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<title>GNU Compiler Collection (GCC) Internals: Machine-Independent Predicates</title>
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<a name="Machine_002dIndependent-Predicates"></a>
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<p>
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Next: <a href="Defining-Predicates.html#Defining-Predicates" accesskey="n" rel="next">Defining Predicates</a>, Up: <a href="Predicates.html#Predicates" accesskey="u" rel="up">Predicates</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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</div>
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<hr>
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<a name="Machine_002dIndependent-Predicates-1"></a>
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<h4 class="subsection">16.7.1 Machine-Independent Predicates</h4>
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<a name="index-machine_002dindependent-predicates"></a>
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<a name="index-generic-predicates"></a>
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<p>These are the generic predicates available to all back ends. They are
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defined in <samp>recog.c</samp>. The first category of predicates allow
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only constant, or <em>immediate</em>, operands.
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</p>
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<dl>
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<dt><a name="index-immediate_005foperand"></a>Function: <strong>immediate_operand</strong></dt>
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<dd><p>This predicate allows any sort of constant that fits in <var>mode</var>.
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It is an appropriate choice for instructions that take operands that
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must be constant.
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</p></dd></dl>
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<dl>
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<dt><a name="index-const_005fint_005foperand"></a>Function: <strong>const_int_operand</strong></dt>
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<dd><p>This predicate allows any <code>CONST_INT</code> expression that fits in
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<var>mode</var>. It is an appropriate choice for an immediate operand that
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does not allow a symbol or label.
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</p></dd></dl>
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<dl>
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<dt><a name="index-const_005fdouble_005foperand"></a>Function: <strong>const_double_operand</strong></dt>
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<dd><p>This predicate accepts any <code>CONST_DOUBLE</code> expression that has
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exactly <var>mode</var>. If <var>mode</var> is <code>VOIDmode</code>, it will also
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accept <code>CONST_INT</code>. It is intended for immediate floating point
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constants.
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</p></dd></dl>
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<p>The second category of predicates allow only some kind of machine
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register.
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</p>
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<dl>
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<dt><a name="index-register_005foperand"></a>Function: <strong>register_operand</strong></dt>
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<dd><p>This predicate allows any <code>REG</code> or <code>SUBREG</code> expression that
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is valid for <var>mode</var>. It is often suitable for arithmetic
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instruction operands on a RISC machine.
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</p></dd></dl>
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<dl>
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<dt><a name="index-pmode_005fregister_005foperand"></a>Function: <strong>pmode_register_operand</strong></dt>
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<dd><p>This is a slight variant on <code>register_operand</code> which works around
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a limitation in the machine-description reader.
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</p>
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<div class="smallexample">
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<pre class="smallexample">(match_operand <var>n</var> "pmode_register_operand" <var>constraint</var>)
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</pre></div>
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<p>means exactly what
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</p>
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<div class="smallexample">
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<pre class="smallexample">(match_operand:P <var>n</var> "register_operand" <var>constraint</var>)
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</pre></div>
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<p>would mean, if the machine-description reader accepted ‘<samp>:P</samp>’
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mode suffixes. Unfortunately, it cannot, because <code>Pmode</code> is an
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alias for some other mode, and might vary with machine-specific
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options. See <a href="Misc.html#Misc">Misc</a>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-scratch_005foperand"></a>Function: <strong>scratch_operand</strong></dt>
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<dd><p>This predicate allows hard registers and <code>SCRATCH</code> expressions,
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but not pseudo-registers. It is used internally by <code>match_scratch</code>;
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it should not be used directly.
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</p></dd></dl>
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<p>The third category of predicates allow only some kind of memory reference.
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</p>
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<dl>
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<dt><a name="index-memory_005foperand"></a>Function: <strong>memory_operand</strong></dt>
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<dd><p>This predicate allows any valid reference to a quantity of mode
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<var>mode</var> in memory, as determined by the weak form of
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<code>GO_IF_LEGITIMATE_ADDRESS</code> (see <a href="Addressing-Modes.html#Addressing-Modes">Addressing Modes</a>).
