Subzero: Convert NULL->nullptr.

src/IceRegAlloc.cpp

 //===- subzero/src/IceRegAlloc.cpp - Linear-scan implementation -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the LinearScan class, which performs the
@@ skipping 392 matching lines @@
     // preference when the current Variable has an unambiguous "first"
     // definition.  The preference is some source Variable of the
     // defining instruction that either is assigned a register that is
     // currently free, or that is assigned a register that is not free
     // but overlap is allowed.  Overlap is allowed when the Variable
     // under consideration is single-definition, and its definition is
     // a simple assignment - i.e., the register gets copied/aliased
     // but is never modified.  Furthermore, overlap is only allowed
     // when preferred Variable definition instructions do not appear
     // within the current Variable's live range.
-    Variable *Prefer = NULL;
+    Variable *Prefer = nullptr;
     int32_t PreferReg = Variable::NoRegister;
     bool AllowOverlap = false;
     if (FindPreference) {
       if (const Inst *DefInst = VMetadata->getFirstDefinition(Cur)) {
         assert(DefInst->getDest() == Cur);
         bool IsAssign = DefInst->isSimpleAssign();
         bool IsSingleDef = !VMetadata->isMultiDef(Cur);
         for (SizeT i = 0; i < DefInst->getSrcSize(); ++i) {
           // TODO(stichnot): Iterate through the actual Variables of the
           // instruction, not just the source operands.  This could
@@ skipping 319 matching lines @@
     Str << "\n";
   }
   Str << "++++++ Inactive:\n";
   for (const Variable *Item : Inactive) {
     dumpLiveRange(Item, Func);
     Str << "\n";
   }
 }
 
 } // end of namespace Ice