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<div class="section" id="torch-export">
<span id="id1"></span><h1>torch.export<a class="headerlink" href="#torch-export" title="Permalink to this heading">¶</a></h1>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>This feature is a prototype under active development and there WILL BE
BREAKING CHANGES in the future.</p>
</div>
<div class="section" id="overview">
<h2>Overview<a class="headerlink" href="#overview" title="Permalink to this heading">¶</a></h2>
<p><a class="reference internal" href="#torch.export.export" title="torch.export.export"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.export.export()</span></code></a> takes an arbitrary Python callable (a
<a class="reference internal" href="generated/torch.nn.Module.html#torch.nn.Module" title="torch.nn.Module"><code class="xref py py-class docutils literal notranslate"><span class="pre">torch.nn.Module</span></code></a>, a function or a method) and produces a traced graph
representing only the Tensor computation of the function in an Ahead-of-Time
(AOT) fashion, which can subsequently be executed with different outputs or
serialized.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">torch</span>
<span class="kn">from</span> <span class="nn">torch.export</span> <span class="kn">import</span> <span class="n">export</span>
<span class="k">class</span> <span class="nc">Mod</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">:</span> <span class="n">torch</span><span class="o">.</span><span class="n">Tensor</span><span class="p">,</span> <span class="n">y</span><span class="p">:</span> <span class="n">torch</span><span class="o">.</span><span class="n">Tensor</span><span class="p">)</span> <span class="o">-></span> <span class="n">torch</span><span class="o">.</span><span class="n">Tensor</span><span class="p">:</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">sin</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="n">b</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">cos</span><span class="p">(</span><span class="n">y</span><span class="p">)</span>
<span class="k">return</span> <span class="n">a</span> <span class="o">+</span> <span class="n">b</span>
<span class="n">example_args</span> <span class="o">=</span> <span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="mi">10</span><span class="p">),</span> <span class="n">torch</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="mi">10</span><span class="p">))</span>
<span class="n">exported_program</span><span class="p">:</span> <span class="n">torch</span><span class="o">.</span><span class="n">export</span><span class="o">.</span><span class="n">ExportedProgram</span> <span class="o">=</span> <span class="n">export</span><span class="p">(</span>
<span class="n">Mod</span><span class="p">(),</span> <span class="n">args</span><span class="o">=</span><span class="n">example_args</span>
<span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">exported_program</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ExportedProgram</span><span class="p">:</span>
<span class="k">class</span> <span class="nc">GraphModule</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg0_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">10</span><span class="p">,</span> <span class="mi">10</span><span class="p">],</span> <span class="n">arg1_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">10</span><span class="p">,</span> <span class="mi">10</span><span class="p">]):</span>
<span class="c1"># code: a = torch.sin(x)</span>
<span class="n">sin</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">10</span><span class="p">,</span> <span class="mi">10</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">sin</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="n">arg0_1</span><span class="p">);</span>
<span class="c1"># code: b = torch.cos(y)</span>
<span class="n">cos</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">10</span><span class="p">,</span> <span class="mi">10</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">cos</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="n">arg1_1</span><span class="p">);</span>
<span class="c1"># code: return a + b</span>
<span class="n">add</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">10</span><span class="p">,</span> <span class="mi">10</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">add</span><span class="o">.</span><span class="n">Tensor</span><span class="p">(</span><span class="n">sin</span><span class="p">,</span> <span class="n">cos</span><span class="p">);</span>
<span class="k">return</span> <span class="p">(</span><span class="n">add</span><span class="p">,)</span>
<span class="n">Graph</span> <span class="n">signature</span><span class="p">:</span> <span class="n">ExportGraphSignature</span><span class="p">(</span>
<span class="n">parameters</span><span class="o">=</span><span class="p">[],</span>
<span class="n">buffers</span><span class="o">=</span><span class="p">[],</span>
<span class="n">user_inputs</span><span class="o">=</span><span class="p">[</span><span class="s1">'arg0_1'</span><span class="p">,</span> <span class="s1">'arg1_1'</span><span class="p">],</span>
<span class="n">user_outputs</span><span class="o">=</span><span class="p">[</span><span class="s1">'add'</span><span class="p">],</span>
<span class="n">inputs_to_parameters</span><span class="o">=</span><span class="p">{},</span>
<span class="n">inputs_to_buffers</span><span class="o">=</span><span class="p">{},</span>
<span class="n">buffers_to_mutate</span><span class="o">=</span><span class="p">{},</span>
<span class="n">backward_signature</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span>
<span class="n">assertion_dep_token</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span>
<span class="p">)</span>
<span class="n">Range</span> <span class="n">constraints</span><span class="p">:</span> <span class="p">{}</span>
</pre></div>
</div>
<p><code class="docutils literal notranslate"><span class="pre">torch.export</span></code> produces a clean intermediate representation (IR) with the
following invariants. More specifications about the IR can be found
<a class="reference internal" href="export.ir_spec.html#export-ir-spec"><span class="std std-ref">here</span></a>.</p>
<ul class="simple">
<li><p><strong>Soundness</strong>: It is guaranteed to be a sound representation of the original
program, and maintains the same calling conventions of the original program.</p></li>
<li><p><strong>Normalized</strong>: There are no Python semantics within the graph. Submodules
from the original programs are inlined to form one fully flattened
computational graph.</p></li>
<li><p><strong>Graph properties</strong>: The graph is purely functional, meaning it does not
contain operations with side effects such as mutations or aliasing. It does
not mutate any intermediate values, parameters, or buffers.</p></li>
<li><p><strong>Metadata</strong>: The graph contains metadata captured during tracing, such as a
stacktrace from user’s code.</p></li>
</ul>
<p>Under the hood, <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> leverages the following latest technologies:</p>
