Enable RediSearch LTO on Rocky Linux 10

RediSearch enables LTO by default in unstable and requires a clang whose
LLVM major matches rustc's (currently LLVM 21 from rustc 1.94). The LLVM
project does not publish a dnf repository for RHEL/Rocky, so we install
the official LLVM 21 tarball into /opt/llvm and add it to PATH.

Restricted to Rocky 10. The upstream LLVM 21 binaries require
GLIBCXX_3.4.30+ which is only available on Rocky 10's system libstdc++;
Rocky 8 and 9 ship 3.4.25 and 3.4.28 respectively. Making LTO work
there would require bundling a newer libstdc++ alongside the produced
redisearch.so on every customer machine, which is out of scope for now.
Rocky 8/9 continue to build with LTO=0.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: AngelYanev

.github/actions/build-package/action.yml

@@ -92,8 +92,15 @@ runs:
         export DISABLE_WERRORS=yes
         export BUILD_TLS=yes
         export USE_SYSTEMD=yes
-        # Override RediSearch's new LTO=1 default; toolchain support TBD.
-        export LTO=0
+        # Enable RediSearch LTO only where LLVM 21 is available (Rocky 10).
+        # Rocky 8/9 lack libstdc++ with GLIBCXX_3.4.30+ that upstream LLVM 21
+        # binaries require, so keep LTO=0 there.
+        if [ -x /opt/llvm/bin/clang-21 ]; then
+          export LTO=1
+          export PATH=/opt/llvm/bin:$PATH
+        else
+          export LTO=0
+        fi
 
         if [ "${{ steps.version.outputs.VERSION }}" = "unstable" ]; then
           # Clone Redis unstable branch instead of downloading release tarball

dockerfiles/Dockerfile.rockylinux10

@@ -42,8 +42,12 @@ RUN echo '[goreleaser]\nname=GoReleaser\nbaseurl=https://repo.goreleaser.com/yum
 COPY install/install_cmake.sh /tmp/
 RUN bash /tmp/install_cmake.sh
 
+# Install LLVM 21 for RediSearch LTO (Rocky 10 only; see install_llvm.sh).
+COPY install/install_llvm.sh /tmp/
+RUN bash /tmp/install_llvm.sh
+
 # Set environment
-ENV PATH="/usr/local/bin:/opt/venv/bin:${PATH}"
+ENV PATH="/opt/llvm/bin:/usr/local/bin:/opt/venv/bin:${PATH}"
 WORKDIR /build
 
 # Default command

install/install_llvm.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+# Install upstream LLVM 21 toolchain for RediSearch's LTO build (rustc 1.94
+# ships LLVM 21, and RediSearch requires the C compiler's LLVM major to match).
+# LLVM has no dnf repo for RHEL/Rocky, so we fetch the official tarball.
+#
+# Only intended for Rocky Linux 10: its system libstdc++ already provides
+# GLIBCXX_3.4.32, so the prebuilt LLVM binaries (which need 3.4.30+) load as-is.
+# Rocky 8/9 ship older libstdc++ and would need additional bundling work, so
+# LTO stays disabled there for now.
+
+set -euo pipefail
+
+LLVM_VERSION="${LLVM_VERSION:-21.1.8}"
+MAJOR="${LLVM_VERSION%%.*}"
+
+case "$(uname -m)" in
+	x86_64)  asset="LLVM-${LLVM_VERSION}-Linux-X64.tar.xz" ;;
+	aarch64) asset="LLVM-${LLVM_VERSION}-Linux-ARM64.tar.xz" ;;
+	*) echo "Unsupported arch: $(uname -m)" >&2; exit 1 ;;
+esac
+
+install_root="/opt/llvm-${LLVM_VERSION}"
+mkdir -p "$install_root"
+curl -fsSL "https://github.com/llvm/llvm-project/releases/download/llvmorg-${LLVM_VERSION}/${asset}" \
+	| tar -xJ -C "$install_root" --strip-components=1
+ln -sfn "$install_root" /opt/llvm
+
+# RediSearch's build scripts look up clang-${MAJOR}, lld-${MAJOR}, etc. on PATH;
+# the upstream tarball ships unsuffixed names only, so alias them.
+for tool in clang clang++ clang-cpp lld ld.lld ld64.lld lld-link llc opt \
+            llvm-ar llvm-nm llvm-ranlib llvm-strip llvm-objcopy llvm-objdump \
+            llvm-readelf llvm-config; do
+	src="/opt/llvm/bin/${tool}"
+	dst="/opt/llvm/bin/${tool}-${MAJOR}"
+	[ -e "$src" ] && [ ! -e "$dst" ] && ln -sfn "$src" "$dst"
+done
+
+echo 'export PATH=/opt/llvm/bin:$PATH' > /etc/profile.d/llvm.sh
+
+/opt/llvm/bin/clang-${MAJOR} --version
+/opt/llvm/bin/ld.lld-${MAJOR} --version