[BOLT][DWARF] Get DWO file via relative path if the CompilationDir does not exist

bolt/lib/Core/BinaryContext.cpp

@@ -33,6 +33,7 @@
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Regex.h"
 #include <algorithm>
 #include <functional>
@@ -1632,19 +1633,29 @@ void BinaryContext::preprocessDWODebugInfo() {
           DwarfUnit->getUnitDIE().find(
               {dwarf::DW_AT_dwo_name, dwarf::DW_AT_GNU_dwo_name}),
           "");
-      SmallString<16> AbsolutePath;
+      SmallString<16> AbsolutePath(DWOName);
+      std::string DWOCompDir = DwarfUnit->getCompilationDir();
       if (!opts::CompDirOverride.empty()) {
-        sys::path::append(AbsolutePath, opts::CompDirOverride);
-        sys::path::append(AbsolutePath, DWOName);
+        DWOCompDir = opts::CompDirOverride;
+      } else if (!sys::fs::exists(DWOCompDir) && sys::fs::exists(DWOName)) {
+        DWOCompDir = ".";
+        this->outs()
+            << "BOLT-WARNING: Debug Fission: Debug Compilation Directory of "
+            << DWOName
+            << " does not exist. Relative path will be used to process .dwo "
+               "files.\n";
       }
+      // Prevent failures when DWOName is already an absolute path.
+      sys::fs::make_absolute(DWOCompDir, AbsolutePath);
       DWARFUnit *DWOCU =
           DwarfUnit->getNonSkeletonUnitDIE(false, AbsolutePath).getDwarfUnit();
       if (!DWOCU->isDWOUnit()) {
         this->outs()
             << "BOLT-WARNING: Debug Fission: DWO debug information for "
             << DWOName
             << " was not retrieved and won't be updated. Please check "
-               "relative path.\n";
+               "relative path or use '--comp-dir-override' to specify the base "
+               "location.\n";
         continue;
       }
       DWOCUs[*DWOId] = DWOCU;

bolt/lib/Rewrite/DWARFRewriter.cpp

@@ -1846,15 +1846,16 @@ void DWARFRewriter::writeDWOFiles(
   }
 
   std::string CompDir = CU.getCompilationDir();
+  SmallString<16> AbsolutePath(DWOName);
 
   if (!opts::DwarfOutputPath.empty())
     CompDir = opts::DwarfOutputPath.c_str();
   else if (!opts::CompDirOverride.empty())
     CompDir = opts::CompDirOverride;
-
-  SmallString<16> AbsolutePath;
-  sys::path::append(AbsolutePath, CompDir);
-  sys::path::append(AbsolutePath, DWOName);
+  else if (!sys::fs::exists(CompDir))
+    CompDir = ".";
+  // Prevent failures when DWOName is already an absolute path.
+  sys::fs::make_absolute(CompDir, AbsolutePath);
 
   std::error_code EC;
   std::unique_ptr<ToolOutputFile> TempOut =

bolt/test/dwo-name-retrieving.test

@@ -0,0 +1,19 @@
+## Test DWO retrieval via relative path with a missing CompDir.
+## Also, verify no crash for an absolute DWOName path.
+
+## The case where DWOName is a relative path, and debug compilation directory does not exist.
+# RUN: rm -rf %t && mkdir -p %t && cd %t
+# RUN: %clang %cflags -g -gsplit-dwarf -fdebug-compilation-dir=/path/does/not/exist %p/Inputs/hello.c -o main.exe
+# RUN: llvm-bolt %t/main.exe -o %t/main.exe.bolt -update-debug-sections 2>&1 | FileCheck %s -check-prefix=DWO-NAME-REL
+
+# DWO-NAME-REL: BOLT-WARNING: Debug Fission: Debug Compilation Directory of main.exe-hello.dwo does not exist.
+# DWO-NAME-REL-NOT: Debug Fission: DWO debug information for
+
+## The case where DWOName is a absolute path, and a dwp file is provided.
+# RUN: %clang %cflags -g -gsplit-dwarf %p/Inputs/hello.c -o %t/main.exe
+# RUN: llvm-dwp -e %t/main.exe -o  %t/main.exe.dwp
+# RUN: llvm-bolt %t/main.exe -o %t/main.exe.bolt -update-debug-sections -dwp=%t/main.exe.dwp 2>&1 | FileCheck %s -check-prefix=DWO-NAME-ABS
+
+# DWO-NAME-ABS-NOT: BOLT-WARNING: Debug Fission: Debug Compilation Directory of {{.*}}/main.exe-hello.dwo does not exist.
+# DWO-NAME-ABS-NOT: Debug Fission: DWO debug information for
+# DWO-NAME-ABS-NOT: Assertion `FD >= 0 && "File not yet open!"' failed.