odex files are replaced with Executable and Linkable Format (ELF) executables. dex files as part of APK files, while the. To maintain backward compatibility, ART uses the same input bytecode as Dalvik, supplied through standard. At the same time, ART brings improvements in performance, garbage collection, applications debugging and profiling. By reducing the overall amount of compilation that needs to be performed across the operation of an application, a mobile device's processor usage is reduced and battery runtime is improved. Unlike Dalvik, which since Android 2.2 "Froyo" uses just-in-time (JIT) compilation to compile the bytecode every time an application is launched, ART introduces use of ahead-of-time (AOT) compilation by performing it upon the installation of an application. ART replaces Dalvik, which is the process virtual machine originally used by Android, and performs transformation of the application's bytecode into native instructions that are later executed by the device's runtime environment. The main difference however, is that ART compiles everything ahead of time, whereas dalvik only compiled a subset of the bytecode using heuristics to detect the code that was executed most frequently, and it compiled during execution.Īndroid Runtime (ART) is an application runtime environment used by the Android mobile operating system. This is called AOT (ahead-of-time) compilation.īoth tools are normally run at install time on the device.Īnother factor to take into account is that dalvik used a JIT (just-in-time) compiler - meaning that it was also able to compile bytecode to native code. So instead of having bytecode that is interpreted by a virtual machine, it now has native code that can be executed natively by the processor. The result is essentially an elf file that is then executed natively. This is very similar to the original dex file, except that it uses some optimized opcodes, like the optimized invoke virtual instruction.ĭex2oat takes a dex file and compiles it. The result of dexopt is an odex (optimized dex) file. It does things like replacing a virtual invoke instruction with an optimized version that includes the vtable index of the method being called, so that it doesn't have to perform a method lookup during execution. Dexopt does some optimizations on the dex file.
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