Index: lib/Target/ARM/AsmParser/ARMAsmParser.cpp
===================================================================
--- lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -8996,6 +8996,8 @@
   return PlainMatchResult;
 }
 
+std::string ARMMnemonicSpellCheck(std::string S, uint64_t FBS);
+
 static const char *getSubtargetFeatureName(uint64_t Val);
 bool ARMAsmParser::MatchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
                                            OperandVector &Operands,
@@ -9089,9 +9091,13 @@
 
     return Error(ErrorLoc, "invalid operand for instruction");
   }
-  case Match_MnemonicFail:
-    return Error(IDLoc, "invalid instruction",
+  case Match_MnemonicFail: {
+    uint64_t FBS = ComputeAvailableFeatures(getSTI().getFeatureBits());
+    std::string Suggestion = ARMMnemonicSpellCheck(
+      std::string(((ARMOperand &)*Operands[0]).getToken()), FBS);
+    return Error(IDLoc, "invalid instruction" + Suggestion,
                  ((ARMOperand &)*Operands[0]).getLocRange());
+  }
   case Match_RequiresNotITBlock:
     return Error(IDLoc, "flag setting instruction only valid outside IT block");
   case Match_RequiresITBlock:
Index: test/MC/ARM/invalid-instructions.s
===================================================================
--- /dev/null
+++ test/MC/ARM/invalid-instructions.s
@@ -0,0 +1,51 @@
+@ RUN: not llvm-mc -triple=arm -show-encoding < %s 2>&1 | FileCheck %s
+
+@ First check what happens when an instruction is omitted:
+
+  r1, r2, r3
+
+@ CHECK: error: unexpected token in operand
+@ CHECK-NEXT: r1, r2, r3
+@ CHECK-NEXT:   ^
+
+@ We don't want to see a suggestion here; the edit distance is too large to
+@ give sensible suggestions:
+
+  aaaaaaaaaaaaaaa r1, r2, r3
+
+@ CHECK: error: invalid instruction
+@ CHECK-NEXT: aaaaaaaaaaaaaaa r1, r2, r3
+@ CHECK-NEXT: ^
+
+@ Check that we get one suggestion: 'adXd' is 1 edit away, an insertion,
+@ from an alternative 'add':
+
+  adXd r1, r2, r3
+
+@ CHECK: error: invalid instruction, did you mean: add?
+@ CHECK-NEXT: adXd r1, r2, r3
+@ CHECK-NEXT: ^
+
+@ Check edit distance 1, a deletion:
+
+  ad r1, r2, r3
+
+@ CHECK: error: invalid instruction, did you mean: adc, add, adr, and?
+@ CHECK-NEXT: ad r1, r2, r3
+@ CHECK-NEXT: ^
+
+@ Let's check another one that is 1 edit away, an subsitution:
+
+  ldrea r1, r2, r3
+
+@ CHECK: error: invalid instruction, did you mean: ldrex?
+@ CHECK-NEXT: ldrea r1, r2, r3
+@ CHECK-NEXT: ^
+
+@ Check an instruction that is 2 edits away, resuling in a number of suggestions:
+
+  ldre r1, r2, r3
+
+@CHECK: error: invalid instruction, did you mean: ldr, ldrb, ldrd, ldrex, ldrh, ldrt?
+@CHECK-NEXT: ldre r1, r2, r3
+@CHECK-NEXT: ^
Index: utils/TableGen/AsmMatcherEmitter.cpp
===================================================================
--- utils/TableGen/AsmMatcherEmitter.cpp
+++ utils/TableGen/AsmMatcherEmitter.cpp
@@ -2711,6 +2711,72 @@
   OS << "}\n\n";
 }
 
