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 <a name="CC0-Condition-Codes"></a>
 <div class="header">
 <p>
 Next: <a href="MODE_005fCC-Condition-Codes.html#MODE_005fCC-Condition-Codes" accesskey="n" rel="next">MODE_CC Condition Codes</a>, Up: <a href="Condition-Code.html#Condition-Code" accesskey="u" rel="up">Condition Code</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Representation-of-condition-codes-using-_0028cc0_0029"></a>
 <h4 class="subsection">17.16.1 Representation of condition codes using <code>(cc0)</code></h4>
 <a name="index-cc0-1"></a>

 <a name="index-cc_005fstatus"></a>
 <p>The file <samp>conditions.h</samp> defines a variable <code>cc_status</code> to
 describe how the condition code was computed (in case the interpretation of
 the condition code depends on the instruction that it was set by).  This
 variable contains the RTL expressions on which the condition code is
 currently based, and several standard flags.
 </p>
 <p>Sometimes additional machine-specific flags must be defined in the machine
 description header file.  It can also add additional machine-specific
 information by defining <code>CC_STATUS_MDEP</code>.
 </p>
 <dl>
 <dt><a name="index-CC_005fSTATUS_005fMDEP"></a>Macro: <strong>CC_STATUS_MDEP</strong></dt>
 <dd><p>C code for a data type which is used for declaring the <code>mdep</code>
 component of <code>cc_status</code>.  It defaults to <code>int</code>.
 </p>
 <p>This macro is not used on machines that do not use <code>cc0</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-CC_005fSTATUS_005fMDEP_005fINIT"></a>Macro: <strong>CC_STATUS_MDEP_INIT</strong></dt>
 <dd><p>A C expression to initialize the <code>mdep</code> field to &ldquo;empty&rdquo;.
 The default definition does nothing, since most machines don&rsquo;t use
 the field anyway.  If you want to use the field, you should probably
 define this macro to initialize it.
 </p>
 <p>This macro is not used on machines that do not use <code>cc0</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-NOTICE_005fUPDATE_005fCC"></a>Macro: <strong>NOTICE_UPDATE_CC</strong> <em>(<var>exp</var>, <var>insn</var>)</em></dt>
 <dd><p>A C compound statement to set the components of <code>cc_status</code>
 appropriately for an insn <var>insn</var> whose body is <var>exp</var>.  It is
 this macro&rsquo;s responsibility to recognize insns that set the condition
 code as a byproduct of other activity as well as those that explicitly
 set <code>(cc0)</code>.
 </p>
 <p>This macro is not used on machines that do not use <code>cc0</code>.
 </p>
 <p>If there are insns that do not set the condition code but do alter
 other machine registers, this macro must check to see whether they
 invalidate the expressions that the condition code is recorded as
 reflecting.  For example, on the 68000, insns that store in address
 registers do not set the condition code, which means that usually
 <code>NOTICE_UPDATE_CC</code> can leave <code>cc_status</code> unaltered for such
 insns.  But suppose that the previous insn set the condition code
 based on location &lsquo;<samp>a4@(102)</samp>&rsquo; and the current insn stores a new
 value in &lsquo;<samp>a4</samp>&rsquo;.  Although the condition code is not changed by
 this, it will no longer be true that it reflects the contents of
 &lsquo;<samp>a4@(102)</samp>&rsquo;.  Therefore, <code>NOTICE_UPDATE_CC</code> must alter
 <code>cc_status</code> in this case to say that nothing is known about the
 condition code value.
 </p>
 <p>The definition of <code>NOTICE_UPDATE_CC</code> must be prepared to deal
 with the results of peephole optimization: insns whose patterns are
 <code>parallel</code> RTXs containing various <code>reg</code>, <code>mem</code> or
 constants which are just the operands.  The RTL structure of these
 insns is not sufficient to indicate what the insns actually do.  What
 <code>NOTICE_UPDATE_CC</code> should do when it sees one is just to run
 <code>CC_STATUS_INIT</code>.
 </p>
 <p>A possible definition of <code>NOTICE_UPDATE_CC</code> is to call a function
 that looks at an attribute (see <a href="Insn-Attributes.html#Insn-Attributes">Insn Attributes</a>) named, for example,
 &lsquo;<samp>cc</samp>&rsquo;.  This avoids having detailed information about patterns in
 two places, the <samp>md</samp> file and in <code>NOTICE_UPDATE_CC</code>.
 </p></dd></dl>

