The Java frontend translates Java bytecode (.class files) into LLVM
bytecode. Take a look at this link:

https://llvm.org/svn/llvm-project/java/trunk/docs/java-frontend.txt



You may take a look at [dragonegg](https://dragonegg.llvm.org/), which enables llvm to use gcc&#39;s frontends. As gcc already has a frontend for java, called **gcj**, perhaps llvm can use it to compile java code. But I&#39;m not sure how well llvm interfaces with the gcc frontend, so this may not work.

I have executed a java class using vmkit ( http://vmkit.llvm.org/ ) based on LLVM. It uses LLVM for compiling and optimizing high-level languages to machine code. J3 is an implementation of a JVM with VMKit.

[**NOTE: From November 2015 it is no longer open source, so this hack is mostly useless.**]

[RoboVM](http://www.robovm.com/develop/documentation/) might become the solution you&#39;re looking for. It&#39;s open source and compiles JVM bytecode (.class files) to machine code. 

I assume they do it using something like class2llvm.

Unfortunately, it&#39;s still in alpha. I just tested it on HelloWorld.java. It gave 5x speed up of load time running on a single core. (Most of the run time is load time.)

&gt; `echo Hello World! : &lt;1 ms  : 31K` (/usr/bin/echo binary)
&gt;
&gt; `java HelloWorld   : ~70 ms : 0.4K` (HelloWorld.class JVM bytecode)
&gt;
&gt; `./HelloWorld      : ~13 ms : 9.4MB` (9.3MB binary + 57K robovm-rt.jar)

Note that java calls a 32MB $JAVA_HOME/lib/rt.jar file (and maybe more). Searching in such a large file must be part of the reason java is so slow to load. If RoboVM gets smarter, perhaps it can throw out most of the 9.3MB binary for an even faster load?

The website mentions iOS, but I think that&#39;s because they&#39;re selling their add-on UI libraries. RoboVM compiled fine for me on a flavor of Ubuntu. Just make sure to do

&gt; $ sudo apt-get install g++-multilib

first (and maybe install libpthread-stubs0-dev and libpthread-workqueue0...don&#39;t know if they mattered).


Reading the [R-project][1] website, there are some (unclear) references to multithreading with R, but it is unclear how the base product and [CRAN][2] libraries are compiled.

[Revolution Analytics][3] offers multithreaded base(?) download for Windows and Redhat.

Would some of the other Linux distributions also include multithreaded R (and packages)?


  [1]: http://www.r-project.org/
  [2]: http://cran.cnr.berkeley.edu/
  [3]: http://www.revolutionanalytics.com/products/revolution-r.php

multithreading with R?

The error is as above. I have what should be all the necessary files include in the eclipse project:

    /usr/include/c++/4.6
    /usr/include
    /usr/include/linux
    /usr/local/include
etc. 

I tried `std::cout` and `using namespace std;` `cout` but it still says unresolved. 

I have imported `iostream` and `cstdlib`.

Also, I&#39;m on Ubuntu 12.04 with eclipse 3.7.2.

Code snippet:

    #include &lt;cstdio&gt;
    #include &lt;cstdlib&gt;
    #include &lt;cstring&gt;
    #include &lt;iostream&gt;
    #include &quot;XPLMDisplay.h&quot;
    #include &quot;XPLMGraphics.h&quot;

    int XPluginStart(char * outName,  char * outSig,  char * outDesc) {
        /* ... */
        std::cout &lt;&lt; &quot;test&quot; &lt;&lt; std::endl;
        /* ... */
    }

using namespace std;


----------


UPDATE: I had created the eclipse project from existing code. Creating a new c++ project fixes it. I&#39;ll accept an answer that explains what setting in the existing project could cause this (so I don&#39;t have to cut &amp; paste all my projects).

Eclipse CDT: Symbol &#39;cout&#39; could not be resolved

From what I&#39;ve read, there is a llvm program that converts java bytecode to llvm&#39;s intermediate form called class2llvm. My question is, how do I access this. What front end do I have to install in order to access this. 

VMkit is their implementation of a JVM, but I am looking for how to compile the java source code with llvm, not how to run it.

Is there a llvm java front end that converts java source to llvm&#39;s intermediate form?