<ul class="simple">
<li><p><strong>TorchDynamo (torch._dynamo)</strong> is an internal API that uses a CPython feature
called the Frame Evaluation API to safely trace PyTorch graphs. This
provides a massively improved graph capturing experience, with much fewer
rewrites needed in order to fully trace the PyTorch code.</p></li>
<li><p><strong>AOT Autograd</strong> provides a functionalized PyTorch graph and ensures the graph
is decomposed/lowered to the ATen operator set.</p></li>
<li><p><strong>Torch FX (torch.fx)</strong> is the underlying representation of the graph,
allowing flexible Python-based transformations.</p></li>
</ul>
<div class="section" id="existing-frameworks">
<h3>Existing frameworks<a class="headerlink" href="#existing-frameworks" title="Permalink to this heading">¶</a></h3>
<p><a class="reference internal" href="generated/torch.compile.html#torch.compile" title="torch.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.compile()</span></code></a> also utilizes the same PT2 stack as <code class="docutils literal notranslate"><span class="pre">torch.export</span></code>, but
is slightly different:</p>
<ul class="simple">
<li><p><strong>JIT vs. AOT</strong>: <a class="reference internal" href="generated/torch.compile.html#torch.compile" title="torch.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.compile()</span></code></a> is a JIT compiler whereas
which is not intended to be used to produce compiled artifacts outside of
deployment.</p></li>
<li><p><strong>Partial vs. Full Graph Capture</strong>: When <a class="reference internal" href="generated/torch.compile.html#torch.compile" title="torch.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.compile()</span></code></a> runs into an
untraceable part of a model, it will “graph break” and fall back to running
the program in the eager Python runtime. In comparison, <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> aims
to get a full graph representation of a PyTorch model, so it will error out
when something untraceable is reached. Since <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> produces a full
graph disjoint from any Python features or runtime, this graph can then be
saved, loaded, and run in different environments and languages.</p></li>
<li><p><strong>Usability tradeoff</strong>: Since <a class="reference internal" href="generated/torch.compile.html#torch.compile" title="torch.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.compile()</span></code></a> is able to fallback to the
Python runtime whenever it reaches something untraceable, it is a lot more
flexible. <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> will instead require users to provide more
information or rewrite their code to make it traceable.</p></li>
</ul>
<p>Compared to <a class="reference internal" href="fx.html#torch.fx.symbolic_trace" title="torch.fx.symbolic_trace"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.fx.symbolic_trace()</span></code></a>, <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> traces using
TorchDynamo which operates at the Python bytecode level, giving it the ability
to trace arbitrary Python constructs not limited by what Python operator
overloading supports. Additionally, <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> keeps fine-grained track of
tensor metadata, so that conditionals on things like tensor shapes do not
fail tracing. In general, <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> is expected to work on more user
programs, and produce lower-level graphs (at the <code class="docutils literal notranslate"><span class="pre">torch.ops.aten</span></code> operator
level). Note that users can still use <a class="reference internal" href="fx.html#torch.fx.symbolic_trace" title="torch.fx.symbolic_trace"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.fx.symbolic_trace()</span></code></a> as a
preprocessing step before <code class="docutils literal notranslate"><span class="pre">torch.export</span></code>.</p>
<p>Compared to <a class="reference internal" href="generated/torch.jit.script.html#torch.jit.script" title="torch.jit.script"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.jit.script()</span></code></a>, <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> does not capture Python
control flow or data structures, but it supports more Python language features
than TorchScript (as it is easier to have comprehensive coverage over Python
bytecodes). The resulting graphs are simpler and only have straight line control
flow (except for explicit control flow operators).</p>
<p>Compared to <a class="reference internal" href="generated/torch.jit.trace.html#torch.jit.trace" title="torch.jit.trace"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.jit.trace()</span></code></a>, <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> is sound: it is able to
trace code that performs integer computation on sizes and records all of the
side-conditions necessary to show that a particular trace is valid for other
inputs.</p>
</div>
</div>
<div class="section" id="exporting-a-pytorch-model">
<h2>Exporting a PyTorch Model<a class="headerlink" href="#exporting-a-pytorch-model" title="Permalink to this heading">¶</a></h2>
<div class="section" id="an-example">
<h3>An Example<a class="headerlink" href="#an-example" title="Permalink to this heading">¶</a></h3>
<p>The main entrypoint is through <a class="reference internal" href="#torch.export.export" title="torch.export.export"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.export.export()</span></code></a>, which takes a
callable (<a class="reference internal" href="generated/torch.nn.Module.html#torch.nn.Module" title="torch.nn.Module"><code class="xref py py-class docutils literal notranslate"><span class="pre">torch.nn.Module</span></code></a>, function, or method) and sample inputs, and
captures the computation graph into an <a class="reference internal" href="#torch.export.ExportedProgram" title="torch.export.ExportedProgram"><code class="xref py py-class docutils literal notranslate"><span class="pre">torch.export.ExportedProgram</span></code></a>. An
example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">torch</span>
<span class="kn">from</span> <span class="nn">torch.export</span> <span class="kn">import</span> <span class="n">export</span>
<span class="c1"># Simple module for demonstration</span>
<span class="k">class</span> <span class="nc">M</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span> <span class="o">-></span> <span class="kc">None</span><span class="p">:</span>
<span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">()</span>
<span class="bp">self</span><span class="o">.</span><span class="n">conv</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Conv2d</span><span class="p">(</span>
<span class="n">in_channels</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">out_channels</span><span class="o">=</span><span class="mi">16</span><span class="p">,</span> <span class="n">kernel_size</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">padding</span><span class="o">=</span><span class="mi">1</span>
