Merge clang, llvm, lld, lldb, compiler-rt and libc++ 5.0.0 release.

MFC r309126 (by emaste):

  Correct lld llvm-tblgen dependency file name

MFC r309169:

  Get rid of separate Subversion mergeinfo properties for llvm-dwarfdump
  and llvm-lto.  The mergeinfo confuses Subversion enormously, and these
  directories will just use the mergeinfo for llvm itself.

MFC r312765:

  Pull in r276136 from upstream llvm trunk (by Wei Mi):

    Use ValueOffsetPair to enhance value reuse during SCEV expansion.

    In D12090, the ExprValueMap was added to reuse existing value during
    SCEV expansion. However, const folding and sext/zext distribution can
    make the reuse still difficult.

    A simplified case is: suppose we know S1 expands to V1 in
    ExprValueMap, and
      S1 = S2 + C_a
      S3 = S2 + C_b
    where C_a and C_b are different SCEVConstants. Then we'd like to
    expand S3 as V1 - C_a + C_b instead of expanding S2 literally. It is
    helpful when S2 is a complex SCEV expr and S2 has no entry in
    ExprValueMap, which is usually caused by the fact that S3 is
    generated from S1 after const folding.

    In order to do that, we represent ExprValueMap as a mapping from SCEV
    to ValueOffsetPair. We will save both S1->{V1, 0} and S2->{V1, C_a}
    into the ExprValueMap when we create SCEV for V1. When S3 is
    expanded, it will first expand S2 to V1 - C_a because of S2->{V1,
    C_a} in the map, then expand S3 to V1 - C_a + C_b.

    Differential Revision: https://reviews.llvm.org/D21313

  This should fix assertion failures when building OpenCV >= 3.1.

  PR:		215649

MFC r312831:

  Revert r312765 for now, since it causes assertions when building
  lang/spidermonkey24.

  Reported by:	antoine
  PR:		215649

MFC r316511 (by jhb):

  Add an implementation of __ffssi2() derived from __ffsdi2().

  Newer versions of GCC include an __ffssi2() symbol in libgcc and the
  compiler can emit calls to it in generated code.  This is true for at
  least GCC 6.2 when compiling world for mips and mips64.

  Reviewed by:	jmallett, dim
  Sponsored by:	DARPA / AFRL
  Differential Revision:	https://reviews.freebsd.org/D10086

MFC r318601 (by adrian):

  [libcompiler-rt] add bswapdi2/bswapsi2

  This is required for mips gcc 6.3 userland to build/run.

  Reviewed by:	emaste, dim
  Approved by:	emaste
  Differential Revision:	https://reviews.freebsd.org/D10838

MFC r318884 (by emaste):

  lldb: map TRAP_CAP to a trace trap

  In the absense of a more specific handler for TRAP_CAP (generated by
  ENOTCAPABLE or ECAPMODE while in capability mode) treat it as a trace
  trap.

  Example usage (testing the bug in PR219173):

  % proccontrol -m trapcap lldb usr.bin/hexdump/obj/hexdump -- -Cv -s 1 /bin/ls
  ...
  (lldb) run
  Process 12980 launching
  Process 12980 launched: '.../usr.bin/hexdump/obj/hexdump' (x86_64)
  Process 12980 stopped
  * thread #1, stop reason = trace
      frame #0: 0x0000004b80c65f1a libc.so.7`__sys_lseek + 10
  ...

  In the future we should have LLDB control the trapcap procctl itself
  (as it does with ASLR), as well as report a specific stop reason.
  This change eliminates an assertion failure from LLDB for now.

MFC r319796:

  Remove a few unneeded files from libllvm, libclang and liblldb.

MFC r319885 (by emaste):

  lld: ELF: Fix ICF crash on absolute symbol relocations.

  If two sections contained relocations to absolute symbols with the same
  value we would crash when trying to access their sections. Add a check that
  both symbols point to sections before accessing their sections, and treat
  absolute symbols as equal if their values are equal.

  Obtained from:	LLD commit r292578

MFC r319918:

  Revert r319796 for now, it can cause undefined references when linking
  in some circumstances.

  Reported by:	Shawn Webb <shawn.webb@hardenedbsd.org>

MFC r319957 (by emaste):

  lld: Add armelf emulation mode

  Obtained from:	LLD r305375

MFC r321369:

  Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
  5.0.0 (trunk r308421).  Upstream has branched for the 5.0.0 release,
  which should be in about a month.  Please report bugs and regressions,
  so we can get them into the release.

  Please note that from 3.5.0 onwards, clang, llvm and lldb require C++11
  support to build; see UPDATING for more information.

MFC r321420:

  Add a few more object files to liblldb, which should solve errors when
  linking the lldb executable in some cases.  In particular, when the
  -ffunction-sections -fdata-sections options are turned off, or
  ineffective.

  Reported by:	Shawn Webb, Mark Millard

MFC r321433:

  Cleanup stale Options.inc files from the previous libllvm build for
  clang 4.0.0.  Otherwise, these can get included before the two newly
  generated ones (which are different) for clang 5.0.0.

  Reported by:	Mark Millard

MFC r321439 (by bdrewery):

  Move llvm Options.inc hack from r321433 for NO_CLEAN to lib/clang/libllvm.

  The files are only ever generated to .OBJDIR, not to WORLDTMP (as a
  sysroot) and are only ever included from a compilation.  So using
  a beforebuild target here removes the file before the compilation
  tries to include it.

MFC r321664:

  Pull in r308891 from upstream llvm trunk (by Benjamin Kramer):

    [CodeGenPrepare] Cut off FindAllMemoryUses if there are too many uses.

    This avoids excessive compile time. The case I'm looking at is
    Function.cpp from an old version of LLVM that still had the giant
    memcmp string matcher in it. Before r308322 this compiled in about 2
    minutes, after it, clang takes infinite* time to compile it. With
    this patch we're at 5 min, which is still bad but this is a
    pathological case.

    The cut off at 20 uses was chosen by looking at other cut-offs in LLVM
    for user scanning. It's probably too high, but does the job and is
    very unlikely to regress anything.

