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NEGATE_EXPR
The behavior of this operation on signed arithmetic overflow is
controlled by the flag_wrapv
and flag_trapv
variables.
ABS_EXPR
abs
, labs
and llabs
builtins for
integer types, and the fabs
, fabsf
and fabsl
builtins for floating point types. The type of abs operation can
be determined by looking at the type of the expression.
This node is not used for complex types. To represent the modulus
or complex abs of a complex value, use the BUILT_IN_CABS
,
BUILT_IN_CABSF
or BUILT_IN_CABSL
builtins, as used
to implement the C99 cabs
, cabsf
and cabsl
built-in functions.
BIT_NOT_EXPR
TRUTH_NOT_EXPR
BOOLEAN_TYPE
or INTEGER_TYPE
.
PREDECREMENT_EXPR
PREINCREMENT_EXPR
POSTDECREMENT_EXPR
POSTINCREMENT_EXPR
PREDECREMENT_EXPR
and
PREINCREMENT_EXPR
, the value of the expression is the value
resulting after the increment or decrement; in the case of
POSTDECREMENT_EXPR
and POSTINCREMENT_EXPR
is the value
before the increment or decrement occurs. The type of the operand, like
that of the result, will be either integral, boolean, or floating-point.
FIX_TRUNC_EXPR
FLOAT_EXPR
FIXME: How is the operand supposed to be rounded? Is this dependent on
-mieee?
COMPLEX_EXPR
CONJ_EXPR
REALPART_EXPR
IMAGPART_EXPR
NON_LVALUE_EXPR
NOP_EXPR
char*
to an
int*
does not require any code be generated; such a conversion is
represented by a NOP_EXPR
. The single operand is the expression
to be converted. The conversion from a pointer to a reference is also
represented with a NOP_EXPR
.
CONVERT_EXPR
NOP_EXPR
s, but are used in those
situations where code may need to be generated. For example, if an
int*
is converted to an int
code may need to be generated
on some platforms. These nodes are never used for C++-specific
conversions, like conversions between pointers to different classes in
an inheritance hierarchy. Any adjustments that need to be made in such
cases are always indicated explicitly. Similarly, a user-defined
conversion is never represented by a CONVERT_EXPR
; instead, the
function calls are made explicit.
FIXED_CONVERT_EXPR
LSHIFT_EXPR
RSHIFT_EXPR
BIT_IOR_EXPR
BIT_XOR_EXPR
BIT_AND_EXPR
TRUTH_ANDIF_EXPR
TRUTH_ORIF_EXPR
BOOLEAN_TYPE
or INTEGER_TYPE
.
TRUTH_AND_EXPR
TRUTH_OR_EXPR
TRUTH_XOR_EXPR
BOOLEAN_TYPE
or INTEGER_TYPE
.
POINTER_PLUS_EXPR
PLUS_EXPR
MINUS_EXPR
MULT_EXPR
The behavior of these operations on signed arithmetic overflow is
controlled by the flag_wrapv
and flag_trapv
variables.
RDIV_EXPR
TRUNC_DIV_EXPR
FLOOR_DIV_EXPR
CEIL_DIV_EXPR
ROUND_DIV_EXPR
TRUNC_DIV_EXPR
rounds towards zero, FLOOR_DIV_EXPR
rounds towards negative infinity, CEIL_DIV_EXPR
rounds towards
positive infinity and ROUND_DIV_EXPR
rounds to the closest integer.
Integer division in C and C++ is truncating, i.e. TRUNC_DIV_EXPR
.
The behavior of these operations on signed arithmetic overflow, when
dividing the minimum signed integer by minus one, is controlled by the
flag_wrapv
and flag_trapv
variables.
TRUNC_MOD_EXPR
FLOOR_MOD_EXPR
CEIL_MOD_EXPR
ROUND_MOD_EXPR
a
and b
is
defined as a - (a/b)*b
where the division calculated using
the corresponding division operator. Hence for TRUNC_MOD_EXPR
this definition assumes division using truncation towards zero, i.e.
TRUNC_DIV_EXPR
. Integer remainder in C and C++ uses truncating
division, i.e. TRUNC_MOD_EXPR
.
EXACT_DIV_EXPR
EXACT_DIV_EXPR
code is used to represent integer divisions where
the numerator is known to be an exact multiple of the denominator. This
allows the backend to choose between the faster of TRUNC_DIV_EXPR
,
CEIL_DIV_EXPR
and FLOOR_DIV_EXPR
for the current target.
LT_EXPR
LE_EXPR
GT_EXPR
GE_EXPR
EQ_EXPR
NE_EXPR
For floating point comparisons, if we honor IEEE NaNs and either operand
is NaN, then NE_EXPR
always returns true and the remaining operators
always return false. On some targets, comparisons against an IEEE NaN,
other than equality and inequality, may generate a floating point exception.
ORDERED_EXPR
UNORDERED_EXPR
UNLT_EXPR
UNLE_EXPR
UNGT_EXPR
UNGE_EXPR
UNEQ_EXPR
LTGT_EXPR
UNLT_EXPR
returns true if either operand is an IEEE
NaN or the first operand is less than the second. With the possible
exception of LTGT_EXPR
, all of these operations are guaranteed
not to generate a floating point exception. The result
type of these expressions will always be of integral or boolean type.
These operations return the result type's zero value for false,
and the result type's one value for true.
MODIFY_EXPR
VAR_DECL
, INDIRECT_REF
, COMPONENT_REF
, or
other lvalue.
These nodes are used to represent not only assignment with `=' but
also compound assignments (like `+='), by reduction to `='
assignment. In other words, the representation for `i += 3' looks
just like that for `i = i + 3'.
