为什么与本地C/C ++相比，JIT版本的语言仍然更慢并且内存效率更低? [英] Why are JIT-ed languages still slower and less memory efficient than native C/C++?
问题描述
解释器需要做很多额外的工作，因此可以理解，翻译器的运行速度明显慢于本机代码.但是C#或Java之类的语言具有JIT编译器，据说可以编译为平台本机代码.
Interpreters do a lot of extra work, so it is understandable that they end up significantly slower than native machine code. But languages such as C# or Java have JIT compilers, which supposedly compile to platform native machine code.
但是，根据基准看起来足够合法，在大多数情况下，速度还是比C/C ++慢2-4倍?当然，与平均优化的C/C ++代码相比，我的意思是.我很清楚JIT编译的优化好处以及它们产生代码的能力，这些代码比未经过优化的C + C ++更快.
And yet, according to benchmarks that seem legit enough, in most of the cases are still 2-4x times slower than C/C++? Of course, I mean compared to equally optimized C/C++ code. I am well aware of the optimization benefits of JIT compilation and their ability to produce code that is faster than poorly optimized C+C++.
And after all that noise about how good the Java memory allocation is, why such a horrendous memory usage? 2x to 50x, on average about 30x times more memory is being used across that particular benchmark suite, which is nothing to sneeze at...
请注意，我不想启动WAR，而是在询问定义这些性能和效率指标的技术细节.
NOTE that I don't want to start a WAR, I am asking about the technical details which define those performance and efficiency figures.
推荐答案
某些差异的原因；
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JIT编译器大多数情况下都可以快速编译，而跳过一些需要较长时间才能找到的优化.
JIT compilers mostly compile quickly and skip some optimizations that take longer to find.
VM通常会强制执行安全措施，这会降低执行速度.例如.除非保证在正确的范围内，否则数组访问始终在.Net中进行边界检查
VM's often enforce safety and this slows execution. E.g. Array access is always bounds checked in .Net unless guaranteed within the correct range
在C ++中使用SSE(如果适用，可以提高性能)很容易，而在当前VM上很难使用
Using SSE (great for performance if applicable) is easy from C++ and hard from current VM's
与其他方面相比，C ++中的性能在其他方面具有更高的优先级
Performance gets more priority in C++ over other aspects when compared to VM's
VM经常会保留一段时间未使用的内存，然后再返回到似乎使用"更多内存的操作系统.
VM's often keep unused memory a while before returning to the OS seeming to 'use' more memory.
某些虚拟机使对象的值类型为int/ulong ..，这增加了对象内存开销
Some VM's make objects of value types like int/ulong.. adding object memory overhead
某些VM的自动对齐数据结构浪费大量内存(以提高性能)
Some VM's auto-Align data structures a lot wasting memory (for performance gains)
某些VM将布尔值实现为int(4个字节)，几乎没有关注内存保存.
Some VM's implement a boolean as int (4 bytes), showing little focus on memoryconservation.
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