<p>From what I've read, there is a llvm program that converts java bytecode to llvm's intermediate form called class2llvm. My question is, how do I access this. What front end do I have to install in order to access this.</p>
<p>VMkit is their implementation of a JVM, but I am looking for how to compile the java source code with llvm, not how to run it.</p>


While writing a new jUnit4 test, I&#39;m wondering whether to use `@RunWith(MockitoJUnitRunner.class)` or `MockitoAnnotations.initMocks(this)`.

I created a new test &amp; the wizard automatically generated a test with the Runner. Javadocs for MockitoJUnitRunner state the following:

&gt; Compatible with JUnit 4.4 and higher, this runner adds following behavior: 
&gt;
&gt; Initializes mocks annotated with Mock, so that explicit usage of MockitoAnnotations.initMocks(Object) is not necessary. Mocks are initialized before each test method. 
Validates framework usage after each test method. 

It&#39;s not clear to me whether using the Runner has any advantage over the `initMocks()` method I have been using in past.

@RunWith(MockitoJUnitRunner.class) vs MockitoAnnotations.initMocks(this)

I have a crazy question about Java switches.

    int key = 2;

	switch (key) {
        case 1:
            int value = 1;
            break;
        case 2:
            value = 2;
            System.out.println(value);
            break;
        default:
            break;
	}

Scenario 1 - When the `key` is two it successfully print the value as 2.
&lt;br&gt;Scenario 2 - When I&#39;m going to comment `value = 2` in `case 2:` it squawks saying the *The local variable value may not have been initialized*.

Questions : 
&lt;br&gt;&lt;br&gt;Scenario 1 : If the execution flow doesn&#39;t go to `case 1:` (when the `key = 2`), then how does it know the type of the value variable as `int`?
&lt;br&gt;&lt;br&gt;Scenario 2 : If the compiler knows the type of the value variable as `int`, then it must have accessed to the `int value = 1;` expression in `case 1:`.(Declaration and Initialization). Then why does it sqawrk When I&#39;m going to comment `value = 2` in `case 2:`, saying the *The local variable value may not have been initialized*.

Declaring and initializing variables within Java switches

I know that command line interfaces like Git and others are able to hide input from a user (useful for passwords). Is there a way to programmtically do this in Java? I&#39;m taking password input from a user and I would like their input to be &quot;hidden&quot; on that particular line (but not on all of them). Here&#39;s my code for it (though I doubt it would be helpful...)

    try (Scanner input = new Scanner(System.in)) {
      //I&#39;m guessing it&#39;d probably be some property you set on the scanner or System.in right here...
      System.out.print(&quot;Please input the password for &quot; + name + &quot;: &quot;);
      password = input.nextLine();
    }

Hide input on command line

**Problem:**  
We have a Spring MVC-based RESTful API which contains sensitive information. The API should be secured, however sending the user&#39;s credentials (user/pass combo) with each request is not desirable. Per REST guidelines (and internal business requirements), the server must remain stateless. The API will be consumed by another server in a mashup-style approach.

**Requirements:**

 - Client makes a request to `.../authenticate` (unprotected URL) with credentials; server returns a secure token which contains enough information for the server to validate future requests and remain stateless. This would likely consist of the same information as Spring Security&#39;s [Remember-Me Token][1].

 - Client makes subsequent requests to various (protected) URLs, appending the previously obtained token as a query parameter (or, less desirably, an HTTP request header).

 - Client cannot be expected to store cookies.

 - Since we use Spring already, the solution should make use of Spring Security.

We&#39;ve been banging our heads against the wall trying to make this work, so hopefully someone out there has already solved this problem. 

Given the above scenario, how might you solve this particular need?

  [1]: http://static.springsource.org/spring-security/site/docs/3.1.x/reference/remember-me.html

RESTful Authentication via Spring

I have Intellij ultimate 11.1, with the scala plugin installed.

I installed scala 2.9.2 using homebrew, which put scala in:

    /usr/local/Cellar/scala/2.9.2&gt;



    &gt;which scala
    /usr/local/bin/scala
    &gt;scala -version
    Scala code runner version 2.9.2 -- Copyright 2002-2011, LAMP/EPFL

Creating a new java module project, I get this:

![enter image description here][1]

![enter image description here][2]

![enter image description here][3]

![enter image description here][4]

Can someone help me fix these issues, why didn&#39;t the scala plugin make this work out of the box? :)


  [1]: http://i.stack.imgur.com/ti6LL.png
  [2]: http://i.stack.imgur.com/onerW.png
  [3]: http://i.stack.imgur.com/Pv4e2.png
  [4]: http://i.stack.imgur.com/HAr6n.png

Setting up scala with IntelliJ

LLVM has [phi](http://llvm.org/docs/LangRef.html#i_phi) instruction with quite weird explanation:

&gt; *The &#39;phi&#39; instruction is used to implement the φ node in the SSA graph representing the function.*

Typically it is used to implement branching. If I understood correctly, it is needed to make dependency analysis possible and in some cases it could help to avoid unnecessary loading. However it&#39;s still hard to understand what it does exactly.

