target".</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="#langhlsupp">What support is there for higher level source
+ language constructs for building a compiler?</a></li>
+ </ol>
+
<li><a href="#cfe">Using the GCC Front End</a>
<ol>
<li>
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>
rebuilding.</p>
</div>
+<!-- *********************************************************************** -->
+<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
+ 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
+ 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
+ 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 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>
+</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="cfe">Using the GCC Front End</a>
</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></li>
+
+<div class="doc_code">$ llvm-g++ x.cpp -o program</div>
+
+<p>or:</p>
+
+<div class="doc_code">
+ llvm-g++ a.cpp -c
+ llvm-g++ b.cpp -c
+ llvm-g++ a.o b.o -o program
+</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><p>Convert the LLVM code to C code, using the LLC tool with the C
+backend:</p></li>
+
+<div class="doc_code">$ llc -march=c program.bc -o program.c</div>
+
+<li><p>Finally, compile the c file:</p></li>
+
+<div class="doc_code">$ cc x.c</div>
+
+</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>
+</div>
+
+
+
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="cfe_code">Questions about code generated by the GCC front-end</a>
projects / oota-llvm.git / blobdiff