Fix a bug that caused a crash if a setcc had zero uses.

llvm-svn: 574
diff --git a/llvm/lib/Target/Sparc/SparcInstrSelection.cpp b/llvm/lib/Target/Sparc/SparcInstrSelection.cpp
index c73264c..fde7282 100644
--- a/llvm/lib/Target/Sparc/SparcInstrSelection.cpp
+++ b/llvm/lib/Target/Sparc/SparcInstrSelection.cpp
@@ -1688,7 +1688,7 @@
     // to follow SSA def-use edges here, not BURG tree edges.
     // 
     Instruction* result = subtreeRoot->getInstruction();
-    Value* firstUse = (Value*) * result->use_begin();
+    Value* firstUse = result->use_empty() ? 0 : *result->use_begin();
     bool discardResult =
       (result->use_size() == 1
        && firstUse->isInstruction()