 <hr>
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 Next: <a href="MODE_005fCC-Condition-Codes.html#MODE_005fCC-Condition-Codes" accesskey="n" rel="next">MODE_CC Condition Codes</a>, Up: <a href="Condition-Code.html#Condition-Code" accesskey="u" rel="up">Condition Code</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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	<a name="CC0-Condition-Codes"></a>
	<div class="header">
	<p>
	Next: <a href="MODE_005fCC-Condition-Codes.html#MODE_005fCC-Condition-Codes" accesskey="n" rel="next">MODE_CC Condition Codes</a>, Up: <a href="Condition-Code.html#Condition-Code" accesskey="u" rel="up">Condition Code</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="Representation-of-condition-codes-using-_0028cc0_0029"></a>
	<h4 class="subsection">17.16.1 Representation of condition codes using <code>(cc0)</code></h4>
	<a name="index-cc0-1"></a>

	<a name="index-cc_005fstatus"></a>
	<p>The file <samp>conditions.h</samp> defines a variable <code>cc_status</code> to
	describe how the condition code was computed (in case the interpretation of
	the condition code depends on the instruction that it was set by). This
	variable contains the RTL expressions on which the condition code is
	currently based, and several standard flags.
	</p>
	<p>Sometimes additional machine-specific flags must be defined in the machine
	description header file. It can also add additional machine-specific
	information by defining <code>CC_STATUS_MDEP</code>.
	</p>
	<dl>
	<dt><a name="index-CC_005fSTATUS_005fMDEP"></a>Macro: <strong>CC_STATUS_MDEP</strong></dt>
	<dd><p>C code for a data type which is used for declaring the <code>mdep</code>
	component of <code>cc_status</code>. It defaults to <code>int</code>.
	</p>
	<p>This macro is not used on machines that do not use <code>cc0</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-CC_005fSTATUS_005fMDEP_005fINIT"></a>Macro: <strong>CC_STATUS_MDEP_INIT</strong></dt>
	<dd><p>A C expression to initialize the <code>mdep</code> field to “empty”.
	The default definition does nothing, since most machines don’t use
	the field anyway. If you want to use the field, you should probably
	define this macro to initialize it.
	</p>
	<p>This macro is not used on machines that do not use <code>cc0</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-NOTICE_005fUPDATE_005fCC"></a>Macro: <strong>NOTICE_UPDATE_CC</strong> <em>(<var>exp</var>, <var>insn</var>)</em></dt>
	<dd><p>A C compound statement to set the components of <code>cc_status</code>
	appropriately for an insn <var>insn</var> whose body is <var>exp</var>. It is
	this macro’s responsibility to recognize insns that set the condition
	code as a byproduct of other activity as well as those that explicitly
	set <code>(cc0)</code>.
	</p>
	<p>This macro is not used on machines that do not use <code>cc0</code>.
	</p>
	<p>If there are insns that do not set the condition code but do alter
	other machine registers, this macro must check to see whether they
	invalidate the expressions that the condition code is recorded as
	reflecting. For example, on the 68000, insns that store in address
	registers do not set the condition code, which means that usually
	<code>NOTICE_UPDATE_CC</code> can leave <code>cc_status</code> unaltered for such
	insns. But suppose that the previous insn set the condition code
	based on location ‘<samp>a4@(102)</samp>’ and the current insn stores a new
	value in ‘<samp>a4</samp>’. Although the condition code is not changed by
	this, it will no longer be true that it reflects the contents of
	‘<samp>a4@(102)</samp>’. Therefore, <code>NOTICE_UPDATE_CC</code> must alter
	<code>cc_status</code> in this case to say that nothing is known about the
	condition code value.
	</p>
	<p>The definition of <code>NOTICE_UPDATE_CC</code> must be prepared to deal
	with the results of peephole optimization: insns whose patterns are
	<code>parallel</code> RTXs containing various <code>reg</code>, <code>mem</code> or
	constants which are just the operands. The RTL structure of these
	insns is not sufficient to indicate what the insns actually do. What
	<code>NOTICE_UPDATE_CC</code> should do when it sees one is just to run
	<code>CC_STATUS_INIT</code>.
	</p>
	<p>A possible definition of <code>NOTICE_UPDATE_CC</code> is to call a function
	that looks at an attribute (see <a href="Insn-Attributes.html#Insn-Attributes">Insn Attributes</a>) named, for example,
	‘<samp>cc</samp>’. This avoids having detailed information about patterns in
	two places, the <samp>md</samp> file and in <code>NOTICE_UPDATE_CC</code>.
	</p></dd></dl>

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	Next: <a href="MODE_005fCC-Condition-Codes.html#MODE_005fCC-Condition-Codes" accesskey="n" rel="next">MODE_CC Condition Codes</a>, Up: <a href="Condition-Code.html#Condition-Code" accesskey="u" rel="up">Condition Code</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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