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122 lines
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<title>Storage References - GNU Compiler Collection (GCC) Internals</title>
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<a name="Storage-References"></a>
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Next: <a rel="next" accesskey="n" href="Unary-and-Binary-Expressions.html#Unary-and-Binary-Expressions">Unary and Binary Expressions</a>,
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Previous: <a rel="previous" accesskey="p" href="Constant-expressions.html#Constant-expressions">Constant expressions</a>,
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Up: <a rel="up" accesskey="u" href="Expression-trees.html#Expression-trees">Expression trees</a>
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<h4 class="subsection">10.6.2 References to storage</h4>
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<p><a name="index-ADDR_005fEXPR-1841"></a><a name="index-INDIRECT_005fREF-1842"></a><a name="index-MEM_005fREF-1843"></a><a name="index-ARRAY_005fREF-1844"></a><a name="index-ARRAY_005fRANGE_005fREF-1845"></a><a name="index-TARGET_005fMEM_005fREF-1846"></a><a name="index-COMPONENT_005fREF-1847"></a>
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<dl>
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<dt><code>ARRAY_REF</code><dd>These nodes represent array accesses. The first operand is the array;
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the second is the index. To calculate the address of the memory
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accessed, you must scale the index by the size of the type of the array
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elements. The type of these expressions must be the type of a component of
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the array. The third and fourth operands are used after gimplification
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to represent the lower bound and component size but should not be used
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directly; call <code>array_ref_low_bound</code> and <code>array_ref_element_size</code>
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instead.
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<br><dt><code>ARRAY_RANGE_REF</code><dd>These nodes represent access to a range (or “slice”) of an array. The
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operands are the same as that for <code>ARRAY_REF</code> and have the same
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meanings. The type of these expressions must be an array whose component
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type is the same as that of the first operand. The range of that array
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type determines the amount of data these expressions access.
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<br><dt><code>TARGET_MEM_REF</code><dd>These nodes represent memory accesses whose address directly map to
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an addressing mode of the target architecture. The first argument
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is <code>TMR_SYMBOL</code> and must be a <code>VAR_DECL</code> of an object with
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a fixed address. The second argument is <code>TMR_BASE</code> and the
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third one is <code>TMR_INDEX</code>. The fourth argument is
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<code>TMR_STEP</code> and must be an <code>INTEGER_CST</code>. The fifth
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argument is <code>TMR_OFFSET</code> and must be an <code>INTEGER_CST</code>.
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Any of the arguments may be NULL if the appropriate component
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does not appear in the address. Address of the <code>TARGET_MEM_REF</code>
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is determined in the following way.
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<pre class="smallexample"> &TMR_SYMBOL + TMR_BASE + TMR_INDEX * TMR_STEP + TMR_OFFSET
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</pre>
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<p>The sixth argument is the reference to the original memory access, which
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is preserved for the purposes of the RTL alias analysis. The seventh
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argument is a tag representing the results of tree level alias analysis.
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<br><dt><code>ADDR_EXPR</code><dd>These nodes are used to represent the address of an object. (These
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expressions will always have pointer or reference type.) The operand may
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be another expression, or it may be a declaration.
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<p>As an extension, GCC allows users to take the address of a label. In
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this case, the operand of the <code>ADDR_EXPR</code> will be a
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<code>LABEL_DECL</code>. The type of such an expression is <code>void*</code>.
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<p>If the object addressed is not an lvalue, a temporary is created, and
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the address of the temporary is used.
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<br><dt><code>INDIRECT_REF</code><dd>These nodes are used to represent the object pointed to by a pointer.
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The operand is the pointer being dereferenced; it will always have
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pointer or reference type.
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<br><dt><code>MEM_REF</code><dd>These nodes are used to represent the object pointed to by a pointer
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offset by a constant.
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The first operand is the pointer being dereferenced; it will always have
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pointer or reference type. The second operand is a pointer constant.
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Its type is specifying the type to be used for type-based alias analysis.
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<br><dt><code>COMPONENT_REF</code><dd>These nodes represent non-static data member accesses. The first
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operand is the object (rather than a pointer to it); the second operand
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is the <code>FIELD_DECL</code> for the data member. The third operand represents
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the byte offset of the field, but should not be used directly; call
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<code>component_ref_field_offset</code> instead.
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</dl>
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</body></html>
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