Index: llvm/test/tools/llvm-objdump/X86/source-interleave-invalid-source.test
===================================================================
--- llvm/test/tools/llvm-objdump/X86/source-interleave-invalid-source.test
+++ llvm/test/tools/llvm-objdump/X86/source-interleave-invalid-source.test
@@ -1,5 +1,5 @@
 ## Test llvm-objdump's --source behaviour when a line number is greater than the
-## file length.
+## file length and ensure that we emit a warning.
 
 # RUN: sed -e "s,SRC_COMPDIR,%/p/Inputs,g" %p/Inputs/source-interleave.ll > %t.ll
 # RUN: sed -e "s,line: 7,line: 9999,g" %t.ll > %t2.ll
@@ -8,9 +8,10 @@
 # RUN: llc -o %t2.o -filetype=obj -mtriple=x86_64-pc-linux %t2.ll
 
 # RUN: llvm-objdump --source %t.o | FileCheck %s --check-prefixes=CHECK,GOOD
-# RUN: llvm-objdump --source %t2.o | FileCheck %s --implicit-check-not="int *b = &a;"
+# RUN: llvm-objdump --source %t2.o 2>&1 | FileCheck %s --check-prefixes=CHECK,WARN --implicit-check-not="int *b = &a;"
 
 # CHECK:      main:
 # CHECK-NEXT: ; int main() {
+# WARN:       warning: debug info line number 9999 exceeds the number of lines in
 # GOOD:       ;   int *b = &a;
 # CHECK:      ;   return *b + foo();
Index: llvm/test/tools/llvm-objdump/X86/source-interleave-missing-source.test
===================================================================
--- llvm/test/tools/llvm-objdump/X86/source-interleave-missing-source.test
+++ llvm/test/tools/llvm-objdump/X86/source-interleave-missing-source.test
@@ -1,5 +1,5 @@
 ## Test that if the source cannot be found that disassembly is still printed,
-## and that no source is printed.
+## that no source is printed, and that we emit a warning.
 
 # RUN: sed -e "s,SRC_COMPDIR,%/t,g" %p/Inputs/source-interleave.ll > %t.ll
 # RUN: sed -e "s,SRC_COMPDIR,%/p/Inputs,g" %p/Inputs/source-interleave.ll > %t2.ll
@@ -7,9 +7,10 @@
 # RUN: llc -o %t.o -filetype=obj -mtriple=x86_64-pc-linux %t.ll
 # RUN: llc -o %t2.o -filetype=obj -mtriple=x86_64-pc-linux %t2.ll
 
-# RUN: llvm-objdump --source %t.o | FileCheck %s --implicit-check-not='main()'
+# RUN: llvm-objdump --source %t.o 2>&1 | FileCheck %s --check-prefixes=WARN,CHECK --implicit-check-not='main()'
 # RUN: llvm-objdump --source %t2.o | FileCheck %s --check-prefixes=CHECK,SOURCE
 
+# WARN:        warning: failed to find source
 # CHECK:       0000000000000010 main:
 # SOURCE-NEXT: ; int main() {
 # CHECK-NEXT:   10:   55                      pushq   %rbp
Index: llvm/test/tools/llvm-objdump/X86/source-interleave-no-debug-info.test
===================================================================
--- llvm/test/tools/llvm-objdump/X86/source-interleave-no-debug-info.test
+++ llvm/test/tools/llvm-objdump/X86/source-interleave-no-debug-info.test
@@ -1,13 +1,14 @@
 ## Test that if an object has no debug information, only the disassembly is
-## printed when --source is specified.
+## printed when --source is specified, and that we emit a warning.
 
