Suppress -Wliblto warning when -flto is not present

[rnk]

Summary

Without -flto, it's unlikely that users will experience LLVM version
skew. The system installation of libLTO should be able to handle any
pre-compiled LLVM bitcode from static archives.

[rnk]

Superseded by D26984

lib/Driver/Tools.cpp

if (Version[0] >= 133) {
     // Search for libLTO in <InstalledDir>/../lib/libLTO.dylib
     StringRef P = llvm::sys::path::parent_path(D.Dir);
     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 {
+    } else if (D.isUsingLTO()) {
+      // Warn if we're using LTO with the system version of libLTO. It might not
+      // understand LLVM bitcode generated by our version of LLVM.
       D.Diag(diag::warn_drv_lto_libpath);
     }
   }
 
   // ld64 version 262 and above run the deduplicate pass by default.
   if (Version[0] >= 262 && shouldLinkerNotDedup(C.getJobs().empty(), Args))
     CmdArgs.push_back("-no_deduplicate");
 

test/Driver/darwin-ld-lto.c

-// REQUIRES: system-darwin
-
 // Check that ld gets "-lto_library" and warnings about libLTO.dylib path.
 
 // RUN: mkdir -p %T/bin
 // RUN: mkdir -p %T/lib
 // RUN: touch %T/lib/libLTO.dylib
 // RUN: %clang -target x86_64-apple-darwin10 -### %s \
 // RUN:   -ccc-install-dir %T/bin -mlinker-version=133 2> %t.log
 // RUN: FileCheck -check-prefix=LINK_LTOLIB_PATH %s -input-file %t.log
 //
 // LINK_LTOLIB_PATH: {{ld(.exe)?"}}
 // LINK_LTOLIB_PATH: "-lto_library"
 
-// RUN: %clang -target x86_64-apple-darwin10 -### %s \
+// Only warn if -flto is on the command line.
+//
+// RUN: %clang -target x86_64-apple-darwin10 -### %s -flto \
 // RUN:   -ccc-install-dir %S/dummytestdir -mlinker-version=133 2> %t.log
 // RUN: FileCheck -check-prefix=LINK_LTOLIB_PATH_WRN %s -input-file %t.log
 //
 // LINK_LTOLIB_PATH_WRN: warning: libLTO.dylib relative to clang installed dir not found; using 'ld' default search path instead
 
+// Don't warn if -flto isn't present of -Wno-liblto is present.
+//
+// RUN: %clang -target x86_64-apple-darwin10 -### %s \
+// RUN:   -ccc-install-dir %S/dummytestdir -mlinker-version=133 2> %t.log
+// RUN: FileCheck -check-prefix=LINK_LTOLIB_PATH_NOWRN %s -input-file %t.log
+//
 // RUN: %clang -target x86_64-apple-darwin10 -### %s \
 // RUN:   -ccc-install-dir %S/dummytestdir -mlinker-version=133 -Wno-liblto 2> %t.log
 // RUN: FileCheck -check-prefix=LINK_LTOLIB_PATH_NOWRN %s -input-file %t.log
 //
 // LINK_LTOLIB_PATH_NOWRN-NOT: warning: libLTO.dylib relative to clang installed dir not found; using 'ld' default search path instead