Subzero: Clean up some uses of *_cast<>.

src/IceTargetLoweringX8664.cpp

 //===- subzero/src/IceTargetLoweringX8664.cpp - x86-64 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 394 matching lines @@
 
   // NeedsLea is a flags indicating whether Mem needs to be materialized to a
   // GPR prior to being used. A LEA is needed if Mem.Offset is a constant
   // relocatable, or if Mem.Offset is negative. In both these cases, the LEA is
   // needed to ensure the sandboxed memory operand will only use the lower
   // 32-bits of T+Offset.
   bool NeedsLea = false;
   if (Offset != nullptr) {
     if (const auto *CR = llvm::dyn_cast<ConstantRelocatable>(Offset)) {
       NeedsLea = CR->getName() != "" || CR->getOffset() < 0;
-    } else if (const auto *Imm = llvm::cast<ConstantInteger32>(Offset)) {
+    } else if (const auto *Imm = llvm::dyn_cast<ConstantInteger32>(Offset)) {
       NeedsLea = Imm->getValue() < 0;
     } else {
       llvm::report_fatal_error("Unexpected Offset type.");
     }
   }
 
   int32_t RegNum = Variable::NoRegister;
   int32_t RegNum32 = Variable::NoRegister;
   if (T != nullptr) {
     if (T->hasReg()) {
@@ skipping 380 matching lines @@
 #define X(tag, sizeLog2, align, elts, elty, str, rcstr)                        \
   static_assert(_table1_##tag == _table2_##tag,                                \
                 "Inconsistency between ICETYPEX8664_TABLE and ICETYPE_TABLE");
 ICETYPE_TABLE
 #undef X
 } // end of namespace dummy3
 } // end of anonymous namespace
 
 } // end of namespace X8664
 } // end of namespace Ice