[Driver] Removal of C_INCLUDE_DIRS feature

[brad]

Summary

Removing the C_INCLUDE_DIRS feature.

Fix https://github.com/llvm/llvm-project/issues/61328

[MaskRay]

Technically there is some risk but I think the blast radius, if present, is extremely small.

C_INCLUDE_DIRS is not recognized by GCC.

If I use https://sourcegraph.com/search?q=context:global+%5CbC_INCLUDE_DIRS%3D+-f:clang/&patternType=regexp&case=yes&sm=1&groupBy=repo to find the use cases, one project has a use like add_opt C_INCLUDE_DIRS=$C_INCLUDES, but the search patch seems likely redundant.

[brad]

Just FYI I am not in a rush to commit this. I am posting this more so as a means of prodding for discussion of the feature.

[probinson]

In D159054#4626772, @brad wrote:

Just FYI I am not in a rush to commit this. I am posting this more so as a means of prodding for discussion of the feature.

So far nobody has popped up to say they want it.

@MaskRay I poked around a bit on sourcegraph.com and didn't see any statement about what it actually searches, other than vague "all your repositories" and "all your code." The "your" bit makes me wonder how broad it is really. The website doesn't say.

[MaskRay]

In D159054#4628278, @probinson wrote:

In D159054#4626772, @brad wrote:

Just FYI I am not in a rush to commit this. I am posting this more so as a means of prodding for discussion of the feature.

So far nobody has popped up to say they want it.

@MaskRay I poked around a bit on sourcegraph.com and didn't see any statement about what it actually searches, other than vague "all your repositories" and "all your code." The "your" bit makes me wonder how broad it is really. The website doesn't say.

They index quite a lot: https://about.sourcegraph.com/blog/indexing-the-oss-universe-update-more-code-hosts

I also tried using my company's internal code search and I cannot find environment variables using C_INCLUDE_DIRS.

[brad]

I was going to hold this over for a bit longer. 2 weeks and if no one says anything then go ahead?

[probinson]

@MaskRay thanks for the info!

In D159054#4638322, @brad wrote:

I was going to hold this over for a bit longer. 2 weeks and if no one says anything then go ahead?

The main thing to worry about, clearly, is what happens as the change percolates downstream and into distros. But you probably know more about that than I do anyhow. :)

[brad]

In D159054#4638511, @probinson wrote:

The main thing to worry about, clearly, is what happens as the change percolates downstream and into distros. But you probably know more about that than I do anyhow. :)

Yes, that is why I am a bit hesitant; as I know people are not always paying attention to mailing lists and maybe even notice something like this, even if in use. The kinds of changes
that even if they were sitting around for 6 month still come as a surprise.

clang/CMakeLists.txt

 endif()
 
 include(CheckIncludeFile)
 check_include_file(sys/resource.h CLANG_HAVE_RLIMITS)
 
 set(CLANG_RESOURCE_DIR "" CACHE STRING
   "Relative directory from the Clang binary to its resource files.")
 
-set(C_INCLUDE_DIRS "" CACHE STRING
-  "Colon separated list of directories clang will search for headers.")
-
 set(GCC_INSTALL_PREFIX "" CACHE PATH "Directory where gcc is installed." )
 set(DEFAULT_SYSROOT "" CACHE STRING
   "Default <path> to all compiler invocations for --sysroot=<path>." )
 
 set(ENABLE_LINKER_BUILD_ID OFF CACHE BOOL "pass --build-id to ld")
 
 set(ENABLE_X86_RELAX_RELOCATIONS ON CACHE BOOL
     "enable x86 relax relocations by default")

clang/include/clang/Config/config.h.cmake

 #define CLANG_SYSTEMZ_DEFAULT_ARCH "${CLANG_SYSTEMZ_DEFAULT_ARCH}"
 
 /* Multilib basename for libdir. */
 #define CLANG_INSTALL_LIBDIR_BASENAME "${CLANG_INSTALL_LIBDIR_BASENAME}"
 
 /* Relative directory for resource files */
 #define CLANG_RESOURCE_DIR "${CLANG_RESOURCE_DIR}"
 
-/* Directories clang will search for headers */
-#define C_INCLUDE_DIRS "${C_INCLUDE_DIRS}"
-
 /* Directories clang will search for configuration files */
 #cmakedefine CLANG_CONFIG_FILE_SYSTEM_DIR "${CLANG_CONFIG_FILE_SYSTEM_DIR}"
 #cmakedefine CLANG_CONFIG_FILE_USER_DIR "${CLANG_CONFIG_FILE_USER_DIR}"
 
