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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="application/xhtml+xml; charset=UTF-8" />
<meta name="generator" content="AsciiDoc 8.6.10" />
<title></title>
<style type="text/css">
/* Shared CSS for AsciiDoc xhtml11 and html5 backends */
/* Default font. */
body {
font-family: Georgia,serif;
}
/* Title font. */
h1, h2, h3, h4, h5, h6,
div.title, caption.title,
thead, p.table.header,
#toctitle,
#author, #revnumber, #revdate, #revremark,
#footer {
font-family: Arial,Helvetica,sans-serif;
}
body {
margin: 1em 5% 1em 5%;
}
a {
color: blue;
text-decoration: underline;
}
a:visited {
color: fuchsia;
}
em {
font-style: italic;
color: navy;
}
strong {
font-weight: bold;
color: #083194;
}
h1, h2, h3, h4, h5, h6 {
color: #527bbd;
margin-top: 1.2em;
margin-bottom: 0.5em;
line-height: 1.3;
}
h1, h2, h3 {
border-bottom: 2px solid silver;
}
h2 {
padding-top: 0.5em;
}
h3 {
float: left;
}
h3 + * {
clear: left;
}
h5 {
font-size: 1.0em;
}
div.sectionbody {
margin-left: 0;
}
hr {
border: 1px solid silver;
}
p {
margin-top: 0.5em;
margin-bottom: 0.5em;
}
ul, ol, li > p {
margin-top: 0;
}
ul > li { color: #aaa; }
ul > li > * { color: black; }
.monospaced, code, pre {
font-family: "Courier New", Courier, monospace;
font-size: inherit;
color: navy;
padding: 0;
margin: 0;
}
pre {
white-space: pre-wrap;
}
#author {
color: #527bbd;
font-weight: bold;
font-size: 1.1em;
}
#email {
}
#revnumber, #revdate, #revremark {
}
#footer {
font-size: small;
border-top: 2px solid silver;
padding-top: 0.5em;
margin-top: 4.0em;
}
#footer-text {
float: left;
padding-bottom: 0.5em;
}
#footer-badges {
float: right;
padding-bottom: 0.5em;
}
#preamble {
margin-top: 1.5em;
margin-bottom: 1.5em;
}
div.imageblock, div.exampleblock, div.verseblock,
div.quoteblock, div.literalblock, div.listingblock, div.sidebarblock,
div.admonitionblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
div.admonitionblock {
margin-top: 2.0em;
margin-bottom: 2.0em;
margin-right: 10%;
color: #606060;
}
div.content { /* Block element content. */
padding: 0;
}
/* Block element titles. */
div.title, caption.title {
color: #527bbd;
font-weight: bold;
text-align: left;
margin-top: 1.0em;
margin-bottom: 0.5em;
}
div.title + * {
margin-top: 0;
}
td div.title:first-child {
margin-top: 0.0em;
}
div.content div.title:first-child {
margin-top: 0.0em;
}
div.content + div.title {
margin-top: 0.0em;
}
div.sidebarblock > div.content {
background: #ffffee;
border: 1px solid #dddddd;
border-left: 4px solid #f0f0f0;
padding: 0.5em;
}
div.listingblock > div.content {
border: 1px solid #dddddd;
border-left: 5px solid #f0f0f0;
background: #f8f8f8;
padding: 0.5em;
}
div.quoteblock, div.verseblock {
padding-left: 1.0em;
margin-left: 1.0em;
margin-right: 10%;
border-left: 5px solid #f0f0f0;
color: #888;
}
div.quoteblock > div.attribution {
padding-top: 0.5em;
text-align: right;
}
div.verseblock > pre.content {
font-family: inherit;
font-size: inherit;
}
div.verseblock > div.attribution {
padding-top: 0.75em;
text-align: left;
}
/* DEPRECATED: Pre version 8.2.7 verse style literal block. */
div.verseblock + div.attribution {
text-align: left;
}
div.admonitionblock .icon {
vertical-align: top;
font-size: 1.1em;
font-weight: bold;
text-decoration: underline;
color: #527bbd;
padding-right: 0.5em;
}
div.admonitionblock td.content {
padding-left: 0.5em;
border-left: 3px solid #dddddd;
}
div.exampleblock > div.content {
border-left: 3px solid #dddddd;
padding-left: 0.5em;
}
div.imageblock div.content { padding-left: 0; }
span.image img { border-style: none; vertical-align: text-bottom; }
a.image:visited { color: white; }
dl {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
dt {
margin-top: 0.5em;
margin-bottom: 0;
font-style: normal;
color: navy;
}
dd > *:first-child {
margin-top: 0.1em;
}
ul, ol {
list-style-position: outside;
}
ol.arabic {
list-style-type: decimal;
}
ol.loweralpha {
list-style-type: lower-alpha;
}
ol.upperalpha {
list-style-type: upper-alpha;
