Uses slt and sltu for signed vs. unsigned comparison by the MIPS assembler.

runtime/vm/flow_graph_compiler_mips.cc

Index: runtime/vm/flow_graph_compiler_mips.cc
===================================================================
--- runtime/vm/flow_graph_compiler_mips.cc	(revision 22132)
+++ runtime/vm/flow_graph_compiler_mips.cc	(working copy)
@@ -601,10 +601,12 @@
   __ lw(T2, FieldAddress(S4, ArgumentsDescriptor::positional_count_offset()));
   // Check that min_num_pos_args <= num_pos_args.
   Label wrong_num_arguments;
-  __ BranchLess(T2, Smi::RawValue(min_num_pos_args), &wrong_num_arguments);
+  __ BranchSignedLess(T2, Smi::RawValue(min_num_pos_args),
+                      &wrong_num_arguments);
 
   // Check that num_pos_args <= max_num_pos_args.
-  __ BranchGreater(T2, Smi::RawValue(max_num_pos_args), &wrong_num_arguments);
+  __ BranchSignedGreater(T2, Smi::RawValue(max_num_pos_args),
+                         &wrong_num_arguments);
 
   // Copy positional arguments.
   // Argument i passed at fp[kLastParamSlotIndex + num_args - 1 - i] is copied
@@ -724,7 +726,7 @@
       // arguments have been passed, where k is param_pos, the position of this
       // optional parameter in the formal parameter list.
       const int param_pos = num_fixed_params + i;
-      __ BranchGreater(T2, param_pos, &next_parameter);
+      __ BranchSignedGreater(T2, param_pos, &next_parameter);
       // Load T3 with default argument.
       const Object& value = Object::ZoneHandle(
           parsed_function().default_parameter_values().At(i));
@@ -885,7 +887,8 @@
 
       // Skip Branch if T1 is less than the threshold.
       Label dont_branch;
-      __ BranchLess(T1, FLAG_optimization_counter_threshold, &dont_branch);
+      __ BranchSignedLess(T1, FLAG_optimization_counter_threshold,
+                          &dont_branch);
 
       ASSERT(function_reg == T0);
       __ Branch(&StubCode::OptimizeFunctionLabel());