[DWARF] Make -g with empty assembler source work better.

This was sometimes causing clang or llvm-mc to crash, and in other
cases could emit a bogus DWARF line-table header. I did an interim
patch in r352541; this patch should be a cleaner and more complete
fix, and retains the test.

Addresses PR40538.

Differential Revision: https://reviews.llvm.org/D58750

llvm-svn: 355226

1 files changed, 10 insertions, 1 deletions

diff --git a/clang/tools/driver/cc1as_main.cpp b/clang/tools/driver/cc1as_main.cpp
index 0a38e355c7a..a234ba3fc1b 100644
--- a/clang/tools/driver/cc1as_main.cpp
+++ b/clang/tools/driver/cc1as_main.cpp
@@ -336,7 +336,7 @@ static bool ExecuteAssembler(AssemblerInvocation &Opts,
   SourceMgr SrcMgr;
 
   // Tell SrcMgr about this buffer, which is what the parser will pick up.
-  SrcMgr.AddNewSourceBuffer(std::move(*Buffer), SMLoc());
+  unsigned BufferIndex = SrcMgr.AddNewSourceBuffer(std::move(*Buffer), SMLoc());
 
   // Record the location of the include directories so that the lexer can find
   // it later.
@@ -393,12 +393,21 @@ static bool ExecuteAssembler(AssemblerInvocation &Opts,
     Ctx.setDwarfDebugProducer(StringRef(Opts.DwarfDebugProducer));
   if (!Opts.DebugCompilationDir.empty())
     Ctx.setCompilationDir(Opts.DebugCompilationDir);
+  else {
+    // If no compilation dir is set, try to use the current directory.
+    SmallString<128> CWD;
+    if (!sys::fs::current_path(CWD))
+      Ctx.setCompilationDir(CWD);
+  }
   if (!Opts.DebugPrefixMap.empty())
     for (const auto &KV : Opts.DebugPrefixMap)
       Ctx.addDebugPrefixMapEntry(KV.first, KV.second);
   if (!Opts.MainFileName.empty())
     Ctx.setMainFileName(StringRef(Opts.MainFileName));
   Ctx.setDwarfVersion(Opts.DwarfVersion);
+  if (Opts.GenDwarfForAssembly)
+    Ctx.setGenDwarfRootFile(Opts.InputFile,
+                            SrcMgr.getMemoryBuffer(BufferIndex)->getBuffer());
 
   // Build up the feature string from the target feature list.
   std::string FS;