Conservatively disable use of integer division on Android ARM64 devices.

runtime/vm/cpu_arm.cc

Index: runtime/vm/cpu_arm.cc
diff --git a/runtime/vm/cpu_arm.cc b/runtime/vm/cpu_arm.cc
index d0ecc0dbe23952f8f8312101b4f948c6f9025f41..9ab9adf272b93224aeb8af7f4c4ec12bbd3dd665 100644
--- a/runtime/vm/cpu_arm.cc
+++ b/runtime/vm/cpu_arm.cc
@@ -207,15 +207,25 @@ void HostCPUFeatures::InitOnce() {
   // - Qualcomm Krait CPUs (QCT APQ8064) in Nexus 4 and 7 incorrectly report
   //   that they lack integer division.
   // - Marvell Armada 370/XP incorrectly reports that it has integer division.
-  // - Qualcomm Snapdragon 820/821 CPUs (MSM 8996 and MSM8996pro) in Xiaomi MI5
-  // and Pixel lack integer division even though ARMv8 requires it in A32.
   bool is_krait = CpuInfo::FieldContains(kCpuInfoHardware, "QCT APQ8064");
   bool is_armada_370xp =
       CpuInfo::FieldContains(kCpuInfoHardware, "Marvell Armada 370/XP");
-  bool is_snapdragon = CpuInfo::FieldContains(kCpuInfoHardware, "MSM8996");
+#if defined(HOST_OS_ANDROID)
+  bool is_android = true;
+#else
+  bool is_android = false;

[zra, 2017/04/05 20:29:10]

I'd prefer using OS::Name() over HOST_OS_ANDROID. And shouldn't it be
TARGET_OS_ANDROID, anyway?

+#endif
   if (is_krait) {
     integer_division_supported_ = FLAG_use_integer_division;
-  } else if (is_armada_370xp || is_snapdragon) {
+  } else if (is_android && is_arm64) {
+    // Various Android ARM64 devices, including the Qualcomm Snapdragon 820/821
+    // CPUs (MSM 8996 and MSM8996pro) in Xiaomi MI5 and Pixel lack integer
+    // division even though ARMv8 requires it in A32. Instead of attempting to
+    // track all of these devices, we conservatively disable use of integer
+    // division on Android ARM64 devices.
+    // TODO(29270): /proc/self/auxv might be more reliable here.
+    integer_division_supported_ = false;
+  } else if (is_armada_370xp) {
     integer_division_supported_ = false;
   } else {
     integer_division_supported_ =