Fix HConstant(double, ...) constructor

It must always populate int32_value_, even if that's lossy, because other code (specifically, constant folding for truncating operations) relies on it.

BUG=v8:3865
LOG=y

Review URL: https://codereview.chromium.org/897263002

Cr-Commit-Position: refs/heads/master@{#26453}

src/hydrogen-instructions.cc

@@ -2810,7 +2810,7 @@ HConstant::HConstant(double double_value, Representation r,
                                            !std::isnan(double_value)) |
                  IsUndetectableField::encode(false) |
                  InstanceTypeField::encode(kUnknownInstanceType)),
-      int32_value_(HasInteger32Value() ? DoubleToInt32(double_value) : 0),
+      int32_value_(DoubleToInt32(double_value)),
       double_value_(double_value) {
   bit_field_ = HasSmiValueField::update(
       bit_field_, HasInteger32Value() && Smi::IsValid(int32_value_));

test/mjsunit/regress/regress-3865.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+function bar() {
+  var radix = 10;
+  return 21 / radix | 0;
+}
+assertEquals(2, bar());
+assertEquals(2, bar());
+%OptimizeFunctionOnNextCall(bar);
+assertEquals(2, bar());