[SystemZ] Use POPCNT instruction on z196

We already exploit a number of instructions specific to z196,
but not yet POPCNT.  Add support for the population-count
facility, MC support for the POPCNT instruction, CodeGen
support for using POPCNT, and implement the getPopcntSupport
TargetTransformInfo hook.

llvm-svn: 233689
diff --git a/llvm/lib/Target/SystemZ/SystemZSubtarget.cpp b/llvm/lib/Target/SystemZ/SystemZSubtarget.cpp
index 4b5c23c..0999b45 100644
--- a/llvm/lib/Target/SystemZ/SystemZSubtarget.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZSubtarget.cpp
@@ -38,7 +38,8 @@
                                    const TargetMachine &TM)
     : SystemZGenSubtargetInfo(TT, CPU, FS), HasDistinctOps(false),
       HasLoadStoreOnCond(false), HasHighWord(false), HasFPExtension(false),
-      HasFastSerialization(false), HasInterlockedAccess1(false),
+      HasPopulationCount(false), HasFastSerialization(false),
+      HasInterlockedAccess1(false),
       TargetTriple(TT), InstrInfo(initializeSubtargetDependencies(CPU, FS)),
       TLInfo(TM, *this), TSInfo(*TM.getDataLayout()), FrameLowering() {}