Subzero: Make sure register preferences obey register class constraints.

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 215 matching lines @@
         }
       }
       Str << "\n";
     }
 
     Variable *Prefer = Cur.Var->getPreferredRegister();
     int32_t PreferReg = Prefer && Prefer->hasRegTmp() ? Prefer->getRegNumTmp()
                                                       : Variable::NoRegister;
     bool AllowedToOverlap = Cur.Var->getRegisterOverlap() &&
                             PreferReg != Variable::NoRegister &&
+                            RegMask[PreferReg] &&
                             !PrecoloredUnhandled[PreferReg];
     if (PreferReg != Variable::NoRegister &&
         (AllowedToOverlap || Free[PreferReg])) {
       // First choice: a preferred register that is either free or is
       // allowed to overlap with its linked variable.
       Cur.Var->setRegNumTmp(PreferReg);
       if (Func->getContext()->isVerbose(IceV_LinearScan)) {
         Str << "Preferring   ";
         Cur.dump(Func);
         Str << "\n";
@@ skipping 222 matching lines @@
   }
   Str << "++++++ Inactive:\n";
   for (UnorderedRanges::const_iterator I = Inactive.begin(), E = Inactive.end();
        I != E; ++I) {
     I->dump(Func);
     Str << "\n";
   }
 }
 
 } // end of namespace Ice