    Fixes PR33900.

    * I'm impatient and aborted after 15 minutes, on the bug report it was
      killed after 2h.

  Pull in r308986 from upstream llvm trunk (by Simon Pilgrim):

    [X86][CGP] Reduce memcmp() expansion to 2 load pairs (PR33914)

    D35067/rL308322 attempted to support up to 4 load pairs for memcmp
    inlining which resulted in regressions for some optimized libc memcmp
    implementations (PR33914).

    Until we can match these more optimal cases, this patch reduces the
    memcmp expansion to a maximum of 2 load pairs (which matches what we
    do for -Os).

    This patch should be considered for the 5.0.0 release branch as well

    Differential Revision: https://reviews.llvm.org/D35830

  These fix a hang (or extremely long compile time) when building older
  LLVM ports.

  Reported by:    antoine
  PR:             219139

MFC r321719:

  Pull in r309503 from upstream clang trunk (by Richard Smith):

    PR33902: Invalidate line number cache when adding more text to
    existing buffer.

    This led to crashes as the line number cache would report a bogus
    line number for a line of code, and we'd try to find a nonexistent
    column within the line when printing diagnostics.

  This fixes an assertion when building the graphics/champlain port.

  Reported by:	antoine, kwm
  PR:		219139

MFC r321723:

  Upgrade our copies of clang, llvm, lld and lldb to r309439 from the
  upstream release_50 branch.  This is just after upstream's 5.0.0-rc1.

MFC r322320:

  Upgrade our copies of clang, llvm and libc++ to r310316 from the
  upstream release_50 branch.

MFC r322326 (by emaste):

  lldb: Make i386-*-freebsd expression work on JIT path

  * Enable i386 ABI creation for freebsd
  * Added an extra argument in ABISysV_i386::PrepareTrivialCall for mmap
    syscall
  * Unlike linux, the last argument of mmap is actually 64-bit(off_t).
    This requires us to push an additional word for the higher order bits.
  * Prior to this change, ktrace dump will show mmap failures due to
    invalid argument coming from the 6th mmap argument.

  Submitted by:	Karnajit Wangkhem
  Differential Revision:	https://reviews.llvm.org/D34776

MFC r322360 (by emaste):

  lldb: Report inferior signals as signals, not exceptions, on FreeBSD

  This is the FreeBSD equivalent of LLVM r238549.

  This serves 2 purposes:

  * LLDB should handle inferior process signals SIGSEGV/SIGILL/SIGBUS/
    SIGFPE the way it is suppose to be handled. Prior to this fix these
    signals will neither create a coredump, nor exit from the debugger
    or work for signal handling scenario.
  * eInvalidCrashReason need not report "unknown crash reason" if we have
    a valid si_signo

  llvm.org/pr23699

  Patch by Karnajit Wangkhem

  Differential Revision:  https://reviews.llvm.org/D35223

  Submitted by:	Karnajit Wangkhem
  Obtained from:	LLVM r310591

MFC r322474 (by emaste):

  lld: Add `-z muldefs` option.

  Obtained from:	LLVM r310757

MFC r322740:

  Upgrade our copies of clang, llvm, lld and libc++ to r311219 from the
  upstream release_50 branch.

MFC r322855:

  Upgrade our copies of clang, llvm, lldb and compiler-rt to r311606 from
  the upstream release_50 branch.

  As of this version, lib/msun's trig test should also work correctly
  again (see bug 220989 for more information).

  PR:		220989

MFC r323112:

  Upgrade our copies of clang, llvm, lldb and compiler-rt to r312293 from
  the upstream release_50 branch.  This corresponds to 5.0.0 rc4.

  As of this version, the cad/stepcode port should now compile in a more
  reasonable time on i386 (see bug 221836 for more information).

  PR:		221836

MFC r323245:

  Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
  5.0.0 release (upstream r312559).

  Release notes for llvm, clang and lld will be available here soon:
  <http://releases.llvm.org/5.0.0/docs/ReleaseNotes.html>
  <http://releases.llvm.org/5.0.0/tools/clang/docs/ReleaseNotes.html>
  <http://releases.llvm.org/5.0.0/tools/lld/docs/ReleaseNotes.html>

  Relnotes:	yes

(cherry picked from commit 12cd91cf4c6b96a24427c0de5374916f2808d263)

