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 <a name="Constants"></a>
 <div class="header">
 <p>
 Next: <a href="Regs-and-Memory.html#Regs-and-Memory" accesskey="n" rel="next">Regs and Memory</a>, Previous: <a href="Machine-Modes.html#Machine-Modes" accesskey="p" rel="prev">Machine Modes</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</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="Constant-Expression-Types"></a>
 <h3 class="section">13.7 Constant Expression Types</h3>
 <a name="index-RTL-constants"></a>
 <a name="index-RTL-constant-expression-types"></a>

 <p>The simplest RTL expressions are those that represent constant values.
 </p>
 <dl compact="compact">
 <dd><a name="index-const_005fint"></a>
 </dd>
 <dt><code>(const_int <var>i</var>)</code></dt>
 <dd><p>This type of expression represents the integer value <var>i</var>.  <var>i</var>
 is customarily accessed with the macro <code>INTVAL</code> as in
 <code>INTVAL (<var>exp</var>)</code>, which is equivalent to <code>XWINT (<var>exp</var>, 0)</code>.
 </p>
 <p>Constants generated for modes with fewer bits than in
 <code>HOST_WIDE_INT</code> must be sign extended to full width (e.g., with
 <code>gen_int_mode</code>).  For constants for modes with more bits than in
 <code>HOST_WIDE_INT</code> the implied high order bits of that constant are
 copies of the top bit.  Note however that values are neither
 inherently signed nor inherently unsigned; where necessary, signedness
 is determined by the rtl operation instead.
 </p>
 <a name="index-const0_005frtx"></a>
 <a name="index-const1_005frtx"></a>
 <a name="index-const2_005frtx"></a>
 <a name="index-constm1_005frtx"></a>
 <p>There is only one expression object for the integer value zero; it is
 the value of the variable <code>const0_rtx</code>.  Likewise, the only
 expression for integer value one is found in <code>const1_rtx</code>, the only
 expression for integer value two is found in <code>const2_rtx</code>, and the
 only expression for integer value negative one is found in
 <code>constm1_rtx</code>.  Any attempt to create an expression of code
 <code>const_int</code> and value zero, one, two or negative one will return
 <code>const0_rtx</code>, <code>const1_rtx</code>, <code>const2_rtx</code> or
 <code>constm1_rtx</code> as appropriate.
 </p>
 <a name="index-const_005ftrue_005frtx"></a>
 <p>Similarly, there is only one object for the integer whose value is
 <code>STORE_FLAG_VALUE</code>.  It is found in <code>const_true_rtx</code>.  If
 <code>STORE_FLAG_VALUE</code> is one, <code>const_true_rtx</code> and
 <code>const1_rtx</code> will point to the same object.  If
 <code>STORE_FLAG_VALUE</code> is -1, <code>const_true_rtx</code> and
 <code>constm1_rtx</code> will point to the same object.
 </p>
 <a name="index-const_005fdouble"></a>
 </dd>
 <dt><code>(const_double:<var>m</var> <var>i0</var> <var>i1</var> &hellip;)</code></dt>
 <dd><p>Represents either a floating-point constant of mode <var>m</var> or an
 integer constant too large to fit into <code>HOST_BITS_PER_WIDE_INT</code>
 bits but small enough to fit within twice that number of bits (GCC
 does not provide a mechanism to represent even larger constants).  In
 the latter case, <var>m</var> will be <code>VOIDmode</code>.  For integral values
 constants for modes with more bits than twice the number in
 <code>HOST_WIDE_INT</code> the implied high order bits of that constant are
 copies of the top bit of <code>CONST_DOUBLE_HIGH</code>.  Note however that
 integral values are neither inherently signed nor inherently unsigned;
 where necessary, signedness is determined by the rtl operation
 instead.
 </p>
 <a name="index-CONST_005fDOUBLE_005fLOW"></a>
 <p>If <var>m</var> is <code>VOIDmode</code>, the bits of the value are stored in
 <var>i0</var> and <var>i1</var>.  <var>i0</var> is customarily accessed with the macro
 <code>CONST_DOUBLE_LOW</code> and <var>i1</var> with <code>CONST_DOUBLE_HIGH</code>.