<span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">relu</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">ReLU</span><span class="p">()</span>
<span class="bp">self</span><span class="o">.</span><span class="n">maxpool</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">MaxPool2d</span><span class="p">(</span><span class="n">kernel_size</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">:</span> <span class="n">torch</span><span class="o">.</span><span class="n">Tensor</span><span class="p">,</span> <span class="o">*</span><span class="p">,</span> <span class="n">constant</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span> <span class="o">-></span> <span class="n">torch</span><span class="o">.</span><span class="n">Tensor</span><span class="p">:</span>
<span class="n">a</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">conv</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="n">a</span><span class="o">.</span><span class="n">add_</span><span class="p">(</span><span class="n">constant</span><span class="p">)</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">maxpool</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">relu</span><span class="p">(</span><span class="n">a</span><span class="p">))</span>
<span class="n">example_args</span> <span class="o">=</span> <span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">256</span><span class="p">,</span> <span class="mi">256</span><span class="p">),)</span>
<span class="n">example_kwargs</span> <span class="o">=</span> <span class="p">{</span><span class="s2">"constant"</span><span class="p">:</span> <span class="n">torch</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">256</span><span class="p">,</span> <span class="mi">256</span><span class="p">)}</span>
<span class="n">exported_program</span><span class="p">:</span> <span class="n">torch</span><span class="o">.</span><span class="n">export</span><span class="o">.</span><span class="n">ExportedProgram</span> <span class="o">=</span> <span class="n">export</span><span class="p">(</span>
<span class="n">M</span><span class="p">(),</span> <span class="n">args</span><span class="o">=</span><span class="n">example_args</span><span class="p">,</span> <span class="n">kwargs</span><span class="o">=</span><span class="n">example_kwargs</span>
<span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">exported_program</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ExportedProgram</span><span class="p">:</span>
<span class="k">class</span> <span class="nc">GraphModule</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg0_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">16</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">3</span><span class="p">],</span> <span class="n">arg1_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">16</span><span class="p">],</span> <span class="n">arg2_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">256</span><span class="p">,</span> <span class="mi">256</span><span class="p">],</span> <span class="n">arg3_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">256</span><span class="p">,</span> <span class="mi">256</span><span class="p">]):</span>
<span class="c1"># code: a = self.conv(x)</span>
<span class="n">convolution</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">256</span><span class="p">,</span> <span class="mi">256</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">convolution</span><span class="o">.</span><span class="n">default</span><span class="p">(</span>
<span class="n">arg2_1</span><span class="p">,</span> <span class="n">arg0_1</span><span class="p">,</span> <span class="n">arg1_1</span><span class="p">,</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">],</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">],</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">],</span> <span class="kc">False</span><span class="p">,</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">],</span> <span class="mi">1</span>
<span class="p">);</span>
<span class="c1"># code: a.add_(constant)</span>
<span class="n">add</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">256</span><span class="p">,</span> <span class="mi">256</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">add</span><span class="o">.</span><span class="n">Tensor</span><span class="p">(</span><span class="n">convolution</span><span class="p">,</span> <span class="n">arg3_1</span><span class="p">);</span>
<span class="c1"># code: return self.maxpool(self.relu(a))</span>
<span class="n">relu</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">256</span><span class="p">,</span> <span class="mi">256</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">relu</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="n">add</span><span class="p">);</span>
<span class="n">max_pool2d_with_indices</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">max_pool2d_with_indices</span><span class="o">.</span><span class="n">default</span><span class="p">(</span>
<span class="n">relu</span><span class="p">,</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">3</span><span class="p">]</span>
<span class="p">);</span>
<span class="n">getitem</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">85</span><span class="p">,</span> <span class="mi">85</span><span class="p">]</span> <span class="o">=</span> <span class="n">max_pool2d_with_indices</span><span class="p">[</span><span class="mi">0</span><span class="p">];</span>
<span class="k">return</span> <span class="p">(</span><span class="n">getitem</span><span class="p">,)</span>
<span class="n">Graph</span> <span class="n">signature</span><span class="p">:</span> <span class="n">ExportGraphSignature</span><span class="p">(</span>
<span class="n">parameters</span><span class="o">=</span><span class="p">[</span><span class="s1">'L__self___conv.weight'</span><span class="p">,</span> <span class="s1">'L__self___conv.bias'</span><span class="p">],</span>
<span class="n">buffers</span><span class="o">=</span><span class="p">[],</span>
<span class="n">user_inputs</span><span class="o">=</span><span class="p">[</span><span class="s1">'arg2_1'</span><span class="p">,</span> <span class="s1">'arg3_1'</span><span class="p">],</span>
<span class="n">user_outputs</span><span class="o">=</span><span class="p">[</span><span class="s1">'getitem'</span><span class="p">],</span>
<span class="n">inputs_to_parameters</span><span class="o">=</span><span class="p">{</span>
<span class="s1">'arg0_1'</span><span class="p">:</span> <span class="s1">'L__self___conv.weight'</span><span class="p">,</span>
<span class="s1">'arg1_1'</span><span class="p">:</span> <span class="s1">'L__self___conv.bias'</span><span class="p">,</span>
<span class="p">},</span>
<span class="n">inputs_to_buffers</span><span class="o">=</span><span class="p">{},</span>
<span class="n">buffers_to_mutate</span><span class="o">=</span><span class="p">{},</span>
<span class="n">backward_signature</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span>
<span class="n">assertion_dep_token</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span>
<span class="p">)</span>