1 files changed, 860 insertions, 0 deletions

diff --git a/contrib/llvm/tools/clang/lib/Driver/ToolChains/Linux.cpp b/contrib/llvm/tools/clang/lib/Driver/ToolChains/Linux.cpp
new file mode 100644
index 0000000..08a27fa
--- /dev/null
+++ b/contrib/llvm/tools/clang/lib/Driver/ToolChains/Linux.cpp
@@ -0,0 +1,860 @@
+//===--- Linux.h - Linux ToolChain Implementations --------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Linux.h"
+#include "Arch/ARM.h"
+#include "Arch/Mips.h"
+#include "Arch/PPC.h"
+#include "CommonArgs.h"
+#include "clang/Basic/VirtualFileSystem.h"
+#include "clang/Config/config.h"
+#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 <system_error>
+
+using namespace clang::driver;
+using namespace clang::driver::toolchains;
+using namespace clang;
+using namespace llvm::opt;
+
+using tools::addPathIfExists;
+
+/// \brief Get our best guess at the multiarch triple for a target.
+///
+/// Debian-based systems are starting to use a multiarch setup where they use
+/// a target-triple directory in the library and header search paths.
+/// Unfortunately, this triple does not align with the vanilla target triple,
+/// so we provide a rough mapping here.
+static std::string getMultiarchTriple(const Driver &D,
+                                      const llvm::Triple &TargetTriple,
+                                      StringRef SysRoot) {
+  llvm::Triple::EnvironmentType TargetEnvironment =
+      TargetTriple.getEnvironment();
+
+  // For most architectures, just use whatever we have rather than trying to be
+  // clever.
+  switch (TargetTriple.getArch()) {
+  default:
+    break;
+
+  // We use the existence of '/lib/<triple>' as a directory to detect some
+  // common linux triples that don't quite match the Clang triple for both
+  // 32-bit and 64-bit targets. Multiarch fixes its install triples to these
+  // regardless of what the actual target triple is.
+  case llvm::Triple::arm:
+  case llvm::Triple::thumb:
+    if (TargetEnvironment == llvm::Triple::GNUEABIHF) {
+      if (D.getVFS().exists(SysRoot + "/lib/arm-linux-gnueabihf"))
+        return "arm-linux-gnueabihf";
+    } else {
+      if (D.getVFS().exists(SysRoot + "/lib/arm-linux-gnueabi"))
+        return "arm-linux-gnueabi";
+    }
+    break;
+  case llvm::Triple::armeb:
+  case llvm::Triple::thumbeb:
+    if (TargetEnvironment == llvm::Triple::GNUEABIHF) {
+      if (D.getVFS().exists(SysRoot + "/lib/armeb-linux-gnueabihf"))
+        return "armeb-linux-gnueabihf";
+    } else {
+      if (D.getVFS().exists(SysRoot + "/lib/armeb-linux-gnueabi"))
+        return "armeb-linux-gnueabi";
+    }
+    break;
+  case llvm::Triple::x86:
+    if (D.getVFS().exists(SysRoot + "/lib/i386-linux-gnu"))
+      return "i386-linux-gnu";
+    break;
+  case llvm::Triple::x86_64:
+    // We don't want this for x32, otherwise it will match x86_64 libs
+    if (TargetEnvironment != llvm::Triple::GNUX32 &&
+        D.getVFS().exists(SysRoot + "/lib/x86_64-linux-gnu"))
+      return "x86_64-linux-gnu";
+    break;
+  case llvm::Triple::aarch64:
+    if (D.getVFS().exists(SysRoot + "/lib/aarch64-linux-gnu"))
+      return "aarch64-linux-gnu";
+    break;
+  case llvm::Triple::aarch64_be:
+    if (D.getVFS().exists(SysRoot + "/lib/aarch64_be-linux-gnu"))
+      return "aarch64_be-linux-gnu";
+    break;
+  case llvm::Triple::mips:
+    if (D.getVFS().exists(SysRoot + "/lib/mips-linux-gnu"))
+      return "mips-linux-gnu";
+    break;
+  case llvm::Triple::mipsel:
+    if (D.getVFS().exists(SysRoot + "/lib/mipsel-linux-gnu"))
+      return "mipsel-linux-gnu";
+    break;
+  case llvm::Triple::mips64:
+    if (D.getVFS().exists(SysRoot + "/lib/mips64-linux-gnu"))
+      return "mips64-linux-gnu";
+    if (D.getVFS().exists(SysRoot + "/lib/mips64-linux-gnuabi64"))
+      return "mips64-linux-gnuabi64";
+    break;
+  case llvm::Triple::mips64el:
+    if (D.getVFS().exists(SysRoot + "/lib/mips64el-linux-gnu"))
+      return "mips64el-linux-gnu";
+    if (D.getVFS().exists(SysRoot + "/lib/mips64el-linux-gnuabi64"))
+      return "mips64el-linux-gnuabi64";
+    break;
+  case llvm::Triple::ppc:
+    if (D.getVFS().exists(SysRoot + "/lib/powerpc-linux-gnuspe"))
+      return "powerpc-linux-gnuspe";
+    if (D.getVFS().exists(SysRoot + "/lib/powerpc-linux-gnu"))
+      return "powerpc-linux-gnu";
+    break;
+  case llvm::Triple::ppc64:
+    if (D.getVFS().exists(SysRoot + "/lib/powerpc64-linux-gnu"))
+      return "powerpc64-linux-gnu";
+    break;
+  case llvm::Triple::ppc64le:
+    if (D.getVFS().exists(SysRoot + "/lib/powerpc64le-linux-gnu"))
+      return "powerpc64le-linux-gnu";
+    break;
+  case llvm::Triple::sparc:
+    if (D.getVFS().exists(SysRoot + "/lib/sparc-linux-gnu"))
+      return "sparc-linux-gnu";
+    break;
+  case llvm::Triple::sparcv9:
+    if (D.getVFS().exists(SysRoot + "/lib/sparc64-linux-gnu"))
+      return "sparc64-linux-gnu";
+    break;
+  case llvm::Triple::systemz:
+    if (D.getVFS().exists(SysRoot + "/lib/s390x-linux-gnu"))
+      return "s390x-linux-gnu";
+    break;
+  }
+  return TargetTriple.str();
+}
+
+static StringRef getOSLibDir(const llvm::Triple &Triple, const ArgList &Args) {
+  if (tools::isMipsArch(Triple.getArch())) {
+    if (Triple.isAndroid()) {
+      StringRef CPUName;
+      StringRef ABIName;
+      tools::mips::getMipsCPUAndABI(Args, Triple, CPUName, ABIName);
+      if (CPUName == "mips32r6")
+        return "libr6";
+      if (CPUName == "mips32r2")
+        return "libr2";
+    }
+    // lib32 directory has a special meaning on MIPS targets.