 /* Default <path> to all compiler invocations for --sysroot=<path>. */
 #define DEFAULT_SYSROOT "${DEFAULT_SYSROOT}"
 
 /* Directory where gcc is installed. */

clang/lib/Driver/ToolChains/Darwin.cpp

 //===--- Darwin.cpp - Darwin Tool and ToolChain Implementations -*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Darwin.h"
 #include "Arch/AArch64.h"
 #include "Arch/ARM.h"
 #include "CommonArgs.h"
 #include "clang/Basic/AlignedAllocation.h"
 #include "clang/Basic/ObjCRuntime.h"
-#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/ProfileData/InstrProf.h"

     SmallString<128> P(D.ResourceDir);
     llvm::sys::path::append(P, "include");
     addSystemInclude(DriverArgs, CC1Args, P);
   }
 
   if (NoStdInc || NoStdlibInc)
     return;
 
-  // Check for configure-time C include directories.
-  llvm::StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (!CIncludeDirs.empty()) {
-    llvm::SmallVector<llvm::StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (llvm::StringRef dir : dirs) {
-      llvm::StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : llvm::StringRef(Sysroot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-  } else {
-    // Otherwise, add <sysroot>/usr/include.
-    SmallString<128> P(Sysroot);
-    llvm::sys::path::append(P, "usr", "include");
-    addExternCSystemInclude(DriverArgs, CC1Args, P.str());
-  }
+  // Add <sysroot>/usr/include.
+  SmallString<128> P(Sysroot);
+  llvm::sys::path::append(P, "usr", "include");
+  addExternCSystemInclude(DriverArgs, CC1Args, P.str());
 }
 
 bool DarwinClang::AddGnuCPlusPlusIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                               llvm::opt::ArgStringList &CC1Args,
                                               llvm::SmallString<128> Base,
                                               llvm::StringRef Version,
                                               llvm::StringRef ArchDir,
                                               llvm::StringRef BitDir) const {

clang/lib/Driver/ToolChains/FreeBSD.cpp

 //===--- FreeBSD.cpp - FreeBSD ToolChain Implementations --------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "FreeBSD.h"
 #include "Arch/ARM.h"
 #include "Arch/Mips.h"
 #include "Arch/Sparc.h"
 #include "CommonArgs.h"
-#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
 using namespace clang::driver;
if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> Dir(D.ResourceDir);
     llvm::sys::path::append(Dir, "include");
     addSystemInclude(DriverArgs, CC1Args, Dir.str());
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  // Check for configure-time C include directories.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? StringRef(D.SysRoot) : "";
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-    return;
-  }
-
   addExternCSystemInclude(DriverArgs, CC1Args,
                           concat(D.SysRoot, "/usr/include"));
 }
 
 void FreeBSD::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                     llvm::opt::ArgStringList &CC1Args) const {
   addSystemInclude(DriverArgs, CC1Args,
                    concat(getDriver().SysRoot, "/usr/include/c++/v1"));

clang/lib/Driver/ToolChains/Fuchsia.cpp

 //===--- Fuchsia.cpp - Fuchsia ToolChain Implementations --------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Fuchsia.h"
 #include "CommonArgs.h"
-#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/MultilibBuilder.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/ProfileData/InstrProf.h"
if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> P(D.ResourceDir);
     llvm::sys::path::append(P, "include");
     addSystemInclude(DriverArgs, CC1Args, P);
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  // Check for configure-time C include directories.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : StringRef(D.SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-    return;
-  }
-
   if (!D.SysRoot.empty()) {
     SmallString<128> P(D.SysRoot);
     llvm::sys::path::append(P, "include");
     addExternCSystemInclude(DriverArgs, CC1Args, P.str());
   }
 }
 
 void Fuchsia::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,

clang/lib/Driver/ToolChains/Haiku.cpp

 //===--- Haiku.cpp - Haiku ToolChain Implementations ------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Haiku.h"
 #include "CommonArgs.h"
-#include "clang/Config/config.h"
 #include "llvm/Support/Path.h"
 
 using namespace clang::driver;
 using namespace clang::driver::toolchains;
 using namespace clang;
 using namespace llvm::opt;
 
