recommended after macro name">;
-def pp_nonportable_path : Warning<
-  "non-portable path to file '%0'; specified path differs in case from file"
-  " name on disk">,
-  InGroup<NonportableIncludePath>;
   
 def pp_pragma_once_in_main_file : Warning<"#pragma once in main file">,
   InGroup<DiagGroup<"pragma-once-outside-header">>;
diff --git a/clang/include/clang/Basic/FileManager.h b/clang/include/clang/Basic/FileManager.h
index b6a9ca702842..17758ec3f398 100644
--- a/clang/include/clang/Basic/FileManager.h
+++ b/clang/include/clang/Basic/FileManager.h
@@ -52,7 +52,6 @@ public:
 /// descriptor for the file.
 class FileEntry {
   const char *Name;           // Name of the file.
-  std::string RealPathName;   // Real path to the file; could be empty.
   off_t Size;                 // File size in bytes.
   time_t ModTime;             // Modification time of file.
   const DirectoryEntry *Dir;  // Directory file lives in.
@@ -83,7 +82,6 @@ public:
   }
 
   const char *getName() const { return Name; }
-  StringRef tryGetRealPathName() const { return RealPathName; }
   bool isValid() const { return IsValid; }
   off_t getSize() const { return Size; }
   unsigned getUID() const { return UID; }
diff --git a/clang/include/clang/Basic/VirtualFileSystem.h b/clang/include/clang/Basic/VirtualFileSystem.h
index 4353f8458811..bc09e6787884 100644
--- a/clang/include/clang/Basic/VirtualFileSystem.h
+++ b/clang/include/clang/Basic/VirtualFileSystem.h
@@ -91,13 +91,6 @@ public:
   virtual ~File();
   /// \brief Get the status of the file.
   virtual llvm::ErrorOr<Status> status() = 0;
-  /// \brief Get the name of the file
-  virtual llvm::ErrorOr<StringRef> getName() {
-    if (auto Status = status())
-      return Status->getName();
-    else
-      return Status.getError();
-  }
   /// \brief Get the contents of the file as a \p MemoryBuffer.
   virtual llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
   getBuffer(const Twine &Name, int64_t FileSize = -1,
diff --git a/clang/include/clang/Lex/DirectoryLookup.h b/clang/include/clang/Lex/DirectoryLookup.h
index ee0af292e6fc..20c4bb03ab6e 100644
--- a/clang/include/clang/Lex/DirectoryLookup.h
+++ b/clang/include/clang/Lex/DirectoryLookup.h
@@ -151,9 +151,6 @@ public:
   ///
   /// \param HS The header search instance to search with.
   ///
-  /// \param IncludeLoc the source location of the #include or #import
-  /// directive.
-  ///
   /// \param SearchPath If not NULL, will be set to the search path relative
   /// to which the file was found.
   ///
@@ -175,7 +172,6 @@ public:
   /// a framework include ("Foo.h" -> "Foo/Foo.h"), set the new name to this
   /// vector and point Filename to it.
   const FileEntry *LookupFile(StringRef &Filename, HeaderSearch &HS,
-                              SourceLocation IncludeLoc,
                               SmallVectorImpl<char> *SearchPath,
                               SmallVectorImpl<char> *RelativePath,
                               Module *RequestingModule,
diff --git a/clang/include/clang/Lex/HeaderSearch.h b/clang/include/clang/Lex/HeaderSearch.h
index 7bac01ef3a4c..152258af1669 100644
--- a/clang/include/clang/Lex/HeaderSearch.h
+++ b/clang/include/clang/Lex/HeaderSearch.h
@@ -580,9 +580,8 @@ private:
   /// \brief Look up the file with the specified name and determine its owning
   /// module.
   const FileEntry *
-  getFileAndSuggestModule(StringRef FileName, SourceLocation IncludeLoc,
-                          const DirectoryEntry *Dir, bool IsSystemHeaderDir,
-                          Module *RequestingModule,
+  getFileAndSuggestModule(StringRef FileName, const DirectoryEntry *Dir,
+                          bool IsSystemHeaderDir, Module *RequestingModule,
                           ModuleMap::KnownHeader *SuggestedModule);
 
