R600: Don't try to fix reg class when copying IMPLICIT_DEF to a register

The test case for this is way too complex to be useful as a lit test,
and I was unable to reduce it.

https://bugs.freedesktop.org/show_bug.cgi?id=65438

llvm-svn: 183937

llvm/lib/Target/R600/AMDILISelDAGToDAG.cpp

@@ -766,7 +766,8 @@ void AMDGPUDAGToDAGISel::PostprocessISelDAG() {
         continue;
       }
 
-      if (!Val.getNode()->isMachineOpcode()) {
+      if (!Val.getNode()->isMachineOpcode() ||
+          Val.getNode()->getMachineOpcode() == AMDGPU::IMPLICIT_DEF) {
         continue;
       }