 </p>
 <p>If the constant is floating point (regardless of its precision), then
 the number of integers used to store the value depends on the size of
 <code>REAL_VALUE_TYPE</code> (see <a href="Floating-Point.html#Floating-Point">Floating Point</a>).  The integers
 represent a floating point number, but not precisely in the target
 machine&rsquo;s or host machine&rsquo;s floating point format.  To convert them to
 the precise bit pattern used by the target machine, use the macro
 <code>REAL_VALUE_TO_TARGET_DOUBLE</code> and friends (see <a href="Data-Output.html#Data-Output">Data Output</a>).
 </p>
 <a name="index-const_005ffixed"></a>
 </dd>
 <dt><code>(const_fixed:<var>m</var> &hellip;)</code></dt>
 <dd><p>Represents a fixed-point constant of mode <var>m</var>.
 The operand is a data structure of type <code>struct fixed_value</code> and
 is accessed with the macro <code>CONST_FIXED_VALUE</code>.  The high part of
 data is accessed with <code>CONST_FIXED_VALUE_HIGH</code>; the low part is
 accessed with <code>CONST_FIXED_VALUE_LOW</code>.
 </p>
 <a name="index-const_005fvector"></a>
 </dd>
 <dt><code>(const_vector:<var>m</var> [<var>x0</var> <var>x1</var> &hellip;])</code></dt>
 <dd><p>Represents a vector constant.  The square brackets stand for the vector
 containing the constant elements.  <var>x0</var>, <var>x1</var> and so on are
 the <code>const_int</code>, <code>const_double</code> or <code>const_fixed</code> elements.
 </p>
 <p>The number of units in a <code>const_vector</code> is obtained with the macro
 <code>CONST_VECTOR_NUNITS</code> as in <code>CONST_VECTOR_NUNITS (<var>v</var>)</code>.
 </p>
 <p>Individual elements in a vector constant are accessed with the macro
 <code>CONST_VECTOR_ELT</code> as in <code>CONST_VECTOR_ELT (<var>v</var>, <var>n</var>)</code>
 where <var>v</var> is the vector constant and <var>n</var> is the element
 desired.
 </p>
 <a name="index-const_005fstring"></a>
 </dd>
 <dt><code>(const_string <var>str</var>)</code></dt>
 <dd><p>Represents a constant string with value <var>str</var>.  Currently this is
 used only for insn attributes (see <a href="Insn-Attributes.html#Insn-Attributes">Insn Attributes</a>) since constant
 strings in C are placed in memory.
 </p>
 <a name="index-symbol_005fref"></a>
 </dd>
 <dt><code>(symbol_ref:<var>mode</var> <var>symbol</var>)</code></dt>
 <dd><p>Represents the value of an assembler label for data.  <var>symbol</var> is
 a string that describes the name of the assembler label.  If it starts
 with a &lsquo;<samp>*</samp>&rsquo;, the label is the rest of <var>symbol</var> not including
 the &lsquo;<samp>*</samp>&rsquo;.  Otherwise, the label is <var>symbol</var>, usually prefixed
 with &lsquo;<samp>_</samp>&rsquo;.
 </p>
 <p>The <code>symbol_ref</code> contains a mode, which is usually <code>Pmode</code>.
 Usually that is the only mode for which a symbol is directly valid.
 </p>
 <a name="index-label_005fref"></a>
 </dd>
 <dt><code>(label_ref:<var>mode</var> <var>label</var>)</code></dt>
 <dd><p>Represents the value of an assembler label for code.  It contains one
 operand, an expression, which must be a <code>code_label</code> or a <code>note</code>
 of type <code>NOTE_INSN_DELETED_LABEL</code> that appears in the instruction
 sequence to identify the place where the label should go.
 </p>
 <p>The reason for using a distinct expression type for code label
 references is so that jump optimization can distinguish them.
 </p>
 <p>The <code>label_ref</code> contains a mode, which is usually <code>Pmode</code>.
 Usually that is the only mode for which a label is directly valid.
