Add capability for cmake to fetch libtorch itself if not found #173

kjh-giesbertz · 2026-01-22T09:54:46Z

Currently the user needs to install torch him-/herself to be able to use skala. libtorch can actually be downloaded from the pytorch site, so the PR adds this functionality to cmake.

The cpu version is pretty straightforward.
Tested on:
- Mac
- Linux (wsl)
- Windows
The gpu version is more tricky as the download needs to match the particular cuda version. The script is supposed to test whether there is a match and if not, falls back to the cpu version. The versions are quite strict though: 12.6, 12.8 and 13.0.
- Linux (cuda 12.8)
- Windows

…sion is probably ok (at leat on my mac it works), but gpu still needs to filter versions correctly.

…loads are available. Still needs to be tested.

…es set.

…nd_package(CUDA REQUIRED) needed to included. The CUDA_VERSION_STRING conflicts, so renamed that to CUDA_VERSION_NO_DOT.

Copilot

Pull request overview

This PR adds automatic LibTorch download functionality to the CMake build system, eliminating the requirement for users to manually install PyTorch/LibTorch before building the project. The implementation handles platform-specific downloads (Linux, macOS, Windows) and includes CUDA-aware selection for GPU support.

Changes:

Added new CMake module skala-torch.cmake that detects and downloads LibTorch if not found on the system
Modified gauxc-onedft.cmake to use the new module instead of directly calling find_package(Torch)

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 13 comments.

File	Description
cmake/skala-torch.cmake	New module implementing LibTorch auto-download with platform detection, CUDA version matching, and fallback to CPU version
cmake/gauxc-onedft.cmake	Replaced direct Torch package search with include of new skala-torch module

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Copilot · 2026-01-27T11:07:18Z

cmake/skala-torch.cmake

+    if(NOT EXISTS ${LIBTORCH_DOWNLOAD_DIR})
+        message(STATUS "Downloading libtorch from ${LIBTORCH_URL}")
+        file(DOWNLOAD ${LIBTORCH_URL} ${LIBTORCH_ZIP}
+            SHOW_PROGRESS
+            STATUS DOWNLOAD_STATUS)
+
+        list(GET DOWNLOAD_STATUS 0 STATUS_CODE)
+        if(NOT STATUS_CODE EQUAL 0)
+            message(FATAL_ERROR "Failed to download libtorch: ${DOWNLOAD_STATUS}")
+        endif()
+
+        # Extract libtorch
+        message(STATUS "Extracting libtorch...")
+        file(ARCHIVE_EXTRACT INPUT ${LIBTORCH_ZIP} DESTINATION ${CMAKE_BINARY_DIR})
+
+        # Clean up zip file
+        file(REMOVE ${LIBTORCH_ZIP})
+    endif()


The check for existing LibTorch directory may lead to using an incompatible or corrupted installation. If a previous download was interrupted or if the directory exists but is incomplete/corrupted, the script will skip downloading and proceed to use the potentially broken installation. Consider adding validation (e.g., checking for a specific file like libtorch/share/cmake/Torch/TorchConfig.cmake) or using a stamp file to verify successful extraction.

Copilot · 2026-01-27T11:07:19Z

cmake/skala-torch.cmake

@@ -0,0 +1,76 @@
+# Find or download LibTorch


Filename inconsistency: This file is named "skala-torch.cmake" but other dependency management files in the cmake directory use the "gauxc-" prefix (e.g., gauxc-eigen3.cmake, gauxc-cub.cmake, gauxc-exchcxx.cmake). For consistency with the established naming convention, consider renaming this file to "gauxc-torch.cmake" or similar.

Copilot · 2026-01-27T11:07:19Z

cmake/skala-torch.cmake

+
+    # Set libtorch version and download URL
+    set(LIBTORCH_VERSION "2.9.1")
+    set(USE_CUDA_LIBTORCH FALSE) #default is not to use the cuda version but cpu version


Missing space after '#' in comment. For consistency with CMake commenting style used elsewhere in the codebase, there should be a space between the '#' and the comment text.