 public:
diff --git a/clang/lib/Basic/FileManager.cpp b/clang/lib/Basic/FileManager.cpp
index f9fa23389923..c4cc8dc5419d 100644
--- a/clang/lib/Basic/FileManager.cpp
+++ b/clang/lib/Basic/FileManager.cpp
@@ -312,9 +312,6 @@ const FileEntry *FileManager::getFile(StringRef Filename, bool openFile,
   UFE.InPCH = Data.InPCH;
   UFE.File = std::move(F);
   UFE.IsValid = true;
-  if (UFE.File)
-    if (auto RealPathName = UFE.File->getName())
-      UFE.RealPathName = RealPathName->str();
   return &UFE;
 }
 
diff --git a/clang/lib/Basic/VirtualFileSystem.cpp b/clang/lib/Basic/VirtualFileSystem.cpp
index 120d7e0d9e05..d64c4e3d8c06 100644
--- a/clang/lib/Basic/VirtualFileSystem.cpp
+++ b/clang/lib/Basic/VirtualFileSystem.cpp
@@ -140,19 +140,16 @@ namespace {
 class RealFile : public File {
   int FD;
   Status S;
-  std::string RealName;
   friend class RealFileSystem;
-  RealFile(int FD, StringRef NewName, StringRef NewRealPathName)
+  RealFile(int FD, StringRef NewName)
       : FD(FD), S(NewName, {}, {}, {}, {}, {},
-                  llvm::sys::fs::file_type::status_error, {}),
-        RealName(NewRealPathName.str()) {
+                  llvm::sys::fs::file_type::status_error, {}) {
     assert(FD >= 0 && "Invalid or inactive file descriptor");
   }
 
 public:
   ~RealFile() override;
   ErrorOr<Status> status() override;
-  ErrorOr<StringRef> getName() override;
   ErrorOr<std::unique_ptr<MemoryBuffer>> getBuffer(const Twine &Name,
                                                    int64_t FileSize,
                                                    bool RequiresNullTerminator,
@@ -173,10 +170,6 @@ ErrorOr<Status> RealFile::status() {
   return S;
 }
 
-ErrorOr<StringRef> RealFile::getName() {
-  return RealName.empty() ? S.getName() : StringRef(RealName);
-}
-
 ErrorOr<std::unique_ptr<MemoryBuffer>>
 RealFile::getBuffer(const Twine &Name, int64_t FileSize,
                     bool RequiresNullTerminator, bool IsVolatile) {
@@ -214,10 +207,9 @@ ErrorOr<Status> RealFileSystem::status(const Twine &Path) {
 ErrorOr<std::unique_ptr<File>>
 RealFileSystem::openFileForRead(const Twine &Name) {
   int FD;
-  SmallString<256> RealName;
-  if (std::error_code EC = sys::fs::openFileForRead(Name, FD, &RealName))
+  if (std::error_code EC = sys::fs::openFileForRead(Name, FD))
     return EC;
-  return std::unique_ptr<File>(new RealFile(FD, Name.str(), RealName.str()));
+  return std::unique_ptr<File>(new RealFile(FD, Name.str()));
 }
 
 llvm::ErrorOr<std::string> RealFileSystem::getCurrentWorkingDirectory() const {
diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index e5cc30e41c57..f7fc0b0f65fc 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -250,9 +250,8 @@ const char *DirectoryLookup::getName() const {
 }
 
