AsmParser: Don't crash on malformed attribute groups

This fixes PR21785.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223801 91177308-0d34-0410-b5e6-96231b3b80d8

lib/AsmParser/LLParser.cpp

@@ -869,7 +869,9 @@ bool LLParser::ParseUnnamedAttrGrp() {
   LocTy AttrGrpLoc = Lex.getLoc();
   Lex.Lex();
 
-  assert(Lex.getKind() == lltok::AttrGrpID);
+  if (Lex.getKind() != lltok::AttrGrpID)
+    return TokError("expected attribute group id");
+
   unsigned VarID = Lex.getUIntVal();
   std::vector<unsigned> unused;
   LocTy BuiltinLoc;

test/Assembler/invalid-attrgrp.ll

@@ -0,0 +1,4 @@
+; RUN: not llvm-as < %s 2>&1 | FileCheck %s
+
+attributes
+; CHECK: expected attribute group id