Kaleidoscope [example][1] explains it fairly nicely for `if` case. However it&#39;s not that clear how to implement logical operations like `&amp;&amp;` and `||`. If I type the following to [online llvm](http://llvm.org/demo/index.cgi) compiler:

    void main1(bool r, bool y) {
        bool l = y || r;
    }

Last several lines completely confuse me:

    ; &lt;label&gt;:10                                      ; preds = %7, %0
    %11 = phi i1 [ true, %0 ], [ %9, %7 ]
    %12 = zext i1 %11 to i8

Looks like phi node produces a result which can be used. And I was under impression that phi node just defines from which paths values coming.

Could someone explain what is a Phi node, and how to implement `||` with it?

[1]: https://llvm.org/docs/tutorial/MyFirstLanguageFrontend/LangImpl05.html#llvm-ir-for-if-then-else

What exactly PHI instruction does and how to use it in LLVM

I know I can type ``print someFloatVariable`` when I set a breakpoint or ``po [self someIvarHoldingAnObject]``, but I can&#39;t do useful things like:

    [self setAlpha:1];

Then it spits out:

&gt; error: &#39;[self&#39; is not a valid command.

Weird thing is that I can call `po [self someIvarHoldingAnObject]` and it will print it&#39;s description.

I believe I&#39;ve seen a video a year ago where someone demonstrated how to execute code through the console at runtime, and if I am not mistaken this guy also provided arguments and assigned objects to pointers. How to do that?

How to call methods or execute code in LLDB debugger?

Currently I am interested in ARM in general and specifically iphone/android targets. But I just want to know more about clang, since it feels to play important role in the years to come.

I tried

    clang -cc1 --help|grep -i list
    clang -cc1 --help|grep arch|grep -v search
    clang -cc1 --help|grep target

     -triple &lt;value&gt;         Specify target triple (e.g. i686-apple-darwin9)

I know clang has -triplet parameter, but how can I list all possible values for it?
I found that clang is very different to gcc in respect to cross compiling, in GCC world you should have separate binary for everything, like PLATFORM_make or PLATFORM_ld (i*86-pc-cygwin i*86-*-linux-gnu etc. http://git.savannah.gnu.org/cgit/libtool.git/tree/doc/PLATFORMS)

in clang world, it&#39;s only one binary (as I read on some forums). But how do I get the list of supported targets? And if my target it not supported on my distro(linux/windows/macos/whatever) how can I get the one that supports more platform?

if I SVN latest clang like this:

    svn co http://llvm.org/svn/llvm-project/cfe/trunk clang

will I get most of platforms?
It looks like Clang was not built with cross compiling in mind right away, but since it&#39;s llvm based it should be very cross-friendly in theory? thank you!


clang: how to list supported target architectures?

(Preface: I&#39;m pretty new to C/C++ and I don&#39;t really know how debugging in native code actually works.)

Some sources say that gdb and lldb can debug [any program compiled to machine code](http://www.lego.com/en-us/mindstorms/products/fan-made-bonus-robots/ev3meg). Others say that to debug with gdb you **must** compile in gcc [with the `-g` flag](http://tedlab.mit.edu/~dr/gdbintro.html). The documentation for gcc itself suggests this is optional, and that in fact if you use it, it can cause problems for debuggers _other than_ gdb. Clang also has a `-g` flag and the documentation basically just says &quot;Generate debug information.&quot;

So are these debuggers restricted to their own toolchains (GNU and LLVM), or are they somehow independent of the compiler used?

Is it possible to debug a gcc-compiled program using lldb, or debug a clang-compiled program using gdb?

I am investigating potential code-completion speedups while using clang&#39;s code-completion mechanism. The flow described below is what I found in [rtags](https://github.com/Andersbakken/rtags), by Anders Bakken.

