Introduce %_IsMinusZero.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 8049b689eacf5e4ca579e42fa61d130eaccb8dff..a809ffd3cc236d997725a190b9cbba38005030dd 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -2472,6 +2472,34 @@ void LCodeGen::DoCmpHoleAndBranch(LCmpHoleAndBranch* instr) {
 }
 
 
+void LCodeGen::DoCompareMinusZeroAndBranch(LCompareMinusZeroAndBranch* instr) {
+  Representation rep = instr->hydrogen()->value()->representation();
+  ASSERT(!rep.IsInteger32());
+  Label if_false;
+  Register scratch = ToRegister(instr->temp());
+
+  if (rep.IsDouble()) {
+    DwVfpRegister value = ToDoubleRegister(instr->value());
+    __ VFPCompareAndSetFlags(value, 0.0);
+    __ b(ne, &if_false);
+    __ VmovHigh(scratch, value);
+    __ cmp(scratch, Operand(0x80000000));
+  } else {
+    Register value = ToRegister(instr->value());
+    __ CheckMap(
+        value, scratch, Heap::kHeapNumberMapRootIndex, &if_false, DO_SMI_CHECK);
+    __ ldr(scratch, FieldMemOperand(value, HeapNumber::kExponentOffset));
+    __ ldr(ip, FieldMemOperand(value, HeapNumber::kMantissaOffset));
+    __ cmp(scratch, Operand(0x80000000));
+    __ cmp(ip, Operand(0x00000000), eq);
+  }
+  EmitBranch(instr, eq);
+
+  __ bind(&if_false);
+  EmitFalseBranch(instr, al);
+}
+
+
 Condition LCodeGen::EmitIsObject(Register input,
                                  Register temp1,
                                  Label* is_not_object,