GNU Compiler Collection (GCC) Internals: Storage References

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10.6.2 References to storage

ARRAY_REF

These nodes represent array accesses. The first operand is the array; the second is the index. To calculate the address of the memory accessed, you must scale the index by the size of the type of the array elements. The type of these expressions must be the type of a component of the array. The third and fourth operands are used after gimplification to represent the lower bound and component size but should not be used directly; call array_ref_low_bound and array_ref_element_size instead.

ARRAY_RANGE_REF

These nodes represent access to a range (or “slice”) of an array. The operands are the same as that for ARRAY_REF and have the same meanings. The type of these expressions must be an array whose component type is the same as that of the first operand. The range of that array type determines the amount of data these expressions access.

TARGET_MEM_REF

These nodes represent memory accesses whose address directly map to an addressing mode of the target architecture. The first argument is TMR_SYMBOL and must be a VAR_DECL of an object with a fixed address. The second argument is TMR_BASE and the third one is TMR_INDEX. The fourth argument is TMR_STEP and must be an INTEGER_CST. The fifth argument is TMR_OFFSET and must be an INTEGER_CST. Any of the arguments may be NULL if the appropriate component does not appear in the address. Address of the TARGET_MEM_REF is determined in the following way.

&TMR_SYMBOL + TMR_BASE + TMR_INDEX * TMR_STEP + TMR_OFFSET

The sixth argument is the reference to the original memory access, which is preserved for the purposes of the RTL alias analysis. The seventh argument is a tag representing the results of tree level alias analysis.

ADDR_EXPR

These nodes are used to represent the address of an object. (These expressions will always have pointer or reference type.) The operand may be another expression, or it may be a declaration.

As an extension, GCC allows users to take the address of a label. In this case, the operand of the ADDR_EXPR will be a LABEL_DECL. The type of such an expression is void*.

If the object addressed is not an lvalue, a temporary is created, and the address of the temporary is used.

INDIRECT_REF

These nodes are used to represent the object pointed to by a pointer. The operand is the pointer being dereferenced; it will always have pointer or reference type.

MEM_REF

These nodes are used to represent the object pointed to by a pointer offset by a constant. The first operand is the pointer being dereferenced; it will always have pointer or reference type. The second operand is a pointer constant. Its type is specifying the type to be used for type-based alias analysis.

COMPONENT_REF

These nodes represent non-static data member accesses. The first operand is the object (rather than a pointer to it); the second operand is the FIELD_DECL for the data member. The third operand represents the byte offset of the field, but should not be used directly; call component_ref_field_offset instead.

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