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| <a name="Expressions"></a> |
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| Next: <a href="Tagging-Insns.html#Tagging-Insns" accesskey="n" rel="next">Tagging Insns</a>, Previous: <a href="Defining-Attributes.html#Defining-Attributes" accesskey="p" rel="prev">Defining Attributes</a>, Up: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="u" rel="up">Insn Attributes</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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| <a name="Attribute-Expressions"></a> |
| <h4 class="subsection">16.19.2 Attribute Expressions</h4> |
| <a name="index-attribute-expressions"></a> |
| |
| <p>RTL expressions used to define attributes use the codes described above |
| plus a few specific to attribute definitions, to be discussed below. |
| Attribute value expressions must have one of the following forms: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-const_005fint-and-attributes"></a> |
| </dd> |
| <dt><code>(const_int <var>i</var>)</code></dt> |
| <dd><p>The integer <var>i</var> specifies the value of a numeric attribute. <var>i</var> |
| must be non-negative. |
| </p> |
| <p>The value of a numeric attribute can be specified either with a |
| <code>const_int</code>, or as an integer represented as a string in |
| <code>const_string</code>, <code>eq_attr</code> (see below), <code>attr</code>, |
| <code>symbol_ref</code>, simple arithmetic expressions, and <code>set_attr</code> |
| overrides on specific instructions (see <a href="Tagging-Insns.html#Tagging-Insns">Tagging Insns</a>). |
| </p> |
| <a name="index-const_005fstring-and-attributes"></a> |
| </dd> |
| <dt><code>(const_string <var>value</var>)</code></dt> |
| <dd><p>The string <var>value</var> specifies a constant attribute value. |
| If <var>value</var> is specified as ‘<samp>"*"</samp>’, it means that the default value of |
| the attribute is to be used for the insn containing this expression. |
| ‘<samp>"*"</samp>’ obviously cannot be used in the <var>default</var> expression |
| of a <code>define_attr</code>. |
| </p> |
| <p>If the attribute whose value is being specified is numeric, <var>value</var> |
| must be a string containing a non-negative integer (normally |
| <code>const_int</code> would be used in this case). Otherwise, it must |
| contain one of the valid values for the attribute. |
| </p> |
| <a name="index-if_005fthen_005felse-and-attributes"></a> |
| </dd> |
| <dt><code>(if_then_else <var>test</var> <var>true-value</var> <var>false-value</var>)</code></dt> |
| <dd><p><var>test</var> specifies an attribute test, whose format is defined below. |
| The value of this expression is <var>true-value</var> if <var>test</var> is true, |
| otherwise it is <var>false-value</var>. |
| </p> |
| <a name="index-cond-and-attributes"></a> |
| </dd> |
| <dt><code>(cond [<var>test1</var> <var>value1</var> …] <var>default</var>)</code></dt> |
| <dd><p>The first operand of this expression is a vector containing an even |
| number of expressions and consisting of pairs of <var>test</var> and <var>value</var> |
| expressions. The value of the <code>cond</code> expression is that of the |
| <var>value</var> corresponding to the first true <var>test</var> expression. If |
| none of the <var>test</var> expressions are true, the value of the <code>cond</code> |
| expression is that of the <var>default</var> expression. |
| </p></dd> |
| </dl> |
| |
| <p><var>test</var> expressions can have one of the following forms: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-const_005fint-and-attribute-tests"></a> |
| </dd> |
| <dt><code>(const_int <var>i</var>)</code></dt> |
| <dd><p>This test is true if <var>i</var> is nonzero and false otherwise. |
| </p> |
| <a name="index-not-and-attributes"></a> |
| <a name="index-ior-and-attributes"></a> |
| <a name="index-and-and-attributes"></a> |
| </dd> |
| <dt><code>(not <var>test</var>)</code></dt> |