<span class="n">Range</span> <span class="n">constraints</span><span class="p">:</span> <span class="p">{}</span>
</pre></div>
</div>
<p>Inspecting the <code class="docutils literal notranslate"><span class="pre">ExportedProgram</span></code>, we can note the following:</p>
<ul class="simple">
<li><p>The <a class="reference internal" href="fx.html#torch.fx.Graph" title="torch.fx.Graph"><code class="xref py py-class docutils literal notranslate"><span class="pre">torch.fx.Graph</span></code></a> contains the computation graph of the original
program, along with records of the original code for easy debugging.</p></li>
<li><p>The graph contains only <code class="docutils literal notranslate"><span class="pre">torch.ops.aten</span></code> operators found <a class="reference external" href="https://github.com/pytorch/pytorch/blob/main/aten/src/ATen/native/native_functions.yaml">here</a>
and custom operators, and is fully functional, without any inplace operators
such as <code class="docutils literal notranslate"><span class="pre">torch.add_</span></code>.</p></li>
<li><p>The parameters (weight and bias to conv) are lifted as inputs to the graph,
resulting in no <code class="docutils literal notranslate"><span class="pre">get_attr</span></code> nodes in the graph, which previously existed in
the result of <a class="reference internal" href="fx.html#torch.fx.symbolic_trace" title="torch.fx.symbolic_trace"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.fx.symbolic_trace()</span></code></a>.</p></li>
<li><p>The <a class="reference internal" href="#torch.export.ExportGraphSignature" title="torch.export.ExportGraphSignature"><code class="xref py py-class docutils literal notranslate"><span class="pre">torch.export.ExportGraphSignature</span></code></a> models the input and output
signature, along with specifying which inputs are parameters.</p></li>
<li><p>The resulting shape and dtype of tensors produced by each node in the graph is
noted. For example, the <code class="docutils literal notranslate"><span class="pre">convolution</span></code> node will result in a tensor of dtype
<code class="docutils literal notranslate"><span class="pre">torch.float32</span></code> and shape (1, 16, 256, 256).</p></li>
</ul>
</div>
<div class="section" id="non-strict-export">
<span id="id2"></span><h3>Non-Strict Export<a class="headerlink" href="#non-strict-export" title="Permalink to this heading">¶</a></h3>
<p>In PyTorch 2.3, we introduced a new mode of tracing called <strong>non-strict mode</strong>.
It’s still going through hardening, so if you run into any issues, please file
them to Github with the “oncall: export” tag.</p>
<p>In <em>non-strict mode</em>, we trace through the program using the Python interpreter.
Your code will execute exactly as it would in eager mode; the only difference is
that all Tensor objects will be replaced by ProxyTensors, which will record all
their operations into a graph.</p>
<p>In <em>strict</em> mode, which is currently the default, we first trace through the
program using TorchDynamo, a bytecode analysis engine. TorchDynamo does not
actually execute your Python code. Instead, it symbolically analyzes it and
builds a graph based on the results. This analysis allows torch.export to
provide stronger guarantees about safety, but not all Python code is supported.</p>
<p>An example of a case where one might want to use non-strict mode is if you run
into a unsupported TorchDynamo feature that might not be easily solved, and you
know the python code is not exactly needed for computation. For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">contextlib</span>
<span class="kn">import</span> <span class="nn">torch</span>
<span class="k">class</span> <span class="nc">ContextManager</span><span class="p">():</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">count</span> <span class="o">=</span> <span class="mi">0</span>
<span class="k">def</span> <span class="fm">__enter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">count</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="k">def</span> <span class="fm">__exit__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc_type</span><span class="p">,</span> <span class="n">exc_value</span><span class="p">,</span> <span class="n">traceback</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">count</span> <span class="o">-=</span> <span class="mi">1</span>
<span class="k">class</span> <span class="nc">M</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span>
<span class="k">with</span> <span class="n">ContextManager</span><span class="p">():</span>
<span class="k">return</span> <span class="n">x</span><span class="o">.</span><span class="n">sin</span><span class="p">()</span> <span class="o">+</span> <span class="n">x</span><span class="o">.</span><span class="n">cos</span><span class="p">()</span>
<span class="n">export</span><span class="p">(</span><span class="n">M</span><span class="p">(),</span> <span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">3</span><span class="p">),),</span> <span class="n">strict</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span> <span class="c1"># Non-strict traces successfully</span>
<span class="n">export</span><span class="p">(</span><span class="n">M</span><span class="p">(),</span> <span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">3</span><span class="p">),))</span> <span class="c1"># Strict mode fails with torch._dynamo.exc.Unsupported: ContextManager</span>
</pre></div>
</div>
<p>In this example, the first call using non-strict mode (through the
<code class="docutils literal notranslate"><span class="pre">strict=False</span></code> flag) traces successfully whereas the second call using strict
mode (default) results with a failure, where TorchDynamo is unable to support
context managers. One option is to rewrite the code (see <a class="reference internal" href="#limitations-of-torch-export"><span class="std std-ref">Limitations of torch.export</span></a>), but seeing as the context manager does not affect the tensor
computations in the model, we can go with the non-strict mode’s result.</p>
</div>
<div class="section" id="expressing-dynamism">
<h3>Expressing Dynamism<a class="headerlink" href="#expressing-dynamism" title="Permalink to this heading">¶</a></h3>
<p>By default <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> will trace the program assuming all input shapes are
<strong>static</strong>, and specializing the exported program to those dimensions. However,
some dimensions, such as a batch dimension, can be dynamic and vary from run to
run. Such dimensions must be specified by using the
<code class="xref py py-func docutils literal notranslate"><span class="pre">torch.export.Dim()</span></code> API to create them and by passing them into
<a class="reference internal" href="#torch.export.export" title="torch.export.export"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.export.export()</span></code></a> through the <code class="docutils literal notranslate"><span class="pre">dynamic_shapes</span></code> argument. An example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">torch</span>
<span class="kn">from</span> <span class="nn">torch.export</span> <span class="kn">import</span> <span class="n">Dim</span><span class="p">,</span> <span class="n">export</span>
