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rtl.texi: Document the rtl classes and their relation to formats.

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1999-04-26 09:47 -0400  Zack Weinberg  <zack@rabi.columbia.edu>
	* rtl.texi: Document the rtl classes and their relation to
	formats.

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@ -1,3 +1,8 @@
1999-04-26 09:47 -0400 Zack Weinberg <zack@rabi.columbia.edu>
* rtl.texi: Document the rtl classes and their relation to
formats.
Mon Apr 26 01:02:38 1999 Richard Henderson <rth@cygnus.com>
* alpha.md (fix_trunc patterns): Use reg_no_subreg_operand on op0

135
gcc/rtl.texi
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@ -20,6 +20,7 @@ form uses nested parentheses to indicate the pointers in the internal form.
@menu
* RTL Objects:: Expressions vs vectors vs strings vs integers.
* RTL Classes:: Categories of RTL expresion objects, and their structure.
* Accessors:: Macros to access expression operands or vector elts.
* Flags:: Other flags in an RTL expression.
* Machine Modes:: Describing the size and format of a datum.
@ -39,7 +40,7 @@ form uses nested parentheses to indicate the pointers in the internal form.
* Reading RTL:: Reading textual RTL from a file.
@end menu
@node RTL Objects, Accessors, RTL, RTL
@node RTL Objects, RTL Classes, RTL, RTL
@section RTL Object Types
@cindex RTL object types
@ -108,11 +109,68 @@ manual, they are shown as follows: @code{const_int}.
In a few contexts a null pointer is valid where an expression is normally
wanted. The written form of this is @code{(nil)}.
@node Accessors, Flags, RTL Objects, RTL
@section Access to Operands
@cindex accessors
@cindex access to operands
@cindex operand access
@node RTL Classes, Accessors, RTL Objects, RTL
@section RTL Classes and Formats
@cindex RTL classes
@cindex classes of RTX codes
@cindex RTX codes, classes of
@findex GET_RTX_CLASS
The various expression codes are divided into several @dfn{classes},
which are represented by single characters. You can determine the class
of an RTX code with the macro @code{GET_RTX_CLASS (@var{code})}.
Currently, @file{rtx.def} defines these classes:
@table @code
@item o
An RTX code that represents an actual object, such as a register
(@code{REG}) or a memory location (@code{MEM}, @code{SYMBOL_REF}).
Constants and basic transforms on objects (@code{ADDRESSOF},
@code{HIGH}, @code{LO_SUM}) are also included. Note that @code{SUBREG}
and @code{STRICT_LOW_PART} are not in this class, but in class @code{x}.
@item <
An RTX code for a comparison, such as @code{NE} or @code{LT}.
@item 1
An RTX code for a unary arithmetic operation, such as @code{NEG},
@code{NOT}, or @code{ABS}. This category also includes value extension
(sign or zero) and conversions between integer and floating point.
@item c
An RTX code for a commutative binary operation, such as @code{PLUS} or
@code{AND}. @code{NE} and @code{EQ} are comparisons, so they have class
@code{<}.
@item 2
An RTX code for a non-commutative binary operation, such as @code{MINUS},
@code{DIV}, or @code{ASHIFTRT}.
@item b
An RTX code for a bitfield operation. Currently only
@code{ZERO_EXTRACT} and @code{SIGN_EXTRACT}. These have three inputs
and are lvalues (so they can be used for insertion as well). @xref{Bit
Fields}.
@item 3
An RTX code for other three input operations. Currently only
@code{IF_THEN_ELSE}.
@item i
An RTX code for an entire instruction: @code{INSN}, @code{JUMP_INSN}, and
@code{CALL_INSN}. @xref{Insns}.
@item m
An RTX code for something that matches in insns, such as
@code{MATCH_DUP}. These only occur in machine descriptions.
@item x
All other RTX codes. This category includes the remaining codes used
only in machine descriptions (@code{DEFINE_*}, etc.). It also includes
all the codes describing side effects (@code{SET}, @code{USE},
@code{CLOBBER}, etc.) and the non-insns that may appear on an insn
chain, such as @code{NOTE}, @code{BARRIER}, and @code{CODE_LABEL}.
@end table
@cindex RTL format
For each expression type @file{rtl.def} specifies the number of
@ -120,7 +178,7 @@ contained objects and their kinds, with four possibilities: @samp{e} for
expression (actually a pointer to an expression), @samp{i} for integer,
@samp{w} for wide integer, @samp{s} for string, and @samp{E} for vector
of expressions. The sequence of letters for an expression code is
called its @dfn{format}. Thus, the format of @code{subreg} is
called its @dfn{format}. For example, the format of @code{subreg} is
@samp{ei}.@refill
@cindex RTL format characters
@ -154,8 +212,8 @@ An omitted vector is effectively the same as a vector of no elements.
special ways by small parts of the compiler.
@end table
There are macros to get the number of operands, the format, and the
class of an expression code:
There are macros to get the number of operands and the format
of an expression code:
@table @code
@findex GET_RTX_LENGTH
@ -165,53 +223,40 @@ Number of operands of an RTX of code @var{code}.
@findex GET_RTX_FORMAT
@item GET_RTX_FORMAT (@var{code})
The format of an RTX of code @var{code}, as a C string.
@end table
@findex GET_RTX_CLASS
@cindex classes of RTX codes
@item GET_RTX_CLASS (@var{code})
A single character representing the type of RTX operation that code
@var{code} performs.
The following classes are defined:
Some classes of RTX codes always have the same format. For example, it
is safe to assume that all comparison operations have format @code{ee}.
@table @code
@item o
An RTX code that represents an actual object, such as @code{reg} or
@code{mem}. @code{subreg} is not in this class.
@item 1
All codes of this class have format @code{e}.
@item <
An RTX code for a comparison. The codes in this class are
@code{NE}, @code{EQ}, @code{LE}, @code{LT}, @code{GE}, @code{GT},
@code{LEU}, @code{LTU}, @code{GEU}, @code{GTU}.@refill
@item 1
An RTX code for a unary arithmetic operation, such as @code{neg}.
@item c
An RTX code for a commutative binary operation, other than @code{NE}
and @code{EQ} (which have class @samp{<}).
@item 2
An RTX code for a noncommutative binary operation, such as @code{MINUS}.
@itemx c
@itemx 2
All codes of these classes have format @code{ee}.
@item b
An RTX code for a bitfield operation, either @code{ZERO_EXTRACT} or
@code{SIGN_EXTRACT}.
@item 3
An RTX code for other three input operations, such as @code{IF_THEN_ELSE}.
@itemx 3
All codes of these classes have format @code{eee}.
@item i
An RTX code for a machine insn (@code{INSN}, @code{JUMP_INSN}, and
@code{CALL_INSN}).@refill
All codes of this class have formats that begin with @code{iuueiee}.
@xref{Insns}. Note that not all RTL objects linked onto an insn chain
are of class @code{i}.
@item m
An RTX code for something that matches in insns, such as @code{MATCH_DUP}.
@item o
@itemx m
@itemx x
You can make no assumptions about the format of these codes.
@end table
@item x
All other RTX codes.
@end table
@end table
@node Accessors, Flags, RTL Classes, RTL
@section Access to Operands
@cindex accessors
@cindex access to operands
@cindex operand access
@findex XEXP
@findex XINT