Index: lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- lib/CodeGen/CGDebugInfo.cpp
+++ lib/CodeGen/CGDebugInfo.cpp
@@ -181,8 +181,7 @@
   SourceManager &SM = CGM.getContext().getSourceManager();
   auto *Scope = cast<llvm::DIScope>(LexicalBlockStack.back());
   PresumedLoc PCLoc = SM.getPresumedLoc(CurLoc);
-
-  if (PCLoc.isInvalid() || Scope->getFilename() == PCLoc.getFilename())
+  if (PCLoc.isInvalid() || Scope->getFile() == getOrCreateFile(CurLoc))
     return;
 
   if (auto *LBF = dyn_cast<llvm::DILexicalBlockFile>(Scope)) {
@@ -410,13 +409,13 @@
   SourceManager &SM = CGM.getContext().getSourceManager();
   PresumedLoc PLoc = SM.getPresumedLoc(Loc);
 
-  if (PLoc.isInvalid() || StringRef(PLoc.getFilename()).empty())
+  StringRef FileName = PLoc.getFilename();
+  if (PLoc.isInvalid() || FileName.empty())
     // If the location is not valid then use main input file.
     return getOrCreateMainFile();
 
   // Cache the results.
-  const char *fname = PLoc.getFilename();
-  auto It = DIFileCache.find(fname);
+  auto It = DIFileCache.find(FileName.data());
 
   if (It != DIFileCache.end()) {
     // Verify that the information still exists.
@@ -431,11 +430,41 @@
   if (CSKind)
     CSInfo.emplace(*CSKind, Checksum);
 
-  llvm::DIFile *F = DBuilder.createFile(
-      remapDIPath(PLoc.getFilename()), remapDIPath(getCurrentDirname()), CSInfo,
-      getSource(SM, SM.getFileID(Loc)));
+  StringRef Dir;
+  StringRef File;
+  std::string RemappedFile = remapDIPath(FileName);
+  std::string CurDir = remapDIPath(getCurrentDirname());
+  SmallString<128> DirBuf;
+  SmallString<128> FileBuf;
+  if (llvm::sys::path::is_absolute(RemappedFile)) {
+    // Strip the common prefix (if it is more than just "/") from current
+    // directory and FileName for a more space-efficient encoding.
+    auto FileIt = llvm::sys::path::begin(RemappedFile);
+    auto FileE = llvm::sys::path::end(RemappedFile);
+    auto CurDirIt = llvm::sys::path::begin(CurDir);
+    auto CurDirE = llvm::sys::path::end(CurDir);
+    for (; CurDirIt != CurDirE && *CurDirIt == *FileIt; ++CurDirIt, ++FileIt)
+      llvm::sys::path::append(DirBuf, *CurDirIt);
+    if (std::distance(llvm::sys::path::begin(CurDir), CurDirIt) == 1) {
+      // The common prefix only the root; stripping it would cause
+      // LLVM diagnostic locations to be more confusing.
+      Dir = {};
+      File = RemappedFile;
+    } else {
+      for (; FileIt != FileE; ++FileIt)
+        llvm::sys::path::append(FileBuf, *FileIt);
+      Dir = DirBuf;
+      File = FileBuf;
+    }
+  } else {
+    Dir = CurDir;
+    File = RemappedFile;
+  }
+  llvm::DIFile *F =
+      DBuilder.createFile(File, Dir, CSInfo,
+                          getSource(SM, SM.getFileID(Loc)));
 
-  DIFileCache[fname].reset(F);
+  DIFileCache[FileName.data()].reset(F);
   return F;
 }
 