Suggested change

set(USE_CUDA_LIBTORCH FALSE) #default is not to use the cuda version but cpu version

set(USE_CUDA_LIBTORCH FALSE) # default is not to use the cuda version but cpu version

Copilot · 2026-01-27T11:07:19Z

cmake/skala-torch.cmake

+# Find or download LibTorch
+find_package(Torch QUIET)
+
+if(NOT Torch_FOUND)
+    message(STATUS "Torch not found. Downloading libtorch...")
+
+    # Set libtorch version and download URL
+    set(LIBTORCH_VERSION "2.9.1")


Missing documentation for LibTorch version and CUDA version compatibility. Consider adding a comment at the top of the file explaining which LibTorch version is being downloaded, which CUDA versions are supported, and where to find information about updating these versions. This would help future maintainers understand the constraints and how to update the version when needed.

Copilot · 2026-01-27T11:07:19Z

cmake/skala-torch.cmake

+    set(LIBTORCH_VERSION "2.9.1")
+    set(USE_CUDA_LIBTORCH FALSE) #default is not to use the cuda version but cpu version
+    if(GAUXC_HAS_CUDA)
+	find_package(CUDAToolkit)


Inconsistent indentation detected. This file uses tabs for indentation, but the rest of the codebase (e.g., gauxc-eigen3.cmake, gauxc-cutlass.cmake) uses 2 spaces. Please convert all tabs to 2 spaces for consistency with the project's coding conventions.

Copilot · 2026-01-27T11:07:20Z

cmake/skala-torch.cmake

+    set(USE_CUDA_LIBTORCH FALSE) #default is not to use the cuda version but cpu version
+    if(GAUXC_HAS_CUDA)
+	find_package(CUDAToolkit)
+        set(SUPPORTED_CUDA_VERSION_NO_DOTS "126" "128" "130")


The CUDA version format should support CUDA 12.1, 12.4, and other minor versions within major version 12. The current supported list only includes "126" (12.6), "128" (12.8), and "130" (13.0), but CUDA 12.1 and 12.4 are common versions that would be rejected. Consider either expanding the supported version list or using a more flexible version matching approach (e.g., checking only the major version or using VERSION_GREATER_EQUAL comparisons).

Suggested change

set(SUPPORTED_CUDA_VERSION_NO_DOTS "126" "128" "130")

set(SUPPORTED_CUDA_VERSION_NO_DOTS "121" "124" "126" "128" "130")

Copilot · 2026-01-27T11:07:20Z

cmake/skala-torch.cmake

+    # Download libtorch
+    if(NOT EXISTS ${LIBTORCH_DOWNLOAD_DIR})
+        message(STATUS "Downloading libtorch from ${LIBTORCH_URL}")
+        file(DOWNLOAD ${LIBTORCH_URL} ${LIBTORCH_ZIP}
+            SHOW_PROGRESS
+            STATUS DOWNLOAD_STATUS)
+
+        list(GET DOWNLOAD_STATUS 0 STATUS_CODE)
+        if(NOT STATUS_CODE EQUAL 0)
+            message(FATAL_ERROR "Failed to download libtorch: ${DOWNLOAD_STATUS}")
+        endif()
+
+        # Extract libtorch
+        message(STATUS "Extracting libtorch...")
+        file(ARCHIVE_EXTRACT INPUT ${LIBTORCH_ZIP} DESTINATION ${CMAKE_BINARY_DIR})
+
+        # Clean up zip file
+        file(REMOVE ${LIBTORCH_ZIP})


Consider using FetchContent_Declare with URL instead of manual file(DOWNLOAD) and file(ARCHIVE_EXTRACT). The codebase consistently uses FetchContent for dependency management (see gauxc-eigen3.cmake, gauxc-onedft.cmake). FetchContent provides better integration with CMake's build system, automatic caching, and cleaner error handling. This would also eliminate the need for manual cleanup of the zip file and provide better consistency with other dependency handling in the project.

