[PATCH] D38883: [CMake][OpenMP] Customize default offloading arch

Artem Belevich via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Fri Oct 13 10:52:39 PDT 2017

tra added inline comments.

Comment at: lib/Driver/ToolChains/Cuda.cpp:170-182
-    // This code prevents IsValid from being set when
-    // no libdevice has been found.
-    bool allEmpty = true;
-    std::string LibDeviceFile;
-    for (auto key : LibDeviceMap.keys()) {
-      LibDeviceFile = LibDeviceMap.lookup(key);
-      if (!LibDeviceFile.empty())
Hahnfeld wrote:
> tra wrote:
> > I'd keep this code. It appears to serve useful purpose as it requires CUDA installation to have at least some libdevice library in it.  It gives us a change to find a valid installation, instead of ailing some time later when we ask for a libdevice file and fail because there are none.
> We had some internal discussions about this after I submitted the patch here.
> The main question is: Do we want to support CUDA installations without libdevice and are there use cases for that? I'd say that the user should be able to use a toolchain without libdevice together with `-nocudalib`.
Sounds reasonable. How about keeping the code but putting it under `if(!hasArg(nocudalib))`?

Comment at: lib/Driver/ToolChains/Cuda.cpp:556
+      DAL->AddJoinedArg(nullptr, Opts.getOption(options::OPT_march_EQ),
+                        CLANG_OPENMP_NVPTX_DEFAULT_ARCH);
Hahnfeld wrote:
> tra wrote:
> > This sets default GPU arch for *everyone* based on OPENMP requirements. Perhaps this should be predicated on this being openmp compilation.
> > 
> > IMO to avoid unnecessary surprises, the default for CUDA compilation should follow defaults of nvcc. sm_30 becomes default only in CUDA-9.
> > 
> This branch is only executed for OpenMP, see above
OK. I've missed that 'if'.


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