 /// Haiku - Haiku tool chain which can call as(1) and ld(1) directly.
if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> Dir(D.ResourceDir);
     llvm::sys::path::append(Dir, "include");
     addSystemInclude(DriverArgs, CC1Args, Dir.str());
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  // Add dirs specified via 'configure --with-c-include-dirs'.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (!CIncludeDirs.empty()) {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs) {
-      StringRef Prefix =
-        llvm::sys::path::is_absolute(dir) ? StringRef(D.SysRoot) : "";
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-    return;
-  }
-
   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/boot/system/non-packaged/develop/headers");
   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/boot/system/develop/headers/os");
   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/boot/system/develop/headers/os/app");
   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/boot/system/develop/headers/os/device");
   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/boot/system/develop/headers/os/drivers");
   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/boot/system/develop/headers/os/game");
   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/boot/system/develop/headers/os/interface");
   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/boot/system/develop/headers/os/kernel");

clang/lib/Driver/ToolChains/Hurd.cpp

if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> P(D.ResourceDir);
     llvm::sys::path::append(P, "include");
     addSystemInclude(DriverArgs, CC1Args, P);
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  // Check for configure-time C include directories.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> Dirs;
-    CIncludeDirs.split(Dirs, ":");
-    for (StringRef Dir : Dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(Dir) ? "" : StringRef(SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + Dir);
-    }
-    return;
-  }
-
-  // Lacking those, try to detect the correct set of system includes for the
-  // target triple.
-
+  // Try to detect the correct set of system includes for the target triple.
   AddMultilibIncludeArgs(DriverArgs, CC1Args);
 
   // On systems using multiarch, add /usr/include/$triple before
   // /usr/include.
   std::string MultiarchIncludeDir = getMultiarchTriple(D, getTriple(), SysRoot);
   if (!MultiarchIncludeDir.empty() &&
       D.getVFS().exists(SysRoot + "/usr/include/" + MultiarchIncludeDir))
     addExternCSystemInclude(DriverArgs, CC1Args,

clang/lib/Driver/ToolChains/Linux.cpp

 //===--- Linux.h - Linux ToolChain Implementations --------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Linux.h"
 #include "Arch/ARM.h"
 #include "Arch/LoongArch.h"
 #include "Arch/Mips.h"
 #include "Arch/PPC.h"
 #include "Arch/RISCV.h"
 #include "CommonArgs.h"
-#include "clang/Config/config.h"
+#include "clang/Config/config.h" // CLANG_DEFAULT_PIE_ON_LINUX
 #include "clang/Driver/Distro.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/ScopedPrinter.h"

   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
   // LOCAL_INCLUDE_DIR
   addSystemInclude(DriverArgs, CC1Args, concat(SysRoot, "/usr/local/include"));
   // TOOL_INCLUDE_DIR
   AddMultilibIncludeArgs(DriverArgs, CC1Args);
 
-  // Check for configure-time C include directories.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : StringRef(SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-    return;
-  }
-
   // On systems using multiarch and Android, add /usr/include/$triple before
   // /usr/include.
   std::string MultiarchIncludeDir = getMultiarchTriple(D, getTriple(), SysRoot);
   if (!MultiarchIncludeDir.empty() &&
       D.getVFS().exists(concat(SysRoot, "/usr/include", MultiarchIncludeDir)))
     addExternCSystemInclude(
         DriverArgs, CC1Args,
         concat(SysRoot, "/usr/include", MultiarchIncludeDir));

clang/lib/Driver/ToolChains/NetBSD.cpp

 //===--- NetBSD.cpp - NetBSD ToolChain Implementations ----------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "NetBSD.h"
 #include "Arch/ARM.h"
 #include "Arch/Mips.h"
 #include "Arch/Sparc.h"
 #include "CommonArgs.h"
-#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
 using namespace clang::driver;

     SmallString<128> Dir(D.ResourceDir);
     llvm::sys::path::append(Dir, "include");
     addSystemInclude(DriverArgs, CC1Args, Dir.str());
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  // Check for configure-time C include directories.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? StringRef(D.SysRoot) : "";
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-    return;
-  }
-
   addExternCSystemInclude(DriverArgs, CC1Args,
                           concat(D.SysRoot, "/usr/include"));
 }
 
 void NetBSD::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                    llvm::opt::ArgStringList &CC1Args) const {
   const std::string Candidates[] = {
     // directory relative to build tree

clang/lib/Driver/ToolChains/OHOS.cpp

 //===--- OHOS.cpp - OHOS ToolChain Implementations --------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "OHOS.h"
 #include "Arch/ARM.h"
 #include "CommonArgs.h"
-#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/FileSystem.h"
if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> P(D.ResourceDir);
     llvm::sys::path::append(P, "include");
     addSystemInclude(DriverArgs, CC1Args, P);
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  // Check for configure-time C include directories.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? StringRef(SysRoot) : "";
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-    return;
-  }
-
   addExternCSystemInclude(DriverArgs, CC1Args,
                           SysRoot + "/usr/include/" +
                               getMultiarchTriple(Triple));
   addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/include");
   addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/include");
 }
 