<span class="k">class</span> <span class="nc">M</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">()</span>
<span class="bp">self</span><span class="o">.</span><span class="n">branch1</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Sequential</span><span class="p">(</span>
<span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Linear</span><span class="p">(</span><span class="mi">64</span><span class="p">,</span> <span class="mi">32</span><span class="p">),</span> <span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">ReLU</span><span class="p">()</span>
<span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">branch2</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Sequential</span><span class="p">(</span>
<span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Linear</span><span class="p">(</span><span class="mi">128</span><span class="p">,</span> <span class="mi">64</span><span class="p">),</span> <span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">ReLU</span><span class="p">()</span>
<span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">buffer</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">32</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x1</span><span class="p">,</span> <span class="n">x2</span><span class="p">):</span>
<span class="n">out1</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">branch1</span><span class="p">(</span><span class="n">x1</span><span class="p">)</span>
<span class="n">out2</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">branch2</span><span class="p">(</span><span class="n">x2</span><span class="p">)</span>
<span class="k">return</span> <span class="p">(</span><span class="n">out1</span> <span class="o">+</span> <span class="bp">self</span><span class="o">.</span><span class="n">buffer</span><span class="p">,</span> <span class="n">out2</span><span class="p">)</span>
<span class="n">example_args</span> <span class="o">=</span> <span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="mi">32</span><span class="p">,</span> <span class="mi">64</span><span class="p">),</span> <span class="n">torch</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="mi">32</span><span class="p">,</span> <span class="mi">128</span><span class="p">))</span>
<span class="c1"># Create a dynamic batch size</span>
<span class="n">batch</span> <span class="o">=</span> <span class="n">Dim</span><span class="p">(</span><span class="s2">"batch"</span><span class="p">)</span>
<span class="c1"># Specify that the first dimension of each input is that batch size</span>
<span class="n">dynamic_shapes</span> <span class="o">=</span> <span class="p">{</span><span class="s2">"x1"</span><span class="p">:</span> <span class="p">{</span><span class="mi">0</span><span class="p">:</span> <span class="n">batch</span><span class="p">},</span> <span class="s2">"x2"</span><span class="p">:</span> <span class="p">{</span><span class="mi">0</span><span class="p">:</span> <span class="n">batch</span><span class="p">}}</span>
<span class="n">exported_program</span><span class="p">:</span> <span class="n">torch</span><span class="o">.</span><span class="n">export</span><span class="o">.</span><span class="n">ExportedProgram</span> <span class="o">=</span> <span class="n">export</span><span class="p">(</span>
<span class="n">M</span><span class="p">(),</span> <span class="n">args</span><span class="o">=</span><span class="n">example_args</span><span class="p">,</span> <span class="n">dynamic_shapes</span><span class="o">=</span><span class="n">dynamic_shapes</span>
<span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">exported_program</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ExportedProgram</span><span class="p">:</span>
<span class="k">class</span> <span class="nc">GraphModule</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg0_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">32</span><span class="p">,</span> <span class="mi">64</span><span class="p">],</span> <span class="n">arg1_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">32</span><span class="p">],</span> <span class="n">arg2_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">64</span><span class="p">,</span> <span class="mi">128</span><span class="p">],</span> <span class="n">arg3_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">64</span><span class="p">],</span> <span class="n">arg4_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">32</span><span class="p">],</span> <span class="n">arg5_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="n">s0</span><span class="p">,</span> <span class="mi">64</span><span class="p">],</span> <span class="n">arg6_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="n">s0</span><span class="p">,</span> <span class="mi">128</span><span class="p">]):</span>
<span class="c1"># code: out1 = self.branch1(x1)</span>
<span class="n">permute</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">64</span><span class="p">,</span> <span class="mi">32</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">permute</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="n">arg0_1</span><span class="p">,</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">]);</span>
<span class="n">addmm</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="n">s0</span><span class="p">,</span> <span class="mi">32</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">addmm</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="n">arg1_1</span><span class="p">,</span> <span class="n">arg5_1</span><span class="p">,</span> <span class="n">permute</span><span class="p">);</span>
<span class="n">relu</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="n">s0</span><span class="p">,</span> <span class="mi">32</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">relu</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="n">addmm</span><span class="p">);</span>
<span class="c1"># code: out2 = self.branch2(x2)</span>
<span class="n">permute_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">128</span><span class="p">,</span> <span class="mi">64</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">permute</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="n">arg2_1</span><span class="p">,</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">]);</span>
<span class="n">addmm_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="n">s0</span><span class="p">,</span> <span class="mi">64</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">addmm</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="n">arg3_1</span><span class="p">,</span> <span class="n">arg6_1</span><span class="p">,</span> <span class="n">permute_1</span><span class="p">);</span>
<span class="n">relu_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="n">s0</span><span class="p">,</span> <span class="mi">64</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">relu</span><span class="o">.</span><span class="n">default</span><span class="p">(</span><span class="n">addmm_1</span><span class="p">);</span> <span class="n">addmm_1</span> <span class="o">=</span> <span class="kc">None</span>
