<li>The <tt>configure</tt> script finds the right C compiler, but it uses the
LLVM linker from a previous build. What do I do?</li>
<li>When creating a dynamic library, I get a strange GLIBC error.</li>
- <li>I've updated my source tree from CVS, and now my build is trying to use a
- file/directory that doesn't exist.</li>
+ <li>I've updated my source tree from Subversion, and now my build is trying
+ to use a file/directory that doesn't exist.</li>
<li>I've modified a Makefile in my source tree, but my build tree keeps using
the old version. What do I do?</li>
<li>I've upgraded to a new version of LLVM, and I get strange build
<li>Compiling LLVM with GCC 3.3.2 fails, what should I do?</li>
<li>When I use the test suite, all of the C Backend tests fail. What is
wrong?</li>
- <li>After CVS update, rebuilding gives the error "No rule to make
- target".</li>
+ <li>After Subversion update, rebuilding gives the error "No rule to make
+ target".</li>
+ <li><a href="#llvmc">The <tt>llvmc</tt> program gives me errors/doesn't
+ work.</a></li>
</ol></li>
<li><a href="#felangs">Source Languages</a>
<ol>
<li><a href="#langs">What source languages are supported?</a></li>
+ <li><a href="#langirgen">I'd like to write a self-hosting LLVM compiler. How
+ should I interface with the LLVM middle-end optimizers and back-end code
+ generators?</a></div>
<li><a href="#langhlsupp">What support is there for higher level source
language constructs for building a compiler?</a></li>
<li><a href="GetElementPtr.html">I don't understand the GetElementPtr
<li><a href="#cfe_code">Questions about code generated by the GCC front-end</a>
<ol>
- <li><a href="#__main">What is this <tt>__main()</tt> call that gets inserted into
- <tt>main()</tt>?</a></li>
<li><a href="#iosinit">What is this <tt>llvm.global_ctors</tt> and
<tt>_GLOBAL__I__tmp_webcompile...</tt> stuff that happens when I
#include <iostream>?</a></li>
<p>Some porting problems may exist in the following areas:</p>
<ul>
-
<li>The GCC front end code is not as portable as the LLVM suite, so it may not
- compile as well on unsupported platforms.</li>
+ compile as well on unsupported platforms.</li>
<li>The LLVM build system relies heavily on UNIX shell tools, like the Bourne
- Shell and sed. Porting to systems without these tools (MacOS 9, Plan 9) will
- require more effort.</li>
-
+ Shell and sed. Porting to systems without these tools (MacOS 9, Plan 9)
+ will require more effort.</li>
</ul>
</div>
it:</p>
<ol>
-
<li><p>Adjust your <tt>PATH</tt> environment variable so that the correct
- program appears first in the <tt>PATH</tt>. This may work, but may not be
- convenient when you want them <i>first</i> in your path for other
- work.</p></li>
+ program appears first in the <tt>PATH</tt>. This may work, but may not be
+ convenient when you want them <i>first</i> in your path for other
+ work.</p></li>
<li><p>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that is
- correct. In a Borne compatible shell, the syntax would be:</p>
-
- <p><tt>PATH=[the path without the bad program] ./configure ...</tt></p>
+ correct. In a Borne compatible shell, the syntax would be:</p>
+
+<div class="doc_code">
+<pre>
+% PATH=[the path without the bad program] ./configure ...
+</pre>
+</div>
<p>This is still somewhat inconvenient, but it allows <tt>configure</tt>
- to do its work without having to adjust your <tt>PATH</tt>
- permanently.</p></li>
-
+ to do its work without having to adjust your <tt>PATH</tt>
+ permanently.</p></li>
</ol>
</div>
</div>
<div class="question">
-<p>I've updated my source tree from CVS, and now my build is trying to use a
-file/directory that doesn't exist.</p>
+<p>I've updated my source tree from Subversion, and now my build is trying to
+use a file/directory that doesn't exist.</p>
</div>
<div class="answer">
</div>
<div class="answer">
-
<p>If the Makefile already exists in your object tree, you
can just run the following command in the top level directory of your object
tree:</p>
-<p><tt>./config.status <relative path to Makefile></tt><p>
+<div class="doc_code">
+<pre>% ./config.status <relative path to Makefile></pre>
+</div>
<p>If the Makefile is new, you will have to modify the configure script to copy
it over.</p>
<p>For example, if you built LLVM with the command:</p>
-<p><tt>gmake ENABLE_PROFILING=1</tt>
+<div class="doc_code">
+<pre>% gmake ENABLE_PROFILING=1</pre>
+</div>
<p>...then you must run the tests with the following commands:</p>
-<p><tt>cd llvm/test<br>gmake ENABLE_PROFILING=1</tt></p>
+<div class="doc_code">
+<pre>
+% cd llvm/test
+% gmake ENABLE_PROFILING=1
+</pre>
+</div>
</div>
<div class="answer">
<p>This is <a href="http://gcc.gnu.org/PR?13392">a bug in GCC</a>, and
- affects projects other than LLVM. Try upgrading or downgrading your GCC.</p>
+affects projects other than LLVM. Try upgrading or downgrading your GCC.</p>
</div>
<div class="question">
-<p>After CVS update, rebuilding gives the error "No rule to make target".</p>
+<p>After Subversion update, rebuilding gives the error "No rule to make
+target".</p>
</div>
<div class="answer">
<p>If the error is of the form:</p>
<div class="doc_code">
-<tt>
+<pre>
gmake[2]: *** No rule to make target `/path/to/somefile', needed by
`/path/to/another/file.d'.<br>
Stop.
