From 0e738323a9c445e31b4e1b1dcb2beb19d6f103ef Mon Sep 17 00:00:00 2001 From: Jon Chesterfield Date: Mon, 15 Nov 2021 15:56:00 +0000 Subject: [PATCH] [openmp][amdgpu] Add comment warning that libm may be broken Using llvm-link to add rocm device-libs probably doesn't work Reviewed By: arsenm Differential Revision: https://reviews.llvm.org/D112639 --- clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp b/clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp index b138000..863e2c5 100644 --- a/clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp +++ b/clang/lib/Driver/ToolChains/AMDGPUOpenMP.cpp @@ -106,6 +106,22 @@ const char *AMDGCN::OpenMPLinker::constructLLVMLinkCommand( } if (HasLibm) { + // 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 SmallVector BCLibs = AMDGPUOpenMPTC.getCommonDeviceLibNames(Args, SubArchName.str()); llvm::for_each(BCLibs, [&](StringRef BCFile) { -- 2.7.4