add test

Author: Jinjie-Huang

bolt/lib/Core/BinaryContext.cpp

@@ -1638,8 +1638,12 @@ void BinaryContext::preprocessDWODebugInfo() {
         sys::path::append(AbsolutePath, opts::CompDirOverride);
         sys::path::append(AbsolutePath, DWOName);
       } else if (!sys::fs::exists(DwarfUnit->getCompilationDir()) &&
-                 sys::fs::exists(DWOName))
+                 sys::fs::exists(DWOName)) {
+        this->outs()
+            << "BOLT-WARNING: Debug Fission: Debug Compilation Dir wrong for "
+            << DWOName << ". DWO Name will be directly used for retrieving.\n";
         AbsolutePath = DWOName;
+      }
       DWARFUnit *DWOCU =
           DwarfUnit->getNonSkeletonUnitDIE(false, AbsolutePath).getDwarfUnit();
       if (!DWOCU->isDWOUnit()) {

bolt/lib/Rewrite/DWARFRewriter.cpp

@@ -1851,8 +1851,8 @@ void DWARFRewriter::writeDWOFiles(
     CompDir = opts::DwarfOutputPath.c_str();
   else if (!opts::CompDirOverride.empty())
     CompDir = opts::CompDirOverride;
-  else if (!sys::fs::exists(CompDir))
-    CompDir = ".";
+  else if (!sys::fs::exists(CompDir) && sys::fs::exists(DWOName))
+    CompDir = "";
 
   SmallString<16> AbsolutePath;
   sys::path::append(AbsolutePath, CompDir);

bolt/test/dwo-name-retrieving.c

@@ -0,0 +1,16 @@
+// This test checks retrieving dwo file diercetly with dwo name,
+// if the Debug Compilation Dir does not exist.
+
+int main() { return 0; }
+
+// RUN: rm -rf %t && mkdir -p %t && cd %t
+// RUN: %clang %cflags -g -gsplit-dwarf -fdebug-compilation-dir=/path/does/not/exist %s -o main.exe
+// RUN: llvm-bolt %t/main.exe -o %t/main.exe.bolt -update-debug-sections  2>&1 | FileCheck %s -check-prefix=NOT-EXIST
+
+// NOT-EXIST: BOLT-WARNING: Debug Fission: Debug Compilation Dir wrong for
+
+// RUN: rm -rf %t && mkdir -p %t && cd %t
+// RUN: %clang %cflags -g -gsplit-dwarf -fdebug-compilation-dir=/path/does/not/exist %s -o %t/main.exe
+// RUN: llvm-bolt %t/main.exe -o %t/main.exe.bolt -update-debug-sections  2>&1 | FileCheck %s -check-prefix=FOUND
+
+// FOUND-NOT: Debug Fission: DWO debug information for