11.6.2 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.

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.

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 serving as constant offset applied to the pointer being dereferenced with its type specifying the type to be used for type-based alias analysis. The type of the node specifies the alignment of the 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_BASE and is a pointer to the object being accessed. The second argument is TMR_OFFSET which is a pointer constant with dual purpose serving both as constant offset and holder of the type used for type-based alias analysis. The first two operands have exactly the same semantics as MEM_REF. The third and fourth operand are TMR_INDEX and TMR_STEP where the former is an integer and the latter an integer constant. The fifth and last operand is TMR_INDEX2 which is an alternate non-constant offset. Any of the third to last operands may be NULL if the corresponding component does not appear in the address, but TMR_INDEX and TMR_STEP shall be always supplied in pair. The Address of the TARGET_MEM_REF is determined in the following way.

          TMR_BASE + TMR_OFFSET + TMR_INDEX * TMR_STEP + TMR_INDEX2
     

The type of the node specifies the alignment of the access.