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llvm/llvm-project/libclc/10909c6bed4839c674d254204ebdcb2d4732321b
commit
10909c6bed4839c674d254204ebdcb2d4732321b
[log]
author
Wenju He <wenju.he@intel.com>
Fri Sep 05 19:58:07 2025 +0800
committer
Copybara-Service <copybara-worker@google.com>
Fri Sep 05 05:00:46 2025 -0700
tree
e67d21ce6f0753fabb2b3580924c534d5f521178
parent
769a6a6192a6da824c00b2a5f7916b17dd83b0d1 [diff]
[libclc] Override generic symbol using llvm-link --override flag instead of using weak linkage (#156778)

Before this PR, weak linkage is applied to a few CLC generic functions
to allow target specific implementation to override generic one.
However, adding weak linkage has a side effect of preventing
inter-procedural optimization, such as PostOrderFunctionAttrsPass,
because weak function doesn't have exact definition (as determined by
hasExactDefinition in the pass).

This PR resolves the issue by adding --override flag for every
non-generic bitcode file in llvm-link run. This approach eliminates the
need for weak linkage while still allowing target-specific
implementation to override generic one.
llvm-diff shows imporoved attribute deduction for some functions in
amdgcn--amdhsa.bc, e.g.
  %23 = tail call half @llvm.sqrt.f16(half %22)
=>
  %23 = tail call noundef half @llvm.sqrt.f16(half %22)

GitOrigin-RevId: 28d9255aa7c05738c7fd88711006d71d4dfc952a
4 files changed
tree: e67d21ce6f0753fabb2b3580924c534d5f521178
  1. clc/
  2. cmake/
  3. opencl/
  4. test/
  5. utils/
  6. www/
  7. check_external_calls.sh
  8. CMakeLists.txt
  9. compile-test.sh
  10. CREDITS.TXT
  11. libclc.pc.in
  12. LICENSE.TXT
  13. Maintainers.md
  14. README.md
README.md

libclc

libclc is an open source implementation of the library requirements of the OpenCL C programming language, as specified by the OpenCL 1.1 Specification. The following sections of the specification impose library requirements:

  • 6.1: Supported Data Types
  • 6.2.3: Explicit Conversions
  • 6.2.4.2: Reinterpreting Types Using as_type() and as_typen()
  • 6.9: Preprocessor Directives and Macros
  • 6.11: Built-in Functions
  • 9.3: Double Precision Floating-Point
  • 9.4: 64-bit Atomics
  • 9.5: Writing to 3D image memory objects
  • 9.6: Half Precision Floating-Point

libclc is intended to be used with the Clang compiler's OpenCL frontend.

libclc is designed to be portable and extensible. To this end, it provides generic implementations of most library requirements, allowing the target to override the generic implementation at the granularity of individual functions.

libclc currently supports PTX, AMDGPU, SPIRV and CLSPV targets, but support for more targets is welcome.

Compiling and installing

(in the following instructions you can use make or ninja)

For an in-tree build, Clang must also be built at the same time:

$ cmake <path-to>/llvm-project/llvm/CMakeLists.txt -DLLVM_ENABLE_PROJECTS="libclc;clang" \
    -DCMAKE_BUILD_TYPE=Release -G Ninja
$ ninja

Then install:

$ ninja install

Note you can use the DESTDIR Makefile variable to do staged installs.

$ DESTDIR=/path/for/staged/install ninja install

To build out of tree, or in other words, against an existing LLVM build or install:

$ cmake <path-to>/llvm-project/libclc/CMakeLists.txt -DCMAKE_BUILD_TYPE=Release \
  -G Ninja -DLLVM_DIR=$(<path-to>/llvm-config --cmakedir)
$ ninja

Then install as before.

In both cases this will include all supported targets. You can choose which targets are enabled by passing -DLIBCLC_TARGETS_TO_BUILD to CMake. The default is all.

In both cases, the LLVM used must include the targets you want libclc support for (AMDGPU and NVPTX are enabled in LLVM by default). Apart from SPIRV where you do not need an LLVM target but you do need the llvm-spirv tool available. Either build this in-tree, or place it in the directory pointed to by LLVM_TOOLS_BINARY_DIR.

Website

https://libclc.llvm.org/