}
ol.lowerroman {
list-style-type: lower-roman;
}
ol.upperroman {
list-style-type: upper-roman;
}
div.compact ul, div.compact ol,
div.compact p, div.compact p,
div.compact div, div.compact div {
margin-top: 0.1em;
margin-bottom: 0.1em;
}
tfoot {
font-weight: bold;
}
td > div.verse {
white-space: pre;
}
div.hdlist {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
div.hdlist tr {
padding-bottom: 15px;
}
dt.hdlist1.strong, td.hdlist1.strong {
font-weight: bold;
}
td.hdlist1 {
vertical-align: top;
font-style: normal;
padding-right: 0.8em;
color: navy;
}
td.hdlist2 {
vertical-align: top;
}
div.hdlist.compact tr {
margin: 0;
padding-bottom: 0;
}
.comment {
background: yellow;
}
.footnote, .footnoteref {
font-size: 0.8em;
}
span.footnote, span.footnoteref {
vertical-align: super;
}
#footnotes {
margin: 20px 0 20px 0;
padding: 7px 0 0 0;
}
#footnotes div.footnote {
margin: 0 0 5px 0;
}
#footnotes hr {
border: none;
border-top: 1px solid silver;
height: 1px;
text-align: left;
margin-left: 0;
width: 20%;
min-width: 100px;
}
div.colist td {
padding-right: 0.5em;
padding-bottom: 0.3em;
vertical-align: top;
}
div.colist td img {
margin-top: 0.3em;
}
@media print {
#footer-badges { display: none; }
}
#toc {
margin-bottom: 2.5em;
}
#toctitle {
color: #527bbd;
font-size: 1.1em;
font-weight: bold;
margin-top: 1.0em;
margin-bottom: 0.1em;
}
div.toclevel0, div.toclevel1, div.toclevel2, div.toclevel3, div.toclevel4 {
margin-top: 0;
margin-bottom: 0;
}
div.toclevel2 {
margin-left: 2em;
font-size: 0.9em;
}
div.toclevel3 {
margin-left: 4em;
font-size: 0.9em;
}
div.toclevel4 {
margin-left: 6em;
font-size: 0.9em;
}
span.aqua { color: aqua; }
span.black { color: black; }
span.blue { color: blue; }
span.fuchsia { color: fuchsia; }
span.gray { color: gray; }
span.green { color: green; }
span.lime { color: lime; }
span.maroon { color: maroon; }
span.navy { color: navy; }
span.olive { color: olive; }
span.purple { color: purple; }
span.red { color: red; }
span.silver { color: silver; }
span.teal { color: teal; }
span.white { color: white; }
span.yellow { color: yellow; }
span.aqua-background { background: aqua; }
span.black-background { background: black; }
span.blue-background { background: blue; }
span.fuchsia-background { background: fuchsia; }
span.gray-background { background: gray; }
span.green-background { background: green; }
span.lime-background { background: lime; }
span.maroon-background { background: maroon; }
span.navy-background { background: navy; }
span.olive-background { background: olive; }
span.purple-background { background: purple; }
span.red-background { background: red; }
span.silver-background { background: silver; }
span.teal-background { background: teal; }
span.white-background { background: white; }
span.yellow-background { background: yellow; }
span.big { font-size: 2em; }
span.small { font-size: 0.6em; }
span.underline { text-decoration: underline; }
span.overline { text-decoration: overline; }
span.line-through { text-decoration: line-through; }
div.unbreakable { page-break-inside: avoid; }
/*
* xhtml11 specific
*
* */
div.tableblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
div.tableblock > table {
border: 3px solid #527bbd;
}
thead, p.table.header {
font-weight: bold;
color: #527bbd;
}
p.table {
margin-top: 0;
}
/* Because the table frame attribute is overriden by CSS in most browsers. */
div.tableblock > table[frame="void"] {
border-style: none;
}
div.tableblock > table[frame="hsides"] {
border-left-style: none;
border-right-style: none;
}
div.tableblock > table[frame="vsides"] {
border-top-style: none;
border-bottom-style: none;
}
/*
* html5 specific
*
* */
table.tableblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
thead, p.tableblock.header {
font-weight: bold;
color: #527bbd;
}
p.tableblock {
margin-top: 0;
}
table.tableblock {
border-width: 3px;
border-spacing: 0px;
border-style: solid;
border-color: #527bbd;
border-collapse: collapse;
}
th.tableblock, td.tableblock {
border-width: 1px;
