TableGen: AsmMatcher diagnostics preference detail.

Don't override a custom diagnostic w/ a generic InvalidOperand, all else
being equal.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159238 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/AsmMatcherEmitter.cpp b/utils/TableGen/AsmMatcherEmitter.cpp
index fb8d704..f5e094e 100644
--- a/utils/TableGen/AsmMatcherEmitter.cpp
+++ b/utils/TableGen/AsmMatcherEmitter.cpp
@@ -2663,7 +2663,9 @@
   OS << "      if (!HadMatchOtherThanPredicate &&\n";
   OS << "          (it == MnemonicRange.first || ErrorInfo <= i+1)) {\n";
   OS << "        ErrorInfo = i+1;\n";
-  OS << "        RetCode = Diag;\n";
+  OS << "        // InvalidOperand is the default. Prefer specificity.\n";
+  OS << "        if (Diag != Match_InvalidOperand)\n";
+  OS << "          RetCode = Diag;\n";
   OS << "      }\n";
   OS << "      // Otherwise, just reject this instance of the mnemonic.\n";
   OS << "      OperandsValid = false;\n";