RTL expressions contain several flags (one-bit bitfields) that are used in certain types of expression. Most often they are accessed with the following macros:
MEM_VOLATILE_P (x)
mem
expressions, nonzero for volatile memory references.
Stored in the volatil
field and printed as `/v
'.
MEM_IN_STRUCT_P (x)
mem
expressions, nonzero for reference to an entire
structure, union or array, or to a component of one. Zero for
references to a scalar variable or through a pointer to a scalar.
Stored in the in_struct
field and printed as `/s
'.
REG_LOOP_TEST_P
reg
expressions, nonzero if this register's entire life is
contained in the exit test code for some loop. Stored in the
in_struct
field and printed as `/s
'.
REG_USERVAR_P (x)
reg
, nonzero if it corresponds to a variable present in
the user's source code. Zero for temporaries generated internally by
the compiler. Stored in the volatil
field and printed as
`/v
'.
REG_FUNCTION_VALUE_P (x)
reg
if it is the place in which this function's
value is going to be returned. (This happens only in a hard
register.) Stored in the integrated
field and printed as
`/i
'.
The same hard register may be used also for collecting the values of
functions called by this one, but REG_FUNCTION_VALUE_P
is zero
in this kind of use.
SUBREG_PROMOTED_VAR_P
subreg
if it was made when accessing an object that
was promoted to a wider mode in accord with the PROMOTED_MODE
machine
description macro (see Storage Layout). In this case, the mode of
the subreg
is the declared mode of the object and the mode of
SUBREG_REG
is the mode of the register that holds the object.
Promoted variables are always either sign- or zero-extended to the wider
mode on every assignment. Stored in the in_struct
field and
printed as `/s
'.
SUBREG_PROMOTED_UNSIGNED_P
subreg
that has SUBREG_PROMOTED_VAR_P
nonzero
if the object being referenced is kept zero-extended and zero if it
is kept sign-extended. Stored in the unchanging
field and
printed as `/u
'.
RTX_UNCHANGING_P (x)
reg
or mem
if the value is not changed.
(This flag is not set for memory references via pointers to constants.
Such pointers only guarantee that the object will not be changed
explicitly by the current function. The object might be changed by
other functions or by aliasing.) Stored in the
unchanging
field and printed as `/u
'.
RTX_INTEGRATED_P (insn)
integrated
field and printed as `/i
'. This
may be deleted; nothing currently depends on it.
SYMBOL_REF_USED (x)
symbol_ref
, indicates that x has been used. This is
normally only used to ensure that x is only declared external
once. Stored in the used
field.
SYMBOL_REF_FLAG (x)
symbol_ref
, this is used as a flag for machine-specific purposes.
Stored in the volatil
field and printed as `/v
'.
LABEL_OUTSIDE_LOOP_P
label_ref
expressions, nonzero if this is a reference to a
label that is outside the innermost loop containing the reference to the
label. Stored in the in_struct
field and printed as `/s
'.
INSN_DELETED_P (insn)
volatil
field and printed as `/v
'.
INSN_ANNULLED_BRANCH_P (insn)
insn
in the delay slot of a branch insn, indicates that an
annulling branch should be used. See the discussion under
sequence
below. Stored in the unchanging
field and printed
as `/u
'.
INSN_FROM_TARGET_P (insn)
insn
in a delay slot of a branch, indicates that the insn
is from the target of the branch. If the branch insn has
INSN_ANNULLED_BRANCH_P
set, this insn should only be executed if
the branch is taken. For annulled branches with this bit clear, the
insn should be executed only if the branch is not taken. Stored in the
in_struct
field and printed as `/s
'.
CONSTANT_POOL_ADDRESS_P (x)
symbol_ref
if it refers to part of the current
function's ``constants pool''. These are addresses close to the
beginning of the function, and GNU CC assumes they can be addressed
directly (perhaps with the help of base registers). Stored in the
unchanging
field and printed as `/u
'.
CONST_CALL_P (x)
call_insn
, indicates that the insn represents a call to a const
function. Stored in the unchanging
field and printed as `/u
'.
LABEL_PRESERVE_P (x)
code_label
, indicates that the label can never be deleted.
Labels referenced by a non-local goto will have this bit set. Stored
in the in_struct
field and printed as `/s
'.
SCHED_GROUP_P (insn)
use
insns before a call_insn
may
not be separated from the call_insn
. Stored in the in_struct
field and printed as `/s
'.
These are the fields which the above macros refer to:
used
In a symbol_ref
, it indicates that an external declaration for
the symbol has already been written.
In a reg
, it is used by the leaf register renumbering code to ensure
that each register is only renumbered once.
volatil
mem
, symbol_ref
and reg
expressions and in insns. In RTL dump files, it is printed as
`/v
'.
In a mem
expression, it is 1 if the memory reference is volatile.
Volatile memory references may not be deleted, reordered or combined.
In a symbol_ref
expression, it is used for machine-specific
purposes.
In a reg
expression, it is 1 if the value is a user-level variable.
0 indicates an internal compiler temporary.
In an insn, 1 means the insn has been deleted.
in_struct
mem
expressions, it is 1 if the memory datum referred to is
all or part of a structure or array; 0 if it is (or might be) a scalar
variable. A reference through a C pointer has 0 because the pointer
might point to a scalar variable. This information allows the compiler
to determine something about possible cases of aliasing.
In an insn in the delay slot of a branch, 1 means that this insn is from the target of the branch.
During instruction scheduling, in an insn, 1 means that this insn must be scheduled as part of a group together with the previous insn.
In reg
expressions, it is 1 if the register has its entire life
contained within the test expression of some loop.
In subreg
expressions, 1 means that the subreg
is accessing
an object that has had its mode promoted from a wider mode.
In label_ref
expressions, 1 means that the referenced label is
outside the innermost loop containing the insn in which the label_ref
was found.
In code_label
expressions, it is 1 if the label may never be deleted.
This is used for labels which are the target of non-local gotos.
In an RTL dump, this flag is represented as `/s
'.
unchanging
reg
and mem
expressions, 1 means
that the value of the expression never changes.
In subreg
expressions, it is 1 if the subreg
references an
unsigned object whose mode has been promoted to a wider mode.
In an insn, 1 means that this is an annulling branch.
In a symbol_ref
expression, 1 means that this symbol addresses
something in the per-function constants pool.
In a call_insn
, 1 means that this instruction is a call to a
const function.
In an RTL dump, this flag is represented as `/u
'.
integrated
In a reg
expression, this flag indicates the register
containing the value to be returned by the current function. On
machines that pass parameters in registers, the same register number
may be used for parameters as well, but this flag is not set on such
uses.