padding: 4px;
border-style: solid;
border-color: #527bbd;
}
table.tableblock.frame-topbot {
border-left-style: hidden;
border-right-style: hidden;
}
table.tableblock.frame-sides {
border-top-style: hidden;
border-bottom-style: hidden;
}
table.tableblock.frame-none {
border-style: hidden;
}
th.tableblock.halign-left, td.tableblock.halign-left {
text-align: left;
}
th.tableblock.halign-center, td.tableblock.halign-center {
text-align: center;
}
th.tableblock.halign-right, td.tableblock.halign-right {
text-align: right;
}
th.tableblock.valign-top, td.tableblock.valign-top {
vertical-align: top;
}
th.tableblock.valign-middle, td.tableblock.valign-middle {
vertical-align: middle;
}
th.tableblock.valign-bottom, td.tableblock.valign-bottom {
vertical-align: bottom;
}
/*
* manpage specific
*
* */
body.manpage h1 {
padding-top: 0.5em;
padding-bottom: 0.5em;
border-top: 2px solid silver;
border-bottom: 2px solid silver;
}
body.manpage h2 {
border-style: none;
}
body.manpage div.sectionbody {
margin-left: 3em;
}
@media print {
body.manpage div#toc { display: none; }
}
</style>
<script type="text/javascript">
/*<+'])');
// Function that scans the DOM tree for header elements (the DOM2
// nodeIterator API would be a better technique but not supported by all
// browsers).
var iterate = function (el) {
for (var i = el.firstChild; i != null; i = i.nextSibling) {
if (i.nodeType == 1 /* Node.ELEMENT_NODE */) {
var mo = re.exec(i.tagName);
if (mo && (i.getAttribute("class") || i.getAttribute("className")) != "float") {
result[result.length] = new TocEntry(i, getText(i), mo[1]-1);
}
iterate(i);
}
}
}
iterate(el);
return result;
}
var toc = document.getElementById("toc");
if (!toc) {
return;
}
// Delete existing TOC entries in case we're reloading the TOC.
var tocEntriesToRemove = [];
var i;
for (i = 0; i < toc.childNodes.length; i++) {
var entry = toc.childNodes[i];
if (entry.nodeName.toLowerCase() == 'div'
&& entry.getAttribute("class")
&& entry.getAttribute("class").match(/^toclevel/))
tocEntriesToRemove.push(entry);
}
for (i = 0; i < tocEntriesToRemove.length; i++) {
toc.removeChild(tocEntriesToRemove[i]);
}
// Rebuild TOC entries.
var entries = tocEntries(document.getElementById("content"), toclevels);
for (var i = 0; i < entries.length; ++i) {
var entry = entries[i];
if (entry.element.id == "")
entry.element.id = "_toc_" + i;
var a = document.createElement("a");
a.href = "#" + entry.element.id;
a.appendChild(document.createTextNode(entry.text));
var div = document.createElement("div");
div.appendChild(a);
div.className = "toclevel" + entry.toclevel;
toc.appendChild(div);
}
if (entries.length == 0)
toc.parentNode.removeChild(toc);
},
/////////////////////////////////////////////////////////////////////
// Footnotes generator
/////////////////////////////////////////////////////////////////////
/* Based on footnote generation code from:
* http://www.brandspankingnew.net/archive/2005/07/format_footnote.html
*/
footnotes: function () {
// Delete existing footnote entries in case we're reloading the footnodes.
var i;
var noteholder = document.getElementById("footnotes");
if (!noteholder) {
return;
}
var entriesToRemove = [];
for (i = 0; i < noteholder.childNodes.length; i++) {
var entry = noteholder.childNodes[i];
if (entry.nodeName.toLowerCase() == 'div' && entry.getAttribute("class") == "footnote")
entriesToRemove.push(entry);
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<body class="article">
<div id="header">
</div>
<div id="content">
<div class="sect1">
<h2 id="_hello_llvm">Hello LLVM</h2>
<div class="sectionbody">
<div class="paragraph"><p>This is a mini tutorial on how to generate output code for LLVM. LLVM
is an abstract, low-level machine language. LLVM is used in a number
of major projects such as the clang C/C++ compiler. It’s also used to
implement various so-called JIT (Just in Time) compilation features.</p></div>
<div class="paragraph"><p>LLVM is an extremely large project that can be daunting to jump into.