<span class="c1"># code: return (out1 + self.buffer, out2)</span>
<span class="n">add</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="n">s0</span><span class="p">,</span> <span class="mi">32</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">add</span><span class="o">.</span><span class="n">Tensor</span><span class="p">(</span><span class="n">relu</span><span class="p">,</span> <span class="n">arg4_1</span><span class="p">);</span>
<span class="k">return</span> <span class="p">(</span><span class="n">add</span><span class="p">,</span> <span class="n">relu_1</span><span class="p">)</span>
<span class="n">Graph</span> <span class="n">signature</span><span class="p">:</span> <span class="n">ExportGraphSignature</span><span class="p">(</span>
<span class="n">parameters</span><span class="o">=</span><span class="p">[</span>
<span class="s1">'branch1.0.weight'</span><span class="p">,</span>
<span class="s1">'branch1.0.bias'</span><span class="p">,</span>
<span class="s1">'branch2.0.weight'</span><span class="p">,</span>
<span class="s1">'branch2.0.bias'</span><span class="p">,</span>
<span class="p">],</span>
<span class="n">buffers</span><span class="o">=</span><span class="p">[</span><span class="s1">'L__self___buffer'</span><span class="p">],</span>
<span class="n">user_inputs</span><span class="o">=</span><span class="p">[</span><span class="s1">'arg5_1'</span><span class="p">,</span> <span class="s1">'arg6_1'</span><span class="p">],</span>
<span class="n">user_outputs</span><span class="o">=</span><span class="p">[</span><span class="s1">'add'</span><span class="p">,</span> <span class="s1">'relu_1'</span><span class="p">],</span>
<span class="n">inputs_to_parameters</span><span class="o">=</span><span class="p">{</span>
<span class="s1">'arg0_1'</span><span class="p">:</span> <span class="s1">'branch1.0.weight'</span><span class="p">,</span>
<span class="s1">'arg1_1'</span><span class="p">:</span> <span class="s1">'branch1.0.bias'</span><span class="p">,</span>
<span class="s1">'arg2_1'</span><span class="p">:</span> <span class="s1">'branch2.0.weight'</span><span class="p">,</span>
<span class="s1">'arg3_1'</span><span class="p">:</span> <span class="s1">'branch2.0.bias'</span><span class="p">,</span>
<span class="p">},</span>
<span class="n">inputs_to_buffers</span><span class="o">=</span><span class="p">{</span><span class="s1">'arg4_1'</span><span class="p">:</span> <span class="s1">'L__self___buffer'</span><span class="p">},</span>
<span class="n">buffers_to_mutate</span><span class="o">=</span><span class="p">{},</span>
<span class="n">backward_signature</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span>
<span class="n">assertion_dep_token</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span>
<span class="p">)</span>
<span class="n">Range</span> <span class="n">constraints</span><span class="p">:</span> <span class="p">{</span><span class="n">s0</span><span class="p">:</span> <span class="n">RangeConstraint</span><span class="p">(</span><span class="n">min_val</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">max_val</span><span class="o">=</span><span class="mi">9223372036854775806</span><span class="p">)}</span>
</pre></div>
</div>
<p>Some additional things to note:</p>
<ul class="simple">
<li><p>Through the <code class="xref py py-func docutils literal notranslate"><span class="pre">torch.export.Dim()</span></code> API and the <code class="docutils literal notranslate"><span class="pre">dynamic_shapes</span></code> argument, we specified the first
dimension of each input to be dynamic. Looking at the inputs <code class="docutils literal notranslate"><span class="pre">arg5_1</span></code> and
<code class="docutils literal notranslate"><span class="pre">arg6_1</span></code>, they have a symbolic shape of (s0, 64) and (s0, 128), instead of
the (32, 64) and (32, 128) shaped tensors that we passed in as example inputs.
<code class="docutils literal notranslate"><span class="pre">s0</span></code> is a symbol representing that this dimension can be a range
of values.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">exported_program.range_constraints</span></code> describes the ranges of each symbol
appearing in the graph. In this case, we see that <code class="docutils literal notranslate"><span class="pre">s0</span></code> has the range
[2, inf]. For technical reasons that are difficult to explain here, they are
assumed to be not 0 or 1. This is not a bug, and does not necessarily mean
that the exported program will not work for dimensions 0 or 1. See
<a class="reference external" href="https://docs.google.com/document/d/16VPOa3d-Liikf48teAOmxLc92rgvJdfosIy-yoT38Io/edit?fbclid=IwAR3HNwmmexcitV0pbZm_x1a4ykdXZ9th_eJWK-3hBtVgKnrkmemz6Pm5jRQ#heading=h.ez923tomjvyk">The 0/1 Specialization Problem</a>
for an in-depth discussion of this topic.</p></li>
</ul>
<p>We can also specify more expressive relationships between input shapes, such as
where a pair of shapes might differ by one, a shape might be double of
another, or a shape is even. An example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">M</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">):</span>
<span class="k">return</span> <span class="n">x</span> <span class="o">+</span> <span class="n">y</span><span class="p">[</span><span class="mi">1</span><span class="p">:]</span>
<span class="n">x</span><span class="p">,</span> <span class="n">y</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="mi">5</span><span class="p">),</span> <span class="n">torch</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="mi">6</span><span class="p">)</span>
<span class="n">dimx</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">export</span><span class="o">.</span><span class="n">Dim</span><span class="p">(</span><span class="s2">"dimx"</span><span class="p">,</span> <span class="nb">min</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="nb">max</span><span class="o">=</span><span class="mi">6</span><span class="p">)</span>
<span class="n">dimy</span> <span class="o">=</span> <span class="n">dimx</span> <span class="o">+</span> <span class="mi">1</span>
<span class="n">exported_program</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">export</span><span class="o">.</span><span class="n">export</span><span class="p">(</span>
<span class="n">M</span><span class="p">(),</span> <span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">),</span> <span class="n">dynamic_shapes</span><span class="o">=</span><span class="p">({</span><span class="mi">0</span><span class="p">:</span> <span class="n">dimx</span><span class="p">},</span> <span class="p">{</span><span class="mi">0</span><span class="p">:</span> <span class="n">dimy</span><span class="p">}),</span>
<span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">exported_program</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ExportedProgram</span><span class="p">:</span>
<span class="k">class</span> <span class="nc">GraphModule</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg0_1</span><span class="p">:</span> <span class="s2">"f32[s0]"</span><span class="p">,</span> <span class="n">arg1_1</span><span class="p">:</span> <span class="s2">"f32[s0 + 1]"</span><span class="p">):</span>
