-@c Copyright (C) 1988, 89, 92, 94, 97, 1998, 1999 Free Software Foundation, Inc.
+@c Copyright (C) 1988, 89, 92, 94, 97, 1998, 1999, 2000 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
@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.
* Reading RTL:: Reading textual RTL from a file.
@end menu
-@node RTL Objects, Accessors, RTL, RTL
+@node RTL Objects
@section RTL Object Types
@cindex RTL object types
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
+@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
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
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
@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 <
-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}.
+All codes of this class have format @code{e}.
-@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}.
+@item <
+@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
-
-@item m
-An RTX code for something that matches in insns, such as @code{MATCH_DUP}.
+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 x
-All other RTX codes.
-@end table
+@item o
+@itemx m
+@itemx x
+You can make no assumptions about the format of these codes.
@end table
+@node Accessors
+@section Access to Operands
+@cindex accessors
+@cindex access to operands
+@cindex operand access
+
@findex XEXP
@findex XINT
@findex XWINT
can be used to assign the operands, lengths and vector elements as well as
to access them.
-@node Flags, Machine Modes, Accessors, RTL
+@node Flags
@section Flags in an RTL Expression
@cindex flags in RTL expression
uses.
@end table
-@node Machine Modes, Constants, Flags, RTL
+@node Machine Modes
@section Machine Modes
@cindex machine modes
less than or equal to @code{HOST_BITS_PER_INT}.
@findex GET_MODE_ALIGNMENT
-@item GET_MODE_ALIGNMENT (@var{m)})
+@item GET_MODE_ALIGNMENT (@var{m})
Return the required alignment, in bits, for an object of mode @var{m}.
@findex GET_MODE_UNIT_SIZE
@code{BITS_PER_UNIT} or @code{BITS_PER_WORD}, respectively. On 32-bit
machines, these are @code{QImode} and @code{SImode}, respectively.
-@node Constants, Regs and Memory, Machine Modes, RTL
+@node Constants
@section Constant Expression Types
@cindex RTL constants
@cindex RTL constant expression types
@var{m} should be @code{Pmode}.
@end table
-@node Regs and Memory, Arithmetic, Constants, RTL
+@node Regs and Memory
@section Registers and Memory
@cindex RTL register expressions
@cindex RTL memory expressions
by incrementing it, but there is no need to mention this in the RTL.
@findex mem
-@item (mem:@var{m} @var{addr})
+@item (mem:@var{m} @var{addr} @var{alias})
This RTX represents a reference to main memory at an address
represented by the expression @var{addr}. @var{m} specifies how large
-a unit of memory is accessed.
+a unit of memory is accessed. @var{alias} specifies an alias set for the
+reference. In general two items are in different alias sets if they cannot
+reference the same memory address.
@findex addressof
@item (addressof:@var{m} @var{reg})
expression for the address of its stack slot.
@end table
-@node Arithmetic, Comparisons, Regs and Memory, RTL
+@node Arithmetic
@section RTL Expressions for Arithmetic
@cindex arithmetic, in RTL
@cindex math, in RTL
valid.
@end table
-@node Comparisons, Bit Fields, Arithmetic, RTL
+@node Comparisons
@section Comparison Operations
@cindex RTL comparison operations
comparison operators may be used to compare the condition codes
@code{(cc0)} against zero, as in @code{(eq (cc0) (const_int 0))}. Such
a construct actually refers to the result of the preceding instruction
-in which the condition codes were set. The instructing setting the
+in which the condition codes were set. The instruction setting the
condition code must be adjacent to the instruction using the condition
code; only @code{note} insns may separate them.
for insn attributes. @xref{Insn Attributes}.
@end table
-@node Bit Fields, Conversions, Comparisons, RTL
+@node Bit Fields
@section Bit Fields
@cindex bit fields
are filled to an entire word with zeros instead of by sign-extension.
@end table
-@node Conversions, RTL Declarations, Bit Fields, RTL
+@node Conversions
@section Conversions
@cindex conversions
@cindex machine mode conversions
towards zero.
@end table
-@node RTL Declarations, Side Effects, Conversions, RTL
+@node RTL Declarations
@section Declarations
@cindex RTL declarations
@cindex declarations, RTL
register when @var{m} is less than a word.
@end table
-@node Side Effects, Incdec, RTL Declarations, RTL
+@node Side Effects
@section Side Effect Expressions
@cindex RTL side effect expressions
and of @var{min} and @var{max} to @var{base}. See rtl.def for details.@refill
@end table
-@node Incdec, Assembler, Side Effects, RTL
+@node Incdec
@section Embedded Side-Effects on Addresses
@cindex RTL preincrement
@cindex RTL postincrement
additional parallel stores would require doubling the number of entries
in the machine description.
-@node Assembler, Insns, Incdec, RTL
+@node Assembler
@section Assembler Instructions as Expressions
@cindex assembler instructions in RTL
output operand. They are also distinguished by the output-operand index
number, which is 0, 1, @dots{} for successive output operands.
-@node Insns, Calls, Assembler, RTL
+@node Insns
@section Insns
@cindex insns
phase is completed and contains the number of times this label is
referenced in the current function.
+@findex LABEL_ALTERNATE_NAME
+The field @code{LABEL_ALTERNATE_NAME} is used to associate a name with
+a @code{code_label}. If this field is defined, the alternate name will
+be emitted instead of an internally generated label name.
+
@findex barrier
@item barrier
Barriers are placed in the instruction stream when control cannot flow
unique id; the first operand of an @code{expr_list} is printed in the
ordinary way as an expression.
-@node Calls, Sharing, Insns, RTL
+@node Calls
@section RTL Representation of Function-Call Insns
@cindex calling functions in RTL
@cindex RTL function-call insns
@cindex @code{const_int}, RTL sharing
@item
-There is only one @code{const_int} expression with value 0, only
-one with value 1, and only one with value @minus{}1.
-Some other integer values are also stored uniquely.
+All @code{const_int} expressions with equal values are shared.
@cindex @code{pc}, RTL sharing
@item
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