[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, 6 insertions, 5 deletions

diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index a66a4eb29af..4b487825935 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -845,9 +845,13 @@ bool AsmParser::enabledGenDwarfForAssembly() {
   // If we haven't encountered any .file directives (which would imply that
   // the assembler source was produced with debug info already) then emit one
   // describing the assembler source file itself.
-  if (getContext().getGenDwarfFileNumber() == 0)
+  if (getContext().getGenDwarfFileNumber() == 0) {
+    const MCDwarfFile &RootFile =
+        getContext().getMCDwarfLineTable(/*CUID=*/0).getRootFile();
     getContext().setGenDwarfFileNumber(getStreamer().EmitDwarfFileDirective(
-        0, StringRef(), getContext().getMainFileName()));
+        /*CUID=*/0, getContext().getCompilationDir(), RootFile.Name,
+        RootFile.Checksum, RootFile.Source));
+  }
   return true;
 }
 
@@ -900,9 +904,6 @@ bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
       eatToEndOfStatement();
   }
 
-  // Make sure we get proper DWARF even for empty files.
-  (void)enabledGenDwarfForAssembly();
-
   getTargetParser().onEndOfFile();
   printPendingErrors();