+    // It contains N32 ABI binaries. Use this folder if produce
+    // code for N32 ABI only.
+    if (tools::mips::hasMipsAbiArg(Args, "n32"))
+      return "lib32";
+    return Triple.isArch32Bit() ? "lib" : "lib64";
+  }
+
+  // It happens that only x86 and PPC use the 'lib32' variant of oslibdir, and
+  // using that variant while targeting other architectures causes problems
+  // because the libraries are laid out in shared system roots that can't cope
+  // with a 'lib32' library search path being considered. So we only enable
+  // them when we know we may need it.
+  //
+  // FIXME: This is a bit of a hack. We should really unify this code for
+  // reasoning about oslibdir spellings with the lib dir spellings in the
+  // GCCInstallationDetector, but that is a more significant refactoring.
+  if (Triple.getArch() == llvm::Triple::x86 ||
+      Triple.getArch() == llvm::Triple::ppc)
+    return "lib32";
+
+  if (Triple.getArch() == llvm::Triple::x86_64 &&
+      Triple.getEnvironment() == llvm::Triple::GNUX32)
+    return "libx32";
+
+  return Triple.isArch32Bit() ? "lib" : "lib64";
+}
+
+static void addMultilibsFilePaths(const Driver &D, const MultilibSet &Multilibs,
+                                  const Multilib &Multilib,
+                                  StringRef InstallPath,
+                                  ToolChain::path_list &Paths) {
+  if (const auto &PathsCallback = Multilibs.filePathsCallback())
+    for (const auto &Path : PathsCallback(Multilib))
+      addPathIfExists(D, InstallPath + Path, Paths);
+}
+
+Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+    : Generic_ELF(D, Triple, Args) {
+  GCCInstallation.init(Triple, Args);
+  Multilibs = GCCInstallation.getMultilibs();
+  llvm::Triple::ArchType Arch = Triple.getArch();
+  std::string SysRoot = computeSysRoot();
+
+  // Cross-compiling binutils and GCC installations (vanilla and openSUSE at
+  // least) put various tools in a triple-prefixed directory off of the parent
+  // of the GCC installation. We use the GCC triple here to ensure that we end
+  // up with tools that support the same amount of cross compiling as the
+  // detected GCC installation. For example, if we find a GCC installation
+  // targeting x86_64, but it is a bi-arch GCC installation, it can also be
+  // used to target i386.
+  // FIXME: This seems unlikely to be Linux-specific.
+  ToolChain::path_list &PPaths = getProgramPaths();
+  PPaths.push_back(Twine(GCCInstallation.getParentLibPath() + "/../" +
+                         GCCInstallation.getTriple().str() + "/bin")
+                       .str());
+
+  Distro Distro(D.getVFS());
+
+  if (Distro.IsOpenSUSE() || Distro.IsUbuntu()) {
+    ExtraOpts.push_back("-z");
+    ExtraOpts.push_back("relro");
+  }
+
+  if (Arch == llvm::Triple::arm || Arch == llvm::Triple::thumb)
+    ExtraOpts.push_back("-X");
+
+  const bool IsAndroid = Triple.isAndroid();
+  const bool IsMips = tools::isMipsArch(Arch);
+  const bool IsHexagon = Arch == llvm::Triple::hexagon;
+
+  if (IsMips && !SysRoot.empty())
+    ExtraOpts.push_back("--sysroot=" + SysRoot);
+
+  // Do not use 'gnu' hash style for Mips targets because .gnu.hash
+  // and the MIPS ABI require .dynsym to be sorted in different ways.
+  // .gnu.hash needs symbols to be grouped by hash code whereas the MIPS
+  // ABI requires a mapping between the GOT and the symbol table.
+  // Android loader does not support .gnu.hash.
+  // Hexagon linker/loader does not support .gnu.hash
+  if (!IsMips && !IsAndroid && !IsHexagon) {
+    if (Distro.IsRedhat() || Distro.IsOpenSUSE() ||
+        (Distro.IsUbuntu() && Distro >= Distro::UbuntuMaverick))
+      ExtraOpts.push_back("--hash-style=gnu");
+
+    if (Distro.IsDebian() || Distro.IsOpenSUSE() || Distro == Distro::UbuntuLucid ||
+        Distro == Distro::UbuntuJaunty || Distro == Distro::UbuntuKarmic)
+      ExtraOpts.push_back("--hash-style=both");
+  }
+
+  if (Distro.IsRedhat() && Distro != Distro::RHEL5 && Distro != Distro::RHEL6)
+    ExtraOpts.push_back("--no-add-needed");
+
+#ifdef ENABLE_LINKER_BUILD_ID
+  ExtraOpts.push_back("--build-id");
+#endif
+
+  if (Distro.IsOpenSUSE())
+    ExtraOpts.push_back("--enable-new-dtags");
+
+  // The selection of paths to try here is designed to match the patterns which
+  // the GCC driver itself uses, as this is part of the GCC-compatible driver.
+  // This was determined by running GCC in a fake filesystem, creating all
+  // possible permutations of these directories, and seeing which ones it added
+  // to the link paths.
+  path_list &Paths = getFilePaths();
+
+  const std::string OSLibDir = getOSLibDir(Triple, Args);
+  const std::string MultiarchTriple = getMultiarchTriple(D, Triple, SysRoot);
+
+  // Add the multilib suffixed paths where they are available.
+  if (GCCInstallation.isValid()) {
+    const llvm::Triple &GCCTriple = GCCInstallation.getTriple();
+    const std::string &LibPath = GCCInstallation.getParentLibPath();
+    const Multilib &Multilib = GCCInstallation.getMultilib();
+    const MultilibSet &Multilibs = GCCInstallation.getMultilibs();
+
+    // Add toolchain / multilib specific file paths.
+    addMultilibsFilePaths(D, Multilibs, Multilib,
+                          GCCInstallation.getInstallPath(), Paths);
+
+    // Sourcery CodeBench MIPS toolchain holds some libraries under
+    // a biarch-like suffix of the GCC installation.
+    addPathIfExists(D, GCCInstallation.getInstallPath() + Multilib.gccSuffix(),
+                    Paths);
+
+    // GCC cross compiling toolchains will install target libraries which ship
+    // as part of the toolchain under <prefix>/<triple>/<libdir> rather than as
+    // any part of the GCC installation in
+    // <prefix>/<libdir>/gcc/<triple>/<version>. This decision is somewhat
+    // debatable, but is the reality today. We need to search this tree even
+    // when we have a sysroot somewhere else. It is the responsibility of
+    // whomever is doing the cross build targeting a sysroot using a GCC
+    // installation that is *not* within the system root to ensure two things:
+    //
+    //  1) Any DSOs that are linked in from this tree or from the install path
+    //     above must be present on the system root and found via an
+    //     appropriate rpath.
+    //  2) There must not be libraries installed into
+    //     <prefix>/<triple>/<libdir> unless they should be preferred over
+    //     those within the system root.
+    //
+    // Note that this matches the GCC behavior. See the below comment for where
+    // Clang diverges from GCC's behavior.
+    addPathIfExists(D, LibPath + "/../" + GCCTriple.str() + "/lib/../" +
+                           OSLibDir + Multilib.osSuffix(),
+                    Paths);
+
+    // If the GCC installation we found is inside of the sysroot, we want to
+    // prefer libraries installed in the parent prefix of the GCC installation.
+    // It is important to *not* use these paths when the GCC installation is
+    // outside of the system root as that can pick up unintended libraries.
+    // This usually happens when there is an external cross compiler on the
+    // host system, and a more minimal sysroot available that is the target of
+    // the cross. Note that GCC does include some of these directories in some
+    // configurations but this seems somewhere between questionable and simply
+    // a bug.
+    if (StringRef(LibPath).startswith(SysRoot)) {
+      addPathIfExists(D, LibPath + "/" + MultiarchTriple, Paths);
+      addPathIfExists(D, LibPath + "/../" + OSLibDir, Paths);
+    }
+  }
+
+  // Similar to the logic for GCC above, if we currently running Clang inside
+  // of the requested system root, add its parent library paths to
+  // those searched.
+  // FIXME: It's not clear whether we should use the driver's installed
+  // directory ('Dir' below) or the ResourceDir.
+  if (StringRef(D.Dir).startswith(SysRoot)) {
+    addPathIfExists(D, D.Dir + "/../lib/" + MultiarchTriple, Paths);
+    addPathIfExists(D, D.Dir + "/../" + OSLibDir, Paths);
+  }
+
+  addPathIfExists(D, SysRoot + "/lib/" + MultiarchTriple, Paths);
+  addPathIfExists(D, SysRoot + "/lib/../" + OSLibDir, Paths);
+  addPathIfExists(D, SysRoot + "/usr/lib/" + MultiarchTriple, Paths);
+  addPathIfExists(D, SysRoot + "/usr/lib/../" + OSLibDir, Paths);
+
+  // Try walking via the GCC triple path in case of biarch or multiarch GCC
+  // installations with strange symlinks.
+  if (GCCInstallation.isValid()) {
+    addPathIfExists(D,
+                    SysRoot + "/usr/lib/" + GCCInstallation.getTriple().str() +
+                        "/../../" + OSLibDir,
+                    Paths);
+
+    // Add the 'other' biarch variant path
+    Multilib BiarchSibling;
+    if (GCCInstallation.getBiarchSibling(BiarchSibling)) {
+      addPathIfExists(D, GCCInstallation.getInstallPath() +
+                             BiarchSibling.gccSuffix(),
+                      Paths);
+    }
+
+    // See comments above on the multilib variant for details of why this is
+    // included even from outside the sysroot.
+    const std::string &LibPath = GCCInstallation.getParentLibPath();
+    const llvm::Triple &GCCTriple = GCCInstallation.getTriple();
+    const Multilib &Multilib = GCCInstallation.getMultilib();
+    addPathIfExists(D, LibPath + "/../" + GCCTriple.str() + "/lib" +
+                           Multilib.osSuffix(),
+                    Paths);
+
+    // See comments above on the multilib variant for details of why this is
+    // only included from within the sysroot.
+    if (StringRef(LibPath).startswith(SysRoot))
+      addPathIfExists(D, LibPath, Paths);
+  }
+
+  // Similar to the logic for GCC above, if we are currently running Clang
+  // inside of the requested system root, add its parent library path to those
+  // searched.
+  // FIXME: It's not clear whether we should use the driver's installed
+  // directory ('Dir' below) or the ResourceDir.
+  if (StringRef(D.Dir).startswith(SysRoot))
+    addPathIfExists(D, D.Dir + "/../lib", Paths);
+
+  addPathIfExists(D, SysRoot + "/lib", Paths);
+  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
+}
+
+bool Linux::HasNativeLLVMSupport() const { return true; }
+
+Tool *Linux::buildLinker() const { return new tools::gnutools::Linker(*this); }
+
+Tool *Linux::buildAssembler() const {
+  return new tools::gnutools::Assembler(*this);
+}
+
+std::string Linux::computeSysRoot() const {
+  if (!getDriver().SysRoot.empty())
+    return getDriver().SysRoot;
+
+  if (!GCCInstallation.isValid() || !tools::isMipsArch(getTriple().getArch()))
+    return std::string();
+
+  // Standalone MIPS toolchains use different names for sysroot folder
+  // and put it into different places. Here we try to check some known
+  // variants.
+
+  const StringRef InstallDir = GCCInstallation.getInstallPath();
+  const StringRef TripleStr = GCCInstallation.getTriple().str();
+  const Multilib &Multilib = GCCInstallation.getMultilib();
+
+  std::string Path =
+      (InstallDir + "/../../../../" + TripleStr + "/libc" + Multilib.osSuffix())
+          .str();
+
+  if (getVFS().exists(Path))
+    return Path;
+
+  Path = (InstallDir + "/../../../../sysroot" + Multilib.osSuffix()).str();
+
+  if (getVFS().exists(Path))
+    return Path;
+
+  return std::string();
+}
+
+std::string Linux::getDynamicLinker(const ArgList &Args) const {
+  const llvm::Triple::ArchType Arch = getArch();
+  const llvm::Triple &Triple = getTriple();
+
+  const Distro Distro(getDriver().getVFS());
+
+  if (Triple.isAndroid())
+    return Triple.isArch64Bit() ? "/system/bin/linker64" : "/system/bin/linker";
+
+  if (Triple.isMusl()) {
+    std::string ArchName;
+    bool IsArm = false;
+
+    switch (Arch) {
+    case llvm::Triple::arm:
+    case llvm::Triple::thumb:
+      ArchName = "arm";
+      IsArm = true;
+      break;
+    case llvm::Triple::armeb:
+    case llvm::Triple::thumbeb:
+      ArchName = "armeb";
+      IsArm = true;
+      break;
+    default:
+      ArchName = Triple.getArchName().str();
+    }
+    if (IsArm &&
+        (Triple.getEnvironment() == llvm::Triple::MuslEABIHF ||
+         tools::arm::getARMFloatABI(*this, Args) == tools::arm::FloatABI::Hard))
+      ArchName += "hf";
+
+    return "/lib/ld-musl-" + ArchName + ".so.1";
+  }
+
+  std::string LibDir;
+  std::string Loader;
+
+  switch (Arch) {
+  default:
+    llvm_unreachable("unsupported architecture");
+
+  case llvm::Triple::aarch64:
+    LibDir = "lib";
+    Loader = "ld-linux-aarch64.so.1";
+    break;
+  case llvm::Triple::aarch64_be:
+    LibDir = "lib";
+    Loader = "ld-linux-aarch64_be.so.1";
+    break;
+  case llvm::Triple::arm:
+  case llvm::Triple::thumb:
+  case llvm::Triple::armeb:
+  case llvm::Triple::thumbeb: {
+    const bool HF =
+        Triple.getEnvironment() == llvm::Triple::GNUEABIHF ||
+        tools::arm::getARMFloatABI(*this, Args) == tools::arm::FloatABI::Hard;
+
+    LibDir = "lib";
+    Loader = HF ? "ld-linux-armhf.so.3" : "ld-linux.so.3";
+    break;
+  }
+  case llvm::Triple::mips:
+  case llvm::Triple::mipsel:
+  case llvm::Triple::mips64:
+  case llvm::Triple::mips64el: {
+    bool LE = (Triple.getArch() == llvm::Triple::mipsel) ||
+              (Triple.getArch() == llvm::Triple::mips64el);
+    bool IsNaN2008 = tools::mips::isNaN2008(Args, Triple);
+
+    LibDir = "lib" + tools::mips::getMipsABILibSuffix(Args, Triple);
+
+    if (tools::mips::isUCLibc(Args))
+      Loader = IsNaN2008 ? "ld-uClibc-mipsn8.so.0" : "ld-uClibc.so.0";
+    else if (!Triple.hasEnvironment() &&
+             Triple.getVendor() == llvm::Triple::VendorType::MipsTechnologies)
+      Loader = LE ? "ld-musl-mipsel.so.1" : "ld-musl-mips.so.1";
+    else
+      Loader = IsNaN2008 ? "ld-linux-mipsn8.so.1" : "ld.so.1";
+
+    break;
+  }
+  case llvm::Triple::ppc:
+    LibDir = "lib";
+    Loader = "ld.so.1";
+    break;
+  case llvm::Triple::ppc64:
+    LibDir = "lib64";
+    Loader =
+        (tools::ppc::hasPPCAbiArg(Args, "elfv2")) ? "ld64.so.2" : "ld64.so.1";
+    break;
+  case llvm::Triple::ppc64le:
+    LibDir = "lib64";
+    Loader =
+        (tools::ppc::hasPPCAbiArg(Args, "elfv1")) ? "ld64.so.1" : "ld64.so.2";
+    break;
+  case llvm::Triple::sparc:
+  case llvm::Triple::sparcel:
+    LibDir = "lib";
+    Loader = "ld-linux.so.2";
+    break;
+  case llvm::Triple::sparcv9:
+    LibDir = "lib64";
+    Loader = "ld-linux.so.2";
+    break;
+  case llvm::Triple::systemz:
+    LibDir = "lib";
+    Loader = "ld64.so.1";
+    break;
+  case llvm::Triple::x86:
+    LibDir = "lib";
+    Loader = "ld-linux.so.2";
+    break;
+  case llvm::Triple::x86_64: {
+    bool X32 = Triple.getEnvironment() == llvm::Triple::GNUX32;
+
+    LibDir = X32 ? "libx32" : "lib64";
+    Loader = X32 ? "ld-linux-x32.so.2" : "ld-linux-x86-64.so.2";
+    break;
+  }
+  }
+
+  if (Distro == Distro::Exherbo && (Triple.getVendor() == llvm::Triple::UnknownVendor ||
+                                    Triple.getVendor() == llvm::Triple::PC))
+    return "/usr/" + Triple.str() + "/lib/" + Loader;
+  return "/" + LibDir + "/" + Loader;
+}
+
+void Linux::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
+                                      ArgStringList &CC1Args) const {
+  const Driver &D = getDriver();
+  std::string SysRoot = computeSysRoot();
+
+  if (DriverArgs.hasArg(clang::driver::options::OPT_nostdinc))
+    return;
+
+  if (!DriverArgs.hasArg(options::OPT_nostdlibinc))
+    addSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/local/include");
+
+  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.
+
+  // Add include directories specific to the selected multilib set and multilib.
+  if (GCCInstallation.isValid()) {
+    const auto &Callback = Multilibs.includeDirsCallback();
+    if (Callback) {
+      for (const auto &Path : Callback(GCCInstallation.getMultilib()))
+        addExternCSystemIncludeIfExists(
+            DriverArgs, CC1Args, GCCInstallation.getInstallPath() + Path);
+    }
+  }
+
+  // Implement generic Debian multiarch support.
+  const StringRef X86_64MultiarchIncludeDirs[] = {
+      "/usr/include/x86_64-linux-gnu",
+
+      // FIXME: These are older forms of multiarch. It's not clear that they're
+      // in use in any released version of Debian, so we should consider
+      // removing them.
+      "/usr/include/i686-linux-gnu/64", "/usr/include/i486-linux-gnu/64"};
+  const StringRef X86MultiarchIncludeDirs[] = {
+      "/usr/include/i386-linux-gnu",
+
+      // FIXME: These are older forms of multiarch. It's not clear that they're
+      // in use in any released version of Debian, so we should consider