However, using it in a simple manner is not so bad. To explore the
basics, we’re going to use the <code>llvmlite</code> package. This is available
in the Anaconda Python distribution so if you’re using that, you
should already have it.</p></div>
<div class="sect2">
<h3 id="_llvm_preliminaries">LLVM Preliminaries</h3>
<div class="paragraph"><p>Your first task is to make sure Anaconda Python and the clang C/C++
compiler have been installed on your machine.</p></div>
</div>
<div class="sect2">
<h3 id="_hello_world">Hello World</h3>
<div class="paragraph"><p>The first step in using LLVM is to make a LLVM module which contains
all of the code you will be generating. Create a file
<code>hellollvm.py</code> and put this code into it:</p></div>
<div class="listingblock">
<div class="content">
<pre><code># hellollvm.py
from llvmlite.ir import Module
mod = Module('hello')
print(mod)</code></pre>
</div></div>
<div class="paragraph"><p>Run the program and you should get some output like this:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>bash % python3 hellollvm.py
; ModuleID = "hello"
target triple = "unknown-unknown-unknown"
target datalayout = ""
bash %</code></pre>
</div></div>
<div class="paragraph"><p>The output you’re using is LLVM low-level code—a kind of architecture
independent assembly language. At this point, it’s not too
interesting. However, let’s declare a function to put in the module.
Change the program to the following to declare a function with the C
prototype <code>int hello()</code>:</p></div>
<div class="listingblock">
<div class="content">
<pre><code># hellollvm.py
from llvmlite.ir import (
Module, Function, FunctionType, IntType
)
mod = Module('hello')
int_type = IntType(32)
hello_func = Function(mod, FunctionType(int_type, []), name='hello')
print(mod)</code></pre>
</div></div>
<div class="paragraph"><p>Running the program, you should now get the following:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>bash % python3 hellollvm.py
; ModuleID = "hello"
target triple = "unknown-unknown-unknown"
target datalayout = ""
declare i32 @"hello"()
bash %</code></pre>
</div></div>
<div class="paragraph"><p>Again, it’s not too interesting at this point. However, you can see
how a function declaration was placed in the module output. The LLVM
statement <code>declare i32 @"hello"()</code> is declaring a function that
returns a 32-bit integer and takes no arguments.</p></div>
<div class="paragraph"><p>Let’s add some code to the function. To do this, you first need to
create a basic block. A basic block is a container that holds
low-level instructions. Add the following to the program:</p></div>
<div class="listingblock">
<div class="content">
<pre><code># hellollvm.py
from llvmlite.ir import (
Module, Function, FunctionType, IntType, IRBuilder
)
mod = Module('hello')
int_type = IntType(32)
hello_func = Function(mod, FunctionType(int_type, []), name='hello')
block = hello_func.append_basic_block('entry')
builder = IRBuilder(block)
builder.ret(Constant(IntType(32), 37))
print(mod)</code></pre>
</div></div>
<div class="paragraph"><p>Running the program should now produce this:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>; ModuleID = "hello"
target triple = "unknown-unknown-unknown"
target datalayout = ""
define i32 @"hello"()
{
entry:
ret i32 37
}</code></pre>
</div></div>
<div class="paragraph"><p>There you are---a complete LLVM function that does nothing but return
the value 37. Now, a question arises: How do you go about getting it to run?</p></div>
</div>
<div class="sect2">
<h3 id="_compilation_to_a_standalone_executable">Compilation to a Standalone Executable</h3>
<div class="paragraph"><p>If you want to run your LLVM generated code, one approach is to feed it
to a LLVM-based compiler such as <code>clang</code>. Save your generated
code to a file <code>hello.ll</code>:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>bash % python3 hellollvm.py > hello.ll
bash %</code></pre>
</div></div>
<div class="paragraph"><p>Now, write a short C program to bootstrap the function:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>/* main.c */
#include <stdio.h>
extern int hello();
int main() {
printf("hello() returned %i\n", hello());
}</code></pre>
</div></div>
<div class="paragraph"><p>Compile this program together with <code>hello.ll</code> to make an executable:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>bash % clang main.c hello.ll
bash % ./a.out
hello() returned 37
bash %</code></pre>
</div></div>
<div class="paragraph"><p>This basic technique for invoking your code and creating stand-alone
programs will be useful for testing and development. You also get the
advantage of being able to use C library functions such as
<code>printf()</code>. Without this, you’d have to figure out how to perform
I/O directly using low-level LLVM instructions—which would not be
fun.</p></div>
</div>
<div class="sect2">
<h3 id="_just_in_time_compilation">Just in Time Compilation</h3>
<div class="paragraph"><p>In our example, we are creating LLVM instructions, writing them to a
file, and using the <code>clang</code> compiler to produce an executable.
