From 3cefe91b74f65f0db71472e01ca83c69e2cd81cc Mon Sep 17 00:00:00 2001
From: Marek Polacek <polacek@redhat.com>
Date: Tue, 14 May 2024 13:48:30 -0400
Subject: [PATCH] c++: add test for DR 2855

Let

  int8_t x = 127;

This DR says that while

  x++;

invokes UB,

  ++x;

does not.  The resolution was to make the first one valid.  The
following test verifies that we don't report any errors in a constexpr
context.

	DR 2855

gcc/testsuite/ChangeLog:

	* g++.dg/DRs/dr2855.C: New test.
---
 gcc/testsuite/g++.dg/DRs/dr2855.C | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/DRs/dr2855.C

diff --git a/gcc/testsuite/g++.dg/DRs/dr2855.C b/gcc/testsuite/g++.dg/DRs/dr2855.C
new file mode 100644
index 000000000000..b4609ceaa158
--- /dev/null
+++ b/gcc/testsuite/g++.dg/DRs/dr2855.C
@@ -0,0 +1,16 @@
+// DR 2855, Undefined behavior in postfix increment
+// { dg-do compile { target c++14 } }
+
+using int8_t = signed char;
+
+constexpr int
+f ()
+{
+  int8_t x = 127;
+  x++;
+  int8_t z = 127;
+  ++z;
+  return x + z;
+}
+
+constexpr int i = f();
-- 
2.47.2