 const FileEntry *HeaderSearch::getFileAndSuggestModule(
-    StringRef FileName, SourceLocation IncludeLoc, const DirectoryEntry *Dir,
-    bool IsSystemHeaderDir, Module *RequestingModule,
-    ModuleMap::KnownHeader *SuggestedModule) {
+    StringRef FileName, const DirectoryEntry *Dir, bool IsSystemHeaderDir,
+    Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule) {
   // If we have a module map that might map this header, load it and
   // check whether we'll have a suggestion for a module.
   const FileEntry *File = getFileMgr().getFile(FileName, /*OpenFile=*/true);
@@ -273,7 +272,6 @@ const FileEntry *HeaderSearch::getFileAndSuggestModule(
 const FileEntry *DirectoryLookup::LookupFile(
     StringRef &Filename,
     HeaderSearch &HS,
-    SourceLocation IncludeLoc,
     SmallVectorImpl<char> *SearchPath,
     SmallVectorImpl<char> *RelativePath,
     Module *RequestingModule,
@@ -299,7 +297,7 @@ const FileEntry *DirectoryLookup::LookupFile(
       RelativePath->append(Filename.begin(), Filename.end());
     }
 
-    return HS.getFileAndSuggestModule(TmpDir, IncludeLoc, getDir(),
+    return HS.getFileAndSuggestModule(TmpDir, getDir(),
                                       isSystemHeaderDirectory(),
                                       RequestingModule, SuggestedModule);
   }
@@ -587,7 +585,7 @@ const FileEntry *HeaderSearch::LookupFile(
       RelativePath->append(Filename.begin(), Filename.end());
     }
     // Otherwise, just return the file.
-    return getFileAndSuggestModule(Filename, IncludeLoc, nullptr,
+    return getFileAndSuggestModule(Filename, nullptr,
                                    /*IsSystemHeaderDir*/false,
                                    RequestingModule, SuggestedModule);
   }
@@ -624,7 +622,7 @@ const FileEntry *HeaderSearch::LookupFile(
           Includer ? getFileInfo(Includer).DirInfo != SrcMgr::C_User :
           BuildSystemModule;
       if (const FileEntry *FE = getFileAndSuggestModule(
-              TmpDir, IncludeLoc, IncluderAndDir.second, IncluderIsSystemHeader,
+              TmpDir, IncluderAndDir.second, IncluderIsSystemHeader,
               RequestingModule, SuggestedModule)) {
         if (!Includer) {
           assert(First && "only first includer can have no file");
@@ -715,7 +713,7 @@ const FileEntry *HeaderSearch::LookupFile(
     bool InUserSpecifiedSystemFramework = false;
     bool HasBeenMapped = false;
     const FileEntry *FE = SearchDirs[i].LookupFile(
-        Filename, *this, IncludeLoc, SearchPath, RelativePath, RequestingModule,
+        Filename, *this, SearchPath, RelativePath, RequestingModule,
         SuggestedModule, InUserSpecifiedSystemFramework, HasBeenMapped,
         MappedName);
     if (HasBeenMapped) {
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index dccb588cb2a5..34adf7fac29a 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -24,9 +24,6 @@
 #include "clang/Lex/ModuleLoader.h"
 #include "clang/Lex/Pragma.h"
 #include "llvm/ADT/APInt.h"
-#include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/StringExtras.h"
-#include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/SaveAndRestore.h"
@@ -1559,41 +1556,6 @@ static void diagnoseAutoModuleImport(
                                       ("@import " + PathString + ";").str());
 }
 
