GNU Info
(gcc-295.info)RTL Classes
RTL Classes and Formats
=======================
The various expression codes are divided into several "classes",
which are represented by single characters. You can determine the class
of an RTX code with the macro `GET_RTX_CLASS (CODE)'. Currently,
`rtx.def' defines these classes:
`o'
An RTX code that represents an actual object, such as a register
(`REG') or a memory location (`MEM', `SYMBOL_REF'). Constants and
basic transforms on objects (`ADDRESSOF', `HIGH', `LO_SUM') are
also included. Note that `SUBREG' and `STRICT_LOW_PART' are not
in this class, but in class `x'.
`<'
An RTX code for a comparison, such as `NE' or `LT'.
`1'
An RTX code for a unary arithmetic operation, such as `NEG',
`NOT', or `ABS'. This category also includes value extension
(sign or zero) and conversions between integer and floating point.
`c'
An RTX code for a commutative binary operation, such as `PLUS' or
`AND'. `NE' and `EQ' are comparisons, so they have class `<'.
`2'
An RTX code for a non-commutative binary operation, such as
`MINUS', `DIV', or `ASHIFTRT'.
`b'
An RTX code for a bitfield operation. Currently only
`ZERO_EXTRACT' and `SIGN_EXTRACT'. These have three inputs and
are lvalues (so they can be used for insertion as well). Note:
Bit Fields.
`3'
An RTX code for other three input operations. Currently only
`IF_THEN_ELSE'.
`i'
An RTX code for an entire instruction: `INSN', `JUMP_INSN', and
`CALL_INSN'. Note: Insns.
`m'
An RTX code for something that matches in insns, such as
`MATCH_DUP'. These only occur in machine descriptions.
`x'
All other RTX codes. This category includes the remaining codes
used only in machine descriptions (`DEFINE_*', etc.). It also
includes all the codes describing side effects (`SET', `USE',
`CLOBBER', etc.) and the non-insns that may appear on an insn
chain, such as `NOTE', `BARRIER', and `CODE_LABEL'.
For each expression type `rtl.def' specifies the number of contained
objects and their kinds, with four possibilities: `e' for expression
(actually a pointer to an expression), `i' for integer, `w' for wide
integer, `s' for string, and `E' for vector of expressions. The
sequence of letters for an expression code is called its "format". For
example, the format of `subreg' is `ei'.
A few other format characters are used occasionally:
`u'
`u' is equivalent to `e' except that it is printed differently in
debugging dumps. It is used for pointers to insns.
`n'
`n' is equivalent to `i' except that it is printed differently in
debugging dumps. It is used for the line number or code number of
a `note' insn.
`S'
`S' indicates a string which is optional. In the RTL objects in
core, `S' is equivalent to `s', but when the object is read, from
an `md' file, the string value of this operand may be omitted. An
omitted string is taken to be the null string.
`V'
`V' indicates a vector which is optional. In the RTL objects in
core, `V' is equivalent to `E', but when the object is read from
an `md' file, the vector value of this operand may be omitted. An
omitted vector is effectively the same as a vector of no elements.
`0'
`0' means a slot whose contents do not fit any normal category.
`0' slots are not printed at all in dumps, and are often used in
special ways by small parts of the compiler.
There are macros to get the number of operands and the format of an
expression code:
`GET_RTX_LENGTH (CODE)'
Number of operands of an RTX of code CODE.
`GET_RTX_FORMAT (CODE)'
The format of an RTX of code CODE, as a C string.
Some classes of RTX codes always have the same format. For example,
it is safe to assume that all comparison operations have format `ee'.
`1'
All codes of this class have format `e'.
`<'
`c'
`2'
All codes of these classes have format `ee'.
`b'
`3'
All codes of these classes have format `eee'.
`i'
All codes of this class have formats that begin with `iuueiee'.
Note: Insns. Note that not all RTL objects linked onto an insn
chain are of class `i'.
`o'
`m'
`x'
You can make no assumptions about the format of these codes.
automatically generated by info2www version 1.2.2.9