Translation units are parsed by a daemon monitoring files for changes. This is done by called `clang_parseTranslationUnit` and related functions(`reparse*`, `dispose*`). When the user requests a completion at a given line and column in a source file, the daemon passes the cached translation unit for the last saved version of the source file and the current source file to `clang_codeCompleteAt`. ([Clang CodeComplete docs](http://clang.llvm.org/doxygen/group__CINDEX__CODE__COMPLET.html)).

The flags passed to `clang_parseTranslationUnit`(from [CompletionThread::process, line 271](https://github.com/Andersbakken/rtags/blob/master/src/CompletionThread.cpp)) are `CXTranslationUnit_PrecompiledPreamble|CXTranslationUnit_CacheCompletionResults|CXTranslationUnit_SkipFunctionBodes`. The flags passed to `clang_codeCompleteAt`(from [CompletionThread::process, line 305](https://github.com/Andersbakken/rtags/blob/master/src/CompletionThread.cpp)) are `CXCodeComplete_IncludeMacros|CXCodeComplete_IncludeCodePatterns`.

The call to `clang_codeCompleteAt` is very slow - it takes around 3-5 seconds to obtain a completion even in the cases where the completion location is a legitimate member access code, a subset of the intended use case mentioned in the documentation of [`clang_codeCompleteAt`](http://clang.llvm.org/doxygen/group__CINDEX__CODE__COMPLET.html#ga50fedfa85d8d1517363952f2e10aa3bf). This seems way too slow by IDE code-completion standards. Is there a way of speeding this up?

Faster code-completion with clang

The design of GHC is based on something called STG, which stands for &quot;spineless, tagless G-machine&quot;.

Now G-machine is apparently short for &quot;graph reduction machine&quot;, which defines how laziness is implemented. Unevaluated thunks are stored as an expression tree, and executing the program involves _reducing_ these down to normal form. (A _tree_ is an acyclic graph, but Haskell&#39;s pervasive recursion means that Haskell expressions form general _graphs_, hence graph-reduction and not tree-reduction.)

What is less clear are the terms &quot;spineless&quot; and &quot;tagless&quot;.

1. I _think_ that &quot;spineless&quot; refers to the fact that function applications do not have a &quot;spine&quot; of function application nodes. Instead, you have an object that names the function called and points to all of its arguments. Is that correct?

2. I thought that &quot;tagless&quot; referred to constructor nodes not being &quot;tagged&quot; with a constructor ID, and instead case-expressions are resolved using a jump instruction. But now I&#39;m not sure that&#39;s correct. Instead, it seems to refer to the fact that nodes aren&#39;t tagged with their evaluation state. Can anyone clarify which (if any) of these interpretations is correct?


Understanding STG

There are three opcodes to invoke Java methods. It is clear that invokeStatic is just for static method invocation.

As far as I know invokespecial is used when invoking constructor and private methods. So, do we need to differenticate private and public method invocation at run time? It could be invoked with same opcode say invokevirtual?

Does JVM deals with private and public method definition? As far as I know  public and private keywords is just needed at development phase for encapsulation?


Why invokeSpecial is needed when invokeVirtual exists

I&#39;ve got some code that uses try with resources and in jacoco it&#39;s coming up as only half covered. All the source code lines are green, but I get a little yellow symbol telling me that only 4 of 8 branches are covered.

![enter image description here][1]

I&#39;m having trouble figuring out what all the branches are, and how to write code that covers them. Three possible places throw `PipelineException`. These are `createStageList()`, `processItem()` and the implied `close()`

 1. Not throwing any exceptions, 
 1. throwing an exception from `createStageList()`
 1. throwing an exception from `processItem()`
 1. throwing an exception from `close()`
 1. throwing an exception from `processItem()` and `close()`

I can&#39;t think of any other cases, yet I still only have 4 of 8 covered.

Can someone explain to me why it&#39;s 4 of 8 and is there anyway to hit all 8 branches? I&#39;m not skilled with decyrpting/reading/interpreting byte code, but maybe you are... :) I&#39;ve already seen https://github.com/jacoco/jacoco/issues/82, but neither it nor the issue it references help very much (other than noting that this is due to compiler generated blocks)

Hmm, just as I finish writing this I had a thought on what case(s) might not be not tested by what I mention above... I&#39;ll post an answer if I got it right. I&#39;m sure this question and it&#39;s answer will help someone in any case.

**EDIT:** Nope, I didn&#39;t find it. Throwing RuntimeExceptions (not handled by the catch block) didn&#39;t cover any more branches

  [1]: http://i.stack.imgur.com/SggR6.png

8 branches for try with resources - jacoco coverage possible?

