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<h3 class="section">13.2 RTL Classes and Formats</h3>
<p><a name="index-RTL-classes-2549"></a><a name="index-classes-of-RTX-codes-2550"></a><a name="index-RTX-codes_002c-classes-of-2551"></a><a name="index-GET_005fRTX_005fCLASS-2552"></a>
The various expression codes are divided into several <dfn>classes</dfn>,
which are represented by single characters. You can determine the class
of an RTX code with the macro <code>GET_RTX_CLASS (</code><var>code</var><code>)</code>.
Currently, <samp><span class="file">rtl.def</span></samp> defines these classes:
<dl>
<dt><code>RTX_OBJ</code><dd>An RTX code that represents an actual object, such as a register
(<code>REG</code>) or a memory location (<code>MEM</code>, <code>SYMBOL_REF</code>).
<code>LO_SUM</code>) is also included; instead, <code>SUBREG</code> and
<code>STRICT_LOW_PART</code> are not in this class, but in class <code>x</code>.
<br><dt><code>RTX_CONST_OBJ</code><dd>An RTX code that represents a constant object. <code>HIGH</code> is also
included in this class.
<br><dt><code>RTX_COMPARE</code><dd>An RTX code for a non-symmetric comparison, such as <code>GEU</code> or
<code>LT</code>.
<br><dt><code>RTX_COMM_COMPARE</code><dd>An RTX code for a symmetric (commutative) comparison, such as <code>EQ</code>
or <code>ORDERED</code>.
<br><dt><code>RTX_UNARY</code><dd>An RTX code for a unary arithmetic operation, such as <code>NEG</code>,
<code>NOT</code>, or <code>ABS</code>. This category also includes value extension
(sign or zero) and conversions between integer and floating point.
<br><dt><code>RTX_COMM_ARITH</code><dd>An RTX code for a commutative binary operation, such as <code>PLUS</code> or
<code>AND</code>. <code>NE</code> and <code>EQ</code> are comparisons, so they have class
<code><</code>.
<br><dt><code>RTX_BIN_ARITH</code><dd>An RTX code for a non-commutative binary operation, such as <code>MINUS</code>,
<code>DIV</code>, or <code>ASHIFTRT</code>.
<br><dt><code>RTX_BITFIELD_OPS</code><dd>An RTX code for a bit-field operation. Currently only
<code>ZERO_EXTRACT</code> and <code>SIGN_EXTRACT</code>. These have three inputs
and are lvalues (so they can be used for insertion as well).
See <a href="Bit_002dFields.html#Bit_002dFields">Bit-Fields</a>.
<br><dt><code>RTX_TERNARY</code><dd>An RTX code for other three input operations. Currently only
<code>IF_THEN_ELSE</code>, <code>VEC_MERGE</code>, <code>SIGN_EXTRACT</code>,
<code>ZERO_EXTRACT</code>, and <code>FMA</code>.
<br><dt><code>RTX_INSN</code><dd>An RTX code for an entire instruction: <code>INSN</code>, <code>JUMP_INSN</code>, and
<code>CALL_INSN</code>. See <a href="Insns.html#Insns">Insns</a>.
<br><dt><code>RTX_MATCH</code><dd>An RTX code for something that matches in insns, such as
<code>MATCH_DUP</code>. These only occur in machine descriptions.
<br><dt><code>RTX_AUTOINC</code><dd>An RTX code for an auto-increment addressing mode, such as
<code>POST_INC</code>. ‘<samp><span class="samp">XEXP (</span><var>x</var><span class="samp">, 0)</span></samp>’ gives the auto-modified
register.
<br><dt><code>RTX_EXTRA</code><dd>All other RTX codes. This category includes the remaining codes used
only in machine descriptions (<code>DEFINE_*</code>, etc.). It also includes
all the codes describing side effects (<code>SET</code>, <code>USE</code>,
<code>CLOBBER</code>, etc.) and the non-insns that may appear on an insn
chain, such as <code>NOTE</code>, <code>BARRIER</code>, and <code>CODE_LABEL</code>.
