Subzero: Use a proper RegNumT type instead of int32_t/SizeT.

src/IceRegistersMIPS32.h

 //===- subzero/src/IceRegistersMIPS32.h - Register information --*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 35 matching lines @@
                                                                                \
   Encoded_##val encode,
   REGMIPS32_GPR_TABLE
 #undef X
       Encoded_Not_GPR = -1
 };
 
 // TODO(jvoung): Floating point and vector registers...
 // Need to model overlap and difference in encoding too.
 
-static inline GPRRegister getEncodedGPR(int32_t RegNum) {
-  assert(Reg_GPR_First <= RegNum && RegNum <= Reg_GPR_Last);
+static inline GPRRegister getEncodedGPR(RegNumT RegNum) {
+  assert(int(Reg_GPR_First) <= int(RegNum));
+  assert(unsigned(RegNum) <= Reg_GPR_Last);
   return GPRRegister(RegNum - Reg_GPR_First);
 }
 
-const char *getRegName(int32_t RegNum);
+const char *getRegName(RegNumT RegNum);
 
 } // end of namespace RegMIPS32
 
 // Extend enum RegClass with MIPS32-specific register classes (if any).
 enum RegClassMIPS32 : uint8_t { RCMIPS32_NUM = RC_Target };
 
 } // end of namespace MIPS32
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEREGISTERSMIPS32_H