diff --git a/clang/include/clang/Basic/LangOptions.h b/clang/include/clang/Basic/LangOptions.h
--- a/clang/include/clang/Basic/LangOptions.h
+++ b/clang/include/clang/Basic/LangOptions.h
@@ -479,9 +479,9 @@
   /// The seed used by the randomize structure layout feature.
   std::string RandstructSeed;
 
-  /// Indicates whether the __FILE__ macro should use the target's
-  /// platform-specific file separator or whether it should use the build
-  /// environment's platform-specific file separator.
+  /// Indicates whether to use target's platform-specific file separator when
+  /// __FILE__ macro is used and when concatenating filename with directory or
+  /// to use build environment environment's platform-specific file separator.
   ///
   /// The plaform-specific path separator is the backslash(\) for Windows and
   /// forward slash (/) elsewhere.
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -528,6 +528,7 @@
   // Get absolute path name.
   SourceManager &SM = CGM.getContext().getSourceManager();
   auto &CGO = CGM.getCodeGenOpts();
+  const LangOptions &LO = CGM.getLangOpts();
   std::string MainFileName = CGO.MainFileName;
   if (MainFileName.empty())
     MainFileName = "<stdin>";
@@ -542,9 +543,15 @@
     MainFileDir = std::string(MainFile->getDir().getName());
     if (!llvm::sys::path::is_absolute(MainFileName)) {
       llvm::SmallString<1024> MainFileDirSS(MainFileDir);
-      llvm::sys::path::append(MainFileDirSS, MainFileName);
-      MainFileName =
-          std::string(llvm::sys::path::remove_leading_dotslash(MainFileDirSS));
+      llvm::sys::path::Style Style =
+          LO.UseTargetPathSeparator
+              ? (CGM.getTarget().getTriple().isOSWindows()
+                     ? llvm::sys::path::Style::windows_backslash
+                     : llvm::sys::path::Style::posix)
+              : llvm::sys::path::Style::native;
+      llvm::sys::path::append(MainFileDirSS, Style, MainFileName);
+      MainFileName = std::string(
+          llvm::sys::path::remove_leading_dotslash(MainFileDirSS, Style));
     }
     // If the main file name provided is identical to the input file name, and
     // if the input file is a preprocessed source, use the module name for
@@ -560,7 +567,6 @@
   }
 
   llvm::dwarf::SourceLanguage LangTag;
-  const LangOptions &LO = CGM.getLangOpts();
   if (LO.CPlusPlus) {
     if (LO.ObjC)
       LangTag = llvm::dwarf::DW_LANG_ObjC_plus_plus;
diff --git a/clang/test/CodeGen/debug-info-slash.c b/clang/test/CodeGen/debug-info-slash.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/debug-info-slash.c
@@ -0,0 +1,6 @@
+// RUN: %clang -target x86_64-pc-win32  -ffile-reproducible -emit-llvm -S -g %s -o - | FileCheck --check-prefix=WIN %s
+// RUN: %clang -target x86_64-linux-gnu  -ffile-reproducible -emit-llvm -S -g %s -o - | FileCheck --check-prefix=LINUX %s
+int main() { return 0; }
+
+// WIN:   !DIFile(filename: "{{.*}}\\debug-info-slash.c"
+// LINUX: !DIFile(filename: "{{.*}}/debug-info-slash.c"
diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -791,7 +791,11 @@
     // Don't emit the filename if we're writing to stdout or to /dev/null.
     PathRef = {};
   } else {
-    llvm::sys::path::remove_dots(PathStore, /*remove_dot_dot=*/true);
+    llvm::sys::path::Style Style =
+        llvm::sys::path::is_absolute(PathRef, llvm::sys::path::Style::posix)
+            ? llvm::sys::path::Style::posix
+            : llvm::sys::path::Style::windows_backslash;
+    llvm::sys::path::remove_dots(PathStore, /*remove_dot_dot=*/true, Style);
     PathRef = PathStore;
   }
 
diff --git a/llvm/test/DebugInfo/COFF/build-info.ll b/llvm/test/DebugInfo/COFF/build-info.ll
--- a/llvm/test/DebugInfo/COFF/build-info.ll
+++ b/llvm/test/DebugInfo/COFF/build-info.ll
@@ -10,6 +10,16 @@
 
 ; CHECK: {{.*}} | S_BUILDINFO [size = 8] BuildId = `[[INFO_IDX]]`
 
+; Test path is canonicalized to windows backslash style when output object file
+; name is not starting with '/'.
+; RUN: rm -rf %t-dir
+; RUN: mkdir %t-dir
+; RUN: cd %t-dir
+; RUN: llc -filetype=obj -mtriple i686-pc-windows-msvc %s -o ../build-info.o
+; RUN: llvm-readobj --codeview ../build-info.o | FileCheck %s --check-prefix=OBJ
+
+; OBJ: ObjectName: ..\build-info.o
+
 ; ModuleID = 'D:\src\scopes\foo.cpp'
 source_filename = "D:\5Csrc\5Cscopes\5Cfoo.cpp"
 target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"