<code>SUBREG</code> is also part of this class.
</dl>
<p><a name="index-RTL-format-2553"></a>For each expression code, <samp><span class="file">rtl.def</span></samp> specifies the number of
contained objects and their kinds using a sequence of characters
called the <dfn>format</dfn> of the expression code. For example,
the format of <code>subreg</code> is ‘<samp><span class="samp">ei</span></samp>’.
<p><a name="index-RTL-format-characters-2554"></a>These are the most commonly used format characters:
<dl>
<dt><code>e</code><dd>An expression (actually a pointer to an expression).
<br><dt><code>i</code><dd>An integer.
<br><dt><code>w</code><dd>A wide integer.
<br><dt><code>s</code><dd>A string.
<br><dt><code>E</code><dd>A vector of expressions.
</dl>
<p>A few other format characters are used occasionally:
<dl>
<dt><code>u</code><dd>‘<samp><span class="samp">u</span></samp>’ is equivalent to ‘<samp><span class="samp">e</span></samp>’ except that it is printed differently
in debugging dumps. It is used for pointers to insns.
<br><dt><code>n</code><dd>‘<samp><span class="samp">n</span></samp>’ is equivalent to ‘<samp><span class="samp">i</span></samp>’ except that it is printed differently
in debugging dumps. It is used for the line number or code number of a
<code>note</code> insn.
<br><dt><code>S</code><dd>‘<samp><span class="samp">S</span></samp>’ indicates a string which is optional. In the RTL objects in
core, ‘<samp><span class="samp">S</span></samp>’ is equivalent to ‘<samp><span class="samp">s</span></samp>’, but when the object is read,
from an ‘<samp><span class="samp">md</span></samp>’ file, the string value of this operand may be omitted.
An omitted string is taken to be the null string.
<br><dt><code>V</code><dd>‘<samp><span class="samp">V</span></samp>’ indicates a vector which is optional. In the RTL objects in
core, ‘<samp><span class="samp">V</span></samp>’ is equivalent to ‘<samp><span class="samp">E</span></samp>’, but when the object is read
from an ‘<samp><span class="samp">md</span></samp>’ file, the vector value of this operand may be omitted.
An omitted vector is effectively the same as a vector of no elements.
<br><dt><code>B</code><dd>‘<samp><span class="samp">B</span></samp>’ indicates a pointer to basic block structure.
<br><dt><code>0</code><dd>‘<samp><span class="samp">0</span></samp>’ means a slot whose contents do not fit any normal category.
‘<samp><span class="samp">0</span></samp>’ slots are not printed at all in dumps, and are often used in
special ways by small parts of the compiler.
</dl>
<p>There are macros to get the number of operands and the format
of an expression code:
<a name="index-GET_005fRTX_005fLENGTH-2555"></a>
<dl><dt><code>GET_RTX_LENGTH (</code><var>code</var><code>)</code><dd>Number of operands of an RTX of code <var>code</var>.
<p><a name="index-GET_005fRTX_005fFORMAT-2556"></a><br><dt><code>GET_RTX_FORMAT (</code><var>code</var><code>)</code><dd>The format of an RTX of code <var>code</var>, as a C string.
</dl>
<p>Some classes of RTX codes always have the same format. For example, it
is safe to assume that all comparison operations have format <code>ee</code>.
<dl>
<dt><code>1</code><dd>All codes of this class have format <code>e</code>.
<br><dt><code><</code><dt><code>c</code><dt><code>2</code><dd>All codes of these classes have format <code>ee</code>.
<br><dt><code>b</code><dt><code>3</code><dd>All codes of these classes have format <code>eee</code>.
<br><dt><code>i</code><dd>All codes of this class have formats that begin with <code>iuueiee</code>.
See <a href="Insns.html#Insns">Insns</a>. Note that not all RTL objects linked onto an insn chain
are of class <code>i</code>.
<br><dt><code>o</code><dt><code>m</code><dt><code>x</code><dd>You can make no assumptions about the format of these codes.
</dl>
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