rtl.texi

早期freebsd实现

@cindex @code{integrated}, in @code{reg}
@item REG_FUNCTION_VALUE_P (@var{x})
Nonzero in a @code{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 @code{integrated} field and printed as
@samp{/i}.

The same hard register may be used also for collecting the values of
functions called by this one, but @code{REG_FUNCTION_VALUE_P} is zero
in this kind of use.

@findex SUBREG_PROMOTED_VAR_P
@cindex @code{subreg} and @samp{/s}
@cindex @code{in_struct}, in @code{subreg}
@item SUBREG_PROMOTED_VAR_P
Nonzero in a @code{subreg} if it was made when accessing an object that
was promoted to a wider mode in accord with the @code{PROMOTED_MODE} machine
description macro (@pxref{Storage Layout}).  In this case, the mode of
the @code{subreg} is the declared mode of the object and the mode of
@code{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 @code{in_struct} field and
printed as @samp{/s}.

@findex SUBREG_PROMOTED_UNSIGNED_P
@cindex @code{subreg} and @samp{/u}
@cindex @code{unchanging}, in @code{subreg}
@item SUBREG_PROMOTED_UNSIGNED_P
Nonzero in a @code{subreg} that has @code{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 @code{unchanging} field and
printed as @samp{/u}.

@findex RTX_UNCHANGING_P 
@cindex @code{reg} and @samp{/u}
@cindex @code{mem} and @samp{/u}
@cindex @code{unchanging}, in @code{reg} and @code{mem}
@cindex @samp{/u} in RTL dump
@item RTX_UNCHANGING_P (@var{x})
Nonzero in a @code{reg} or @code{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
@code{unchanging} field and printed as @samp{/u}.

@findex RTX_INTEGRATED_P 
@cindex @code{integrated}, in @code{insn}
@item RTX_INTEGRATED_P (@var{insn})
Nonzero in an insn if it resulted from an in-line function call.
Stored in the @code{integrated} field and printed as @samp{/i}.  This
may be deleted; nothing currently depends on it.

@findex SYMBOL_REF_USED
@cindex @code{used}, in @code{symbol_ref}
@item SYMBOL_REF_USED (@var{x})
In a @code{symbol_ref}, indicates that @var{x} has been used.  This is
normally only used to ensure that @var{x} is only declared external
once.  Stored in the @code{used} field.

@findex SYMBOL_REF_FLAG
@cindex @code{symbol_ref} and @samp{/v}
@cindex @code{volatil}, in @code{symbol_ref}
@item SYMBOL_REF_FLAG (@var{x})
In a @code{symbol_ref}, this is used as a flag for machine-specific purposes.
Stored in the @code{volatil} field and printed as @samp{/v}.

@findex LABEL_OUTSIDE_LOOP_P
@cindex @code{label_ref} and @samp{/s}
@cindex @code{in_struct}, in @code{label_ref}
@item LABEL_OUTSIDE_LOOP_P
In @code{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 @code{in_struct} field and printed as @samp{/s}.

@findex INSN_DELETED_P 
@cindex @code{volatil}, in @code{insn}
@item INSN_DELETED_P (@var{insn})
In an insn, nonzero if the insn has been deleted.  Stored in the
@code{volatil} field and printed as @samp{/v}.

@findex INSN_ANNULLED_BRANCH_P
@cindex @code{insn} and @samp{/u}
@cindex @code{unchanging}, in @code{insn}
@item INSN_ANNULLED_BRANCH_P (@var{insn})
In an @code{insn} in the delay slot of a branch insn, indicates that an
annulling branch should be used.  See the discussion under
@code{sequence} below.  Stored in the @code{unchanging} field and printed
as @samp{/u}.

@findex INSN_FROM_TARGET_P
@cindex @code{insn} and @samp{/s}
@cindex @code{in_struct}, in @code{insn}
@cindex @samp{/s} in RTL dump
@item INSN_FROM_TARGET_P (@var{insn})
In an @code{insn} in a delay slot of a branch, indicates that the insn
is from the target of the branch.  If the branch insn has
@code{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
@code{in_struct} field and printed as @samp{/s}.

@findex CONSTANT_POOL_ADDRESS_P 
@cindex @code{symbol_ref} and @samp{/u}
@cindex @code{unchanging}, in @code{symbol_ref}
@item CONSTANT_POOL_ADDRESS_P (@var{x})
Nonzero in a @code{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
@code{unchanging} field and printed as @samp{/u}.

@findex CONST_CALL_P
@cindex @code{call_insn} and @samp{/u}
@cindex @code{unchanging}, in @code{call_insn}
@item CONST_CALL_P (@var{x})
In a @code{call_insn}, indicates that the insn represents a call to a const
function.  Stored in the @code{unchanging} field and printed as @samp{/u}.

@findex LABEL_PRESERVE_P
@cindex @code{code_label} and @samp{/i}
@cindex @code{in_struct}, in @code{code_label}
@item LABEL_PRESERVE_P (@var{x})
In a @code{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 @code{in_struct} field and printed as @samp{/s}.

