optimization - Redundant opcodes in Android dex -

-

i'm looking android performance issues @ moment , noticing sub-optimal patterns in dex code. i'm wondering if knows if expected, , rationale behind might be.

for example, consider following java code:

m_testfield += i;  dosomething(m_testfield);

when built , run through baksmali looks following:

iget v1, p0, lcom/example/mainactivity$fieldtest;->m_testfield:i  add-int/2addr v1, v0  iput v1, p0, lcom/example/mainactivity$fieldtest;->m_testfield:i  iget v1, p0, lcom/example/mainactivity$fieldtest;->m_testfield:i  invoke-direct {p0, v1}, lcom/example/mainactivity$fieldtest;->dosomething(i)v

the part that's concerning me iget opcode read value of instance field register v1. same field written same v1 register in preceding opcode, opcode appear redundant.

the thing can think of done make more thread-safe. surely should programmer's responsibility (by using sync blocks) instead of compiler's responsibility. although i'm not 100% certain, think above behaviour quite different c/c++ compilers do.

i should same dex produced when proguard used. should mention i'm using latest android tools , late model jdk.

every access field independent. behavior describe, need add local variable:

int local = m_testfield; // iget local = local + i; m_testfield = local; // iput dosomething(local);

that said, combination of interpreter, just-in-time compiler , ahead-of-time compiler may end making these optimizations @ runtime anyway.


Comments

Post a Comment

Popular posts from this blog

node.js - Mongoose: Cast to ObjectId failed for value on newly created object after setting the value -

-
this question has answer here: what's mongoose error cast objectid failed value xxx @ path “_id”? 7 answers even though has been asked many times because entity has no valid objectid field. i came across situation objectid set value can casted objectid still error. the schema: var serviceschema = parammongoose.schema({ servicename:{ type: parammongoose.schema.types.objectid , ref: 'servicenames',required:true } }); pseudo code: servicefromdb=new service({servicename:'some name'}); servicefromdb.servicename='000000000000000000000001'; servicefromdb.save(function(paramerror,paramdata){ if(paramerror){ console.log('but but...',servicefromdb,paramerror) } }); the output of code is: but but... { servicename: 000000000000000000000001, _id: 55079a90286f49280364f78b } { [casterror: cast objectid faile...
Read more

gradle error "Cannot convert the provided notation to a File or URI" -

-
i have defined 2 system properties in gradle.properties: systemprop.builddir=build systemprop.cfgdir=build\\cfg and have following task defined in build.gradle: task clean(group:'clean',description:'clean project') << { ant.sequential { delete(dir: system.properties.builddir) mkdir(dir: system.properties.builddir) delete(dir: system.properties.cfgdir) mkdir(dir: system.properties.cfgdir) } } this generates following error: execution failed task ':clean'. > cannot convert provided notation file or uri: {dir=build}. following types/formats supported: - string or charsequence path, e.g 'src/main/java' or '/usr/include' - string or charsequence uri, e.g 'file:/usr/include' - file instance. - uri or url instance. but equivalent block of code not generate error , works expected: task clean(group:'clean',description:'clean project') << { ...
Read more

python - NameError: name 'subprocess' is not defined -

-
i'm trying make rng website: http://jamesdotcom.com/?p=417 . when run following code: captureimage = subprocess.popen( [ "fswebcam", "-r", "356x292", "-d", "/dev/video0", "static.jpg", "--skip", "10" ], stdout=devnull, stderr=devnull) captureimage.communicate() i following error message: nameerror: name 'subprocess' not defined what should do? thanks have imported first? import subprocess captureimage = subprocess.popen(["fswebcam", ...) subprocess included in python standard library since python 2.4. should not necessary install it.
Read more