Special Accessors - GNU Compiler Collection (GCC) Internals

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12.4 Access to Special Operands

Some RTL nodes have special annotations associated with them.

MEM

MEM_ALIAS_SET (x): If 0, x is not in any alias set, and may alias anything. Otherwise, x can only alias MEMs in a conflicting alias set. This value is set in a language-dependent manner in the front-end, and should not be altered in the back-end. In some front-ends, these numbers may correspond in some way to types, or other language-level entities, but they need not, and the back-end makes no such assumptions. These set numbers are tested with alias_sets_conflict_p.
MEM_EXPR (x): If this register is known to hold the value of some user-level declaration, this is that tree node. It may also be a COMPONENT_REF, in which case this is some field reference, and TREE_OPERAND (x, 0) contains the declaration, or another COMPONENT_REF, or null if there is no compile-time object associated with the reference.
MEM_OFFSET (x): The offset from the start of MEM_EXPR as a CONST_INT rtx.
MEM_SIZE (x): The size in bytes of the memory reference as a CONST_INT rtx. This is mostly relevant for BLKmode references as otherwise the size is implied by the mode.
MEM_ALIGN (x): The known alignment in bits of the memory reference.

REG

ORIGINAL_REGNO (x): This field holds the number the register “originally” had; for a pseudo register turned into a hard reg this will hold the old pseudo register number.
REG_EXPR (x): If this register is known to hold the value of some user-level declaration, this is that tree node.
REG_OFFSET (x): If this register is known to hold the value of some user-level declaration, this is the offset into that logical storage.

SYMBOL_REF

SYMBOL_REF_DECL (x)

If the symbol_ref x was created for a VAR_DECL or a FUNCTION_DECL, that tree is recorded here. If this value is null, then x was created by back end code generation routines, and there is no associated front end symbol table entry.

SYMBOL_REF_DECL may also point to a tree of class 'c', that is, some sort of constant. In this case, the symbol_ref is an entry in the per-file constant pool; again, there is no associated front end symbol table entry.

SYMBOL_REF_CONSTANT (x)

If `CONSTANT_POOL_ADDRESS_P (x)' is true, this is the constant pool entry for x. It is null otherwise.

SYMBOL_REF_DATA (x)

A field of opaque type used to store SYMBOL_REF_DECL or SYMBOL_REF_CONSTANT.

SYMBOL_REF_FLAGS (x)

In a symbol_ref, this is used to communicate various predicates about the symbol. Some of these are common enough to be computed by common code, some are specific to the target. The common bits are:

SYMBOL_FLAG_FUNCTION: Set if the symbol refers to a function.
SYMBOL_FLAG_LOCAL: Set if the symbol is local to this “module”. See TARGET_BINDS_LOCAL_P.
SYMBOL_FLAG_EXTERNAL: Set if this symbol is not defined in this translation unit. Note that this is not the inverse of SYMBOL_FLAG_LOCAL.
SYMBOL_FLAG_SMALL: Set if the symbol is located in the small data section. See TARGET_IN_SMALL_DATA_P.
SYMBOL_REF_TLS_MODEL (x): This is a multi-bit field accessor that returns the tls_model to be used for a thread-local storage symbol. It returns zero for non-thread-local symbols.
SYMBOL_FLAG_HAS_BLOCK_INFO: Set if the symbol has SYMBOL_REF_BLOCK and SYMBOL_REF_BLOCK_OFFSET fields.
SYMBOL_FLAG_ANCHOR: Set if the symbol is used as a section anchor. “Section anchors” are symbols that have a known position within an object_block and that can be used to access nearby members of that block. They are used to implement -fsection-anchors.
If this flag is set, then SYMBOL_FLAG_HAS_BLOCK_INFO will be too.

Bits beginning with SYMBOL_FLAG_MACH_DEP are available for the target's use.

SYMBOL_REF_BLOCK (x)

If `SYMBOL_REF_HAS_BLOCK_INFO_P (x)', this is the `object_block' structure to which the symbol belongs, or NULL if it has not been assigned a block.

SYMBOL_REF_BLOCK_OFFSET (x)

If `SYMBOL_REF_HAS_BLOCK_INFO_P (x)', this is the offset of x from the first object in `SYMBOL_REF_BLOCK (x)'. The value is negative if x has not yet been assigned to a block, or it has not been given an offset within that block.