[PATCH] D119841: [OpenMP] Pass AMDGPU math libraries into the linker wrapper
Johannes Doerfert via Phabricator via cfe-commits
cfe-commits at lists.llvm.org
Tue Feb 15 11:53:46 PST 2022
jdoerfert added a subscriber: arsenm.
jdoerfert added inline comments.
================
Comment at: clang/lib/Driver/ToolChains/Clang.cpp:8195
+ // Get the AMDGPU math libraries.
+ // FIXME: This method is bad, remove once AMDGPU has a proper math library.
+ for (auto &I : llvm::make_range(OpenMPTCRange.first, OpenMPTCRange.second)) {
----------------
jhuber6 wrote:
> jdoerfert wrote:
> > Can you elaborate on this comment, what's bad, how would the better version look
> It's explained in more detail where this is done for the AMDGPU ToolChain, e.g.
> ```
> // This is not certain to work. The device libs added here, and passed to
> // llvm-link, are missing attributes that they expect to be inserted when
> // passed to mlink-builtin-bitcode. The amdgpu backend does not generate
> // conservatively correct code when attributes are missing, so this may
> // be the root cause of miscompilations. Passing via mlink-builtin-bitcode
> // ultimately hits CodeGenModule::addDefaultFunctionDefinitionAttributes
> // on each function, see D28538 for context.
> // Potential workarounds:
> // - unconditionally link all of the device libs to every translation
> // unit in clang via mlink-builtin-bitcode
> // - build a libm bitcode file as part of the DeviceRTL and explictly
> // mlink-builtin-bitcode the rocm device libs components at build time
> // - drop this llvm-link fork in favour or some calls into LLVM, chosen
> // to do basically the same work as llvm-link but with that call first
> // - write an opt pass that sets that on every function it sees and pipe
> // the device-libs bitcode through that on the way to this llvm-link
> ```
> Should I copy the gist here?
Is it still relevant? We don't use llvm-link here, do we?
@arsenm, the backend is (almost) OK with the lack of attributes, is it not?
================
Comment at: clang/lib/Driver/ToolChains/Clang.cpp:8205
+ if (llvm::find(LibraryArgs, "m") == LibraryArgs.end() && !D.CCCIsCXX())
+ continue;
+
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I'd switch the conditions.
More importantly, does this require that the user passes -lm to the linker invocation? I'm not convinced we should not always link these in.
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https://reviews.llvm.org/D119841/new/
https://reviews.llvm.org/D119841
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