You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
181 lines
9.9 KiB
HTML
181 lines
9.9 KiB
HTML
<html lang="en">
|
|
<head>
|
|
<title>Defining Predicates - GNU Compiler Collection (GCC) Internals</title>
|
|
<meta http-equiv="Content-Type" content="text/html">
|
|
<meta name="description" content="GNU Compiler Collection (GCC) Internals">
|
|
<meta name="generator" content="makeinfo 4.13">
|
|
<link title="Top" rel="start" href="index.html#Top">
|
|
<link rel="up" href="Predicates.html#Predicates" title="Predicates">
|
|
<link rel="prev" href="Machine_002dIndependent-Predicates.html#Machine_002dIndependent-Predicates" title="Machine-Independent Predicates">
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
|
<!--
|
|
Copyright (C) 1988-2015 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with the
|
|
Invariant Sections being ``Funding Free Software'', the Front-Cover
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
|
(see below). A copy of the license is included in the section entitled
|
|
``GNU Free Documentation License''.
|
|
|
|
(a) The FSF's Front-Cover Text is:
|
|
|
|
A GNU Manual
|
|
|
|
(b) The FSF's Back-Cover Text is:
|
|
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
|
software. Copies published by the Free Software Foundation raise
|
|
funds for GNU development.-->
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
|
<style type="text/css"><!--
|
|
pre.display { font-family:inherit }
|
|
pre.format { font-family:inherit }
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
|
pre.smallexample { font-size:smaller }
|
|
pre.smalllisp { font-size:smaller }
|
|
span.sc { font-variant:small-caps }
|
|
span.roman { font-family:serif; font-weight:normal; }
|
|
span.sansserif { font-family:sans-serif; font-weight:normal; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
<div class="node">
|
|
<a name="Defining-Predicates"></a>
|
|
<p>
|
|
Previous: <a rel="previous" accesskey="p" href="Machine_002dIndependent-Predicates.html#Machine_002dIndependent-Predicates">Machine-Independent Predicates</a>,
|
|
Up: <a rel="up" accesskey="u" href="Predicates.html#Predicates">Predicates</a>
|
|
<hr>
|
|
</div>
|
|
|
|
<h4 class="subsection">16.7.2 Defining Machine-Specific Predicates</h4>
|
|
|
|
<p><a name="index-defining-predicates-3301"></a><a name="index-define_005fpredicate-3302"></a><a name="index-define_005fspecial_005fpredicate-3303"></a>
|
|
Many machines have requirements for their operands that cannot be
|
|
expressed precisely using the generic predicates. You can define
|
|
additional predicates using <code>define_predicate</code> and
|
|
<code>define_special_predicate</code> expressions. These expressions have
|
|
three operands:
|
|
|
|
<ul>
|
|
<li>The name of the predicate, as it will be referred to in
|
|
<code>match_operand</code> or <code>match_operator</code> expressions.
|
|
|
|
<li>An RTL expression which evaluates to true if the predicate allows the
|
|
operand <var>op</var>, false if it does not. This expression can only use
|
|
the following RTL codes:
|
|
|
|
<dl>
|
|
<dt><code>MATCH_OPERAND</code><dd>When written inside a predicate expression, a <code>MATCH_OPERAND</code>
|
|
expression evaluates to true if the predicate it names would allow
|
|
<var>op</var>. The operand number and constraint are ignored. Due to
|
|
limitations in <samp><span class="command">genrecog</span></samp>, you can only refer to generic
|
|
predicates and predicates that have already been defined.
|
|
|
|
<br><dt><code>MATCH_CODE</code><dd>This expression evaluates to true if <var>op</var> or a specified
|
|
subexpression of <var>op</var> has one of a given list of RTX codes.
|
|
|
|
<p>The first operand of this expression is a string constant containing a
|
|
comma-separated list of RTX code names (in lower case). These are the
|
|
codes for which the <code>MATCH_CODE</code> will be true.
|
|
|
|
<p>The second operand is a string constant which indicates what
|
|
subexpression of <var>op</var> to examine. If it is absent or the empty
|
|
string, <var>op</var> itself is examined. Otherwise, the string constant
|
|
must be a sequence of digits and/or lowercase letters. Each character
|
|
indicates a subexpression to extract from the current expression; for
|
|
the first character this is <var>op</var>, for the second and subsequent
|
|
characters it is the result of the previous character. A digit
|
|
<var>n</var> extracts ‘<samp><span class="samp">XEXP (</span><var>e</var><span class="samp">, </span><var>n</var><span class="samp">)<!-- /@w --></span></samp>’; a letter <var>l</var>
|
|
extracts ‘<samp><span class="samp">XVECEXP (</span><var>e</var><span class="samp">, 0, </span><var>n</var><span class="samp">)<!-- /@w --></span></samp>’ where <var>n</var> is the
|
|
alphabetic ordinal of <var>l</var> (0 for `a', 1 for 'b', and so on). The
|
|
<code>MATCH_CODE</code> then examines the RTX code of the subexpression
|
|
extracted by the complete string. It is not possible to extract
|
|
components of an <code>rtvec</code> that is not at position 0 within its RTX
|
|
object.
