TableGen: Convert an assert() to a proper diagnostic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163726 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/AsmMatcherEmitter.cpp b/utils/TableGen/AsmMatcherEmitter.cpp
index 78eb641..fcd32dc 100644
--- a/utils/TableGen/AsmMatcherEmitter.cpp
+++ b/utils/TableGen/AsmMatcherEmitter.cpp
@@ -1020,7 +1020,9 @@
     throw TGError(Rec->getLoc(), "register class has no class info!");
   }
 
-  assert(Rec->isSubClassOf("Operand") && "Unexpected operand!");
+  if (!Rec->isSubClassOf("Operand"))
+    throw TGError(Rec->getLoc(), "Operand `" + Rec->getName() +
+                  "' does not derive from class Operand!\n");
   Record *MatchClass = Rec->getValueAsDef("ParserMatchClass");
   if (ClassInfo *CI = AsmOperandClasses[MatchClass])
     return CI;