[SystemZ]  Enable LoopDataPrefetch pass.

Loop data prefetching has shown some improvements on benchmarks, and is
enabled at -O1 and above.

Review: Ulrich Weigand
llvm-svn: 308024
diff --git a/llvm/lib/Target/SystemZ/SystemZTargetMachine.cpp b/llvm/lib/Target/SystemZ/SystemZTargetMachine.cpp
index cb81c0e..025bf73 100644
--- a/llvm/lib/Target/SystemZ/SystemZTargetMachine.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZTargetMachine.cpp
@@ -143,8 +143,10 @@
 } // end anonymous namespace
 
 void SystemZPassConfig::addIRPasses() {
-  if (getOptLevel() != CodeGenOpt::None)
+  if (getOptLevel() != CodeGenOpt::None) {
     addPass(createSystemZTDCPass());
+    addPass(createLoopDataPrefetchPass());
+  }
 
   TargetPassConfig::addIRPasses();
 }