iOS App瘦身注意armv7 armv7s arm64
之前每个版本的ipa包打出来都才20M出头，后来不知道从哪个版本起打的包每次都将近40M，但是工程中也没有明显的增加很大第三方类或者图
片、静态文件。于是就开始了各种瘦身计划：压缩图片，删除不必要静态库。做了一番改动后发现包只比原来小了1M多，收效甚微。后来听同事说了
armv6 armv7 armv7s arm64引起编译包翻倍增大的问题，于是就试了一下，果然ipa包又回到了以前的大小。下边来说一下关于ios这个指令集(一下内容
引子DevDiv社区jas，内容稍有修改)。
目前ios的指令集有以下几种：
- armv6
- iPhone
- iPhone2
- iPhone3G
- 第一代和第二代iPod Touch
- armv7
- iPhone4
- iPhone4S
- armv7s
- iPhone5
- iPhone5C
- arm64
- iPhone5S
机器对指令集的支持是向下兼容的，因此armv7的指令集是可以运行在iphone5S的，只是效率没那么高而已~
在xcodeTARGETS里边Architectures:
Architecture ： 指你想支持的指令集。
Valid architectures : 指即将编译的指令集。
Build Active Architecture Only : 只是否只编译当前适用的指令集。
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现在是2014年初，其实4和4S的用户还是蛮多的，而iphone3之类的机器几乎没有了，所以我们的指令集最低必须基于armv7.
因此,Architecture的值选择：armv7 armv7s arm64
PS:选arm64时需要最低支持5.1.1:
Convert Your App to a 64-Bit Binary After Updating It for iOS 7
Xcode 5.0.1 can build your app with both 32-bit and 64-bit binaries included. This combined binary requires a minimum deployment target of iOS 5.1.1 or later. The 64-bit binary runs only on 64-bit devices running iOS 7.0.3 and later. If you have an existing app, you should first update your app for iOS 7 and then port it to run on 64-bit processors. By updating it first for iOS 7, you can remove deprecated code paths and use modern practices. If you’re creating a new app, target iOS 7 and compile 32-bit and 64-bit versions of your app.
The architecture for 64-bit apps on iOS is almost identical to the architecture for OS X apps, making it easy to create a common code base that runs in both operating systems. Converting a Cocoa Touch app to 64-bit follows a similar transition process as the one for Cocoa apps on OS X. Pointers and some common C types change from 32 bits to 64 bits. Code that relies on the NSInteger and CGFloat types needs to be carefully examined.
Start by building the app for the 64-bit runtime, fixing any warnings that occur as well as searching your code for specific 64-bit issues. For example:
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Make sure all function calls have a proper prototype.
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Avoid truncating 64-bit values by accidentally assigning them to a 32-bit data type.
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Ensure that calculations are performed correctly in the 64-bit version of your app.
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Create data structures whose layouts are identical in the 32-bit and 64-bit versions of your app (such as when you write a data file to iCloud).
1，如果想自己的app在各个机器都能够最高效率的运行，则需要将Build Active Architecture Only改为NO,Valid architectures选择对应的指令集：armv7 armv7s arm64。这个会为各个指令集编译对应的代码，因此最后的 ipa体积基本翻了3倍,Release版本必须NO。
2，如果想让app体积保持最小，则现阶段应该选择Valid architectures为armv7,这样Build Active Architecture Only选YES或NO就无所谓了