Disable all standard lib functions for NVVM.

[jlebar]

Summary

NVVM doesn't have a standard library, as currently implemented, so this
just isn't going to work. I'd like to revisit this, since it's hiding
opportunities for optimization, but correctness comes first.

Thank you to hfinkel for pointing me in the right direction here.

[tra]

LGTM.

llvm/trunk/lib/Analysis/TargetLibraryInfo.cpp

if (!T.isOSLinux()) {
     TLI.setUnavailable(LibFunc::ftello64);
     TLI.setUnavailable(LibFunc::lstat64);
     TLI.setUnavailable(LibFunc::open64);
     TLI.setUnavailable(LibFunc::stat64);
     TLI.setUnavailable(LibFunc::statvfs64);
     TLI.setUnavailable(LibFunc::tmpfile64);
   }
 
+  // As currently implemented in clang, NVPTX code has no standard library to
+  // speak of.  Headers provide a standard-ish library implementation, but many
+  // of the signatures are wrong -- for example, many libm functions are not
+  // extern "C".
+  //
+  // libdevice, an IR library provided by nvidia, is linked in by the front-end,
+  // but only used functions are provided to llvm.  Moreover, most of the
+  // functions in libdevice don't map precisely to standard library functions.
+  //
+  // FIXME: Having no standard library prevents e.g. many fastmath
+  // optimizations, so this situation should be fixed.
+  if (T.isNVPTX())
+    TLI.disableAllFunctions();
+
   TLI.addVectorizableFunctionsFromVecLib(ClVectorLibrary);
 }
 
 TargetLibraryInfoImpl::TargetLibraryInfoImpl() {
   // Default to everything being available.
   memset(AvailableArray, -1, sizeof(AvailableArray));
 
   initialize(*this, Triple(), StandardNames);