[BOLT][DWARF] Get DWO file via relative path if the CompilationDir does not exist (#154515)

In distributed builds, the DWARF CompilationDir is often invalid,
causing BOLT to fail when locating DWO files. If the default path does
not exist, it seems better to consider the DWOName as a relative path in
this case.

The implementation of this patch will try to search for the DWO file in
the following order:
1. CompDirOverride + DWOName (if CompDirOverride specified)
2. CompilationDir + DWOName (if CompilationDir exists)
3. **Current directory + DWOName (relative path as a fallback)**

This patch also fixes a crash that occurs when DWOName is an absolute path and a DWP file is provided.

Author: Jinjie-Huang

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.