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

runtime/vm/stub_code_mips.cc

Index: runtime/vm/stub_code_mips.cc
===================================================================
--- runtime/vm/stub_code_mips.cc	(revision 22132)
+++ runtime/vm/stub_code_mips.cc	(working copy)
@@ -286,7 +286,7 @@
   __ AddImmediate(T2, kWordSize);
   __ Bind(&loop_condition);
   __ AddImmediate(A1, -Smi::RawValue(1));  // A1 is Smi.
-  __ BranchGreaterEqual(A1, ZR, &loop);
+  __ BranchSignedGreaterEqual(A1, ZR, &loop);
 }
 
 
@@ -806,7 +806,7 @@
   __ lw(A3, Address(A2));
   __ Push(A3);
   __ addiu(A1, A1, Immediate(1));
-  __ BranchLess(A1, T1, &push_arguments);
+  __ BranchSignedLess(A1, T1, &push_arguments);
   __ delay_slot()->addiu(A2, A2, Immediate(kWordSize));
 
   __ Bind(&done_push_arguments);
@@ -1403,7 +1403,8 @@
   Label is_hot;
   if (FlowGraphCompiler::CanOptimize()) {
     ASSERT(FLAG_optimization_counter_threshold > 1);
-    __ BranchGreaterEqual(T7, FLAG_optimization_counter_threshold, &is_hot);
+    __ BranchSignedGreaterEqual(T7, FLAG_optimization_counter_threshold,
+                                &is_hot);
     // As long as VM has no OSR do not optimize in the middle of the function
     // but only at exit so that we have collected all type feedback before
     // optimizing.