@findex SCHED_GROUP_P
@cindex @code{insn} and @samp{/i}
@cindex @code{in_struct}, in @code{insn}
@item SCHED_GROUP_P (@var{insn})
During instruction scheduling, in an insn, indicates that the previous insn
must be scheduled together with this insn.  This is used to ensure that
certain groups of instructions will not be split up by the instruction
scheduling pass, for example, @code{use} insns before a @code{call_insn} may
not be separated from the @code{call_insn}.  Stored in the @code{in_struct}
field and printed as @samp{/s}.
@end table

These are the fields which the above macros refer to:

@table @code
@findex used
@item used
Normally, this flag is used only momentarily, at the end of RTL
generation for a function, to count the number of times an expression
appears in insns.  Expressions that appear more than once are copied,
according to the rules for shared structure (@pxref{Sharing}).

In a @code{symbol_ref}, it indicates that an external declaration for
the symbol has already been written.

In a @code{reg}, it is used by the leaf register renumbering code to ensure
that each register is only renumbered once.

@findex volatil
@item volatil
This flag is used in @code{mem}, @code{symbol_ref} and @code{reg}
expressions and in insns.  In RTL dump files, it is printed as
@samp{/v}.

@cindex volatile memory references
In a @code{mem} expression, it is 1 if the memory reference is volatile.
Volatile memory references may not be deleted, reordered or combined.

In a @code{symbol_ref} expression, it is used for machine-specific 
purposes.

In a @code{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.

@findex in_struct
@item in_struct
In @code{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 @code{reg} expressions, it is 1 if the register has its entire life
contained within the test expression of some loopl.

In @code{subreg} expressions, 1 means that the @code{subreg} is accessing
an object that has had its mode promoted from a wider mode.

In @code{label_ref} expressions, 1 means that the referenced label is
outside the innermost loop containing the insn in which the @code{label_ref}
was found.

In @code{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 @samp{/s}.

@findex unchanging
@item unchanging
In @code{reg} and @code{mem} expressions, 1 means
that the value of the expression never changes.

In @code{subreg} expressions, it is 1 if the @code{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 @code{symbol_ref} expression, 1 means that this symbol addresses
something in the per-function constants pool.

In a @code{call_insn}, 1 means that this instruction is a call to a
const function.

In an RTL dump, this flag is represented as @samp{/u}.

@findex integrated
@item integrated
In some kinds of expressions, including insns, this flag means the
rtl was produced by procedure integration.

In a @code{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.
@end table

@node Machine Modes, Constants, Flags, RTL
@section Machine Modes
@cindex machine modes

@findex enum machine_mode
A machine mode describes a size of data object and the representation used
for it.  In the C code, machine modes are represented by an enumeration
type, @code{enum machine_mode}, defined in @file{machmode.def}.  Each RTL
expression has room for a machine mode and so do certain kinds of tree
expressions (declarations and types, to be precise).

In debugging dumps and machine descriptions, the machine mode of an RTL
expression is written after the expression code with a colon to separate
them.  The letters @samp{mode} which appear at the end of each machine mode
name are omitted.  For example, @code{(reg:SI 38)} is a @code{reg}
expression with machine mode @code{SImode}.  If the mode is
@code{VOIDmode}, it is not written at all.

Here is a table of machine modes.  The term ``byte'' below refers to an
object of @code{BITS_PER_UNIT} bits (@pxref{Storage Layout}).

@table @code
@findex QImode
@item QImode
``Quarter-Integer'' mode represents a single byte treated as an integer.

@findex HImode
@item HImode
``Half-Integer'' mode represents a two-byte integer.

@findex PSImode
@item PSImode
``Partial Single Integer'' mode represents an integer which occupies
four bytes but which doesn't really use all four.  On some machines,
this is the right mode to use for pointers.

@findex SImode
@item SImode
``Single Integer'' mode represents a four-byte integer.

@findex PDImode
@item PDImode
``Partial Double Integer'' mode represents an integer which occupies
eight bytes but which doesn't really use all eight.  On some machines,
this is the right mode to use for certain pointers.

@findex DImode
@item DImode
``Double Integer'' mode represents an eight-byte integer.

@findex TImode
@item TImode
``Tetra Integer'' (?) mode represents a sixteen-byte integer.

@findex SFmode
@item SFmode
``Single Floating'' mode represents a single-precision (four byte) floating
point number.

@findex DFmode
@item DFmode
``Double Floating'' mode represents a double-precision (eight byte) floating
point number.

@findex XFmode
@item XFmode
``Extended Floating'' mode represents a triple-precision (twelve byte)
floating point number.  This mode is used for IEEE extended floating
point.

@findex TFmode
@item TFmode
``Tetra Floating'' mode represents a quadruple-precision (sixteen byte)
floating point number.

@findex CCmode
@item CCmode
``Condition Code'' mode represents the value of a condition code, which
is a machine-specific set of bits used to represent the result of a
comparison operation.  Other machine-specific modes may also be used for
the condition code.  These modes are not used on machines that use
@code{cc0} (see @pxref{Condition Code}).

@findex BLKmode
@item BLKmode
``Block'' mode represents values that are aggregates to which none of
the other modes apply.  In RTL, only memory references can have this mode,
and only if they appear in string-move or vector instructions.  On machines
which have no such instructions, @code{BLKmode} will not appear in RTL.

@findex VOIDmode
@item VOIDmode
Void mode means the absence of a mode or an unspecified mode.
For example, RTL expressions of code @code{const_int} have mode
@code{VOIDmode} because they can be taken to have whatever mode the context
requires.  In debugging dumps of RTL, @code{VOIDmode} is expressed by
the absence of any mode.

@findex SCmode
@findex DCmode