| <dt><code>(ior <var>test1</var> <var>test2</var>)</code></dt> |
| <dt><code>(and <var>test1</var> <var>test2</var>)</code></dt> |
| <dd><p>These tests are true if the indicated logical function is true. |
| </p> |
| <a name="index-match_005foperand-and-attributes"></a> |
| </dd> |
| <dt><code>(match_operand:<var>m</var> <var>n</var> <var>pred</var> <var>constraints</var>)</code></dt> |
| <dd><p>This test is true if operand <var>n</var> of the insn whose attribute value |
| is being determined has mode <var>m</var> (this part of the test is ignored |
| if <var>m</var> is <code>VOIDmode</code>) and the function specified by the string |
| <var>pred</var> returns a nonzero value when passed operand <var>n</var> and mode |
| <var>m</var> (this part of the test is ignored if <var>pred</var> is the null |
| string). |
| </p> |
| <p>The <var>constraints</var> operand is ignored and should be the null string. |
| </p> |
| <a name="index-match_005ftest-and-attributes"></a> |
| </dd> |
| <dt><code>(match_test <var>c-expr</var>)</code></dt> |
| <dd><p>The test is true if C expression <var>c-expr</var> is true. In non-constant |
| attributes, <var>c-expr</var> has access to the following variables: |
| </p> |
| <dl compact="compact"> |
| <dt><var>insn</var></dt> |
| <dd><p>The rtl instruction under test. |
| </p></dd> |
| <dt><var>which_alternative</var></dt> |
| <dd><p>The <code>define_insn</code> alternative that <var>insn</var> matches. |
| See <a href="Output-Statement.html#Output-Statement">Output Statement</a>. |
| </p></dd> |
| <dt><var>operands</var></dt> |
| <dd><p>An array of <var>insn</var>’s rtl operands. |
| </p></dd> |
| </dl> |
| |
| <p><var>c-expr</var> behaves like the condition in a C <code>if</code> statement, |
| so there is no need to explicitly convert the expression into a boolean |
| 0 or 1 value. For example, the following two tests are equivalent: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(match_test "x & 2") |
| (match_test "(x & 2) != 0") |
| </pre></div> |
| |
| <a name="index-le-and-attributes"></a> |
| <a name="index-leu-and-attributes"></a> |
| <a name="index-lt-and-attributes"></a> |
| <a name="index-gt-and-attributes"></a> |
| <a name="index-gtu-and-attributes"></a> |
| <a name="index-ge-and-attributes"></a> |
| <a name="index-geu-and-attributes"></a> |
| <a name="index-ne-and-attributes"></a> |
| <a name="index-eq-and-attributes"></a> |
| <a name="index-plus-and-attributes"></a> |
| <a name="index-minus-and-attributes"></a> |
| <a name="index-mult-and-attributes"></a> |
| <a name="index-div-and-attributes"></a> |
| <a name="index-mod-and-attributes"></a> |
| <a name="index-abs-and-attributes"></a> |
| <a name="index-neg-and-attributes"></a> |
| <a name="index-ashift-and-attributes"></a> |
| <a name="index-lshiftrt-and-attributes"></a> |
| <a name="index-ashiftrt-and-attributes"></a> |
| </dd> |
| <dt><code>(le <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dt><code>(leu <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dt><code>(lt <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dt><code>(ltu <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dt><code>(gt <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dt><code>(gtu <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dt><code>(ge <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dt><code>(geu <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dt><code>(ne <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dt><code>(eq <var>arith1</var> <var>arith2</var>)</code></dt> |
| <dd><p>These tests are true if the indicated comparison of the two arithmetic |
| expressions is true. Arithmetic expressions are formed with |
| <code>plus</code>, <code>minus</code>, <code>mult</code>, <code>div</code>, <code>mod</code>, |
| <code>abs</code>, <code>neg</code>, <code>and</code>, <code>ior</code>, <code>xor</code>, <code>not</code>, |
| <code>ashift</code>, <code>lshiftrt</code>, and <code>ashiftrt</code> expressions. |
| </p> |
