<li><a href="#build">Build Problems</a>
<ol>
<li>When I run configure, it finds the wrong C compiler.</li>
- <li>I compile the code, and I get some error about <tt>/localhome</tt>.</li>
<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>
<li><a href="#langs">What source languages are supported?</a></li>
<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
+ instruction. Help!</a></li>
</ol>
<li><a href="#cfe">Using the GCC Front End</a>
How can I disable all optimizations when compiling code using the LLVM GCC front end?
</li>
+ <li><a href="#translatec++">Can I use LLVM to convert C++ code to C code?</a></li>
+
</ol>
</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>
</div>
-<div class="question">
-<p>I compile the code, and I get some error about <tt>/localhome</tt>.</p>
-</div>
-
-<div class="answer">
-
-<p>There are several possible causes for this. The first is that you didn't set
-a pathname properly when using <tt>configure</tt>, and it defaulted to a
-pathname that we use on our research machines.</p>
-
-<p>Another possibility is that we hardcoded a path in our Makefiles. If you see
-this, please email the LLVM bug mailing list with the name of the offending
-Makefile and a description of what is wrong with it.</p>
-
-</div>
-
<div class="question">
<p>The <tt>configure</tt> script finds the right C compiler, but it uses the
LLVM linker from a previous build. What do I do?</p>
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="doc_section">
- <a name="felangs">Source Languages</a>
+<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="question"><p>What source languages are supported?</p></div>
-<div name="langs" class="answer">
+<!-- *********************************************************************** -->
+<div class="doc_section"><a name="felangs">Source Languages</a></div>
+
+<div class="question"><p>
+ <a name="langs">What source languages are supported?</a></p>
+</div>
+<div class="answer">
<p>LLVM currently has full support for C and C++ source languages. These are
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 name="langhlsupp" class="question">
- <p>What support is there for a higher level source language constructs for
- building a compiler?</p>
+<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">
<p>Currently, there isn't much. LLVM supports an intermediate representation
which is useful for code representation but will not support the high level
(abstract syntax tree) representation needed by most compilers. There are no
- facilities for lexical nor semantica analysis. There is, however, a <i>mostly
+ facilities for lexical nor semantic analysis. There is, however, a <i>mostly
implemented</i> configuration-driven
<a href="CompilerDriver.html">compiler driver</a> which simplifies the task
of running optimizations, linking, and executable generation.</p>
- <p>You might be interested in following the progress of the <a
- href="http://hlvm.org">HLVM Project</a> which is attempting to address these
- issues.</p>
</div>
+
+<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>.</p>
+</div>
+
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="cfe">Using the GCC Front End</a>
<p>
To work around this, perform the following steps:
</p>
-
<ol>
- <li>
- Make sure the CC and CXX environment variables contains the full path to the
- LLVM GCC front end.
- </li>
+ <li>Make sure the CC and CXX environment variables contains the full path to
+ the LLVM GCC front end.</li>
- <li>
- Make sure that the regular C compiler is first in your PATH.
- </li>
+ <li>Make sure that the regular C compiler is first in your PATH. </li>
- <li>
- Add the string "-Wl,-native" to your CFLAGS environment variable.
- </li>
+ <li>Add the string "-Wl,-native" to your CFLAGS environment variable.</li>
</ol>
<p>
-This will allow the gccld linker to create a native code executable instead of
-a shell script that runs the JIT. Creating native code requires standard
-linkage, which in turn will allow the configure script to find out if code is
-not linking on your system because the feature isn't available on your system.
-</p>
+This will allow the <tt>llvm-ld</tt> linker to create a native code executable
+instead of shell script that runs the JIT. Creating native code requires
+standard linkage, which in turn will allow the configure script to find out if
+code is not linking on your system because the feature isn't available on your
+system.</p>
</div>
<div class="question">
<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>
</div>
+
+<div class="question">
+<p>
+<a name="translatec++">Can I use LLVM to convert C++ code to C code?</a>
+</p>
+</div>
+
+<div class="answer">
+<p>Yes, you can use LLVM to convert code from any language LLVM supports to C.
+Note that the generated C code will be very low level (all loops are lowered
+to gotos, etc) and not very pretty (comments are stripped, original source
+formatting is totally lost, variables are renamed, expressions are regrouped),
+so this may not be what you're looking for. However, this is a good way to add
+C++ support for a processor that does not otherwise have a C++ compiler.
+</p>
+
+<p>Use commands like this:</p>
+
+<ol>
+ <li><p>Compile your program as normal with llvm-g++:</p>
+
+<div class="doc_code">
+<pre>
+% llvm-g++ x.cpp -o program
+</pre>
+</div>
+
+ <p>or:</p>
+
+<div class="doc_code">
+<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></li>
+
+ <li><p>Convert the LLVM code to C code, using the LLC tool with the C
+ backend:</p>
+
+<div class="doc_code">
+<pre>
+% llc -march=c program.bc -o program.c
+</pre>
+</div></li>
+
+<li><p>Finally, compile the C file:</p>
+
+<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>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>
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