I have Java 6 and 7 installed on my machine. Gradle uses 1.7 (checked using `gradle -v`). But I need to compile my code to be compatible with Java 1.6. As far as I understand the documentation I can use the `sourceCompatibility` property to do so (and indirectly the `targetCompatibility` which defaults to the  `sourceCompatibility`).

So I added the following line to my build file (on the root level, not in any closure):

    sourceCompatibility = 1.6

(to be sure I also added the `targetCompatibility = 1.6` in some trials, but that should not make a difference)


To check whether the result was actually compatible with 1.6 I unzipped the resulting jar, `cd` into the `WEB-INF/classes` folder and used `javap -verbose` on the first `.class` file I encountered. But no matter whether I set the target compatibility or whether I used 1.5 instead of 1.6 or whether I specified it as string (`&#39;1.6&#39;`), each time the result of javap was

    minor version: 0
    major version: 51

Afaik this means it is Java 1.7 Bytecode, which is wrong.

Any ideas why the `sourceCompatibility`-setting doesn&#39;t work? Or is `javap` not the correct way to check the compatibility?


**UPDATE:**
Yes, this is actually a multi-project build but I only checked one of the subprojects&#39; build results. In this subproject&#39;s build file I made the mentioned changes to be sure they are actually applied. In addition, I added the following in the root project&#39;s build file (as @Vidya proposed as well):

    allprojects {
        sourceCompatibility = 1.6
        targetCompatibility = 1.6
    }

But this didn&#39;t help either.

**UPDATE 2:**
I checked the setting of sourceCompatibility with this snippet in the relevant build.gradle files:

    compileJava.doFirst {
        println &quot;source compatibility &quot; + sourceCompatibility
    }

It revealed that my sourceCompatibility is set to 1.7 although I tried to set it to 1.6. When I extracted the simplest subproject and built in on its own the sourceCompatibility is set correctly and the Java Byte code is compatible to 1.6. However, even this sub-project uses the wrong sourceCompatibility when used in the multi project build.


BTW: The plugins I use in some of the sub projects are: `java`, `war`, `jetty`, `gwt`

**UPDATE 3:**
I changed the built scripts to just use the java plugin (and thus just construct some jars) and removed the usage of the `war`, `jetty` and `gwt` plugin. But still all the projects are set to sourceCompatibility 1.7 despite me setting it in the `allprojects` section and in some of the sub projects. All that is left now in the build scripts is the declaration of some decencies (maven, files and other sub projects), the declaration of the repositories to use, the declaration of some others tasks (that the build-task does not depend on, so it shouldn&#39;t be affected) and the configuration of the manifest file for the created jar files (I add a specification and an implementation version and title to the manifest file). 

I don&#39;t see how any of that would affect the sourceCompatibility setting.

Gradle sourceCompatibility has no effect to subprojects

I&#39;ve recently been looking at The [Java Virtual Machine Specifications][1] (JVMS) to try to better understand the what makes my programs work, but I&#39;ve found a section that I&#39;m not quite getting...

Section [4.7.4][2] describes the *StackMapTable* Attribute, and in that section the document goes into details about stack map frames. The issue is that it&#39;s a little wordy and I learn best by example; not by reading.

I understand that the first stack map frame is derived from the method descriptor, but I don&#39;t understand how (which is supposedly explained [here][3].) Also, I don&#39;t entirely understand what the stack map frames do. I would assume they&#39;re similar to blocks in Java, but it appears as though you can&#39;t have stack map frames inside each other.

Anyway, I have two specific questions:

  -  What do the stack map frames do?
  -  How is the first stack map frame created?

and one general question:

  -  Can someone provide an explanation less wordy and easier to understand than the one given in the JVMS?


  [1]: http://docs.oracle.com/javase/specs/jvms/se8/html/index.html
  [2]: http://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.4
  [3]: http://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.10.1.6

Content Type	Original Author	Original Content on Stackoverflow
Question	FeelTheBurns	View Question on Stackoverflow
Solution 1 - Java	Ashkan	View Answer on Stackoverflow
Solution 2 - Java	lei_z	View Answer on Stackoverflow
Solution 3 - Java	Ashkan	View Answer on Stackoverflow
Solution 4 - Java	expz	View Answer on Stackoverflow

Is there a llvm java front end that converts java source to llvm's intermediate form?

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Solution 4 - Java

Eclipse CDT: Symbol 'cout' could not be resolved

multithreading with R?

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