 void OHOS::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,

clang/lib/Driver/ToolChains/OpenBSD.cpp

 //===--- OpenBSD.cpp - OpenBSD ToolChain Implementations --------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "OpenBSD.h"
 #include "Arch/ARM.h"
 #include "Arch/Mips.h"
 #include "Arch/Sparc.h"
 #include "CommonArgs.h"
-#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
 using namespace clang::driver;
if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> Dir(D.ResourceDir);
     llvm::sys::path::append(Dir, "include");
     addSystemInclude(DriverArgs, CC1Args, Dir.str());
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  // Check for configure-time C include directories.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? StringRef(D.SysRoot) : "";
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-    return;
-  }
-
   addExternCSystemInclude(DriverArgs, CC1Args,
                           concat(D.SysRoot, "/usr/include"));
 }
 
 void OpenBSD::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                     llvm::opt::ArgStringList &CC1Args) const {
   addSystemInclude(DriverArgs, CC1Args,
                    concat(getDriver().SysRoot, "/usr/include/c++/v1"));

clang/lib/Driver/ToolChains/Solaris.cpp

 //===--- Solaris.cpp - Solaris ToolChain Implementations --------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Solaris.h"
 #include "CommonArgs.h"
 #include "clang/Basic/LangStandard.h"
-#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "clang/Driver/ToolChain.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/FileSystem.h"
if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> P(D.ResourceDir);
     llvm::sys::path::append(P, "include");
     addSystemInclude(DriverArgs, CC1Args, P);
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  // Check for configure-time C include directories.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : StringRef(D.SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-    return;
-  }
-
   // Add include directories specific to the selected multilib set and multilib.
   if (GCCInstallation.isValid()) {
     const MultilibSet::IncludeDirsFunc &Callback =
         Multilibs.includeDirsCallback();
     if (Callback) {
       for (const auto &Path : Callback(GCCInstallation.getMultilib()))
         addExternCSystemIncludeIfExists(
             DriverArgs, CC1Args, GCCInstallation.getInstallPath() + Path);

clang/lib/Driver/ToolChains/WebAssembly.cpp

 //===--- WebAssembly.cpp - WebAssembly ToolChain Implementation -*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "WebAssembly.h"
 #include "CommonArgs.h"
 #include "Gnu.h"
 #include "clang/Basic/Version.h"
-#include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/VirtualFileSystem.h"

     SmallString<128> P(D.ResourceDir);
     llvm::sys::path::append(P, "include");
     addSystemInclude(DriverArgs, CC1Args, P);
   }
 
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
-  // Check for configure-time C include directories.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs) {
-      StringRef Prefix =
-          llvm::sys::path::is_absolute(dir) ? "" : StringRef(D.SysRoot);
-      addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
-    }
-    return;
-  }
-
   if (getTriple().getOS() != llvm::Triple::UnknownOS) {
     const std::string MultiarchTriple =
         getMultiarchTriple(D, getTriple(), D.SysRoot);
     addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include/" + MultiarchTriple);
   }
   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include");
 }
 

clang/lib/Lex/InitHeaderSearch.cpp

 //===--- InitHeaderSearch.cpp - Initialize header search paths ------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the InitHeaderSearch class.
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/Basic/DiagnosticFrontend.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/LangOptions.h"
-#include "clang/Config/config.h" // C_INCLUDE_DIRS
 #include "clang/Lex/HeaderMap.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/HeaderSearchOptions.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Twine.h"
if (HSOpts.UseBuiltinIncludes) {
     AddUnmappedPath(P, ExternCSystem, false);
   }
 
   // All remaining additions are for system include directories, early exit if
   // we aren't using them.
   if (!HSOpts.UseStandardSystemIncludes)
     return;
 
-  // Add dirs specified via 'configure --with-c-include-dirs'.
-  StringRef CIncludeDirs(C_INCLUDE_DIRS);
-  if (CIncludeDirs != "") {
-    SmallVector<StringRef, 5> dirs;
-    CIncludeDirs.split(dirs, ":");
-    for (StringRef dir : dirs)
-      AddPath(dir, ExternCSystem, false);
-    return;
-  }
-
   switch (os) {
   case llvm::Triple::Win32:
     switch (triple.getEnvironment()) {
     default: llvm_unreachable("Include management is handled in the driver.");
     case llvm::Triple::Cygnus:
       AddPath("/usr/include/w32api", System, false);
       break;
     case llvm::Triple::GNU: