[cfe-dev] Failures with -DGCC_INSTALL_PREFIX

[David Greene via cfe-dev]

Hi,

When clang is configured with -DGCC_INSTALL_PREFIX, the test
Driver/android-ndk-standalone fails to find the android gcc
installation.

I believe it may be due to this code in GCCInstallationDetector::init:

  StringRef GCCToolchainDir = getGCCToolchainDir(Args);
  if (GCCToolchainDir != "") {
    if (GCCToolchainDir.back() == '/')
      GCCToolchainDir = GCCToolchainDir.drop_back(); // remove the /

    Prefixes.push_back(GCCToolchainDir);
  } else {
    // If we have a SysRoot, try that first.
    if (!D.SysRoot.empty()) {
      Prefixes.push_back(D.SysRoot);
      AddDefaultGCCPrefixes(TargetTriple, Prefixes, D.SysRoot);
    }

    // Then look for gcc installed alongside clang.
    Prefixes.push_back(D.InstalledDir + "/..");

    // Next, look for prefix(es) that correspond to distribution-supplied gcc
    // installations.
    if (D.SysRoot.empty()) {
      // Typically /usr.
      AddDefaultGCCPrefixes(TargetTriple, Prefixes, D.SysRoot);
    }
  }

getGCCToolchainDir return GCC_INSTALL_PREFIX if no toolchain option is
given:

static llvm::StringRef getGCCToolchainDir(const ArgList &Args) {
  const Arg *A = Args.getLastArg(clang::driver::options::OPT_gcc_toolchain);
  if (A)
    return A->getValue();
  return GCC_INSTALL_PREFIX;
}

Since GCC_INSTALL_PREFIX is non-empty, we fail to check the sysroot for
an installation.

What is the expected behavior in this case?  We want to run all of the
regression tests to make sure we don't break anything, but we also need
to set GCC_INSTALL_PREFIX.  Should GCCInstallationDetector::init be
changed to look at sysroot first?

In this case we're configuring for x86_64-unknown-linux-gnu.
Theoretically we could ignore GCC_INSTALL_PREFIX since the target
triples don't match, but I'm not sure if that's the right way to go.

Thanks for your help!

                               -David