今天在测试app时，发现app store上版本有奔溃现象，但是直接用xcode跑本地程序没问题。猜测release&debug版本造成的，后发现targets的 optimization level设置问题，将release版本的optimization level改为none后程序不再崩溃。

参考见： http://www.mindjuice.net/2011/11/30/how-to-fix-an-app-that-crashes-in-release-but-not-debug/

关于优化级别：GCC_OPTIMIZATION_LEVEL 描述如下
None: Do not optimize. [-O0]

With this setting, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results.  Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you would expect from the source code.

Fast: Optimizing compilation takes somewhat more time, and a lot more memory for a large function. [-O, -O1]

With this setting, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. In Apple's compiler, strict aliasing, block reordering, and inter-block scheduling are disabled by default when optimizing.

Faster: The compiler performs nearly all supported optimizations that do not involve a space-speed tradeoff. [-O2]

With this setting, the compiler does not perform loop unrolling or function inlining, or register renaming.  As compared to the 'Fast' setting, this setting increases both compilation time and the performance of the generated code.

Fastest: Turns on all optimizations specified by the 'Faster' setting and also turns on function inlining and register renaming options. This setting may result in a larger binary. [-O3]

Fastest, smallest: Optimize for size.  This setting enables all 'Faster' optimizations that do not typically increase code size.  It also performs further optimizations designed to reduce code size.