[Driver] Add -print-runtime-dir

[zero9178]

Summary

This patch adds a new command line option to clang which outputs the directory containing clangs runtime libraries to stdout.

The primary use case for this command line flag is for build systems using clang-cl. Build systems when using clang-cl invoke the linker, that is either link or lld-link in this case, directly instead of invoking the compiler for the linking process as is common with the other drivers. This leads to issues when runtime libraries of clang, such as sanitizers or profiling, have to be linked in as the compiler cannot communicate the link directory to the linker.

Using this flag, build systems would be capable of getting the directory containing all of clang's runtime libraries and add it to the linker path.

One such implementation is in LLVM's CMake scripts which currently gets the path to the builtins library and uses the containing directory. This also has issues however when the builtins library does not exist, which AFAIK is not a prerequisite to using clang-cl. More info here: https://reviews.llvm.org/D98786

[rnk]

lgtm

I'm somewhat surprised this doesn't exist already, but I looked at the -print-* options and don't see anything.

clang/include/clang/Driver/Options.td

 def print_resource_dir : Flag<["-", "--"], "print-resource-dir">,
   HelpText<"Print the resource directory pathname">;
 def print_search_dirs : Flag<["-", "--"], "print-search-dirs">,
   HelpText<"Print the paths used for finding libraries and programs">;
 def print_targets : Flag<["-", "--"], "print-targets">,
   HelpText<"Print the registered targets">;
 def print_rocm_search_dirs : Flag<["-", "--"], "print-rocm-search-dirs">,
   HelpText<"Print the paths used for finding ROCm installation">;
+def print_runtime_dir : Flag<["-", "--"], "print-runtime-dir">,
+  HelpText<"Print the directory pathname containing clangs runtime libraries">;
 def private__bundle : Flag<["-"], "private_bundle">;
 def pthreads : Flag<["-"], "pthreads">;
 defm pthread : BoolOption<"", "pthread",
   LangOpts<"POSIXThreads">, DefaultFalse,
   PosFlag<SetTrue, [], "Support POSIX threads in generated code">,
   NegFlag<SetFalse>, BothFlags<[CC1Option]>>;
 def p : Flag<["-"], "p">;
 def pie : Flag<["-"], "pie">, Group<Link_Group>;

clang/lib/Driver/Driver.cpp

for (const std::string &Path : TC.getFilePaths()) {
         llvm::outs() << sysroot << Path.substr(1);
       else
         llvm::outs() << Path;
     }
     llvm::outs() << "\n";
     return false;
   }
 
+  if (C.getArgs().hasArg(options::OPT_print_runtime_dir)) {
+    if (auto RuntimePath = TC.getRuntimePath()) {
+      llvm::outs() << *RuntimePath << '\n';
+      return false;
+    }
+    llvm::outs() << TC.getCompilerRTPath() << '\n';
+    return false;
+  }
+
   // FIXME: The following handlers should use a callback mechanism, we don't
   // know what the client would like to do.
   if (Arg *A = C.getArgs().getLastArg(options::OPT_print_file_name_EQ)) {
     llvm::outs() << GetFilePath(A->getValue(), TC) << "\n";
     return false;
   }
 
   if (Arg *A = C.getArgs().getLastArg(options::OPT_print_prog_name_EQ)) {

clang/test/Driver/immediate-options.c

 
 // RUN: %clang -dumpversion | FileCheck %s -check-prefix=DUMPVERSION
 // DUMPVERSION: {{[0-9]+\.[0-9.]+}}
 
 // Test if the -print-resource-dir option is accepted without error.
 // Allow unspecified output because the value of CLANG_RESOURCE_DIR is unknown.
 // RUN: %clang -print-resource-dir | FileCheck %s -check-prefix=PRINT-RESOURCE-DIR
 // PRINT-RESOURCE-DIR: {{.+}}
+
+// Default resource-dir layout
+// RUN: %clang -print-runtime-dir --target=x86_64-pc-windows-msvc \
+// RUN:        -resource-dir=%S/Inputs/resource_dir \
+// RUN:      | FileCheck --check-prefix=PRINT-RUNTIME-DIR %s
+// PRINT-RUNTIME-DIR: lib{{/|\\}}windows
+
+// Per target dir layout
+// RUN: %clang -print-runtime-dir --target=x86_64-pc-windows-msvc \
+// RUN:        -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:      | FileCheck --check-prefix=PRINT-RUNTIME-DIR-PER-TARGET %s
+// PRINT-RUNTIME-DIR-PER-TARGET: lib{{/|\\}}x86_64-pc-windows-msvc