[DarwinDriver] Use -lto_library to specify the path for libLTO.dylib

[bruno]

Summary

Usually, when using LTO with a clang installation newer than the system one, there's a libLTO.dylib version mismatch and LTO fails. One solution to this is to make ld point to the right libLTO.dylib by changing DYLD_LIBRARY_PATH.

However, ld64 supports specifying the complete path to the desired libLTO.dylib through the -lto_library option. This patch adds support for the clang driver to use this option whenever it's capable of finding a libLTO.dylib in clang's installed library directory. This way, we don't need to rely on DYLD_LIBRARY_PATH nor get caught by version mismatches.

[dexonsmith]

The code LGTM, but there ought to be a way to add a LIT test for this.

Looking for -object_path_lto, I found this:

RUN: %clang -target x86_64-apple-darwin10 -### %s \
RUN: -mlinker-version=117 -flto 2> %t.log
RUN: cat %t.log
RUN: FileCheck -check-prefix=LINK_OBJECT_LTO_PATH %s < %t.log

LINK_OBJECT_LTO_PATH: {{ld(.exe)?"}}

// LINK_OBJECT_LTO_PATH: "-object_path_lto"

in test/Driver/darwin-ld.c. Can you add a similar test there?

[bruno]

Added test per Duncan's comment.

[dexonsmith]

Sorry for the review fragmentation, but I just noticed there's no test
for the new warning. Can you add one? After that, LGTM.

[bruno]

Done way back in r248932

include/clang/Basic/DiagnosticDriverKinds.td

 def err_drv_no_neon_modifier : Error<"[no]neon is not accepted as modifier, please use [no]simd instead">;
 
 def warn_O4_is_O3 : Warning<"-O4 is equivalent to -O3">, InGroup<Deprecated>;
+def warn_lto_libpath : Warning<"libLTO.dylib relative to clang installed dir not found; using 'ld' default search path instead">;
 def warn_drv_optimization_value : Warning<"optimization level '%0' is not supported; using '%1%2' instead">,
   InGroup<InvalidCommandLineArgument>;
 def warn_ignored_gcc_optimization : Warning<"optimization flag '%0' is not supported">,

lib/Driver/Tools.cpp

                    options::OPT_fno_application_extension, false))
     CmdArgs.push_back("-application_extension");
 
-  // If we are using LTO, then automatically create a temporary file path for
-  // the linker to use, so that it's lifetime will extend past a possible
-  // dsymutil step.
-  if (Version[0] >= 116 && D.IsUsingLTO(Args) && NeedsTempPath(Inputs)) {
-    const char *TmpPath = C.getArgs().MakeArgString(
-        D.GetTemporaryPath("cc", types::getTypeTempSuffix(types::TY_Object)));
-    C.addTempFile(TmpPath);
-    CmdArgs.push_back("-object_path_lto");
-    CmdArgs.push_back(TmpPath);
+  if (D.IsUsingLTO(Args)) {
+    // If we are using LTO, then automatically create a temporary file path for
+    // the linker to use, so that it's lifetime will extend past a possible
+    // dsymutil step.
+    if (Version[0] >= 116 && NeedsTempPath(Inputs)) {
+      const char *TmpPath = C.getArgs().MakeArgString(
+          D.GetTemporaryPath("cc", types::getTypeTempSuffix(types::TY_Object)));
+      C.addTempFile(TmpPath);
+      CmdArgs.push_back("-object_path_lto");
+      CmdArgs.push_back(TmpPath);
+    }
+
+    // Use -lto_library option to specify the libLTO.dylib path. Try to find
+    // it in clang installed libraries. If not found, the option is not used
+    // and 'ld' will use its default mechanism to search for libLTO.dylib.
+    if (Version[0] >= 133) {
+      // Search for libLTO in <InstalledDir>/../lib/libLTO.dylib
+      StringRef P = llvm::sys::path::parent_path(D.getInstalledDir());
+      SmallString<128> LibLTOPath(P);
+      llvm::sys::path::append(LibLTOPath, "lib");
+      llvm::sys::path::append(LibLTOPath, "libLTO.dylib");
+      if (llvm::sys::fs::exists(LibLTOPath)) {
+        CmdArgs.push_back("-lto_library");
+        CmdArgs.push_back(C.getArgs().MakeArgString(LibLTOPath));
+      } else {
+        D.Diag(diag::warn_lto_libpath);
+      }
+    }
   }
 
   // Derived from the "link" spec.

test/Driver/darwin-ld.c

 // LINK_OBJECT_LTO_PATH: {{ld(.exe)?"}}
 // LINK_OBJECT_LTO_PATH: "-object_path_lto"
 
+// RUN: %clang -target x86_64-apple-darwin10 -### %s \
+// RUN:   -mlinker-version=133 -flto 2> %t.log
+// RUN: cat %t.log
+// RUN: FileCheck -check-prefix=LINK_LTOLIB_PATH %s < %t.log
+//
+// LINK_LTOLIB_PATH: {{ld(.exe)?"}}
+// LINK_LTOLIB_PATH: "-lto_library"
+
 // RUN: %clang -target x86_64-apple-darwin10 -### %t.o \
 // RUN:   -force_load a -force_load b 2> %t.log
 // RUN: cat %t.log