-</tt>
+</pre>
</div>
-<p>This may occur anytime files are moved within the CVS repository or removed
-entirely. In this case, the best solution is to erase all <tt>.d</tt> files,
-which list dependencies for source files, and rebuild:</p>
+<p>This may occur anytime files are moved within the Subversion repository or
+removed entirely. In this case, the best solution is to erase all
+<tt>.d</tt> files, which list dependencies for source files, and rebuild:</p>
<div class="doc_code">
<pre>
rebuilding.</p>
</div>
+<div class="question"><p><a name="llvmc">
+The <tt>llvmc</tt> program gives me errors/doesn't work.</a></p>
+</div>
+
+<div class="answer">
+<p><tt>llvmc</tt> is experimental and isn't really supported. We suggest
+using <tt>llvm-gcc</tt> instead.</p>
+</div>
+
<!-- *********************************************************************** -->
<div class="doc_section"><a name="felangs">Source Languages</a></div>
available through a special version of GCC that LLVM calls the
<a href="#cfe">C Front End</a></p>
<p>There is an incomplete version of a Java front end available in the
- <tt>llvm-java</tt> CVS repository. There is no documentation on this yet so
+ <tt>java</tt> module. There is no documentation on this yet so
you'll need to download the code, compile it, and try it.</p>
- <p>In the <tt>examples/BFtoLLVM</tt> directory is a translator for the
- BrainF*** language (2002 Language Specification).</p>
- <p>In the <tt>projects/Stacker</tt> directory is a compiler and runtime
+ <p>In the <tt>stacker</tt> module is a compiler and runtime
library for the Stacker language, a "toy" language loosely based on Forth.</p>
<p>The PyPy developers are working on integrating LLVM into the PyPy backend
so that PyPy language can translate to LLVM.</p>
</div>
-<div class="question"><a name="langhlsupp">
- <p>What support is there for a higher level source language constructs for
+
+<div class="question"><p><a name="langirgen">
+ I'd like to write a self-hosting LLVM compiler. How should I interface with
+ the LLVM middle-end optimizers and back-end code generators?
+</a></p></div>
+<div class="answer">
+ <p>Your compiler front-end will communicate with LLVM by creating a module in
+ the LLVM intermediate representation (IR) format. Assuming you want to
+ write your language's compiler in the language itself (rather than C++),
+ there are 3 major ways to tackle generating LLVM IR from a front-end:</p>
+ <ul>
+ <li>
+ <strong>Call into the LLVM libraries code using your language's FFI
+ (foreign function interface).</strong>
+ <ul>
+ <li><em>for:</em> best tracks changes to the LLVM IR, .ll syntax,
+ and .bc format</li>
+ <li><em>for:</em> enables running LLVM optimization passes without a
+ emit/parse overhead</li>
+ <li><em>for:</em> adapts well to a JIT context</li>
+ <li><em>against:</em> lots of ugly glue code to write</li>
+ </ul>
+ </li>
+ <li>
+ <strong>Emit LLVM assembly from your compiler's native language.</strong>
+ <ul>
+ <li><em>for:</em> very straightforward to get started</li>
+ <li><em>against:</em> the .ll parser is slower than the bitcode reader
+ when interfacing to the middle end</li>
+ <li><em>against:</em> you'll have to re-engineer the LLVM IR object
+ model and asm writer in your language</li>
+ <li><em>against:</em> it may be harder to track changes to the IR</li>
+ </ul>
+ </li>
+ <li>
+ <strong>Emit LLVM bitcode from your compiler's native language.</strong>
+ <ul>
+ <li><em>for:</em> can use the more-efficient bitcode reader when
+ interfacing to the middle end</li>
+ <li><em>against:</em> you'll have to re-engineer the LLVM IR object
+ model and bitcode writer in your language</li>
+ <li><em>against:</em> it may be harder to track changes to the IR</li>
+ </ul>
+ </li>
+ </ul>
+ <p>If you go with the first option, the C bindings in include/llvm-c should
+ help a lot, since most languages have strong support for interfacing with
+ C. The most common hurdle with calling C from managed code is interfacing
+ with the garbage collector. The C interface was designed to require very
+ little memory management, and so is straightforward in this regard.</p>
+</div>
+
+<div class="question"><p><a name="langhlsupp">
+ What support is there for a higher level source language constructs for
building a compiler?</a></p>
</div>
<div class="answer">
of running optimizations, linking, and executable generation.</p>
</div>
-<div class="question"><a name="langhlsupp">
- <p>I don't understand the GetElementPtr
- instruction. Help!</a></p>
+<div class="question"><p><a name="langhlsupp">
+ I don't understand the GetElementPtr instruction. Help!</a></p>
</div>
<div class="answer">
<p>See <a href="GetElementPtr.html">The Often Misunderstood GEP
- Instruction</a>.</li>
+ Instruction</a>.</p>
</div>