+      // removing them.
+      "/usr/include/x86_64-linux-gnu/32", "/usr/include/i686-linux-gnu",
+      "/usr/include/i486-linux-gnu"};
+  const StringRef AArch64MultiarchIncludeDirs[] = {
+      "/usr/include/aarch64-linux-gnu"};
+  const StringRef ARMMultiarchIncludeDirs[] = {
+      "/usr/include/arm-linux-gnueabi"};
+  const StringRef ARMHFMultiarchIncludeDirs[] = {
+      "/usr/include/arm-linux-gnueabihf"};
+  const StringRef ARMEBMultiarchIncludeDirs[] = {
+      "/usr/include/armeb-linux-gnueabi"};
+  const StringRef ARMEBHFMultiarchIncludeDirs[] = {
+      "/usr/include/armeb-linux-gnueabihf"};
+  const StringRef MIPSMultiarchIncludeDirs[] = {"/usr/include/mips-linux-gnu"};
+  const StringRef MIPSELMultiarchIncludeDirs[] = {
+      "/usr/include/mipsel-linux-gnu"};
+  const StringRef MIPS64MultiarchIncludeDirs[] = {
+      "/usr/include/mips64-linux-gnu", "/usr/include/mips64-linux-gnuabi64"};
+  const StringRef MIPS64ELMultiarchIncludeDirs[] = {
+      "/usr/include/mips64el-linux-gnu",
+      "/usr/include/mips64el-linux-gnuabi64"};
+  const StringRef PPCMultiarchIncludeDirs[] = {
+      "/usr/include/powerpc-linux-gnu"};
+  const StringRef PPC64MultiarchIncludeDirs[] = {
+      "/usr/include/powerpc64-linux-gnu"};
+  const StringRef PPC64LEMultiarchIncludeDirs[] = {
+      "/usr/include/powerpc64le-linux-gnu"};
+  const StringRef SparcMultiarchIncludeDirs[] = {
+      "/usr/include/sparc-linux-gnu"};
+  const StringRef Sparc64MultiarchIncludeDirs[] = {
+      "/usr/include/sparc64-linux-gnu"};
+  const StringRef SYSTEMZMultiarchIncludeDirs[] = {
+      "/usr/include/s390x-linux-gnu"};
+  ArrayRef<StringRef> MultiarchIncludeDirs;
+  switch (getTriple().getArch()) {
+  case llvm::Triple::x86_64:
+    MultiarchIncludeDirs = X86_64MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::x86:
+    MultiarchIncludeDirs = X86MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::aarch64:
+  case llvm::Triple::aarch64_be:
+    MultiarchIncludeDirs = AArch64MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::arm:
+  case llvm::Triple::thumb:
+    if (getTriple().getEnvironment() == llvm::Triple::GNUEABIHF)
+      MultiarchIncludeDirs = ARMHFMultiarchIncludeDirs;
+    else
+      MultiarchIncludeDirs = ARMMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::armeb:
+  case llvm::Triple::thumbeb:
+    if (getTriple().getEnvironment() == llvm::Triple::GNUEABIHF)
+      MultiarchIncludeDirs = ARMEBHFMultiarchIncludeDirs;
+    else
+      MultiarchIncludeDirs = ARMEBMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::mips:
+    MultiarchIncludeDirs = MIPSMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::mipsel:
+    MultiarchIncludeDirs = MIPSELMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::mips64:
+    MultiarchIncludeDirs = MIPS64MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::mips64el:
+    MultiarchIncludeDirs = MIPS64ELMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::ppc:
+    MultiarchIncludeDirs = PPCMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::ppc64:
+    MultiarchIncludeDirs = PPC64MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::ppc64le:
+    MultiarchIncludeDirs = PPC64LEMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::sparc:
+    MultiarchIncludeDirs = SparcMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::sparcv9:
+    MultiarchIncludeDirs = Sparc64MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::systemz:
+    MultiarchIncludeDirs = SYSTEMZMultiarchIncludeDirs;
+    break;
+  default:
+    break;
+  }
+  for (StringRef Dir : MultiarchIncludeDirs) {
+    if (D.getVFS().exists(SysRoot + Dir)) {
+      addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + Dir);
+      break;
+    }
+  }
+
+  if (getTriple().getOS() == llvm::Triple::RTEMS)
+    return;
+
+  // Add an include of '/include' directly. This isn't provided by default by
+  // system GCCs, but is often used with cross-compiling GCCs, and harmless to
+  // add even when Clang is acting as-if it were a system compiler.
+  addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/include");
+
+  addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/include");
+}
+
+static std::string DetectLibcxxIncludePath(StringRef base) {
+  std::error_code EC;
+  int MaxVersion = 0;
+  std::string MaxVersionString = "";
+  for (llvm::sys::fs::directory_iterator LI(base, EC), LE; !EC && LI != LE;
+       LI = LI.increment(EC)) {
+    StringRef VersionText = llvm::sys::path::filename(LI->path());
+    int Version;
+    if (VersionText[0] == 'v' &&
+        !VersionText.slice(1, StringRef::npos).getAsInteger(10, Version)) {
+      if (Version > MaxVersion) {
+        MaxVersion = Version;
+        MaxVersionString = VersionText;
+      }
+    }
+  }
+  return MaxVersion ? (base + "/" + MaxVersionString).str() : "";
+}
+
+std::string Linux::findLibCxxIncludePath() const {
+  const std::string LibCXXIncludePathCandidates[] = {
+      DetectLibcxxIncludePath(getDriver().Dir + "/../include/c++"),
+      // If this is a development, non-installed, clang, libcxx will
+      // not be found at ../include/c++ but it likely to be found at
+      // one of the following two locations:
+      DetectLibcxxIncludePath(getDriver().SysRoot + "/usr/local/include/c++"),
+      DetectLibcxxIncludePath(getDriver().SysRoot + "/usr/include/c++") };
+  for (const auto &IncludePath : LibCXXIncludePathCandidates) {
+    if (IncludePath.empty() || !getVFS().exists(IncludePath))
+      continue;
+    // Use the first candidate that exists.