<span class="c1"># code: return x + y[1:]</span>
<span class="n">slice_1</span><span class="p">:</span> <span class="s2">"f32[s0]"</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">slice</span><span class="o">.</span><span class="n">Tensor</span><span class="p">(</span><span class="n">arg1_1</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">9223372036854775807</span><span class="p">);</span> <span class="n">arg1_1</span> <span class="o">=</span> <span class="kc">None</span>
<span class="n">add</span><span class="p">:</span> <span class="s2">"f32[s0]"</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">add</span><span class="o">.</span><span class="n">Tensor</span><span class="p">(</span><span class="n">arg0_1</span><span class="p">,</span> <span class="n">slice_1</span><span class="p">);</span> <span class="n">arg0_1</span> <span class="o">=</span> <span class="n">slice_1</span> <span class="o">=</span> <span class="kc">None</span>
<span class="k">return</span> <span class="p">(</span><span class="n">add</span><span class="p">,)</span>
<span class="n">Graph</span> <span class="n">signature</span><span class="p">:</span> <span class="n">ExportGraphSignature</span><span class="p">(</span>
<span class="n">input_specs</span><span class="o">=</span><span class="p">[</span>
<span class="n">InputSpec</span><span class="p">(</span><span class="n">kind</span><span class="o">=<</span><span class="n">InputKind</span><span class="o">.</span><span class="n">USER_INPUT</span><span class="p">:</span> <span class="mi">1</span><span class="o">></span><span class="p">,</span> <span class="n">arg</span><span class="o">=</span><span class="n">TensorArgument</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s1">'arg0_1'</span><span class="p">),</span> <span class="n">target</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">persistent</span><span class="o">=</span><span class="kc">None</span><span class="p">),</span>
<span class="n">InputSpec</span><span class="p">(</span><span class="n">kind</span><span class="o">=<</span><span class="n">InputKind</span><span class="o">.</span><span class="n">USER_INPUT</span><span class="p">:</span> <span class="mi">1</span><span class="o">></span><span class="p">,</span> <span class="n">arg</span><span class="o">=</span><span class="n">TensorArgument</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s1">'arg1_1'</span><span class="p">),</span> <span class="n">target</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">persistent</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span>
<span class="p">],</span>
<span class="n">output_specs</span><span class="o">=</span><span class="p">[</span>
<span class="n">OutputSpec</span><span class="p">(</span><span class="n">kind</span><span class="o">=<</span><span class="n">OutputKind</span><span class="o">.</span><span class="n">USER_OUTPUT</span><span class="p">:</span> <span class="mi">1</span><span class="o">></span><span class="p">,</span> <span class="n">arg</span><span class="o">=</span><span class="n">TensorArgument</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s1">'add'</span><span class="p">),</span> <span class="n">target</span><span class="o">=</span><span class="kc">None</span><span class="p">)]</span>
<span class="p">)</span>
<span class="n">Range</span> <span class="n">constraints</span><span class="p">:</span> <span class="p">{</span><span class="n">s0</span><span class="p">:</span> <span class="n">ValueRanges</span><span class="p">(</span><span class="n">lower</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">upper</span><span class="o">=</span><span class="mi">6</span><span class="p">,</span> <span class="n">is_bool</span><span class="o">=</span><span class="kc">False</span><span class="p">),</span> <span class="n">s0</span> <span class="o">+</span> <span class="mi">1</span><span class="p">:</span> <span class="n">ValueRanges</span><span class="p">(</span><span class="n">lower</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">upper</span><span class="o">=</span><span class="mi">7</span><span class="p">,</span> <span class="n">is_bool</span><span class="o">=</span><span class="kc">False</span><span class="p">)}</span>
</pre></div>
</div>
<p>Some things to note:</p>
<ul class="simple">
<li><p>By specifying <code class="docutils literal notranslate"><span class="pre">{0:</span> <span class="pre">dimx}</span></code> for the first input, we see that the resulting
shape of the first input is now dynamic, being <code class="docutils literal notranslate"><span class="pre">[s0]</span></code>. And now by specifying
<code class="docutils literal notranslate"><span class="pre">{0:</span> <span class="pre">dimy}</span></code> for the second input, we see that the resulting shape of the
second input is also dynamic. However, because we expressed <code class="docutils literal notranslate"><span class="pre">dimy</span> <span class="pre">=</span> <span class="pre">dimx</span> <span class="pre">+</span> <span class="pre">1</span></code>,
instead of <code class="docutils literal notranslate"><span class="pre">arg1_1</span></code>’s shape containing a new symbol, we see that it is
now being represented with the same symbol used in <code class="docutils literal notranslate"><span class="pre">arg0_1</span></code>, <code class="docutils literal notranslate"><span class="pre">s0</span></code>. We can
see that relationship of <code class="docutils literal notranslate"><span class="pre">dimy</span> <span class="pre">=</span> <span class="pre">dimx</span> <span class="pre">+</span> <span class="pre">1</span></code> is being shown through <code class="docutils literal notranslate"><span class="pre">s0</span> <span class="pre">+</span> <span class="pre">1</span></code>.</p></li>
<li><p>Looking at the range constraints, we see that <code class="docutils literal notranslate"><span class="pre">s0</span></code> has the range [3, 6],
which is specified initially, and we can see that <code class="docutils literal notranslate"><span class="pre">s0</span> <span class="pre">+</span> <span class="pre">1</span></code> has the solved
range of [4, 7].</p></li>
</ul>
</div>
<div class="section" id="serialization">
<h3>Serialization<a class="headerlink" href="#serialization" title="Permalink to this heading">¶</a></h3>
<p>To save the <code class="docutils literal notranslate"><span class="pre">ExportedProgram</span></code>, users can use the <a class="reference internal" href="#torch.export.save" title="torch.export.save"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.export.save()</span></code></a> and
<a class="reference internal" href="#torch.export.load" title="torch.export.load"><code class="xref py py-func docutils literal notranslate"><span class="pre">torch.export.load()</span></code></a> APIs. A convention is to save the <code class="docutils literal notranslate"><span class="pre">ExportedProgram</span></code>
using a <code class="docutils literal notranslate"><span class="pre">.pt2</span></code> file extension.</p>
<p>An example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">torch</span>
