[clang] [Darwin][Driver][clang] apple-none-macho orders the resource directory after internal-externc-isystem when nostdlibinc is used (PR #120507)

[Jon Roelofs via cfe-commits]

================
@@ -2631,55 +2643,65 @@ void DarwinClang::AddClangCXXStdlibIncludeArgs(
   }
 
   case ToolChain::CST_Libstdcxx:
-    llvm::SmallString<128> UsrIncludeCxx = Sysroot;
-    llvm::sys::path::append(UsrIncludeCxx, "usr", "include", "c++");
-
-    llvm::Triple::ArchType arch = getTriple().getArch();
-    bool IsBaseFound = true;
-    switch (arch) {
-    default: break;
-
-    case llvm::Triple::x86:
-    case llvm::Triple::x86_64:
-      IsBaseFound = AddGnuCPlusPlusIncludePaths(DriverArgs, CC1Args, UsrIncludeCxx,
-                                                "4.2.1",
-                                                "i686-apple-darwin10",
-                                                arch == llvm::Triple::x86_64 ? "x86_64" : "");
-      IsBaseFound |= AddGnuCPlusPlusIncludePaths(DriverArgs, CC1Args, UsrIncludeCxx,
-                                                "4.0.0", "i686-apple-darwin8",
-                                                 "");
-      break;
+    AddGnuCPlusPlusIncludePaths(DriverArgs, CC1Args);
+    break;
+  }
+}
 
-    case llvm::Triple::arm:
-    case llvm::Triple::thumb:
-      IsBaseFound = AddGnuCPlusPlusIncludePaths(DriverArgs, CC1Args, UsrIncludeCxx,
-                                                "4.2.1",
-                                                "arm-apple-darwin10",
-                                                "v7");
-      IsBaseFound |= AddGnuCPlusPlusIncludePaths(DriverArgs, CC1Args, UsrIncludeCxx,
-                                                "4.2.1",
-                                                "arm-apple-darwin10",
-                                                 "v6");
-      break;
+void MachO::AddGnuCPlusPlusIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {}
 
-    case llvm::Triple::aarch64:
-      IsBaseFound = AddGnuCPlusPlusIncludePaths(DriverArgs, CC1Args, UsrIncludeCxx,
-                                                "4.2.1",
-                                                "arm64-apple-darwin10",
-                                                "");
-      break;
-    }
+void DarwinClang::AddGnuCPlusPlusIncludePaths(
+    const llvm::opt::ArgList &DriverArgs,
+    llvm::opt::ArgStringList &CC1Args) const {
+  llvm::SmallString<128> Sysroot = GetEffectiveSysroot(DriverArgs);
 
-    if (!IsBaseFound) {
-      getDriver().Diag(diag::warn_drv_libstdcxx_not_found);
-    }
+  llvm::SmallString<128> UsrIncludeCxx = Sysroot;
----------------
jroelofs wrote:

`Sysroot` isn't used after this point, but I'm not sure if llvm will coalesce the two stack objects for these two `SmallString`s. Maybe this ought to be:

```
llvm::SmallString<128> UserIncludeCxx = GetEffectiveSysroot(DriverArgs);
```

and drop the other one, to be sure we don't use loads of extra stack when computing this.

https://github.com/llvm/llvm-project/pull/120507