 </p>
 <a name="index-const"></a>
 </dd>
 <dt><code>(const:<var>m</var> <var>exp</var>)</code></dt>
 <dd><p>Represents a constant that is the result of an assembly-time
 arithmetic computation.  The operand, <var>exp</var>, is an expression that
 contains only constants (<code>const_int</code>, <code>symbol_ref</code> and
 <code>label_ref</code> expressions) combined with <code>plus</code> and
 <code>minus</code>.  However, not all combinations are valid, since the
 assembler cannot do arbitrary arithmetic on relocatable symbols.
 </p>
 <p><var>m</var> should be <code>Pmode</code>.
 </p>
 <a name="index-high"></a>
 </dd>
 <dt><code>(high:<var>m</var> <var>exp</var>)</code></dt>
 <dd><p>Represents the high-order bits of <var>exp</var>, usually a
 <code>symbol_ref</code>.  The number of bits is machine-dependent and is
 normally the number of bits specified in an instruction that initializes
 the high order bits of a register.  It is used with <code>lo_sum</code> to
 represent the typical two-instruction sequence used in RISC machines to
 reference a global memory location.
 </p>
 <p><var>m</var> should be <code>Pmode</code>.
 </p></dd>
 </dl>

 <a name="index-CONST0_005fRTX"></a>
 <a name="index-CONST1_005fRTX"></a>
 <a name="index-CONST2_005fRTX"></a>
 <p>The macro <code>CONST0_RTX (<var>mode</var>)</code> refers to an expression with
 value 0 in mode <var>mode</var>.  If mode <var>mode</var> is of mode class
 <code>MODE_INT</code>, it returns <code>const0_rtx</code>.  If mode <var>mode</var> is of
 mode class <code>MODE_FLOAT</code>, it returns a <code>CONST_DOUBLE</code>
 expression in mode <var>mode</var>.  Otherwise, it returns a
 <code>CONST_VECTOR</code> expression in mode <var>mode</var>.  Similarly, the macro
 <code>CONST1_RTX (<var>mode</var>)</code> refers to an expression with value 1 in
 mode <var>mode</var> and similarly for <code>CONST2_RTX</code>.  The
 <code>CONST1_RTX</code> and <code>CONST2_RTX</code> macros are undefined
 for vector modes.
 </p>
 <hr>
 <div class="header">
 <p>
 Next: <a href="Regs-and-Memory.html#Regs-and-Memory" accesskey="n" rel="next">Regs and Memory</a>, Previous: <a href="Machine-Modes.html#Machine-Modes" accesskey="p" rel="prev">Machine Modes</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</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="Constants"></a>
	<div class="header">
	<p>
	Next: <a href="Regs-and-Memory.html#Regs-and-Memory" accesskey="n" rel="next">Regs and Memory</a>, Previous: <a href="Machine-Modes.html#Machine-Modes" accesskey="p" rel="prev">Machine Modes</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</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="Constant-Expression-Types"></a>
	<h3 class="section">13.7 Constant Expression Types</h3>
	<a name="index-RTL-constants"></a>
	<a name="index-RTL-constant-expression-types"></a>

	<p>The simplest RTL expressions are those that represent constant values.
	</p>
	<dl compact="compact">
	<dd><a name="index-const_005fint"></a>
	</dd>
	<dt><code>(const_int <var>i</var>)</code></dt>
	<dd><p>This type of expression represents the integer value <var>i</var>. <var>i</var>
	is customarily accessed with the macro <code>INTVAL</code> as in
	<code>INTVAL (<var>exp</var>)</code>, which is equivalent to <code>XWINT (<var>exp</var>, 0)</code>.
	</p>
	<p>Constants generated for modes with fewer bits than in
	<code>HOST_WIDE_INT</code> must be sign extended to full width (e.g., with
	<code>gen_int_mode</code>). For constants for modes with more bits than in
	<code>HOST_WIDE_INT</code> the implied high order bits of that constant are
	copies of the top bit. Note however that values are neither
	inherently signed nor inherently unsigned; where necessary, signedness
	is determined by the rtl operation instead.
