[libclc] Override generic symbol using llvm-link --override flag instead of using weak linkage #156778
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…ead of using weak linkage 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)
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✅ With the latest revision this PR passed the C/C++ code formatter. |
arsenm
approved these changes
Sep 4, 2025
frasercrmck
approved these changes
Sep 4, 2025
Good question. IIUC that means in the future we could use thin-lto for libclc compilation, right? I think --internalize flag, which is currently required to internalize symbols in CLC library, has similar problem. We can investigate how to mitigate the issues later. |
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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)