INIT_EXPR
MODIFY_EXPR
, but are used only when a
variable is initialized, rather than assigned to subsequently. This
means that we can assume that the target of the initialization is not
used in computing its own value; any reference to the lhs in computing
the rhs is undefined.
COMPOUND_EXPR
COND_EXPR
?:
expressions. The first operand
is of boolean or integral type. If it evaluates to a nonzero value,
the second operand should be evaluated, and returned as the value of the
expression. Otherwise, the third operand is evaluated, and returned as
the value of the expression.
The second operand must have the same type as the entire expression,
unless it unconditionally throws an exception or calls a noreturn
function, in which case it should have void type. The same constraints
apply to the third operand. This allows array bounds checks to be
represented conveniently as (i >= 0 && i < 10) ? i : abort()
.
As a GNU extension, the C language front-ends allow the second
operand of the ?:
operator may be omitted in the source.
For example, x ? : 3
is equivalent to x ? x : 3
,
assuming that x
is an expression without side-effects.
In the tree representation, however, the second operand is always
present, possibly protected by SAVE_EXPR
if the first
argument does cause side-effects.
CALL_EXPR
CALL_EXPR
s are implemented as
expression nodes with a variable number of operands. Rather than using
TREE_OPERAND
to extract them, it is preferable to use the
specialized accessor macros and functions that operate specifically on
CALL_EXPR
nodes.
CALL_EXPR_FN
returns a pointer to the
function to call; it is always an expression whose type is a
POINTER_TYPE
.
The number of arguments to the call is returned by call_expr_nargs
,
while the arguments themselves can be accessed with the CALL_EXPR_ARG
macro. The arguments are zero-indexed and numbered left-to-right.
You can iterate over the arguments using FOR_EACH_CALL_EXPR_ARG
, as in:
tree call, arg; call_expr_arg_iterator iter; FOR_EACH_CALL_EXPR_ARG (arg, iter, call) /* arg is bound to successive arguments of call. */ ...;
For non-static
member functions, there will be an operand corresponding to the
this
pointer. There will always be expressions corresponding to
all of the arguments, even if the function is declared with default
arguments and some arguments are not explicitly provided at the call
sites.
CALL_EXPR
s also have a CALL_EXPR_STATIC_CHAIN
operand that
is used to implement nested functions. This operand is otherwise null.
CLEANUP_POINT_EXPR
CONSTRUCTOR
TREE_LIST
. If the TREE_TYPE
of the
CONSTRUCTOR
is a RECORD_TYPE
or UNION_TYPE
, then
the TREE_PURPOSE
of each node in the TREE_LIST
will be a
FIELD_DECL
and the TREE_VALUE
of each node will be the
expression used to initialize that field.
If the TREE_TYPE
of the CONSTRUCTOR
is an
ARRAY_TYPE
, then the TREE_PURPOSE
of each element in the
TREE_LIST
will be an INTEGER_CST
or a RANGE_EXPR
of
two INTEGER_CST
s. A single INTEGER_CST
indicates which
element of the array (indexed from zero) is being assigned to. A
RANGE_EXPR
indicates an inclusive range of elements to
initialize. In both cases the TREE_VALUE
is the corresponding
initializer. It is re-evaluated for each element of a
RANGE_EXPR
. If the TREE_PURPOSE
is NULL_TREE
, then
the initializer is for the next available array element.
In the front end, you should not depend on the fields appearing in any
particular order. However, in the middle end, fields must appear in
declaration order. You should not assume that all fields will be
represented. Unrepresented fields will be set to zero.
COMPOUND_LITERAL_EXPR
COMPOUND_LITERAL_EXPR_DECL_EXPR
is a DECL_EXPR
containing an anonymous VAR_DECL
for
the unnamed object represented by the compound literal; the
DECL_INITIAL
of that VAR_DECL
is a CONSTRUCTOR
representing the brace-enclosed list of initializers in the compound
literal. That anonymous VAR_DECL
can also be accessed directly
by the COMPOUND_LITERAL_EXPR_DECL
macro.
SAVE_EXPR
SAVE_EXPR
represents an expression (possibly involving
side-effects) that is used more than once. The side-effects should
occur only the first time the expression is evaluated. Subsequent uses
should just reuse the computed value. The first operand to the
SAVE_EXPR
is the expression to evaluate. The side-effects should
be executed where the SAVE_EXPR
is first encountered in a
depth-first preorder traversal of the expression tree.
TARGET_EXPR
TARGET_EXPR
represents a temporary object. The first operand
is a VAR_DECL
for the temporary variable. The second operand is
the initializer for the temporary. The initializer is evaluated and,
if non-void, copied (bitwise) into the temporary. If the initializer
is void, that means that it will perform the initialization itself.
Often, a TARGET_EXPR
occurs on the right-hand side of an
assignment, or as the second operand to a comma-expression which is
itself the right-hand side of an assignment, etc. In this case, we say
that the TARGET_EXPR
is “normal”; otherwise, we say it is
“orphaned”. For a normal TARGET_EXPR
the temporary variable
should be treated as an alias for the left-hand side of the assignment,
rather than as a new temporary variable.
The third operand to the TARGET_EXPR
, if present, is a
cleanup-expression (i.e., destructor call) for the temporary. If this
expression is orphaned, then this expression must be executed when the
statement containing this expression is complete. These cleanups must
always be executed in the order opposite to that in which they were
encountered. Note that if a temporary is created on one branch of a
conditional operator (i.e., in the second or third operand to a
COND_EXPR
), the cleanup must be run only if that branch is
actually executed.
VA_ARG_EXPR
va_arg (ap, type)
.
Its TREE_TYPE
yields the tree representation for type
and
its sole argument yields the representation for ap
.