docs/manual/optimizations.html

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<h2>Optimizations</h2>

The optimization step of ProGuard can be switched off with the
<a href="usage.html#dontoptimize"><code>-dontoptimize</code></a> option. For
more fine-grained control over individual optimizations, experts can use the
<a href="usage.html#optimizations"><code>-optimizations</code></a> option,
with a filter based on the optimization names listed below. The filter works
like any <a href="usage.html#filters">filter</a> in ProGuard.
<p>

The following wildcards are supported:

<table cellspacing="10">
<tr><td valign="top"><code><b>?</b></code></td>
    <td>matches any single character in an optimization name.</td></tr>
<tr><td valign="top"><code><b>*</b></code></td>
    <td>matches any part of an optimization name.</td></tr>
</table>

An optimization that is preceded by an exclamation mark '<b>!</b>' is
<i>excluded</i> from further attempts to match with <i>subsequent</i>
optimization names in the filter. Make sure to specify filters correctly,
since they are not checked for potential typos.
<p>

For example,
"<code>code/simplification/variable,code/simplification/arithmetic</code>"
only performs the two specified peephole optimizations.
<p>

For example, "<code>!method/propagation/*</code>" performs all optimizations,
except the ones that propagate values between methods.
<p>

For example,
"<code>!code/simplification/advanced,code/simplification/*</code>" only
performs all peephole optimizations.
<p>
Some optimizations necessarily imply other optimizations. These are then
indicated. Note that the list is likely to change over time, as optimizations
are added and reorganized.
<p>

<dl>
<dt><code><b>class/marking/final</b></code></dt>
<dd>Marks classes as final, whenever possible.</dd>

<dt><code><b>class/merging/vertical</b></code></dt>
<dd>Merges classes vertically in the class hierarchy, whenever possible.</dd>

<dt><code><b>class/merging/horizontal</b></code></dt>
<dd>Merges classes horizontally in the class hierarchy, whenever possible.</dd>

<dt><div>(&rArr; <code>code/removal/advanced</code>)</div>
    <code><b>field/removal/writeonly</b></code></dt>
<dd>Removes write-only fields.</dd>

<dt><code><b>field/marking/private</b></code></dt>
<dd>Marks fields as private, whenever possible.</dd>

<dt><div>(&rArr; <code>code/simplification/advanced</code>)</div>
    <code><b>field/propagation/value</b></code></dt>
<dd>Propagates the values of fields across methods.</dd>

<dt><code><b>method/marking/private</b></code></dt>
<dd>Marks methods as private, whenever possible (<i>devirtualization</i>).</dd>

<dt><div>(&rArr; <code>code/removal/advanced</code>)</div>
    <code><b>method/marking/static</b></code></dt>
<dd>Marks methods as static, whenever possible (<i>devirtualization</i>).</dd>

<dt><code><b>method/marking/final</b></code></dt>
<dd>Marks methods as final, whenever possible.</dd>

<dt><div>(&rArr; <code>code/removal/advanced</code>)</div>
    <code><b>method/removal/parameter</b></code></dt>
<dd>Removes unused method parameters.</dd>

<dt><div>(&rArr; <code>code/simplification/advanced</code>)</div>
    <code><b>method/propagation/parameter</b></code></dt>
<dd>Propagates the values of method parameters from method invocations to
    the invoked methods.</dd>

<dt><div>(&rArr; <code>code/simplification/advanced</code>)</div>
    <code><b>method/propagation/returnvalue</b></code></dt>
<dd>Propagates the values of method return values from methods to their
    invocations.</dd>

<dt><code><b>method/inlining/short</b></code></dt>
<dd>Inlines short methods.</dd>

<dt><code><b>method/inlining/unique</b></code></dt>
<dd>Inlines methods that are only called once.</dd>

<dt><code><b>method/inlining/tailrecursion</b></code></dt>
<dd>Simplifies tail recursion calls, whenever possible.</dd>

<dt><code><b>code/merging</b></code></dt>
<dd>Merges identical blocks of code by modifying branch targets.</dd>

<dt><code><b>code/simplification/variable</b></code></dt>
<dd>Performs peephole optimizations for variable loading and storing.</dd>

<dt><code><b>code/simplification/arithmetic</b></code></dt>
<dd>Performs peephole optimizations for arithmetic instructions.</dd>

<dt><code><b>code/simplification/cast</b></code></dt>
<dd>Performs peephole optimizations for casting operations.</dd>

<dt><code><b>code/simplification/field</b></code></dt>
<dd>Performs peephole optimizations for field loading and storing.</dd>

<dt><div>(&rArr; <code>code/removal/simple</code>)</div>
    <code><b>code/simplification/branch</b></code></dt>
<dd>Performs peephole optimizations for branch instructions.</dd>

<dt><code><b>code/simplification/string</b></code></dt>
<dd>Performs peephole optimizations for constant strings.</dd>

<dt><div>(<i>best used with</i> <code>code/removal/advanced</code>)</div>
    <code><b>code/simplification/advanced</b></code></dt>
<dd>Simplifies code based on control flow analysis and data flow
    analysis.</dd>

<dt><div>(&rArr; <code>code/removal/exception</code>)</div>
    <code><b>code/removal/advanced</b></code></dt>
<dd>Removes dead code based on control flow analysis and data flow
    analysis.</dd>

<dt><div>(&rArr; <code>code/removal/exception</code>)</div>
    <code><b>code/removal/simple</b></code></dt>
<dd>Removes dead code based on a simple control flow analysis.</dd>

<dt><code><b>code/removal/variable</b></code></dt>
<dd>Removes unused variables from the local variable frame.</dd>

<dt><code><b>code/removal/exception</b></code></dt>
<dd>Removes exceptions with empty try blocks.</dd>

<dt><code><b>code/allocation/variable</b></code></dt>
<dd>Optimizes variable allocation on the local variable frame.</dd>
</dl>
<p>

ProGuard also provides some unofficial settings to control optimizations, that
may disappear in future versions. These are Java system properties, which
can be set as JVM arguments (with <code>-D.....)</code>:
<dl>
<dt><code><b>maximum.inlined.code.length</b></code> (default = 8 bytes)</dt>
<dd>Specifies the maximum code length (expressed in bytes) of short methods
    that are eligible to be inlined. Inlining methods that are too long may
    unnecessarily inflate the code size.</dd>

<dt><code><b>maximum.resulting.code.length</b></code> (default = 8000 bytes
    for JSE, 2000 bytes for JME)</dt>
<dd>Specifies the maximum resulting code length (expressed in bytes) allowed
    when inlining methods. Many Java virtual machines do not apply just-in-time
    compilation to methods that are too long, so it's important not to let them
    grow too large.</dd>

<dt><code><b>optimize.conservatively</b></code> (default = unset)</dt>
<dd>Allows input code with ordinary instructions intentionally throwing
    <code>NullPointerException</code>,
    <code>ArrayIndexOutOfBoundsException</code>, or
    <code>ClassCastException</code>, without any other useful purposes. By
    default, ProGuard may just discard such seemingly useless instructions,
    resulting in better optimization of most common code.</dd>
</dl>

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