Add an option to support debug fission on implicit ThinLTO.

Summary:
This adds an option -gsplit-dwarf=<arg>. LLVM can create .dwo files in the given directory
during the implicit ThinLTO link stage.

Reviewers: tejohnson, dblaikie, pcc

Reviewed By: pcc

Subscribers: steven_wu, aprantl, JDevlieghere, yunlian, probinson, mehdi_amini, inglorion, cfe-commits

Differential Revision: https://reviews.llvm.org/D44788

llvm-svn: 335546

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -416,6 +416,12 @@ void tools::AddGoldPlugin(const ToolChain &ToolChain, const ArgList &Args,
       CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=O") + OOpt));
   }
 
+  if (Args.hasArg(options::OPT_gsplit_dwarf)) {
+    CmdArgs.push_back(
+        Args.MakeArgString(Twine("-plugin-opt=dwo_dir=") +
+            Output.getFilename() + "_dwo"));
+  }
+
   if (IsThinLTO)
     CmdArgs.push_back("-plugin-opt=thinlto");
 

clang/test/Driver/lto-dwo.c

@@ -0,0 +1,6 @@
+// Confirm that -gsplit-dwarf=DIR is passed to linker
+
+// RUN: %clang -target x86_64-unknown-linux -### %s -flto=thin -gsplit-dwarf -o a.out 2> %t
+// RUN: FileCheck -check-prefix=CHECK-LINK-DWO-DIR-DEFAULT < %t %s
+//
+// CHECK-LINK-DWO-DIR-DEFAULT: "-plugin-opt=dwo_dir=a.out_dwo"