Revert "[clang] - Simplify tools::SplitDebugName."

This reverts commit r347035 as it introduced assertion failures under
certain conditions. More information can be found here:
https://reviews.llvm.org/rL347035

llvm-svn: 347676
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 6b2083c..c0f3454 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3966,7 +3966,7 @@
   const char *SplitDWARFOut;
   if (SplitDWARF) {
     CmdArgs.push_back("-split-dwarf-file");
-    SplitDWARFOut = SplitDebugName(Args, Output);
+    SplitDWARFOut = SplitDebugName(Args, Input, Output);
     CmdArgs.push_back(SplitDWARFOut);
   }
 
@@ -5933,7 +5933,7 @@
   if ((getDebugFissionKind(D, Args, A) == DwarfFissionKind::Split) &&
       (T.isOSLinux() || T.isOSFuchsia())) {
     CmdArgs.push_back("-split-dwarf-file");
-    CmdArgs.push_back(SplitDebugName(Args, Output));
+    CmdArgs.push_back(SplitDebugName(Args, Input, Output));
   }
 
   assert(Input.isFilename() && "Invalid input.");
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 03298a1..e802ce7 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -808,15 +808,26 @@
   return false;
 }
 
-const char *tools::SplitDebugName(const ArgList &Args,
+const char *tools::SplitDebugName(const ArgList &Args, const InputInfo &Input,
                                   const InputInfo &Output) {
   if (Arg *A = Args.getLastArg(options::OPT_gsplit_dwarf_EQ))
     if (StringRef(A->getValue()) == "single")
       return Args.MakeArgString(Output.getFilename());
 
-  SmallString<128> T(Output.getFilename());
-  llvm::sys::path::replace_extension(T, "dwo");
-  return Args.MakeArgString(T);
+  Arg *FinalOutput = Args.getLastArg(options::OPT_o);
+  if (FinalOutput && Args.hasArg(options::OPT_c)) {
+    SmallString<128> T(FinalOutput->getValue());
+    llvm::sys::path::replace_extension(T, "dwo");
+    return Args.MakeArgString(T);
+  } else {
+    // Use the compilation dir.
+    SmallString<128> T(
+        Args.getLastArgValue(options::OPT_fdebug_compilation_dir));
+    SmallString<128> F(llvm::sys::path::stem(Input.getBaseInput()));
+    llvm::sys::path::replace_extension(F, "dwo");
+    T += F;
+    return Args.MakeArgString(F);
+  }
 }
 
 void tools::SplitDebugInfo(const ToolChain &TC, Compilation &C, const Tool &T,
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.h b/clang/lib/Driver/ToolChains/CommonArgs.h
index 3704b2e..fe82aa6 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.h
+++ b/clang/lib/Driver/ToolChains/CommonArgs.h
@@ -63,7 +63,7 @@
                         const Tool &T);
 
 const char *SplitDebugName(const llvm::opt::ArgList &Args,
-                           const InputInfo &Output);
+                           const InputInfo &Input, const InputInfo &Output);
 
 void SplitDebugInfo(const ToolChain &TC, Compilation &C, const Tool &T,
                     const JobAction &JA, const llvm::opt::ArgList &Args,
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index 1af9935..d7797d9 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -817,7 +817,7 @@
   if (Args.hasArg(options::OPT_gsplit_dwarf) &&
       getToolChain().getTriple().isOSLinux())
     SplitDebugInfo(getToolChain(), C, *this, JA, Args, Output,
-                   SplitDebugName(Args, Output));
+                   SplitDebugName(Args, Inputs[0], Output));
 }
 
 namespace {
diff --git a/clang/lib/Driver/ToolChains/MinGW.cpp b/clang/lib/Driver/ToolChains/MinGW.cpp
index 836d7c1..db468fd 100644
--- a/clang/lib/Driver/ToolChains/MinGW.cpp
+++ b/clang/lib/Driver/ToolChains/MinGW.cpp
@@ -54,7 +54,7 @@
 
   if (Args.hasArg(options::OPT_gsplit_dwarf))
     SplitDebugInfo(getToolChain(), C, *this, JA, Args, Output,
-                   SplitDebugName(Args, Output));
+                   SplitDebugName(Args, Inputs[0], Output));
 }
 
 void tools::MinGW::Linker::AddLibGCC(const ArgList &Args,