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</p></dd></dl>
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<dl>
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<dt><a name="index-address_005foperand"></a>Function: <strong>address_operand</strong></dt>
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<dd><p>This predicate is a little unusual; it allows any operand that is a
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valid expression for the <em>address</em> of a quantity of mode
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<var>mode</var>, again determined by the weak form of
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<code>GO_IF_LEGITIMATE_ADDRESS</code>. To first order, if
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‘<samp>(mem:<var>mode</var> (<var>exp</var>))<!-- /@w --></samp>’ is acceptable to
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<code>memory_operand</code>, then <var>exp</var> is acceptable to
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<code>address_operand</code>. Note that <var>exp</var> does not necessarily have
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the mode <var>mode</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-indirect_005foperand"></a>Function: <strong>indirect_operand</strong></dt>
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<dd><p>This is a stricter form of <code>memory_operand</code> which allows only
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memory references with a <code>general_operand</code> as the address
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expression. New uses of this predicate are discouraged, because
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<code>general_operand</code> is very permissive, so it’s hard to tell what
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an <code>indirect_operand</code> does or does not allow. If a target has
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different requirements for memory operands for different instructions,
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it is better to define target-specific predicates which enforce the
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hardware’s requirements explicitly.
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</p></dd></dl>
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<dl>
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<dt><a name="index-push_005foperand"></a>Function: <strong>push_operand</strong></dt>
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<dd><p>This predicate allows a memory reference suitable for pushing a value
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onto the stack. This will be a <code>MEM</code> which refers to
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<code>stack_pointer_rtx</code>, with a side-effect in its address expression
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(see <a href="Incdec.html#Incdec">Incdec</a>); which one is determined by the
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<code>STACK_PUSH_CODE</code> macro (see <a href="Frame-Layout.html#Frame-Layout">Frame Layout</a>).
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</p></dd></dl>
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<dl>
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<dt><a name="index-pop_005foperand"></a>Function: <strong>pop_operand</strong></dt>
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<dd><p>This predicate allows a memory reference suitable for popping a value
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off the stack. Again, this will be a <code>MEM</code> referring to
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<code>stack_pointer_rtx</code>, with a side-effect in its address
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expression. However, this time <code>STACK_POP_CODE</code> is expected.
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</p></dd></dl>
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<p>The fourth category of predicates allow some combination of the above
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operands.
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</p>
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<dl>
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<dt><a name="index-nonmemory_005foperand"></a>Function: <strong>nonmemory_operand</strong></dt>
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<dd><p>This predicate allows any immediate or register operand valid for <var>mode</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-nonimmediate_005foperand"></a>Function: <strong>nonimmediate_operand</strong></dt>
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<dd><p>This predicate allows any register or memory operand valid for <var>mode</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-general_005foperand"></a>Function: <strong>general_operand</strong></dt>
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<dd><p>This predicate allows any immediate, register, or memory operand
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valid for <var>mode</var>.
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</p></dd></dl>
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<p>Finally, there are two generic operator predicates.
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</p>
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<dl>
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<dt><a name="index-comparison_005foperator"></a>Function: <strong>comparison_operator</strong></dt>
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<dd><p>This predicate matches any expression which performs an arithmetic
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comparison in <var>mode</var>; that is, <code>COMPARISON_P</code> is true for the
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expression code.
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</p></dd></dl>
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<dl>
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<dt><a name="index-ordered_005fcomparison_005foperator"></a>Function: <strong>ordered_comparison_operator</strong></dt>
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<dd><p>This predicate matches any expression which performs an arithmetic
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comparison in <var>mode</var> and whose expression code is valid for integer
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modes; that is, the expression code will be one of <code>eq</code>, <code>ne</code>,
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<code>lt</code>, <code>ltu</code>, <code>le</code>, <code>leu</code>, <code>gt</code>, <code>gtu</code>,
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<code>ge</code>, <code>geu</code>.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Defining-Predicates.html#Defining-Predicates" accesskey="n" rel="next">Defining Predicates</a>, Up: <a href="Predicates.html#Predicates" accesskey="u" rel="up">Predicates</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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