Subzero: x8664: Fix a "uitofp i32 to double" lowering error.

src/IceTargetLoweringX86BaseImpl.h

 //===- subzero/src/IceTargetLoweringX86BaseImpl.h - x86 lowering -*- C++ -*-==//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 3044 matching lines @@
         T_1 = makeReg(IceType_i64);
       } else {
         assert(Src0RM->getType() != IceType_i64);
         assert(Traits::Is64Bit || Src0RM->getType() != IceType_i32);
         T_1 = makeReg(IceType_i32);
       }
       Variable *T_2 = makeReg(DestTy);
       if (Src0RM->getType() == T_1->getType())
         _mov(T_1, Src0RM);
       else
-        _movzx(T_1, Src0RM);
+        _movzx(T_1, Src0RM)->setMustKeep();
       _cvt(T_2, T_1, Traits::Insts::Cvt::Si2ss);
       _mov(Dest, T_2);
     }
     break;
   }
   case InstCast::Bitcast: {
     Operand *Src0 = Instr->getSrc(0);
     if (DestTy == Src0->getType()) {
       auto *Assign = InstAssign::create(Func, Dest, Src0);
       lowerAssign(Assign);
@@ skipping 5014 matching lines @@
         emitGlobal(*Var, SectionSuffix);
       }
     }
   } break;
   }
 }
 } // end of namespace X86NAMESPACE
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGX86BASEIMPL_H