+    return IncludePath;
+  }
+  return "";
+}
+
+void Linux::addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
+                                     llvm::opt::ArgStringList &CC1Args) const {
+  // We need a detected GCC installation on Linux to provide libstdc++'s
+  // headers.
+  if (!GCCInstallation.isValid())
+    return;
+
+  // By default, look for the C++ headers in an include directory adjacent to
+  // the lib directory of the GCC installation. Note that this is expect to be
+  // equivalent to '/usr/include/c++/X.Y' in almost all cases.
+  StringRef LibDir = GCCInstallation.getParentLibPath();
+  StringRef InstallDir = GCCInstallation.getInstallPath();
+  StringRef TripleStr = GCCInstallation.getTriple().str();
+  const Multilib &Multilib = GCCInstallation.getMultilib();
+  const std::string GCCMultiarchTriple = getMultiarchTriple(
+      getDriver(), GCCInstallation.getTriple(), getDriver().SysRoot);
+  const std::string TargetMultiarchTriple =
+      getMultiarchTriple(getDriver(), getTriple(), getDriver().SysRoot);
+  const GCCVersion &Version = GCCInstallation.getVersion();
+
+  // The primary search for libstdc++ supports multiarch variants.
+  if (addLibStdCXXIncludePaths(LibDir.str() + "/../include",
+                               "/c++/" + Version.Text, TripleStr,
+                               GCCMultiarchTriple, TargetMultiarchTriple,
+                               Multilib.includeSuffix(), DriverArgs, CC1Args))
+    return;
+
+  // Otherwise, fall back on a bunch of options which don't use multiarch
+  // layouts for simplicity.
+  const std::string LibStdCXXIncludePathCandidates[] = {
+      // Gentoo is weird and places its headers inside the GCC install,
+      // so if the first attempt to find the headers fails, try these patterns.
+      InstallDir.str() + "/include/g++-v" + Version.Text,
+      InstallDir.str() + "/include/g++-v" + Version.MajorStr + "." +
+          Version.MinorStr,
+      InstallDir.str() + "/include/g++-v" + Version.MajorStr,
+      // Android standalone toolchain has C++ headers in yet another place.
+      LibDir.str() + "/../" + TripleStr.str() + "/include/c++/" + Version.Text,
+      // Freescale SDK C++ headers are directly in <sysroot>/usr/include/c++,
+      // without a subdirectory corresponding to the gcc version.
+      LibDir.str() + "/../include/c++",
+  };
+
+  for (const auto &IncludePath : LibStdCXXIncludePathCandidates) {
+    if (addLibStdCXXIncludePaths(IncludePath, /*Suffix*/ "", TripleStr,
+                                 /*GCCMultiarchTriple*/ "",
+                                 /*TargetMultiarchTriple*/ "",
+                                 Multilib.includeSuffix(), DriverArgs, CC1Args))
+      break;
+  }
+}
+
+void Linux::AddCudaIncludeArgs(const ArgList &DriverArgs,
+                               ArgStringList &CC1Args) const {
+  CudaInstallation.AddCudaIncludeArgs(DriverArgs, CC1Args);
+}
+
+void Linux::AddIAMCUIncludeArgs(const ArgList &DriverArgs,
+                                ArgStringList &CC1Args) const {
+  if (GCCInstallation.isValid()) {
+    CC1Args.push_back("-isystem");
+    CC1Args.push_back(DriverArgs.MakeArgString(
+        GCCInstallation.getParentLibPath() + "/../" +
+        GCCInstallation.getTriple().str() + "/include"));
+  }
+}
+
+bool Linux::isPIEDefault() const { return getSanitizerArgs().requiresPIE(); }
+
+SanitizerMask Linux::getSupportedSanitizers() const {
+  const bool IsX86 = getTriple().getArch() == llvm::Triple::x86;
+  const bool IsX86_64 = getTriple().getArch() == llvm::Triple::x86_64;
+  const bool IsMIPS64 = getTriple().getArch() == llvm::Triple::mips64 ||
+                        getTriple().getArch() == llvm::Triple::mips64el;
+  const bool IsPowerPC64 = getTriple().getArch() == llvm::Triple::ppc64 ||
+                           getTriple().getArch() == llvm::Triple::ppc64le;
+  const bool IsAArch64 = getTriple().getArch() == llvm::Triple::aarch64 ||
+                         getTriple().getArch() == llvm::Triple::aarch64_be;
+  const bool IsArmArch = getTriple().getArch() == llvm::Triple::arm ||
+                         getTriple().getArch() == llvm::Triple::thumb ||
+                         getTriple().getArch() == llvm::Triple::armeb ||
+                         getTriple().getArch() == llvm::Triple::thumbeb;
+  SanitizerMask Res = ToolChain::getSupportedSanitizers();
+  Res |= SanitizerKind::Address;
+  Res |= SanitizerKind::Fuzzer;
+  Res |= SanitizerKind::KernelAddress;
+  Res |= SanitizerKind::Vptr;
+  Res |= SanitizerKind::SafeStack;
+  if (IsX86_64 || IsMIPS64 || IsAArch64)
+    Res |= SanitizerKind::DataFlow;
+  if (IsX86_64 || IsMIPS64 || IsAArch64 || IsX86 || IsArmArch)
+    Res |= SanitizerKind::Leak;
+  if (IsX86_64 || IsMIPS64 || IsAArch64 || IsPowerPC64)
+    Res |= SanitizerKind::Thread;
+  if (IsX86_64 || IsMIPS64 || IsPowerPC64 || IsAArch64)
+    Res |= SanitizerKind::Memory;
+  if (IsX86_64 || IsMIPS64)
+    Res |= SanitizerKind::Efficiency;
+  if (IsX86 || IsX86_64) {
+    Res |= SanitizerKind::Function;
+  }
+  return Res;
+}
+
+void Linux::addProfileRTLibs(const llvm::opt::ArgList &Args,
+                             llvm::opt::ArgStringList &CmdArgs) const {
+  if (!needsProfileRT(Args)) return;
+
+  // Add linker option -u__llvm_runtime_variable to cause runtime
+  // initialization module to be linked in.
+  if (!Args.hasArg(options::OPT_coverage))
+    CmdArgs.push_back(Args.MakeArgString(
+        Twine("-u", llvm::getInstrProfRuntimeHookVarName())));
+  ToolChain::addProfileRTLibs(Args, CmdArgs);
+}