Fix SLTIU instruction in MIPS assembler, disassembler, and simulator.

runtime/vm/simulator_mips.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <setjmp.h>
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_MIPS)
 
@@ skipping 2165 matching lines @@
       break;
     }
     case SLTI: {
       // Format(instr, "slti 'rt, 'rs, 'imms");
       int32_t rs_val = get_register(instr->RsField());
       int32_t imm_val = instr->SImmField();
       set_register(instr->RtField(), rs_val < imm_val ? 1 : 0);
       break;
     }
     case SLTIU: {
-      // Format(instr, "slti 'rt, 'rs, 'immu");
+      // Format(instr, "sltiu 'rt, 'rs, 'imms");
       uint32_t rs_val = get_register(instr->RsField());
-      uint32_t imm_val = instr->UImmField();
-      set_register(instr->RtField(), rs_val < imm_val ? 1 : 0);
+      int32_t imm_val = instr->SImmField();  // Sign extend to 32-bit.
+      uint32_t immu_val = static_cast<uint32_t>(imm_val);  // Treat as unsigned.
+      set_register(instr->RtField(), rs_val < immu_val ? 1 : 0);
       break;
     }
     case SDC1: {
       // Format(instr, "sdc1 'ft, 'imms('rs)");
       int32_t base_val = get_register(instr->RsField());
       int32_t imm_val = instr->SImmField();
       uword addr = base_val + imm_val;
       if (Simulator::IsIllegalAddress(addr)) {
         HandleIllegalAccess(addr, instr);
       } else {
@@ skipping 274 matching lines @@
   set_register(kExceptionObjectReg, bit_cast<int32_t>(raw_exception));
   set_register(kStackTraceObjectReg, bit_cast<int32_t>(raw_stacktrace));
   buf->Longjmp();
 }
 
 }  // namespace dart
 
 #endif  // !defined(HOST_ARCH_MIPS)
 
 #endif  // defined TARGET_ARCH_MIPS