	</p>
	<a name="index-const0_005frtx"></a>
	<a name="index-const1_005frtx"></a>
	<a name="index-const2_005frtx"></a>
	<a name="index-constm1_005frtx"></a>
	<p>There is only one expression object for the integer value zero; it is
	the value of the variable <code>const0_rtx</code>. Likewise, the only
	expression for integer value one is found in <code>const1_rtx</code>, the only
	expression for integer value two is found in <code>const2_rtx</code>, and the
	only expression for integer value negative one is found in
	<code>constm1_rtx</code>. Any attempt to create an expression of code
	<code>const_int</code> and value zero, one, two or negative one will return
	<code>const0_rtx</code>, <code>const1_rtx</code>, <code>const2_rtx</code> or
	<code>constm1_rtx</code> as appropriate.
	</p>
	<a name="index-const_005ftrue_005frtx"></a>
	<p>Similarly, there is only one object for the integer whose value is
	<code>STORE_FLAG_VALUE</code>. It is found in <code>const_true_rtx</code>. If
	<code>STORE_FLAG_VALUE</code> is one, <code>const_true_rtx</code> and
	<code>const1_rtx</code> will point to the same object. If
	<code>STORE_FLAG_VALUE</code> is -1, <code>const_true_rtx</code> and
	<code>constm1_rtx</code> will point to the same object.
	</p>
	<a name="index-const_005fdouble"></a>
	</dd>
	<dt><code>(const_double:<var>m</var> <var>i0</var> <var>i1</var> …)</code></dt>
	<dd><p>Represents either a floating-point constant of mode <var>m</var> or an
	integer constant too large to fit into <code>HOST_BITS_PER_WIDE_INT</code>
	bits but small enough to fit within twice that number of bits (GCC
	does not provide a mechanism to represent even larger constants). In
	the latter case, <var>m</var> will be <code>VOIDmode</code>. For integral values
	constants for modes with more bits than twice the number in
	<code>HOST_WIDE_INT</code> the implied high order bits of that constant are
	copies of the top bit of <code>CONST_DOUBLE_HIGH</code>. Note however that
	integral values are neither inherently signed nor inherently unsigned;
	where necessary, signedness is determined by the rtl operation
	instead.
	</p>
	<a name="index-CONST_005fDOUBLE_005fLOW"></a>
	<p>If <var>m</var> is <code>VOIDmode</code>, the bits of the value are stored in
	<var>i0</var> and <var>i1</var>. <var>i0</var> is customarily accessed with the macro
	<code>CONST_DOUBLE_LOW</code> and <var>i1</var> with <code>CONST_DOUBLE_HIGH</code>.
	</p>
	<p>If the constant is floating point (regardless of its precision), then
	the number of integers used to store the value depends on the size of
	<code>REAL_VALUE_TYPE</code> (see <a href="Floating-Point.html#Floating-Point">Floating Point</a>). The integers
	represent a floating point number, but not precisely in the target
	machine’s or host machine’s floating point format. To convert them to
	the precise bit pattern used by the target machine, use the macro
	<code>REAL_VALUE_TO_TARGET_DOUBLE</code> and friends (see <a href="Data-Output.html#Data-Output">Data Output</a>).
	</p>
	<a name="index-const_005ffixed"></a>
	</dd>
	<dt><code>(const_fixed:<var>m</var> …)</code></dt>
	<dd><p>Represents a fixed-point constant of mode <var>m</var>.
	The operand is a data structure of type <code>struct fixed_value</code> and
	is accessed with the macro <code>CONST_FIXED_VALUE</code>. The high part of
	data is accessed with <code>CONST_FIXED_VALUE_HIGH</code>; the low part is
	accessed with <code>CONST_FIXED_VALUE_LOW</code>.
	</p>
	<a name="index-const_005fvector"></a>
	</dd>
	<dt><code>(const_vector:<var>m</var> [<var>x0</var> <var>x1</var> …])</code></dt>
	<dd><p>Represents a vector constant. The square brackets stand for the vector
	containing the constant elements. <var>x0</var>, <var>x1</var> and so on are
	the <code>const_int</code>, <code>const_double</code> or <code>const_fixed</code> elements.
	</p>
	<p>The number of units in a <code>const_vector</code> is obtained with the macro
	<code>CONST_VECTOR_NUNITS</code> as in <code>CONST_VECTOR_NUNITS (<var>v</var>)</code>.
	</p>
	<p>Individual elements in a vector constant are accessed with the macro
	<code>CONST_VECTOR_ELT</code> as in <code>CONST_VECTOR_ELT (<var>v</var>, <var>n</var>)</code>
	where <var>v</var> is the vector constant and <var>n</var> is the element
	desired.
