Driver: Add magic handling for "reserved library names", starting with

-lstdc++. This is the best gross solution for a gross problem.

This issue is that historically, GCC has add -L options to its internally
library directories. This has allowed users and platforms to end up depending on
the layout of GCC's internal library directories.

We want to correct this mistake by eliminating that -L, but this means that
existing libraries which are in the GCC lib dir won't be found. We are going to
handle this by treating those -l names as "reserved", and requiring toolchains
to know how to add the right full path to the reserved library.

The immediately side effect of this is that users trying to use -L to find their
own -lstdc++ will need to start using -nostdlib (which is a good idea
anyway). Another side effect is that -stdlib=libc++ -lstdc++ will now do the
"right" thing, for curious definitions of right.

llvm-svn: 114144

clang/include/clang/Driver/Options.td

@@ -38,6 +38,7 @@ def u_Group               : OptionGroup<"<u group>">;
 
 def pedantic_Group        : OptionGroup<"<pedantic group>">,
   Group<CompileOnly_Group>;
+def reserved_lib_Group   : OptionGroup<"<reserved libs group>">;
 
 // Temporary groups for clang options which we know we don't support,
 // but don't want to verbosely warn the user about.
@@ -742,4 +743,8 @@ def _write_user_dependencies : Flag<"--write-user-dependencies">, Alias<MMD>;
 def _ : Joined<"--">, Flags<[Unsupported]>;
 
 // Special internal option to handle -Xlinker --no-demangle.
-def Z_Xlinker__no_demangle : Flag<"-Z-Xlinker-no-demangle">, Flags<[Unsupported]>;
+def Z_Xlinker__no_demangle : Flag<"-Z-Xlinker-no-demangle">, Flags<[Unsupported, NoArgumentUnused]>;
+
+// Reserved library options.
+def Z_reserved_lib_stdcxx : Flag<"-Z-reserved-lib-stdc++">,
+    Flags<[LinkerInput, NoArgumentUnused, Unsupported]>, Group<reserved_lib_Group>;

clang/lib/Driver/Driver.cpp

@@ -115,6 +115,7 @@ InputArgList *Driver::ParseArgStrings(const char **ArgBegin,
 DerivedArgList *Driver::TranslateInputArgs(const InputArgList &Args) const {
   DerivedArgList *DAL = new DerivedArgList(Args);
 
+  bool HasNostdlib = Args.hasArg(options::OPT_nostdlib);
   for (ArgList::const_iterator it = Args.begin(),
          ie = Args.end(); it != ie; ++it) {
     const Arg *A = *it;
@@ -157,6 +158,17 @@ DerivedArgList *Driver::TranslateInputArgs(const InputArgList &Args) const {
       continue;
     }
 
+    // Rewrite reserved library names, unless -nostdlib is present.
+    if (!HasNostdlib && A->getOption().matches(options::OPT_l)) {
+      llvm::StringRef Value = A->getValue(Args);
+
+      if (Value == "stdc++") {
+        DAL->AddFlagArg(A, Opts->getOption(
+                              options::OPT_Z_reserved_lib_stdcxx));
+        continue;
+      }
+    }
+
     DAL->append(*it);
   }
 

clang/lib/Driver/Tools.cpp

@@ -104,10 +104,20 @@ static void AddLinkerInputs(const ToolChain &TC,
           << TC.getTripleString();
     }
 
-    if (II.isFilename())
+    // Add filenames immediately.
+    if (II.isFilename()) {
       CmdArgs.push_back(II.getFilename());
-    else
-      II.getInputArg().renderAsInput(Args, CmdArgs);
+      continue;
+    }
+
+    // Otherwise, this is a linker input argument.
+    const Arg &A = II.getInputArg();
+
+    // Handle reserved library options.
+    if (A.getOption().matches(options::OPT_Z_reserved_lib_stdcxx)) {
+      TC.AddClangCXXStdlibLibArgs(Args, CmdArgs);
+    } else
+      A.renderAsInput(Args, CmdArgs);
   }
 }
 
@@ -3242,7 +3252,8 @@ void visualstudio::Link::ConstructJob(Compilation &C, const JobAction &JA,
   ArgStringList CmdArgs;
 
   if (Output.isFilename()) {
-    CmdArgs.push_back(Args.MakeArgString(std::string("-out:") + Output.getFilename()));
+    CmdArgs.push_back(Args.MakeArgString(std::string("-out:") +
+                                         Output.getFilename()));
   } else {
     assert(Output.isNothing() && "Invalid output.");
   }