[DWARFv5] Allow ".loc 0" to refer to the root file.

DWARF v5 explicitly represents file #0 in the line table.  Prior
versions did not, so ".loc 0" is still an error in those cases.

Differential Revision: https://reviews.llvm.org/D48452

llvm-svn: 335350

1 files changed, 5 insertions, 3 deletions

diff --git a/llvm/lib/MC/MCContext.cpp b/llvm/lib/MC/MCContext.cpp
index 5c4d67b10dd..e4f90f4987a 100644
--- a/llvm/lib/MC/MCContext.cpp
+++ b/llvm/lib/MC/MCContext.cpp
@@ -556,11 +556,13 @@ Expected<unsigned> MCContext::getDwarfFile(StringRef Directory,
 /// isValidDwarfFileNumber - takes a dwarf file number and returns true if it
 /// currently is assigned and false otherwise.
 bool MCContext::isValidDwarfFileNumber(unsigned FileNumber, unsigned CUID) {
-  const SmallVectorImpl<MCDwarfFile> &MCDwarfFiles = getMCDwarfFiles(CUID);
-  if (FileNumber == 0 || FileNumber >= MCDwarfFiles.size())
+  const MCDwarfLineTable &LineTable = getMCDwarfLineTable(CUID);
+  if (FileNumber == 0)
+    return getDwarfVersion() >= 5 && LineTable.hasRootFile();
+  if (FileNumber >= LineTable.getMCDwarfFiles().size())
     return false;
 
-  return !MCDwarfFiles[FileNumber].Name.empty();
+  return !LineTable.getMCDwarfFiles()[FileNumber].Name.empty();
 }
 
 /// Remove empty sections from SectionStartEndSyms, to avoid generating