blocks|key|2990302|text|嗯，你应该看看Brian+Goetz的文章，看看有没有例子。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2990303|简而言之，HotSpot能够并且将：|2990304|如果无法从其他object|2990305|Eliminate死代码访问监视器，则|unordered-list-item|2990306|内联方法|ordered-list-item|2990307|会连接相同threads|2990308|Eliminate锁上的相邻synchronized块(因此，大多数微基准测试都是针对非volatile监视器接口调用的|offset|length|style|CODE|2990309|内存写操作，方法的直接方法调用仅在一次实现时实现|2990310|2990311|等等|2990312|entityMap^0|0|0|0|0|0|0|E|C|18|8|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|12|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|13|8|@]|9|@]|A|$]]|$1|I|3|J|5|K|7|14|8|@]|9|@]|A|$]]|$1|L|3|M|5|K|7|15|8|@]|9|@]|A|$]]|$1|N|3|O|5|K|7|16|8|@$P|17|Q|18|R|S]|$P|19|Q|1A|R|S]]|9|@]|A|$]]|$1|T|3|U|5|6|7|1B|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1D|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|Z|$]]

Well, you should scan Brian Goetz's articles for examples.

In brief, HotSpot can and will:

<ol>
<li>Inline methods</li>
<li>Join adjacent <code>synchronized</code> blocks on the same object</li>
<li>Eliminate locks if monitor is not reachable from other threads</li>
<li>Eliminate dead code (hence most of micro-benchmarks are senseless)</li>
<li>Drop memory write for non-<code>volatile</code> variables</li>
<li>Replace interface calls with direct method calls for methods only implemented once</li>
</ol>

et cetera

blocks|key|4888609|text|Jikes+RVM站点上有一个关于现代JVM使用的优化的很好的演示文稿：ACACES’06+-+Dynamic+Compilation+and+Adaptive+Optimization+in+Virtual+Machines|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4888610|它讨论了架构、权衡、度量和技术。并列出了至少20个JVM用来优化机器代码的方法。|4888611|entityMap|0|LINK|mutability|MUTABLE|url|http://www.complang.tuwien.ac.at/andi/ACACES06.pdf^0|10|25|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

There is a great presentation on the optimizations used by modern JVMs on the Jikes RVM site:
<a href="http://www.complang.tuwien.ac.at/andi/ACACES06.pdf" rel="nofollow noreferrer">ACACES’06 - Dynamic Compilation and Adaptive Optimization in Virtual Machines</a>

It discusses architecture, tradeoffs, measurements and techniques. And names at least 20 things JVMs do to optimize the machine code.

blocks|key|4606225|text|我认为有趣的东西是那些传统编译器不能与JIT相反的东西。内联方法、消除死代码、CSE、实时分析等都是由一般的c%2B%2B编译器完成的，这里没有什么特别之处。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4606226|但是，基于乐观的假设来优化一些东西，然后如果它们被证明是错误的，那么就去优化吧？(假设有一个特定的类型，如果不这样做，删除以后无论如何都会失败的分支，..)如果我们可以保证目前只存在一个类(同样，只有在去优化的情况下才能可靠地工作)，那么是否可以删除虚拟调用？我认为，自适应优化是真正区别于您运行的mill+c%2B%2B编译器的一件事。|4606227|也许还可以提到JIT所做的运行时分析，以分析它应该应用哪些优化(尽管对于所有的分析导向优化来说，这不再是唯一的)。|4606228|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

I think the interesting stuff are those things that a conventional compiler can't do contrary to the JIT. Inlining methods, eliminating dead code, CSE, live analysis, etc. are all done by your average c++ compiler as well, nothing "special" here

But optimizing something based on optimistic assumptions and then deoptimizing later if they turn out to be wrong? (assuming a specific type, removing branches that will fail later anyhow if not done,..) Removing virtual calls if we can guarantee that there exists only one class at the moment (again something that only reliably works with deoptimization)? Adaptive optimization is I think the one thing that really distinguishes the JIT from your run of the mill c++ compiler.

