1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
|
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>IRTranslator — LLVM 13 documentation</title>
<link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
<link rel="stylesheet" href="../_static/llvm-theme.css" type="text/css" />
<script id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script>
<script src="../_static/jquery.js"></script>
<script src="../_static/underscore.js"></script>
<script src="../_static/doctools.js"></script>
<link rel="index" title="Index" href="../genindex.html" />
<link rel="search" title="Search" href="../search.html" />
<link rel="next" title="Legalizer" href="Legalizer.html" />
<link rel="prev" title="Core Pipeline" href="Pipeline.html" />
<style type="text/css">
table.right { float: right; margin-left: 20px; }
table.right td { border: 1px solid #ccc; }
</style>
</head><body>
<div class="logo">
<a href="../index.html">
<img src="../_static/logo.png"
alt="LLVM Logo" width="250" height="88"/></a>
</div>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
accesskey="I">index</a></li>
<li class="right" >
<a href="Legalizer.html" title="Legalizer"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="Pipeline.html" title="Core Pipeline"
accesskey="P">previous</a> |</li>
<li><a href="https://llvm.org/">LLVM Home</a> | </li>
<li><a href="../index.html">Documentation</a>»</li>
<li class="nav-item nav-item-1"><a href="../Reference.html" >Reference</a> »</li>
<li class="nav-item nav-item-2"><a href="index.html" >Global Instruction Selection</a> »</li>
<li class="nav-item nav-item-3"><a href="Pipeline.html" accesskey="U">Core Pipeline</a> »</li>
<li class="nav-item nav-item-this"><a href="">IRTranslator</a></li>
</ul>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<h3>Documentation</h3>
<ul class="want-points">
<li><a href="https://llvm.org/docs/GettingStartedTutorials.html">Getting Started/Tutorials</a></li>
<li><a href="https://llvm.org/docs/UserGuides.html">User Guides</a></li>
<li><a href="https://llvm.org/docs/Reference.html">Reference</a></li>
</ul>
<h3>Getting Involved</h3>
<ul class="want-points">
<li><a href="https://llvm.org/docs/Contributing.html">Contributing to LLVM</a></li>
<li><a href="https://llvm.org/docs/HowToSubmitABug.html">Submitting Bug Reports</a></li>
<li><a href="https://llvm.org/docs/GettingInvolved.html#mailing-lists">Mailing Lists</a></li>
<li><a href="https://llvm.org/docs/GettingInvolved.html#irc">IRC</a></li>
<li><a href="https://llvm.org/docs/GettingInvolved.html#meetups-and-social-events">Meetups and Social Events</a></li>
</ul>
<h3>Additional Links</h3>
<ul class="want-points">
<li><a href="https://llvm.org/docs/FAQ.html">FAQ</a></li>
<li><a href="https://llvm.org/docs/Lexicon.html">Glossary</a></li>
<li><a href="https://llvm.org/pubs">Publications</a></li>
<li><a href="https://github.com/llvm/llvm-project//">Github Repository</a></li>
</ul>
<div role="note" aria-label="source link">
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../_sources/GlobalISel/IRTranslator.rst.txt"
rel="nofollow">Show Source</a></li>
</ul>
</div>
<div id="searchbox" style="display: none" role="search">
<h3 id="searchlabel">Quick search</h3>
<div class="searchformwrapper">
<form class="search" action="../search.html" method="get">
<input type="text" name="q" aria-labelledby="searchlabel" />
<input type="submit" value="Go" />
</form>
</div>
</div>
<script>$('#searchbox').show(0);</script>
</div>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body" role="main">
<div class="section" id="irtranslator">
<span id="id1"></span><h1>IRTranslator<a class="headerlink" href="#irtranslator" title="Permalink to this headline">¶</a></h1>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><p><a class="reference internal" href="#target-intrinsics" id="id2">Target Intrinsics</a></p></li>
<li><p><a class="reference internal" href="#translating-function-calls" id="id3">Translating Function Calls</a></p>
<ul>
<li><p><a class="reference internal" href="#aggregates" id="id4">Aggregates</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#translation-of-constants" id="id5">Translation of Constants</a></p></li>
</ul>
</div>
<p>This pass translates the input LLVM-IR <code class="docutils literal notranslate"><span class="pre">Function</span></code> to a GMIR
<code class="docutils literal notranslate"><span class="pre">MachineFunction</span></code>. This is typically a direct translation but does
occasionally get a bit more involved. For example:</p>
<div class="highlight-llvm notranslate"><div class="highlight"><pre><span></span><span class="nv nv-Anonymous">%2</span> <span class="p">=</span> <span class="k">add</span> <span class="k">i32</span> <span class="nv nv-Anonymous">%0</span><span class="p">,</span> <span class="nv nv-Anonymous">%1</span>
</pre></div>
</div>
<p>becomes:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>%2:_(s32) = G_ADD %0:_(s32), %1:_(s32)
</pre></div>
</div>
<p>whereas</p>
<div class="highlight-llvm notranslate"><div class="highlight"><pre><span></span><span class="k">call</span> <span class="k">i32</span> <span class="vg">@puts</span><span class="p">(</span><span class="k">i8</span><span class="p">*</span> <span class="nv">%cast210</span><span class="p">)</span>