 # RUN: sed -e "s,SRC_COMPDIR,%/p/Inputs,g" %p/Inputs/source-interleave.ll > %t.ll
 # RUN: llc -o %t.o -filetype=obj -mtriple=x86_64-pc-linux %t.ll
 # RUN: llvm-objcopy --strip-debug %t.o %t2.o
 
 # RUN: llvm-objdump --source %t.o | FileCheck %s --check-prefixes=CHECK,SOURCE
-# RUN: llvm-objdump --source %t2.o | FileCheck %s --implicit-check-not='main()'
+# RUN: llvm-objdump --source %t2.o 2>&1 | FileCheck %s --check-prefixes=WARN,CHECK --implicit-check-not='main()'
 
+# WARN:        warning: failed to parse debug info which may be missing
 # CHECK:       0000000000000010 main:
 # SOURCE-NEXT: ; int main() {
 # CHECK-NEXT:   10:   55                      pushq   %rbp
Index: llvm/tools/llvm-objdump/llvm-objdump.cpp
===================================================================
--- llvm/tools/llvm-objdump/llvm-objdump.cpp
+++ llvm/tools/llvm-objdump/llvm-objdump.cpp
@@ -51,6 +51,7 @@
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Format.h"
+#include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/GraphWriter.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/InitLLVM.h"
@@ -522,13 +523,18 @@
   std::unordered_map<std::string, std::unique_ptr<MemoryBuffer>> SourceCache;
   // Mark the line endings of the cached source
   std::unordered_map<std::string, std::vector<StringRef>> LineCache;
+  // Keep track of missing sources
+  StringSet<> MissingSources;
+  // Only emit 'no debug info' warning once
+  bool WarnedNoDebugInfo;
 
 private:
   bool cacheSource(const DILineInfo& LineInfoFile);
 
 public:
   SourcePrinter() = default;
-  SourcePrinter(const ObjectFile *Obj, StringRef DefaultArch) : Obj(Obj) {
+  SourcePrinter(const ObjectFile *Obj, StringRef DefaultArch)
+      : Obj(Obj), WarnedNoDebugInfo(false) {
     symbolize::LLVMSymbolizer::Options SymbolizerOpts(
         DILineInfoSpecifier::FunctionNameKind::None, true, false, false,
         DefaultArch);
@@ -546,8 +552,13 @@
     Buffer = MemoryBuffer::getMemBuffer(*LineInfo.Source);
   } else {
     auto BufferOrError = MemoryBuffer::getFile(LineInfo.FileName);
-    if (!BufferOrError)
+    if (!BufferOrError) {
+      bool NewMissingSource =
+          std::get<1>(MissingSources.insert(LineInfo.FileName));
+      if (NewMissingSource)
+        warn(Twine("failed to find source " + LineInfo.FileName));
       return false;
+    }
     Buffer = std::move(*BufferOrError);
   }
   // Chomp the file to get lines
@@ -579,7 +590,16 @@
   else
     LineInfo = *ExpectedLineInfo;
 
-  if ((LineInfo.FileName == "<invalid>") || LineInfo.Line == 0 ||
+
+  if (LineInfo.FileName == "<invalid>") {
+    if(!WarnedNoDebugInfo) {
+      warn(Twine("failed to parse debug info which may be missing"));
+      WarnedNoDebugInfo = true;
+    }
+    return;
+  }
+
+  if (LineInfo.Line == 0 ||
       ((OldLineInfo.Line == LineInfo.Line) &&
        (OldLineInfo.FileName == LineInfo.FileName)))
     return;
@@ -592,8 +612,12 @@
         return;
     auto LineBuffer = LineCache.find(LineInfo.FileName);
     if (LineBuffer != LineCache.end()) {
-      if (LineInfo.Line > LineBuffer->second.size())
+      if (LineInfo.Line > LineBuffer->second.size()) {
+        warn(formatv(
+            "debug info line number {0} exceeds the number of lines in {1}",
+            LineInfo.Line, LineInfo.FileName));
         return;
+      }
       // Vector begins at 0, line numbers are non-zero
       OS << Delimiter << LineBuffer->second[LineInfo.Line - 1] << '\n';
     }