Maybe also mention the runtime profiling done by the JIT to analyse which optimizations it should apply (not that unique anymore with all the profile-guided optimizations though).

blocks|key|2990243|text|在this+article中有一个古老但可能仍然有效的概述。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2990244|亮点似乎是基于可用的运行时性能分析信息执行经典优化：|2990245|2990246|JITting+"hot“进入本机代码|unordered-list-item|2990247|自适应内联-内联给定方法分派的最常调用的实现，以避免巨大的代码量|2990248|2990249|还有一些次要的优化，比如世代GC，它使得分配短生命周期的对象变得更便宜，以及各种其他更小的优化，以及自那篇文章发表以来添加的任何其他优化。|2990250|还有一个更详细的official+whitepaper，以及一个相当详细的HotSpot+Internals+wiki+page，其中列出了如何编写快速的Java代码，使您可以推断优化了哪些用例。|2990251|entityMap|0|LINK|mutability|MUTABLE|url|http://www.artima.com/designtechniques/hotspotP.html|1|http://www.oracle.com/technetwork/java/whitepaper-135217.html|2|https://wiki.openjdk.java.net/display/HotSpot/PerformanceTechniques^0|1|C|0|0|0|0|0|0|0|0|8|J|1|11|R|2|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|6|7|16|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|17|8|@]|9|@]|C|$]]|$1|G|3|H|5|I|7|18|8|@]|9|@]|C|$]]|$1|J|3|K|5|I|7|19|8|@]|9|@]|C|$]]|$1|L|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]|$1|M|3|N|5|6|7|1B|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|1C|8|@]|9|@$A|1D|B|1E|1|1F]|$A|1G|B|1H|1|1I]]|C|$]]|$1|Q|3|-4|5|6|7|1J|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]|Y|$5|T|U|V|C|$W|Z]]|10|$5|T|U|V|C|$W|11]]]]

There's an old but likely still valid overview in <a href="http://www.artima.com/designtechniques/hotspotP.html" rel="nofollow noreferrer">this article</a>.

The highlights seem to be performing classical optimizations based on available runtime profiling information:

<ul>
<li>JITting "hot spots" into native code</li>
<li>Adaptive inlining – inlining the most commonly called implementations for a given method dispatch to avoid a huge code size</li>
</ul>

And some minor ones like generational GC which makes allocating short lived objects cheaper, and various other smaller optimizations, plus whatever else was added since that article was published.

There's also a more detailed <a href="http://www.oracle.com/technetwork/java/whitepaper-135217.html" rel="nofollow noreferrer">official whitepaper</a>, and a fairly nitty-gritty <a href="https://wiki.openjdk.java.net/display/HotSpot/PerformanceTechniques" rel="nofollow noreferrer">HotSpot Internals wiki page</a> that lists how to write fast Java code that should let you extrapolate what use cases were optimized.

blocks|key|724655|text|跳转到等效的本机代码，而不是操作码的JVM解释。不需要在机器代码中为Java应用程序的大量使用部分(相当于JVM的扩展)模拟机器(+JVM)，这可以很好地提高速度。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|724656|当然，这就是HotSpot的大部分功能。|724657|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Jumps to equivalent native machine code instead of JVM interpretation of the op-codes. The lack of a need to simulate a machine (the JVM) in machine code for a heavily used part of a Java application (which is the equivalent of an extension of the JVM) provides a good speed increase.

Of course, that's most of what HotSpot is.

In a lecture about JIT in Hotspot I want to give as many examples as possible of the specific optimizations that JIT performs. 

I know just about "method inlining", but there should be much more. Give a vote for every example.

Hotspot JIT optimizations

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在一次关于JIT In Hotspot的讲座中，我想给出尽可能多的JIT具体优化的例子。我只知道“方法内联”，但应该知道更多。为每一个例子投一票。

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