[Driver] Make -print-libgcc-file-name print compiler-rt lib when used

[mgorny]

Summary

Make the -print-libgcc-file-name option print an appropriate compiler
runtime library, that is libgcc.a if gcc runtime is used
and an appropriate compiler-rt library if that runtime is used.

The main use for this is to allow linking executables built with
-nodefaultlibs (e.g. to avoid linking to the standard C++ library) to
the compiler runtime library, e.g. using:

clang++ ... -nodefaultlibs $(clang++ ... -print-libgcc-file-name)

in which case currently a program built like this linked to the gcc
runtime unconditionally. The patch fixes it to use compiler-rt libraries
instead when compiler-rt is the active runtime.

[bruno]

Testcase?

docs/CommandGuide/clang.rst

398

You can probably drop the "appropriately"

include/clang/Driver/Options.td

1865

Same here

[mgorny]

Updated the docs. I'll look into the test case tomorrow.

[mgorny]

A simple test case included.

[bruno]

LGTM

[mgorny]

Thanks for the review.

[mgorny]

It seems that my test doesn't work on Darwin, and I should exclude the libgcc part there. Do you happen to have any suggestion how to do that?

I'm going to wait for other buildbots to finish to see if I haven't broken any other platform, then revert it and look for a proper way to restrict the tests.

[mgorny]

Reverted, I need to update it to run libgcc part of the test only on platforms supporting that.

[mgorny]

I have updated the patch to include a feature check for platforms rejecting -rtlib=libgcc and split the test appropriately. Could you re-review, please?

[mgorny]

Including a fix for montavista toolchain checks that miss passing -rtlib= and therefore could fail depending on DEFAULT_* value.

[mgorny]

I'm sorry, I mixed branches up. Here's the correct patch with both updates.

[phosek]

I have submitted the same change D25256 a few days ago but this one seems to be getting more traction so I'm going to abandon mine in favor of this one.

lib/Driver/Driver.cpp

1000

I think you should use TC.getCompilerRT rather than TC.getCompilerRTArgString here.

[mgorny]

Updated to use TC.getCompilerRT().

[ggreif]

LGTM.

[mgorny]

Thanks for the review.

[bruno]

LGTM

[mgorny]

r283746

docs/CommandGuide/clang.rst

.. option:: -o <file>
   Write output to file.
 
 .. option:: -print-file-name=<file>
 
   Print the full library path of file.
 
 .. option:: -print-libgcc-file-name
 
-  Print the library path for "libgcc.a".
+  Print the library path for the currently used compiler runtime library
+  ("libgcc.a" or "libclang_rt.builtins.*.a").
 
 .. option:: -print-prog-name=<name>
 
   Print the full program path of name.
 
 .. option:: -print-search-dirs
 
   Print the paths used for finding libraries and programs.

include/clang/Driver/Options.td

 def prebind__all__twolevel__modules : Flag<["-"], "prebind_all_twolevel_modules">;
 def prebind : Flag<["-"], "prebind">;
 def preload : Flag<["-"], "preload">;
 def print_file_name_EQ : Joined<["-", "--"], "print-file-name=">,
   HelpText<"Print the full library path of <file>">, MetaVarName<"<file>">;
 def print_ivar_layout : Flag<["-"], "print-ivar-layout">, Flags<[CC1Option]>,
   HelpText<"Enable Objective-C Ivar layout bitmap print trace">;
 def print_libgcc_file_name : Flag<["-", "--"], "print-libgcc-file-name">,
-  HelpText<"Print the library path for \"libgcc.a\"">;
+  HelpText<"Print the library path for the currently used compiler runtime "
+           "library (\"libgcc.a\" or \"libclang_rt.builtins.*.a\")">;
 def print_multi_directory : Flag<["-", "--"], "print-multi-directory">;
 def print_multi_lib : Flag<["-", "--"], "print-multi-lib">;
 def print_multi_os_directory : Flag<["-", "--"], "print-multi-os-directory">,
   Flags<[Unsupported]>;
 def print_prog_name_EQ : Joined<["-", "--"], "print-prog-name=">,
   HelpText<"Print the full program path of <name>">, MetaVarName<"<name>">;
 def print_search_dirs : Flag<["-", "--"], "print-search-dirs">,
   HelpText<"Print the paths used for finding libraries and programs">;

