[Driver] Support direct split DWARF emission for Fuchsia

[phosek]

Summary

This enables the driver support for direct split DWARF emission for
Fuchsia in addition to Linux.

[phosek]

I'm fine moving the test to test/Driver/split-debug.c if you prefer to have all target tests in a single file.

[echristo]

I'm ok with the "here are a bunch of fuchsia tests" file :)

-eric

clang/cmake/caches/Fuchsia-stage2.cmake

 set(LLVM_INSTALL_TOOLCHAIN_ONLY ON CACHE BOOL "")
 set(LLVM_TOOLCHAIN_TOOLS
   dsymutil
   llc
   llvm-ar
   llvm-cov
   llvm-cxxfilt
   llvm-dwarfdump
+  llvm-dwp
   llvm-lib
   llvm-nm
   llvm-objcopy
   llvm-objdump
   llvm-profdata
   llvm-ranlib
   llvm-readelf
   llvm-readobj

clang/lib/Driver/ToolChains/Clang.cpp

if (checkDebugInfoOption(A, Args, D, TC)) {
         DebugInfoKind = codegenoptions::LimitedDebugInfo;
         CmdArgs.push_back("-dwarf-ext-refs");
         CmdArgs.push_back("-fmodule-format=obj");
       }
     }
 
   // -gsplit-dwarf should turn on -g and enable the backend dwarf
   // splitting and extraction.
-  // FIXME: Currently only works on Linux.
-  if (T.isOSLinux()) {
+  // FIXME: Currently only works on Linux and Fuchsia.
+  if (T.isOSLinux() || T.isOSFuchsia()) {
     if (!SplitDWARFInlining)
       CmdArgs.push_back("-fno-split-dwarf-inlining");
 
     if (SplitDWARFArg) {
       if (DebugInfoKind == codegenoptions::NoDebugInfo)
         DebugInfoKind = codegenoptions::LimitedDebugInfo;
       CmdArgs.push_back("-enable-split-dwarf");
     }
else
     EmitCodeView = Args.hasArg(options::OPT_gcodeview);
 
   const Arg *SplitDWARFArg = nullptr;
   RenderDebugOptions(TC, D, RawTriple, Args, EmitCodeView, IsWindowsMSVC,
                      CmdArgs, DebugInfoKind, SplitDWARFArg);
 
   // Add the split debug info name to the command lines here so we
   // can propagate it to the backend.
-  bool SplitDWARF = SplitDWARFArg && RawTriple.isOSLinux() &&
+  bool SplitDWARF = SplitDWARFArg &&
+                    (RawTriple.isOSLinux() || RawTriple.isOSFuchsia()) &&
                     (isa<AssembleJobAction>(JA) || isa<CompileJobAction>(JA) ||
                      isa<BackendJobAction>(JA));
   const char *SplitDWARFOut;
   if (SplitDWARF) {
     CmdArgs.push_back("-split-dwarf-file");
     SplitDWARFOut = SplitDebugName(Args, Input);
     CmdArgs.push_back(SplitDWARFOut);
   }
CollectArgsForIntegratedAssembler(C, Args, CmdArgs,
                                     getToolChain().getDriver());
 
   Args.AddAllArgs(CmdArgs, options::OPT_mllvm);
 
   assert(Output.isFilename() && "Unexpected lipo output.");
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());
 
+  const llvm::Triple &T = getToolChain().getTriple();
   if (Args.hasArg(options::OPT_gsplit_dwarf) &&
-      getToolChain().getTriple().isOSLinux()) {
+      (T.isOSLinux() || T.isOSFuchsia())) {
     CmdArgs.push_back("-split-dwarf-file");
     CmdArgs.push_back(SplitDebugName(Args, Input));
   }
 
   assert(Input.isFilename() && "Invalid input.");
   CmdArgs.push_back(Input.getFilename());
 
   const char *Exec = getToolChain().getDriver().getClangProgramPath();

clang/test/Driver/fuchsia.c

 
 // RUN: %clang %s -### --target=x86_64-fuchsia \
 // RUN:     -flto=thin -flto-jobs=8 2>&1 \
 // RUN:     -fuse-ld=lld \
 // RUN:     | FileCheck %s -check-prefix=CHECK-THINLTO
 // CHECK-THINLTO: "-plugin-opt=mcpu=x86-64"
 // CHECK-THINLTO: "-plugin-opt=thinlto"
 // CHECK-THINLTO: "-plugin-opt=jobs=8"
+
+// RUN: %clang %s -### --target=x86_64-fuchsia \
+// RUN:     -gsplit-dwarf -c %s 2>&1 \
+// RUN:     | FileCheck %s -check-prefix=CHECK-SPLIT-DWARF
+// CHECK-SPLIT-DWARF: "-split-dwarf-file" "fuchsia.dwo"