Next: , Up: Expression trees

10.6.1 Constant expressions

The table below begins with constants, moves on to unary expressions, then proceeds to binary expressions, and concludes with various other kinds of expressions:

These nodes represent integer constants. Note that the type of these constants is obtained with TREE_TYPE; they are not always of type int. In particular, char constants are represented with INTEGER_CST nodes. The value of the integer constant e is represented in an array of HOST_WIDE_INT. There are enough elements in the array to represent the value without taking extra elements for redundant 0s or -1. The number of elements used to represent e is available via TREE_INT_CST_NUNITS. Element i can be extracted by using TREE_INT_CST_ELT (e, i). TREE_INT_CST_LOW is a shorthand for TREE_INT_CST_ELT (e, 0).

The functions tree_fits_shwi_p and tree_fits_uhwi_p can be used to tell if the value is small enough to fit in a signed HOST_WIDE_INT or an unsigned HOST_WIDE_INT respectively. The value can then be extracted using tree_to_shwi and tree_to_uhwi.

FIXME: Talk about how to obtain representations of this constant, do comparisons, and so forth.
These nodes represent fixed-point constants. The type of these constants is obtained with TREE_TYPE. TREE_FIXED_CST_PTR points to a struct fixed_value; TREE_FIXED_CST returns the structure itself. struct fixed_value contains data with the size of two HOST_BITS_PER_WIDE_INT and mode as the associated fixed-point machine mode for data.
These nodes are used to represent complex number constants, that is a __complex__ whose parts are constant nodes. The TREE_REALPART and TREE_IMAGPART return the real and the imaginary parts respectively.
These nodes are used to represent vector constants, whose parts are constant nodes. Each individual constant node is either an integer or a double constant node. The first operand is a TREE_LIST of the constant nodes and is accessed through TREE_VECTOR_CST_ELTS.
These nodes represent string-constants. The TREE_STRING_LENGTH returns the length of the string, as an int. The TREE_STRING_POINTER is a char* containing the string itself. The string may not be NUL-terminated, and it may contain embedded NUL characters. Therefore, the TREE_STRING_LENGTH includes the trailing NUL if it is present.

For wide string constants, the TREE_STRING_LENGTH is the number of bytes in the string, and the TREE_STRING_POINTER points to an array of the bytes of the string, as represented on the target system (that is, as integers in the target endianness). Wide and non-wide string constants are distinguished only by the TREE_TYPE of the STRING_CST.

FIXME: The formats of string constants are not well-defined when the target system bytes are not the same width as host system bytes.