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| <a name="Subst-Iterators-1"></a> |
| <h4 class="subsection">16.23.4 Subst Iterators</h4> |
| <a name="index-subst-iterators-in-_002emd-files"></a> |
| <a name="index-define_005fsubst-5"></a> |
| <a name="index-define_005fsubst_005fattr"></a> |
| |
| <p>Subst iterators are special type of iterators with the following |
| restrictions: they could not be declared explicitly, they always have |
| only two values, and they do not have explicit dedicated name. |
| Subst-iterators are triggered only when corresponding subst-attribute is |
| used in RTL-pattern. |
| </p> |
| <p>Subst iterators transform templates in the following way: the templates |
| are duplicated, the subst-attributes in these templates are replaced |
| with the corresponding values, and a new attribute is implicitly added |
| to the given <code>define_insn</code>/<code>define_expand</code>. The name of the |
| added attribute matches the name of <code>define_subst</code>. Such |
| attributes are declared implicitly, and it is not allowed to have a |
| <code>define_attr</code> named as a <code>define_subst</code>. |
| </p> |
| <p>Each subst iterator is linked to a <code>define_subst</code>. It is declared |
| implicitly by the first appearance of the corresponding |
| <code>define_subst_attr</code>, and it is not allowed to define it explicitly. |
| </p> |
| <p>Declarations of subst-attributes have the following syntax: |
| </p> |
| <a name="index-define_005fsubst_005fattr-1"></a> |
| <div class="smallexample"> |
| <pre class="smallexample">(define_subst_attr "<var>name</var>" |
| "<var>subst-name</var>" |
| "<var>no-subst-value</var>" |
| "<var>subst-applied-value</var>") |
| </pre></div> |
| |
| <p><var>name</var> is a string with which the given subst-attribute could be |
| referred to. |
| </p> |
| <p><var>subst-name</var> shows which <code>define_subst</code> should be applied to an |
| RTL-template if the given subst-attribute is present in the |
| RTL-template. |
| </p> |
| <p><var>no-subst-value</var> is a value with which subst-attribute would be |
| replaced in the first copy of the original RTL-template. |
| </p> |
| <p><var>subst-applied-value</var> is a value with which subst-attribute would be |
| replaced in the second copy of the original RTL-template. |
| </p> |
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