lib/Driver/Driver.cpp

bool Driver::HandleImmediateArgs(const Compilation &C) {
   }
 
   if (Arg *A = C.getArgs().getLastArg(options::OPT_print_prog_name_EQ)) {
     llvm::outs() << GetProgramPath(A->getValue(), TC) << "\n";
     return false;
   }
 
   if (C.getArgs().hasArg(options::OPT_print_libgcc_file_name)) {
+    ToolChain::RuntimeLibType RLT = TC.GetRuntimeLibType(C.getArgs());
+    switch (RLT) {
+    case ToolChain::RLT_CompilerRT:
+      llvm::outs() << TC.getCompilerRT(C.getArgs(), "builtins") << "\n";
+      break;
+    case ToolChain::RLT_Libgcc:
       llvm::outs() << GetFilePath("libgcc.a", TC) << "\n";
+      break;
+    }
     return false;
   }
 
   if (C.getArgs().hasArg(options::OPT_print_multi_lib)) {
     for (const Multilib &Multilib : TC.getMultilibs())
       llvm::outs() << Multilib << "\n";
     return false;
   }

test/Driver/montavista-gcc-toolchain.c

 // Test that the montavista gcc-toolchain is correctly detected
 //
-// RUN: %clang -print-libgcc-file-name 2>&1 \
+// RUN: %clang -rtlib=platform -print-libgcc-file-name 2>&1 \
 // RUN:     --target=i686-montavista-linux \
 // RUN:     --gcc-toolchain=%S/Inputs/montavista_i686_tree/usr \
 // RUN:   | FileCheck %s
 
 // Test for header search toolchain detection.
 // CHECK: montavista_i686_tree/usr/lib/gcc/i686-montavista-linux/4.2.0{{/|\\}}libgcc.a

test/Driver/print-libgcc-file-name-clangrt.c

+// Test that -print-libgcc-file-name correctly respects -rtlib=compiler-rt.
+
+// RUN: %clang -rtlib=compiler-rt -print-libgcc-file-name 2>&1 \
+// RUN:     --target=x86_64-pc-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-CLANGRT-X8664 %s
+// CHECK-CLANGRT-X8664: libclang_rt.builtins-x86_64.a
+
+// RUN: %clang -rtlib=compiler-rt -print-libgcc-file-name 2>&1 \
+// RUN:     --target=i686-pc-linux \
+// RUN:   | FileCheck --check-prefix=CHECK-CLANGRT-I686 %s
+// CHECK-CLANGRT-I686: libclang_rt.builtins-i686.a

test/Driver/print-libgcc-file-name-libgcc.c

+// Test that -print-libgcc-file-name correctly respects -rtlib=libgcc.
+
+// REQUIRES: libgcc
+
+// RUN: %clang -rtlib=libgcc -print-libgcc-file-name 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-LIBGCC %s
+// CHECK-LIBGCC: libgcc.a

test/lit.cfg

 if platform.system() not in ['Windows']:
     config.available_features.add('ansi-escape-sequences')
 
 # Capability to print utf8 to the terminal.
 # Windows expects codepage, unless Wide API.
 if platform.system() not in ['Windows']:
     config.available_features.add('utf8-capable-terminal')
 
+# Support for libgcc runtime. Used to rule out tests that require
+# clang to run with -rtlib=libgcc.
+if platform.system() not in ['Darwin', 'Fuchsia']:
+    config.available_features.add('libgcc')
+
 # Native compilation: Check if triples match.
 # FIXME: Consider cases that target can be executed
 # even if host_triple were different from target_triple.
 if config.host_triple == config.target_triple:
     config.available_features.add("native")
 
 # Case-insensitive file system
 def is_filesystem_case_insensitive():