-namespace {
-  // Given a vector of path components and a string containing the real
-  // path to the file, build a properly-cased replacement in the vector,
-  // and return true if the replacement should be suggested.
-  bool TrySimplifyPath(SmallVectorImpl<StringRef> &Components,
-                       StringRef RealPathName) {
-    auto RealPathComponentIter = llvm::sys::path::rbegin(RealPathName);
-    auto RealPathComponentEnd = llvm::sys::path::rend(RealPathName);
-    int Cnt = 0;
-    bool SuggestReplacement = false;
-    // Below is a best-effort to handle ".." in paths. It is admittedly
-    // not 100% correct in the presence of symlinks.
-    for(auto &Component : llvm::reverse(Components)) {
-      if ("." == Component) {
-      } else if (".." == Component) {
-        ++Cnt;
-      } else if (Cnt) {
-        --Cnt;
-      } else if (RealPathComponentIter != RealPathComponentEnd) {
-        if (Component != *RealPathComponentIter) {
-          // If these path components differ by more than just case, then we
-          // may be looking at symlinked paths. Bail on this diagnostic to avoid
-          // noisy false positives.
-          SuggestReplacement = RealPathComponentIter->equals_lower(Component);
-          if (!SuggestReplacement)
-            break;
-          Component = *RealPathComponentIter;
-        }
-        ++RealPathComponentIter;
-      }
-    }
-    return SuggestReplacement;
-  }
-}
-
 /// HandleIncludeDirective - The "\#include" tokens have just been read, read
 /// the file to be included from the lexer, then include it!  This is a common
 /// routine with functionality shared between \#include, \#include_next and
@@ -1758,35 +1720,6 @@ void Preprocessor::HandleIncludeDirective(SourceLocation HashLoc,
     }
   }
 