Index: lib/CodeGen/CodeGenAction.cpp
===================================================================
--- lib/CodeGen/CodeGenAction.cpp
+++ lib/CodeGen/CodeGenAction.cpp
@@ -549,12 +549,16 @@
   SourceLocation DILoc;
 
   if (D.isLocationAvailable()) {
-    D.getLocation(&Filename, &Line, &Column);
-    const FileEntry *FE = FileMgr.getFile(Filename);
-    if (FE && Line > 0) {
-      // If -gcolumn-info was not used, Column will be 0. This upsets the
-      // source manager, so pass 1 if Column is not set.
-      DILoc = SourceMgr.translateFileLineCol(FE, Line, Column ? Column : 1);
+    D.getLocation(Filename, Line, Column);
+    if (Line > 0) {
+      const FileEntry *FE = FileMgr.getFile(Filename);
+      if (!FE)
+        FE = FileMgr.getFile(D.getAbsolutePath());
+      if (FE) {
+        // If -gcolumn-info was not used, Column will be 0. This upsets the
+        // source manager, so pass 1 if Column is not set.
+        DILoc = SourceMgr.translateFileLineCol(FE, Line, Column ? Column : 1);
+      }
     }
     BadDebugInfo = DILoc.isInvalid();
   }
Index: test/CodeGen/debug-info-abspath.c
===================================================================
--- test/CodeGen/debug-info-abspath.c
+++ test/CodeGen/debug-info-abspath.c
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -debug-info-kind=limited -triple %itanium_abi_triple \
+// RUN:   %s -emit-llvm -o - | FileCheck %s
+
+// RUN: cp %s %t.c
+// RUN: %clang_cc1 -debug-info-kind=limited -triple %itanium_abi_triple \
+// RUN:   %t.c -emit-llvm -o - | FileCheck %s --check-prefix=INTREE
+void foo() {}
+
+// Since %s is an absolute path, directory should be a nonempty
+// prefix, but the CodeGen part should be part of the filename.
+
+// CHECK: DIFile(filename: "{{.*}}CodeGen{{.*}}debug-info-abspath.c"
+// CHECK-SAME:   directory: "{{.+}}")
+
+// INTREE: DIFile({{.*}}directory: "{{.+}}CodeGen{{.*}}")
Index: test/CodeGen/debug-prefix-map.c
===================================================================
--- test/CodeGen/debug-prefix-map.c
+++ test/CodeGen/debug-prefix-map.c
@@ -17,18 +17,22 @@
 }
 
 // CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{/|\\5C}}<stdin>"
-// CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}"
-// CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{[/\\]}}Inputs/stdio.h"
+// CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}",
+// CHECK-NO-MAIN-FILE-NAME-SAME:    directory: "")
+// CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{[/\\]}}Inputs/stdio.h",
+// CHECK-NO-MAIN-FILE-NAME-SAME:    directory: "")
 // CHECK-NO-MAIN-FILE-NAME-NOT: !DIFile(filename:
 
 // CHECK-EVIL: !DIFile(filename: "/var=empty{{[/\\]}}{{.*}}"
-// CHECK-EVIL: !DIFile(filename: "/var=empty{{[/\\]}}Inputs/stdio.h"
+// CHECK-EVIL: !DIFile(filename: "/var=empty{{[/\\]}}{{.*}}Inputs/stdio.h",
+// CHECK-EVIL-SAME:    directory: "")
 // CHECK-EVIL-NOT: !DIFile(filename:
 
 // CHECK: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}"
-// CHECK: !DIFile(filename: "/var/empty{{[/\\]}}Inputs/stdio.h"
+// CHECK: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}Inputs/stdio.h",
+// CHECK-SAME:    directory: "")
 // CHECK-NOT: !DIFile(filename:
 
-// CHECK-COMPILATION-DIR: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}", directory: "/var/empty")
-// CHECK-COMPILATION-DIR: !DIFile(filename: "/var/empty{{[/\\]}}Inputs/stdio.h", directory: "/var/empty")
+// CHECK-COMPILATION-DIR: !DIFile(filename: "{{.*}}", directory: "/var/empty")
+// CHECK-COMPILATION-DIR: !DIFile(filename: "Inputs/stdio.h", directory: "/var/empty")
 // CHECK-COMPILATION-DIR-NOT: !DIFile(filename:
Index: test/Modules/module-debuginfo-prefix.m
===================================================================
--- test/Modules/module-debuginfo-prefix.m
+++ test/Modules/module-debuginfo-prefix.m
@@ -20,4 +20,4 @@
 @import DebugObjC;
 #endif
 
-// CHECK: !DIFile({{.*}}"/OVERRIDE/DebugObjC.h"
+// CHECK: !DIFile(filename: "/OVERRIDE/DebugObjC.h", directory: "")