| <a name="index-get_005fattr"></a> |
| <p><code>const_int</code> and <code>symbol_ref</code> are always valid terms (see <a href="Insn-Lengths.html#Insn-Lengths">Insn Lengths</a>,for additional forms). <code>symbol_ref</code> is a string |
| denoting a C expression that yields an <code>int</code> when evaluated by the |
| ‘<samp>get_attr_…</samp>’ routine. It should normally be a global |
| variable. |
| </p> |
| <a name="index-eq_005fattr"></a> |
| </dd> |
| <dt><code>(eq_attr <var>name</var> <var>value</var>)</code></dt> |
| <dd><p><var>name</var> is a string specifying the name of an attribute. |
| </p> |
| <p><var>value</var> is a string that is either a valid value for attribute |
| <var>name</var>, a comma-separated list of values, or ‘<samp>!</samp>’ followed by a |
| value or list. If <var>value</var> does not begin with a ‘<samp>!</samp>’, this |
| test is true if the value of the <var>name</var> attribute of the current |
| insn is in the list specified by <var>value</var>. If <var>value</var> begins |
| with a ‘<samp>!</samp>’, this test is true if the attribute’s value is |
| <em>not</em> in the specified list. |
| </p> |
| <p>For example, |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(eq_attr "type" "load,store") |
| </pre></div> |
| |
| <p>is equivalent to |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(ior (eq_attr "type" "load") (eq_attr "type" "store")) |
| </pre></div> |
| |
| <p>If <var>name</var> specifies an attribute of ‘<samp>alternative</samp>’, it refers to the |
| value of the compiler variable <code>which_alternative</code> |
| (see <a href="Output-Statement.html#Output-Statement">Output Statement</a>) and the values must be small integers. For |
| example, |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(eq_attr "alternative" "2,3") |
| </pre></div> |
| |
| <p>is equivalent to |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(ior (eq (symbol_ref "which_alternative") (const_int 2)) |
| (eq (symbol_ref "which_alternative") (const_int 3))) |
| </pre></div> |
| |
| <p>Note that, for most attributes, an <code>eq_attr</code> test is simplified in cases |
| where the value of the attribute being tested is known for all insns matching |
| a particular pattern. This is by far the most common case. |
| </p> |
| <a name="index-attr_005fflag"></a> |
| </dd> |
| <dt><code>(attr_flag <var>name</var>)</code></dt> |
| <dd><p>The value of an <code>attr_flag</code> expression is true if the flag |
| specified by <var>name</var> is true for the <code>insn</code> currently being |
| scheduled. |
| </p> |
| <p><var>name</var> is a string specifying one of a fixed set of flags to test. |
| Test the flags <code>forward</code> and <code>backward</code> to determine the |
| direction of a conditional branch. |
| </p> |
| <p>This example describes a conditional branch delay slot which |
| can be nullified for forward branches that are taken (annul-true) or |
| for backward branches which are not taken (annul-false). |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(define_delay (eq_attr "type" "cbranch") |
| [(eq_attr "in_branch_delay" "true") |
| (and (eq_attr "in_branch_delay" "true") |
| (attr_flag "forward")) |
| (and (eq_attr "in_branch_delay" "true") |
| (attr_flag "backward"))]) |
| </pre></div> |
| |
| <p>The <code>forward</code> and <code>backward</code> flags are false if the current |
| <code>insn</code> being scheduled is not a conditional branch. |
| </p> |
| <p><code>attr_flag</code> is only used during delay slot scheduling and has no |
| meaning to other passes of the compiler. |
| </p> |
| <a name="index-attr"></a> |
| </dd> |
| <dt><code>(attr <var>name</var>)</code></dt> |
| <dd><p>The value of another attribute is returned. This is most useful |
| for numeric attributes, as <code>eq_attr</code> and <code>attr_flag</code> |
| produce more efficient code for non-numeric attributes. |
| </p></dd> |
| </dl> |
| |
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