[Driver] Introduce -stdlib++-isystem

There are times when we wish to explicitly control the C++ standard
library search paths used by the driver. For example, when we're
building against the Android NDK, we might want to use the NDK's C++
headers (which have a custom inline namespace) even if we have C++
headers installed next to the driver. We might also be building against
a non-standard directory layout and wanting to specify the C++ standard
library include directories explicitly.

We could accomplish this by passing -nostdinc++ and adding an explicit
-isystem for our custom search directories. However, users of our
toolchain may themselves want to use -nostdinc++ and a custom C++ search
path (libc++'s build does this, for example), and our added -isystem
won't respect the -nostdinc++, leading to multiple C++ header
directories on the search path, which causes build failures.

Add a new driver option -stdlib++-isystem to support this use case.
Passing this option suppresses adding the default C++ library include
paths in the driver, and it also respects -nostdinc++ to allow users to
still override the C++ library paths themselves.

It's a bit unfortunate that we end up with both -stdlib++-isystem and
-cxx-isystem, but their semantics differ significantly. -cxx-isystem is
unaffected by -nostdinc++ and is added to the end of the search path
(which is not appropriate for C++ standard library headers, since they
often #include_next into other system headers), while -stdlib++-isystem
respects -nostdinc++, is added to the beginning of the search path, and
suppresses the default C++ library include paths.

Differential Revision: https://reviews.llvm.org/D64089

llvm-svn: 367982

1 files changed, 12 insertions, 5 deletions

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 4681e013893..bac6cff62f0 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -1235,6 +1235,9 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
       // Do not claim the argument so that the use of the argument does not
       // silently go unnoticed on toolchains which do not honour the option.
       continue;
+    } else if (A->getOption().matches(options::OPT_stdlibxx_isystem)) {
+      // Translated to -internal-isystem by the driver, no need to pass to cc1.
+      continue;
     }
 
     // Not translated, render as usual.
@@ -1289,11 +1292,15 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
   // of an offloading programming model.
 
   // Add C++ include arguments, if needed.
-  if (types::isCXX(Inputs[0].getType()))
-    forAllAssociatedToolChains(C, JA, getToolChain(),
-                               [&Args, &CmdArgs](const ToolChain &TC) {
-                                 TC.AddClangCXXStdlibIncludeArgs(Args, CmdArgs);
-                               });
+  if (types::isCXX(Inputs[0].getType())) {
+    bool HasStdlibxxIsystem = Args.hasArg(options::OPT_stdlibxx_isystem);
+    forAllAssociatedToolChains(
+        C, JA, getToolChain(),
+        [&Args, &CmdArgs, HasStdlibxxIsystem](const ToolChain &TC) {
+          HasStdlibxxIsystem ? TC.AddClangCXXStdlibIsystemArgs(Args, CmdArgs)
+                             : TC.AddClangCXXStdlibIncludeArgs(Args, CmdArgs);
+        });
+  }
 
   // Add system include arguments for all targets but IAMCU.
   if (!IsIAMCU)