<span class="kn">import</span> <span class="nn">io</span>
<span class="k">class</span> <span class="nc">MyModule</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span>
<span class="k">return</span> <span class="n">x</span> <span class="o">+</span> <span class="mi">10</span>
<span class="n">exported_program</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">export</span><span class="o">.</span><span class="n">export</span><span class="p">(</span><span class="n">MyModule</span><span class="p">(),</span> <span class="n">torch</span><span class="o">.</span><span class="n">randn</span><span class="p">(</span><span class="mi">5</span><span class="p">))</span>
<span class="n">torch</span><span class="o">.</span><span class="n">export</span><span class="o">.</span><span class="n">save</span><span class="p">(</span><span class="n">exported_program</span><span class="p">,</span> <span class="s1">'exported_program.pt2'</span><span class="p">)</span>
<span class="n">saved_exported_program</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">export</span><span class="o">.</span><span class="n">load</span><span class="p">(</span><span class="s1">'exported_program.pt2'</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="specializations">
<h3>Specializations<a class="headerlink" href="#specializations" title="Permalink to this heading">¶</a></h3>
<p>A key concept in understanding the behavior of <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> is the
difference between <em>static</em> and <em>dynamic</em> values.</p>
<p>A <em>dynamic</em> value is one that can change from run to run. These behave like
normal arguments to a Python function—you can pass different values for an
argument and expect your function to do the right thing. Tensor <em>data</em> is
treated as dynamic.</p>
<p>A <em>static</em> value is a value that is fixed at export time and cannot change
between executions of the exported program. When the value is encountered during
tracing, the exporter will treat it as a constant and hard-code it into the
graph.</p>
<p>When an operation is performed (e.g. <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">+</span> <span class="pre">y</span></code>) and all inputs are static, then
the output of the operation will be directly hard-coded into the graph, and the
operation won’t show up (i.e. it will get constant-folded).</p>
<p>When a value has been hard-coded into the graph, we say that the graph has been
<em>specialized</em> to that value.</p>
<p>The following values are static:</p>
<div class="section" id="input-tensor-shapes">
<h4>Input Tensor Shapes<a class="headerlink" href="#input-tensor-shapes" title="Permalink to this heading">¶</a></h4>
<p>By default, <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> will trace the program specializing on the input
tensors’ shapes, unless a dimension is specified as dynamic via the
<code class="docutils literal notranslate"><span class="pre">dynamic_shapes</span></code> argument to <code class="docutils literal notranslate"><span class="pre">torch.export</span></code>. This means that if there exists
shape-dependent control flow, <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> will specialize on the branch
that is being taken with the given sample inputs. For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">torch</span>
<span class="kn">from</span> <span class="nn">torch.export</span> <span class="kn">import</span> <span class="n">export</span>
<span class="k">class</span> <span class="nc">Mod</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span>
<span class="k">if</span> <span class="n">x</span><span class="o">.</span><span class="n">shape</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">></span> <span class="mi">5</span><span class="p">:</span>
<span class="k">return</span> <span class="n">x</span> <span class="o">+</span> <span class="mi">1</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">return</span> <span class="n">x</span> <span class="o">-</span> <span class="mi">1</span>
<span class="n">example_inputs</span> <span class="o">=</span> <span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">rand</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">),)</span>
<span class="n">exported_program</span> <span class="o">=</span> <span class="n">export</span><span class="p">(</span><span class="n">Mod</span><span class="p">(),</span> <span class="n">example_inputs</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">exported_program</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ExportedProgram</span><span class="p">:</span>
<span class="k">class</span> <span class="nc">GraphModule</span><span class="p">(</span><span class="n">torch</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">Module</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg0_1</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">]):</span>
<span class="n">add</span><span class="p">:</span> <span class="n">f32</span><span class="p">[</span><span class="mi">10</span><span class="p">,</span> <span class="mi">2</span><span class="p">]</span> <span class="o">=</span> <span class="n">torch</span><span class="o">.</span><span class="n">ops</span><span class="o">.</span><span class="n">aten</span><span class="o">.</span><span class="n">add</span><span class="o">.</span><span class="n">Tensor</span><span class="p">(</span><span class="n">arg0_1</span><span class="p">,</span> <span class="mi">1</span><span class="p">);</span>
<span class="k">return</span> <span class="p">(</span><span class="n">add</span><span class="p">,)</span>
</pre></div>
</div>
<p>The conditional of (<code class="docutils literal notranslate"><span class="pre">x.shape[0]</span> <span class="pre">></span> <span class="pre">5</span></code>) does not appear in the
<code class="docutils literal notranslate"><span class="pre">ExportedProgram</span></code> because the example inputs have the static
shape of (10, 2). Since <code class="docutils literal notranslate"><span class="pre">torch.export</span></code> specializes on the inputs’ static
shapes, the else branch (<code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">-</span> <span class="pre">1</span></code>) will never be reached. To preserve the dynamic
branching behavior based on the shape of a tensor in the traced graph,
<code class="xref py py-func docutils literal notranslate"><span class="pre">torch.export.Dim()</span></code> will need to be used to specify the dimension
of the input tensor (<code class="docutils literal notranslate"><span class="pre">x.shape[0]</span></code>) to be dynamic, and the source code will
need to be <a class="reference internal" href="#data-shape-dependent-control-flow"><span class="std std-ref">rewritten</span></a>.</p>
<p>Note that tensors that are part of the module state (e.g. parameters and
buffers) always have static shapes.</p>
</div>
<div class="section" id="python-primitives">
<h4>Python Primitives<a class="headerlink" href="#python-primitives" title="Permalink to this heading">¶</a></h4>
<p><code class="docutils literal notranslate"><span class="pre">torch.export</span></code> also specializes on Python primtivies,