Index: llvm/trunk/lib/CodeGen/MIRParser/MIRParser.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/MIRParser/MIRParser.cpp
+++ llvm/trunk/lib/CodeGen/MIRParser/MIRParser.cpp
@@ -18,6 +18,7 @@
 #include "llvm/AsmParser/Parser.h"
 #include "llvm/CodeGen/MIRYamlMapping.h"
 #include "llvm/IR/Module.h"
+#include "llvm/Support/LineIterator.h"
 #include "llvm/Support/SMLoc.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/MemoryBuffer.h"
@@ -49,6 +50,11 @@
   ///
   /// Return true if an error occurred.
   bool parseMachineFunction(yaml::Input &In);
+
+private:
+  /// Return a MIR diagnostic converted from an LLVM assembly diagnostic.
+  SMDiagnostic diagFromLLVMAssemblyDiag(const SMDiagnostic &Error,
+                                        SMRange SourceRange);
 };
 
 } // end anonymous namespace
@@ -81,8 +87,10 @@
           dyn_cast_or_null<yaml::BlockScalarNode>(In.getCurrentNode())) {
     M = parseAssembly(MemoryBufferRef(BSN->getValue(), Filename), Error,
                       Context);
-    if (!M)
+    if (!M) {
+      Error = diagFromLLVMAssemblyDiag(Error, BSN->getSourceRange());
       return M;
+    }
     In.nextDocument();
     if (!In.setCurrentDocument())
       return M;
@@ -111,6 +119,37 @@
   return false;
 }
 
+SMDiagnostic MIRParserImpl::diagFromLLVMAssemblyDiag(const SMDiagnostic &Error,
+                                                     SMRange SourceRange) {
+  assert(SourceRange.isValid());
+
+  // Translate the location of the error from the location in the llvm IR string
+  // to the corresponding location in the MIR file.
+  auto LineAndColumn = SM.getLineAndColumn(SourceRange.Start);
+  unsigned Line = LineAndColumn.first + Error.getLineNo() - 1;
+  unsigned Column = Error.getColumnNo();
+  StringRef LineStr = Error.getLineContents();
+  SMLoc Loc = Error.getLoc();
+
+  // Get the full line and adjust the column number by taking the indentation of
+  // LLVM IR into account.
+  for (line_iterator L(*SM.getMemoryBuffer(SM.getMainFileID()), false), E;
+       L != E; ++L) {
+    if (L.line_number() == Line) {
+      LineStr = *L;
+      Loc = SMLoc::getFromPointer(LineStr.data());
+      auto Indent = LineStr.find(Error.getLineContents());
+      if (Indent != StringRef::npos)
+        Column += Indent;
+      break;
+    }
+  }
+
+  return SMDiagnostic(SM, Loc, Filename, Line, Column, Error.getKind(),
+                      Error.getMessage(), LineStr, Error.getRanges(),
+                      Error.getFixIts());
+}
+
 std::unique_ptr<Module> llvm::parseMIRFile(StringRef Filename,
                                            SMDiagnostic &Error,
                                            LLVMContext &Context) {
Index: llvm/trunk/test/CodeGen/MIR/llvm-ir-error-reported.mir
===================================================================
--- llvm/trunk/test/CodeGen/MIR/llvm-ir-error-reported.mir
+++ llvm/trunk/test/CodeGen/MIR/llvm-ir-error-reported.mir
@@ -0,0 +1,22 @@
+# RUN: not llc -start-after branch-folder -stop-after branch-folder -o /dev/null %s 2>&1 | FileCheck %s
+# This test ensures an error is reported if the embedded LLVM IR contains an
+# error.
+
+--- |
+  
+  ; CHECK: [[@LINE+3]]:15: error: use of undefined value '%a'
+  define i32 @foo(i32 %x, i32 %y) {
+    %z = alloca i32, align 4
+    store i32 %a, i32* %z, align 4
+    br label %Test
+  Test:
+    %m = load i32, i32* %z, align 4
+    %cond = icmp eq i32 %y, %m
+    br i1 %cond, label %IfEqual, label %IfUnequal
+  IfEqual:
+    ret i32 1
+  IfUnequal:
+    ret i32 0
+  }
+  
+...