[MCDwarf] Respect -fdebug-prefix-map= for generated assembly debug info (DWARF v5)

For generated assembly debug info, MCDwarfLineTableHeader::CompilationDir is an
unmapped path set in MCContext::setGenDwarfRootFile. Remap it.

A relative destination path of -fdebug-prefix-map= exposes a llvm-dwarfdump bug
which joins relative DW_AT_comp_dir and directories[0].

Fix https://github.com/llvm/llvm-project/issues/56609

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D131749

1 files changed, 9 insertions, 3 deletions

diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index 91a636b..cc1a662 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -416,9 +416,15 @@ void MCDwarfLineTableHeader::emitV5FileDirTables(
                                     : dwarf::DW_FORM_string);
   MCOS->emitULEB128IntValue(MCDwarfDirs.size() + 1);
   // Try not to emit an empty compilation directory.
-  const StringRef CompDir = CompilationDir.empty()
-                                ? MCOS->getContext().getCompilationDir()
-                                : StringRef(CompilationDir);
+  SmallString<256> Dir;
+  StringRef CompDir = MCOS->getContext().getCompilationDir();
+  if (!CompilationDir.empty()) {
+    Dir = CompilationDir;
+    MCOS->getContext().remapDebugPath(Dir);
+    CompDir = Dir.str();
+    if (LineStr)
+      CompDir = LineStr->getSaver().save(CompDir);
+  }
   if (LineStr) {
     // Record path strings, emit references here.
     LineStr->emitRef(MCOS, CompDir);