From 9cfa899b87c583e0dcd20e4d35c8e9d337ee14f9 Mon Sep 17 00:00:00 2001
From: Jean Perier <jperier@nvidia.com>
Date: Mon, 11 Apr 2022 09:32:03 +0200
Subject: [PATCH] [flang] add a static assert in CheckUnitNumberInRangeImpl

Add a check that CheckUnitNumberInRangeImpl is not needlessly instantiated.

Differential Revision: https://reviews.llvm.org/D123285
---
 flang/runtime/io-api.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/flang/runtime/io-api.cpp b/flang/runtime/io-api.cpp
index 80f4583f42d6..43e49daa1284 100644
--- a/flang/runtime/io-api.cpp
+++ b/flang/runtime/io-api.cpp
@@ -1280,6 +1280,9 @@ template <typename INT>
 static enum Iostat CheckUnitNumberInRangeImpl(INT unit, bool handleError,
     char *ioMsg, std::size_t ioMsgLength, const char *sourceFile,
     int sourceLine) {
+  static_assert(sizeof(INT) >= sizeof(ExternalUnit),
+      "only intended to be used when the INT to ExternalUnit conversion is "
+      "narrowing");
   if (unit != static_cast<ExternalUnit>(unit)) {
     Terminator oom{sourceFile, sourceLine};
     IoErrorHandler errorHandler{oom};