<!-- *********************************************************************** -->
<p>
The only way this can happen is if you haven't installed the runtime library. To
correct this, do:</p>
+
+<div class="doc_code">
<pre>
- % cd llvm/runtime
- % make clean ; make install-bytecode
+% cd llvm/runtime
+% make clean ; make install-bytecode
</pre>
</div>
+</div>
<div class="question">
<p>
<p>Use commands like this:</p>
<ol>
-<li><p>Compile your program as normal with llvm-g++:</p></li>
+ <li><p>Compile your program as normal with llvm-g++:</p>
-<div class="doc_code">$ llvm-g++ x.cpp -o program</div>
+<div class="doc_code">
+<pre>
+% llvm-g++ x.cpp -o program
+</pre>
+</div>
-<p>or:</p>
<div class="doc_code">
- llvm-g++ a.cpp -c<br>
- llvm-g++ b.cpp -c<br>
- llvm-g++ a.o b.o -o program
+<pre>
+% llvm-g++ a.cpp -c
+% llvm-g++ b.cpp -c
+% llvm-g++ a.o b.o -o program
+</pre>
</div>
-<p>With llvm-gcc3, this will generate program and program.bc. The .bc file is
-the LLVM version of the program all linked together.</p>
+ <p>With llvm-gcc3, this will generate program and program.bc. The .bc
+ file is the LLVM version of the program all linked together.</p></li>
-<li><p>Convert the LLVM code to C code, using the LLC tool with the C
-backend:</p></li>
+
<li><p>Convert the LLVM code to C code, using the LLC tool with the C
+ backend:</p>
-<div class="doc_code">$ llc -march=c program.bc -o program.c</div>
+<div class="doc_code">
+<pre>
+% llc -march=c program.bc -o program.c
+</pre>
+</div></li>
-<li><p>Finally, compile the c file:</p></li>
+<li><p>Finally, compile the C file:</p>
-<div class="doc_code">$ cc x.c</div>
+<div class="doc_code">
+<pre>
+% cc x.c
+</pre>
+</div></li>
</ol>
-<p>Note that, by default, the C backend does not support exception handling.
-If you want/need it for a certain program, you can enable it by passing
-"-enable-correct-eh-support" to the llc program. The resultant code will
-use setjmp/longjmp to implement exception support that is correct but
-relatively slow.
-</p>
+<p>Note that, by default, the C backend does not support exception handling. If
+you want/need it for a certain program, you can enable it by passing
+"-enable-correct-eh-support" to the llc program. The resultant code will use
+setjmp/longjmp to implement exception support that is correct but relatively
+slow.</p>
-<p>Also note: this specific sequence of commands won't work if you use a
-function defined in the C++ runtime library (or any other C++ library). To
-access an external C++ library, you must manually
-compile libstdc++ to LLVM bytecode, statically link it into your program, then
-use the commands above to convert the whole result into C code. Alternatively,
-you can compile the libraries and your application into two different chunks
-of C code and link them.</p>
+<p>Also note: this specific sequence of commands won't work if you use a
+function defined in the C++ runtime library (or any other C++ library). To
+access an external C++ library, you must manually compile libstdc++ to LLVM
+bitcode, statically link it into your program, then use the commands above to
+convert the whole result into C code. Alternatively, you can compile the
+libraries and your application into two different chunks of C code and link
+them.</p>
</div>
-
-
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="cfe_code">Questions about code generated by the GCC front-end</a>
</div>
-<div class="question"><p>
-<a name="__main"></a>
-What is this <tt>__main()</tt> call that gets inserted into <tt>main()</tt>?
-</p></div>
-
-<div class="answer">
-<p>
-The <tt>__main</tt> call is inserted by the C/C++ compiler in order to guarantee
-that static constructors and destructors are called when the program starts up
-and shuts down. In C, you can create static constructors and destructors by
-using GCC extensions, and in C++ you can do so by creating a global variable
-whose class has a ctor or dtor.
-</p>
-
-<p>
-The actual implementation of <tt>__main</tt> lives in the
-<tt>llvm/runtime/GCCLibraries/crtend/</tt> directory in the source-base, and is
-linked in automatically when you link the program.
-</p>
-</div>
-
-<!--=========================================================================-->
-
<div class="question">
<a name="iosinit"></a>
<p> What is this <tt>llvm.global_ctors</tt> and
variable before you use it. For example, the C function:</p>
<div class="doc_code">
- <tt>int X() { int i; return i; }</tt>
+<pre>
+int X() { int i; return i; }
+</pre>
</div>
-<p>Is compiled to "<tt>ret int undef</tt>" because "i" never has a value
-specified for it.
-</p>
+<p>Is compiled to "<tt>ret i32 undef</tt>" because "<tt>i</tt>" never has
+a value specified for it.</p>
</div>
<!-- *********************************************************************** -->
projects / oota-llvm.git / blobdiff