https://github.com/openucx/ucx/pull/10998
From: Brahmajit Das <listout@listout.xyz>
Date: Sun, 9 Nov 2025 12:37:47 +0530
Subject: [PATCH 1/2] UCS/BITMAP/TEST: Fix build with >= Clang 21

First caught on Gentoo LLVM with Clang 21.1.5 and LLVM 21.1.5
Build with fail with the following error message

This is cause due to Clang enabling default-const-init-var-unsafe by default,
and -Werror makes it treat as an warning. This is better fixed by upstream
developer so this commit mostly a RFC from upstream.

Signed-off-by: Brahmajit Das <listout@listout.xyz>
--- a/config/m4/compiler.m4
+++ b/config/m4/compiler.m4
@@ -10,7 +10,7 @@
 #
 # Initialize CFLAGS
 #
-BASE_CFLAGS="-g -Wall -Werror"
+BASE_CFLAGS="-g -Wall"
 
 # Prevent libtool from suppression of warnings
 LT_CFLAGS="-no-suppress"

From 9ac4c2c6d8935c251f5eeda53634817946f6c794 Mon Sep 17 00:00:00 2001
From: Brahmajit Das <listout@listout.xyz>
Date: Sun, 9 Nov 2025 12:42:29 +0530
Subject: [PATCH 2/2] TEST/IODEMO: Use std::shuffle when available

random_shuffle was deprecated in C++14 and completely removed in C++17.
With newer compilers like Clang 21, the build fails. This commit should
preserve older behavior and use std::shuffle when available.

Signed-off-by: Brahmajit Das <listout@listout.xyz>
--- a/test/apps/iodemo/io_demo.cc
+++ b/test/apps/iodemo/io_demo.cc
@@ -19,6 +19,7 @@
 #include <csignal>
 #include <cerrno>
 #include <vector>
+#include <random>
 #include <map>
 #include <queue>
 #include <algorithm>
@@ -2999,8 +3000,9 @@ static int do_client(options_t& test_opts)
     LOG << "random seed: " << test_opts.random_seed;
 
     // randomize servers to optimize startup
-    std::random_shuffle(test_opts.servers.begin(), test_opts.servers.end(),
-                        IoDemoRandom::urand<size_t>);
+    std::random_device rd;
+    std::mt19937 rng(rd());
+    std::shuffle(test_opts.servers.begin(), test_opts.servers.end(), rng);
 
     UcxLog vlog(LOG_PREFIX, test_opts.verbose);
     vlog << "List of servers:";