Copilot · 2026-01-27T11:07:21Z

cmake/skala-torch.cmake

+    # Set CMAKE_PREFIX_PATH to find the downloaded libtorch
+    set(CMAKE_PREFIX_PATH "${LIBTORCH_DOWNLOAD_DIR};${CMAKE_PREFIX_PATH}")


The CMAKE_PREFIX_PATH is modified but not scoped properly. This modification affects the entire project, which could have unintended side effects. Consider using set(CMAKE_PREFIX_PATH ... PARENT_SCOPE) if this is intended to propagate to the parent scope, or document why this global modification is necessary. Also, the modification happens outside the if(NOT EXISTS) block, so it will be set even when LibTorch was already extracted, which is correct but could be clearer.

Suggested change

# Set CMAKE_PREFIX_PATH to find the downloaded libtorch

set(CMAKE_PREFIX_PATH "${LIBTORCH_DOWNLOAD_DIR};${CMAKE_PREFIX_PATH}")

# Extend CMAKE_PREFIX_PATH so that this directory (and any code including it)

# can locate the downloaded LibTorch. This is intentionally done at directory

# scope so that subsequent find_package(Torch) calls in the project can reuse

# the same installation. It is placed outside the download/extract block so

# that an already-extracted LibTorch is still picked up on re-configure.

list(PREPEND CMAKE_PREFIX_PATH "${LIBTORCH_DOWNLOAD_DIR}")

Copilot · 2026-01-27T11:07:21Z

cmake/skala-torch.cmake

+	    find_package(CUDA REQUIRED) # Needed for Caffe cmake, since it use the old CUDA inclusion
+	    set(USE_CUDA_LIBTORCH TRUE)
+	    message(STATUS "CUDAToolkit_INCLUDE_DIRS: ${CUDAToolkit_INCLUDE_DIRS}")
+	    set(CUDA_INCLUDE_DIRS "${CUDAToolkit_INCLUDE_DIRS}") # and pass over the correct headers to Caffe cmake


The find_package(CUDA) module is deprecated in modern CMake (deprecated since CMake 3.10) in favor of find_package(CUDAToolkit). The comment mentions "Caffe cmake" which seems out of place in a LibTorch download script. If this is truly needed for LibTorch's internal CMake, please clarify the comment. Otherwise, consider removing this deprecated call and relying solely on CUDAToolkit.

Suggested change

find_package(CUDA REQUIRED) # Needed for Caffe cmake, since it use the old CUDA inclusion

set(USE_CUDA_LIBTORCH TRUE)

message(STATUS "CUDAToolkit_INCLUDE_DIRS: ${CUDAToolkit_INCLUDE_DIRS}")

set(CUDA_INCLUDE_DIRS "${CUDAToolkit_INCLUDE_DIRS}") # and pass over the correct headers to Caffe cmake

set(USE_CUDA_LIBTORCH TRUE)

message(STATUS "CUDAToolkit_INCLUDE_DIRS: ${CUDAToolkit_INCLUDE_DIRS}")

# Provide CUDA_INCLUDE_DIRS for any legacy CMake code that still expects this variable,

# using the paths reported by CUDAToolkit instead of the deprecated CUDA module.

set(CUDA_INCLUDE_DIRS "${CUDAToolkit_INCLUDE_DIRS}")

Copilot · 2026-01-27T11:07:21Z

cmake/skala-torch.cmake

+        file(DOWNLOAD ${LIBTORCH_URL} ${LIBTORCH_ZIP}
+            SHOW_PROGRESS
+            STATUS DOWNLOAD_STATUS)
+
+        list(GET DOWNLOAD_STATUS 0 STATUS_CODE)
+        if(NOT STATUS_CODE EQUAL 0)
+            message(FATAL_ERROR "Failed to download libtorch: ${DOWNLOAD_STATUS}")
+        endif()
+
+        # Extract libtorch
+        message(STATUS "Extracting libtorch...")
+        file(ARCHIVE_EXTRACT INPUT ${LIBTORCH_ZIP} DESTINATION ${CMAKE_BINARY_DIR})


