The new Android runtime ART, which was available for testing in 4.4 KitKat and released in 5.0 Lollipop, compiles applications at install time so that they run and load faster. One of the utilities used for this compilation process is called dex2oat.

I spent some time trying to figure out how to use dex2oat in order to compile an edited APK and overwrite an app without reinstalling it, but was not successful. I'm going to put here what I learned and some resoucres so that maybe it can help someone else.

dex2oat
You can access the dex2oat utility by using a terminal command line app, such as Terminal Emulator. You may need root to access it. Calling the dex2oat utility without any options will output its usage information to the log. Here are the contents of the log, which outlines how to use dex2oat:

Usage: dex2oat [options]...
--dex-file=<dex-file>: specifies a .dex file to compile.
Example: --dex-file=/system/framework/core.jar
--zip-fd=<file-descriptor>: specifies a file descriptor of a zip file
containing a classes.dex file to compile.
Example: --zip-fd=5
--zip-location=<zip-location>: specifies a symbolic name for the file
corresponding to the file descriptor specified by --zip-fd.
Example: --zip-location=/system/app/Calculator.apk
--oat-file=<file.oat>: specifies the oat output destination via a filename.
Example: --oat-file=/system/framework/boot.oat
--oat-fd=<number>: specifies the oat output destination via a file descriptor.
Example: --oat-fd=6
--oat-location=<oat-name>: specifies a symbolic name for the file corresponding
to the file descriptor specified by --oat-fd.
Example: --oat-location=/data/dalvik-cache/system@app@Calculator.apk.oat
--oat-symbols=<file.oat>: specifies the oat output destination with full symbols.
Example: --oat-symbols=/symbols/system/framework/boot.oat
--bitcode=<file.bc>: specifies the optional bitcode filename.
Example: --bitcode=/system/framework/boot.bc
--image=<file.art>: specifies the output image filename.
Example: --image=/system/framework/boot.art
--image-classes=<classname-file>: specifies classes to include in an image.
Example: --image=frameworks/base/preloaded-classes
--base=<hex-address>: specifies the base address when creating a boot image.
Example: --base=0x50000000
--boot-image=<file.art>: provide the image file for the boot class path.
Example: --boot-image=/system/framework/boot.art
Default: $ANDROID_ROOT/system/framework/boot.art
--android-root=<path>: used to locate libraries for portable linking.
Example: --android-root=out/host/linux-x86
Default: $ANDROID_ROOT
--instruction-set=(arm|arm64|mips|x86|x86_64): compile for a particular
instruction set.
Example: --instruction-set=x86
Default: arm
--instruction-set-features=...,: Specify instruction set features
Example: --instruction-set-features=div
Default: default
--compiler-backend=(Quick|Optimizing|Portable): select compiler backend
set.
Example: --compiler-backend=Portable
Default: Quick
--compiler-filter=(verify-none|interpret-only|space|balanced|speed|everything):
select compiler filter.
Example: --compiler-filter=everything
Default: speed
--huge-method-max=<method-instruction-count>: the threshold size for a huge
method for compiler filter tuning.
Example: --huge-method-max=10000
Default: 10000
--huge-method-max=<method-instruction-count>: threshold size for a huge
method for compiler filter tuning.
Example: --huge-method-max=10000
Default: 10000
--large-method-max=<method-instruction-count>: threshold size for a large
method for compiler filter tuning.
Example: --large-method-max=600
Default: 600
--small-method-max=<method-instruction-count>: threshold size for a small
method for compiler filter tuning.
Example: --small-method-max=60
Default: 60
--tiny-method-max=<method-instruction-count>: threshold size for a tiny
method for compiler filter tuning.
Example: --tiny-method-max=20
Default: 20
--num-dex-methods=<method-count>: threshold size for a small dex file for
compiler filter tuning. If the input has fewer than this many methods
and the filter is not interpret-only or verify-none, overrides the
filter to use speed
Example: --num-dex-method=900
Default: 900
--host: used with Portable backend to link against host runtime libraries
--dump-timing: display a breakdown of where time was spent
--include-patch-information: Include patching information so the generated code
can have its base address moved without full recompilation.
--no-include-patch-information: Do not include patching information.
--include-debug-symbols: Include ELF symbols in this oat file
--no-include-debug-symbols: Do not include ELF symbols in this oat file
--runtime-arg <argument>: used to specify various arguments for the runtime,
such as initial heap size, maximum heap size, and verbose output.
Use a separate --runtime-arg switch for each argument.
Example: --runtime-arg -Xms256m
--profile-file=<filename>: specify profiler output file to use for compilation.
--print-pass-names: print a list of pass names
--disable-passes=<pass-names>: disable one or more passes separated by comma.
Example: --disable-passes=UseCount,BBOptimizations

Resources

Here are some resources that may help you learn more about dex2oat:

• MatthiasSchaff: A multi-part series that talks about what ART is and how Android converts old dex apps to the new oat format without needing an app release.
• Technical Details of Android ART: A Quora answer that goes into some detail about how Android uses dex2oat to convert the Dalvik bytecode to native code stored in an oat file.
• Anatomy of Android ART Runtime: Translated from Chinese to English so kind of hard to read, but may be useful.
• GoogleSource: Source code of the dex2oat utility released in AOSP 4.4 KitKat.