	</p>
	<a name="index-const_005fstring"></a>
	</dd>
	<dt><code>(const_string <var>str</var>)</code></dt>
	<dd><p>Represents a constant string with value <var>str</var>. Currently this is
	used only for insn attributes (see <a href="Insn-Attributes.html#Insn-Attributes">Insn Attributes</a>) since constant
	strings in C are placed in memory.
	</p>
	<a name="index-symbol_005fref"></a>
	</dd>
	<dt><code>(symbol_ref:<var>mode</var> <var>symbol</var>)</code></dt>
	<dd><p>Represents the value of an assembler label for data. <var>symbol</var> is
	a string that describes the name of the assembler label. If it starts
	with a ‘<samp>*</samp>’, the label is the rest of <var>symbol</var> not including
	the ‘<samp>*</samp>’. Otherwise, the label is <var>symbol</var>, usually prefixed
	with ‘<samp>_</samp>’.
	</p>
	<p>The <code>symbol_ref</code> contains a mode, which is usually <code>Pmode</code>.
	Usually that is the only mode for which a symbol is directly valid.
	</p>
	<a name="index-label_005fref"></a>
	</dd>
	<dt><code>(label_ref:<var>mode</var> <var>label</var>)</code></dt>
	<dd><p>Represents the value of an assembler label for code. It contains one
	operand, an expression, which must be a <code>code_label</code> or a <code>note</code>
	of type <code>NOTE_INSN_DELETED_LABEL</code> that appears in the instruction
	sequence to identify the place where the label should go.
	</p>
	<p>The reason for using a distinct expression type for code label
	references is so that jump optimization can distinguish them.
	</p>
	<p>The <code>label_ref</code> contains a mode, which is usually <code>Pmode</code>.
	Usually that is the only mode for which a label is directly valid.
	</p>
	<a name="index-const"></a>
	</dd>
	<dt><code>(const:<var>m</var> <var>exp</var>)</code></dt>
	<dd><p>Represents a constant that is the result of an assembly-time
	arithmetic computation. The operand, <var>exp</var>, is an expression that
	contains only constants (<code>const_int</code>, <code>symbol_ref</code> and
	<code>label_ref</code> expressions) combined with <code>plus</code> and
	<code>minus</code>. However, not all combinations are valid, since the
	assembler cannot do arbitrary arithmetic on relocatable symbols.
	</p>
	<p><var>m</var> should be <code>Pmode</code>.
	</p>
	<a name="index-high"></a>
	</dd>
	<dt><code>(high:<var>m</var> <var>exp</var>)</code></dt>
	<dd><p>Represents the high-order bits of <var>exp</var>, usually a
	<code>symbol_ref</code>. The number of bits is machine-dependent and is
	normally the number of bits specified in an instruction that initializes
	the high order bits of a register. It is used with <code>lo_sum</code> to
	represent the typical two-instruction sequence used in RISC machines to
	reference a global memory location.
	</p>
	<p><var>m</var> should be <code>Pmode</code>.
	</p></dd>
	</dl>

	<a name="index-CONST0_005fRTX"></a>
	<a name="index-CONST1_005fRTX"></a>
	<a name="index-CONST2_005fRTX"></a>
	<p>The macro <code>CONST0_RTX (<var>mode</var>)</code> refers to an expression with
	value 0 in mode <var>mode</var>. If mode <var>mode</var> is of mode class
	<code>MODE_INT</code>, it returns <code>const0_rtx</code>. If mode <var>mode</var> is of
	mode class <code>MODE_FLOAT</code>, it returns a <code>CONST_DOUBLE</code>
	expression in mode <var>mode</var>. Otherwise, it returns a
	<code>CONST_VECTOR</code> expression in mode <var>mode</var>. Similarly, the macro
	<code>CONST1_RTX (<var>mode</var>)</code> refers to an expression with value 1 in
	mode <var>mode</var> and similarly for <code>CONST2_RTX</code>. The
	<code>CONST1_RTX</code> and <code>CONST2_RTX</code> macros are undefined
	for vector modes.
	</p>
	<hr>
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