This CMake logic downloads and extracts a third-party binary (libtorch) from download.pytorch.org during the build without any integrity verification, creating a supply-chain risk: if the download endpoint or TLS chain is compromised, an attacker could supply a malicious libtorch archive that is then extracted and linked into your build. Because this code runs automatically when Torch is not found, the build may silently consume and execute unverified remote code. Consider pinning the download to a verified artifact by enforcing an expected hash (for example via CMake's hash-checking options) or using a distribution mechanism that provides cryptographic signature verification before extraction.

Klaas Giesbertz and others added 2 commits January 19, 2026 13:31

Initial version for lettign cmake add libtorch automatically. cpu ver…

78895e8

…sion is probably ok (at leat on my mac it works), but gpu still needs to filter versions correctly.

Include and verify the possible CUDA versions for which libtorch down…

3e2faef

…loads are available. Still needs to be tested.

kjh-giesbertz marked this pull request as draft January 22, 2026 09:55

kjh-giesbertz marked this pull request as ready for review January 22, 2026 09:55

kjh-giesbertz marked this pull request as draft January 22, 2026 09:55

Klaas Giesbertz added 3 commits January 22, 2026 11:34

Added the message modewq

442f29d

and quotation marks...

0c6d7ec

Needed to find the cuda tollkit to get the proper environment variabl…

6cf0b67

…es set.

kjh-giesbertz marked this pull request as ready for review January 22, 2026 14:31

The Caffe cmake from libtorch uses the old way to include CUDA, so fi…

b0e70e4

…nd_package(CUDA REQUIRED) needed to included. The CUDA_VERSION_STRING conflicts, so renamed that to CUDA_VERSION_NO_DOT.

awvwgk requested review from awvwgk and Copilot January 27, 2026 11:00

awvwgk self-assigned this Jan 27, 2026

Copilot started reviewing on behalf of awvwgk January 27, 2026 11:00 View session

awvwgk added the Skala Related to the Skala exchange-correlation functional label Jan 27, 2026

Copilot AI reviewed Jan 27, 2026

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Add capability for cmake to fetch libtorch itself if not found #173

Add capability for cmake to fetch libtorch itself if not found #173

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kjh-giesbertz commented Jan 22, 2026 •

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	set(USE_CUDA_LIBTORCH FALSE) #default is not to use the cuda version but cpu version
	set(USE_CUDA_LIBTORCH FALSE) # default is not to use the cuda version but cpu version

	set(SUPPORTED_CUDA_VERSION_NO_DOTS "126" "128" "130")
	set(SUPPORTED_CUDA_VERSION_NO_DOTS "121" "124" "126" "128" "130")

		# Set CMAKE_PREFIX_PATH to find the downloaded libtorch
		set(CMAKE_PREFIX_PATH "${LIBTORCH_DOWNLOAD_DIR};${CMAKE_PREFIX_PATH}")

-    # Set CMAKE_PREFIX_PATH to find the downloaded libtorch
-    set(CMAKE_PREFIX_PATH "${LIBTORCH_DOWNLOAD_DIR};${CMAKE_PREFIX_PATH}")
+    # Extend CMAKE_PREFIX_PATH so that this directory (and any code including it)
+    # can locate the downloaded LibTorch. This is intentionally done at directory
+    # scope so that subsequent find_package(Torch) calls in the project can reuse
+    # the same installation. It is placed outside the download/extract block so
+    # that an already-extracted LibTorch is still picked up on re-configure.
+    list(PREPEND CMAKE_PREFIX_PATH "${LIBTORCH_DOWNLOAD_DIR}")

Add capability for cmake to fetch libtorch itself if not found #173

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kjh-giesbertz commented Jan 22, 2026 •

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