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Chris Lattner 2007-11-07 06:46:51 +00:00
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@ -88,9 +88,9 @@ of the variable in the symbol table along with its Value*.</li>
extending the type system in all sorts of interesting ways. Simple arrays are extending the type system in all sorts of interesting ways. Simple arrays are
very easy and are quite useful for many different applications. Adding them is very easy and are quite useful for many different applications. Adding them is
mostly an exercise in learning how the LLVM <a mostly an exercise in learning how the LLVM <a
href="../LangRef.html#i_getelementptr">getelementptr</a> instruction works. href="../LangRef.html#i_getelementptr">getelementptr</a> instruction works: it
The getelementptr instruction is so nifty/unconventional, it <a is so nifty/unconventional, it <a
href="../GetElementPtr.html">has its own FAQ</a>!). If you add support href="../GetElementPtr.html">has its own FAQ</a>! If you add support
for recursive types (e.g. linked lists), make sure to read the <a for recursive types (e.g. linked lists), make sure to read the <a
href="../ProgrammersManual.html#TypeResolve">section in the LLVM href="../ProgrammersManual.html#TypeResolve">section in the LLVM
Programmer's Manual</a> that describes how to construct them.</li> Programmer's Manual</a> that describes how to construct them.</li>
@ -160,8 +160,8 @@ IR</a></div>
<div class="doc_text"> <div class="doc_text">
<p>We have a couple common questions about code in the LLVM IR form, lets just <p>We have a couple common questions about code in the LLVM IR form - lets just
get these out of the way right now shall we?</p> get these out of the way right now, shall we?</p>
</div> </div>
@ -177,7 +177,7 @@ Kaleidoscope will work the same way on any target that it runs on. Many other
languages have this property, e.g. lisp, java, haskell, javascript, python, etc languages have this property, e.g. lisp, java, haskell, javascript, python, etc
(note that while these languages are portable, not all their libraries are).</p> (note that while these languages are portable, not all their libraries are).</p>
<p>One nice aspect of LLVM is that it is often capable of preserving language <p>One nice aspect of LLVM is that it is often capable of preserving target
independence in the IR: you can take the LLVM IR for a Kaleidoscope-compiled independence in the IR: you can take the LLVM IR for a Kaleidoscope-compiled
program and run it on any target that LLVM supports, even emitting C code and program and run it on any target that LLVM supports, even emitting C code and
compiling that on targets that LLVM doesn't support natively. You can trivially compiling that on targets that LLVM doesn't support natively. You can trivially
@ -215,7 +215,7 @@ the actual source code.</p>
you are willing to fix primitive types to a fixed size (say int = 32-bits, you are willing to fix primitive types to a fixed size (say int = 32-bits,
and long = 64-bits), don't care about ABI compatibility with existing binaries, and long = 64-bits), don't care about ABI compatibility with existing binaries,
and are willing to give up some other minor features, you can have portable and are willing to give up some other minor features, you can have portable
code. This can even make real sense for specialized domains such as an code. This can make sense for specialized domains such as an
in-kernel language.</p> in-kernel language.</p>
</div> </div>
@ -227,7 +227,8 @@ in-kernel language.</p>
<div class="doc_text"> <div class="doc_text">
<p>Many of the languages above are also "safe" languages: it is impossible for <p>Many of the languages above are also "safe" languages: it is impossible for
a program written in Java to corrupt its address space and crash the process. a program written in Java to corrupt its address space and crash the process
(assuming the JVM has no bugs).
Safety is an interesting property that requires a combination of language Safety is an interesting property that requires a combination of language
design, runtime support, and often operating system support.</p> design, runtime support, and often operating system support.</p>
@ -277,13 +278,13 @@ whether an argument is sign or zero extended, information about pointers
aliasing, etc. Many of the enhancements are user-driven: people want LLVM to aliasing, etc. Many of the enhancements are user-driven: people want LLVM to
do some specific feature, so they go ahead and extend it to do so.</p> do some specific feature, so they go ahead and extend it to do so.</p>
<p>Third, it <em>is certainly possible</em> to add language-specific <p>Third, it <em>is possible and easy</em> to add language-specific
optimizations, and you have a number of choices in how to do it. As one trivial optimizations, and you have a number of choices in how to do it. As one trivial
example, it is possible to add language-specific optimization passes that example, it is easy to add language-specific optimization passes that
"know" things about code compiled for a language. In the case of the C family, "know" things about code compiled for a language. In the case of the C family,
there is an optimziation pass that "knows" about the standard C library there is an optimization pass that "knows" about the standard C library
functions. If you call "exit(0)" in main(), it knows that it is safe to functions. If you call "exit(0)" in main(), it knows that it is safe to
optimize that into "return 0;" for example, because C specifies what the 'exit' optimize that into "return 0;" because C specifies what the 'exit'
function does.</p> function does.</p>
<p>In addition to simple library knowledge, it is possible to embed a variety of <p>In addition to simple library knowledge, it is possible to embed a variety of