[Clang] Automatically link the compiler-rt for GPUs if present

[jhuber6]

Summary:
This automically links copmiler-rt for offloading languages if it
exists in the resource directory.

[llvmbot]

@llvm/pr-subscribers-clang-driver

@llvm/pr-subscribers-clang

Author: Joseph Huber (jhuber6)

Changes

Summary:
This automically links copmiler-rt for offloading languages if it
exists in the resource directory.

---

Full diff: https://github.com/llvm/llvm-project/pull/109152.diff

1 Files Affected:

• (modified) clang/lib/Driver/ToolChains/Clang.cpp (+6)

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index c00df5f5bc729c..1e615214580134 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -9239,6 +9239,12 @@ void LinkerWrapper::ConstructJob(Compilation &C, const JobAction &JA,
         CmdArgs.push_back(Args.MakeArgString(
             "--device-linker=" + TC.getTripleString() + "=" + "-lm"));
       }
+      auto HasCompilerRT = getToolChain().getVFS().exists(
+          TC.getCompilerRT(Args, "builtins", ToolChain::FT_Static));
+      if (HasCompilerRT)
+        CmdArgs.push_back(
+            Args.MakeArgString("--device-linker=" + TC.getTripleString() + "=" +
+                               "-lclang_rt.builtins"));
     });
   }
 

[jplehr]

I guess that makes sense.

[shiltian]

I'm not sure about this. What does compiler-rt provide?

[jhuber6]

I'm not sure about this. What does compiler-rt provide?

It's clang_rt.builtins. So, basically complex number multiplication / division, wide integer stuff (I think the backend handles i128 now though). We currently have a wrapper header that defined __mulsc3 for the device even though it's supposed to come from the compiler-rt.

[shiltian]

I like this direction and I think it should be the right way. However, IMHO, I think it needs discussion (and potentially an RFC).

[jhuber6]

I like this direction and I think it should be the right way. However, IMHO, I think it needs discussion (and potentially an RFC).

Moving from the header to the definition in compiler-rt would warrant an RFC, this patch just automatically links something that exists and will only provide definitions if they are undefined. So the only effect this has right now is linking in a symbol that would otherwise be a linker error.

[jplehr]

I ran this through a buildbot config and found no errors.

[jplehr]

I think this is a reasonable change.