</pre></div>
</div>
<p>is translated according to the ABI rules of the target.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The currently implemented portion of the <a class="reference internal" href="../LangRef.html"><span class="doc">LLVM Language Reference Manual</span></a> is sufficient for
many compilations but it is not 100% complete. Users seeking to compile
LLVM-IR containing some of the rarer features may need to implement the
translation.</p>
</div>
<div class="section" id="target-intrinsics">
<h2><a class="toc-backref" href="#id2">Target Intrinsics</a><a class="headerlink" href="#target-intrinsics" title="Permalink to this headline">¶</a></h2>
<p>There has been some (off-list) debate about whether to add target hooks for
translating target intrinsics. Among those who discussed it, it was generally
agreed that the IRTranslator should be able to lower target intrinsics in a
customizable way but no work has happened to implement this at the time of
writing.</p>
</div>
<div class="section" id="translating-function-calls">
<span id="translator-call-lower"></span><h2><a class="toc-backref" href="#id3">Translating Function Calls</a><a class="headerlink" href="#translating-function-calls" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal notranslate"><span class="pre">IRTranslator</span></code> also implements the ABI’s calling convention by lowering
calls, returns, and arguments to the appropriate physical register usage and
instruction sequences. This is achieved using the <code class="docutils literal notranslate"><span class="pre">CallLowering</span></code>
implementation,</p>
<div class="section" id="aggregates">
<span id="irtranslator-aggregates"></span><h3><a class="toc-backref" href="#id4">Aggregates</a><a class="headerlink" href="#aggregates" title="Permalink to this headline">¶</a></h3>
<div class="admonition caution">
<p class="admonition-title">Caution</p>
<p>This has changed since it was written and is no longer accurate. It has not
been refreshed in this pass of improving the documentation as I haven’t
worked much in this part of the codebase and it should have attention from
someone more knowledgeable about it.</p>
</div>
<p>Aggregates are lowered into multiple virtual registers, similar to
SelectionDAG’s multiple vregs via <code class="docutils literal notranslate"><span class="pre">GetValueVTs</span></code>.</p>
<p><code class="docutils literal notranslate"><span class="pre">TODO</span></code>:
As some of the bits are undef (padding), we should consider augmenting the
representation with additional metadata (in effect, caching computeKnownBits
information on vregs).
See <a class="reference external" href="https://llvm.org/PR26161">PR26161</a>: [GlobalISel] Value to vreg during
IR to MachineInstr translation for aggregate type</p>
</div>
</div>
<div class="section" id="translation-of-constants">
<span id="irtranslator-constants"></span><h2><a class="toc-backref" href="#id5">Translation of Constants</a><a class="headerlink" href="#translation-of-constants" title="Permalink to this headline">¶</a></h2>
<p>Constant operands are translated as a use of a virtual register that is defined
by a <code class="docutils literal notranslate"><span class="pre">G_CONSTANT</span></code> or <code class="docutils literal notranslate"><span class="pre">G_FCONSTANT</span></code> instruction. These instructions are
placed in the entry block to allow them to be subject to the continuous CSE
implementation (<code class="docutils literal notranslate"><span class="pre">CSEMIRBuilder</span></code>). Their debug location information is removed
to prevent this from confusing debuggers.</p>
<p>This is beneficial as it allows us to fold constants into immediate operands
during <a class="reference internal" href="InstructionSelect.html#instructionselect"><span class="std std-ref">InstructionSelect</span></a>, while still avoiding redundant materializations
for expensive non-foldable constants. However, this can lead to unnecessary
spills and reloads in an -O0 pipeline, as these virtual registers can have long
live ranges. This can be mitigated by running a <a class="reference external" href="https://github.com/llvm/llvm-project/blob/main/llvm/lib/CodeGen/GlobalISel/Localizer.cpp">localizer</a>
after the translator.</p>
</div>
</div>
<div class="clearer"></div>
</div>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
>index</a></li>
<li class="right" >
<a href="Legalizer.html" title="Legalizer"
>next</a> |</li>
<li class="right" >
<a href="Pipeline.html" title="Core Pipeline"
>previous</a> |</li>
<li><a href="https://llvm.org/">LLVM Home</a> | </li>
<li><a href="../index.html">Documentation</a>»</li>
<li class="nav-item nav-item-1"><a href="../Reference.html" >Reference</a> »</li>
<li class="nav-item nav-item-2"><a href="index.html" >Global Instruction Selection</a> »</li>
<li class="nav-item nav-item-3"><a href="Pipeline.html" >Core Pipeline</a> »</li>
<li class="nav-item nav-item-this"><a href="">IRTranslator</a></li>
</ul>
</div>
<div class="footer" role="contentinfo">
© Copyright 2003-2021, LLVM Project.
Last updated on 2021-09-18.
Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 3.5.4.
</div>
</body>
</html>
|