-  // Issue a diagnostic if the name of the file on disk has a different case
-  // than the one we're about to open.
-  const bool CheckIncludePathPortability =
-    File && !File->tryGetRealPathName().empty();
-
-  if (CheckIncludePathPortability) {
-    StringRef Name = LangOpts.MSVCCompat ? NormalizedPath.c_str() : Filename;
-    StringRef RealPathName = File->tryGetRealPathName();
-    SmallVector<StringRef, 16> Components(llvm::sys::path::begin(Name),
-                                          llvm::sys::path::end(Name));
-
-    if (TrySimplifyPath(Components, RealPathName)) {
-      SmallString<128> Path;
-      Path.reserve(Name.size()+2);
-      Path.push_back(isAngled ? '<' : '"');
-      for (auto Component : Components) {
-        Path.append(Component);
-        // Append the separator the user used, or the close quote
-        Path.push_back(
-          Path.size() <= Filename.size() ? Filename[Path.size()-1] :
-            (isAngled ? '>' : '"'));
-      }
-      auto Replacement = Path.str().str();
-      SourceRange Range(FilenameTok.getLocation(), CharEnd);
-      Diag(FilenameTok, diag::pp_nonportable_path) << Replacement <<
-        FixItHint::CreateReplacement(Range, Replacement);
-    }
-  }
-
   // Should we enter the source file? Set to false if either the source file is
   // known to have no effect beyond its effect on module visibility -- that is,
   // if it's got an include guard that is already defined or is a modular header
diff --git a/clang/test/Lexer/Inputs/case-insensitive-include.h b/clang/test/Lexer/Inputs/case-insensitive-include.h
deleted file mode 100644
index 60bdf36dbb7f..000000000000
--- a/clang/test/Lexer/Inputs/case-insensitive-include.h
+++ /dev/null
@@ -1,5 +0,0 @@
-#pragma once
-
-struct S {
-  int x;
-};
diff --git a/clang/test/Lexer/case-insensitive-include-ms.c b/clang/test/Lexer/case-insensitive-include-ms.c
deleted file mode 100644
index 86bd8bba68eb..000000000000
--- a/clang/test/Lexer/case-insensitive-include-ms.c
+++ /dev/null
@@ -1,18 +0,0 @@
-// REQUIRES: case-insensitive-filesystem
-
-// RUN: mkdir -p %T/apath
-// RUN: cp %S/Inputs/case-insensitive-include.h %T
-// RUN: cd %T
-// RUN: %clang_cc1 -fsyntax-only -fms-compatibility %s -include %s -I %T -verify
-// RUN: %clang_cc1 -fsyntax-only -fms-compatibility -fdiagnostics-parseable-fixits %s -include %s -I %T 2>&1 | FileCheck %s
-
-#include "..\Output\.\case-insensitive-include.h"
-#include "..\Output\.\Case-Insensitive-Include.h" // expected-warning {{non-portable path}}
-// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:10-[[@LINE-1]]:50}:"\"..\\Output\\.\\case-insensitive-include.h\""
-#include "..\output\.\case-insensitive-include.h" // expected-warning {{non-portable path}}
-// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:10-[[@LINE-1]]:50}:"\"..\\Output\\.\\case-insensitive-include.h\""
-
-#include "apath\..\.\case-insensitive-include.h"
-#include "apath\..\.\Case-Insensitive-Include.h" // expected-warning {{non-portable path}}
-// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:10-[[@LINE-1]]:49}:"\"apath\\..\\.\\case-insensitive-include.h\""
-#include "APath\..\.\case-insensitive-include.h" // For the sake of efficiency, this case is not diagnosed. :-(
diff --git a/clang/test/Lexer/case-insensitive-include.c b/clang/test/Lexer/case-insensitive-include.c
deleted file mode 100644
index d25ff025a823..000000000000
--- a/clang/test/Lexer/case-insensitive-include.c
+++ /dev/null
@@ -1,27 +0,0 @@
-// REQUIRES: case-insensitive-filesystem
-
-// RUN: mkdir -p %T/apath
-// RUN: cp %S/Inputs/case-insensitive-include.h %T
-// RUN: cd %T
-// RUN: %clang_cc1 -fsyntax-only %s -include %s -I %T -verify
-// RUN: %clang_cc1 -fsyntax-only -fdiagnostics-parseable-fixits %s -include %s -I %T 2>&1 | FileCheck %s
-
-#include "case-insensitive-include.h"
-#include "Case-Insensitive-Include.h" // expected-warning {{non-portable path}}
-// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:10-[[@LINE-1]]:38}:"\"case-insensitive-include.h\""
-
-#include "../Output/./case-insensitive-include.h"
-#include "../Output/./Case-Insensitive-Include.h" // expected-warning {{non-portable path}}
-// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:10-[[@LINE-1]]:50}:"\"../Output/./case-insensitive-include.h\""
-#include "../output/./case-insensitive-include.h" // expected-warning {{non-portable path}}
-// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:10-[[@LINE-1]]:50}:"\"../Output/./case-insensitive-include.h\""
-
-#include "apath/.././case-insensitive-include.h"
-#include "apath/.././Case-Insensitive-Include.h" // expected-warning {{non-portable path}}
-// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:10-[[@LINE-1]]:49}:"\"apath/.././case-insensitive-include.h\""
-#include "APath/.././case-insensitive-include.h" // For the sake of efficiency, this case is not diagnosed. :-(
-
-#include "../Output/./apath/.././case-insensitive-include.h"
-#include "../Output/./APath/.././case-insensitive-include.h" // For the sake of efficiency, this case is not diagnosed. :-(
-#include "../output/./apath/.././case-insensitive-include.h" // expected-warning {{non-portable path}}
-// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:10-[[@LINE-1]]:61}:"\"../Output/./apath/.././case-insensitive-include.h\""
diff --git a/clang/test/PCH/case-insensitive-include.c b/clang/test/PCH/case-insensitive-include.c
index 1dcda273c2f2..707de702f15d 100644
--- a/clang/test/PCH/case-insensitive-include.c
+++ b/clang/test/PCH/case-insensitive-include.c
@@ -2,7 +2,7 @@
 
 // Test this without pch.
 // RUN: cp %S/Inputs/case-insensitive-include.h %T
-// RUN: %clang_cc1 -Wno-nonportable-include-path -fsyntax-only %s -include %s -I %T -verify
+// RUN: %clang_cc1 -fsyntax-only %s -include %s -I %T -verify
 
 // Test with pch.
 // RUN: %clang_cc1 -emit-pch -o %t.pch %s -I %T