sycl: zstd_STATIC_LIBRARY is NOTFOUND building on almalinux 8

[dvrogozh]

Describe the bug

We are working to support Pytorch CI with intel/llvm compiler, see intel/torch-xpu-ops#3934. Pytorch build is done on almalinux 8 (RHEL 8 derivative) and requires support for --offload-compress which depends on ZSTD library. The libzstd library on Fedora family is available only as a shared library. Building against system installed dependencies is a strong requirement within Linux ecosystem especially for Linux distro packaging of the components. The build of intel/llvm compiler is failing on such setup because SYCL library configuration mistakenly relies only on static ZSTD library:

llvm/sycl/source/CMakeLists.txt

Line 176 in b09acde

target_link_libraries(${LIB_NAME} PRIVATE ${zstd_STATIC_LIBRARY})

Compare with how similar places implemented in other places in LLVM:

llvm/llvm/lib/Support/CMakeLists.txt

Lines 28 to 38 in b09acde

	if(LLVM_ENABLE_ZSTD)
	if(TARGET zstd::libzstd_shared AND NOT LLVM_USE_STATIC_ZSTD)
	set(zstd_target zstd::libzstd_shared)
	else()
	set(zstd_target zstd::libzstd_static)
	endif()
	endif()
	if(LLVM_ENABLE_ZSTD)
	list(APPEND imported_libs ${zstd_target})
	endif()

and:

llvm/lld/ELF/CMakeLists.txt

Lines 9 to 18 in b09acde

	if(LLVM_ENABLE_ZSTD)
	if(TARGET zstd::libzstd_shared AND NOT LLVM_USE_STATIC_ZSTD)
	set(zstd_target zstd::libzstd_shared)
	else()
	set(zstd_target zstd::libzstd_static)
	endif()
	endif()
	if(LLVM_ENABLE_ZSTD)
	list(APPEND imported_libs ${zstd_target})

To reproduce

$ docker pull pytorch/manylinux2_28-builder:xpu-main
$ docker run -it --rm -v $(pwd):/opt/_llvm pytorch/manylinux2_28-builder:xpu-main
# /opt/python/cp314-cp314/bin/python3 -m venv /opt/_build
# . /opt/_build/bin/activate
# pip install cmake ninja
# dnf install -y libtool libzstd-devel
# cmake -B build -S llvm -G Ninja \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=$(pwd)/install \
    -DBUILD_SHARED_LIBS=ON \
    -DLLVM_BUILD_TOOLS=ON \
    -DLLVM_ENABLE_ASSERTIONS=ON \
    -DLLVM_ENABLE_DOXYGEN=OFF \
    -DLLVM_ENABLE_LLD=OFF \
    -DLLVM_ENABLE_PROJECTS='clang;sycl;llvm-spirv;opencl;xpti;xptifw;compiler-rt;libdevice;sycl-jit' \
    -DLLVM_ENABLE_RTTI=ON \
    -DLLVM_ENABLE_SPHINX=OFF \
    -DLLVM_ENABLE_ZSTD=ON \
    -DLLVM_EXTERNAL_PROJECTS='sycl;llvm-spirv;opencl;xpti;xptifw;compiler-rt;libdevice;sycl-jit' \
    -DLLVM_SPIRV_ENABLE_LIBSPIRV_DIS=OFF \
    -DLLVM_TARGETS_TO_BUILD='host;SPIRV' \
    -DSYCL_ENABLE_EXTENSION_JIT=ON \
    -DSYCL_ENABLE_MAJOR_RELEASE_PREVIEW_LIB=OFF \
    -DSYCL_ENABLE_WERROR=OFF \
    -DSYCL_ENABLE_XPTI_TRACING=ON \
    -DLLVM_EXTERNAL_LIBDEVICE_SOURCE_DIR=$(pwd)/libdevice \
    -DLLVM_EXTERNAL_LLVM_SPIRV_SOURCE_DIR=$(pwd)/llvm-spirv \
    -DLLVM_EXTERNAL_SYCL_JIT_SOURCE_DIR=$(pwd)/sycl-jit \
    -DLLVM_EXTERNAL_SYCL_SOURCE_DIR=$(pwd)/sycl \
    -DLLVM_EXTERNAL_XPTI_SOURCE_DIR=$(pwd)/xpti \
    -DLLVM_EXTERNAL_XPTIFW_SOURCE_DIR=$(pwd)/xptifw \
    -DSYCL_INCLUDE_TESTS=OFF \
    -DXPTI_ENABLE_WERROR=OFF
<...>
CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
zstd_STATIC_LIBRARY (ADVANCED)
    linked by target "sycl" in directory /opt/_llvm/sycl/source

-- Generating done (5.3s)
CMake Generate step failed.  Build files cannot be regenerated correctly.

Environment

• OS: Linux
• DPC++ version: b09acde (latest main as of 6/12/2026)

Additional context

• Proposed fix to align with LLVM behavior: [SYCL] Support build with shared libzstd #22294

CC: @sarnex, @uditagarwal97