[Driver] Support using toolchain libc and libc++ for baremetal (#96736)

We want to support using a complete Clang/LLVM toolchain that includes
LLVM libc and libc++ for baremetal targets. To do so, we need the driver
to add the necessary include paths.

2 files changed, 53 insertions, 9 deletions

diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 8f4cc47..977e083 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -811,6 +811,12 @@ std::optional<std::string> ToolChain::getStdlibPath() const {
   return getTargetSubDirPath(P);
 }
 
+std::optional<std::string> ToolChain::getStdlibIncludePath() const {
+  SmallString<128> P(D.Dir);
+  llvm::sys::path::append(P, "..", "include");
+  return getTargetSubDirPath(P);
+}
+
 ToolChain::path_list ToolChain::getArchSpecificLibPaths() const {
   path_list Paths;
 
diff --git a/clang/lib/Driver/ToolChains/BareMetal.cpp b/clang/lib/Driver/ToolChains/BareMetal.cpp
index dd365e6..11f9487 100644
--- a/clang/lib/Driver/ToolChains/BareMetal.cpp
+++ b/clang/lib/Driver/ToolChains/BareMetal.cpp
@@ -270,15 +270,19 @@ void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
     addSystemInclude(DriverArgs, CC1Args, Dir.str());
   }
 
-  if (!DriverArgs.hasArg(options::OPT_nostdlibinc)) {
-    const SmallString<128> SysRoot(computeSysRoot());
-    if (!SysRoot.empty()) {
-      for (const Multilib &M : getOrderedMultilibs()) {
-        SmallString<128> Dir(SysRoot);
-        llvm::sys::path::append(Dir, M.includeSuffix());
-        llvm::sys::path::append(Dir, "include");
-        addSystemInclude(DriverArgs, CC1Args, Dir.str());
-      }
+  if (DriverArgs.hasArg(options::OPT_nostdlibinc))
+    return;
+
+  if (std::optional<std::string> Path = getStdlibIncludePath())
+    addSystemInclude(DriverArgs, CC1Args, *Path);
+
+  const SmallString<128> SysRoot(computeSysRoot());
+  if (!SysRoot.empty()) {
+    for (const Multilib &M : getOrderedMultilibs()) {
+      SmallString<128> Dir(SysRoot);
+      llvm::sys::path::append(Dir, M.includeSuffix());
+      llvm::sys::path::append(Dir, "include");
+      addSystemInclude(DriverArgs, CC1Args, Dir.str());
     }
   }
 }
@@ -296,6 +300,40 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
     return;
 
   const Driver &D = getDriver();
+  std::string Target = getTripleString();
+
+  auto AddCXXIncludePath = [&](StringRef Path) {
+    std::string Version = detectLibcxxVersion(Path);
+    if (Version.empty())
+      return;
+
+    {
+      // First the per-target include dir: include/<target>/c++/v1.
+      SmallString<128> TargetDir(Path);
+      llvm::sys::path::append(TargetDir, Target, "c++", Version);
+      addSystemInclude(DriverArgs, CC1Args, TargetDir);
+    }
+
+    {
+      // Then the generic dir: include/c++/v1.
+      SmallString<128> Dir(Path);
+      llvm::sys::path::append(Dir, "c++", Version);
+      addSystemInclude(DriverArgs, CC1Args, Dir);
+    }
+  };
+
+  switch (GetCXXStdlibType(DriverArgs)) {
+    case ToolChain::CST_Libcxx: {
+      SmallString<128> P(D.Dir);
+      llvm::sys::path::append(P, "..", "include");
+      AddCXXIncludePath(P);
+      break;
+    }
+    case ToolChain::CST_Libstdcxx:
+      // We only support libc++ toolchain installation.
+      break;
+  }
+
   std::string SysRoot(computeSysRoot());
   if (SysRoot.empty())
     return;