MIPS: Use BOVC/BNVC for overflow checking on r6.

src/crankshaft/mips/lithium-codegen-mips.cc

Index: src/crankshaft/mips/lithium-codegen-mips.cc
diff --git a/src/crankshaft/mips/lithium-codegen-mips.cc b/src/crankshaft/mips/lithium-codegen-mips.cc
index a82b262dbbbb86c172ec81cdb8bfb5672ef11528..d2a3ccdbfb5be04bcdfa78ea7be86c1bdf42fef7 100644
--- a/src/crankshaft/mips/lithium-codegen-mips.cc
+++ b/src/crankshaft/mips/lithium-codegen-mips.cc
@@ -1854,21 +1854,21 @@ void LCodeGen::DoAddI(LAddI* instr) {
       __ Addu(ToRegister(result), ToRegister(left), ToOperand(right));
     }
   } else {  // can_overflow.
-    Register overflow = scratch0();
     Register scratch = scratch1();
+    Label no_overflow;
     if (right->IsStackSlot()) {
       Register right_reg = EmitLoadRegister(right, scratch);
-      __ AdduAndCheckForOverflow(ToRegister(result),
-                                 ToRegister(left),
-                                 right_reg,
-                                 overflow);  // Reg at also used as scratch.
+      __ AdduAndCheckForOverflow(ToRegister(result), ToRegister(left),
+                                 right_reg, nullptr,
+                                 &no_overflow);  // Reg at also used as scratch.
     } else {
       DCHECK(right->IsRegister() || right->IsConstantOperand());
       __ AdduAndCheckForOverflow(ToRegister(result), ToRegister(left),
-                                 ToOperand(right), overflow, scratch);
+                                 ToOperand(right), nullptr, &no_overflow,
+                                 scratch);
     }
-    DeoptimizeIf(lt, instr, Deoptimizer::kOverflow, overflow,
-                 Operand(zero_reg));
+    DeoptimizeIf(al, instr);
+    __ bind(&no_overflow);
   }
 }