It’s possible that this won’t work due to the local setup on
your machine (maybe you don’t have clang installed correctly).
One feature of LLVM is that it can compile it’s own code to executable
machine instructions without ever going to a file or using clang.
You can do this entirely in Python and have Python call the resulting
function.</p></div>
<div class="paragraph"><p>This part is rather tricky and obscure, but add the following code to
<code>hellollvm.py</code>:</p></div>
<div class="listingblock">
<div class="content">
<pre><code># hellollvm.py
... keep earlier LLVM example here ...
def run_jit(module):
import llvmlite.binding as llvm
llvm.initialize()
llvm.initialize_native_target()
llvm.initialize_native_asmprinter()
target = llvm.Target.from_default_triple()
target_machine = target.create_target_machine()
compiled_mod = llvm.parse_assembly(str(module))
engine = llvm.create_mcjit_compiler(compiled_mod, target_machine)
# Look up the function pointer (a Python int)
func_ptr = engine.get_function_address("hello")
# Turn into a Python callable using ctypes
from ctypes import CFUNCTYPE, c_int
hello = CFUNCTYPE(c_int)(func_ptr)
res = hello()
print('hello() returned', res)
# Run it!
run_jit(mod)</code></pre>
</div></div>
<div class="paragraph"><p>If you run this, you should see the program run the code, and
produce output such as this:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>bash % python3 hellollvm.py
hello() returned 37
bash %</code></pre>
</div></div>
<div class="paragraph"><p>This version runs entirely inside an active Python interpreter process.
If you can’t get clang to work, you can always use this as a fallback.</p></div>
</div>
<div class="sect2">
<h3 id="_local_variables_and_math_operations">Local Variables and Math Operations</h3>
<div class="paragraph"><p>To do more with LLVM, you need to use more instructions on the
<code>builder</code> object in the example. To declare a local variable "x",
you use this method:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>x = builder.alloca(int_type, name="x")</code></pre>
</div></div>
<div class="paragraph"><p>To load and store values, you use these instructions:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>r = builder.load(x) # Load a value from x into r
builder.store(r, x) # Store r into y</code></pre>
</div></div>
<div class="paragraph"><p>To perform arithmetic, you use instructions such as these:</p></div>
<div class="listingblock">
<div class="content">
<pre><code>r3 = builder.add(r1, r2) # r3 = r1 + r2
r3 = builder.mul(r1, r2) # r3 = r1 + r2</code></pre>
</div></div>
<div class="paragraph"><p>Here is an example that implements the program given at the start
of this exercise:</p></div>
<div class="listingblock">
<div class="content">
<pre><code># hellollvm.py
from llvmlite.ir import (
Module, Function, FunctionType, IntType,
Constant, IRBuilder
)
mod = Module('hello')
int_type = IntType(32)
hello_func = Function(mod, FunctionType(int_type, []), name='hello')
block = hello_func.append_basic_block('entry')
builder = IRBuilder(block)
x = builder.alloca(int_type, name='x')
y = builder.alloca(int_type, name='y')
builder.store(Constant(int_type, 4), x)
builder.store(Constant(int_type, 5), y)
r1 = builder.load(x)
r2 = builder.mul(r1, r1)
r3 = builder.load(y)
r4 = builder.mul(r3, r3)
r5 = builder.add(r2, r4)
d = builder.alloca(int_type, name='d')
builder.store(r5, d)
builder.ret(builder.load(d))
print(mod)</code></pre>
</div></div>
<div class="paragraph"><p>An important thing about LLVM is that it is NOT a stack machine. It is based
on registers and Single Static Assignment (SSA). Basically, every operation
produces a new variable that can only be assigned once. It also requires explicit
load/store instructions to go between local variables and registers. In the
above example, you can’t do an instruction such as <code>builder.add(x, y)</code> between
local variables. You have to load the variables into registers first and
perform the instruction on the registers.</p></div>
<div class="paragraph"><p>Try compiling the above program and running you code again:</p></div>
<div class="listingblock">