|
|
|
|
<br><dt><code>MATCH_TEST</code><dd>This expression has one operand, a string constant containing a C
|
|
expression. The predicate's arguments, <var>op</var> and <var>mode</var>, are
|
|
available with those names in the C expression. The <code>MATCH_TEST</code>
|
|
evaluates to true if the C expression evaluates to a nonzero value.
|
|
<code>MATCH_TEST</code> expressions must not have side effects.
|
|
|
|
<br><dt><code>AND</code><dt><code>IOR</code><dt><code>NOT</code><dt><code>IF_THEN_ELSE</code><dd>The basic ‘<samp><span class="samp">MATCH_</span></samp>’ expressions can be combined using these
|
|
logical operators, which have the semantics of the C operators
|
|
‘<samp><span class="samp">&&</span></samp>’, ‘<samp><span class="samp">||</span></samp>’, ‘<samp><span class="samp">!</span></samp>’, and ‘<samp><span class="samp">? :<!-- /@w --></span></samp>’ respectively. As
|
|
in Common Lisp, you may give an <code>AND</code> or <code>IOR</code> expression an
|
|
arbitrary number of arguments; this has exactly the same effect as
|
|
writing a chain of two-argument <code>AND</code> or <code>IOR</code> expressions.
|
|
</dl>
|
|
|
|
<li>An optional block of C code, which should execute
|
|
‘<samp><span class="samp">return true<!-- /@w --></span></samp>’ if the predicate is found to match and
|
|
‘<samp><span class="samp">return false<!-- /@w --></span></samp>’ if it does not. It must not have any side
|
|
effects. The predicate arguments, <var>op</var> and <var>mode</var>, are
|
|
available with those names.
|
|
|
|
<p>If a code block is present in a predicate definition, then the RTL
|
|
expression must evaluate to true <em>and</em> the code block must
|
|
execute ‘<samp><span class="samp">return true<!-- /@w --></span></samp>’ for the predicate to allow the operand.
|
|
The RTL expression is evaluated first; do not re-check anything in the
|
|
code block that was checked in the RTL expression.
|
|
</ul>
|
|
|
|
<p>The program <samp><span class="command">genrecog</span></samp> scans <code>define_predicate</code> and
|
|
<code>define_special_predicate</code> expressions to determine which RTX
|
|
codes are possibly allowed. You should always make this explicit in
|
|
the RTL predicate expression, using <code>MATCH_OPERAND</code> and
|
|
<code>MATCH_CODE</code>.
|
|
|
|
<p>Here is an example of a simple predicate definition, from the IA64
|
|
machine description:
|
|
|
|
<pre class="smallexample"> ;; <span class="roman">True if </span><var>op</var><span class="roman"> is a </span><code>SYMBOL_REF</code><span class="roman"> which refers to the sdata section.</span>
|
|
(define_predicate "small_addr_symbolic_operand"
|
|
(and (match_code "symbol_ref")
|
|
(match_test "SYMBOL_REF_SMALL_ADDR_P (op)")))
|
|
</pre>
|
|
<p class="noindent">And here is another, showing the use of the C block.
|
|
|
|
<pre class="smallexample"> ;; <span class="roman">True if </span><var>op</var><span class="roman"> is a register operand that is (or could be) a GR reg.</span>
|
|
(define_predicate "gr_register_operand"
|
|
(match_operand 0 "register_operand")
|
|
{
|
|
unsigned int regno;
|
|
if (GET_CODE (op) == SUBREG)
|
|
op = SUBREG_REG (op);
|
|
|
|
regno = REGNO (op);
|
|
return (regno >= FIRST_PSEUDO_REGISTER || GENERAL_REGNO_P (regno));
|
|
})
|
|
</pre>
|
|
<p>Predicates written with <code>define_predicate</code> automatically include
|
|
a test that <var>mode</var> is <code>VOIDmode</code>, or <var>op</var> has the same
|
|
mode as <var>mode</var>, or <var>op</var> is a <code>CONST_INT</code> or
|
|
<code>CONST_DOUBLE</code>. They do <em>not</em> check specifically for
|
|
integer <code>CONST_DOUBLE</code>, nor do they test that the value of either
|
|
kind of constant fits in the requested mode. This is because
|
|
target-specific predicates that take constants usually have to do more
|
|
stringent value checks anyway. If you need the exact same treatment
|
|
of <code>CONST_INT</code> or <code>CONST_DOUBLE</code> that the generic predicates
|
|
provide, use a <code>MATCH_OPERAND</code> subexpression to call
|
|
<code>const_int_operand</code>, <code>const_double_operand</code>, or
|
|
<code>immediate_operand</code>.
|
|
|
|
<p>Predicates written with <code>define_special_predicate</code> do not get any
|
|
automatic mode checks, and are treated as having special mode handling
|
|
by <samp><span class="command">genrecog</span></samp>.
|
|
|
|
<p>The program <samp><span class="command">genpreds</span></samp> is responsible for generating code to
|
|
test predicates. It also writes a header file containing function
|
|
declarations for all machine-specific predicates. It is not necessary
|
|
to declare these predicates in <samp><var>cpu</var><span class="file">-protos.h</span></samp>.
|
|
|
|
<!-- Most of this node appears by itself (in a different place) even -->
|
|
<!-- when the INTERNALS flag is clear. Passages that require the internals -->
|
|
<!-- manual's context are conditionalized to appear only in the internals manual. -->
|
|
</body></html>
|
|
|