+static void emitMnemonicSpellChecker(raw_ostream &OS, CodeGenTarget &Target,
+                                     unsigned VariantCount) {
+  OS << "// Simple implementation of Levenshtein Distance calculation.\n";
+  OS << "static unsigned EditDistance(std::string S, std::string T) {\n";
+  OS << "  assert(S.size() && T.size());\n";
+  OS << "  const unsigned N = S.size() + 1;\n";
+  OS << "  const unsigned M = T.size() + 1;\n";
+  OS << "  std::vector<std::vector<unsigned> >Mat(M, std::vector<unsigned>(N));\n";
+  OS << "\n";
+  OS << "  for (unsigned i = 0; i<M; i++)\n";
+  OS << "    Mat[i][0] = i;\n";
+  OS << "  for (unsigned i = 0; i<N; i++)\n";
+  OS << "    Mat[0][i] = i;\n";
+  OS << "\n";
+  OS << "  auto Min = [] (unsigned N, unsigned M) { return N < M ? N : M; };\n";
+  OS << "  for (unsigned i = 1; i<N; i++) {\n";
+  OS << "    for (unsigned j = 1; j<M; j++) {\n";
+  OS << "      const unsigned Cost = S[i-1] == T[j-1] ? 0 : 1;\n";
+  OS << "      Mat[j][i] = Min(Mat[j-1][i] + 1, Min(Mat[j][i-1] + 1, Mat[j-1][i-1] + Cost));\n";
+  OS << "    }\n";
+  OS << "  }\n";
+  OS << "  return Mat[M-1][N-1];\n";
+  OS << "}\n";
+  OS << "\n";
+  OS << "std::string " << Target.getName() << "MnemonicSpellCheck(std::string S, uint64_t FBS) {\n";
+  if (!VariantCount)
+    OS <<  "  return \"\";";
+  else {
+    OS << "  unsigned MinDist = ~0;\n";
+    OS << "  std::vector<std::string> Candidates;\n";
+    OS << "  std::string Prev = \"\";\n";
+    OS << "  auto End = std::end(MatchTable0);\n";
+    OS << "\n";
+    OS << "  for (auto I = std::begin(MatchTable0); I < End; I++) {\n";
+    OS << "    if (!(I->RequiredFeatures & FBS))\n";
+    OS << "      continue;\n";
+    OS << "    std::string T(I->getMnemonic().str());\n";
+    OS << "    // Avoid recomputing the edit distance for the same string.\n";
+    OS << "    if(T == Prev)\n";
+    OS << "      continue;\n";
+    OS << "\n";
+    OS << "    Prev = T;\n";
+    OS << "    unsigned Dist = EditDistance(S, T);\n";
+    OS << "    if (Dist < MinDist) {\n";
+    OS << "      Candidates.clear();\n";
+    OS << "      Candidates.push_back(T);\n";
+    OS << "      MinDist = Dist;\n";
+    OS << "    } else if (Dist == MinDist)\n";
+    OS << "      Candidates.push_back(T);\n";
+    OS << "  }\n";
+    OS << "\n";
+    OS << "  // Edit distance bigger than 2 are probably not useful suggestions.\n";
+    OS << "  if (MinDist > 2 || Candidates.empty())\n";
+    OS << "    return \"\";\n";
+    OS << "\n";
+    OS << "  std::string Res = \", did you mean: \";\n";
+    OS << "  unsigned i = 0;\n";
+    OS << "  for( ; i < Candidates.size() - 1; i++)\n";
+    OS << "    Res += Candidates[i] + \", \";\n";
+    OS << "  return Res + Candidates[i] + \"?\";\n";
+  }
+  OS << "}\n";
+  OS << "\n";
+}
+
+
 void AsmMatcherEmitter::run(raw_ostream &OS) {
   CodeGenTarget Target(Records);
   Record *AsmParser = Target.getAsmParser();
@@ -2974,6 +3040,8 @@
     OS << "};\n\n";
   }
 
+  emitMnemonicSpellChecker(OS, Target, VariantCount);
+
   // Finally, build the match function.
   OS << "unsigned " << Target.getName() << ClassName << "::\n"
      << "MatchInstructionImpl(const OperandVector &Operands,\n";