Index: lib/IR/Verifier.cpp
===================================================================
--- lib/IR/Verifier.cpp
+++ lib/IR/Verifier.cpp
@@ -281,6 +281,9 @@
   /// Whether the current function has a DISubprogram attached to it.
   bool HasDebugInfo = false;
 
+  /// Whether source was present on the first DIFile encountered in each CU.
+  DenseMap<const DICompileUnit *, bool> HasSourceDebugInfo;
+
   /// Stores the count of how many objects were passed to llvm.localescape for a
   /// given function and the largest index passed to llvm.localrecover.
   DenseMap<Function *, std::pair<unsigned, unsigned>> FrameEscapeInfo;
@@ -519,6 +522,9 @@
   /// Module-level verification that all @llvm.experimental.deoptimize
   /// declarations share the same calling convention.
   void verifyDeoptimizeCallingConvs();
+
+  /// Verify all-or-nothing property of DIFile source attribute within a CU.
+  void verifySourceDebugInfo(const DICompileUnit &U, const DIFile &F);
 };
 
 } // end anonymous namespace
@@ -1032,6 +1038,8 @@
   AssertDI(!N.getFile()->getFilename().empty(), "invalid filename", &N,
            N.getFile());
 
+  verifySourceDebugInfo(N, *N.getFile());
+
   AssertDI((N.getEmissionKind() <= DICompileUnit::LastEmissionKind),
            "invalid emission kind", &N);
 
@@ -1109,6 +1117,8 @@
     AssertDI(N.isDistinct(), "subprogram definitions must be distinct", &N);
     AssertDI(Unit, "subprogram definitions must have a compile unit", &N);
     AssertDI(isa<DICompileUnit>(Unit), "invalid unit type", &N, Unit);
+    if (N.getFile())
+      verifySourceDebugInfo(*N.getUnit(), *N.getFile());
   } else {
     // Subprogram declarations (part of the type hierarchy).
     AssertDI(!Unit, "subprogram declarations must not have a compile unit", &N);
@@ -4744,6 +4754,14 @@
   }
 }
 
+void Verifier::verifySourceDebugInfo(const DICompileUnit &U, const DIFile &F) {
+  bool HasSource = F.getSource().hasValue();
+  if (!HasSourceDebugInfo.count(&U))
+    HasSourceDebugInfo[&U] = HasSource;
+  AssertDI(HasSource == HasSourceDebugInfo[&U],
+           "inconsistent use of embedded source");
+}
+
 //===----------------------------------------------------------------------===//
 //  Implement the public interfaces to this file...
 //===----------------------------------------------------------------------===//
Index: test/Assembler/debug-info-source-invalid.ll
===================================================================
--- /dev/null
+++ test/Assembler/debug-info-source-invalid.ll
@@ -0,0 +1,27 @@
+; RUN: llvm-as < %s 2>&1 >/dev/null | FileCheck %s
+
+; Ensure we reject debug info where the DIFiles of a DICompileUnit mix source
+; and no-source.
+
+define dso_local void @foo() !dbg !5 {
+  ret void
+}
+
+define dso_local void @bar() !dbg !6 {
+  ret void
+}
+
+!llvm.dbg.cu = !{!4}
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 2, !"Dwarf Version", i32 5}
+!1 = !{i32 2, !"Debug Info Version", i32 3}
+
+!2 = !DIFile(filename: "foo.c", directory: "dir", source: "void foo() { }\0A")
+; CHECK: inconsistent use of embedded source
+; CHECK: warning: ignoring invalid debug info
+!3 = !DIFile(filename: "bar.h", directory: "dir")
+
+!4 = distinct !DICompileUnit(language: DW_LANG_C99, file: !2)
+!5 = distinct !DISubprogram(name: "foo", file: !2, unit: !4)
+!6 = distinct !DISubprogram(name: "bar", file: !3, unit: !4)
Index: test/Assembler/debug-info-source.ll
===================================================================
--- /dev/null
+++ test/Assembler/debug-info-source.ll
@@ -0,0 +1,41 @@
+; RUN: llvm-as < %s | llvm-dis | llvm-as | llvm-dis | FileCheck %s
+; RUN: verify-uselistorder %s
+
+; Ensure we accept debug info where DIFiles within a DICompileUnit either all
+; have source, or none have source.
+
+define dso_local void @foo() !dbg !6 {
+  ret void
+}
+
+define dso_local void @bar() !dbg !7 {
+  ret void
+}
+
+define dso_local void @baz() !dbg !9 {
+  ret void
+}
+
+define dso_local void @qux() !dbg !11 {
+  ret void
+}
+
+!llvm.dbg.cu = !{!0, !2}
+!llvm.module.flags = !{!4, !5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1)
+; CHECK: !1 = !DIFile(filename: "foo.c", directory: "dir", source: "void foo() { }\0A")
+!1 = !DIFile(filename: "foo.c", directory: "dir", source: "void foo() { }\0A")
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3)
+; CHECK: !3 = !DIFile(filename: "qux.h", directory: "dir")
+!3 = !DIFile(filename: "qux.h", directory: "dir")
+!4 = !{i32 2, !"Dwarf Version", i32 5}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "foo", file: !1, unit: !0)
+!7 = distinct !DISubprogram(name: "bar", file: !8, unit: !0)
+; CHECK: !8 = !DIFile(filename: "bar.h", directory: "dir", source: "void bar() { }\0A")
+!8 = !DIFile(filename: "bar.h", directory: "dir", source: "void bar() { }\0A")
+!9 = distinct !DISubprogram(name: "baz", file: !10, unit: !2)
+; CHECK: !10 = !DIFile(filename: "baz.c", directory: "dir")
+!10 = !DIFile(filename: "baz.c", directory: "dir")
+!11 = distinct !DISubprogram(name: "qux", file: !3, unit: !2)